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[flybobby]

Another problematic day!
In a bid to give my boat a little more power, I replaced the 6v gel cell with a 12v gel cell.  I thought this would give my Johnson 600 motor the juice it needs!
The Johnson 600 is rated 6 -12v, so thought 12v would be no problem, how wrong was I? ::)  5 mins running (very well and a good speed) later, the blue smoke arrived! Motor fried!! Too hot to handle!!  I let it cool down and tried a little throttle again, more arcing followed by smoke!
Where have i gone wrong, or have I been misled that it would take 12v? ???

I have a Johnson 888 kicking around the workshop, anyone know the spec of this motor, or what voltage she will take?

[grasshopper]

Think the problem was caused by just doubling the voltage, forgetting of course, that the current would also increase proportionally if you used the same propellor!
I am assuming that you mean the motor is arcing? - if so, sounds like you've cooked your commutator and brushes. motor probably now scrap only.
Similar story with your speed controller....

[flybobby]

Thanks!!  :(

[flybobby]

Thats blown it, new motor and speed controlller needed! :(

[Sub driver]

you have forgotton that a 12v gell weighs more + more drag on the hull and more momentum needed,so the motor has to work a lot harder than before, it will slow it down but the volts are going in so the difference has to go somewhere ie heat, bin the gell and get either nicads ( faster discharge rate) or Nimh slightly slower discharge rate but longer runs than a nicad . Gells are ok for a slow scale boat but for performance you need the Nicads mainly or Nimh. you will be shocked by the difference in performance. Have a look at this web site www.component-shop.co.uk.    gels are designed as a stand by battery on trickle discharge and are no good for anything wanting a fast discharge

You may be surprised about the prices too 7.2 v 4300mah NIMH ( thats 4.3 AMPS ) per pack = £ 19.95 each they will also make up to your specs.

when you get a new motor / speedo stick the boat in the bath with an ammeter set on amps in line and run it whilst holding it still and read off the amps...that way you will know what the set up is pulling rather than just guess and have another return trip to the model shop.

Hope this is of use.

[flybobby]

I know the 12v is heavier, but the boat is the same weight as before(some ballast removed to compenate for heavier bat).
I upped the voltage as the johnson on 6v (nominal voltage) did not give me scale speed.  I am not after a speed boat, just a scale like speed with a fair run time!

My main question is, the johnson 600 is rated 6 - 12v, it worked slowly on 6v but 12v fried it in no time.  I thought it would cope with the voltage reardless of current, but evidently i were mistaken!! ::)
The esc fry up was my fault as I foolishly left out the inline fuse! A mistake I will not make again!! ::)

[Doc]

What it sounds like is just too much load on the motor.  Reducing the pitch of the prop should reduce the load and allow the motor to run on the 12 volts (or same pitch but smaller diameter prop).  That pitch (or diameter) reduction will also reduce speed so you may not get the results you were aiming for to start with.  Then you start looking at a larger motor.  As for the ESC, you can only use what falls within it's current/voltage ratings, no practical way around that.  The only sure way I know how to determine the max current draw for a motor(s) is by doing a 'stall' test.  That will tell you what the ESC's max current rating should be.  Certainly not a bad idea to include a fuse in the circuit, but fusing a less than adequate ESC isn't exactly the best way of doing things (does work to some extent though).
 - 'Doc

[flybobby]

Thanks doc,
The prop is a 40mm brass three blade scale prop from prop shop, nothing too fancy! A bigger motor sounds good to me, but which one?  Would a low drain 12v motor help things here (less rpm) as the johnson spec reacons on 18000+ at 12v.
As for esc, would it be worth getting a 30amp job, just to be safe and putting a 20amp fuse between it and the bat?
I need an amp meter really! ::)