Battery question
 

so I'm perusing the goodies in the RCM storefront...and I see a 3200 25c 4S.

We have a race coming up on 23AUG...and I'm looking to get more batteries for the three classes I'm entering. I'm wondering about this 4S...will it help keep the motor cooler? Will it have less strain on the ESC?

I've been trying to keep up with the logic of higher voltage and less amps being the key to more efficiency...but truth be told I'm having a little trouble grasping the concept.

So....the question I'm asking is basically this:

in a triad of mains (2 7min quals and one 7-10min Main), will it be more effective (better speed and power, lower motor temps) to run a 4S with lower mAh or will I be better off with running my TP 3S 40/80c 5000mAh?

I'm thinking the extra voltage of the 4S would be able to make up for the lower amps the 3200mAh pack has versus the higher amperage of the higher capacity 5000mAh 3S pack.

And then you have the weight benefits of running a lower mAh pack. :yes:

and what about runtime? would I be able to last at least the Main with that 3200 mAh pack?

please advise. :oops:

oh...and my expenditures will be based on the replies here. I'll either go with a couple more 3S batts or, if it that route is not deemed as efficient, then I will purchase some mid-range mAh 4S batts.

:)

You don't mention what car you have or what motor / esc you are running.

To provide a cushion I would go for a 4s 5k...

You'll be losing watt-hours going from a 3s 5000mah to a 4s 3200mah so over all I think you would lose run-time.

What's the vehicle it's going in?

I tryed a simmiler thing with my 1/8 buggy with a 2075kv motor and a hobbywing 150amp esc and 2 3200mah 2s 25c batterys in series at 14v just for a practice and cooked and swelled one of them and they were both very hot. The amp output is only 80amps at 3200mah and 25c and depending on your system it may not be enough and will get your batterys quite hot as mine did. so just be carefull.

I agree, you should go with 4-5k-mah on 4s... but seeing as you have a TP 40C 5000mah, and your mains are only 10 mins long, I would hardly worry about anything. If your mains were longer yes, for instance, I have 30 min mains at my local track, I use 6s 4200mah packs, and swap out at 15 mins, each pack has 20+ mins of runtime though, provides peace of mind.

You COULD use 3200mah 4s pack, but it would have to be a high end pack, such as a TP, Hyp G3, Neu 35C+, etc.

sorry, my bad.

it'll be on a Jammin X1-CRT, stock spur and mebbe an 11 or 12T pinion.

motor/esc will be a Neu 1515/1.5D and probably a MMM.

jammin x1-crt. oopsie.

aha...so I see. I think.

so it appears that the 160amps (combined total, right?) that setup was putting out was not enough?

ah. I have an SMC 40c 4S 5000mAh, but interestingly enough, my motor gets a bit warm with it. :neutral:

am I being too heavy on the trigger? perhaps.


the pack I saw was a PolyQuest 4S, 25c I tink.

Motor getting warm wouldn't be the batteries fault. It's driving style, gearing, ESC settings, or terrain (ie grass) your running it on.

Amps vs voltage concept:

power (watts) = volts x amps.

You need a certain amount of power to move any given setup to a certain speed.

If you use a low voltage, high current (amps) setup, it will run hotter and give less runtime compared to a higher voltage, lower current setup.

For example:

1000watts / 14.8v (4s lipo) = 67amps
1000watts / 11.1v (3s lipo) = 90amps

The more current you pull, the hotter the system will run, and the shorter the runtime will be, all things being equal aaprt form voltage.

That said, your 1515 1.5D would run equally well on 3s or 4s, you just have to match the gearing to the voltage to keep temps, speed and power in check.

I would peronally run 4s lipo, and gear down a bit to reduce the load on the electronics, yielding the best runtime, acceleration and power available.

ah yes. so...if my jammin has the stock spur (i believe it's a 62t) with an 11T (possibly 12t) pinion running on 3S, does that sound like a good gearing?

driving style isn't conservative. you could consider it as a...race pace. not too slow, but not overly fast either.

ok...so on a 3S (40/80c TP 5000mAh) set up with an 11T pinion, the truck is frikkin nuts. wheelies galore, near backflips off the jumps (if i'm too heavy on the throttle on the face) and general mayhem going down the straight.

on 4S, it's even worse. front tires the size of paper plates, double backflips if I hold the throttle in the air off the jumps, and my drive train is screaming for mercy/vengeance.


So...would I need to gear up (say a 13-14t pinion) on a 4S while retaining the stock spur? Or do I need to gear down (a 9T pinion?) to help temps?

I'm lost as of now...the combinations I've tried usually end up in huge amp draws that make the motor quite unhappy.

the best combo i've found for a 3S with the stock spur is an 11T pinion. motor temps usually range from 123-126F, ESC (MMM) is around 125F, and batts are around 110F.

So...if I wanted to duplicate those temps on a 4S, what pinion would I need to run?

123-126F is luke warm on a motor. My truggy is pushing 175 after 20 min mains of conservative driving. And I'm running a 1515 2.5D tekno neu. Ambient air temps were quite high though as well as humidity levels.

3s on a 2700kv motor is enough to race with. It pulls more amps than a lower KV motor on higher cell count, but that's where it's getting the power from. Until you're seeing upwards of what I'm experiencing, I wouldn't go to 4s unless you had a lower KV motor.