how batteries work?

[rydzjunior]

ok, i have bought a dodge rammunition that use a 7.2 volts 2000mah. When i plugged in a battery pack with at least 900 mah and same voltage but smaller batteries, the car was barely moving and seconds later the batteries started to heat up and smell. i think they were not capaple to withstand my big motors truck need of electricity. Could it be because my 900mah pattery pack had not enough electricity capacity(mah) compared to my 2000mah battery pack?

I think the problem is that the batteries in your 900mAh pack are not able to supply the amount of current your truck needs. Drawing too much current from batteries would definitely heat them up.

[rydzjunior]

thats what i thought until i tried energizer ones. i tried 6 to 8 of them (they were d size) to get at least 7.2 volts or more and it did the same thing. the batteries smelled and heated up. energizer batteries have no charge capacity since they cannot be charged, so how did they not draw enough current to my truck? i still think its because my truck needs to much energy. By the way my truck is very cool and fast as a stock gen1 xmod (15km/h). and has lot of power. but the battery lasts only 10 min. approx. this is why i tried to get better and bigger batteries.

[Namuna]

I imagine when you say "Energizers" you mean the Alkaline ones.

Someone can correct me here, but by its' nature, Alkalines don't have near the discharge rate as NiMH rechargables...So you're back to the original problem (overheating).

Check our your local hobby shop and even RadioShack and some department stores that sell RCs (Walmart, Target, Kmart, etc...) for what they have with 7.2v RC NiMH Battery packs (obviously you'll be looking for anything 2000mah or higher).

Good luck.

[rydzjunior]

therefore, if i use rechargeable d sized or c sized 3000 mah to produce 7.2 volts, it should work? and if i do the same thing for double A batteries with 2000mah it should work?

[rody]

I was just reading somewhere about someone who was using a certain mah rating for racing his mini-z. He was saying that the higher rated mah batteries come with a price...lower current delivery, which was why he was using 750 mah as opposed to higher mah rated batteries. Does anyone know if this is actually true? If so, where is the best performance point coupled with decent run times?

I just bought a bunch of 1750 mah aaa rechargeables thinking these are the better batteries, but now I'm wondering if I did the right thing.

[Namuna]

Originally Posted by rody

...He was saying that the higher rated mah batteries come with a price...lower current delivery...

Uhh, actually the OPPOSITE is true. The higher the capacity (the mah rating) the MORE current you can draw from the battery.

In general:
- Higher Voltage = Higher motor speed (in RPMs)
- Higher Capacity(mah) = Longer runtime AND higher current availability to the motor

Example 1:
You have 2 battery packs; one is 9.6v 900mah and the other is 9.6v 1500mah. Now let's say you've got a car that has a motor that can demand up to 2amp (2000ma) current (like while accelerating or going up hills) but on average pulls about 500ma.

With the 900mah battery; it'll probably drive okay but you may notice the battery pack gets pretty warm/hot and it might not be very quick and doesn't do too well with going up inclines.

With the 1500mah battery; you should notice it's got better acceleration ("punch"), can go up those inclines better, the battery isn't nearly as warm/hot and you can drive longer before it goes dead.

Example 2:
You again have 2 battery packs; one is 7.2v 900mah and the other is 11.2v 900mah. Now you've got a car with a less powerful motor that only demands up to 1amp (1000ma) current max. Avg 400mah

With the 7.2v pack; it drives as advertised for that vehicle. Pack is only a little warm after the run.

With the 11.2v pack: You'll notice considerably better top end speed! The acceleration ("punch") and runtime will be fairly similar to the other pack.

If I'm off with any of the examples given, please correct me...But the "In general" info IS accurate.

I don't know if I can agree with all of Namuna's information. Some of the battery companies really limit the current they can provide and therefore can claim really high mAh capacities.

Being the capacity is measured in supplied current at 1 milli-amp (which is nothing). Some batteries makers have tailored to supply small amounts of currents for long times. When you start to have to supply 1 amp, the mAh rating is more of a idea of the true capacity.

Generally, I find it's more dependent on the batteries themselves. The radio shack 700mAh batteries suck. I'm not sure how much current can be drawn from them, but they have very low run times.

I have had powerizer 950mAh (I believe) AAA's that I would compare to the RS ones. I've also had assia 1150mAh batteries that I was pleasantly surprised with. They seemed to have long run times, though probably still not what you would expect from 1150mAh, but probably as long as some good energizer 900mAh.

I believe Namuna is correct in that alkalines can't supply large amounts of current, hence why the hobby RC cars have been using Nicd for so long.

The current being supplied by the batteries is dependent on the resistance of the circuit. The difference in available current only comes into play if the resistance has a low enough resistance to draw more current than a battery is able to provide. Putting in a 1000mAh battery into a car does not mean that it is going to give more current than a 500mAh pack. It will only supply more current if the 500mAh pack was not able to provide as much as the circuit wanted. I hope that all makes sense.

[Ken5149]

so if a remote control car uses 4 AA batteries how many volts does it use?

[Azimov]

so if a remote control car uses 4 AA batteries how many volts does it use?

Well, that's 6 VDC if they are regular alkalines, but that doesn't mean that's what's going to the car's drive motor.
Basically, what you are asking is how to get better current efficiency out of your battery pack. The only way to do this outside of altering the electronics is to use more efficient batteries. That is, less internal resistance. As already stated, NIMHs are your best bet. Just get a pack rated at the voltage and current levels you need.
The ultimate battery pack at present is LiPoly, which has the lowest internal resistance, but a special charger is needed. Lipos allow the car (circuit) to draw much more current and are lightweight as well. They are the most expensive of the lot though.

[Ken5149]

Thanks for the advice. You guys seem to know a lot about remote control cars.

[alfreddajero]

You can also charge the batts on your home charger, i charge 4nimh cells at 2amps-20mv............