One of the biggest problems of off grid energy is getting batteries to work together. You cannot mix different types of batteries, old and new batteries, or batteries of different capacities. The Magnum Energy ME-SBC Smart Battery Combiner easily solves this problem for not a lot of money.
When I was given two barely-used AGM deep cycle batteries, I set out to find a way to incorporate them into my existing flooded battery string. There are various setups using ordinary DC switches, but they tend to be tedious and require constant manual intervention. My search ended happily with the Magnum Energy ME-SBC Smart Battery Combiner.
The basic purpose of the ME-SBC is to combine two batteries or strings of batteries to a single charging source without having a straight wired connection between them. This avoids the issue of dissimilar batteries messing each other up.
Wire the positive of the main battery or battery string to one input of the ME-SBC, and the auxiliary battery or battery string to other input. The two inputs do not have to be the same type or number of batteries as long as the voltages are within spec. The negative is common. You connect the load to the main battery as normal. Adjust the settings on the front faceplate for the desired cut in/cut out voltages, and that’s it. You now have safely combined batteries. The ME-SBC is a “set and forget” system. The MOSFET controlled gate will send DC current between the batteries according to your dial settings.
A series of three LED lights gives a clear indication of what the device is doing. The ME-SBC will pass a maximum current of 25 amps and can work with 12 or 24 volt systems. The documentation does not specify if the 25 amp limit goes down to 12.5 amps when operating on 24 volts but there is a built-in option to make the combiner activate an external solenoid or relay if you want to exceed the internal current limit. My gut says this thing cannot by itself handle 600 watts, which is what you would have when pushing 25 amps at 24 volts. Without a clarification from Magnum Energy tech support, I strongly suggest using the solenoid/relay feature if you expect to go above 12.5 amps on a 24 volt system.
A handy feature on the ME-SBC is the “Remote Voltage Sense” input. It allows the combiner to reference voltage at the actual charge source. This avoids the problem of the device detecting voltage drops either internally or from one of the individual batteries and cycling on and off unnecessarily. It is not needed for operation but since it requires only one single wire run there is no good reason not to take advantage of it.
The ME-SBC includes a very well written manual with clear diagrams (also available on line here) for all the various configurations, including how to connect a solenoid/relay. It has a small footprint of 4.2”h x 5.4”w x 1.4”d (10.67cm x 13.72cm x 3.56cm). Installation difficulty is moderate. Anyone who got far enough to set up their own off grid battery system should also have enough skills to add this accessory.
The biggest disadvantage of the ME-SBC, and it’s not a serious disadvantage, is that you cannot connect a load directly to the auxiliary battery. The device is not designed to power anything; it only allows batteries to charge off each other. This still effectively allows you full use of both batteries, but the distinction is important to understand.
The other disadvantage is that the although the ME-SBC is well proven technology, it is nonetheless an electronic device that adds an additional layer of complexity and point of failure to your system. Off grid hams, preppers, and survivalists place a high premium on reliability over the very valid concern that spare parts for repairs may not be available. If this device breaks down, you will not be totally dead but you will lose all the capacity of the auxiliary battery.
I found a simple, low-tech way around this problem: I installed the ME-SBC for everyday use but keep a manually operated single pole, double throw (SPDT) DC switch in my supplies stash. If the combiner fails during a “shit hits the fan” (SHTF) scenario where there are no UPS trucks delivering replacement parts, I can quickly remove the combiner and install the switch in its place. At that point, I am committing to monitoring voltages myself and switching the charge on and off by hand. Perhaps in a future article I’ll detail how to do this.
PROS: Far easier and safer than manual switches. Adds a great deal of flexibility to off grid systems. Allows mixing different types of batteries.
CONS: Creates a point of failure that may concern off gridders, preppers, and survivalists. Requires above average skills to install.
The bottom line: The Magnum Energy ME-SBC Smart Battery Combiner provides an easy solution to a tricky problem. Dissimilar batteries will work well together without having to sweat the details. Highly recommended.
$119.20 at Northern Arizona Wind & Sun.