Amp draw

[riverman]

Have a 29 inch hobby boat (light/plastic former vector push) that I put two 550 , 17 turn, 4100 kv motors brushed motors in. Has 35 mm props. Looking all around the net and forums for formulas, etc, to figure out what amp size brushed esc I should be getting. Anybody have some info / formulas for calculating max amps?

Running either 7.2 or 8.4 NIMH batteries.

All I need is ball park figure (50 - 100 - 150 = ?) to help decide on esc size.

[Make-a-Wake]

50 amp range total

[rotarypower101]

Is there a amperage draw calculator that will allow me to input cells,capacity, total weight, prop dia/pitch, motor Kv, hull type, and give me a idea of amperage draw and estimated run time?


Found this, but not sure if i am using it right as the prop field seems odd to me, almost like it is asking for a circumference rather than diameter (just a wild guess)

http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en

[Fluid]

Are your motors wired to the controller in series or parallel? This will determine the amp draw and voltage each motor will see and will dramatically effect your speed results. Wired in series will mean half the rpm and twice the amp draw per motor. Wired in parallel means higher rpm and lower amp draw. There is an older speed calculator program around but I don't have a link.




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[ReddyWatts]

I think Fluid meant to say that two brushed motors wired in parallel will draw twice as much as two wired in series using the same battery.

[Fluid]

No, I wrote what happens. Two motors wired in series use half the voltage of two wired in parallel and twice the amperage. Ed Hughy and I have the records to prove it.





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[ReddyWatts]

Right 2 in parallel use higher amperage, not lower.

[Fluid]

No. Parallel means full pack voltage to each motor, amps to each is halved. Series wiring means half the pack voltage to each motor with full amperage to each. Both can deliver the same nominal wattage.

MRP used parallel wiring in their Miss Bud 12-cell hydro in the 1980/90s so they could use two cheap 540 motors geared together and avoid using one large expensive motor. This reduced the amp draw on each motor but gave a full 12 volts to each. Lower amperage helped the motors from overheating without cooling, but brush wear was pretty high. Ed Hughey used parallel wiring for years to set a lot of early FE records, but discovered that with series wiring he could use motors with far fewer turns, reducing resistance and increasing efficiency and power over parallel wiring. Brush wear was also greatly reduced. I used twin 4-turn motors on 8 cell cats to set several FE records myself.

Believe me, this isn't just something I read in an electrical engineering text. I built boats with both setups but preferred series wiring. If each motor only got half the amperage and half the voltage then our boats would not have set any records....



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[ReddyWatts]

Right, the higher the voltage to the motor the higher the amps, not lower.

[ReddyWatts]

Riverman most of the brushed 550 motors will draw less than 35 amps when using the right prop. If your setup is with 2 motors in parallel, then I would get a controller rated atleast 100 amps. It will also work for series motors since they will use less amps.

[Make-a-Wake]

Fluid is right.........................its an absolute: "Wired in series will mean half the rpm and twice the amp draw per motor. "

[ReddyWatts]

If you place 2 resistors in series producing higher resistance will it allow more or less current through the circuit?