Doubling the batt Mah = longer run time?

[wickedgmc]

I would like to challenge that statement. I find a major percentage of my customers back yard bash. Not that they wouldn't race, but there isnt any racing around them. One of my most heard email questions is how to get more runtime.

+1

[AntronX]

So if you have 3000 watts, you divide that by 745.6999 = 4.02+ HP

That's electrical horse power. Don't forget motor efficiency and controller losses. Motor = 85% and ESC = 95%.
0.85 * 0.95 = 0.81

4.02 HP * 0.81 = 3.3 HP (at the shaft)

[Steven Vaccaro]

I happened to miss a word when I first read it.
The sentence, "Most of us that race" I read as "Most of us race". The word "that" makes all the difference.

[Jeff Wohlt]

I won;t argue with Hill on this one. He knows his battery stuff...been doing it for more years than I have been in RC. Packs in para do give more volts as well.

Pull a single pack down with 75 amps and watch your volts...they drop as well. When you para wire them and pull the same amps now with both packs you have more to work with so volts do not go down and most of the time you see more power.

Yes, series doubles volts but para also can have a big effect on power when pulling heavier amps. It is not just a gas tank double in size. Now you can also pull twice the C rating and not have the volts drops so much.

[Jeff Wohlt]

Sorry for my post...I think I just said what Steve Hill said.

[areseaer]

I was always told it was like plumbing. The batt is like a tank of water, the size of the tank is the capacity, the voltage is the pressure in the pipe(wire).
When you use the water(start the motor) the pressure will drop some. Double the capacity (two batts in parallel) would be like having two tanks of water with two pipes to get water from. Series is the same tank with higher pressure in the pipe. So discharge rate would be the flow of water in the pipe, try to get to much and the pressure will drop to low.

[sailr]

No worries Steven. I sometimes read something and get all in a huff. When I do that, I make myself go back and read it again.

I happened to miss a word when I first read it.
The sentence, "Most of us that race" I read as "Most of us race". The word "that" makes all the difference.

[sailr]

No question but the Startup voltage is the same, regardless. The added capacity (amps) allow the batteries to get drained more slowly, thus the volts don't go down as quick as a single or series pack. (I started selling lipos in 2002)

I won;t argue with Hill on this one. He knows his battery stuff...been doing it for more years than I have been in RC. Packs in para do give more volts as well.

Pull a single pack down with 75 amps and watch your volts...they drop as well. When you para wire them and pull the same amps now with both packs you have more to work with so volts do not go down and most of the time you see more power.

Yes, series doubles volts but para also can have a big effect on power when pulling heavier amps. It is not just a gas tank double in size. Now you can also pull twice the C rating and not have the volts drops so much.

[sailr]

Yep, you have to figure in efficiency. Just trying to keep it simple! All motors and esc's have different efficiencies. It's hard to measure without some pretty sophisticated equipment. When we started selling brushless motors in 2002-2003, we hired a lab to get all that data. Cost us a bundle and nobody really cared!

That's electrical horse power. Don't forget motor efficiency and controller losses. Motor = 85% and ESC = 95%.
0.85 * 0.95 = 0.81

4.02 HP * 0.81 = 3.3 HP (at the shaft)

[sailr]

That analogy works good!
I use the volts as pressure in the pipe also. Thanks!

I was always told it was like plumbing. The batt is like a tank of water, the size of the tank is the capacity, the voltage is the pressure in the pipe(wire).
When you use the water(start the motor) the pressure will drop some. Double the capacity (two batts in parallel) would be like having two tanks of water with two pipes to get water from. Series is the same tank with higher pressure in the pipe. So discharge rate would be the flow of water in the pipe, try to get to much and the pressure will drop to low.

[Henrik04]

A little off topic , but is there a way [formula ?] to calculate horsepower of brushless motors ?

One horse power (electric motor) = 746 Watts

One mechanical horse power = 745.6 Watts.

Hope this help.

Henri

[kevinlew211]

EXCUSE ME!?

SERIES increases volts.
PARALLEL increases amps.

This is basic electricity! That was the only question he had. Yes, you will have more volts delivered when you increase the amps. More volts = lower amp DRAW but not less amps CAPACITY. More amps capacity = longer run times. THAT was his question.

He is right, someone here confused about AMP DRAW and lipo's AMP CAPACITY, paralell lipos will give you lipo's DOUBLE AMP CAPACITY handle the motor NOT adding more amp draw to the motor if i can say just a lil bit by increasing the volt just.... a lil bit also.

[Mel279]

Guys. Is this true if i double the batt Mah as in parallel lipo set up would result in longer run time? Ok, for a 6S1P 5000mAh 25C i would get about 4-5min. So, by doubling it , i would get 8-10 min?

Yes u get more runtime but your boat would get heavier which lead to more heat build up on your motor, and its better suited for salwater as u get less heat than freshwater. Frankly I cant run two packs of 6s lipo for more than two mins on freshwater, it burnt my motor but glad its an outrunner, I just replace the burnt winding.

[Himalaya]

Basically Yes, higher pack capacity = longger run time, but it's non-linear. Don't expect a same boat with 10Ah run twice as long as with 5Ah, because more packs means heavier boat, making it run wetter, thus more current draw. My DF Cyberstorm runs 5 minutes with 5Ah and a little less than 8 minutes with 10Ah.