# Li-ion Question



## Pete Thornton (Jan 2, 2008)

Guys,
I'm new to Lithium batteries. Last year I replaced a pair of NiMH packs with Li-ion batteries which have PCB protection built in. They worked fine, I think.

This last weekend I decided to take the loco out for a spin with its new battery packs. I found my on/off switch was broken, and seemed to not switch off. It was likely that it was on for 24 hrs, but with little or no power drain, as the speaker and motor in the loco were disconnected, so it was just quietly powering the rcvr/esc/sound cards. It ran fine though I didn't push it to run for long.

When I got home I took it apart to fix the switch. While I was at it, I put a meter on the batteries - both rated 11.1V 2800mah - and got 10.9V on one and 7.6V on the other. After the new switch was installed, nothing seemed to operate. I put them on charge and left them overnight.
This morning all was well. With a fresh charge, the loco fired up, sound and all, and seems fine.

Here's my Question: I believe the 'PCB protection' will turn off charging when they are full, and turn off discharging when empty. Therefore, when I saw the 7.6V, that pack was probably done/empty, and as soon as I turned the loco on, the PCB shut the pack off - hence nothing worked yesterday despite voltages being readable ? Or is there something else going on that I don't know about ?


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## Greg Elmassian (Jan 3, 2008)

You did not mention if the 2 packs are used at the same time, and if so, in parallel or series in the loco.

Greg


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## Pete Thornton (Jan 2, 2008)

Greg Elmassian said:


> You did not mention if the 2 packs are used at the same time, and if so, in parallel or series in the loco.
> 
> Greg


They are in series - it's a 24V loco. TOC used to rail against the idea of using rechargeables in parallel, and I never did - though I had one loco with 4 x 9.6V packs that could be set up to run as a dual-series+parallel. Usually it ran with one pair.


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## Greg Elmassian (Jan 3, 2008)

So in answer to your original question, if either of the protection circuits in either of the 2 packs "shut off" (which will happen in a severely discharged condition) then since the packs are in series, both have to be "working" to run the loco.

So, indeed with one shut off, the loco would not run.

7.6 volts on one pack, that has 3 batteries in series (or multiples) would be a cell voltage of 2.5 each... clearly severely discharged.

So in answer to your last 2 questions, yes, that is what happened, and no, apparently in this situation there is nothing do you not know about ;-)

I would watch the pack that went down so low to see if there are any issues, but I believe that there was no damage and the protection circuitry did it's job.

Regards, Greg


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## Pete Thornton (Jan 2, 2008)

Thanks Greg.


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