Author Topic: 240 volt from a 120 volt Generator  (Read 6099 times)

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kittysmitty

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240 volt from a 120 volt Generator
« on: October 19, 2014, 11:50:12 AM »
I think I'm going to make the switch from a 12 volt system to a 24 volt system. I have sitting in my garage this battery charger.
http://www.quickusastore.com/sbc-high-power-battery-chargers.html
The charger is 240 volt, and the back up generators I have at the camp are 120 volt. Going back 40 years, I remember learning about transformers, and step up and step down. Can I use a 1:2 transformer and take 120 and turn it into 240 to work with the charger? The charger draws 11.9 amps max, so I would need at least 23.8 amps at 120 volts plus losses. If possible what type of transformer, and what size generator. I do have a 5000 watt 240 generator, but that's my house backup and I would prefer not to haul it to the camp. Thanks

gww

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Re: 240 volt from a 120 volt Generator
« Reply #1 on: October 19, 2014, 03:45:42 PM »
Outback sells a transformer but it is probly $400 bucks.
Gww

joestue

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Re: 240 volt from a 120 volt Generator
« Reply #2 on: October 19, 2014, 06:26:14 PM »
you can also connect a 1:1 isolation transformer as a 1:2 step up autotransformer, and it will effectively double its "rating"

so a 1KW isolation transformer will be good for 2kw input and a 1900 watt output is probably realistic.

lol, if you can get it started and synchronized, you could use your 5kw generator as a 2:1 step up.. but you'll probably have to machine a shaft and bearing to support the generator...
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phil b

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Re: 240 volt from a 120 volt Generator
« Reply #3 on: October 20, 2014, 12:45:34 AM »
Northern Arizona Solar and Wind has a 1:1 Outback transformer for $377.
http://www.solar-electric.com/catalogsearch/result/?q=transformer&cat=0
IIRC, Midnite Solar has one also.http://www.midnitesolar.com/
Phil

joestue

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Re: 240 volt from a 120 volt Generator
« Reply #4 on: October 20, 2014, 02:18:56 AM »
http://www.ebay.com/itm/1KVA-1000VA-120V-240V-Isolation-Toroidal-Power-Transformer-p-n-AN-104115-/251683184599
http://www.antekinc.com/an-104115-1000va-115v-transformer/

the spec sheet claims to be 37 watts full load loss.. looks like it might actually be 1 volt per amp lost, or about double that 37 watts figure.. (maybe half of that is inductance?)
as a voltage doubling auto transformer that's 2 kw power flowing through the system. -- you can probably get 3kw through it with some forced air cooling.
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kittysmitty

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Re: 240 volt from a 120 volt Generator
« Reply #5 on: October 20, 2014, 05:29:41 AM »
Thanks for the replies. For the cost of a transformer, I think I'll take the generator from home, for the once or twice a year it will be required. It's a weekend cabin that I visit once a month so the solar is doing a fine job. Only during hunting season that the solar is sometimes lacking. In addition my 120 volt, 1500 watt camp backup generator would not have the output.

ChrisOlson

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Re: 240 volt from a 120 volt Generator
« Reply #6 on: October 20, 2014, 02:51:27 PM »
Thanks for the replies. For the cost of a transformer, I think I'll take the generator from home, for the once or twice a year it will be required. It's a weekend cabin that I visit once a month so the solar is doing a fine job. Only during hunting season that the solar is sometimes lacking. In addition my 120 volt, 1500 watt camp backup generator would not have the output.

We have an Outback PSX-240 autotransformer that I used to use for hooking a 120V single-phase generator to our 120/240 split-phase XW inverter.  But those autotransformers are very expensive.

The other problem with a small generator is magnetizing the core on a big transformer.  The Outback PSX-240 weighs 50-60 lbs and it has a pretty hefty core.  Our neighbor, who is also off-grid and has a XW Power System, bought a PSX-240 and a Honda EU2000 generator, with the idea of using like we did with a 120V genset feeding the 240V inverter.  The EU2000 would fault when he connected the transformer because its inverter saw a dead short with the inrush current to magnetize the core.  I put my Fluke on it on capture and the core on that transformer has an inrush current of almost 100A.  We tried a long cord on it, and several other things short of making a soft-start for it.  In the end he had go buy a different generator, since a conventional will automatically "soft-start" the transformer, where the inverter gen wouldn't.

Mary B

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Re: 240 volt from a 120 volt Generator
« Reply #7 on: October 20, 2014, 07:06:04 PM »
I have a source for soft starts if interested. up to 30 amps if memory is right... could replace relays with larger too http://harbachelectronics.com/shop/misc/ss-100-240-universal-soft-start-module-copy/  20 amp complete version http://www.ameritron.com/Product.php?productid=ICP-240

ChrisOlson

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Re: 240 volt from a 120 volt Generator
« Reply #8 on: October 20, 2014, 07:32:02 PM »
I was going to build a soft-start for our neighbor using some resistive heating elements in series with the transformer primary, and that could be switched out and bypassed once the transformer came online.  But he said forget it - he just bought a different generator that could handle it.

Frank S

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Re: 240 volt from a 120 volt Generator
« Reply #9 on: October 20, 2014, 11:41:38 PM »
How about a transformer from a metal halide lamp fixture
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southpaw

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Re: 240 volt from a 120 volt Generator
« Reply #10 on: October 23, 2014, 11:00:57 AM »
Looking at the specs online many of the SBC chargers will operate at voltages down to 87v AC. perhaps you don't need to do anything but change the plug on the cord.

XeonPony

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Re: 240 volt from a 120 volt Generator
« Reply #11 on: October 30, 2014, 12:54:46 PM »
How about a transformer from a metal halide lamp fixture

Workes great for building a high voltage transmission system by taping into the start circuite, but do not see how'd they be of any use for dropping the voltage?
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