Decrease in voltage from powersupply in parallel circuit

Thread Starter

tt94

Joined Jan 20, 2023
7
I had a situation couple of days ago i haven't figured out.

I noticed a decrease in voltage from my powersupply (from 29V to 27.5V - 27V or something) as soon as i connected battery 2 in parallel with the other battery. (Total 2 battery in charge)

The first battery took about 1amps (powersupply limited to 10amps), the second battery i connected in parallell took about 2 amps.
For somer reason i noticed a decrease in voltage from the powersupply as soon as the second battery was connected to the circuit to charge.

I adjusted the output voltage to about 29volt from the supply but was around 27volt when 2nd battery was connected.

Thoughts?
 

ThePanMan

Joined Mar 13, 2020
757
Please post a schematic of what you're trying to do. I'm thinking if you have a 29V power supply and a couple 24V batteries in parallel and you're using the PS as a charger - yeah, you're going to see the voltage drop for a while.

If you ARE charging batteries - STOP! Charging them the wrong way can result in a disastrous fire or even explosion. Not all batteries are created equal. Some can handle an abusive charger while others will not. At the least you could ruin your batteries, at the worst you could be dialing 911 in a panic while you choke from toxic smoke.

We'd prefer you stick around a long time. Don't be afraid to ask questions. Someone, I can't think of who, has a signature that says (to the effect) If you ask a dumb question you will learn. If you don't ask - you'll stay dumb. Not saying you're dumb, just pointing out that it's always better to get as much information (within reason) as possible.
 

Thread Starter

tt94

Joined Jan 20, 2023
7
Please post a schematic of what you're trying to do. I'm thinking if you have a 29V power supply and a couple 24V batteries in parallel and you're using the PS as a charger - yeah, you're going to see the voltage drop for a while.

If you ARE charging batteries - STOP! Charging them the wrong way can result in a disastrous fire or even explosion. Not all batteries are created equal. Some can handle an abusive charger while others will not. At the least you could ruin your batteries, at the worst you could be dialing 911 in a panic while you choke from toxic smoke.

We'd prefer you stick around a long time. Don't be afraid to ask questions. Someone, I can't think of who, has a signature that says (to the effect) If you ask a dumb question you will learn. If you don't ask - you'll stay dumb. Not saying you're dumb, just pointing out that it's always better to get as much information (within reason) as possible.
Well, its simply 2 lead acid batteries connected to a PowerSupply in prallalel with eachother. Can make a schematic or even take a picture during the week here.
Why am i going tosee that voltage drop for a while? Im curious haha..

These are the same batteries ( lead acid, 28v ). Im more used to NI-CD batteries.

Thanks. Agree.
 

ThePanMan

Joined Mar 13, 2020
757
These are the same batteries ( lead acid, 28v ).
Off hand I'm not familiar with Lead Acid batteries in a 28 volt configuration. The closest I can come to 28 volts is two 12 volt batteries being held at their float voltage of 13.6 to 13.8 volts. But that's 27.2 to 27.6 volts. I don't know if a 24 volt battery charger will take a battery that high.

I suspect - not disagreeing with you - just suspicious that you're not working with lead acid batteries. But again, I'm not familiar with a 28 volt battery. Generally speaking of lead acid batteries, they're commonly 2.2 volts per cell. A 28 volt battery would have 12.7 cells (roughly). It's just an odd number. So forgive us for asking for pictures and schematics. Because your statement:
its simply 2 lead acid batteries connected to a PowerSupply in prallalel with eachother.
This is a bit confusing as well. Do you mean you have two 12 volt batteries in series with each other connected to a 28 volt power supply parallel to the overall battery arrangement? Or are you saying you have two 28 volt batteries in parallel with a charger? Details matter. It's the difference between a successful project, a failed project or a ton of excitement, flames and screaming. We here at AAC don't like to subject members to the later. Failed projects ? ? ? Well, that's an opportunity for learning. Successful projects are reaffirming. Excitement, flames and screaming means someone's life is in jeopardy. THAT we don't want. Oh, and I am not personally AAC, I'm just another member, same as you are. So I'm not speaking FOR AAC, just speaking as a concerned member.
 

ThePanMan

Joined Mar 13, 2020
757
Ran a search for "28 volt lead acid battery". The ONLY thing I found in a 28 volt configuration were Lithium Ion (Li-Ion). My search also revealed quite a few 12 volt 28 amp hour batteries. But no lead acid batteries in a 28 volt config.
 

BobTPH

Joined Jun 5, 2013
8,665
If the charger has to provide twice the current, abd it is not a regulated supply, the voltage will drop.

By the way, batteries should not be put in parallel unless they are at the same voltage.
 

MisterBill2

Joined Jan 23, 2018
17,827
Really, it does not matter what chemistry the batteries are, as far as the voltage drop issue goes. I am guessing that this is a real world situation and not a simulation. One battery was charging and the voltage was adjusted to 29 volts so that the current was one amp. Then another battery was connected in parallel, which was drawing two amps more. The answer is simple, which is that the supply is not a regulated supply. And a non-regulated supply has internal resistance, and so as the current increases the voltage drops a bit.
In the basic DC circuits course, about week 5, the concept of voltage source internal resistance is presented, along with the information that all real (non-regulated) power supplies show internal resistance in that as the current increases the voltage out decreases.
The fact is that not all adjustable voltage supplies are regulated. Some folks may find that hard to believe, but it is true.
 
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