I'm no expert but seems to me too much torque from the prop running this motor direct with no gear reduction. 80 degree Celsius is 176 degrees Fahrenheit. You could cook dinner off the motor, probably boil water when it hits 120 degrees Celsius. You may have to use a gear reduction. Just?a thought.

On Wed, Jan 29, 2020, 5:13 PM Mich Pop <michpop@...> wrote:

Hi
I've recently finished my conversion of a 29 Roberts 4.5 ton yacht.
1200 watt panels
270 Ah batteries at 48 volt 15s3p
Batrium BMS

My usage stats are

Rpm.? ? Amp.? Knots

530.? ? ?57

500.? ? ?44.? ? ? ?3.5

475.? ? ? 38.? ? ? 3.2

450.? ? ? 31.? ? ? 3.2

400.? ? ? 25

420.? ? ? 30

410.? ? ?28.? ? 2.4

?

?

250 rpm 6 amp

400 rpm 24 amp

450 rpm 35 amp

580 rpm 63 amp

680 rpm 95 amp

We replaced a 20hp bukh diesel and left the prop and shaft as is.
Max rpm of the diesel was 2500 with a 2.5:1 reduction ratio, so max1000 rpm on the 2 bladed 400mm diameter prop. Direct drive, no gear reduction.
Good shaft alignment can be easily rotated by hand. Easy to get cavitation if you rev up too fast.

After 20 min at 500 rpm the 120 frame AC motor reaches 80 degrees Celsius and after 40 min 120 degrees Celsius. There is sufficient ventilation.

The KAC 600 amp max 72 volt Kelly controller 8080I reaches 92 degrees after 30min and reduces high rpm to around 500 rpm and keeps them there remaining at 92 degrees Celsius.

Has anybody had a similar problem and found a good solution?
I'm not interested in cooling. I want to understand why the motor overheats at 2.5kW when it is designed to run at 4kW all day.




Thank you all for your awesome inspiration over the years. Your posts have been really helpful.

Cheers Mich