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Car Forum / Driving, Maintenance, Tuning / RVs / March 2007Inverter / microwave issues.
I just installed a 2000/4000 watt inverter thinking that it could power my 1350W input power Magic Chef microwave. Even with the converter breaker off and the engine running, it could not do popcorn at an appreciable level. Are Magic Chefs bothered by modified sine wave voltage? The watt meter on the inverter read about 1300W so it seemed to be consuming about the right amount of power. |I just installed a 2000/4000 watt inverter thinking that it could power my | 1350W input power Magic Chef microwave. Even with the converter breaker off | and the engine running, it could not do popcorn at an appreciable level. | Are Magic Chefs bothered by modified sine wave voltage? The watt meter on | the inverter read about 1300W so it seemed to be consuming about the right | amount of power. Just a guess but it the MC microwave has a digital processor the hash noise from the inverter might be a problem >"Dan Listermann" <dan@listermann.com> wrote: >I just installed a 2000/4000 watt inverter thinking that it could power my >1350W input power Magic Chef microwave. Even with the converter breaker off >and the engine running, it could not do popcorn at an appreciable level. >Are Magic Chefs bothered by modified sine wave voltage? The watt meter on >the inverter read about 1300W so it seemed to be consuming about the right >amount of power. We have had three microwaves in two rigs with whole-house modified sine wave inverters. In every case, the microwave is the only appliance that doesn't perform well when run from the inverter. It cooks at about half power and makes a buzzing noise. OTOH, our microwave draws 175 amps from the battery bank, so using it with an inverter isn't all that realistic.  SignatureDD I need to try the popcorn with shore power just to see how the oven behaves with good AC. > >"Dan Listermann" <dan@listermann.com> wrote: > [quoted text clipped - 13 lines] > OTOH, our microwave draws 175 amps from the battery bank, so using it > with an inverter isn't all that realistic. >I need to try the popcorn with shore power just to see how the oven behaves >with good AC. Our new-to-us Blue Bird is the first RV we've had with a true Sine-Wave inverter (Pro-Sine 2000). The difference it makes with the microwave is tremendous. Our last couple all sounded like they were really laboring. This one runs smooth, quiet, and cooks a lot faster. --- Don Bradner donb (not don) at arcatapet.com '90 Wanderlodge PT40 "Blue Thunder" towing '07 Jeep Liberty >Our new-to-us Blue Bird is the first RV we've had with a true >Sine-Wave inverter (Pro-Sine 2000). The difference it makes with the >microwave is tremendous. Our last couple all sounded like they were >really laboring. This one runs smooth, quiet, and cooks a lot faster. The solid state switching power suppies in normal kitchen unit do not like the "dirty" sine wav that most inverter put out anf the efficency drops way of and they can sound labored as the power supply struggles with the dirty AC. It is possible to build a power supply that is designed for inverter output as this poster has discovered. ----------------- TheSnoMan.com Is there much chance of damaging the microwave with modified wave power. Maybe it will just take longer to heat? >>Our new-to-us Blue Bird is the first RV we've had with a true >>Sine-Wave inverter (Pro-Sine 2000). The difference it makes with the [quoted text clipped - 8 lines] > ----------------- > TheSnoMan.com >Is there much chance of damaging the microwave with modified wave power. >Maybe it will just take longer to heat? That is a good question. I would have to tend to say possibly and if it did damage it would be to its power supply because the "dirty" AC not only reduces output but its efficency is lower which mean it may run warmer. (the power supply) It would be interesting to put a clamp on amp meter on a mocro running on "shore" power vs inverter power as see what the power draw is because that would give you more insite as to the possible risk of damage to one from long term use on inverter power. If there is a big drop in power draw as well, the risk may be very small. These switching power supply are called that because they "switch" the legs of AC feed to DC output as a predetermined place in the wave cycle which is easy to predict with true sine wave AC. Also 115v is what is considered RMS or average and peak voltage is actually over 140 volts for a brief time with each wave cycle Inverters have more of a square wave output and a flatter average and lower peak voltage as well as a different time interval between wave decays is less and it messes with a power suppy designed for sine wave and a different decay rate. Microwave are sensitive because they use a stepped up voltage for magnitron and if the power supply output is low it will result in lower voltage to magnitron. Devices like laptops and TV's also have switching power supplies but they also have a regulated output of 12 to 20 volts DC to run them and this is usually regulated down from a higher internal voltage in power supply so even if inverter cause efficency drops that can cause a sag in power supply and still be high enough to power it. Laptops in particular can be very immune because most actually run off of 10.8 volts internally and the higher supply voltage with their adaptor is to power their charging curcuitry so this voltage can sag too and only battery charge rate will suffer most of the times. Sorry if I got too deep here. ----------------- TheSnoMan.com As a quick check, I looked at the inverter's built in watt meter when the microwave was running. The oven says that it draws 1350W and puts out 900W. When I was testing it, the meter indicated that it was putting out 1300W or so. This sounds like something, somewhere is getting hotter than it probably should. I will give it a more organized study later. Dan >>Is there much chance of damaging the microwave with modified wave power. >>Maybe it will just take longer to heat? [quoted text clipped - 29 lines] > ----------------- > TheSnoMan.com Try running it at 90%. That should put it at 870W. SignatureJerryD(upstateNY) > As a quick check, I looked at the inverter's built in watt meter when the > microwave was running. The oven says that it draws 1350W and puts out [quoted text clipped - 37 lines] >> ----------------- >> TheSnoMan.com On Fri, 23 Mar 2007 10:16:54 -0400, "JerryD\(upstateNY\)" <jerryd@wherever.com> wrote: >Try running it at 90%. >That should put it at 870W. Actually not. If you had one of the new and recently released true varible output ovens like Panasonic makes (I have one) it woiuld put out about 810 watts at 90% if it was a 900 watt unit but unless you have one of theses when you select anything other than 100% it just cycle the magnitron in it off and on over a 30 second cycle so that it averages 90% (at 90% it is one for 27 seconds and off for 3 and 50% is on for 15 seconds and off for 15 and so on) BTW a true varible output micro is just the greatest to happen to them because you can actually thaw something quickly without cooking it and great from reheating too. ----------------- TheSnoMan.com >As a quick check, I looked at the inverter's built in watt meter when the >microwave was running. The oven says that it draws 1350W and puts out 900W. >When I was testing it, the meter indicated that it was putting out 1300W or >so. This sounds like something, somewhere is getting hotter than it >probably should. I will give it a more organized study later. This tends to suggest a big efficency loss ----------------- TheSnoMan.com > On Tue, 20 Mar2007 17:54:50 -0400, "Dan Listermann" > [quoted text clipped - 7 lines] > really laboring. This one runs smooth, quiet, and cooks a lot faster. > --- Your thoughts on choosing a Pro-Sine 2000 instead of the usual generator for a new RV? Thenks. digger >> Our new-to-us Blue Bird is the first RV we've had with a true >> Sine-Wave inverter (Pro-Sine 2000). The difference it makes with the [quoted text clipped - 4 lines] >Your thoughts on choosing a Pro-Sine 2000 instead of the usual >generator for a new RV? Non-exclusive items. From the low/mid-level on up, a Class A diesel pusher will typically have both an inverter and a generator. The inverter is used for continuous availability of AC and/or use of something like the microwave for a few minutes. The generator is used for extensive AC use, and/or to charge the batteries when they have been run down by lots of inverter use. When dry-camping in Arizona in the winter, my typical generator use is 5 hours per day, 2-1/2 hours each, morning and evening. AC usage is more-or-less continuous throughout the day for computers and peripherals. I have 6 6-volt Lifeline AGMs to power the inverter (660AH at 12 volts). As an aside, this RV is anything but new. It was very high end in 1990, and has a 15 KW generator. Original equipment included a 1500-watt inverter that was massive in size, along with two separate battery chargers. I had budgeted for a sine-wave inverter, probably 2500 or 3000 watts, but it turned out the most recent owner had replaced the inverter and chargers with the Pro-Sine, which is fine. I would likely have used a Magnum if I had made the change. --- Don Bradner donb (not don) at arcatapet.com '90 Wanderlodge PT40 "Blue Thunder" towing '07 Jeep Liberty
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