Higher voltage lower amps thoughts

[joeling]

Hi,

I have been pretty much dormant for the last few months as I was kind of discouraged with my experiments. I was fighting heat issues with the esc. My tinkering revealed that I was pulling in excess of 100A during hard accelaration using a 4S on a 7XL motor in a buggy. This tended to overheat the esc. I had to installed copper heatsinks on the Quark 125 & 60mm fan to cool it. Still the result was inconclusive as the rainy season set in. I recalled also that I had better luck when I was running 5S with a 9920.

To cut the story short, I read in a flying forum that some heli people put a plane esc with 10S lipo into a buggy conversion & it was a good combination as the amp draw was low & everything ran cool. They left out some details on the brake though.

Is this the way to go ? 10S 2000mah is pretty much equivalent to 5S 4000mah in terms of power density right ? To lose less to heat in fact is a good advantage of the HV system over typical systems currently in the market. The only problem is that the motor has to be of a much lower KV rating though. Any thoughts ?

Regards,
Joe Ling

[tallyram]

thats usually better if possible. i run 6s on a 1634kv motor. my packs are 3700mah in series and i still get around 20 minutes of hard running because of efficiency. my truck is very powerful and fun!

[Gustav]

Only problem with going 10s is finding a suitable speed controller and getting it to work in a car with the right neutral point.36 cell BKs and the big schulze are an option though.

That's why i stick with 7s right now with the MGM 16024,rated for 8s but happier at 7s with my set up.As hard as i try i can barely get my esc to break 100F,that's a 1950/10 on 7s pulling one heavy truck,it has a 12 volt fan and a little extra heatsink though.It's not exactly hot over here either.
Anyway,the esc is the limitation,no garantee a plane esc will work with your radio.

[VintageMA]

Be careful with the calculations on power density. If you drop from a 4Ah cell to a 2Ah cell (regardless of the # of S) you still lose the amount of current you can push out. Even if the cell was fully capable of pushing out 20C you are dropping from being able to safely push out 4Ah x 20 = 80 Amps to 2Ah x 20 - 40Amps. With twice the voltage across the ESC and motor, the current draw will go up and it is likely that you will ruin the cells.

As a side note - I am (was) running a 9920 in a 1/8 buggy conversion with a 7XL motor and 4S @ 9000 mAh - close to 30 minute runtime with WOT geared 14/46 with MOD1 gears. The buggy weighs close to 9lbs with the batteries but I easily get over 40MPH, not sure exactly how much over, but I run in a park along side a road with a 40MPH speed limit where people tend to drive faster and I can easily keep up and pass. The motor gets warm (never over 130-140) and the 9920 stays just barely warm to the touch.

I was in the same pradicament as yours when I accidentaly drove through a very deep puddle this past weekend and my ESC went up in a huge cloud of silicone smoke 5 minutes later. After reading the articles of people having all these heat problem with the Quark, and never having a single problem with my 9920 on 4S I decided to go ahead and order another 9920.

My question now is would the 9920 handle 6S? I have two 3S @ 8000 mAh packs I am going to run in series with a a MGM 16024 and LMT 1950/7 motor on a LST2, but would like to try the 6S on the buggy while I wait for the motor to come from BK.

[neweuser]

the 9920 COULD handle 6s, but it would really be pushing it hard.

[Nick]

I run 6s FlightPowers on the 9920, lol... don't bother, I burnt my finger pretty bad from just brushing it on my last run, would just thermal in 3 minutes and is no good until it cools right down. It runs fine just over heats really badly but hell is it powerful!

Saving up for an MGM.

[coolhandcountry]

I am going to try this shortly. I am on a mission to try 12s lipo on a motor.
I will have to get back to you on test results. It won't be until next year though.
Getting new rc for xmas for this.

[zeropointbug]

Jeoling,

I have always wanted to do the same thing, running high voltage on a high turn motor. This WOULD cut the heat losses due to wire resistance in HALF. Say, if a 7XL was running 82% efficiency at 5s LiPo, then a 14XL running on 10s LiPo would maybe run at 86 - 88% efficiency. There are other factors with contribute to heat loss however. The controller is the same thing, for a given ON resistance of a controller, the heat dissipation goes up the square of the current being switched.

So yes, by doubling the system voltage, the overall efficiency goes up quite a bit.

AT THE MOMENT, as battery technology is changing so quickly, there isnt really a standard for voltages yet (not that there should be), but until we remove the BATTERY bottleneck (still not there yet!) there will be alot of options out there, and prices will be higher also.

Not to get too carried away... i hope Quark comes out with a 10-12s LiPo (~60 amps) capable controller next year.