Adapter fails to power DC motor

[Terry Pinnell]

I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

Terry, East Grinstead, UK

 

[Jim Jackson]

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:

I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

 

[George Herold]

On Tuesday, March 3, 2020 at 7:32:36 AM UTC-5, Jim Jackson wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Huh, 3.6 A over current on a 4 A supply is a little sneaky.

Terry, I've used a bunch of Phihong power supplies... I abused 'em
but only with a resistive load. I guess you need a 'bigger boat'
maybe look for a 25 or 30 W supply..
(find another 5V supply in your scrap box and put two in parallel?)

George H.

 

[John S]

On 3/3/2020 6:32 AM, Jim Jackson wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Sounds like it to me. I think the stalled motor inrush is causing it.

 

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
<jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Terry Pinnell]

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

 

On Tue, 03 Mar 2020 16:48:57 +0000, Terry Pinnell
<me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

If there was no load on the big cap, the supply would eventually
charge it. But the start current of the motor could collapse
everything when it was connected. A supercap might work. Or a better
power supply.







--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[George Herold]

On Tuesday, March 3, 2020 at 11:53:11 AM UTC-5, Terry Pinnell wrote:

Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

Are you switching the power at the AC input or DC output?

George H.

 

[Terry Pinnell]

Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

 

[George Herold]

On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:

On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Oh! So this is a hack and the best bet will be a bigger power supply.
but as long as the DC motor isn't starved for torque, then you just need
to limit the current some.. so how about a series resistor, ~0.1 ohms?

George H.

 

[DemonicTubes]

On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:

Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

 

[Rick C]

On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:

On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[DemonicTubes]

On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:

On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power.. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

 

[Rick C]

On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:

On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2..4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[DemonicTubes]

On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote:

On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution.

 

[Jasen Betts]

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:

I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

overcurrent... a fairly common problem when tyrying to run motors off
switching powersupplies.

adding large capacitors may help.

--
Jasen.

 

[Michael Kellett]

On 03/03/2020 12:17, Terry Pinnell wrote:

I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

Terry, East Grinstead, UK

Are you quite sure that the motor stall current is only 4A with full
working voltage applied ? This is quite different from stalling the
motor and measuring the current (which will likely be limited by the
power supply.) I would expect the rated voltage stall current of the
motor to be at least 10x the full load working current.

MK

 

[Terry Pinnell]

George Herold <ggherold@gmail.com> wrote:

On Tuesday, March 3, 2020 at 11:53:11 AM UTC-5, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

Are you switching the power at the AC input or DC output?

Tried both. On the occasion I got the full power, I was tapping the 5V
connecting wire onto the motor's +ve input.

 

[Terry Pinnell]

DemonicTubes <tlackie@gmail.com> wrote:

On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson
jj@franjam.org.uk> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.


I was interested in the product, so looked at the datasheet, where it says

Over-Current Protection >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be
the full stall current of aprox 4A, recovers, kicks in again, recovers,
etc,etc?

Jim

Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.

Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK

Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient. The NiMH batteries power the motor at '3.8 to 4.1 V". This supply runs at 5 volts and he has not said anything about reducing that voltage that I saw. They guy is not very precise in his description of the circuit though. I don't know what he means by "ex-screwdriver 2.4 motor". Is that 2.4 volts? 2.4 amps? Maybe 2.4 revision???

Anyway, a quarter ohm or maybe a bit more resistance should be added between the motor input and the PSU output. That would drop the volt at full power. Or maybe use a smaller resistor (~0.1 ohm) and a diode drop. Or maybe two diode drops, one silicon and one Schottky plus optionally a tenth ohm resistor.

I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Certainly a normal resistor would most likely work. The reason I suggested an NTC ('thermistor' as they are commonly known) is to avoid wasting power. They are readily available and dirt cheap...of course if you don't have one on hand and need to get it working now, yeah just throw a low value resistor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'. They start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution.

It's not, it's a 2.4 V ex-screwdriver motor, originally powered by two
1.2 V NiCads.

For the last 16 years, as I mentioned, it's been powered by three Nimh
batteries (C-type, not AA, another typo, sorry), "...delivering a
voltage of about 3.8 to 4.1 V...". A lower voltage of 2.5 V or so from
two such batteries delivers insufficient current to open and close the
quite heavy curtains. It's running well at present, closing smoothly in
just over 2 secs:
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1
but I'd rather like battery independence.

 

[Terry Pinnell]

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote:
I bought the following 4A 5V supply adapter:
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

overcurrent... a fairly common problem when tyrying to run motors off
switching powersupplies.

adding large capacitors may help.

I have a couple of supercapacitors on order (from China, so maybe I'll
be waiting a long time) but as you see from my earlier post a 100,000uF
electrolytic didn't fix it.