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

Will Matney xformer at citynet.net
Sat Jun 25 19:53:22 UTC 2011


I didn't mean to say you said all that, just that the new inverters are
cheap. I wrote that I thought some ran at around 1 kHZ, as I had an old one
that did, and used a toroidal transformer in it. The new ones, as far as I
am aware, are similar to the new-style switching power supplies, like the
ones Maxim and a few others show in their app notes.



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On 6/25/2011 at 12:37 PM J. Forster wrote:

>> 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
>> hot chassis now that don't use isolation transformers.
>> Best,
>> Will
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>> 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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