I have a Super C motorhome with the Detroit diesel in it. I have 86V coach batteries that are tied together in series as well as parallel. However, I do not know how to charge these batteries up as they sat and went dead. Do I put a 6V, 12V, or 48V charger on? What is the best way to charge these eight batteries? Thank you, and please get back to me. —Phil, Super C motorhome (no other info provided)
Most likely you meant that you have eight 6-volt deep cycle batteries (86V) in your rig. That should not be 86 volts, rather they’re wired in series and then parallel to provide 12 volts, but four times the amp hours. Here is a similar battery bank with four 6-volt batteries. Two are wired in series which is positive to negative and that provides a 12-volt “bank”. The other two are wired the same way, so there are two 12-volt banks that are then wired parallel, which is positive to negative, and that keeps it 12 volts but doubles the amp hours.
In your case, you would have the other four wired the same, two 6-volts in series and then all four banks wired parallel. Typically a 6-volt battery has 230 amp hours, so when they are wired in series, it doubles the voltage to 12 volts but does not double the amp hours. Therefore, each “bank” would have 230 amp hours. When they are wired parallel, it doubles the amp hours, so 230 x 4 = 920 amp hours.
If you were to put a multimeter on any positive and negative post on any of the batteries you should see 12.6 volts if they are fully charged.
How to charge 6-volt batteries
Your rig will either have a converter that is part of the distribution center or, most likely, a large inverter/charger. That not only powers some of the 120-volt components using the house batteries and inverting the 12-volt power to 120-volts, but also charges the batteries with a multi-stage charger. Without knowing the make, model, and year of your motorhome, I cannot determine which charging system you have. However, either will charge the batteries when you are connected to shoreline power or running the generator.
You can also use a multimeter to verify by this placing the probes on the same posts as described before. With the shoreline cord connected, you should see at least 13.2-volts if the batteries are fully charged, as this is the maintenance charge provided by the converter or inverter/charger.
If the batteries are low, you will initially see at least 13.6 volts or much higher if you have the inverter/charger, which would start with a high voltage “bulk stage” charge that could be as high as 16 volts! It would then go into an equalizing charge, and finally a float charge. This is designed to break up sulfation that forms on the plates of flooded lead acid batteries and then equalize all the cells, all of which extends the life of the batteries. This charge could take up to eight hours or longer.
If you want to use an auxiliary charger, it would need to be a 12-volt charger connected to the positive and negative post of one battery, which will charge all the batteries as they are connected, as previously described.
You might also enjoy this from Dave
What is the best option to connect six 6-volt batteries for RV?
I wonder about the best way to configure six 6-volt batteries. I have the traditional method of connecting two 6-volt batteries in series and then connecting them parallel to two additional pairs. But I wonder about the option of connecting the first three batteries in parallel and a second set in series. Does either setup provide a better, stronger, or longer-lasting power supply, or do both configurations yield identical results? —Colin
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
Read more from Dave here.
HAVE A QUESTION FOR DAVE?
Send your inquiries to him using the form below.