weird top balance power reading

Hi everyone.
First post here.
I recently purchased 4 new 200ah cells, which all came charged at 3.27. I wired them in parallel and let them sit for 24 hours. I then purchased a HM310 power supply, set it to 3.65, 10 amps and let them charge. I was hoping for 3.65 in a few days. Charging was going ver very slow.

The voltage across all four batteries started at 3.27. Then today, 24 hours later, it was 3.38. Then all of the sudden it started to drop, now its 1.944 and dropping fast.

Has anyone seen anything like this?

Thanks in advance,
Peter

Try a different meter or replace its battery. I see the battery illuminated at the top left.

The PSU is still reading 3.65.

Aha!

That was it! Back up to 3.3 and going up. Thank you snoobler!

Those dang blasted meter batteries ?
LOL

P.S. Welcome to the forum.

Note that most ship at 50% SoC, so you need at least 40 hours of charging at 10A, and it's unlikely you'll maintain 10A due to the voltage drop between the cells and the PSU.

snoobler said:

Try a different meter or replace its battery. I see the battery illuminated at the top left.

The PSU is still reading 3.65.

Click to expand...

Had to all it out, crazy observation

And you certainly need to charge from opposite ends of the battery pack. Negative on cell 1 and positive on cell 4 for example. This will give a more even charge.

MisterSandals said:

And you certainly need to charge from opposite ends of the battery pack. Negative on cell 1 and positive on cell 4 for example. This will give a more even charge.

Click to expand...

So I have the cells in parallel. I set the DC charger to 3.4, so I could step charge to 3.5 then 3.6 and finally 3.65. As of last evening, the cells remain at 3.3 volts for al the cells. So 12 hours, and no movement on the charge. According to this thread: I need patience, worth about 8days Im assuming. https://diysolarforum.com/threads/t...0ah-stuck-on-3-32v-have-i-been-scammed.16757/

MisterSandals said:

And you certainly need to charge from opposite ends of the battery pack. Negative on cell 1 and positive on cell 4 for example. This will give a more even charge.

Click to expand...

Good catch.

peterjk said:

So I have the cells in parallel. I set the DC charger to 3.4, so I could step charge to 3.5 then 3.6 and finally 3.65. As of last evening, the cells remain at 3.3 volts for al the cells. So 12 hours, and no movement on the charge. According to this thread: I need patience, worth about 8days Im assuming. https://diysolarforum.com/threads/t...0ah-stuck-on-3-32v-have-i-been-scammed.16757/

Click to expand...

@MisterSandals is correct. You could move ONE charge lead to the opposite end.

Note that you are only flowing 0.7A - that's going to take you forever.

I know the guide indicates a 3 step process, but with the voltage drop typical of these units, I would advocate a single shot to 3.65V.

HM310 "Adjustable DC Power Supply (0-30 V 0-10 A)"

That can supply up to 10 amps into four parallel cells at 3.65V
4 x 200 = 800 Ah, 50% charge is 400 Ah to go, 400/10 = 40 hours if not tapering off.
Fine if you like watching grass grow or paint dry.

Same supply can put 10 amps into four series cells (use a BMS!) at 14.6
200 Ah, 50% charge is 100 Ah, 100/10 = 10 hours.

10A isn't a large supply, and remote sense to zero the drop in wiring would speed charging up a bunch.

What I might do if I was impatient (I am), is use PV panels in parallel. Get a high current NPN and configure an emitter-follower:

Base is fed by power supply (regulated voltage to be 3.65V)
Sense wire of power supply goes to emitter (so base voltage about 3.65V + about 0.7 Vbe offset to regulate battery voltage).
Collector of transistor goes to positive terminal of some solar panels.
Negative of supply and solar panels goes to negative of battery.

That should put about Isc of the panels into battery, up until battery can't accept the current without exceeding 3.65V. (CC)
Voltage is then regulated to 3.65V (CV)

During CV, power dissipation in transistor is approximately Voc x tail current (which could be rather high at first.)
Better set up a shut-down circuit, either when Vc rises, or when heatsink reaches some temperature. Thermostat shutting off or thermistor modulating base voltage should do it.

Hi @Hedges , your talking way over my head unfortunately. I understood use a BMS and a standard lithium battery charger [pic is of my Noco Genius which does lithium] to speed things up. Doesn't that defeat the purpose of a Top Balance? and Im not ready for pv panels yet, I'm building a schoolie bus, so panels wont come on till summer.
@snoobler , can you re-explain what you mean...."move ONE charge lead to the opposite end." I'm connected in parallel, you mean like this [see attached], i just moved the Neg connection to the opposite end of the pack, still in parallel set up. I also have some questionable bus bars, they are thin, solver metal. Maybe that's an issue too. Anyone have a source for better bus bars? Recommendations on a bms? I was thinking Electrodacus. I read Will Prowse recommended : https://overkillsolar.com/product/bms-120a-4s-lifepo4/ . I wanted to add, that I have 4 more of these batteries coming, so my eventual goal is to run 8, to make a 12volt 400 Ah bank.

You got it.

peterjk said:

Hi @Hedges , your talking way over my head unfortunately. I understood use a BMS and a standard lithium battery charger [pic is of my Noco Genius which does lithium] to speed things up. Doesn't that defeat the purpose of a Top Balance? and Im not ready for pv panels yet, I'm building a schoolie bus, so panels wont come on till summer.
@snoobler , can you re-explain what you mean...."move ONE charge lead to the opposite end." I'm connected in parallel, you mean like this [see attached], i just moved the Neg connection to the opposite end of the pack, still in parallel set up.

Click to expand...

Building a custom regulated supply would be for someone else, don't worry about that.

Top balance is necessary to get the cell SoC similar so battery charger recognizes pack as full before BMS disconnects.
It's just that charging in parallel from 50% as delivered to near 100% takes 4x as long (power supply max current divided across four cells.)

So the suggested process is to first wire in series with BMS for protection. Charge in series until one cell approaches max allowed voltage. This will be faster because every cell is charged at the current power supply can deliver (it has voltage headroom to deliver same current, more watts.) Maybe each of the cells will end up somewhere between 90% and 100%.

Second, wire in parallel and complete top balancing the last few percent of charging. This will put all cells at 100% (or whatever cutoff point you selected.)

Third, wire in series with BMS and put into use.

You can do the charging from 50% (as delivered) and balancing all at once in parallel. It just takes 40+ hours as current tapers of.

peterjk said:

I also have some questionable bus bars, they are thin, solver metal. Maybe that's an issue too. Anyone have a source for better bus bars?

Click to expand...

In general, if your bus bars are "too thin", they would get warm or hot. Its a pretty easy test... :*)
The "losses" from too small of wire or bus bars are dissipated as heat (handy at times like this!)

Got it ! Trucking on!

Can anyone recommend a good Daly or another BMS for 4 200 Ah cells, that will also work w 8 cells, i will eventually upgrade to ? Im going to have 8 cells, 12 volt, 400Ah.

8s 12V?
120A?

Think that listing says 100A.

Do you plan for 8 cells in series (24V) or 4s2p (12V, separate balancing) or 2p4s (parallel pairs of cells, so BMS thinks you have four, 400Ah cells?)

peterjk said:

Power will be 1 bus mini fridge, led lights, 2 laptops, hair drier, micro wave. So not much really.

Click to expand...

"mini fridge, led lights, 2 laptops"
Not much really

"hair drier, micro wave"
Really very much.

Nice hair, btw.
I see why you want the hair dryer.

Figure hair dryer and microwave will each draw about 1500 to 1800W.
Plan for either 12V, 200A worth of BMS (could be two, 100A BMS for the two packs of cells),
or 24V, 100A BMS.