Help with power supply

[Bluewatersailor]

Evening
We trying to top balance 8x200 ah cells with a 10A 30v power supply in stages 3.4v 3.5v 3.65v
Each cell 3.32v and then we wired them up in Parallel.
Before connecting up we set the power 3.4v turn the current down , turn off the power supply , connected the power supply to the batteries turn on and then turn the current up , it when upto 1.04A and no further , after Six hours it now say 1.01A
Does this sound ok ?
Shouldn't we be able to set the current highter in the beginning then 1.04A
Thanks

 

[Hedges]

200 ah x 8 in parallel = 1600 Ah.
Charging with 1A and 6 hours have gone by.
It's going to be a long night ...

Why did you set current to 1.04A? Is that an adjustable setting of your power supply?
I don't see any reason why you couldn't deliver the maximum 10A. That way you'd only have to wait up to 160 hours, depending on initial SoC.

 

[snoobler]

You are experiencing voltage drop due to:

1) thin wires
2) loose/poor connections
3) resistance in the power supply itself

Measure the voltage at the cells and compare to the power supply readout.

 

[Hedges]

Does your supply have remote sense inputs?
Measure voltage drop across the wires, from supply to battery terminal. That will give more digits precision than calculating Vsupply - Vbat


"in stages 3.4v 3.5v 3.65v"

You could set to a higher voltage stage that is acceptable for the battery.

(Do NOT adjust supply voltage higher than allowed lithium battery voltage to make up for IR drop, which depends on current being accepted by the batteries.)

 

[Bluewatersailor]

I did as will video . Without any connection turned the voltage to 3.4v turn the current nob to zero.
Turnoff the power supply and connect the leads to the batteries , turn on the power supply the voltage shown 3.4v , then I turned the current up as far as it when, but it only delivers 1.04A , I expected to see it go up to 10A .
I have read you need to connect the leads to gather before setting the voltage , why? . And would that made any difference?
I also checked the voltage at the end of the leads when I set the voltage and both read the same .

 

[Hedges]

Don't connect the leads together before setting the voltage. Don't connect the leads to battery before setting voltage.

For some supplies, an analog knob sets voltage and a needle is the display.
If open circuit, voltage shown by needle is the (maximum) setting.
If connected to battery, needle shows battery voltage, but knob may have set a much higher voltage (supply is in CC mode)
If shorted, needle shows zero volts. Supply is in CC mode.

Connecting the leads together is how you get current needle to show current limit adjusted by knob.

So set an confirm voltage with leads disconnected. Set and confirm current with leads shorted.
All assuming a supply with both CV and CC operation.

Probably with 3.4V max, 10A max, the supply is operating CV = 3.4V and battery only gets 1.04A due to wire and battery resistance.
Try again, this time setting 3.5V max and see how much current.
If no different, confirm current limit setting.

 

[Bluewatersailor]

Although the PS is set at 3.4v voltage at the batteries are showing 3.32v .?????reason why ????

Just to get this right , I only need to set the Voltage at the PS ( before its connnect to the batteries ) and
Don't need to do any thing to the current at that point , turn off the PS before connection to batteries .

Once the PS is connected to the batteries switch on then just turn the current knob up as high as it will go .
Correct ?
Very new to power supply so sorry if my question sound stupid .

 

[snoobler]

read my post above.

 

[Bluewatersailor]

You are experiencing voltage drop due to:

1) thin wires
2) loose/poor connections
3) resistance in the power supply itself

Measure the voltage at the cells and compare to the power supply readout.

The power supply read 3.4v the batteries read 3.32v
the PS reading match to my meter connected at the end of the leads .

 

[snoobler]

So the PS has internal resistance that causes it to measure 3.4V when there is a 1A current flowing and the cells are at 3.32V. It won't flow more current because it's limited to 3.4V. Increase voltage.

Are you following the PDF top balancing guide in Resources?

 

[Bluewatersailor]

So the PS has internal resistance that causes it to measure 3.4V when there is a 1A current flowing and the cells are at 3.32V. It won't flow more current because it's limited to 3.4V. Increase voltage.

Are you following the PDF top balancing guide in Resources?

Yes I did down load your guide , which is why I can't .understand why I can't get more current to flow .
Ok so it seen the problem is I need to turn the voltage to the next level to 3.5v .
Correct .
Thanks

 

[snoobler]

It's not "my" guide.

What you are experiencing is normal. 10A @ 3.X volts has high potential for voltage drop due to the resistances mentioned.

Did you series charge them with a BMS first?

 

[Hedges]

So the PS has internal resistance that causes it to measure 3.4V when there is a 1A current flowing and the cells are at 3.32V. It won't flow more current because it's limited to 3.4V. Increase voltage.

Are you following the PDF top balancing guide in Resources?

3.4 - 3.32 = 0.08V
0.08V / 1A = 0.08 ohms

That sounds high for wires.
Where is cell voltage measured? If on the cell terminal not the busbar, could be poor contact.
Measure voltage between busbar and cell terminal (practically the same point, just two different pieces of metal)

You may need to scrub off native aluminum oxide.

 

[snoobler]

Hedges this is extremely common for these cheap 30V/10A power supplies. We have a couple of posts a week about it.

 

[Hedges]

Hedges this is extremely common for these cheap 30V/10A power supplies. We have a couple of posts a week about it.

OK, 0.08 ohms mostly internal to the meter.

0.08 x 10A = 0.80V

"in stages 3.4v 3.5v 3.65v"

Can't crank up supply by 0.80V, only by 0.25V to 3.65V
That should give 3 more amps, for 4A charge current.
Now it'll only take 400 hours, 16 days (if starting from complete discharge.)

Did you series charge them with a BMS first?

With same current limit of supply, same internal resistance of supply, higher operating voltage for series connected cells, it'll charge much faster.
Reliable BMS to watch all individual cells is required.

 

[Bluewatersailor]

3.4 - 3.32 = 0.08V
0.08V / 1A = 0.08 ohms

That sounds high for wires.
Where is cell voltage measured? If on the cell terminal not the busbar, could be poor contact.
Measure voltage between busbar and cell terminal (practically the same point, just two different pieces of metal)

You may need to scrub off native aluminum oxide.

I've measured the voltage from on top of the bolts .
Each batteries measured the same.
Turned it off for now and will have another look on the morning .

 

[Bluewatersailor]

THis maybe where I am going wrong .

( 4.2 Before hooking the power supply to the cells, set the power supply to .2C or less of the combined AH of the cells. This will almost always turn out to be the max current setting of the power supply. )

How do I go about doing this ?
( connect the ps leads to gather and turn the current up as far as it goes )

 

[Hedges]

THis maybe where I am going wrong .

( 4.2 Before hooking the power supply to the cells, set the power supply to .2C or less of the combined AH of the cells. This will almost always turn out to be the max current setting of the power supply. )

How do I go about doing this ?
( connect the ps leads to gather and turn the current up as far as it goes )

With power supply disconnected from cells, short the power supply and see what current reading is. That will give the upper limit on charge current.

"This will almost always turn out to be the max current setting of the power supply"
With 10A supply and a single 200 Ah cell you're at 0.05C; with 8 cells more like 0.006C

You can just turn the supply up to max current.

 

[Bluewatersailor]

Just to report back , thank for all the suggestion ,I got a better PS with big leads and still had the same problem , so I rearranged the bank in series and added the BMS , charges at 14.6 v and 9 A , four hours later the voltage when upto 14.6v and the Amps dropped to Zero , to morrow I do the top balance again,
Although I'm not sure if it worth it as the BMS says all the cells are within 1mv .

So it seen the problem I had was trying to charge the cells when they where very close to the voltage to the power supply,

 

[snoobler]

if you got to 14.6, and all the cells were 3.65V, then you're already top balanced.