question

nagwood avatar image
nagwood asked

Offgrid power assist for a 3 phase generator

Hi there

I'm planning on running my woodworking shop off grid. My biggest 3 phase load is 6HP. I could run this with an 18kva generator to cope with the startup current but I'm then only running the generator at part load which, I gather, isn't necessary a good idea for generator longevity.

My thoughts were to use a smaller generator (say 6kva) for motor running and use 3x multiplus as a power assist for starting.

Am I right in thinking I need 12kva power assist? As the multiplus can withstand short term overloads, does this equate to 3x 6kva (or nearest higher equivalent) or is it 3x 2kva (to give 6kva total)?

The rest of the shop will run off solar/wind.

Many thanks, Nick.

Generatoroffgrid3 phasepowerassist
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
snoobler avatar image
snoobler answered ·

Have you actually measured the inrush of the 6hp load? Surges can easily be 5X or more than the run current.

Does the motor associated with the load have an LRA rating?

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

nagwood avatar image nagwood commented ·
A good question, and no I haven't. My largest single motor is 4HP on a Spindle Moulder from the late 1940's. Definitely no LRA rating! I run 2x 3HP motors together on a tenoner, which is my biggest single load. I realise I can start these separately, but I've used 6HP to give me a little scope for the future.
0 Likes 0 ·
snoobler avatar image
snoobler answered ·

Get a cheap AC clamp ammeter with the INRUSH function so you can measure the actual peak current. That's what you need to plan for.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

nagwood avatar image nagwood commented ·
Many thanks, I shall certainly do that when I start thinking about the real numbers. I guess my questions were "I am thinking correctly if I plan on this extra starting current (as my power assist) coming from the 3x multiplus units? " and "can I consider the size of the multiplus units to be half of the amount required (given the overload built into them), and is this supplied by each multiplus or the sum of all 3? I hope that makes sense. In addition, I do know a 15kva generator will happily start my old 4HP motor.
0 Likes 0 ·