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Need Help

Old 05-13-2007, 09:10 AM
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Larryds
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Default Need Help

Hey guys, I need some help with my Jet Ski. I bought a used Kyosho jet ski and I am having a heating problem. It ran fine the first couple of times I ran it, then after that it would run for about 5 mins and shutdown. It would sit for a couple of minutes then run again and then shutdown. I have replaced the motor because it was getting old, replace with a 12t motor. Next I replaced the ESC. Took it out yesterday after a successful bench run and it ran ok but with exeriencing intermitten power surges. Pulled ski into shore and after openeing top the battery was very hot. Hot enought to melt the wires on the connector. It was a cheap 2000 mah battery. We let it cool and installed a 3000 mah battery and it too got hot but not as hot as the previous battery, was even ran longer and the surges were less often. The esc was also hot. The replacement esc is a car esc. Does that make a difference? Is my interior getting to hot? Run times have been 5 to 10 mins. I stumped. [] Thanks
Old 05-13-2007, 02:14 PM
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Umi_Ryuzuki
 
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Default RE: Need Help

It could be that you have mismatched the motor and propeller.
With the wrong pitch propeller, you could be getting intermittent cavitation causing the rpm to increase, then suddenly bite back into the water(stalling it), and over working the motor and causing it to draw a lot of amps.
Old 05-17-2007, 12:49 AM
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13BT
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Default RE: Need Help

12T is too hot a motor. You can either keep it and use a smaller prop, or fit a milder motor instead.
Old 05-17-2007, 01:30 AM
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Larryds
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Default RE: Need Help

Thanks guys! I will get a 8 of 10 turn motor and see if that helps. I am going to install a computer fan in my pt boat so I will pick up another for the ski just in case. Thanks!
Old 05-17-2007, 01:37 AM
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Default RE: Need Help

I think the 8 or 10 turn motor is going in the wrong direction, it'll be 'hotter' than the 12 turn motor. Milder means more turns, not less. 'Up-grading' to a hotter motor which draws more current means your ESC should be up-graded too, and maybe the battery. Most 'stock' ESCs are just adequate, not much 'left over' for a higher current drawing hotter motor. You never get something for nothing.
- 'Doc
Old 05-17-2007, 02:58 AM
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Larryds
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Default RE: Need Help

So Doc, youre saying that I need a 12 + turn motors? I am new to this electric stuff, learning as I go along. I did get a new ESC and its rate for 12 to 27 turns. A 20 turn and current esc along with a 3000 mah battery would do the trick? Thanks!
Old 05-17-2007, 01:51 PM
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Default RE: Need Help

Rating ESCs by the number of turns a motor has is one of the silliest things 'they've ever done. It doesn't really tell you what the ESC's capabilities are. The number of turns in a motor also doesn't tell you anything useful. Of course, it cuts down on the 'other' stuff you'd need to utilize 'real' numbers such as current draw, etc. As in a meter capable of measuring that stuff, and knowing how to use it. The only useful part of an ESC rated like that is to remember that the limits manufacturers put on the ESC in this way are just that. It's always better to stay away from the 'limits' if you're worried about expense. Working at the 'limit' is pushing things. That works some times, but not always. 'Luck' has a lot to do with it.
Electrical stuff.
The number of turns in a motor; less means 'hotter' and usually faster. More means not as fast, and sometimes more powerful (torgue).
The number of poles in a motor; less means more 'jerky', more means 'smoother' and more torgue.
A battery's Ah or mAh rating is the same as the fuel guage in gallons, shows how much 'milage' you can get. Bigger usually means longer running and more weight.
Voltage equates to horse power, sort of. The limiting factor is how much the rest of the electrical system can handle.
Interference from electrical pulses means you ought to put a capacitor across the poles of the motor, and one from each pole to ground (motor case). Doesn't stop interference completely but it certainly does cut it down.
That doesn't cover everything by any means but are some of the things you should keepin mind.
Good luck.
- 'Doc
Old 05-17-2007, 11:38 PM
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Larryds
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Default RE: Need Help

Thanks doc for putting that into terms my little mind can picture. Local hobby shop has a 18T motor so going to try that. If nothing else I will have a lot of used motors for my brothers truck collection! Thanks!!!

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