I am considering paralleling a couple of 20a variable adjustable psu's for 40a charging. According to what I have read on the world wide inter-web, it can be done quite easily, provided the following conditions are met:... units must be the same brand and same internal parts, (resistors, etc.), be current limiting, and have c.v. as well as c.c settings.The idea is to parallel them by first connecting the + and - leads from both psu's together, to a single + and - lead, which is, in turn, connected to the load/batts. The belief is the voltage drop over the leads will compensate for any minor fluctuations in voltage output of the two psu's. This will, allegedly eliminate the need for a more sophisticated arrangement, including diodes and such.In due course, one must also use one of the psu's as the voltage controller, by setting it at say .01v higher than the other unit, and putting it in c.v. mode, while using the second unit as the amperage controller, by cranking it to max (limited) amps, and placing it in c.c. mode. (both units set at max amps)As I'm sure some of you know, the idea is to cause the two units to properly share the load, by causing the unit in c.v. mode to lower its voltage to match the other's lower voltage setting.My understanding is the unit in c.v. mode will take over on it's own, once charge current tapers to =/< the max (limited) amp setting of the psu's.The units I'm considering paralleling are the gophert cps1620.??? Any thoughts on the feasibility of such a simple set up?(Thinking back, this seems to be essentially what BFL does with his various chargers.) Thanks!!

While I've never done what your proposing I have built many many systems involving charging with solar. In these systems there are often multiple charge controllers providing charging to the same battery bank. They work well in parallel without any "tricks" in the programming. All are programmed to the same battery charging voltage and current limits appropriate for the battery bank. All do their job accordingly.Power supplies may act differently but I really don't think it's even as difficult as you describe.

I agree with this. With a depleted battery bank set one psu at 14.2 and the other at 14.4. Both will chug away nicely as the bank voltage S-L-O-W-L-Y rises to 14.2, then #1 Sun will drop off, and #2 will continue and begin to taper amps as it approaches 14.4.Set both at 14.4 and I think you'll just get tapered amps, only more steeply tapered. Or, mess with the innards and get an automatic alternative to rubbing two sticks together.

The two supplies will share current when they are in current limit. That means setting both supplies to 15.5V or what ever when battery is discharged. You will get 40A. If you set the supplies to 14.4V and when the battery reaches that voltage the supplies will switch from current mode to voltage mode. When in voltage mode, power supplies do not share current well. The higher voltage supply will back bias the other supply. Depending on the cable resistance, you may get something from the lower voltage supply. I think it's a lot easier to get a 40A supply than to constantly baby sit the voltage adjust to get them to share.

I don't understand the OP why it has to be so complicated. I use multiple chargers all the time and the chargers are not exactly the same for voltage. It does work best when all the chargers have the same voltage but "perfection is the enemy of good enough." They all add their full amps until the battery voltage rises enough that the lowest voltage one doesn't have enough "spread" between its voltage and battery voltage to do its rated max current anymore, so that one's amps start to taper. But it still adds those tapering amps until battery voltage reaches that charger's voltage.If the chargers are all set to voltages near where you want Vabs to be, then the main bulk charge is mostly with all doing near full amps.Good enough. Amps will taper when Vabs is reached anyway, so who cares about a few minutes in there when you get fewer amps from some chargers before reaching Vabs? Big deal.You wouldn't try to run a 13.6 with a 14.4 in hopes they will add their amps more than a minute, but you can run a 14.4 with a 14.6 and a 14.8 just fine.If all the chargers have adjustable set points, then just twiddle to get them near the same voltage and that will get it done. Once the battery acceptance rate has fallen so that you have too many chargers on the job, you can leave them all on and they will each do some of the amps or you can yank a charger and put it away if you want when the total max amps of the remaining chargers is enough to meet that falling acceptance rate.

"Or, mess with the innards and get an automatic alternative to rubbing two sticks together."Thanks! I'll try to remember that if I'm ever stranded and in need of making a fire! :)As for #2 taking over, I think with the set-up I described, both psu's share the load until amps taper to at or below the 20a setting, so well into the 40a charge; not when reaching the preset volt setting. Perhaps it has to do with the psu's being c.v., c.c., and current limiting?

Paralleling Power Supply Units Made Easy ??? | Good Sam Community

160 Replies

ken_white
Explorer
Dec 02, 2014
Many bench type power supplies offer both features.

You will not typically find a basic CC power supply, like the CV power supply lines, due to the CC limited consumer application.
jrnymn7
Explorer
Dec 02, 2014
Thanks, Ken.

Yes, I'm trying to find a cc only unit on line, if only to look at its specs, and hopefully learn from them, but have not had any success. All the units are both cc and cv.

But in the case of charging a 6v or 12v battery, with the load continually changing, I'm not convinced even a cc only unit would hold the amps at say 5% of Bank Capacity without voltage going thru the roof. So V has to be limited, correct?
ken_white
Explorer
Dec 02, 2014
jrnymn7 wrote:
Would not a true voltage-limiting cc psu be indicated for proper EQ'ing?

You can use a current limited CV supply if you set the regulated voltage to some higher voltage value than the battery open circuit voltage.

When this occurs the CV output voltage drops and supply goes into a current limit condition and it stays there until the battery voltage approaches the regulated set-point - at this point the current starts to taper until the regulated voltage level is achieved.

A CC supply only has a current adjustment set-point and the output voltage floats in an effort to deliver this current - hence the Constant Current name.

Both supplies operate quite differently but either would work as long as the operator understands how each works and their limitations.

Terminology is important when trying to decide what to buy and/or use.

Just my $0.02
jrnymn7
Explorer
Dec 02, 2014
Would not a true voltage-limiting cc psu be indicated for proper EQ'ing?
ken_white
Explorer
Dec 02, 2014
Salvo wrote:
...This is a stupid discussion!...

Yep...

Reading is fundamental...

:B
Salvo
Explorer
Dec 02, 2014
I knew there was a reason I had him on ignore. He's splitting hairs. No one will use a supply like that. It has no relevance here. You don't have to disconnect the battery to fry the electronics when using a PS he's talking about. A PS with 50V output in CC mode will quickly fry the battery and all the electronics. This is a stupid discussion!

LScamper wrote:
ken white "You do whatever you want, but my comments are for the general case and not a CV supply operating in current limit mode..."

All convertors and power supplies talked about here have a constant voltage set point!

A true constant current supply operating into an open will have infinite voltage!!
ken_white
Explorer
Dec 02, 2014
LScamper wrote:
ken white "You do whatever you want, but my comments are for the general case and not a CV supply operating in current limit mode..."

All convertors and power supplies talked about here have a constant voltage set point!

A true constant current supply operating into an open will have infinite voltage!!

There have been numerous supplies discussed, and true CC and CV with current limit discussed.

I am talking about using a true CC supply, which is what a battery charger under the conditions being described can and may be used.

An ideal CC supply is infinite.

A true CC supply has boundary limits constrained by design.
LScamper
Explorer
Dec 02, 2014
ken white "You do whatever you want, but my comments are for the general case and not a CV supply operating in current limit mode..."

All convertors and power supplies talked about here have a constant voltage set point!

A true constant current supply operating into an open will have infinite voltage!!
ken_white
Explorer
Dec 02, 2014
Salvo wrote:
Can't cry wolf too many times. No precaution is necessary. There's nothing that can get damaged. You can disconnect a PS whenever you want, and under any condition from a battery.

A true CC supply assume any voltage within its operating space to delivered the set-point current.

If it is set for 3 amps, and its operating space is 5-30 volts, then the output could go to 30 volts.

Disconnect the battery which is drawing lots of current and now the current has high impedance load so the voltage increases.

This could be catastrophic...

You do whatever you want, but my comments are for the general case and not a CV supply operating in current limit mode...
Salvo
Explorer
Dec 02, 2014
Can't cry wolf too many times. No precaution is necessary. There's nothing that can get damaged. You can disconnect a PS whenever you want, and under any condition from a battery.

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Paralleling Power Supply Units Made Easy ???

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