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Electric dinghy using a 5kw motor and VEC300 controller connected to a waverunner (jetski) pump

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JonS:
Hi Folks. I'm Jon. I am building an electric dinghy using a 5kw motor and VEC300 controller connected to a waverunner (jetski) pump. I fiberglassed the pump into the floor of a 10 foot rigid floor inflatable (RIB) boat. I am a couple of weeks away from a test in the pool then it is off to the marina.

-jon

Bikemad:
Hi Jon andto the forum.

Now here's the potentially bad news:
If you have simply installed a direct drive between the motor and the Waverunner pump unit (as per the original jetski) you may be disappointed with the boats performance.
This is because the 5kW electric motor develops its maximum torque at much lower rpm than the original gas motor, and the jetski impeller will probably need to spin much faster to produce the expected/required thrust.

Check out this post regarding an 20kW electric motor conversion on a jetski that was very under-powered when initially installed using a direct drive setup.

Whilst I realise the 20kW motor used for the above Jetksi conversion is a lot more powerful than your 5kW motor, I suspect that the same low power problem is likely to similarly affect your motor's power output too. :(

According to the 48V, 72V and 96V datasheets, your 5kW motor's rpm must be loaded below ~3500rpm for the 48V motor (or below 3700~3800rpm for the 72V and 96V motors) for it to be able to produce 5kW or more of output power.

If you can find out what rpm the original jetski developed its maximum output at, you can work out what gearing would be required for your motor to achieve the same impeller rpm with a motor speed of ~3500rpm.

Alan
 

JonS:
Thanks for the response. The speed limit inside marinas where this will be used is 5kts (5.5 mph) so I am not trying to hit planing speeds. 15mph top speed is fine. I found an RPM vs speed curve for the jetski pump I am using and I think I am in the window but we will see soon.
-jon

JonS:
My motor is really noisy when it runs at all speeds. The noise is not mechanical. It has that noise that servo motors often have. Does anyone know if there is an update for the VEC300 that makes it quieter?
thanks
-jon

Bikemad:
Hi Jon,

I'm not aware of any updates for the Vector controllers that would actually reduce the motor noise.

The VEC controllers are Sine Wave controller and they greatly reduce the motor noise under load compared to the HPC square wave controllers.
I suspect that the noise you are hearing is the typical motor noise which occurs when you manually spin the motor (without using power from the controller), so it is unlikely that you will be able to reduce it.

It might be different if the noise was only evident while the motor was under load, but if the motor is still producing the noise while it slows down after quickly releasing the throttle, then the controller is unlikely to be causing it.

Alan
 

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