Help w/selecting Buck & Boost Transformer (208VAC-230VAC)?

I wish to purchase the transformer to run a 230VAC single phase compressor motor on 208VAC service.
During the course of a previous thread it was determined that my electrical
service consists of 2 phases of a 3-phase 240V feed. Hot-to-hot voltage I am getting at my breaker panel is 208VAC. This is all USA 60hz. I'm not familiar with specifications for transformers, so I would appreciate some assistance in determining the specs for the purchase of a Buck-Boost transformer, so I can run the compressor without burning up the motor.
I've found a surplus Buck-Boost transformer with these specs: ACME brand,Catalog #: T-1-81047, Style: ER, Primary Volts: 120 x 240, Secondary Volts: 12 x 24, Single Phase, .050 KVA, 50/60 Hz, Winding Rise 80, Degree C. Enclosure type: 3R Outdoor, Insulation System: B-3223-M Class 130
Would that suit my application? If not, what specs do I need to correctly and safely boost my service to 230VAC? Once again, many thaks for the assistance! Neal
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Need to know what your amp load is a 230V in order to size the BB properly.
RT
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On Mon, 29 Dec 2003 18:28:57 -0400, RTH wrote

The motor is rated at 22FLA. Is this the figure that's needed? I do not know starting amperage if the motor, though if needed I could get that info. This motor will be the only load on this circuit.
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Don't think .050 kva is going to be big enough. Acme does not list selection tables on it's website. I checked another manf. Hevi-Duty Elec and there bb tables indicate that you need a .750 kva to boost 208 to 229 and will handle 31.8 amps. A .500 va will handle about 20 amps.
Suggest you try contacting a local Electrical Dist like Graybar Elec Supply or may WW Grangier for more info. They probably have what you need in stock.
RT
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On Mon, 29 Dec 2003 22:20:42 -0400, RTH wrote

I called SQUARE-D and was told .75 KVA was correct for my application.
Another question is whether to use a 12/24 volts secondary or 16/32 volts secondary. The gent at Square D claims that the 12/24 will give 230VAC output; the 16/32 will yield 236VAC output....these figures assuming consistant 208VAC input voltgae. He also said that although the motor is listed at 230VAC, the specs for motors have a wider voltage tolerance (I think he said it was 15% above & 10% below the listed voltatge). He felt that either Booster would work (the 16/32 however would then be rated at .50KVA for my application instead of the .75KVA rating of the 12/24). Anybody see any great advantage of the one over the other (I may possibly be able to get a 16/32 cheaper)?
On installation: does the Booster get installed downstream of the disconnect box (service panel-booster-disconnect box-motor)? Any other hardware needed to complete a booster circuit or is it pretty much just the Booster transformer wired into the circuit? Thanks again. Neal
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McMaster Carr has an excellent section on buck boost transformers, with a selection guide. I chose mine (to run a 240 volt vacuum pump off of 208) and it worked out fine. Because the transformers only have to handle a very small amount of power, they are pretty small and inexpensive.
Before you look at the catalog, have the full load amps number for your compressor at hand.
Jim
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I have one that they were throwing away at work. It is still on my bench I will look and see what the rating is when I go back in Monday.
Dennis

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RE: Subject
Go to any decent industrial electrical distributor.
Selecting a B/B x'fmr is a very straight forward thing.
All the x'fmr manufacturers publish selection tables.
All you need is input voltage, output voltage, and motor HP.
HTH
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Lew

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On Tue, 30 Dec 2003 1:26:55 -0400, Dennis J Brown wrote

Thanks Dennis. -----
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Why use a boost? You are allowed 10% over and undervoltage to be in spec. 230
V x 0.10 = 23 V 230 - 23 = 207 V should be no problem unless you are operating at the upper limits of motor capacity or just want to play.
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On Wed, 31 Dec 2003 1:13:18 -0400, BCEONL wrote

Well....in a previous thread, all who replied informed me that I would burn out the motor in no time if I ran it on the 208VAC. Disregarding that info in the name of expediancy (and utilizing the resources availible) I ran the compressor motor anyway on the 208. I didn't run it long, just 3-4 times over a couple days to fill up the tank (80 gallon). Seems to run fine. The compressor is an IR and rated for continuous duty. However, I was only running it enough to do a air tank-top off cycle ... from when the pressure switch kicked it on (at about 120 PSI) until it kicked off (at 170PSI)...running just a handful of minutes, at most, per cycle. Since the large pulley has fins to direct cooling air over pump and motor, the motor never even got warm to touch. Again, everyone was saying I'd burn the motor out in short order. I had called Ingersoll Rand yesterday and they said the same thing....that's why I'm looking into the Booster. I have no way if the advise is ultr-conservative, if it's overkill, or if it is incorrect and a booster superfluous. I think one arguement was that input line voltage can ALSO fluctuate (maybe as much as 5% ??)....so given worst case scenarios....lowest line voltage 197VAC, lowest functional motor voltage @ 207VAC....and things look less bright without a booster. However, I haven't measured lower than 207VAC at my breaker box in the handful of times I've taken readings. Would you like to add to the arguement based on practical real-world motor application? Please do as I'm going on the opinions of others. Thanks Cheers, Neal
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You've got the right idea, Neal. One thing, though, measure the voltage *at the motor* while the motor is starting, and also just before the motor shuts off. The reason to measure at these two times is that they're the times of maximum current draw by the motor. Measuring at the motor shows you the voltage after the voltage drop of the wiring. This will always be lower than the voltage you measure at the breaker box due to the IR drop of the wiring and the contact resistance of any switches. This can result in several percent more voltage drop.
Gary
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I see that the compressor cut-off is 170 in your latest post. That's a nice air supply if you have a demand for that much air.
I think the current drawn by the motor will be it's highest at 170. Instead of getting a transformer, I'd just reset the pressure switch cut-off for to about 140, and lower the cut-in a little.Another approach would be to reduce the size of the motor pulley, but resetting the pressures would be easier.
If you had high air demands, this wouldn't be a practical approach, but in a home shop, it shouldn't matter much. If you're using a lot of air on a daily basis, it will be more costly to operate the unit this way, with an increase in the amount of times the motor cycles on.
I don't know if the starter has a motor current protection trip in it, but you might want to check for that. If the unit has motor thermal protection plus current protection (that are operating properly), it's unlikely that you'll burn out the motor.
WB ..............

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You might look into the availability of a 208V motor, especially if you find a surpus unit it might be the better solution.
Rob
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