Understanding battery monitor numbers

[IAmABug]

I have just recently install a Noma 100W panel and controller on my trailer. Chargering 2x 6V batteries. I plan on buying a MPPT next year but that's a different story.

Question is this. I bought two monitors. Installed one to track solar input. Installed the other to track battery bank discharge power used.

I got a total of 196Wh drained from the battery bank, and 891Wh inputed from the solar panel. My batteries stayed at around 12.7v for the 6days we camped. I let them sit with no load for a bit before checking the voltage. First trip with the setup, I am a data guy so I watched the numbers alot. I am very happy

But, why such a big discrepancy between the two numbers?

Any thoughts are welcome.

 

[Mark_K5LXP]

Segal's law - A man with a watch knows what time it is. A man with two watches is never sure.

Sounds to me like the solar meter is reporting charge power, and the battery monitor is reporting *net* power *in and out* of the batteries to the house load. So you likely had 1087Wh delivered to house loads.

Mark B.
Albuquerque, NM

 

[IAmABug]

The monitor(1) in the Solar charger read 891Wh. The monitor(2) on my house batteries read 196Wh.

Neither reads the other while they are on.
(1) only reads when the solar panel is hooked up.
(2) only reads when I use power in the trailer.

(1) is wired direct in (-) battery lead from solar charger to battery thru a 100A shunt.
(2) is wired direct in (-) lead from house battery between the (-) post and (-) frame connection thru a 100A shunt.

Pic of setup.

 

[Wasillaguy]

Controller pumped that much to the Batts, but they weren't necessarily able to use it. Most is lost as heat once Batts are charged. MPPT will help Batts sip up a little more, but it's going to happen any time Batts are full, regardless how much capacity you have.

 

[Contributor]

Something here does not sound right. You say you camped for 6 days and only consumed 196 Wh.

So you used 196Wh/12.7V = 15.43Ah for 6 days? About 2.57Ah per day?

It is not clear to me from your picture how you connected the shunts.

On the shunt measuring consumption, I expect to see one thick cable (4-6 Gauge) on one side of the shunt going to the battery (and nothing else) and the other side of the shunt another thick one going to the frame. All of the RV loads should then connect at the frame. The only other wires added to this shunt should be for the monitor.

On the shunt measuring the input, how did you connect the shunt?

Please explain your hookup.

 

[Ex-Calif]

I think the discrepancy lies in the fact that the shunts are in parallel. Just spit-balling here

I may be wrong but I think the shunts should be in series - that way both shunts will see total power flowed.

Also I think in general the solar monitor meter has one way diodes so it only measure outflow. The battery monitor measures flow in both directions to keep a running total of amps in/out.

If I am right the solar monitor will measure only flow out from the panels and the battery monitor will be a result of charge - consumption.

So if the power consumed in one day is 40 amps and the solar panels supplied 40 amps the solar monitor would show something like 480W supplied and the battery monitor should show full state of charge and amps totalizer at or around zero.

If there is another charge source - like a converter/charger it should be tapped in between the solar shunt and the battery shunt.

 

[Contributor]

He should be able to use two separate shunts the way he intended. I think he did not wire them in correctly. Especially the consumption side, I just can't see him only using 2.57 Ah per day.

 

[Wasillaguy]

Agree. That's too small of a number.

 

[Mark_K5LXP]

You can't put a diode in series with a shunt. The forward drop would render it wildly inaccurate if not inoperative.

Why can't the solar meter count delivered panel power and the battery monitor report net delivered battery power? Without the benefit of a system diagram I think it's as good a guess as any. Having that much panel power "dissipated" or evaporate into the aether seems less plausible.

Mark B.
Albuquerque, NM

 

[IAmABug]

These monitors measure one way. You can switch two wires to read the other direction.

My monitor inside the trailer (not visible in above posted picture) has the negative come off the battery neg, thru the shunt, then to the chassis ground. Positive power for monitor comes direct from battery.

My monitor in the above posted picture has its neg off the solar charger, thru the shunt, to the battery neg. Positive from solar charger goes direct to battery.

In this picture attached it would be number 1 and 3. But my negatives are not connected. They are seperate loops. IE one monitor works even if the other is disconnected and removed.

 

[IAmABug]

He should be able to use two separate shunts the way he intended. I think he did not wire them in correctly. Especially the consumption side, I just can't see him only using 2.57 Ah per day.

No furnace. Only hot water tank, fridge and water pump. Bathroom exhaust fan when needed. All lights are LEDs.

 

[IAmABug]

I will do a wiring diagram in the morning best I can.

 

[Ex-Calif]

You can't put a diode in series with a shunt. The forward drop would render it wildly inaccurate if not inoperative.

Why can't the solar meter count delivered panel power and the battery monitor report net delivered battery power? Without the benefit of a system diagram I think it's as good a guess as any. Having that much panel power "dissipated" or evaporate into the aether seems less plausible.

Mark B.
Albuquerque, NM

I think it is part of the circuitry of the solar monitor. I am not suggesting he add anything.



Clearly if the shunts are in parallel neither shunt will see total consumption.

 

[Ex-Calif]

Here - I found another reference that is pertinent.

 

[Mark_K5LXP]

Agreed, functionally then they only read unidirectionally. The latter 'pertinent' diagram is what you'd expect to see so I guess the jury is out until we get a report from IAmABug of what's actually there.

Mark B.
Albuquerque, NM

 

[Ernie n Tara]

Didn't read every entry, but it would seem that the solar is both charging the batteries and powering the coach while the battery gets the left over power to the extent it can take it. That is the solar voltage is higher than the batteries.

Ernie

 

[Contributor]

No furnace. Only hot water tank, fridge and water pump. Bathroom exhaust fan when needed. All lights are LEDs.

Fridge on propane alone will use up about 20 Ah in a day. You are claiming less than 3.

 

[IAmABug]

Here is a diagram. Best I could do but it should be straight forward.

If my discharge shunt is not installed direct in the main neg of my trailer ( I have a seperate neg run from neg post to shunt to chassis ground ) is it possible I am 'missing' some current discharge?

*Unlabeled wires in diagram are the monitoring wires ( orange and green )

Pic of solar monitor and house battery monitor.

My original numbers where off apparently. This shows even less house draw @ 180

Eventual results I am going for is to make sure they are showing what I desire and are wired to reflect this. Charge vs drain.

 

[IAmABug]

Controller pumped that much to the Batts, but they weren't necessarily able to use it. Most is lost as heat once Batts are charged. MPPT will help Batts sip up a little more, but it's going to happen any time Batts are full, regardless how much capacity you have.

Ok verbal thought time...
Due to the shadows etc the panel varies it's watts volts amps produced so it is not actually pumping alot into the batteries at low light conditions.
100w panel making 13.5V@ 0.5A would be different then 100w panel making 13.5V@ 6A. These would register different Wh, and charge at different rates.
This would make the total Wh larger then the draw off the batteries. Even in low light the monitors reads values but it's not enough to actually charge the battery to full. Makes sense.

My monitor only reads when the charge controller is charging as it is in the lead from the controller(+) to the battery(+). No current if the battery is full and charge controller is off. It shouldn't show anything other then charge going to the batteries how I wired it.

 

[Contributor]

Just for sanity check do this. Charge the Battery to full. Turn off or disconnect the solar input. Turn on the fridge on propane, what current is it drawing? should be around .7 Amps. Next turn on the propane furnace, what current do you see? should be 4 to 7 Amps depending on model. If that is what you are seeing, then it's connected OK. Another sanity check is to use a voltmeter set to measure Amps, they are usually good for 10 to 20 amps unfused - check your meter. Just put it in series between the battery post and cable, it'll do the same as the shunt and give you a current reading.

Once you get your usage figured out, reconnect the solar and see it it affects the way the usage shunt reads.