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

[Will Matney]

I took a look around at a few semiconductor manufacturers, and found an app
note from Freescale (Motorola), on their MC3PHAC AC motor drive chip. It
does use an external timebase of 4 MHz, but they only used a resonator, and
this could be made way more precise. Though this is a 3 phase controller
IC, they do make drives for smaller single phase motors, but I'm not sure
who makes the controller IC's, nor do I know about any external time bases
for them.

It could be as simple as buying a surplus, single phase, AC motor drive,
and setting it up for the correct speed, and adding a good timebase in
place of a resonator. I have seen these types of drives sell for pennies on
the dollar on ebay. It might be worth taking a look at.

Best,

Will

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

On 6/25/2011 at 1:38 PM J. Forster 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.
>
>Yes, of course.
>
>> 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?
>
>The static inverters should not have issues with an induction motor.
>
>> Set it at 60 Hz, and be done with it?
>
>Yes, but you have to get to the H bridge timing logic to do that. That's
>why you need the prints.
>
>-John
>
>===================
>>
>> 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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>>>
>>>
>>>
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>
>
>
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signature database 5851 (20110206) __________
>
>The message was checked by ESET Smart Security.
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