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

J. Forster jfor at quik.com
Sat Jun 25 19:55:48 UTC 2011


Certainly, the inverters can run that low, but if so they sing a lot.

Best,

-John

=================

> John,
>
> 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.
>
> Best,
>
> Will
>
> *********** REPLY SEPARATOR  ***********
>
> 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.
>>
>>-John
>>
>>===================
>>
>>> 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
>>>>voltage.
>>>>
>>>>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
>>>>fails.
>>>>
>>>>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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>
>
>
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