2x24V switchmode power supplies = 48V?...

On Monday, August 3, 2020 at 7:41:38 PM UTC+10, Rob wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
The bigger problem connecting supplies like this is ensuring the
supplies can handle the possibility of current flowing INTO
their outputs. E.g., highly reactive loads (cuz most higher
voltage DC applications tend to not be purely resistive -- motors,
etc.)

The type of load has not even been mentioned, so the poster would
first have to inform us about that.
Click to expand...

Thanks everyone for your valuable insights. The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

Cheers.
 
On Saturday, August 1, 2020 at 10:42:37 AM UTC-7, edward...@gmail.com wrote:

[about connecting DC supplies in series]

> Even with DC-case ground, fine as long as hot and neutral don\'t. As long as you don\'t hook up cases together.

Don\'t forget the third-prong ground! Any metal-cased appliance which can be
touched, must have the case connected to the AC third prong ground.

Even if YOU don\'t connect them together, your AC wiring would have to be made
unsafe in order for the AC power source not to connect \'em. Third prong ground
is passed-trough from input to output on most isolation transformers.
 
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digitaltrousers@gmail.com
wrote:

On Monday, August 3, 2020 at 7:41:38 PM UTC+10, Rob wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
The bigger problem connecting supplies like this is ensuring the
supplies can handle the possibility of current flowing INTO
their outputs. E.g., highly reactive loads (cuz most higher
voltage DC applications tend to not be purely resistive -- motors,
etc.)

The type of load has not even been mentioned, so the poster would
first have to inform us about that.

Thanks everyone for your valuable insights. The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

Cheers.
Click to expand...

Oh one of those adjustable buck converters.
Aren\'t those the ones that Dave Jones on EEVblog was excited about ?

To me, those are not complete power supplies. No place to plug it in.

You need a power supply for your power supply. Why not just buy a
real power supply ?

There are some out there that don\'t take much abuse until they die but
if carefull, aren\'t too bad. And they come with a power supply built
in. Imagine that !
 
digitaltrousers@gmail.com <digitaltrousers@gmail.com> wrote:
On Monday, August 3, 2020 at 7:41:38 PM UTC+10, Rob wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
The bigger problem connecting supplies like this is ensuring the
supplies can handle the possibility of current flowing INTO
their outputs. E.g., highly reactive loads (cuz most higher
voltage DC applications tend to not be purely resistive -- motors,
etc.)

The type of load has not even been mentioned, so the poster would
first have to inform us about that.

Thanks everyone for your valuable insights. The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.
Click to expand...

When your two supplies can deliver more current than the module you
use can be set to (5A?) there will be no additional protection required,
the module will limit the current.

You can just wire them in series after you have made sure there is no
connection between the DC output and the case of the supplies.
 
boB <boB@K7IQ.com> wrote:
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digitaltrousers@gmail.com
wrote:

On Monday, August 3, 2020 at 7:41:38 PM UTC+10, Rob wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
The bigger problem connecting supplies like this is ensuring the
supplies can handle the possibility of current flowing INTO
their outputs. E.g., highly reactive loads (cuz most higher
voltage DC applications tend to not be purely resistive -- motors,
etc.)

The type of load has not even been mentioned, so the poster would
first have to inform us about that.

Thanks everyone for your valuable insights. The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

Cheers.


Oh one of those adjustable buck converters.
Aren\'t those the ones that Dave Jones on EEVblog was excited about ?

To me, those are not complete power supplies. No place to plug it in.

You need a power supply for your power supply. Why not just buy a
real power supply ?
Click to expand...

Well, because those modules have all kinds of interesting features that
an old-style lab supply does not have, and because you can get usable
supplies to power such a module very cheaply.

Of course you can also get a complete lab supply that combines the two
functions and works directly from AC mains, but it will usually cost more.

Maybe in the future, the makes of those buck converter modules realize
there is a market for a model that works from AC mains, and start making
that as well. But part of the cost advantage will be that the buck
converter modules weigh much less than a complete supply and can thus
be shipped from China much cheaper, and you can obtain the fixed DC
supply locally. So this solution may still be more expensive.
 
whit3rd <whit3rd@gmail.com> wrote:
On Saturday, August 1, 2020 at 10:42:37 AM UTC-7, edward...@gmail.com wrote:

[about connecting DC supplies in series]

Even with DC-case ground, fine as long as hot and neutral don\'t. As long as you don\'t hook up cases together.

Don\'t forget the third-prong ground! Any metal-cased appliance which can be
touched, must have the case connected to the AC third prong ground.

Even if YOU don\'t connect them together, your AC wiring would have to be made
unsafe in order for the AC power source not to connect \'em. Third prong ground
is passed-trough from input to output on most isolation transformers.
Click to expand...

Exactly. So you really need to open and disassemble the supply and
remove all connections from output to case ground, when present.
 
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digitaltrousers@gmail.com
wrote:

Thanks everyone for your valuable insights.
The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.
Click to expand...

The Riden programmable power supply will take up to 70V at 6A for
input power. Will your unspecified model photocopier power supplies
deliver 6 Amps? You might consider running the programmable power
supply from a single 24VDC power supply and tolerating a lower output
voltage before investing in a real power supply. Note the input power
supply does not need to be a regulated switching power supply, but can
be a rather crude transformer, bridge, filter, fuse arrangement. The
Riden programmable power supply has its own built in adjustable
regulator.




--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On 04 Aug 2020 15:57:02 GMT, Rob <nomail@example.com> wrote:

boB <boB@K7IQ.com> wrote:
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digitaltrousers@gmail.com
wrote:

On Monday, August 3, 2020 at 7:41:38 PM UTC+10, Rob wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
The bigger problem connecting supplies like this is ensuring the
supplies can handle the possibility of current flowing INTO
their outputs. E.g., highly reactive loads (cuz most higher
voltage DC applications tend to not be purely resistive -- motors,
etc.)

The type of load has not even been mentioned, so the poster would
first have to inform us about that.

Thanks everyone for your valuable insights. The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

Cheers.


Oh one of those adjustable buck converters.
Aren\'t those the ones that Dave Jones on EEVblog was excited about ?

To me, those are not complete power supplies. No place to plug it in.

You need a power supply for your power supply. Why not just buy a
real power supply ?

Well, because those modules have all kinds of interesting features that
an old-style lab supply does not have, and because you can get usable
supplies to power such a module very cheaply.

Of course you can also get a complete lab supply that combines the two
functions and works directly from AC mains, but it will usually cost more.

Maybe in the future, the makes of those buck converter modules realize
there is a market for a model that works from AC mains, and start making
that as well.
Click to expand...

That would be good. Maybe this is just their way of getting started
in the power supply business and that will happen.



But part of the cost advantage will be that the buck
converter modules weigh much less than a complete supply and can thus
be shipped from China much cheaper, and you can obtain the fixed DC
supply locally. So this solution may still be more expensive.
Click to expand...
 
On Wednesday, August 5, 2020 at 4:07:44 AM UTC+10, Jeff Liebermann wrote:
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digital..@gmail.com
wrote:

Thanks everyone for your valuable insights.
The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

The Riden programmable power supply will take up to 70V at 6A for
input power. Will your unspecified model photocopier power supplies
deliver 6 Amps? You might consider running the programmable power
supply from a single 24VDC power supply and tolerating a lower output
voltage before investing in a real power supply. Note the input power
supply does not need to be a regulated switching power supply, but can
be a rather crude transformer, bridge, filter, fuse arrangement. The
Riden programmable power supply has its own built in adjustable
regulator.
Click to expand...
Hi Jeff. The PSUs are capable of 10A each, and have over-current protection.. I can also adjust their output up to nearly 30V. My initial idea was to do a linear power supply with a salvaged UPS transformer, but I\'m cold on that idea because it\'s not efficient and if I forget to turn the SUPPLY off (as opposed to turning off the Riden), there\'s still a fair bit of power going through the regulating zener diode (used to knock the linear supply\'s 86V DC down to 68V to stay under the Riden\'s voltage limit). I just got to thinking, the 2x good quality switchers I got for free would be a better option.
 
digitaltrousers@gmail.com <digitaltrousers@gmail.com> wrote:
On Wednesday, August 5, 2020 at 4:07:44 AM UTC+10, Jeff Liebermann wrote:
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digital..@gmail.com
wrote:

Thanks everyone for your valuable insights.
The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

The Riden programmable power supply will take up to 70V at 6A for
input power. Will your unspecified model photocopier power supplies
deliver 6 Amps? You might consider running the programmable power
supply from a single 24VDC power supply and tolerating a lower output
voltage before investing in a real power supply. Note the input power
supply does not need to be a regulated switching power supply, but can
be a rather crude transformer, bridge, filter, fuse arrangement. The
Riden programmable power supply has its own built in adjustable
regulator.

Hi Jeff. The PSUs are capable of 10A each, and have over-current protection. I can also adjust their output up to nearly 30V. My initial idea was to do a linear power supply with a salvaged UPS transformer, but I\'m cold on that idea because it\'s not efficient and if I forget to turn the SUPPLY off (as opposed to turning off the Riden), there\'s still a fair bit of power going through the regulating zener diode (used to knock the linear supply\'s 86V DC down to 68V to stay under the Riden\'s voltage limit). I just got to thinking, the 2x good quality switchers I got for free would be a better option.
Click to expand...

Another thing you need to check is if those powersupplies like to run
without load. Some switchmode supplies do not really like that. As it
is from a photocopier it is probably going to be OK (as those things
also go in sleepmode etc) but it still does not hurt to check that before
you invest time/money in construction.
 
On Tue, 4 Aug 2020 22:51:58 -0700 (PDT), digitaltrousers@gmail.com
wrote:

On Wednesday, August 5, 2020 at 4:07:44 AM UTC+10, Jeff Liebermann wrote:
On Mon, 3 Aug 2020 20:38:09 -0700 (PDT), digital..@gmail.com
wrote:

Thanks everyone for your valuable insights.
The \"load\" will be one of these: https://hackaday.com/2020/03/16/review-the-riden-rd6006w-dc-power-supply-module/#more-398558
Potentially driving any type of load.

The Riden programmable power supply will take up to 70V at 6A for
input power. Will your unspecified model photocopier power supplies
deliver 6 Amps? You might consider running the programmable power
supply from a single 24VDC power supply and tolerating a lower output
voltage before investing in a real power supply. Note the input power
supply does not need to be a regulated switching power supply, but can
be a rather crude transformer, bridge, filter, fuse arrangement. The
Riden programmable power supply has its own built in adjustable
regulator.

Hi Jeff. The PSUs are capable of 10A each, and have over-current protection. I can also adjust their output up to nearly 30V. My initial idea was to do a linear power supply with a salvaged UPS transformer, but I\'m cold on that idea because it\'s not efficient and if I forget to turn the SUPPLY off (as opposed to turning off the Riden), there\'s still a fair bit of power going through the regulating zener diode (used to knock the linear supply\'s 86V DC down to 68V to stay under the Riden\'s voltage limit). I just got to thinking, the 2x good quality switchers I got for free would be a better option.
Click to expand...

Most of the efficiency losses in a linear power supply are in the
regulator, not the transformer, diodes, or filter caps. In a linear
regulator, you take whatever voltage comes out of the xformer, diodes,
and caps, and reduce it heating up some linear regulator transistors.
As long as you don\'t saturate the xformer core or shove too much
current through the diodes, they stay fairly cool.

If you remove the linear regulator section and replace it with a
switcher, the switcher is much more efficient. Instead of reducing
the output voltage by heating up some transistors, it varies the duty
cycle of the output waveform, and filters the result to produce DC.
The current goes through a switching transistor, which is either on,
or off. When on, the only heating is from the saturation voltage
times the current, which isn\'t much heat. When the switching
transistor is off, there\'s no current, so there\'s no heating.

In your arrangement, the Riden programmable power supply is a
switching regulator. It will offer the same efficiency and heating
whether driven by an xformer, diodes, and capacitor combination, as it
would if driven by a switching power supply brick.

However, I will admit that dropping in a switching power supply brick
is easier. That\'s what Riden does in the RD6006:
<https://tech.scargill.net/riden-rd6006-dc-variable-power-supply/>
Notice the installation of a fan in the box.

Looks like a 60v 10A switcher is available for $27:
<https://www.ebay.com/itm/AC-110V-AC-220V-TO-DC5V-DC12V-DC24V-DC36V-DC48V-DC60V-Switch-Power-Supply-Driver/254418599443>

More:
<https://www.eevblog.com/forum/testgear/ruideng-riden-rd6006-dc-power-supply/>

Good luck.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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