I’m running a 2014 caravan with 400W of solar panel, a SmartSolar MPPT 100/30 charger and two 100AH AGM batteries in parallel. One of the batteries is permanently installed for shorter excursions, one is removable and added in externally via an Anderson plug for longer duration trips off grid and is not always attached . I want to individually monitor the two batteries in conjunction with the solar charger - should I use a SmartShunt for each or a battery monitor like a Smart Battery Sense for each?
Whichever device is used it needs to not get confused between the single and the twin battery set-up. Would a SmartShunt work across the overall 12V rails then have a SmartSense on each battery? Would the SmartShunt get confused when the “size” of the battery bank changes when one is removed or added?
Seems like an odd use-case. A SmartShunt normally goes between the negative battery lead and the system negative (which might be the chassis of the caravan).
To connect the batteries in parallel, you’d have to charge them both up to the same voltage before connecting. If you have a single SmartShunt, then you could change the Ah capacity of the system once the second battery is attached. That way, you’d have accurate State of Charge for the combined pair, which is probably more useful. Then when you remove the second battery later, just change the Ah capacity of the system, and it will relearn the SOC.
Trying to do 2 SmartShunts on 2 separate batteries will just lead to confusion, especially since they are acting as one big battery. e.g. there is no such thing as an isolator that keeps them separate for measurement, yet combines the, for current and combines them for charging. Otherwise you’d need to treat them as 2 separate isolated systems, and would need 2 solar chargers, and a way to combine outputs (1,2, 1+2) if needed, provided voltages are same when combined.
Yes - appreciate that this is probably the wrong way to use these devices. What if I ditch the SmartShunts and just have a smart sense on each battery? Would each one still think its connected to the complete system rather than the individual battery? I suspect the answer is yes. I’m trying to avoid having to change settings each time but understand that this may be the only way to stop the devices giving weird readings at each battery addition or subtraction.
A smartsense only registers voltage and temperature, it does not give state of charge (SOC). As the batteries will be in parallel thry have the same voltage so only 1 Smartsense required.
If you want dual SmartShunts to monitor the batteries individually then see the attached scheme for wiring them up. Option 1 keeps the removable battery SmartShunt with the battery so if it is used or charged when removed then it know about this. Option 2 leaves it in the Caravan so the removable SmartShunt may not be correct when refitting the battery. For both options the fixed battery SmartShunt keeps proper track of that battery. You do not need to keep them independent with separate charge controllers. If you connect the removable battery with a difference in voltage to the fixed battery both SmartShunts will show current flowing to balance the batteries.
@pwfarnell What’s going to happen with the SmartSolar MPPT 100/30 in the two options you present? How will it know what SOC is? e.g. do you bluetooth smart network it just to one SmartShunt? Or not network it at all?
The SmartSolar does not use SOC at all in its workings, it only works off Voltage. The only thing you need to watch out for is if you try and use a VE Smart Network to supply battery voltage from the SmartShunt, if you do only link the fixed battery SmartShunt.
