Please Edumucate Me On Batteries

[OnceAGrasshopper]

I've down some searching - and I'm sure it's here somewhere - just haven't been able to come across the right thread.

Please help me with batteries. Batteries for a Grasshopper, a TA-02 rally car - and likely a Sand Viper. Not real racing just messing around. But hopefully some "racing" with friends at some point.

I'd like to get long(er) run times.

Let's skip LiPo - don't know much about it but it seems to complicate things.

Let's stick with NiCd and NiMH - what's the difference? Is one better?

I see 1500mAh - 1900mAh - and some even higher - what is this? Does more mAh mean longer run time?

My old batteries are 1200mAh - antiquated I'm sure...

Motor on the Grasshopper is a 380. Other cars will have RS540 or similar.

Thanks again guys-

[OnceAGrasshopper]

PS - what about 6 cell vs 7 cell?

Thx again

[BiggusDitchus]

Very basically....

The higher the mah number the longer the runtime (also takes longer to charge), more volts will for a start provide more power to the motor (more rpm, or in effect to your grasshopper for example more speed).

But

If you increase the rpm of the motor by adding more cells you will be drawing more current (amps) which will therefore reduce runtime and reduce to lifespan of the motor due to wear. I would personally stick with 7.2v for most trucks/buggies/cars you probably only want to look at more cells when your talking about running more expensive cars with bigger performance motors.

If your looking for new batteries go for the best quality as opposed to the cheapest battery you can find with the highest mah rating. A cheap 4600mah battery will in most cases not be as good as a quality (more expensive) 3300mah battery for example. Its also best to have a reasonably good charger, you dont need to spend loads on one, but a basic trickle charger is not going to get the best from your batteries.

Im sure Terry will be along sometime with his words of wisdom!

[Eddystone]

Excellent advice there from Biggus - I'll highlight the point about buying the quality batteries before the biggest quoted capacity. Don't fall foul of cheaper batteries that look good with their high capacity as they invariably let you down. Pick a good manufacturer and choose their 3000mAh or above NiMh batteries and you'll get good performance and be running them happily for years to come.

Perhaps someone could suggest to us the names of some good cell manufacturers to help out. I've found GP and SANYO cell packs have lasted me many years happily. I've been seduced by larger capacity cheap packs. They are usually shrinkwrapped so you can't see the cell manufacturer. I've melted the heatshrink on a few packs of Vapextech and Profitexx cells either in the car or on the charger so I wont be buying them again. Currently trying CORE-RC packs as they are a decent price and Core-RC make excellent chargers - hopefully their packs match up to the standard set by the chargers. No problems yet! Now if I'd only followed my own advice at the start and bought the decent battery brands then I'd probably have saved money!!

Other point is forget 7 cell packs - they wont fit in any of your cars.

Richard

[cubsfan2009]

If you increase the rpm of the motor by adding more cells you will be drawing more current (amps) which will therefore reduce runtime and reduce to lifespan of the motor due to wear. I would personally stick with 7.2v for most trucks/buggies/cars you probably only want to look at more cells when your talking about running more expensive cars with bigger performance motors.

Sorry to get technical, but adding cells(voltage) will actually draw less amps to get the same power(watts). In the formula: volts x amps = watts, as the volts go up amps can drop to keep watts the same. Basically you end up with a faster top speed and needing less amps to accelerate. This is why most big trucks and 1/8 vehicles use two packs in series to run higher voltage and help keep the amps down. Everything else is correct though that the motor will wear faster on more cells because of the more watts potential.

[floppydisk35]

Just a hint: If you want a good NiMH, either get yourself a 4200mah Core-RC stick pack (I have one of these, they're very robust and powerful. I get around 1 hour runtimes in my FF01 with a 24/71 gearing, and I'm an absolute PIG), or else a 4600mah DTX stick pack. I heard positive comments about the latter

EDIT: If possible don't bother with NiCD's, they're slower in respect to NiMH's and provide less runtimes. And now NiMH's are costing less each and every day!

[BiggusDitchus]

When buying batteries best advice is to buy from a reputable buyer, any of TC supporters i.e. fusion, stella etc, also rcmart or your local modelshop for example. Ebay is always a great site for buying batteries but a something i have always stuck to is that if you cant see the actual cells because they are shrink wrapped in for instance green or yellow then keep away, what you will find in most cases is very cheap cells.

You need to be looking for batteries that look something like this...

and not... (Im not saying these are bad cells as I dont know the manufacturer its just an example of how they look)

Now this isnt always the case but isnt a bad start.

I have heard that Vapex batteries are good (their packs are shrink wrapped opaque but seems they are an exception to my rule.)

http://www.vapextech.co.uk/acatalog/High_P..._Batteries.html

[DCLXVI]

Very basically....

The higher the mah number the longer the runtime (also takes longer to charge), [...]

Sorry to nitpick but, that depends entirely on the charger, on most modern chargers, you select the charge current for each battery, usually so that the battery will be done in one hour... (3000 mAh charged at 3 amps ect)

To add to the thread...

To me it seems that NiMH batteries have a practical limit of around 3000-3600 mAh, the ones with higher mAh rating usually have some kind of problem, like high self discharge and larger cell size...

I've gone to LiPo and I do not miss NiHM's, though, for a beginner, it might not be advicable as they are somewhat sensitive...

[BiggusDitchus]

Sorry to nitpick but, that depends entirely on the charger, on most modern chargers, you select the charge current for each battery, usually so that the battery will be done in one hour... (3000 mAh charged at 3 amps ect

Sorry but I think your being a little picky on that one, If you own a charger that only charges at say 3 amp etc then a 1500 battery will charge in 1/2 and hour and a 3000 as you say will take 1 hour, that therefore is longer to charge. (and yes a 1500mah nicad will quite happily charge at 3amp). So for people with more basic chargers this is true. (and to be honest its true with chargers that cost more, I use a Much More Cell Master and my 4600mah race batteries take longer to charge than my 3500 batteries I use for my Tamiyas)

I think we need to get away from "nitpicking" and give the guy some useful advice, I have tried to keep it a little more basic yes you could go more indepth but I dont think that is required here!

To me it seems that NiMH batteries have a practical limit of around 3000-3600 mAh, the ones with higher mAh rating usually have some kind of problem, like high self discharge and larger cell size...

Will have to disagree as I have some 4500mah nimh and they fit fine in my Tamiyas and love them, have had no problems at all.. Sub C's have got significantly bigger from 1200mah and 1500mah just compare a 2400 or 3300 with an old Tamiya pack to get more capacity in a sub c it does appear that size matters., although I have some 3300mah packs I use from time to time and they are significantly bigger than the 3500mah I use more often.

I've gone to LiPo and I do not miss NiHM's, though, for a beginner, it might not be advicable as they are somewhat sensitive...

I agree I have tried to avoid LiPo's as my history with things that could go wrong is not great but now I have started to go LiPo I love them the performance difference and the runtime compared to nimh is astounding, at the moment I use them primarily in my crawler and in my Tamtechs and the Carisma 1/14 I race.

[terry.sc]

Sorry to get technical, but adding cells(voltage) will actually draw less amps to get the same power(watts). In the formula: volts x amps = watts, as the volts go up amps can drop to keep watts the same. Basically you end up with a faster top speed and needing less amps to accelerate.

Sorry, but Biggus is right.

If you are running a motor with the same power output on 7 cell as a different motor on 6 cell, you are correct that you will have a lower current draw. But this means you are using a slower motor so it accelerates and has a top speed to match the 6 cell car. Kind of pointless really.

For everyone else, the reason you use a 7 cell pack is to get more speed from the same motor. Using basic electric theory, as the motor is the same (so the resistance is the same) and as V=I x R, as you increase the voltage you increase the current draw. This means the higher the voltage the higher the current draw, so the less runtime.

A perfect example of this is in the Clodbuster, with its power/economy switch. Put it on power and the motors get 7.2v each for more speed, but the battery dies quickly. Switch it to economy and each motor gets 3.6v, but it runs forever thanks to the lower current draw.

This is why most big trucks and 1/8 vehicles use two packs in series to run higher voltage and help keep the amps down.

They run higher voltages to get decent speed out of the low kV motors they have to use to generate the torque needed to move the heavier chassis.

A motor capable of driving a 1/8th at decent speed on 7.4v will draw a lot more current than the motors normally used, but if the same motor was run on 14.8v it will run twice as fast but also have twice the current draw.

[terry.sc]

Let's stick with NiCd and NiMH - what's the difference? Is one better?

The difference is the chemicals used inside the cells. The main reason for the change was the cadmium in nicads is a toxic material and dead nicads are classed as toxic waste - no kidding.

A big advantage is that being newer technology nimh cells have a bigger capacity than nicads could ever reach.

I see 1500mAh - 1900mAh - and some even higher - what is this? Does more mAh mean longer run time?

As has been said above, the mah is the capacity, which controls how long they last. A 3000mah battery will run for twice as long as a 1500mah battery.

My advice would be to choose good quality batteries. Most advice has already been covered above, but wouldn't recommend going above 3800mah packs as some of the higher capacity packs need more care and some have reliability problems. 4200mah packs had serious problems, being over size and rapid self discharging, followed by a habit of exploding if certain charging techniques weren't used. These problems were fixed by a change in the racing rules meaning the newer 4500-4600mah batteries no longer have these reliability or size problems, but the quality high capacity batteries are expensive.

Considering the motors you are using limiting it to 3300-3800mah packs you should still get up to 30 minutes bashing out of them.

Also be aware that if you are upgrading to nimhs you will need a nimh compatible charger. A nicad only charger will overcharge nimh cells which will rapidly shorten their life.

[taliesin]

I've had problems with batteries over 3300mah fitting into the battery compartments of older Tamiya models. Seems like bigger mah packs are longer/thicker and it pinches the wires or else needs some finesse to get in/out of the battery compartment.

Just a small point but maybe worth mentioning.

[OnceAGrasshopper]

Thanks for the great info, guys. Exactly what I needed.

Now I know my NiCd batteries do suck and I need a new charger than can handle NiMH - thanks

Until next time....