DC voltage step down (58V -> less than 50V)

W

WP

Guest
I have searched Google and can't find the answer to my question so I'm
going to ask the experts here.

I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Does anyone know what I can use to step down my voltage ? I looked at
www.linear.com and there are a lot of parts that are close, but none
that meet my requirements.

Thank You
 
I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.
Click to expand...

Hi,

Just my $0.02.

As you say that regulation is not an issue, a crude solution I've used
in the past is low-voltage car headlight bulbs in series with the supply.
You would need about 60 watts worth and to insure that there is always some
load current through them.


Cheers - Joe
 
On Sat, 27 Sep 2003 15:41:35 GMT, WP <cnuk@_at_shaw.ca> wrote:

I have searched Google and can't find the answer to my question so I'm
going to ask the experts here.

I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Does anyone know what I can use to step down my voltage ? I looked at
www.linear.com and there are a lot of parts that are close, but none
that meet my requirements.

Thank You
Click to expand...
If the supply is unregulated, just load it a bit with a power resistor
to pull it down. If it's regulated, futz with the regulator feedback
resistor values to change the output voltage. Actually, you needn't
even bother to do that: the steppers will load it, and the ICs
actually won't explode at 58 volts anyhow: they can probably handle a
lot more than 50 volts in real life.

John
 
Joe McElvenney wrote:
I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Hi,

Just my $0.02.

As you say that regulation is not an issue, a crude solution I've used
in the past is low-voltage car headlight bulbs in series with the supply.
You would need about 60 watts worth and to insure that there is always some
load current through them.


Cheers - Joe
Click to expand...
A buck transformer to lower the voltage to the primary would make a lot
more sense.
--


Michael A. Terrell
Central Florida
 
In article <Pcidb.22077$O85.12263@pd7tw1no>, cnuk@_at_shaw.ca
mentioned...
I have searched Google and can't find the answer to my question so I'm
going to ask the experts here.

I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Does anyone know what I can use to step down my voltage ? I looked at
www.linear.com and there are a lot of parts that are close, but none
that meet my requirements.

Thank You
Click to expand...
First off you should look for an adjustment on the power supply. If
not, you should see if the power supply will drop to 50V under load,
which would be okay. Standard telephone equipment runs on 48 to 54V,
so it should drop somewhat.

Then if you're still not low enough, try putting some 6 amp rectifier
diodes in series with the power supply output. Each diode should drop
a minimum of .6V, but closer to 1V under heavy load. 8 or 10 of those
in series should drop 8V or more.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <3F7608CA.6B351634@earthlink.net>,
mike.terrell@earthlink.net mentioned...
Joe McElvenney wrote:

I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Hi,

Just my $0.02.

As you say that regulation is not an issue, a crude solution I've used
in the past is low-voltage car headlight bulbs in series with the supply.
You would need about 60 watts worth and to insure that there is always some
load current through them.


Cheers - Joe




A buck transformer to lower the voltage to the primary would make a lot
more sense.
Click to expand...
Good idea if the transformer is a regular transformer. But my own
experience is that this type of supply is a high reliability regulated
type and they usually use a ferroresonant constant voltage
transformer. You can drop the AC voltage down to 95VAC and the output
won't change. Then, below that it might not work at all.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
"Watson A.Name - Watt Sun" <alondra101@hotmail.com> wrote in message
news:MPG.19e0cf51927fb675989720@news.dslextreme.com...
In article <Pcidb.22077$O85.12263@pd7tw1no>, cnuk@_at_shaw.ca
mentioned...
I have searched Google and can't find the answer to my question so I'm
going to ask the experts here.

I have an old telephone power supply that outputs approx 58V DC under no
load. I want to use the power supply to drive NEMA 23 stepper motors,
but the driver circuit uses an L298 who's max rating is 50V. Therefore
I need to step the voltage down to something less than 50V. It's
driving motors so it doesn't have to be precise and can fluctuate with
load. I'm hoping for a device that can handle up to 5 or 6 amps.
That's 300W so it's going to be big whatever it is, but that's alright.

Does anyone know what I can use to step down my voltage ? I looked at
www.linear.com and there are a lot of parts that are close, but none
that meet my requirements.

Thank You

First off you should look for an adjustment on the power supply. If
not, you should see if the power supply will drop to 50V under load,
which would be okay. Standard telephone equipment runs on 48 to 54V,
so it should drop somewhat.

Then if you're still not low enough, try putting some 6 amp rectifier
diodes in series with the power supply output. Each diode should drop
a minimum of .6V, but closer to 1V under heavy load. 8 or 10 of those
in series should drop 8V or more.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
Click to expand...
If your power supply is anything like the old telephone power supplies I
remember from the 70s, the output is not regulated at all. In this case you
are seeing 58 volts with no load, which would be about right for a PSU
intended to charge a nominal 48 volt battery stack, which actually charged
up to approximately 51 volts.

So one, rather bulky and heavy solution, should the PSU be of the old,
unregulated type, is to use it to charge four car batteries in series and
use them as both a power backup and for voltage smoothing and regulation.

On the other hand, that's not exactly a miniaturized solution (!) so you
need to know what the input resistance of your load is. If it is low
enough it will, in series with the internal resistance of the PSU, drop the
voltage from 58 to nearer to the 50 volts specified. If it's still high, a
power resistor in parallel with both PSU and load will reduce the load
resistance seen by the PSU and cause the output voltage to decrease further.
You will need to experiment with resistance values and make sure that the
resistor is of sufficient wattage to dissipate the power. Remember P=E^2/R.

I agree that you're probably safe using the PSU as is. especially in light
of the voltage dropping provided by PSU and load resistances, so the power
resistor solution is really a last resort. As a resort, the 4 car batteries
are a bit like Benidorm in august.

Hope this helps.

John
 
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