Understanding battery monitor numbers

[IAmABug]

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.

No voltmeter.

Fridge on propane

Furnace

 

[Contributor]

Those numbers look low, do you have the model numbers?

 

[Contributor]

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?

Not sure that I understand this. There should only be one (1) wire to the negative terminal of the battery to the shunt, the other side of the shunt can have as many as you need. This way all current coming out of the battery goes through the shunt.

Hook it up like this

 

[Wasillaguy]

Current reading off by a factor of 10?

 

[IAmABug]

Dometic DM2652 fridge. 120v or 1500Btu Propane, no 12v option
AirXcel furnace, can't see model. But is stamped 3.1A on the front info plate.

Almost seems I am seeing Amps/10 on the house monitor...

 

[IAmABug]

Current reading off by a factor of 10?

Seems so. Now to figure out why. Would this make it 1800Wh not 180Wh, which seems more logical.

 

[IAmABug]

Not sure that I understand this. There should only be one (1) wire to the negative terminal of the battery to the shunt, the other side of the shunt can have as many as you need. This way all current coming

Each shunt has one wire out to chassis (-)

In this diagram, for the discharge circuit, the dotted zone shows how I have the house monitor hooked up to (-)
Should the shunt be in the 'A' lead instead?

 

[Ex-Calif]

That's what I said in post #6 and diagramed in post #14

I don't know what happens entirely when the shunts are paralleled but it can't be accurate.

I combined Bugs schematics and I think he has this going on.

 

[Ex-Calif]

Each shunt has one wire out to chassis (-)

In this diagram, for the discharge circuit, the dotted zone shows how I have the house monitor hooked up to (-)
Should the shunt be in the 'A' lead instead?

No - You need to wire it like post #14...

If you also have a shore power charger/converter it is wired in between the solar shunt and the battery shunt.

 

[IAmABug]

That's what I said in post #6 and diagramed in post #14

I don't know what happens entirely when the shunts are paralleled but it can't be accurate.

I combined Bugs schematics and I think he has this going on.

View attachment 156841

This is how it is.

I will rewire so the shunts are in series. Thanks all. I will update once it's done.

 

[Ex-Calif]

This is how it is.

I will rewire so the shunts are in series. Thanks all. I will update once it's done.

It's a minor nit but the negative for the battery monitor power should be ahead of the shunt.

As Pedro said there should only be one wire between the shunt and the battery negative terminal.

 

[Contributor]

One last note, when counting coulombs (electrons) with Lead Acid Batteries, you need to put in about 1.2 to 1.3 more than you take out for full restoration. Just the way the chemistry works. You can call these Ah or Wh, rules still applies.

 

[IAmABug]

Ok rewired the setup. My neg lead for the discharge monitor was wrong. Here are some numbers now....
Fridge
Furnace

Seems to be reading correctly. Solar still works the same

Thank you all for helping out with this.

 

[Contributor]

Good Job! Now, go down the line and measure each item as standalone and make a list. This gives you a daily budget for cold camping and warm camping.

Figure fridge is 17Ah/day, lights maybe 3 Ah/day, water pump 1Ah/day. For cold camping, figure 10 hours furnace operation at 50% duty, so maybe 15Ah day.

With 100W solar, you'll likely get about 20Ah a day typically, maybe 30Ah on a very good day. You may want to add another 100W panel for cold weather boondocking camping.

 

[IAmABug]

Good Job! Now, go down the line and measure each item as standalone and make a list. This gives you a daily budget for cold camping and warm camping.

Figure fridge is 17Ah/day, lights maybe 3 Ah/day, water pump 1Ah/day. For cold camping, figure 10 hours furnace operation at 50% duty, so maybe 15Ah day.

With 100W solar, you'll likely get about 20Ah a day typically, maybe 30Ah on a very good day. You may want to add another 100W panel for cold weather boondocking camping.

My goal is one 100w hardwired on roof and one 100w floater for when I need the extra power. Trailer doesn't have much room on the roof for many panels.

The list is a great idea.

 

[John From Detroit]

In the first diagram the shunt is shorted
Multiple shunts in the 2nd diagram means you need two monitors or a very good computer to figure it out. Only one shunt should be needed.
Wires to everything.... +(Battery)-===Shunt----Chassis ground and wires to some stuff.
I did not show the monitor but it also connects to the shunt. both sides.

 

[Lou Schneider]

I think you'd be better off having a bi-directional amp-hour meter on the battery. Since the "discharge" meter only indicates current flow in one direction you don't know how much of the solar current is going into the battery vs. how much is being directly consumed by the loads. A unidirectional meter is OK for a charging source but not for a battery where there is current flow in both directions (charge and discharge).

Here's one example of a bi-directional battery monitor. It shows the instantaneous current flowing in or out of the battery along with the cumulative amp-hours. The amp-hours increase as the battery charges, then decrease as it discharges.


https://www.amazon.com/Renogy-500A-Battery-Monitor-Programmable/dp/B07RP5B5P7

 

[Wasillaguy]

Or don't worry about it. In a short period of time you will likely cease even looking at solar numbers, unless you are into serious boondocking and/or moving around portable panels.
Watching batt volts will likely tell you all you need to know on a daily basis.
You can find a good used Fluke ac/dc clamp meter for troubleshooting for <$100 should you ever suspect a problem, and it is valuable to diagnose any circuit.