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Old 05-10-2013, 16:36   #1
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Solar Power and Battery Monitor Shunt Questions

Hi all,

I just installed my three-panel solar system (3x 175w, 24v panels, 565ah agm bank) and everything is working as it should. My only hiccup is that my battery monitor shows my batteries at 69%, while also indicating that my battery voltage is 13.8v, which is pretty damn close to full I think. My solar controller (Outback MPPT 60) shows 20-30 amps going out to the batteries, so they are getting plenty of juice. Now to my question.
I mounted the negative cable from the controller on the battery-side of the shunt for the battery monitor. Do I need to switch it to the load-side of the shunt in order for the monitor to read the incoming amps, and so the current state of charge? The monitor is a Xantrex, and both it and the solar controller have very basic installation instructions and diagrams.
I know that both systems are working, they are just not talking to each other completely.

Any help is greatly appreciated.

Cheers, Bill
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Old 05-10-2013, 16:56   #2
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Re: Solar Power and Battery Monitor Shunt Questions

If you look at the xantrex Installation guide, you notice that there is only one wire from the battery side of the shunt to the main (house)battery. My best guess is that the negative from the solar charger needs to be on the line side of the shunt. I have a Xantrex and all the house negatives go to the line side of the shunt, and only one battery cable is connected between battery side of shunt and house battery.
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Old 05-10-2013, 16:59   #3
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Re: Solar Power and Battery Monitor Shunt Questions

Yes, there should be a connection on both sides of the shunt. This allows the battery monitor to measure both the charging current (the current from your sources of current) and the discharge or load current that flows out of your batteries. The connection to the positive battery terminal allows the battery voltage to be measured. The circuits in the battery monitor make assumptions about the relative efficiency of charging and discharging currents and make a stab at the state of charge of the system.
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Old 05-10-2013, 17:22   #4
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Hi Bill
I googed your battery monitor to find the installation manual and user guide. your don't need to put the neg on the load side of the shunt, yes your monitor will show the load current - the charging current and if the cuurent charge is more will show a positive charge. But you don't need to as ypu can already see the charging current.
How long have you been charging for? My voltage goes up to 14+ volts until full then holds at 13.8
13.8 v is usually the float charge voltage after full.
Your solar charger will stop giving out current when full.
My guess is the batteries are stll charging, its takes a long time to fully charge unless on a battery charger on mains power. My batteries never get fully charged on load and I have 320 watts of solar and 400 w wind generator. Too many fridges

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Old 05-10-2013, 18:25   #5
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For the shunt to measure your solar input it has to flow through the shunt. Only the negative battery cable should be connected to one side of the shunt. All other negative cables - loads and charge - have to be connected to the other side of the shunt. This way the current will flow from the Outback+ to the battery, out the negative side of the battery, through the shunt, and back to the Outback.

The battery voltage under charge conditions says very little about the state of charge. Usually all battery monitors are set to "think" that the battery is full when over a certain voltage - usually 14+ - with the amps dropping under 2% of battery capacity. So for a 250 Ah battery this is less than 5 amps at 14+V.

13.8V at 20-30A going in is pretty empty.
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Old 05-10-2013, 19:08   #6
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Did you set the battery monitor to your size battery?
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Old 05-10-2013, 23:27   #7
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Re: Solar Power and Battery Monitor Shunt Questions

Quote:
Originally Posted by montenido View Post
Hi all,

I just installed my three-panel solar system (3x 175w, 24v panels, 565ah agm bank) and everything is working as it should. My only hiccup is that my battery monitor shows my batteries at 69%, while also indicating that my battery voltage is 13.8v, which is pretty damn close to full I think. My solar controller (Outback MPPT 60) shows 20-30 amps going out to the batteries, so they are getting plenty of juice.
When using battery voltage to estimate the state of charge the amount of current going into or out of the battery makes an enormous difference.
A battery at a constant SOC could vary from 11.5 to 14.7 V (or even more) depending on the current it was discharging or receiving.

You can adjust the estimate of the SOC based on current, battery size and temperature, but it's not a very practical technique.

There are two voltage points that do give some practical estimation of the SOC:

1. Resting battery voltage
This is when no current has gone into or out of the battery preferably for 24 hours or more. It needs to compensated for temperature, battery type and the voltage reading has to more accurate than most multimeters are capable of delivering without calibration. (There can also be some anomalous effects due to surface charge)

2. Battery return amps.
When the charging current falls to below 1-2% (so 5-10A for a 500 AHr battery) and the voltage is close to the bulk voltage (say above 14.4v for a wet cell) the battery is reasonably full (90%+). This is a good time to manually reset your battery monitor to full and have your solar regulator drop it back to float.

So a random voltage of 13.8v tells us nothing about the SOC.

If the voltage was 13.8v for a 565AHr bank when the batteries were receiving 20-30A (solar input minus load) indicates that the batteries were a long way from full (its way short of the criterion 2 above which shows a full battery) and 69% sounds about right or even a bit optimistic.


If the outback has dropped back to a float voltage check it is doing so when the above criterion 2 is reached. This indicates that the important absorption time has been set correctly. Another indicator is a 565 AHr battery bank should only be accepting in the order of 3A into the batteries when the controller drops back to float.

It should be easy to see if the shunt is reading the solar input just by looking at the battery monitor and turning the solar off and on.
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Old 06-10-2013, 08:40   #8
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Re: Solar Power and Battery Monitor Shunt Questions

You can also call Outback technical support and they will walk you thru all the setups.
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Old 06-10-2013, 09:41   #9
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Re: Solar Power and Battery Monitor Shunt Questions

Please post photos of your panel mounts and system.
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Old 06-10-2013, 09:55   #10
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Re: Solar Power and Battery Monitor Shunt Questions

What part of "ONLY ONE wire from the shunt to the battery bank!!" don't you get?
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Old 06-10-2013, 14:03   #11
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Re: Solar Power and Battery Monitor Shunt Questions

13.8v is not a full battery. that is a charging battery. 12.5-12.8 is a full battery. if you take a dead battery, and put a charger on it (or a large solar panel) it's going to read 13.8volts even though it's dead. and will continue to read that while it charges and after it's charged...


yes you need to put the solar controller neg on the load side of your xantrax shunt. not the battery side



Quote:
Originally Posted by montenido View Post
Hi all,

I just installed my three-panel solar system (3x 175w, 24v panels, 565ah agm bank) and everything is working as it should. My only hiccup is that my battery monitor shows my batteries at 69%, while also indicating that my battery voltage is 13.8v, which is pretty damn close to full I think. My solar controller (Outback MPPT 60) shows 20-30 amps going out to the batteries, so they are getting plenty of juice. Now to my question.
I mounted the negative cable from the controller on the battery-side of the shunt for the battery monitor. Do I need to switch it to the load-side of the shunt in order for the monitor to read the incoming amps, and so the current state of charge? The monitor is a Xantrex, and both it and the solar controller have very basic installation instructions and diagrams.
I know that both systems are working, they are just not talking to each other completely.

Any help is greatly appreciated.

Cheers, Bill
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Old 07-10-2013, 22:39   #12
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Re: Solar Power and Battery Monitor Shunt Questions

Hi everybody,
Thanks for the great advice. I did switch the solar negative to the other side of the shunt and all is well. Somneone asked for a couple of pictures, so I am attaching them.
Bear in mind that the wiring for the panels has not been neatened up due to some heavy winds we were having. That also explains the bungee cords on the panels.
Now that the wiring is correct, after three days with no shore power, my batteries are still fully charged. Not bad for running a 12v fridge and freezer. I am really happy if this is any indication of what I will be getting, power-wise, while on the hook.

Cheers, Bill
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Old 18-10-2013, 18:42   #13
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Re: Solar Power Update

Hi everyone,

I just wanted to update you since I unplugged my boat from shore about 2 weeks ago (it is still unplugged). In the morning my batteries show about 85-90% on the monitor. By mid-afternoon, I am at 100%, which just blows me away. I am leaving on my cruise to Mexico on the 23rd, and I am just ecstatic about how well this set up works. I'm glad I didn't go with wind power, and it looks like my Honda 2000 is going to get very little work.

Cheers, Bill
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Old 19-10-2013, 05:11   #14
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Glad to hear it. Can you give us the settings you are using on the Outback?
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Old 19-10-2013, 05:29   #15
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Re: Solar Power and Battery Monitor Shunt Questions

warning, dont use the % of charge as an indication of battery charge. Always use the voltage reading. % of charge is calculated from amps in/amps out a coefficient #
After a few days of not plugging in it can be way off. Hopefully yours is calibrated closely.
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