Rechargable Battery and Electric Motor Questions

I have a Ni-MH battery charger that came with a digital camera that used 2 x 2200mAh AA batteries. It is rated at 2 x 550mA.

For xmas I bought my son a radio controlled car and a set of 1200 mAh Ni-MH AA batteries. The car takes 5 AA batteries, and goes through them in about 45 minutes of use.



The normal battery charger I have takes 4 batteries with an output of 4 x 250mA

So 5 batteries in the car and 4 in the charger, means I have to do more than one charge, and unless I time just it right he can't use the car every day. If I use both chargers however, I can have 5 freshly charged batteries for him every morning.

I have found this calculator

http://convert-to.com/recharging-rec...batteries.html

Which says the camera battery charger will be able to charge the 1200 mAh battery in 2.6 hours.

The car is not as fast as I expected and struggles on hills or on grass. It really needs a flat and level surface. Looking at the motor it's much smaller than the car I had as a kid, which took 10 AA batteries. The instruction manual recommends normal Alkaline batteries (ie: Duracell), but with the speed the car goes through batteries, I'm not prepared to spend that money. I'd be better long term spending the same money on a better car for him.

Two questions

• Is it safe to put a 1200mAh battery in a 550mA charger, which was designed for a camera battery of double the capacity?
• If I bought batteries of 2200+ mAh for the car, would the motor have more any more torque, or would the batteries just last longer? Or would I just burn the motor out?

He's only 3 and is just learning to steer this one, so he's not ready for a proper Tamiya type kit yet.

Thanks

[yorkie_chris]

More mAh will last longer, might have a bit more poke as you may get less voltage drop... but I wouldn't think you'd see much more performance.

I think you can fast charge nimos, ask some of the model plane guys (wideboy maybe)

Yes.
No, Yes. No

BTW, Varta and a few others make batteries that can be charged in as little as 15min when using their charger. The only thing that I would not recommend with these is putting hot batteries into the charger.

[the_lone_wolf]

Originally Posted by yorkie_chris

More mAh will last longer, might have a bit more poke as you may get less voltage drop... but I wouldn't think you'd see much more performance.

This^^^ mAh is how much fuel's in your tank, not how much your engine displaces


Maplins do packs of eight 2500mAh AAs for less than a tenner, and the last time I was in there I picked up an Energizer 8xAA charger for about the same price in the bargain bin

[andrewsmith]

Originally Posted by the_lone_wolf

This^^^ mAh is how much fuel's in your tank, not how much your engine displaces


Maplins do packs of eight 2500mAh AAs for less than a tenner, and the last time I was in there I picked up an Energizer 8xAA charger for about the same price in the bargain bin

Digital can shops are also worth a punt, as I've got uniross ni-ma batteries and a quick charger was a tenner a couple of years ago. Check the - ive end onf the battery, it should say the charge time at what rate.

Edit: the maplin rechargeable batteries are Uniross and they run fine in my small, light tuned R/C's

The main problem with normal bargain bin chargers, fast or not, is the number of channels they use to read the battery charge and the detection methods they use to stop the charge when the batteries are full. A normal fast 4 batt charger might only have 2 channels (2 batts per channel) and stop on temperature, i.e., when any of the batteries gets too hot it'll consider all of them are properly charged. If the batts aren't being used evenly you can see where this is going to end...

As for the maths, they're usually quite simple: take the capacity of the battery (mAh) and the current the charger can deliver (mA), divide one by the other and you have the theoretical time that charger would take to charge those particular batts, i.e., for 2000 mAh batts and a 500 mA charger, you'd get a 4 hour charge time. Due to thermal losses and inefficiency though it'll take longer than that, might be closer to 4.30 / 5 hour charge time, depending on a few factors.

If you're a heavy battery user (and it seems like you'll be for a while), I'd recommend you get a decent smart charger / conditioner with multiple channels (1 per battery), as that's about the only way you have to make sure your batteries will be in tip top condition. My recommendations would be either the PowerEx MH-C9000 (more expensive, but I'd say it's the best you can get) or the LaCrosse BC-900 (slightly cheaper, mine came with batteries and a carrying pouch, still a very good charger but prone to overheating due to being smaller), and then learn how to use them to keep your batteries in good nick. Super fast chargers (15 or 30 mins chargers) are also interesting, but they will literally cook the life out of the batteries much faster than you'd like.

While you're at it, you might want to get some high capacity batteries too (especially if the car is going through them like there's no tomorrow). If you're the "charge and use" kind of guy (as you seem to be right now), get some 2500 - 2700 mAh NiMH batteries (avoid duracell and pretty much every other alkaline battery maker, those guys want to sell you alkalines, not rechargeables...). PowerEx are great, UniRoss are a shot in the dark, might work, might not. If you want batteries that you can charge now and use in a week / month, then Sanyo Eneloop are the way to go. Less total capacity (2000 mAh), but it'll be there when you need it in a month or two, whereas the normal NiMH will self discharge at a much faster rate.

HTH, if I just made it even more complex just give us a shout.

Thank for the replies guys. So the 1200 mAh batteries are fine in the 550mA charger, and I'm not about to set the house on fire

Filipe, that was informative stuff, not too complex thanks. Can you recommend a charger that takes 8 batteries at once? 25 or 30 quid is OK, but that PowerEx one you posted is getting a bit expensive for my needs, I'd be better just replacing the batteries more often.

[Wideboy]

Originally Posted by yorkie_chris

More mAh will last longer, might have a bit more poke as you may get less voltage drop... but I wouldn't think you'd see much more performance.

I think you can fast charge nimos, ask some of the model plane guys (wideboy maybe)

yeah you can pump quite alot into nimo's before they go pop, i usually charge my 900mAh packs at 2Ah and they still live for a long time

changing the battery size on model is fine, obviously you dont want to change the voltage as it will make the ESC (controls the current, motor speed ect) will burn out

Ralph, you could try the PowerEx MH-C800S, but I doubt it will be cheaper than the C9000. Maybe if you shop around online you could find a good deal with batteries included? I got mine from http://eu.nkon.nl, Arjan seems like a really nice guy and his prices are quite decent from what I saw everywhere else...