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incorrect inverter voltage
By Jason Wilkinson, Section Newbies Posted on Sun Jul 05, 2009 at 07:15:28 PM MST
inverter low voltage

HI again, my fridge would make a strange noise at times,paid no notice to it. next ice started forming in the freezer compartment(it's a no-frost fridge) my son said the noise is unusual, i dicided to check ,and found out the inverter was only putting out 85 to 95 v ac i have not notices any change in the lighting, would the low voltage cause any problems to the compressor of the fridge?
ps the inverter starts the fridge very easy

incorrect inverter voltage | 5 comments (5 topical)

Re: incorrect inverter voltage (3.00 / 0) (#1)
by Flux on Sun Jul 05, 2009 at 02:35:04 PM MST

Unless you have a true sine wave inverter you need to be very careful about measuring voltage.

The MSW inverters are basically square waves with about 50% duty cycle. This gives a peak voltage similar to the peak of a true sine so things that use rectified dc work ok ( radios etc.) The rms is also the same as for a sine so that lights ( incandescent) and heaters work ok.

The average cheap multimeter measures mean volts but is scaled to read rms for a sine wave. If used to measure these strange waveforms the form factor is way off and your 90 or so volts is probably in the right order and the thing is probably working ok.

Motors, fridges, microwaves and many other things work well enough on these waveforms but they don't really work as intended for a pure sine wave. A few things either don't work or die on MSW.

You probably have something peculiar with the fridge rather than the inverter.If the inverter is driving the motor without problem then something else is likely to be odd. If the thing wouldn't start or run then it would be an inverter problem.

Flux

Re: incorrect inverter voltage (3.00 / 0) (#2)
by Madscientist267 on Sun Jul 05, 2009 at 03:06:24 PM MST

I agree except for the noise - while it is coming from the motor in the compressor, it is directly caused by the sharp transients that MSW inverters generate.

Beware - things like motors and transformers have a tendency to overheat due to the harmonics generated by the square wave interacting with the coil, and can't be pushed to their rated limits under these circumstances unless special provision is made for additional cooling of the coil as well as the core (hysteresis/eddy losses increase as well).

As you touched on, I've lost a few transformers this way; thankfully they were small and inexpensive to replace.

Also, some capacitive AC/DC converters don't like MSW and have a tendency to burn up as well.

Steve

[ Parent ]

Re: incorrect inverter voltage (3.00 / 0) (#4)
by Jason Wilkinson on Mon Jul 06, 2009 at 10:31:28 AM MST

Thanks to ALL for the respons Flux i have another small inverter 700 watts the output measured with the same multimeter reads 120 vac even though the inverter (MAGNETICS USA MAG 190) is rated 115vac 60hz 4.3a max it work the lights on but not the fridge
KURT The fridge was working the past 3 months onn and off ( my batt bank only allows me 5 to 6 days with the lights before the inverter alarm comes on even though the turbine is on 24/7)since returning the frighe to the grid noise is gone and so is the ice build up
Jason

[ Parent ]

Re: incorrect inverter voltage (3.00 / 0) (#3)
by kurt on Sun Jul 05, 2009 at 04:56:27 PM MST

if you are getting frost build up in the back of the freezer compartment i would bet that either the defrost timer or the defrost heater is bad you can look up instructions on how to diagnose that on the internet or you can call a service tech.

IRC inst.
just a personal rant carry on.

Re: incorrect inverter voltage (3.00 / 0) (#5)
by brkwind2 on Thu Jul 09, 2009 at 06:27:22 PM MST

I had a fridge that did that, the ice would come & go. I finally discovered the defrost timer contacts were going bad. I took it apart & cleaned, soldered & filed flat the contacts. Then put in a relay so the timer only operated it & the relay contacts had the heaters on them. It worked great except there wasn't a lot of room under there for additional parts & balls of tape.
"I get along with all people despite their shortcomings of race, religion or orientation. So long as they recognize my superiority we'll get along fine." "O
[ Parent ]

incorrect inverter voltage | 5 comments (5 topical)

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