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Dumb Question about Charging and C rate

1166 Views 8 Replies 4 Participants Last post by  matt4x4
I have a pack that is 36V(nom) but charges up to 41V(max)
Its taking forever for my crappy 6A charger to charge up even one of these packs. I would guess an hour or two. Plus I have 3 packs.

As I said 36Vnom 41Vmax and 6Ah, times 3 is 18Ah.

I have three 24V-30V 15A Meanwells, and I was thinking to fast charge, but I dont want to go too fast.

18/15 = 1.2C
When set the voltages to both mw's to the exact same voltage, 20.5V, put them in series to get 41V, then connect to the 3 packs which are in parallel (and the exact same voltages!!!!)

I connect my digital multi meter to view voltages on the mw's.

I connect the batteries, and I see the dmm go from 33V and it slowly rises.
I assume its doing 15A into the battery, so thats 1.2C

The mw's fans are blasting away until it reaches 41V then the fans turn low.

At that point, how long do I leave it still running. I keep a close eye on it.

I have a cheap rc watt meter I could view the amps with, its laying around here somewhere. From my understanding, when the fans turn low on the HRP-300-24 it should be pumping out 3A.

My last pack the mw's were running hot, but the safety features on the mw's are superb so I kept close watch, feeling it every now and then.

Your help would be appreciated here, because I dont want to fuck this pack up, like I did my ultra safe LiFePO4's that I hacked up.

FYI - These packs I am running now are LiMn (1.6Ah) and I set to 4.1Vmax/cell. The pack is 10S2P but paralleled so 10S4P to reach the 41Vmax 6Ah, then 3 of those I hook up in parallel. If that makes sense to you.

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Use the wattmeter to see when the amps drop to near zero if you want the maximum charge. That can take some time ,..30-60 mins in the CV phase.
If those are genuine Meanwells (or good clones) then they will have a full CC/CV charge profile that terminated at something like 0.1 A or less, but never actually shut off completely.
As I said 36Vnom 41Vmax and 6Ah, times 3 is 18Ah.
At that point, how long do I leave it still running.
Until your accurate ammeter says rate has declined to .02-.025C.

For 18AH that is around .4A

And don't float, just stop.

In fact many just charge to a V setpoint and stop, but that is less precise, SoC will vary by C rate.

If you are concerned about longevity, keep charge volts well under the vendor specs, maybe 3.5V, especially after the transition to CV Absorb.
Thanks for your input guys/gals.

There is no BMS on my one pack, its a DIY from tool pack batteries. My other pack is a department store multi-tool battery pack (mowers, chain saws, trimmer) I have no worries about that. Though I am debating whether to get the expensive Satiator or EGO's $130(CAD) fast charger.

They are genuine Meanwells HRP-300-24 with 15A - CC/CV - I have 3 - Range 20-30V with the pot. I am investigating how to mod it for current limiting so I can charge smaller Ah packs. I figure at most I dont want to go above 1C even though it could go 1.5C to 2C, for longevity reasons. Also I go to 4.1V not 4.2V (Li-Ion).

I charged to set voltage before, because I thought when the mw's fan turned off it was done, but as I posted its still doing 3A. So I need to install that watt meter, and probably only go until its pumping 1A. I keep a close eye on it when I bulk charge, I baby sit them actually.

My Digital Multi Meter is a Mastercraft from Canadian Tire, it looks like an average one, it doesnt look like a cheap one say from Princess Auto/Harbor Freight.

Oh I forgot to ask, is there a decent quality, value priced watt meter (up to 60V or 80V and 50A) ?
Probably best if I use my DMM for the current and buy a cheap voltage meter.
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If you have been stopping the charge at the end of the CC phase, you will be missing out on 20+ % of the full capacity.
Even 4.1-4.2 v still contains a good 10% of capacity, and providing you dont keep the pack at full voltage for hours, it does minimal harm.
Many people bulk charge to 4-4.1 v , but then put a final 4.2 v full charge in just before use for maximum capacity/ range.
Oh that is a great point. Well I have been reading that charging to 4.1 increases the life of the battery which is always good. So 10% of the capacity is left in the 0.1V, not to sure what to think about that. I shouldnt have range anxiety, just have a pack a little more then I need.

Ok So I been thinking about this now for the last few days.

Make the pack 36V(nom) 41V(max) 4.1V/cell or 42V(max) when guerilla charging because it will be used right away.

Then make the Ah capacity 18Ah or even 24Ah which will give me 12P or 16P which should help with the voltage sag thats been a problem with 4P pack.

I gotta make sure everything is exactly the same voltage when I connect it all up, no more then 0.1V difference.

Set my Meanwells to 41V or 42V, I cant adjust the A output yet, so it will be 15A.

It should be fine should it?
Meanswell may heat up but I dont worry about them.
Fans will turn on full until the last bit, then turn off once it reaches the preset voltage. Then perhaps leave it in for an additional 10 minutes, looking at what the amps are slowing down to.
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Working like a charm guys, thanks.
I was concerned I did it wrong on my first pack, but I realize what I did wrong.

This time around I matched it all, from the individuals then the packs. I matched them all perfectly.

Still doing it with only a dmm to measure volts. I like how it slowly crawls up by 0.10V. Then I am listening hard for pops, but my C rate is 1.25C or there abouts 15A into a 12Ah maybe 11Ah pack.

The thing is one of my mw's is 20.2V and the other is 22.2V, I try to match them equally but those are the lowest they will go. So entire pack is 42.4V which in 10S is 4.24V but when I charge this way, I plan on using it right away.

Should I stop at 41V (4.1V) with capacity still left
or go 42.4V and use it immediately after?

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