Thread: Genset load balancing - help!!

Hi Phil

I have a ~4kW 3 phase gen, and I regularly use just one outlet. Each outlet has a limit of ~1.25kW. My understanding is that balance is not very important as long as no single outlet goes over this limit. I have not noticed any additional vibration etc. when running just one outlet.

Cheers
Si

The only thing I can think of, is to make a powerboard with three single phase outlets, connected to a 3-phase plug. Then get a couple of 2400W tangy heaters and plug them into unused sockets. The cheap ones with just two or three heat settings and no thermostat would give you two or three 'load dumps' to match the tool you are using. Anything under 1200W I would not bother with, since the alternator is not even slightly stressed.
Incidentally I nearly made the same 'mistake'. When I realised, I bought a 6.5kVA single phase genny.

LoL, my brother in law is an electrician and made a similar suggestion using heat lamps. Not a bad idea in winter but not so appealing during summer - he suggested that I set up a pool in the shed so I could cool off An interesting comment Si, a 'reputable' dealer suggested that any 10kva+ 3 phase genset costing less than $15,000 would be better used as a "boat anchor" - he has been involved in many court cases over the dodgy electronics. He said he had seen them burn out after as little as 1000hrs using them as you have suggested whilst a decent unit (above $15,000) would last up to 18,000 hrs. Doing the maths though, since my unit cost $910 if it only did 1,000hrs I could still buy 17 of them and end up with pretty well the same hours per dollar as a $15,000+ unit plus have 17 diesel engines left over. OK, not very environmental or practical but there again, 1000 hours for me is a fair bit of shed time !!!

Seems like there is an opportunity for an aspiring electrical engineer - with thousands of these gensets being sold around the world, there has to be a demand for a load balancing powerboard - I'll buy one !!

Philp
I bought an supposed 11kva Gennie with 3 and single phase to run compressor and power tools on site. Didn't find out till it arrived that each phase was only good for 2000 watt and had a crappy 6 amp breaker. Unusable.
Swaped breakers to 10 amp and now runs compressor and saws no problem.
I try to run tools on different phase but it's regularly just the compressor running alone. It's probably done 500 hours now and seems to be working fine but when it s itself I will replace it with a brand name unit.

Originally Posted by Phily

LoL, my brother in law is an electrician and made a similar suggestion using heat lamps. Not a bad idea in winter but not so appealing during summer

Put them out side on top of your shed and use a fan to blow air up past them - that will make them last much longer. The hot air will rise and draw cooler air toward the shed cooling your shed.
It will be energy wasteful with 2/3rds of your diesel going up into the air as hot air.
Just think of it as Diesel costing 3 times what you are paying for it.

Or maybe plug two leads into a solar investor, feed back into the grid and get a refund cheque from the electricity company? Could work but I think a check of the breaker - potential upgrade might be easier. Thanks for the suggestions

Originally Posted by Phily

I got a bit too enthusiastic setting up my shed on a newly purchased property. As yet no power and as I have some large (single phase) equipment I figured that I'd get a decent genset. Bought a 3phase/single phase diesel genset so I could run my existing single phase gear and have the option to get some 3 phase gear in the future. All good till I came to use it!

Apparently it is pretty common on all sub $10,000 3phase gensets that you have to balance the load across all of the single phase outlets. i.e. if you just use one of the outlets to power your circular saw, you'll stuff up the internals, blow the circuits and void your warranty. Kind of makes it useless unless there are three folk all ready at the same time to turn on three identical machines.

Is anyone aware of a practical way of balancing the loads e.g. an adaptor that can plug in to the 3 single phase outlets to share the power demand evenly across each?

Alternatively, if anyone needs a dedicated 3 phase 11kva generator going cheap let me know!!

Cheers
Phil

know about this one

To my knowledge this problem with 3 phase gen sets has been around for over 30 years.

$15,000 essentially buys the internal electronics so you can use a single phase without blowing the unit.

simplest solution is to have a load on each phase
put your dust collector on one phase.
jointer, thicknesser, saw, etc on another -- on the basis that the DC always runs when the large stationary tools are running
and use a heater or air conditioner on the 3rd phase

with auto switching to turn the heater on when the other tools start up

If your three phase outlet is a five wire system then you could hook up a five wire three phase transformer going to three single phases. The genny would then be protected because the imbalanced loads would go back to the star point through the return line. I used to have a massive 450v three phase star to 450v three phase delta transformer for that exact purpose, 99% of its load was single phase.

Actually getting such a thing may be wishful thinking though, sorry.

Thanks Ian, I wonder however if having the combined draw of an aircon, dust extractor and bench saw all turning on and off at the same time will create other problems for the internal electrics - I suspect that they will be over loaded and blow up anyway.

I was hoping that there was a commercially available unit per Tiff's idea, but it doesn't sound like it. Fortunately the genset didn't cost a great deal - I'd have been seriously upset if I'd forked out $6k to $7k only to find that I had exactly the same issue.

I've been considering upgrading to a 3 phase dust extractor (hence the 3 phase genset idea) so maybe I'll just dedicate it to the extractor and buy a smaller single phase genset for the other equipment. Or just see what happens and if it blows up after 1000hrs use it as an anchor ...... but then I'd have to buy a boat

my main experience is with slightly bigger units than yours trying to power a work camp.

what is possibly a bigger issue for you is how the electronics inside your tools respond to the genie reving up to meet the load as you turn them on and start cutting.
If your DC is on one phase and your table saw on another, at least two of the phases will be approximately balanced.
You then just need a phantom load on the 3rd phase.

if you have a 3-phase DC, then you will have a balanced load straight off
add a 3-phase TS or Band saw or thicknesser / jointer and your problems are almost over

Well it seems the god's of good fortune are on my side. I've just engaged a builder to do some renovations on an old cottage and guess what - he's in the market for a 3 phase generator and has agreed to buy this one off me for the price I paid. Now That is the balanced outcome that I needed!

Next purchase is a single phase generator

Thanks for all the advice and suggestions and for anyone who reads this thread later on, a piece of advice:

DO NOT BUY A CHEAP 3 PHASE GENSET UNLESS YOU ABSOLUTELY NEED THE 3 PHASE AND DO NOT NEED SINGLE PHASE OUTLETS.

Cheers
Phil