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Old 12-30-2019, 08:18 AM   #1
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SOC dropped from 99 to 94, does that seem excessive

I just had a Magnum Battery monitor added to my coach and I'm wondering if the loss I'm receiving in two days is excessive or not.

In two days I've gone from a SOC of 99 to 94, that seems like a lot to me for just two days. I had the battery disconnect switch on, so the only draw I'm aware of is the inverter and the battery monitor system itself. I show a -.02 amp draw which doesn't seem like much.

I'm assuming this is normal amp loss for the inverter and the battery monitor.

My question is, does it seem unusual to go from a SOC of 99 to 94 in two days?
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Old 12-30-2019, 09:03 AM   #2
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I have to ask cause I don't have a playbook. What does SOC stand for?
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Old 12-30-2019, 09:06 AM   #3
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State Of Charge (battery charge level).
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Old 12-30-2019, 09:08 AM   #4
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The SOC (state of charge) draw you have is normal, there are other parasitic draws that drop the battery voltage.
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Old 12-30-2019, 09:20 AM   #5
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Well, an inverter wastes power when just idling, so best to turn it off if you are trying to minimize battery loss. But your 0.02A reading suggests it is Off, so maybe your draw is just the safety equipment (e.g. LP detector, CO detector). Another possibility is that the inverter has a smart sense circuit and is cycling on/off, so causing a higher draw at times yu are not seeing.



You are using 0.02 amps (20 milli-amps) which actually sounds quite low for parasitic load on a nicely equipped motorhome. That's only 0.48 Amp-hrs/day, but we can't say how that affects the SOC without knowing the battery amp-hour capacity you have dialed into the monitor. It calculates SOC based on what you tell it vs actual amps. 1 amp-hour is a 1% drop in SOC if you have a 100 AH battery bank, but it's only 0.25% drop if its a 400 AH battery bank.


Still, it seems the change in SOC is probably more than the 0.02 amp rate suggests. A 5% drop in a 400 AH battery bank is more than a 0.02 amp draw, so maybe you have other laods that come and go and you aren't observing the amp rate from them.
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Old 12-30-2019, 09:49 AM   #6
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Gary, my battery bank is 434 amp hours and it's configured for 430 amp hours. The inverter is off, but the battery monitor itself is on as well as the remote panel inside the coach that I'm getting the SOC and amp discharge reading from.
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Old 12-30-2019, 10:22 AM   #7
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Quote:
Originally Posted by Gary RVRoamer View Post
State Of Charge (battery charge level).
That was my guess but I had to ask to be sure.
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Old 12-30-2019, 11:16 AM   #8
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Gary, do you know the best way to make sure that the negative lead at the inverter is connected to the shunt? They are on opposite sides of my coach so I can't use a multimeter and the cables are not labeled.
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Well, an inverter wastes power when just idling, so best to turn it off if you are trying to minimize battery loss. But your 0.02A reading suggests it is Off, so maybe your draw is just the safety equipment (e.g. LP detector, CO detector). Another possibility is that the inverter has a smart sense circuit and is cycling on/off, so causing a higher draw at times yu are not seeing.



You are using 0.02 amps (20 milli-amps) which actually sounds quite low for parasitic load on a nicely equipped motorhome. That's only 0.48 Amp-hrs/day, but we can't say how that affects the SOC without knowing the battery amp-hour capacity you have dialed into the monitor. It calculates SOC based on what you tell it vs actual amps. 1 amp-hour is a 1% drop in SOC if you have a 100 AH battery bank, but it's only 0.25% drop if its a 400 AH battery bank.


Still, it seems the change in SOC is probably more than the 0.02 amp rate suggests. A 5% drop in a 400 AH battery bank is more than a 0.02 amp draw, so maybe you have other laods that come and go and you aren't observing the amp rate from them.
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Old 12-31-2019, 05:48 AM   #9
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To measure total system draw there should be a single ground cable to the battery (bank) and the shunt should be in that.


If you want to measure continuity to a component your leads won't reach you can use a piece of wire from the meter lead to the point you want to test.
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Old 12-31-2019, 12:20 PM   #10
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It doesn't matter of the inverter negative goes to chassis ground instead of direct to the shunt or battery. You just have to make sure the shunt is between the battery and chassis ground and that nothing is bypassing that.


If you are reading the SOC from the inverter panel, then it is suspect. You want the SOC from the shunt monitor panel.
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