Long Run Times

[Scott Richard]

Please Help, I have a chris craft barrel back and I want long run times, I have tried many different ESC. My problem lies with running two 7.2 stick batts with only one 540 motor. I tried the emaxx novak esc but I had overheating problems very quick while only running one motor (its made for two motors). I just recently purchased the novak super duty and run 2 batts with only one motor (which its made to do that). Still overheating problems. I tried water cooling through the spped of the boat, I have tried forcing the water throught the esc coils with a pump, and I have tried a electric fan. The electric fan didn't have enought supply and return air within the boats hull. And the water cooling didn't cool it either even with the visual of water exiting the back of the hull. Should I switch to 12volt? Not looking for speed but just long run times without my esc overheating.

[CG Bob]

You didn't mention the MAh rating of the batteries you're using, or how long of a run time you're getting. Generally speaking, 100 MAh of battery rating is equal to 1 minute of charge or run time; your time may vary depending on motor, prop and gearing. You also didn't mention if the 540 motor is a stock unit (27 turns) or a modified motor (less than 27 turns, and possibly multiple winds). Most ESC's are matched to a specific type of motor based on the number of turns and battery voltage supplied.

I built the Dumas 1940 Chris Craft 19' Barrel back - dual cockpit. I have a MACK Products #3600 motor and a FMA Direct Volcano ESC. I'm swinging the stock Dumas 3 blade bronze prop. I consistently get 15 minute run times from a 1500 MAh pack and 30 minute runs from a 3000 MAh pack. I run one battery pack at a time, and I get a fairly fast speed. I do not have any water or fan cooling for my system, and it rarely gets too hot to touch. Some pictures and beter desription of the work is posted here. (http://www.rcgroups.com/forums/showthread.php?t=368014&highlight=chris+craft+)

[Doc]

Scott,
Very simply, if the ESC is getting hot then you are running it close to, or over, it's limits. Which ESC to use? Determine the current requirements of your motors, do a 'stall' test. Then, you'll know what 'size' ESC to use.
Manufacturors who rate their ESCs by the number of turns a motor can have are NOT doing anyone a favor. That, alone, just doesn't tell you enough. Most ESCs are rated by the amount of current they can handle at a particular voltage. Knowing what your motor(s) require is how to select an ESC. It's also good to remember that the published ratings are the ~maximum~ ratings. Using an ESC that has more capability than is really needed is a pretty good idea.
- 'Doc

[Doc]

You can get a 'fair' idea of the 'run time' by dividing the total battery rating by the motor's maximum current draw. 1800 mAh x 7.2v = 12.96 watt hours. Motor draws 2 amps? Then 7.2 x 2 = 14.4 watts. 12.96 Wh / 14.4 W = 0.9 Hrs or about 54 minutes. Nothing is ever exact (drag, friction, etc.), so 'fudge' it by 50%, call it 25 minutes run time. Still high but a 'fair' guess, and the maximum you can expect.
The 'm' means miliamps or 1/1000 of an amp. So 1800 mAh is the same as 1.8 amp hours. Lots of "buts" in that equation so don't expect it to be exact by any means! Just another 'FWIW' thingys...
- 'Doc

[carwasher]

don't forget to check that the prop isn't too much for the motor. Also check for binding in the driveline, that can make any motor draw more than it should and increase the heat in the motor and esc.