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

[Will Matney]

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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signature database 5851 (20110206) __________
>
>The message was checked by ESET Smart Security.
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