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[aprssig] Shack backup power

Bob Bruninga bruninga at usna.edu
Mon Sep 12 00:46:13 UTC 2011


All I know is that my 1200W quasi sine inverter in my car trunk that I got from PEP boys for $120 easily starts my refrigerator.  It also starts 5000 BTU ACU units to my unbelievable surprise.

I think it is because these modern modified sine wave inverters have quite a 180 VDC storage capacitor prior to the 60 HZ switchers that can provide the several millisecond starting current?

Oh, you are right.  I said generator... and yes, I have had problems starting  a refrigerator from a generator... but have been amazed at the inverter performance.

---- Original message ----
>From: Steve Noskowicz <noskosteve at yahoo.com>)
>
> While waiting for the OT police to
> show up, Steve, K9DCI comments first:
> RE: Bob's two comments:
>
>> ...to keep the refrigerators ... going ... A 1kw 
>> generator and a can of gas is hard to beat for economy.
>> A typical refrigerator is rated at 400 to 900 watts
>> (when running (and defrosting...
>
>
> I say OOPS!
> What about start-up (locked-rotor).  Having had experience designing (350 W DC Brushless and higher variable speed A/C motor drives) I'm very aware of locked rotor.  I have been using 5-8 times run current to get an idea of locked rotor.  I recently learned that there is a letter on motors with the locked rotor current factor, but don't have a conversion chart.
>
>What are typical fridge locked rotor values/fctors?
>
>I've only got 1 fridg...
>Wagging 800 watt, 6.7A run (no defrost and I'm too lazy to push it out) and 5-8x start, this amounts to 4000 - 6400 surge.  Not a triffle.  I'm pretty sure typical 1kW gensets won't hack this.
>
>For a completely irrelevant example...One of my 400W 800W/surge Coleman inverters has to be switched on before my boat-anchor HP (141T type) spec analyzer that draws (I just measured it - Current clamp) 1.13A or it faults out.
>
>Steve, K9DCI
>
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