I have an underwater motor 1500W 30V 50A & I’m trying to get a speed controller for it.
I can waterproof it & a suitable potentiometer myself.
Would anyone know of a suitable controller & potentiometer ? I have used a 36 V 60A 3000W electronic controller with a small, rather fiddly potentiometer. I used 3 x 12V agm batteries. It worked for 10 minutes before it totally melted. I didn’t think the extra 6 V would have much impact or as some people advised, try 24 V.
It has been recommended to me to try a mechanical rheostat !
Any advise would be very much appreciated.
Hi Hubert
What exactly melted and under what conditions? Full speed, half speed or other. The suggestion to try 24V first could be a valid and safer one.
Rheostat? I personally would not go down that path. For a start you have a torque advantage when using a PWM based system over a rheostat and the sheer size of a suitable unit would be a bit off putting.
Cheers Bob
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Hi Bob,
many thanks for your input. The whole electronic bizo just melted like mozzarella on a pizza.
First I thought of water getting to it but it was bone-dry. I have the feeling the controller wasn’t designed for continuous load. The motor has quite some torque & it dragged me around for a good 15 minutes before the batteries gave out. I tested on-off several times no problems but once I let it run for more than 3 minutes on full power I couldn’t turn it off again & so, all I could do is try not to lose the rig.
Hi Bob,
Saw this but I’m too wary because on another site I saw it for $97.
I was hoping Core would have something as I really prefer to buy in Australia.
Hi Hubert
Sounds pretty catastrophicUsually when this sort of thing fails the mosfets go short circuit and drive the motor full speed which sounds like what has happened. Normally if the mosfets are driven properly they don’t generate much heat at all. The on resistance is only mΩ and the voltage drop across the mosfet is very low. The only time they generate any appreciable heat is during the switch on switch off time when they are transitioning from off to on and vice versa. With a well designed system this time is very short so the heat generating time is very small also and the average heat generated can be quite modest even at high current loads.
It sounds to me that the mosfets have not turned fully on for some reason putting them into the heat generating region permanently. Very hard to diagnose remotely without being able to do some measuring. A controller something like a Golf cart would probably be OK as they are a 48V system although I don’t know why the one you tried would not work. The extra 6V may not have been a good idea but the speed controller should have handled it after all you say it was a 36V controller. But if it was close to max specs it may not have had enough overhead built in. Better to go too big than too small but the one you linked is a bit of an overkill.
By the way this motor is a brushed type I assume. That is the only type that works with a PWM type controller. Brushless no good I think.
Cheers Bob
sounds like you need a professional rheostat just wondering though all the ones i have ever seen have been for use with A.C that is not to say that they wont work with D.C as there basically a vey high current variable resistor though often more than not there wire wound and could most likely increase the inductive variable into the equation…and to add to the complete circuit…although D.C does differ to A.C…but you can get them …you will have to search for one suitable if your going into this direction…electric stove tops have them i knew a mod for them to use with higher current i would have to ask my elders…though…if your interested…scrap one from an industrial electric appliance… if the need be…
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Hi Brian,
thank you for your recommendation. I’ll be going into the city later & will check around any DC shops/auto elec to get more info & learn more on the subject. Hopefully find a practical solution.
Cheers
There have been volumes written on motor speed control. Doctor Google may be a start.
Cheers Bob
