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NiMH Battery Pack Substitution Effect on Charging Circuit

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edy:
Hey folks,

I bought a bunch of Garmin Moto TC Rally cars for my whole family to race as they were on sale and I couldn't pass them up at $12.95CAN a piece ($9.95 US). They are fun little cars to race. I have some old iPhones which I have already downloaded the BlueTooth app for and so we are able to all race at the same time and do virtual tracks.



Anyways, the issue is... one of the cars I bought had a dud battery pack. I know it's the battery pack because I already tested other battery packs (from the working cars) in it, and it worked fine. Also, the charging circuit was also working fine in that car as well. So it is definitely the battery pack, which simply gets hot but doesn't hold a charge. It could even be just one cell in the pack that is bad that is ruining the pack.

I contacted Garmin to see if they have any support or warranty on the battery pack so they could send me a new one, but either way if I have to make my own or buy one and substitute it I will do so. They are just standard ones like this:



Now I already have some separate AA NiMH batteries and a holder at home, and a connector which fits the car connector. I could just strap it in under the plastic shell as it won't fit in the battery compartment if I use AA batteries. I could use AAA but I was wondering if I could get more working time using AA instead:





I can charge the batteries up externally and insert them in when I want to use the car. That shouldn't be an issue. I can't imagine it will cause any problems running the car except for a bit of extra weight with AA instead of AAA and I will get longer operational time as there is higher mAh.

The question is.... If I leave my newly made battery pack hooked up to the car and use the charger built into the car instead of taking them out to charge, will it cause any issues? Remember, the battery pack originally in the car (that never comes out) is 4xAAA in series giving 4.8V and 600mAh rating. I will instead have 4xAA in series, also 4.8V but probably in the 2000mAh range. Is it just a matter of taking longer to charge, or could it overload the charging circuit in the car?

drussell:
It will just take longer to charge.

edy:

--- Quote from: drussell on October 30, 2018, 01:39:11 pm ---It will just take longer to charge.

--- End quote ---

Ok thanks! I was worried about affecting the charging circuit somehow but it makes sense now since my wall-charger will work with both AA and AAA batteries (the bottom part slides up and down to provide the different lengths to meet the different battery sizes).... the actual electronics in the charger are "dumb" and don't know what size battery, as long as they are NiMH cells.

In the case of the car, as long as I have NiMH cells and they are put in series to equal 4.8V, the charging circuit also shouldn't care whether I am charging 4 AAA or 4 AA. I'll try it and see how much longer the car runs! I will have to experiment with the charging time but the circuit does have a light that turns off when it is supposed to be fully charged, so it should still work the same and shut off appropriately. :-+

mvs:

--- Quote from: drussell on October 30, 2018, 01:39:11 pm ---It will just take longer to charge.

--- End quote ---
It is not so easy... Lower relative charge current may affect NiMh charge termination (Negative Delta-Voltage detection). Some charge controllers also limit charging time.

ogden:

--- Quote from: mvs on October 30, 2018, 07:48:06 pm ---It is not so easy... Lower relative charge current may affect NiMh charge termination (Negative Delta-Voltage detection). Some charge controllers also limit charging time.

--- End quote ---

Right. Better use 1000mAh AAA. It's still 1.5x capacity and most likely current capability as well.

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