[time-nuts] No more 60Hz, How do I discipline 120VAC 60Hz from a UPS

J. Forster jfor at quik.com
Sat Jun 25 19:37:05 UTC 2011

> Chris,

No I didn't say the output was 1000 Hz. No way.

What I said (a bit amplified) was that the cheapie inverters use a high
frequency, think 50 KHzish, DC-DC converter to make about 170 VDC, then
use that to feed an "H" bridge, driven with either a square wave or a
modified square wave, to make the output. You snmply need to vary that
drive frequency to get 50, or 60, or any frequency you want.

There is no output transformer. In fact, that is the cleverness of the
design...  no big, heavy, expensive magnetics.



> As John mentioned earlier, the el-cheapo inverters are pretty much
> junk, and run as high as 1 kHz, if I recall. They were made to run small
> TV's, etc, that don't require a fixed line frequency, since they all have
> hot chassis now that don't use isolation transformers.
> Best,
> Will
> *********** REPLY SEPARATOR  ***********
> On 6/25/2011 at 11:55 AM Chris Albertson wrote:
>>> The reason for using 12 Vdc, is that you can pick them up, and 24 Vac
>>> CT
>>> transformer, on the cheap
>>That's a good point.    So use two of them.  One to power a high
>>current amp that produces a 12V AC signal from a high precision 60Hz
>>input.  Then the other to convert the 12V to 120V.  This avoids the
>>need for a high voltage DC power supply.  Likely cuts the total cost
>>in half at least.     So just use use 12V supply to the amp and then a
>>cheap 12V transformer connected "backwards" to step up to the desired
>>The second advantage of this design is that you can connect a lead
>>acid gell cell battery in parallel to the 12V DC supply and if the AC
>>fails the battery will power the amp for a while.   This way there is
>>no switching so the 60Hz wave remains continuously even if AC mains
>>This is something most UPS don't do but for this application you don't
>>want the  60Hz sine wave to be broken.
>>As long as the load is only a few milliamps of AC this should not be
>>hard to do.
>>Chris Albertson
>>Redondo Beach, California

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