What size or how many mAh

[T.S.Davis]

In my sons Stealth we run 8k. Not because we need it but because the boat needs the weight. If we're adding weight we figured we might as well add something that pays back.

Toms Triton can get away with 4400. It's the absolute perfect spec sport though.

There's a fine line with this class. You can be too light. Every boat has its own sweet spot. Some fiddling is in order for sure. It's half the fun.

[Fluid]

Hmmmm, lead is a lot cheaper than LiPos if all you need is weight. Easier to place too.


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[T.S.Davis]

True, but I can throw those same packs in my spec offshore, P mono, P sport if I need them.

[ray schrauwen]

True, but I can throw those same packs in my spec offshore, P mono, P sport if I need them.

This is the direction I like. Going same way. Keeps the voltage up too.

[ray schrauwen]

This is the direction I like. Going same way. Keeps the voltage up too.

Doing things in this 'modular' way is efficient and keeps the costs down.

[T.S.Davis]

BTW We've run the Stealth on a pair of 4s2200's a bunch of times. Those were the previous generation of cells. Worked fine but they would come in pissed off. Tom is doing it with latest Roaring Top cells. They don't even bat an eye. The newer gen cells from most every manufacturer are much better. If you buy decent cells that is. I can't vouch for the cheapies. I've drawn some of my GP cells down into the 2.5v range. They were not happy but still came back. Came in bloated and hot hot hot. Their days are numbered now but in the old days that would have likely burned inside the boat.

Also, a pair of 2200's can multitask too if you have the right boats. They fit really nice in most spec riggers too. Extra wires to route down under the canopy but they fit perfectly. Spec rigger amp draw is so reasonable that the wires don't seem to cause problems.

[boatnik]

Here is a topic that I have not been able to grasp. How to choose a battery that will give your boat the best performance without them swelling up, disintegrating, damaging your ESC and/or motor. What are all of the factors one needs to calculate and consider? For example: I have an old Kyosho Viper that I've had for years. I started tinkering around with it. I installed a water cooled Leopard LPB2845 motor. It's maximum ratings are 30A, 26V, 800W and 2350KV. I also installed a water cooled Dynamite 3860 ESC. Its specs are 30A constant and 180A peak. Input voltage is 2S-3S (7.4V-11.1V) Li-Po. BEC Output is 6V/1A. I'm using the original Futaba FP-R112 JE receiver.
One area that gives me the most confusion is the correlation between amps, volts and watts. I am aware that in terms of LiPo batteries, the MAH rating determines the amount of run time and the "S" rating denotes the number of cells and total volt output. The "C" ratings I'm not too keen on. Is there a step by step methodology or calculations that one uses to determine if a particular battery is too much power for a given motor and ESC pairing? Would some of you more senior and experienced hobbyists help me here? Thanks. Boatnik

[CraigP]

Good questions... Answers are dependent on goals. Do you want to race? Do you sport boat and are looking for longest run time with greatest reliability? Can't get to specific answers without knowing your goals and expectations.

I can tell you that your ESC, rated for 30A continuous and your motor rated the same leaves no headroom to explore prop options, which most boaters want to do. You should run a 60A ESC on a 30A motor. I understand it has a momentary rating of 180A, but that is so much higher, I wouldn't put much stock in that. Motors can take momentary overrates much better then ESC's.

So your motor is rated for 800W. Excellent job getting ALL your specs together! So on 2s at max power, the amp draw would be 800/7.4=108A. This is way over the max amp rating of the motor. So this battery/motor combo isn't good at all. At 3s the amp draw is 800/11.1=72A, still way over the motor spec. So with what you listed, you will only get the following safe power out of the motor on 2s, 30*7.4=222W, only about a quarter of the available power. On 3s it's 30*11.1=333W, 42% of available power.

See you got the wrong motor or battery choice. It's a 6s motor, then you control amps by how much load or prop you put on it. Folks are always doing this, running under the voltage spec and pushing the amps way past rating. It's amps that breaks parts, causes heat and puffs batteries. You're going to get all kinds of posts that say they do it all the time. All I know, its way past what the manufacturer states the motor should be used at. For me, I would start with a 14.8V motor, then run these numbers from there. I hope that helps...

[CraigP]

Oh, on motor specs, each spec is a limiting value. The motor is only supposed to see 30A and not over 26V. The 800W only applies if you apply on-spec volts and amps. The motor will NOT take any amp and volt value that will yield 800W. BTW, I would never get a motor with these specs. It's small, so putting a 6s battery in it doesn't make a lot of sense to the average boater. You didn't mention the ESC's voltage rating...

[ray schrauwen]

Just an FYI, cold cells will swell underload more often than if ambient or warm.

[CraigP]

Strange, I got an email with Ray's response, but the second part is not showing up on the post... Anyway he says heating up cells before a run is for professionals only. Yes, that's very risky business. When a battery is heated, it's terminal voltage will rise. So I would think if you're going to do that, then the batteries would be charged to say 4.16V, or whatever testing shows. But if you charge at ambient to max volts then heat it up, you could get yourself a camp fire starter brick there!

[ray schrauwen]

I edited it for safety reasons.

I've warmed cell before on 35*F days etc. Very carefully but I avoid it if possible. In Canada by end of September it gets very chilly and the last run for many in my area is an apple butter festival at the end of the month. Last time I ran my Q sport there one cell got a tad puff in it from cold since I was propped way down from normal. These packs have never been more than 130F.
Running in the cold can kill packs because the chemistry doesn't like high current draw until it's at a decent temp.

[CraigP]

Yes, that's true. It would be nice to have a heated battery case, something to get and hold them at 85 deg F, like F1 tire warmers. The challenge is to ensure they are at the same temperature, all the way through the battery. Only a good length of time in an enclosed box can do that.

[ray schrauwen]

Hobbyking sells warming bags and I've half finished a warming case made from hobbyking tire warmers.

Some use those 12/24vdc beverage, food cooler/warmers.

[pescador]

I have the same warming bag and tire warmer :), I also use those disposable hand warmers.


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