Inverter power for Microwave unit

Thanks Peter – Gets a bit messy pulling it out – removed the shroud and came across another 4 sets of fixings that still need to come out at least so called it quits before I stuff it up as usual.

Consulted the Tech Specs again and and I might have found a flaw in my assessment – correct details are : Power Supply 1230/240V -50Hz, ‘Rated Power Suppy’ 1200 W, Microwave Output 800W* (* = IEC 60705 Rating Standard),

I made an assumption the 1200W was the ‘start up’ rating, with the draw whilst operating as 800W.

But if the power draw is constant at the 1200W, then the 1000W inverter would be inadequate I guess?

Regards – Phil (Bookkeeper – no tech background and totally out of depth with 12 electrickery)

You will need an inverter with at least 1300W capacity and I reckon your LA batteries will struggle to deliver the required power for very long at all. As the voltage drops, the amps will increase even more to compensate.
Cheers,
Peter
OKA196 motorhome

Well that is an interesting observation and clearly described as far as the exercise went, thanks RMD. You are probably correct about the 1500W unit, I wasn't aware they were around that size - usual assumption from inadequate research.

As far as the existing batteries capacity - that is way out of my scope - should be solid units, not purchased from a dodgy dealer, but I can check that with the supplier.

Cheers - Phil

Phil.
Many batteries have a discharge figure on their case, your may have that stated on the side.
Forgot for above! Perhaps use a WATT meter , ie , 240 v a POWER METER to read the ACTUAL watts while the Mwave is running so you can decide on the Inverter size required. A little bigger than minimum is better!
Just went and tested the small microwave with my Wattmeter and it uses 1300 watts, so 108 amp on 12v inverter, while running. Previously I said 1400 W. The heating power is 700 or 800. not sure there. It isn't a big one.

About charging your van batteries from Tug. Although dc dc in van, the two batteries will be 50% slower to reach their desired charge voltage because ONE DCDC is charging two batteries. If a 20amp DC DC, that is only 10 amps for each battery, and if 50% discharged you are looking at 5 hours + of run time min. to get the batteries up a reasonable amount, if that is only what is used.

With 400wTHEORETICAL WATTS on the van roof, you will NEVER get that output, Maybe 300w in ideal conditions. depending on panel quality of course, and any high output is only for a short time period during the day.

Quote - "As far as the existing batteries capacity - that is way out of my scope - should be solid units, not purchased from a dodgy dealer, but I can check that with the supplier."

Phil, If you supply the make and model of the batteries, there are people on the forum capable of doing some research on them and can advise if they are suitable for your expectations.

Phil
If, theoretically you ran the inverter at 100 amps for an hour , that would be 100AH of use and close to or exceeding the usable normal discharge amount for battery life. Therefore. 5 mins is 1/12 of that amount. About 8 AH used.for the 5 mins. Good for warming your bedtime milk etc. So ok there if the electricals are all up to it. Running and inverter to charge phones is more simply done with a 12v to 5v charge unit, ie, a dash ciggy charger. It will be handy for 240v power tools OR for running their Lithium based chargers.

The limitation will not be the storage capacity of the batteries, but their ability to discharge over 100A without the voltage crashing.
This is a function of the rate that the chemical reaction to make electricity can take place.
Crank batteries have many thin plates to allow this chemical reaction to take place faster than deep cycle batteries which have fewer, thicker plates.

You could rig up a 100A+ load and try it while measuring the battery voltage to see how long before the voltage comes down to (say) 10 or 11 volts. After the load is removed, the voltage will recover, but that is not the problem and dose not help much.
Cheers,
Peter
OKA196 motorhome

Phil.
I agree with Peter and mentioned earlier the ability of the discharge of the batteries. Worth checking. Unfortunately with 12v a high wattage 240v output needs double what a 24v system dc ampere flow is for the same energy delivery to the inverter.

As well as the battery volt-drop that Peter referred to above, it should be noted that the battery rating of 100Ah is sure to be at the 20 hour discharge rate. At higher rates such as the here nominated 100 Amps then the battery delivery capacity is significantly reduced and should be factored into battery performance.

Thanks Alan - and to Peter & M, PeterD, RMD, Macca and of course 2517 – yes there may be another way.

As expected from past experience from many years association with Exploroz, the advice available from you guys is invaluable from both the technical knowledge and the practical experience learned from ‘been there done that’.

There are times though to factor in the variations in the gear we all use because there are so many different configurations available in the many vehicles – e.g. you could write a book about the different batteries and specifications of each it seems and on top of that there are the wiring specs, thickness, length etc, before getting to all the gadgets the ‘power’ is being processed through.

I have wads of notes jotted down now about what my regulators, controllers, chargers etc. can and can’t do, and still come up blank when I think of another modification that ‘might be handy’.
I will now get back to the auto sparky who provided the batteries – buried under a mass of cables and no descriptions on top, and put a few questions to him – which I should have thought of earlier.

Will let you know the outcome in due course.

This is what happens when you find yourself confined to barracks after finding out your ‘pretty heavy cold’ tests positive to covid after feeling a bit blasé all this time without it.

Cheers - Phil

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Hi Phil,
I’m pleased that you feel you have benefited from the contributions. The thing is that there are so many variations available and we all look to “Do it my way”. And we can after absorbing expressions from others.

I find the Yanks fascinating. Now that I have moved to the Dark Side and drive a MB Sprinter I watch a US forum on Sprinters set up as motorhomes or campervans. They try to be individualistic but end up following a common style of tiled flashbacks, commercial style sinks & plumbing ware, timber ceilings, coin pvc flooring, huge 120v inverters and induction cooktops. It is really lemming-like amusing.

And Phil, it really is very pleasing to have you thank us in such a nice way and for your appreciation for our offerings. Cheers Mate.
Oh, p.s. Sorry about the Covid.

Macca.
You appear to have given decent though to your system. With a components sized sufficiently to provide what you need.
Good job!

The other thing I forgot to add was that all the cables connecting the vehicle to the DC/DC Charger, the auxiliary battery to the charger and the battery to the inverter are all 6B&S.

Macca.

2517

Feel free to guide us all forward in alternate ways to solve the problem. AS Pauline says, Please Explain!

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Maybe use LPG ?

Thanks Michael - it certainly seems cable size is paramount in any charging apparatus installation.

I have my auto sparky coming on Friday to assess the concept.

All of the gear in the van to date works wonderfully (Powertech 4 stage 40A DC/DC charger, tied into Enerdrive solar charge controller , two 100AH AGM batteries and the solar panels).

I accept the inverter addition will take it to a whole new level.

If in doubt, will leave it out.

Cheers - Phil

Michael h9 & Phil
Nearly everyone reads the specs of a microwave oven and believe that IS the power. It is ONLY the power being developed by the magnetron into the cabinet as Microwaves energy.
Microwave ovens have huge losses from input to output, and as mentioned just using 700 watts as the base is a flawed process. A 700 watt microwave DEMANDS a CONSTANT 1300 to 1400 watts to run it. SO that DEMAND is what you have to work with, and NOT the stated power on the label. Really, the stated power is irrelevant. Two AGM batteries on PARALLEL have to each be capable of discharge rates of 50amps constant to provide the 100amp approx current flow to inverter while the MW is running. As the batteries discharge, the energy/voltage level available to the inverter lowers because battery voltage begins to drop off and SO, the inverter pulls more current to maintain the inverter output. Vicious circle spiralling downward unless ALL components can handle it for the duration.

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Considering the inefficiency of an inverter/microwave combination I am surprised that anyone would wish to install one into an RV vehicle. The financial cost is not an attractive proposition either. Seems some do not go travelling to "Get away from it all".

My idea of getting away from it all is to make something edible in as little time possible with only a spork to wash. at the end of it. I cook tea almost every night at home and my wife doesn't like camping at all and never comes with me, so I am getting away from a fair bit of it.

I often laugh to myself at the ones who call traveling in a motorhome or caravan and stopping somewhere, as "camping". Hardly camping at all. I, like Michael H9 leaving home, I used to head off into the high country by myself on large trail bike, Wonnongatta, etc and slept in a tent or under a cover. That is More like camping to me!
Backpacking/ Bushwalking sometimes and carrying a little tent and all gear, that is camping too.
Love to hear what people think is camping.

Michael, if that spork has three prongs it is known as a THREEK. Forks have four and called same.