Electrical question......

Greg1959 · Dec 30, 2020

My resulting numbers seem way off...

...I have a 310 watt 24 volt solar panel, 60 Amp MPPT charge controller hooked to a 100 AH AGM 12 volt deep cycle battery. A 1100 watt inverter is connected to the battery.

Just for a experiment, I want to plug in a 600 watt hot plate. How long will the battery run the hot plate until battery is 50% discharged??

Here is my numbers: 600W divided by 120 volts = 5 Amps. 100 AH battery divided 5 Amps = 20 hours run time. 20 hours times 50% equals 10 hours of running That just don't sound right, what am I missing?

PS, I understand that I will have energy loss due to heat, resistance, voltage drop over my lines, etc. I'm ignoring them for the moment(not that significant, i think).

What numbers do you come up with?

paul · Dec 30, 2020

Been a long day I’m not thinking clearly right now and electrical calculations often confuse me on a good day, but are you comparing 12v battery to 120v hotplate? Doesn’t something need to adjust there?

Paul

RM-MN · Dec 30, 2020

600 watts is 600 watts no matter where they come from. Set your 120 volt hot plate aside for a moment and use my 600 watt hotplate that is wired to run off 12 volts. That then becomes 600 divided by 12 or 50 amps. Your 100 amp-hour battery would be fully depleted in 2 hours or 50% depleted in 1 hour. Considering the losses from the inverter, the wires, and the internal resistance of the battery I doubt you would get more than 15 minutes running you 120 volt hot plate.

Philip d · Dec 30, 2020

I’m guessing your close but I’m rusty out of school doing grunt work. I (current) =P (watts) divided by E(voltage) so your correct at 5 amps. There’s also going to be some line losses from resistance in your conductors. It’s been awhile since I calculated battery output in ah but I’m thinking your right or close to it if your battery is storing electrons still at 100ah. Batteries soon loose their ability to keep all the electrons held on one plate and not the other so without factoring that in your close.

Philip d · Dec 30, 2020

That makes more sense

Dennis Minn · Dec 30, 2020

Greg1959,

You need the battery discharge tables for your particular battery. It will show temperature-compensated discharge rates and duration for a fully charged battery. It kind of goes without saying, battery discharges are not linear.

D.

wore out · Dec 30, 2020

"Just for a experiment, I want to plug in a 600 watt hot plate. How long will the battery run the hot plate until battery is 50% discharged??"

So how did your experiment turn out? IMHO, that's the only way you'll get a true/meaningful number.

MarkB_MI · Dec 30, 2020

Like RM said. You are using a 12 volt battery, not a 120 volt battery, and you're drawing 600 watts from it. That's 50 amps, not 5 amps.

Deere Mark · Dec 30, 2020

Here is what you are missing:
A 600 Watt load plugged into an inverter (120 Volts AC) takes about 50 Amps out of the battery (12 Volts DC).
On the AC side, 120 Volts times 5 Amps = 600 Watts.
On the DC side, 12 Volts times 50 Amps = 600 Watts.
Your assumption that 5 Amps will be taken out of the battery (by the inverter) when it is powering a 600 Watt load is wrong.

phil25 · Dec 31, 2020

You are using/want 600watts of heat, normally at 120 volts and 5 amps.. since things have to balance
in ohms laws when one goes down 120 to 12, the other goes up 5 to 50, with watts being the same.
just a simple rule to confuse us...

Electrical question......

Greg1959

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paul

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RM-MN

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Philip d

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Philip d

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Dennis Minn

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wore out

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MarkB_MI

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Deere Mark

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phil25

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