Low motor rpm from HPM-10kW 72V with EZKontrol 721000 controller

[Tez]

Hi everyone,
I am new to this forum and need some advise. I have just converted my 22 ft displacement cabin cruiser from diesel to electric. The setup is a direct drive 10kw 72V bldc Golden motor with EZKontrol 721000 controller. The battery is 24 X 314ah cells in series with jk bms. The system operates smoothly but not reaching potential displacement hull speed. The maximum motor speed at full throttle is only about 700rpm and the bus current approximately 25A. Are there any controller settings that might increase the rpm or will belt reduction gearing and/or a smaller propeller with less pitch be required. The motor revs freely with the propeller shaft disconnected.

[Bikemad]

Hi Tez andto the forum.

I have very little knowledge of the EZ range of controllers, but I suspect that you may well have something set incorrectly in the controller settings if it's only drawing 25A at 700rpm with full throttle.
According to the User manual, the maximum bus current for the B721000 controller is 500A!

Check the Settings for the controller regarding the Max phase current(A), Max rotor speed(rpm) and Max bus current(A) etc. to see if anything is obviously wrong there.

Whilst belt reduction and/or a smaller propeller with less pitch may well be required to improve the efficiency of the motor, I would still expect the bus current to be a huge amount higher than 25A @ 700rpm if the motor is struggling with incorrect gearing/prop size etc..

Perhaps the motor or controller is simply getting too hot and is automatically reducing the current to prevent overheating, but I don't know for sure if this is the default action with the EZkontrol controllers.
If the current draw from cold is significantly higher, then this could be what's happening.

Hopefully, you will be able to monitor their temperatures using the App to see what is happening.

Do you have liquid cooling installed for both the controller and the motor?

Did the original diesel motor drive through a gear reduction unit? If so, what would the original propshaft rpm have been at maximum boat speed?
According to the Dynomometer figures, the HPM-10kW motor achieves maximum power and maximum efficiency @ just over 3,800 rpm, but I would aim for a gear reduction and/or smaller prop etc. that would allow the motor to run somewhere between 3,000 and 3,500rpm at maximum cruising speed.

Alan
 

[Tez]

Hi Alan,

Thank you for the detailed reply. The motor and controller are both liquid cooled and I am confident that overheating isn't the problem. I don't know what a lot of the controller settings mean but the maximum bus current is 150A and from memory I think the max phase current is set at 500A. The max rotor speed settings between 2000 and 4000 have made no difference.

Do you know if the controller gear settings would make any difference? EZ-Kontrol don't provide any setting information.

There are YouTube videos of similar setups in much larger and heavier yachts. One has actually successfully reverted his original gear reduction setup to direct drive. My diesel had about 2:1 reduction and no tacho but I assume the shaft speed would have been around 1200rpm.

The boat now has good torque at slow speeds up to about 3 knots but struggles to go any faster. It only needs a little more grunt. The mystery to me has been why the bus current stays so low under full throttle. load.

Terry

[Bikemad]

Hi Terry,

I'm not familiar with the EZKontroller settings, so I don't know what gear/speed options are available or how they might affect the low rpm torque/current. It might be worth contacting your supplier direct and explain your low power/rpm problem to them to see if they have a simple solution.

If you don't have a switch to select different gears, try to make sure the default gear is set to the highest available and see if it makes any difference.

Are there any error codes (blinking LED) on the controller? If there are, check out page 9 of the User Manual to determine what's causing the error.

If you have (or are able to borrow for testing) a smaller pitch/diameter prop, it would be very useful to see what difference it makes to the rpm, current draw and the maximum boat speed at full throttle.

Hopefully you will be able to get it much closer to the expected ~5.5-6 knots. (1.34 x the square root of the waterline length of boat in feet.)

Alan