After having my brand new Optima Yellow Top truck batteries die twice over the winter, I made a few changes to my charging system. Turns out that I have a small parasitic draw (will track that down once the weather warms up) in the truck that will kill the truck batteries in a week or so. So, I need to be able to charge the truck batteries from the solar system on the camper to prevent this.
What I did was add heaters for the batteries so they can be charged when it is -30*C out, and I am using both the ACR and DCDC charger. The point being to be able to charge the 200AH BattleBorn battery bank, and keep my truck batteries charged too.
Let’s talk about using BOTH the Victron Orion 30A DCDC charger and a BlueSea ACR at the same time. I used to think this wouldn’t work, and it doesn’t, and it does. The input from the truck is fed via 2AWG welding cables protected by 100A breakers, so LOTS of juice can flow over those wires if needed. The DCDC limits charging current to 30A, which is generally a good thing; however, the current only flows one way, from the truck into the camper. The advantage of the ACR or battery isolator device is that it keeps both systems connected when charge is available and disconnects them when either is severely draining the other.
To use both, I simply manually connected them in parallel. The ACR I have is the BlueSea ML-7622 with remote switch. This device can be manually locked ON or OFF, or left to run automatically. I am testing it out in manual mode. So it is essentially a fancy 500A rated battery switch. With the ACR switched OFF, it is no longer in the current path, so the DCDC works as usual. With is switched ON, the ACR allows current to flow both ways.
We haven’t finished with the details/and gotcha’s of doing this, but let’s look at the battery heaters for a moment. I used two heating pads (10A draw/ea) designed for 3D printers and glued those to a sheet of ¼” aluminum that fits under both 100AH BB batteries. Those can get the aluminum VERY hot, so I use a 40*C thermistor to turn off the current flow to the heaters when it gets too hot. I can touch the surface without hurting myself, so I figure the battery cases are fine too. The current to the heaters is controlled by the Victron BMV 712’s “Relay” function, which in turn fires up a 40A relay for the heaters. This Relay function is very powerful. I set mine to turn the heaters on when the temperature falls to +5*C, and off at +10*C. The batteries are in an unsealed enclosure, so the air can warm up in there nicely. But not when it is -30*C out. Add in night time, and the batteries can drain pretty quickly. 12 hours of darkness at 20A and I am potentially pulling 240AH… out of a 200AH battery? Nope. Luckily they don’t have to run for 12 hours, but close enough that over 2-3 days the batteries would be totally discharged. Not good.
To compensate on super cold days, I plug the camper in to shore power, and that keeps the camper batteries topped up… But on “Spring” days like today, where the temperature is fluctuating around 0*C a dozen degrees or so, the batteries stay warm and the 330W solar panel can do its thing.
How does that work? Well, the solar panels charge the camper batteries to 100% by mid afternoon, and then all night long the camper batteries keep themselves warm and because LiFePo4 batteries rest at around 13.4V, they are trickle charging the truck’s AGM batteries (which rest at 12.7V) all night/day long.
Truck starts every time now, no more dead starting batteries!
Downsides/gotchas? I have to remember to switch OFF the ACR when driving, because I have yet to measure how much current the BB batteries will take from the alternator. It could be too much for both the batteries and for the alternator. I have a BlueSea Ammeter that I will be installing to check that.
The DCDC seems to get confused by the voltages it is seeing on the input/output and is actually running while the ACR is on. Having a double pole switch and actually removing the DCDC from the circuit instead of having it in parallel with the ACR would be better, but it doesn’t seem to be hurting anything.
When I have the ammeter and the ACR remote switch mounted in the cab of the truck, I’ll be able to control things more closely. In the meantime, I am happy with the results.
