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

Will Matney xformer at citynet.net
Sat Jun 25 20:23:54 UTC 2011


Sorry, that should have said DC drive, as I was writing while brain
storming. However, a variable AC drive, which does control the frequency,
may be able to be used. I would have to look at this more, but it might be
possible, and these can be bought on the cheap at surplus sellers.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 6/25/2011 at 4:12 PM Will Matney wrote:

>John,
>
>I forgot to add, that an H bridge could work for a clock motor, since
those
>are used to drive ac motors in industry every day. You would have a
sqauare
>wave though, unless it was modified. If I recall, that's the way a lot of
>the AC drives work today, using four sets of switching semiconductors,
>unless the motor is small enough to be ran off a power chip. In this case,
>I wonder how an AC drive would act if it ran a clock motor? Set it at 60
>Hz, and be done with it?
>
>Best,
>
>Will
>
>*********** REPLY SEPARATOR  ***********
>
>On 6/25/2011 at 12:55 PM J. Forster wrote:
>
>>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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>>
>>
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