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#63424 - 03/14/06 06:20 PM Buck and boost transformer
ShockMe77 Offline

Registered: 06/11/05
Posts: 823
Loc: Rahway, New Jersey
When setting up a buck and boost transformer, should the voltage setting be lower, or higher than the desired amount? I have to make sure a pump has exactly 220vac supplied to it and last time I checked the service at this place the voltage 120/240 (but the actual voltage hot-to-hot was 249vac. Should I go with a 10% setting or 15% setting on the buck and boost? And which one's work the best?

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#63425 - 03/14/06 07:50 PM Re: Buck and boost transformer
frenchelectrican Offline


Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
to slect the buck and boost transformer it get little tricky here.

you have to know the amp or hp of the load it willbe running and you can buck it down a bit but here is the catch the buck it will have a 16 or 24 or 32 volts drop [ some have more slection ]

for 240 volt appaction genrally only need one B/B transformer will be needed but one quick head up double check with the NEC code related with B/B set up

this is from Sqd website related with the BB set up caluation to get the correct size

Merci, Marc
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

#63426 - 03/14/06 08:14 PM Re: Buck and boost transformer
Dave T Offline

Registered: 01/22/05
Posts: 157
Loc: Waukesha, WI, USA
With B-B transformers you're never going to be right on the voltage. Personally I would opt for the closest higher voltage that you can zero in on. A NEMA rated motor should operate satisfactory at +-10% of its NP voltage. The motor should run a bit cooler at the higher voltage anyway.
The only uncertainty is how stable the supply voltage is which you probably don't have any control over. If it goes higher than you anticipated when selecting the B-B Xfmr naturally the output will be higher than you anticipated.
So you have to give it your best calculated shot.

#63427 - 03/14/06 08:31 PM Re: Buck and boost transformer
LK Offline

Registered: 01/21/03
Posts: 1721
Loc: New Jersey
"With B-B transformers you're never going to be right on the voltage."
We get calls from office supply companies, all the time, they shop around calling every contractor in the book, looking for 208V for copy machines, what usually happens is the BB set up is uaually cheaper, and they always catch an EC that bids low, thinking he can use BB for this application, problem is, when they call, and say their $12,000 copy machine burned-up, they come to you, might be best to use a better transformer set-up and be sure.

#63428 - 03/14/06 09:52 PM Re: Buck and boost transformer
SolarPowered Offline

Registered: 07/05/04
Posts: 615
Loc: Palo Alto, CA, USA
Does it really need 220? It seems that a lot of motors are rated at 220, but are actually intended to run off of 240.

There's a lot of discussion of that in this thread:

[This message has been edited by SolarPowered (edited 03-15-2006).]

#63429 - 03/15/06 05:37 PM Re: Buck and boost transformer
ShockMe77 Offline

Registered: 06/11/05
Posts: 823
Loc: Rahway, New Jersey
Thank you all very much for the feedback. I'm always appreciative of it so thanks. I'm just like the next guy, who doesn't know everything, but at least I know more than him after my time spent at ECN.

My next question.

One of the legs on the 220volt receptacle that's there now originates on the red leg (245vac to ground, 245vac phase to phase). Will this matter after the installation of the B-B xfmr?


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