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Re: [Amps] Series PC Power Supplies

To: "'Jim Tonne'" <>, <>,<>
Subject: Re: [Amps] Series PC Power Supplies
From: "Harold Mandel" <>
Date: Thu, 1 Jun 2006 16:12:09 -0400
List-post: <>
"Whoa, whoa, whoa!" (HIHI)
(As Dan Ackroyd says in Ghostbusters).

D.C. Power supplies may be paralleled if there are
no problems with approaching the total limit of the combined
ampacities. The internal resistance of the charging circuit
presents some hurdles when putting rectifier units in series.

However, in regulated circumstances where the output voltage of
a combined bank of rectifiers must present a controlled voltage
within hundredths of a volt, (e.g., charging VRLA cells), the rectifiers
all have a "rectifier sharing" circuit that controls the output of each
unit individually by providing a reference voltage in a buss.

The best solution is to get a power supply at the desired voltage
because when putting the individual units in series the regulators
may become out-of-whack as components age with heat, and that may
lead to a catastrophic and/or cascaded failure that wipes out all the

Paralleled supplies to develop better ampacity in a
load environment just require D.C. output cabling heavy enough to balance
load and to overcome the minute amount of D.C. resistance in the cables

I found that when paralleling two Astron 75's better results were achieved
using 2/0AWG WELD type cable with crimped lugs, the Positive lead going to
one power supply and the Negative lead going to the other power supply with
2/0AWG jumpers tying the two supplies together at their outputs. There was
actually a difference in performance when trying the connections any other


-----Original Message-----
From: [] On
Behalf Of Jim Tonne
Sent: Thursday, June 01, 2006 3:18 PM
Subject: Re: [Amps] Series PC Power Supplies

If the supplies are in series wouldn't each be passing
the same number of amps?  What is there to "balance"?
What do you mean by "placing rectifiers across..." each
- Jim WB6BLD

----- Original Message ----- 
From: "Will Matney" <>
To: <>
Sent: Thursday, June 01, 2006 3:07 PM
Subject: Re: [Amps] Series PC Power Supplies

> Another recommended practice is to place rectifiers across the + and - of 
> each supply to try and balance the load. If the load is not balanced 
> across each, one supply can be overburdened if just slightly off from the 
> others. The rectifiers need to be rated at the same current capability of 
> the total supply in a series connection. The low side supplies ground will

> be the supply ground and the ground for the last rectifier in the string. 
> This is shown in several power supply books that mentions seriesing and 
> paralelling supplies for increased voltage or current. Generally though, 
> this practice of using several supplies is not really recommended because 
> of the balancing problems.
> Best,
> Will
> *********** REPLY SEPARATOR  ***********
> On 6/1/06 at 11:57 AM Joe Isabella wrote:
>>Two things...
>>1. You can get a brand new 25A switching supply for $80-90 if you look
>>around.  I bought my Samlex 25A for $80.
>>2. How did you series the supplies you have?  The "first" one will provide
>>your "ground" connection.  Take the red wires from that and connect them
>>to the black wires of the "second" supply.  Now take the red wires from
>>that one, and connect them to the black wires of the "third" supply, which
>>will provide the positive (15 VDC from the black wires of the "first"
>>supply to the red wires of the "third" supply, in this case) to your rig.
>>Make sure you tied the orange wires to each supply's red wires so they all
>>see "power good" line properly.  Make sure you have isolated the black
>>leads from chassis ground on the second & third supplies as as the article
>>says since they need to be floating (otherwise, the 5V from the first &
>>second supplies will be going straight to ground).  If you didn't isolate
>>them, you'll only see the 5V from the "third" supply...
>>Joe, N3JI
>>----- Original Message ----
>>From: aborg <>
>>To: Amps Amps <>
>>Sent: Thursday, June 1, 2006 9:09:38 AM
>>Subject: [Amps] Series PC Power Supplies
>>Hello Amp'ers,
>>Quick technical question. I'm embarrassed that I
>>can't figure this out, but not quite a super tech yet.
>>Here it is. I am attempting to series 3 pc pwr
>>supplies. I can't seemed figure why I'm only seeing 5+
>>volts. The link to the article is below. Here is an
>>excerpt from the article. "Our second means of
>>utilizing this low cost power is to connect the +5 VDC
>>outputs of three separate supplies together in series.
>>This will provide you with +15 VDC at 25 amps on up to
>>the maximum rating of the supplies you have acquired."
>>Can someone be kind enough to relieve from my
>>embarassment ?
>>Do You Yahoo!?
>>Tired of spam?  Yahoo! Mail has the best spam protection around
>>Amps mailing list
>>Amps mailing list
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