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MrBrain
Member Since: 12 Mar 2014
Location: bucks
Posts: 471
  
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Hi guys,
I am seeking help on selecting an invertor.
I want to run a set of small tyre warmers for a mini motorbike. total only 200 watts. the snag is I want to run these for maybe 5/6 hours.
Has anybody calculated the (in)efficiency of invertors and has any recommendations?
If I cant make it work, then I will have to buy a genny.
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 13th Nov 2018 10:06 pm |
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zig
Member Since: 09 Sep 2005
Location: Scotland
Posts: 619
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I assume that with a 200 watt load you will be using an inverter with a 250 or 300 watt rated output.
I would assume a 90% efficiency for the inverter (check inverter specifications to see what they state).
Thus if the load on the inverter is 200 watts then the battery would see a load of 200/0.9 = 222 watts.
For a 12V battery this would mean that the current drawn would be 18.5A (assuming that the voltage drop in the cable between the battery and the inverter is negligible).
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| 13th Nov 2018 11:38 pm |
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Bodsy
Site Sponsor
Member Since: 06 Nov 2006
Location: In the Clubhouse
Posts: 21361
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So using a 300w inverter (although as you’re planning to run it for some time, I would go 500w to keep it cooler)
So assuming 100% efficiency (unlikely) 200w/12v = 16.67 amps
Your cranking battery is 100ah and you can’t really use more than 50% so 50ah/ 16.67 = 3hours MAXIMUM
Ok if you’re running the engine, but if not, then forget it and use a silent generator instead. Bodsys Brake Bible
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Transmission Flush
Software updates/enabling
Clock/ SNOTM /3Flash / 4x4Info /BT Update /Service Reset/Error Codes / Gearbox Reset
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| 13th Nov 2018 11:39 pm |
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MrBrain
Member Since: 12 Mar 2014
Location: bucks
Posts: 471
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I guess one of the questions is "is a bigger invertor running at a smaller load more or less efficient than a smaller invertor at the same load".
Also, I realise they are specified at 90% efficiency, but I wondered if anybody had done real tests?
I wouldn't be using my starter battery. I have a couple of spare 110ah leisure batteries that I can use, or may run it off the caravan twin battery setup.
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| 13th Nov 2018 11:55 pm |
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Hardware
Member Since: 28 Jun 2016
Location: Hiding under the M60
Posts: 12709
 
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wouldn't DC tyre warmer(s) make more sense ? no invertor losses involved then !
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| 14th Nov 2018 12:07 am |
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zig
Member Since: 09 Sep 2005
Location: Scotland
Posts: 619
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Inverter efficiencies are normally specified at rated (maximum) output and will be less efficient if used at at for a lower output.
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| 14th Nov 2018 12:13 am |
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MrBrain
Member Since: 12 Mar 2014
Location: bucks
Posts: 471
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Hardware17 wrote:wouldn't DC tyre warmer(s) make more sense ? no invertor losses involved then !
I don't think I have ever seen them for sale. Plus on a race weekend we have to use a genny, as its all day for three days. This solution is for practice days when we just nip down to a track for a practise.
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| 14th Nov 2018 12:22 am |
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Navigator
Member Since: 17 Mar 2010
Location: Stay at Home. One of the lives you save could be your own.
Posts: 5103
 
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Daylight? Solar panel array to keep battery topped up. Could be permanent on caravan and swapped over to tyre warmer battery as needed.
Gas oven? A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
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| 14th Nov 2018 12:47 am |
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