How to make a low powered microwave.
CAUTION!!! - Microwaves contain lethal voltages (up to 2500 volts)
even when disconnected.
They can kill you if you don't know how to properly work on them.
Additionally operating microwaves with the covers removed
can result in personal injury including burns and blindness.
Do not attempt this unless you know exactly what you are doing,
you have been warned.
There are many lower powered microwaves out there on the market and they will work fine for your off grid use if you have unlimited battery capacity, large inverter and plenty of solar to keep it charged.
With all that being said your typical camper van has basically none of those things all at the same time because of space. This fact is well known with the camper van community over in Europe and they have come up with a solution of low powered microwaves to help. They do this by converting the lowest powered microwave they can from a 600-700 watt model down to a 500 watt model. I would just buy a 500 watt microwave but I can't find any for sale new (very few people want a slow microwave that can just barely pop popcorn.).
Why not go lower you might ask? well the answer is pretty simple - you can't pop popcorn below 500 watts and who doesn't like a nice batch of popcorn from time to time.
That all sounds great that they have them over there for sale on Ebay even but they use 220 volt and so they are rather useless for us that use 120 volt.
I decided to go ahead and make myself a low powered microwave that runs on 120 Volt. Being an electrician and having repaired many microwaves I know that most microwaves up to 1000 watts use the same magnetron, the Galanz M24FA-410A. It is rated for 500 - 1000 watts. I looked for a cheap manual timer microwave with no turntable, no light, soft start unit with the smallest wattage and case that I could find. I didn't have any luck finding any here in the US. The soft start feature that is in most larger microwaves just isn't in the cheap small wattage units found here. I did find a few manual timer models in small wattages and chose the
Westinghouse model #WCM660B . It is advertised as a 600 watt 0.6 cu foot microwave that uses 800 input watts @ around $60. These figures are not accurate, it is closer to a 700 watt microwave that uses 1150 watts and almost 1300 during start-up. I also bought another microwave to see if it had a soft start circuit in it - The
Proctor Silex Model # PS-P60B17L-D5 on sale for $50. It is exactly the same electrically inside as the better built Westinghouse unit.
Microwaves use a capacitor in a voltage doubler circuit to cheaply get enough voltage to make their magnetrons emit microwaves for us to make popcorn with, they could use a bigger transformer but then you would have a heavier more expensive way of getting the voltage it needs plus every different power level microwave would need a different transformer. As I stated earlier the same magnetron is used for many different power level microwaves. How do they do this? a Different capacitor is all. Everything else in a 500 - 1000 watt microwave is the same.
The low powered conversion.
1.) Disconnect light. -20 watts running, -30 watts inrush
2.) Disconnect turntable. -30 watts , -100 watts inrush
3.) Change wattage of microwave by changing capacitor from 0.70 Micro Farad to 0.65 Micro Farad. -280 watts running, no real change in inrush.
Stock Microwave = 1150 watts running, 1210 watts during start-up.
Converted Microwave = 820 watts running, 860 watts during start-up.
This saves you 330 watts while running and 350 watts of inrush. This means you can use a much smaller battery bank and inverter to power your popcorn maker. The trade-off is that it will take longer to do everything and in the end you will use almost the same amount of total power to boil a cup of water but you will do it at a much lower amp draw and without so much inrush - your batteries will be happier.
Make sure you unplug the microwave, then discharge the capacitor before touching anything inside the microwave. Failure to do so will result in injury or death. Make sure when you change the capacitor that you insulate the High Voltage lead for 2500 volts like the original lead.
The 0.65 Micro Farad capacitor can be purchased from
http://www.thriftyapplianceparts.com/5303269585-frigidaire-microwave-capacitor-replacement/ for about $15.50 + $5.50 shipping.
You could also build yourself a 425 watt microwave but I find that they make lousy popcorn (really... lots of unpoped kernels). You can find the 0.60 microfarad capacitor here -
Ebay
