Our 12V electrical system for the camper started simple enough with a small 35Ah LiFePO4 battery from Relion. Then I added a 100W Renogy solar suitcase including a Voyager charge controller to keep the battery topped up. This has been plenty to sustain phone charging, lights, fans, and Bluetooth speakers. Then we bought a Dometic 12V cooler and we are now beginning to push the limit of our small off grid electrical system. We need to monitor the battery state of charge more accurately than ever.
How Is State of Charge Monitored?
A battery is a little like a tank of propane. It’s hard to know how much is in there but at least you could weigh the propane tank. Usually I know I’m out of propane right when the flow of propane resides and my stove goes out. Thankfully, lead acid batteries lose their oomph a little more gradually than propane and the voltage can be used as a proxy to guess the amp hours remaining in the battery. Unfortunately, lithium batteries operate in a narrow voltage range making them more like the propane tank than traditional lead acid. Still, plenty of gadgets will try to guess the State of Charge from voltage. Worse yet, voltage can vary due to charging current, load, and temperature. Guessing State of Charge from voltage is not ideal.
Returning to the propane analogy… how else might we know the state of charge? We can measure how much we put in and how much we take out. That’s what the Victron Smartshunt does for us. It gets wired directly to the negative battery terminal and via bluetooth tells the VictronConnect mobile app all about the current going in and out of our battery.
The Victron Smartshunt came with an auxiliary power wire to be connected on the positive battery terminal. I appreciated that it was complete with a fuse and ring connector. My installation also required a few inches of wire and couple ring connectors not included. These parts are not included because Victron can’t be expected to guess whether customers are pulling 500A or 5A through the Smartshunt. One customer might need 14 gauge wire while another needs 1/0.
Once the shunt was installed I installed VictronConnect on my phone and connected to the shunt via Bluetooth. I was disappointed that the Bluetooth range doesn’t reach more than 10 feet from the battery. This might be less of a problem in practical application but while it’s new I sure would like to watch the battery from the couch.
The SmartShunt monitoring app requires that you set the certain parameters like capacity of your battery, depth of discharge, charge voltage, etc. These are needed for reporting and low charge alarms. I immediately went to set these and was required to update the firmware on the SmartShunt. Neat. This took only a couple minutes.
One the shunt was updated and I had customized a few settings I began watching the current flow into my battery.
This charge voltage isn’t ideal for my lithium battery but at least I can see the shunt is working and there is current flowing into my battery. Once I feel the battery is truly at 100% charge (maybe not with this charger) I will synchronize the app to tell it as much. Remember, the Smartshunt only reads what goes in and out. It’s up to us to tell the Smartshunt when we are full and what our tolerable depth of discharge is.
I have more parts on order to add an SAE connector on my battery box. At that time this battery box with by battery, shunt, and SAE plug will be put back on the camper and I can watch my loads draw down the state of charge and my solar panel restore State of Charge. Until then Happy Camping!
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