Buck Boost for appliances?

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sd4524

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I am working in a condo unit that has a 120/208 service. Both the cooktop and oven are dual rated for 208 and 240. What benefit if any will the customer receive by using a buck boost transformer and 240 vs having 208. The cost is not an issue to me or the customer, they just want what is best. Will the oven take slightly longer to heat up at 208?? Can it have much of an effect on efficiency? The wire is already pulled from panel
Any help is appreciated
 
I don't know how much longer it would take to preheat an oven a 208 over 240, but once someone gets used to a certain time, a couple fewer minutes isn't going to make much difference. Seems to me you're 'spending a dollar to save a dime'.

I wouldn't worry about it too much.
 
sd4524 said:
I am working in a condo unit that has a 120/208 service. Both the cooktop and oven are dual rated for 208 and 240. What benefit if any will the customer receive by using a buck boost transformer and 240 vs having 208. The cost is not an issue to me or the customer, they just want what is best. Will the oven take slightly longer to heat up at 208?? Can it have much of an effect on efficiency? The wire is already pulled from panel
Any help is appreciated
Click to expand...

208 is 86% of 240.
Just like any resistive load; the elements will stay on longer to achieve a given heat load. Pre heating that oven to 350F will take 30 minutes instead of 25 and while the cake bakes and the stat calls for heat the circuit will stay closed longer. On the stove top is where they'll notice it more.
 
Don't forget, since 208v is usually two phases from a 3 phase utility transformer the cooktop will not get perfectly opposite phase angles, less power per VA, and neutral feeders may not balance evenly on these loads.

If using a boost xfmr from an outdoor sub panel, then any overload / explosion resulting from similar misinformed design or installation may give owners a bit more time to exit the premises before said property burns down.
 
When I lived in an apartment served with 208 I really considered putting a boost on my range.

For the oven I don't think it is going to make much difference but the stove top would greatly benefit from it when you want to do things like stir fry or just to bring things to a boil quickly. I never ended up doing it though.
 
sd4524 said:
The cost is not an issue to me or the customer, they just want what is best.
Click to expand...
If cost is not an issue, the people are getting a buck-boost. Easy decision. Nothing will be more energy efficient, however. It will even be worse, but not noticable on the bill, since there are losses in the transformer. The range will heat more quickly, however.

In my mind, any benefit from a buck-boost for a range would be offset by the cost of the transformer. If the cost isn't a concern, by all means, install one.
 
Rich Elec. said:
This subject got me thinking about the other appliances in the condo.
Are there clothes dryers that are rated dual voltage?
Click to expand...

Most all electric ranges and dryers are dual rated and different KW ratings provide for 208 and 240. I also believe that is why dryers use 120 volt motors. A 240 volt motor would not run well on 208.

Same with electric heat units, baseboard fan forced etc.
 
Thanks for the responses. I will use a transformer on the cooktop but not the oven. The dryer would be difficult to install the transformer because we are doing finish now. And the heat/Ac .... come on we're in San Diego on the 25th floor!!
 
The service life of most stuff is reduced by higher temps (from higher voltages), and motors should also be noisier.
 
langjahr@comcast.net said:
. . . motors should also be noisier.
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I don't know about noise, but most motors run cooler with the supply voltage nearer the upper end of their design voltage range.
 
most motors run cooler

most motors run cooler

Can you give me a make & model? I'd like to pursue this with a manufacturer.

Higher V makes less I for the same power demand from the motor, and motor heating is maybe mostly proportional to I^2, so reducing I has more effect on heating than raising V. Not sure, though. . .
 
A motor will have its optimal operating voltage for any given mechanical operating state.

As you increase the supply voltage above the optimal point, the current going into torque production goes down, but the magnetizing current goes up, reducing net efficiency.

As you decrease the supply voltage from the optimal point, the magnetizing current goes down, but the current required to produce the output torque goes up, reducing net efficiency.

The optimal voltage changes somewhat with load; a motor run at less than full load will be slightly more efficient at lower voltage.

-Jon
 
Putting a buck/boost transformer on an appliance that is 120/208 or 240 has a drawback, When you boost each leg to get the 240, you also are increasing the leg to neutral voltage also, the drum motor on a dryer is 120 volt, along with any lights inside the drum if installed. If the appliance is straight 208, there is no problem, or if only one buck boost transformer is used and the high leg is not being used by the appliance for the 120 volt loads.
 
" 208-240 Volt Connection: The Heat Settings recommended on this page are based on a 240 volt power source. If your cooktop is connected to 208 volts, the same heat settings apply but foods may take a little longer to finish cooking." from Thermador CET/CEP Cooktop Care and Use Manual p. 13



208v 240v
9 12
18 24
27 36

kw ratings for stibel eltorn tankless water heaters
 
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