Voltage Fluctuation

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blues

Member
Location
Nevada
I have a toaster oven at the airport that is rated for 208/240. The incoming voltage varies from 218/235. A buck boost xfmr was installed (I assume to raise the voltage to 240). In essence the voltage now fluctuates from 234/252. This is a electronic unit and will reboot itself each time there is voltage varation to some degree. Any suggestions as how to regulated the voltage.

The owner has spent $2000.00 and two years dealing with this problem.

Thanks
Dan Craven
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Buy a new toaster oven. Or find out why the voltage varies so much.

(I'm hoping its not really just a $50 residential type toaster oven. )
 

Cold Fusion

Senior Member
Location
way north
...The incoming voltage varies from 218/235. A buck boost xfmr was installed (I assume to raise the voltage to 240). In essence the voltage now fluctuates from 234/252. This is a electronic unit and will reboot itself each time there is voltage varation to some degree. Any suggestions as how to regulated the voltage. ...
The transformer/conductors feeding the area are too small. Depending on the contract with the electric distribution owner, you might get the distribution owner to upgrade the supply - butI doubt it.

I can think of several methods with varying degrees of regulation, and varying degrees of cost. To answer your question, I would ask, " What is your spec for the regulated voltage? What is your limit on money?"

Hunt has a good question. With the regulation being fairly close to +/-5% of 240V, has anyone called the manufacturer to see what they have to say? Maybe you will get an answer of, "Oh yeah, we see that a lot when the flux capacitor board goes out."

cf
 

jghrist

Senior Member
Are you sure the problem is not caused by the voltage sometimes being above the equipment rating? If this is the case, scrap the buck boost xfmr and the voltage will be in the proper range.
 

hunt4679

Senior Member
Location
Perry, Ohio
If this is just a toaster oven with heater elements (they dont know the differance) just differant heat ranges with differant voltages I would say scrap the transformer and see what happens!
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100122-1705 EST

blues:

It may not be the nominal voltage fluctuations you are seeing but rather large transient voltages, rapid rate of change of voltage, that is the problem.

This is not a US 120 V kitchen type toaster. Is this more than 1500 W?

A Sola constant voltage transformer might solve the problem because it would maintain a relatively constant voltage and filter most transients. Newark shows a 2000 VA 120 to 120 at about $2800. Would require a special winding to get your voltages.

Because this is so costly you might want to try a low pass filter and see if this would solve the problem by reducing high rate of change transients. Corcom manufactures such filters. Corcom is part of Tyco these days.

Consider a 20VQ1
Datasheet http://www.corcom.com/pdf/Q.pdf
Newark as a source http://www.newark.com/tyco-electronics-corcom/20vq1/rfi-filter/dp/52K4506?Ntt=20vq1
$90

Or get a toaster guaranteed to work in your environment.

.
 

Cold Fusion

Senior Member
Location
way north
...A Sola constant voltage transformer might solve the problem because it would maintain a relatively constant voltage and filter most transients. Newark shows a 2000 VA 120 to 120 at about $2800. Would require a special winding to get your voltages. ...
I've had particularly bad luck with Sola CVT on switching power supplies. Even Sola has noticed that. It would appear that the Sola output sine wave has bites out of it to do the regulation - and that burns up the switching power supplies. I've now told you more that I know about this subject, so I will stop

I wouldn't install a sola CVT without the MFG telling me it would work.

cf
 

jwjrw

Senior Member
I did a coffee shop which had a expresso machine that was rated 208/240 but the instructions with it said it would not work properly with less than 230 volts.
 

dbuckley

Senior Member
If you really need to solve this problem, then a company called Salicru make votage regulators that work much better than the ferromagnetic types with difficult loads. It is esentially a transformer with a tap-changer, but the tap-changing is done through semiconductors, so unlike mechanical tap-changers it corrects cycle by cycle.

Because the company are not native English speakers (they're in Barcelona), theres some real howlers both in their documentation and their website, but the products do what they say on the box.

I dont know what their distribution in the USA is like, but here in little ole NZ we have a distributor, so they must have a source in the 'States. All they list for the USA is an email address, which is america at salicru dot com

Another alternative is what is effectively a UPS without a battery; look to Visicomm Industries for their range of static frequency converters; these converters will produce 50hz or 60hz out irrespective of the input frequency, and have a -15%/+20% input voltage toleration, whilst producting 1% reguation at the output. So it'll happily do 60Hz to 60Hz "conversion" whilst regulating the voltage well. These guys are local to the USA.

Note that neither of these options are low cost; if you need stable power of more than a few watts with a difficult load from a dodgy supply, there are no really cheap options. However, at least your customer will know his next few thousand dollars will deliver results not failures.

My final (and low cost) suggestion is for the owner to take the toaster oven to someone who is competent to rip its covers off and alter it; the elements won't care much about the voltage dips, but the electronics do, so dissect the internal wiring to put the electronics power supply onto a different inlet to the rest of the oven, and use a small standard double-conversion computer UPS to supply just the electronics. Of course, this will destroy any listing the device had...
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100122-1952 EST

Sola CVTs as mentioned are ferroresonant, and are current limiting.

Switching power supplies use a rectifier and capacitor input filter. These draw high instantaneous peak current each half cycle to charge the capacitor. If you are moderately above the minimum input voltage then a series input resistor can be added to reduce the peak input current pulse.

When properly sized I have not had problems with Sola transformers.

What dbuckley has mention --- power the electronics from a separate well isolated and regulated power supply makes sense because the amount of power required for this part of the toaster is minute.

The microprocessor and the circuitry that resets it is where the problem is.

.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I have a toaster oven at the airport that is rated for 208/240. The incoming voltage varies from 218/235.
Sounded like a match made in heaven. I also wonder how the unit operated without the BB. If there was an issue before, the BB can't help; it just increases the voltage swing. I also like the suggestion about isolating the electronics.

First, though, I'd investigate the voltage variations. Do they vary with the oven's operation or element cycling, or even without it running? I'd first check at both ends of the power cord, than at the panel, then test at each accessible point.

It's gotta be better to fix the underlying issue than throwing expensive band-aids at it.
 
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