Could you... Would you... Should you...

Ho Ho Ho Scrubba

Not too sure, but I don't think so. Also the old P=Vi rule is for DC. With AC it's different due to rms (root mean square) stuff that relates to alternating current.
Can't remember now with my Alzeheimers and all. There's sure to be some leccie spurts on board who'll set you straight.

Seeya

P.S. Like Santa I also suffered from aneroxia but beat it ..... :-)

Waeco makes bush microwaves. Why not just buy one of them. Much safer :)

I never work out current draw, amp hours or any of that stuff, mum always told me "what you don't know won't hurt you" so i'll blame her if I blow something up.
A mate used a gasless mig welder off my 3000watt inverter, running off 2 950CCA batteries, for about half an hour car still started and batteries still seam fine. So in my opinion it should be fine(I'll probably get corrected on this though), but where's the fun in taking a microwave camping.

Scrubba. I can't see why it wouldn't work. Even if it pulled 100 amps thats still less than an electric winch is dragging out of a battery under load. To ease the preasure on the battery you could run the car while the microwave was on.
Any heavey load like that on a relitively small battery will no doubt shorten it's life.
Setting it at 60% would if nothing else give the inverter, wiring & battery a moment to cool down but certainly wouldn't use less power.
cheers Craig........

Scrubba,

Most electrical appliances have detailed on the back of them their power draw. I just checked a relatively new 700 watt micowave and it draws 1200 watts, so it is possible your 600 may draw 1000 to 1100.

Your calculations seem to be correct for 12 volt. Overall this would indicate your microwave would draw over 20 amps for 15 min of running. Given the rules of a battery only realistically charging to 80% of its capacity from the car (assuming it's a wet cell) bringing it to 64 amps, and trying not to go below 50% of the capacity, you have a theoretical 30%, ie 24 amps to play with. The M/W is sure going to use a lot of your power.

Just something to consider. If you have a means to keep charge up to your battery, there is reason that I can see that it wouldn't work.

Cheers,

Jim.

Only 5% for the invertor, I think not! ;-)

I reckong you'd be drawing close to 100amps, I also reckon my 80 amp/hr battery would die extremely quickly. 1-2 minutes of usefull power at that draw not to mention the pain the battery would be going through.

A gennie would be the only way or lots and lots of big fully charged batteries...
Or a 12v Microwave. I think they are around now.

Darren (GO_OFFROAD) has posted about a serious medical need to run a microwave and I believe he carried a bank of 5 batteries (working from memory here).

Perhaps he will read this and post some information from experience.

He will know what works and what doesn't. The fact that he carried such large battery power is an indication that a lot of power is needed. However he needed to be sure there would be no failures so perhaps somewhere in between is the go if it is not a crucial issue. Which of course your's is not.

Hope to have been of some help.

Cheers,

Jim.

"Interesting" maths but you arrived at the correct answer :)

Just divide the power in watts by the voltage in volts eg. 1000w / 12V = 83A
And that's probably in the ball park for a 600W (output power) microwave and a bit for inverter losses.

Next problem is your 80Ah battery may not be 80Ah! Usually battery capacities are quoted at the C/20 figure in other words your battery will support a discharge of 4A for 20 hours - with a 50Ah battery it would support a discharge of 2A5 for 20 hours etc. At C/1 your battery is more likely to be (guessing here) a 20Ah battery, so an 80A draw will flatten it in around 15 minutes. All this is at 25 deg C things get worse as the temperature drops.

I guess what I'm saying is that it isn't really do-able with a 80Ah battery looks like you'll need at _least_ twice that capacity. If you decide to do it anyway, invest in a cheap digital multi-meter and monitor the battery voltage under load and shut down when the battery falls below 11V

Another thought: is your inverter a square wave type (ie. non sine wave)? If so the big transformer in the microwave may not like that too much – it might work but power output could be low and the transformer might overheat and burn out before too long, otoh it might be OK?

As usual, for all things battery:
http://www.uuhome.de/william.darden/

Mike Harding

mike_harding@fastmail.fm