Series Connect Lab SM Power Supplies

[Larry Underwood]

I need a variable bench supply that will provide 0-32VDC at 30A. I
already have two of these inexpensive (0-16VDC 30A) units. Please see
link below for full specs:

http://www.jaycar.com.au/productView.asp?ID=MP3802&form=CAT2&SUBCATID=999#12

I have heard SMPS's can be operated in series if a diode in placed
across the connected positive and negative leads to prevent one from
loading the other.

Can someone please confirm this?

Also, is it necessary, or preferrable, that both supplies are adjusted
to about the same voltage, ie. 10V and 10V to get 20V, as opposed to
15V and 5V, or 15V and 5V?

Is the amp rating affected at all by doing this?

Thank you for any assistance.

Lary Underwood

 

[Larry Underwood]

Oh, I forgot to ask ... would it be acceptable to string five 6A
diodes in series, rather than use one 30A diode? I realize there will
be a 3.5V drop due to this.

Thanks again,

Larry

 

[Spehro Pefhany]

On Mon, 24 Oct 2011 10:20:44 GMT, the renowned

I need a variable bench supply that will provide 0-32VDC at 30A. I
already have two of these inexpensive (0-16VDC 30A) units. Please see
link below for full specs:

http://www.jaycar.com.au/productView.asp?ID=MP3802&form=CAT2&SUBCATID=999#12

I have heard SMPS's can be operated in series if a diode in placed
across the connected positive and negative leads to prevent one from
loading the other.

Can someone please confirm this?

I don't think so. Those things probably have the negative output
grounded, so connecting them in series will short the "top" one.

Also, is it necessary, or preferrable, that both supplies are adjusted
to about the same voltage, ie. 10V and 10V to get 20V, as opposed to
15V and 5V, or 15V and 5V?

Is the amp rating affected at all by doing this?

See the manual- output current for each output voltage- and choose the
lower of the two currents if they are not equal.

Thank you for any assistance.

Lary Underwood

Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

On Mon, 24 Oct 2011 10:27:43 GMT, the renowned

Oh, I forgot to ask ... would it be acceptable to string five 6A
diodes in series, rather than use one 30A diode? I realize there will
be a 3.5V drop due to this.

No- diodes connected in series will have the same current rating,
since all the current goes through each diode.

Thanks again,

Larry

Best regards,
Spehro Pefhany

 

[MrTallyman]

Oh, I forgot to ask ... would it be acceptable to string five 6A
diodes in series, rather than use one 30A diode? I realize there will
be a 3.5V drop due to this.

Thanks again,

Larry

5 diodes would not drop 3.5 volts. 0.35V maybe.

 

[MrTallyman]

I don't think so. Those things probably have the negative output
grounded, so connecting them in series will short the "top" one.


See the manual- output current for each output voltage- and choose the
lower of the two currents if they are not equal.



Best regards,
Spehro Pefhany

You are an idiot. DC power supplies have full floating outputs.

 

[The Great Attractor]

I need a variable bench supply that will provide 0-32VDC at 30A. I
already have two of these inexpensive (0-16VDC 30A) units.

[...]

Once in the university, there was a need for a 100KV supply. There were
25KV supplies with both terminals isolated from ground. Professor
connected four of these in series without any doubt in mind ))
True story, I omit the names


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

HVDC supplies will almost certainly, always be fully isolated. Any
grounded element is by customer option or deliberate action.
And it will NOT always be the negative node.

 

[Martin Riddle]

You are an idiot. DC power supplies have full floating outputs.

I see no documentation that says this supply has isolated outputs.
I only see two terminals, and the third ground terminal is missing.
With out any experimentation, I would say it cannot be used in that fashion.

Cheers

 

[[email protected]]

5 diodes would not drop 3.5 volts. 0.35V maybe.

AlwaysWrong, how *do* you do it?

 

[Rich Webb]

I need a variable bench supply that will provide 0-32VDC at 30A. I
already have two of these inexpensive (0-16VDC 30A) units.

[...]

Once in the university, there was a need for a 100KV supply. There were
25KV supplies with both terminals isolated from ground. Professor
connected four of these in series without any doubt in mind ))
True story, I omit the names

Reminds me of games that a tech-to-be-nameless (Hi, Mike!) played with a
tray of discarded 9 V batteries. They snap together *so* well in series.

 

[[email protected]]

Maybe he is really, really smart and just pretends to be AlwaysWrong.

*No* one is that smart.

 

[[email protected]]

He said "series."

What diode (or five) would be only .35V at 30A?

 

[Spehro Pefhany]

What diode (or five) would be only .35V at 30A?

This one maybe, if you let it warm up a bit:

www.vishay.com/docs/94226/94226440.pdf

 

[John S]

This one maybe, if you let it warm up a bit:

www.vishay.com/docs/94226/94226440.pdf

Oooooo! Good find, Spehro. He might need to keep the power supplies
below 32V, though, just in case.

 

[[email protected]]

This one maybe, if you let it warm up a bit:

www.vishay.com/docs/94226/94226440.pdf

Leakage current = 1.12A at 30V and 125C. Better not warm it up too much. ;-)

 

[Spehro Pefhany]

Oooooo! Good find, Spehro. He might need to keep the power supplies
below 32V, though, just in case.

Since they'll only go to 16V, that shouldn't be problem...



Best regards,
Spehro Pefhany

 

[John S]

Since they'll only go to 16V, that shouldn't be problem...



Best regards,
Spehro Pefhany

Ah! Correct! My oversight.

Thanks.

 

[mike]

I need a variable bench supply that will provide 0-32VDC at 30A. I
already have two of these inexpensive (0-16VDC 30A) units. Please see
link below for full specs:

http://www.jaycar.com.au/productView.asp?ID=MP3802&form=CAT2&SUBCATID=999#12

I have heard SMPS's can be operated in series if a diode in placed
across the connected positive and negative leads to prevent one from
loading the other.

Can someone please confirm this?

Also, is it necessary, or preferrable, that both supplies are adjusted
to about the same voltage, ie. 10V and 10V to get 20V, as opposed to
15V and 5V, or 15V and 5V?

Is the amp rating affected at all by doing this?

Thank you for any assistance.

Lary Underwood

If the negative is grounded, as implied by the other post, you're screwed.


For floating supplies, I've been screwed too.
Power supplies are not designed to have current stuffed into their
outputs. And some were designed by clueless engineers and not tested
beyond the published specifications. Or some manager decided
to save a dime by removing some protection circuitry he didn't
understand. Couldn't ask the engineer, 'cause they laid him off.

I've had power supplies that would lock up. When the reverse current
went away, they'd go to full voltage at maximum current. Silicon diode
was not sufficient to prevent it. Didn't try a lower voltage diode.
Reverse diode is essential, but may not save you...test it.

Use a single diode. Series won't work; parallel has matching and thermal
problems. Probably works most of the time. Compare the cost of blowing
up what you're powering or the supplies to the cost of the diode.
Decide accordingly.

You can get some interesting limit-cycle oscillations, depending on the
nonlinearity of your load and foldbackness of the TWO current limits.
Once one output goes negative, you can't rely on what the current limit
will do. Test it.

If you want an example of a limit-cycle oscillation, power a disk drive
from a supply with limit
set lower than what it takes to spin it up. Don't use a drive you care
about.

 

[MrTallyman]

I see no documentation that says this supply has isolated outputs.
I only see two terminals, and the third ground terminal is missing.
With out any experimentation, I would say it cannot be used in that fashion.

Cheers

Yes, cheap Chinese tends to lack adherence to any standard.

Still, most DC supplies are full floating, regardless of whether a
ground terminal has been provided as a quick jumper point or not.

Those that do not have the grounding lug typically have the EARTH
ground symbol on the negative output terminal. Floating supplies will
show polarity, but no ground symbol.

Again, they are all typically full floaters because the supply maker
does not know whether the user wants a positive or negative supply. Hard
grounding one lead takes that choice away.

 

[TheGlimmerMan]

AlwaysWrong, how *do* you do it?

0.15V x 5. (in series) (which would not work for this application to
begin with).

Are you saying that they drop three quarters of a volt each?

You are an idiot.

They need to be in parallel and they need to all be thermally bonded to
each other, which still may not work.

**** off and die, Williams, you stupid putz!