Li-po battery charging basics

[JimBear]

Anybody not up for idjit questions ... don't read further than this.

Okay, lipo batteries ... I am going uhm... batty!

We use Ni-MH batteries in most of the cars around here - with the exception of the Axial scx24.

Which leads me to the following:

First original battery went south, probably run-down too far. As far as I can ascertain, there is only one cell working. So, a goner. Bought a second one, perhaps three weeks ago. The battery in question is a Dynamite 350 mAh, 2s, 30C, 7.4v. It says "3C charge rate, 2,59 Wh" on it.

Fine, until yesterday, when my son complains that the car doesn't work anymore. Looked at it, servo works, but nothing pushing the throttle. I tried to charge it with the in-box charger, apparently not the best thing since sliced bread. Shows being done after about 2 minutes. Then I tried it with the Imars III Pro charger -  the device ends the charging after about a minute and a half. I had it set at 0.5v charge rate. Since this was the original battery asked for, I left it at that level (set manually).

Still only servo function. Gah.

Tried to see if I have 2 cells - yes, we have 2, and they show 4,18 v on both.

Am I correct in that the 4,18v on each cell is too low, i.e. below what it should be for it to charge correctly?

[Twinfan]

I'm no expert by any means, but I think 2S LiPO is 8.4v fully charged, so 4.18v per cell sounds correct?

[alvinlwh]

55 minutes ago, JimBear said:

Tried to see if I have 2 cells - yes, we have 2, and they show 4,18 v on both.

Am I correct in that the 4,18v on each cell is too low, i.e. below what it should be for it to charge correctly?

I had just learnt, literally yesterday, that off load test like this are not always accurate. The battery can be dead yet still shows a decent amount of V. 

56 minutes ago, JimBear said:

350 mAh

That is a really tiny battery, can you fit something bigger in there or is there no room? 

[JimBear]

Thanks, @alvinlwh and @Twinfan for your replies!

I ran off and fetched another scx24 (an older c10) and tried the battery in there and sure enough it works fine there (steering/throttle). Although the battery seems weak, it turned off pretty quickly. What's good about the older scx24 is that there is a larger led blinking on the AE-6 esc, so it is clear when it's time to charge.

The battery is tiny, indeed. But I have no idea if there is any better options, really.

I am starting to wonder if there is an issue somewhere else ... if the esc is toast or the motor?

[Twinfan]

Sounds like it could be motor related if the steering still works.

[MadAnt]

Battery seems fine. The problem is with the car's electronics.

[JimBear]

3 hours ago, Twinfan said:

Sounds like it could be motor related if the steering still works.

Well, I changed the motor out, about four weeks ago. I need to do a test with the known working c10 motor. If it still doesn't move, then it is the esc.

[JimBear]

So a small update:

I pulled the motor plug from the C10 and put that one in the Jeep esc and did a test - I have steering (as before) and now throttle. So, the conclusion is that the esc works fine and the battery too - but the Jeep motor doesn't. So off to find another motor it is. At least that is half the expense of an esc. Have to think of the glass as half full.

The charging speed difference ... is it that fast? I mean, it's a tiny battery, but charging for less than 2 minutes, compared to the one that came in the box?

[Twinfan]

It sounds a bit quick to me, but it depends what state it was in when charged.  You'll need to test it properly when you have a new motor 

[JimBear]

Yes, I think so too. I tested the battery in the C10 before and then it ran for half a minute before going off.

May have to get another battery too while I am at it.