Issues with Charging

[gunja99]

Just got a Sky RC T200 charger, which worked well for a few days, but now I am struggling to "balance" the LiPos (I have 2), either to charge or to storage. They're both 2S one 3000 and one 4000mAh. The charger shows the two voltages from each cell. And if I set the charger to LiPo balance or storage it just never finishes. Tried 1Amp, all the way to 4Amps. I've set the time out to around 4 hours (240m). The batteries aren't hot in the slightest, and the actual Amps during charging to go low low... (i.e. 0.1/0.0).

With the 4000mAh hard case I used in the car and ran it low, it charged up to around (I think from memory 4.2V per cell) quite quickly, but the second cell shows around 4.11/4.13, and the 1st 4.20/4.21. Seems not to be able to balance. I'm new to LiPos and read a lot around safety, etc, so trying to be careful. I get options for Amps and the number of cells, and have options for Charge, Auto, Discharge, Balance, etc. Any suggestions please, as neither of the batteries can complete balance, or storage mode atm. DO I need to balance charge every time, as there is a normal charge too?

Cheers

[m4inbrain]

I can speak only for myself, but i personally do balance charge every single time, yes. 

 

I know there's others who only balance after every second/third charge, but i find that kind of a pointless exercise. 

 

What brand are these LiPos you're trying to charge, and did you get them new?

Edited September 2, 2020 by m4inbrain

[gunja99]

Cheers, I thought the same with balance, just seems can't get the 2nd cell to the 4.2 volts (that was weired to me as 3.7 x 2 = 7.4V, but I kind of get it!)

 

Both brand new in the last week or so:

 

https://www.hobbyrc.co.uk/gnb-3000mah-2s-5c-lipo-battery-for-jumper-t16-t18

 

and https://www.modelsport.co.uk/absima-greenhorn-lipo-7-4v-45c-4000-hardcase-t-plug-/rc-car-products/440263

[gunja99]

It's both storage and balance charging it just never finishes! I did factory reset the charger too

Edited September 2, 2020 by gunja99
Added work balance to the line

[m4inbrain]

Never heard of either before, so i can't judge if it's just naff LiPos, sorry.

 

Generally, LiPos are described with their nominal voltage (which is 3.7v per cell), that's where the 7.4 comes from. Fully charged, it should read 8.4v (4.2x2).

 

You said it worked at the beginning, how far did you discharge them in your RC?

[gunja99]

neither has been charged as low as the ESC will let them. In the car (the 4000mAh one), the car was still running so went to "storage" it, as it was getting dark and won't be using it for a week or so. The other is actually in a Transmitter (new Radiomaster TX16S for drone flying), so took it out when left on one bar charge. Do I need to use the discharge mode on the charger then store/balance charge them?

 

When new both batteries were close to the storage charge voltages. I did read someone not to let then cells get more than .2v from each other, and one of them was close to that limit, now about .1V

[m4inbrain]

You don't need to put them into storage for a week. At least, i don't. A month, sure - but for a week you can just leave them and charge them up the day before you intend to run. 

 

No, you don't need to discharge them before charging, as long as they're somewhat close to nominal voltage or below (3.7ish volt). I have dozens of LiPos, running them for over half a decade now, never ever discharged one via the charger. 

 

If one of the LiPos was almost 0.2v out of balance, you should've immediately sent it back. That's way too much for a new pack. A decent pack should be within 0.03v of each other. It probably has a bad cell, that would be my guess. The problem here is that the ESC in your RC reads pack voltage, not cell voltage. Meaning if they're out of balance, it might over-discharge the low cell. If the LVC (Low Voltage Cutoff) is set to, lets say, 3.3v, the truck stops when the ESC reads 6.6v. That could be one cell at 3.6v, and one at 3v, for an extreme example. 

 

I'd let others chime in, this is mostly my opinion, but my guess is that your LiPo is naff, and was from the beginning. Which isn't rare for cheapies. 

[gunja99]

OK so leave them discharged for a week, that's fair enuf. So close or below 3.7 before charging, got ya. If charging making sure use within a day or so. I'm new to LiPos so just being careful!

They weren't 0.2 out on arrival, (we're close to the nominal/storage and both cells close) and have been identical, definately in that 0.03 range. OK that difference makes sense with regards to the whole pack, good to know (makes sense I am a logical computer programmer after all!) Not 100% from record what the ESC (HW 1060). Are these cheapies then? Assumed from "proper" suppliers, and not cheap off ebay/amazon would be alright.

You've been a great help, one last thing. With regards to Amps I should use for charging and discharging, it is 1C (mAh/1000), so 3A and 4A for these two, or less. When it comes to discharge what should I be aiming at, oh silly question as you don't hah! The NiMah and NiCads get hot the Lipos haven't yet!

[m4inbrain]

Yep, wouldn't leave them fully charged - they won't blow up, but it over time it'll damage the electrolyte in them, leading to them holding less charge. 

 

Being careful with LiPos is always advisable, they're no joke when mishandled. The ESC you got is good, but be vary of the fact that it has a "two-stage" cutoff. The 1060, once it reads 6.5v on the pack, will only "restrict" power, not cut off. It will only cut off entirely at 6v flat - which, in my opinion, is incredibly low for a LiPo. I don't think you should ever discharge a LiPo to 3v flat per cell. Gotta be vigilant and realise that your power is restricted, and end the run there. 

 

It's less the supplier, and more the manufacturer that's "the problem". Here's the thing. I don't KNOW if your LiPo is naff, but that's the best guess i can make without checking internal resistance, ruling it out. It's more likely that the LiPo is kaputt, than the charger. I should've phrased it differently, there's actually plenty of "cheap" LiPos out there which are well made and hold up really well (and expensive ones that don't). Generally you'd want to stick to the "well known and loved" brands, like HRB, Rhino, Turnigy (Graphene) etc. That's all i use, and i not once had a problem with a pack that i wasn't responsible for (ruined one by forgetting about it, not storage charging it and after two years it went below 2.5v, irreparably damaged). 

 

Yes, you charge them at 3A and 4A respectively, that's the 1C rate. And yes, i wouldn't know how to discharge batteries via charger, sorry. I only know that it usually takes virtually forever. As in, hours and hours. I think you discharge somewhere between 0.5A and 1A, but you might want to ask someone else to confirm about that.

 

https://rogershobbycenter.com/lipoguide

 

This is a decent guide as a sidenote, explains a few things reasonably well. 

 

 

[gunja99]

Cheers, some great information there. Will have another play tonight. The charger does tell you internal resistance, so will post those figures later. The "adaptor" cables I've made myself to fit Deans and XT30 (the charger fitted with XT60), and think they OK. Taking them down to 3.3 per cell is a good idea then

[m4inbrain]

3.3v is as low as i'd go, yeah. In fact in my rigs i cut off at 3.4v.