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Author Topic: Run motor from inverter  (Read 2377 times)
Greenbeast
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« on: June 04, 2015, 04:08:55 PM »

Looking to run my hog roast spit motor from one (or both) of my tractor batteries, it should take 0.72kWh to run the unit for the required 8 hours
I obviously want too consider DOD for the battery (bank), but what sort of 'cheap' inverter would do this job well. And what margins do i need to give for inefficiency
We'll have a genny for the event but don't want to have it running all day for a 90W load  Grin


edit: i have access to a discarded APC smartUPS 1000 (or maybe a 1500)
« Last Edit: June 04, 2015, 04:19:21 PM by Greenbeast » Logged
book_woorm
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« Reply #1 on: June 04, 2015, 04:35:44 PM »

If your thinking of using an old UPS you need to carefully check its spec. There tends to be three flavours to their behaviour
a) Keeps running until the battery is absolutely flat (usually very old designs)
b) Turns itself off when the battery gets low
c) Turns itself off when the battery gets low OR after 20min or similar short period.

Failing that look in a Maplins catalogue/online for ideas.
 
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Greenbeast
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« Reply #2 on: June 04, 2015, 04:40:19 PM »

it should not be a 20min variety, in fact i have run it with external batteries for a longer period during a power cut
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guydewdney
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« Reply #3 on: June 04, 2015, 06:30:07 PM »

Old wiper motor instead?
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oliver90owner
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« Reply #4 on: June 04, 2015, 06:36:51 PM »

How big are your tractor batteries? Starting current is all that is going to affect a 200W inverter (and the spit can be manually 'helped' at start up?).  Sounds like a washing machine scavenge pump - they are often about 90W?

Does the tractor need both batteries?  If in parallel, one would sart the tractor while the engine was warm, so you could recharge the first if it gets low?

Remember, mains voltage inverters may not be so very efficient and your motor would not pull such a large current if the load is well balanced.

Honda suitcase genny would do it easily, I would think.  What you need is a tractor driven generator.  I have just the thing - about 4kW, I believe.
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Scruff
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« Reply #5 on: June 04, 2015, 07:44:34 PM »

I'd go for a 12v/24v motor too.

Found this the other day, pretty impressed at the capability of a wiper motor.

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Greenbeast
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« Reply #6 on: June 04, 2015, 08:17:52 PM »

The motor is fitted already and the g/f would have parts off me if i started talking about modifying it
The tractor batteries are about 90Ah

It can start and run with one ad in fact i have three at my disposal, but there will be a genny running as we get into the evening for the band and lighting.
The hog roast will be running from morning however, so wanted to cover the first half or so of the run time at least
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Justme
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« Reply #7 on: June 04, 2015, 08:22:30 PM »

Do you ahve all the bits already?

If not hire someone to hand turn it.

8 hours times min wage aint alot.
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Scruff
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« Reply #8 on: June 04, 2015, 08:37:19 PM »

If it's a brushed motor a mod. square wave will probably do you. Motor starting current can be 10 times the nominal load; personally I'd measure the inrush before I invest in an inverter and then find one that's double rated for instantaneous loads or one with a soft starter but thems rare beasts at that end of the market. If the motor was unloaded or already turning (perhaps manually) on start-up then the inrush would be much less. Most manufacturers rate their cheapo MSW's at >80% efficient at a rated load...again probably best measure it.

Guesstimate: 3 x 90Ah starter batteries = (12v x 90Ah x 3batteries)/2 (50% DOD) = 1.620kWh capacity available

80% capacity for inverter losses = 1.3kWh
Batteries would be about 75% SOC after the 8 hours if they have their plated capacity.

Using starter batteries as traction batteries...your call.

Adding a solar module would offset the loss a lot.
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Greenbeast
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« Reply #9 on: June 04, 2015, 08:45:09 PM »

Justme, I've got the batteries and the hog roaster already.
Tested it for an hour today to find out the power consumption

Thanks for the sums scruff
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biff
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« Reply #10 on: June 04, 2015, 08:55:53 PM »

That is an excellent idea Justme,
                             Get some bloke to look after the Bar, B,Q for a days wage, He can turn the spit and top up the fuel. Get him to wear a fancy dress outfit,,A bear,,Gorrila,  Giant Rabbit or a massive big porker,, Yup, a Big fluffy Porker would be just the job and you could lay on a pile of beer for him as well. And when he is not looking you could stick a sign on his back, "GUESS MY NAME" 1 TO ENTER,,ALL DONATED TO CHARITY"..  Maybe cover his wages and beer, whistlie.
   Still it could all go wrong,, He might get sozzled on the beer, fall on top of the Bar,B,Q and dump the lot on the grass. Then turn insulting, It is the kind of thing that happens all the time.
    Are you sure you want to go ahead with this party.?
  I once went to a Haloween bash, dressed as Gorilla in real good Gorilla suit. I tried it out in the car park as the guests were pulling up, I would step out of the nearby bushs and do my Gorilla walk over to their cars . The women screamed the place down and the men all ran for their lives. I got first prize. One gal even told me that she had dumped her boyfriend over me. I thought I was getting lucky but then she said that the boyfriend must be an awful coward to run away from a lunatic like me. Burst my bubble that did. I told her that her screams were the loudest that night.
  Ahhh to be young and silly signofcross
                                     Biff
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An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
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