# Batteries / Inverter

Discussion in 'Tech/Mech General' started by Bart, Sep 8, 2016.

1. ### BartFunster

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using an 800W microwave using my 1500W inverter how long would it take to drain my 3 x 130AH batteries to 50%

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195 / (800/12) = approx 2.5 hours. Ish.

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3. ### TechnoFunsterLife Member

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800 watt microwave will pull at least 1100 watts

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Is that 1100 constantly?

195/(1100/12)= 2 hours ish

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5. ### scotjimlandFunsterLife Member

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800 watt is the microwave or cooking power.. not the energy used..

Power
of a Microwave Oven.

"A typical consumer microwave oven consumes 1,100 W AC and produces 700 W of microwave power, an efficiency of 64%. The other 400 W are dissipated as heat, mostly in the magnetron tube

as calaculated by @Al1 .. 2hr ish

however.. and it's a big however.. that is a theoretical time.. and does not take into account Peukert's law.. ..

expresses approximately the change in capacity of rechargeable lead-acid batteries at different rates of discharge. As the rate increases, the battery's available capacity decreases, approximately according to Peukert's law.

if interested .. https://en.wikipedia.org/wiki/Peukert's_law

and

Last edited: Sep 8, 2016
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Peukerts law takes it to about 30 minutes if my calculator is correct

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7. ### funflairFunsterLife Member

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To me a microwave is something that runs for a short period of time as in 5 or 10 minutes any more than that and you should be thinking about hook up.

Martin

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8. ### scotjimlandFunsterLife Member

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To me a microwave is something you leave at home..

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9. ### BartFunster

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Wow really i'm surprised how long they would keep it going , i used it for like 8 mins as a test and batteries finished out settling down to 91%
i did
exactly this,, that is why i asked the question, as i though 5 mins would of near flattened my batteries, but in fact after i did this small test where i used the microwave for like 8 mins the batteries finished out settling down to 91% which amazed me. i'm just trying to learn what power i have to use if needed.
When i was drawing power from the battery bank in the above test , the percentage that was left in the battery bank dropped to i think as low as 52% while it was drawing the power but as soon as it stopped drawing power the battery percentage slowly went back up again,and this morning was back up to 91% and 12.7 volts
they have not been recharged at all since doing the above test.
does that sound about right ?
I know you are not meant to take more that 50% out of you batteries , but is that 50% when under load or after the have resettled down again ?

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10. ### BartFunster

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well its built into the MH Jim ^^

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11. ### NeilfgFunster

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Would agree with this, microwave short period usage, maybe not always on full power either.

I have finally decided to stick an inverter in the van for a coffee machine (spec says 1100w) have done all the maths adding 20% etc.., but the draw is dependent upon how the machine is used, so decided to set it up at home with a monitor and a spare battery then measuring the amps drawn to make a coffee or two, can then have a think about the measurements and decide if I need more, seperate or different batteries or not.

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12. ### scotjimlandFunsterLife Member

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Thanks Jim

14. ### funflairFunsterLife Member

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So now you know what you can take out and what affect it has on the battery capacity you need to know how you are going to put it back in as batteries like to be charged straight back up again. We use all the usual much maligned 240 volt gadgets off the inverter and the batteries are always charged straight back up, the battery charger has been switched off for 6 or 9 months so most of this is down to the solar.

Martin

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15. ### autorouterFunster

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The battery percentage as soon as it stopped drawing power was 91%. It stayed at 91% until the morning, when you measured 12.7 volts.

When people say that the voltage of the battery is not a very good indication of the % state of charge, this is exactly the kind of thing they have in mind. The voltage straight after the test was quite low, I presume, and gradually rose over several hours to a final value.

If you need a minute-by-minute indication of the remaining capacity, you need a 'battery monitor' device, that has an inbuilt computer to add/subtract the amp-hours as the amps go in and out of the battery. There's also a bit of extra wiring involved compared to just using a voltmeter.

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16. ### BartFunster

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I'm sorted in that aspect , as i have a 120Amp sterling Battery to Battery charger.
Well at least i hope im sorted now the inverter will be added to the system drawing much more power,, that is having said that when it gets used.

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