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diy solar

Battery Monitor funtionality

dmurphy48

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Feb 1, 2021
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I bought one of the $30 AiLi battery monitors off of Amazon and am hooking it up in my RV. I have 200w of Renogy Solar with a 20a charge controller and a 700w inverter all hooked to a 100ah LiPO4 battery. The P- side of the shunt is hooked to my negative cable from the inverter and my negative to the solar controller. The B- is hooked up to the battery negative terminal. I have the monitor shunt hooked up so it can read amps in from the solar and out of the inverter (I did not wire my inverter into the RV system). My question pertains to how the monitor figures out the AH remaining measurement. Does it just mathematically calculate from the measured amps out and subtract from your full battery setting value or does it actually know the AH remaining through a measurement. I am asking because I would like to know if this set up will actually tell me AH remaining if it is not hooked up to my RV system beyond being connected to the battery. When I ran the interior lights and the slide it didn't seem to change the AMP reading on the monitor so I am now assuming my AH measurement may not be worth anything and I just wasted my time setting this up. Should I also add the negative cable from the RV and instead of going to the battery go to the P- side of the shunt? Not sure I can fit another terminal on the shunt but I could try.
 
(+) BATTERY (-) BMS (-) SHUNT (-) -------------> all loads and sources (12V RV, inverter, SCC)

Anything mounted to the left of the shunt doesn't get counted.

If you can't fit it, you can get a bus bar.
 
I too am connecting an AiLi Battery monitor to my system. I am a bit confused. Do I connect the negative leads from my charge controller, Inverter and DC Fuse block to the P- on the shunt and only the B- has a connection to the negative post on the battery?
Or, do I connect the negative leads from my charge controller to the negative post on the battery and only the Inverter and Fuse block have negative leads connected to the P- on the shunt?

Solar Power Diagram Alternative.png
Solar Power Diagram.png
 
. Do I connect the negative leads from my charge controller, Inverter and DC Fuse block to the P- on the shunt and only the B- has a connection to the negative post on the battery?
Yes, the only connection to the battery negative is the B- of the shunt. All other connections to the P-, ( or a negative buss bar connected to P-). This includes the negative cables for the solar controller, inverter and fuse block.
For improved safety all cables connected to the battery positive need fuses or breakers suitably rated to protect the cables that feed the controller, inverter, monitor and fuse block. The position of these protective devices should be as near the battery positive as practical. A battery positive buss bar would help.

You only need a single fuse in the connections to the solar controller in the positive path, 30A for the panel input and 70A on the feed from the battery positive.
A 1A inline fuse to feed the Aili shunt positive, and a fuse for the inverter, 300A seems about right , note the maximum continuous discharge current of the battery is 200A.
The fuse feeding the fuse block will depend on the rated current of the fuse block, the loads connected and the current rating of the cable, typically this will be in the 30A to 50A range.

Mike
 
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Yes, the only connection to the battery negative is the B- of the shunt. All other connections to the P-, ( or a negative buss bar connected to P-). This includes the negative cables for the solar controller, inverter and fuse block.
For improved safety all cables connected to the battery positive need fuses or breakers suitably rated to protect the cables that feed the controller, inverter, monitor and fuse block. The position of these protective devices should be as near the battery positive as practical. A battery positive buss bar would help.

You only need a single fuse in the connections to the solar controller in the positive path, 30A for the panel input and 70A on the feed from the battery positive.
A 1A inline fuse to feed the Aili shunt positive, and a fuse for the inverter, 300A seems about right , note the maximum continuous discharge current of the battery is 200A.
The fuse feeding the fuse block will depend on the rated current of the fuse block, the loads connected and the current rating of the cable, typically this will be in the 30A to 50A range.

Mike
Thank-you Mike.
I realized that the Circuit Breakers I have are designed for audio applications and indicate that they are for 12 or 24 volt applications. With a Voc of 50 is this going to be a problem using these on the PV side? Maybe I need to look elsewhere, but Amazon seems to only have fuses or circuit breakers for up to 36VDC rating.
 
Midnite solar has a range of 150VDC breakers at about $15 each.
Thank-you. Seems like it would be a problem if either the breaker from the SCC to the battery tripped or if the fuse ot the + lead of the battery to the rest of the system blew but the breaker on the PV in of the SCC did not. Am I missing something? seems like having these two power interrupt devices would be a bad thing to have installed. Breakers or fuses to the inverter, DC distribution block, or power to the battery monitor are good practice. Not sure about the others. I know I have them in my drawings above but I am rethinking those now.
 
Thank-you. Seems like it would be a problem if either the breaker from the SCC to the battery tripped or if the fuse ot the + lead of the battery to the rest of the system blew but the breaker on the PV in of the SCC did not. Am I missing something? seems like having these two power interrupt devices would be a bad thing to have installed. Breakers or fuses to the inverter, DC distribution block, or power to the battery monitor are good practice. Not sure about the others. I know I have them in my drawings above but I am rethinking those now.
The protective device is to prevent excess current from the power source, the battery, overloading the cable and whatever is attached to the cable, and causing fire, in the event of a fault of component failure.
Having fuses in the feed from a simple two panel array to the solar controller is not necessary, there is not enough power to cause fuse failure. A breaker or isolator in this feed may be useful for maintenence and commissioning. Most solar controllers tolerate loosing battery power with solar power still applied without damage, but may require reconnection to the battery without solar input to enable correct settings.

Mike
 
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