A Repository For All That Amperage





The system

Measuring a battery at Autozone

Determining maximum cable length

Three '48 volt' strings (banks)

12.8 volt reading on one '12 volt' battery

51.2 volt reading on a '48 volt' string (bank)

I have read a lot of stuff about batteries in my search for the right ones for my situation. The usual advice is to get some good quality 6 volt flooded lead acid deep cycle batteries, as many as you can afford, but not in excess of three 48 volt strings, or something like that, and to keep your eye on the fluid level, etc.. With that configuration you get the best bang for your buck. They also say that deep cycle sealed batteries are good too but they cost more.

I had to rule out the former because that kind of setup requires constant vigilance and maintenance. Some people like maintaining batteries; I do not, but beyond that I am 3000 miles away for up to 7 months of the year. Maintenance-free is the only way to go for me.

I liked what I had read about the Optima Bluetops so I went looking for them. I found them at the local Autozone in Yucca Valley. The manager seemed to know his business and he gave me a good price for a dozen batteries.

Note in 2012: (This article was written in 2008.) Skip the Optima's for solar, though they are probably the best for vehicles.
Check the reviews and get deep cycle batteries that are made for this purpose, and get 16 of them (4 banks).


He also replaced the coincidentally dead battery in my van for free since I had bought it there a few years back (and then proceeded to abuse as described in the intro back on the main Solar page).

I bought a shelving unit at Home Depot to hold the 12 batteries, the main idea being to minimize the footprint in my small utility house. I chose plastic because it does not conduct electricity; one less thing to worry about when working with a wrench or screwdriver. I also shortened the corner risers between the shelves to minimize the height. It works okay - barely. It sags too much, and to that some might comment, "Duh!".
2012: Amen to the "Duh!". Don't get plastic; get heavy-duty steel - on wheels.

If I were to do this over I would reinforce the plastic shelving with some strips of wood screwed and glued tight underneith each shelf. I would give the risers another inch or so for better ventilation and to allow more room for my hands to get in there. Though the current risers seem sturdy, I do intend to drop some tight PVC pipe down through the hollow interlocking risers just to make sure. I would not want a riser to buckle if somebody decided to climb on it.

For each 48 volt string I connected the four batteries in series with three 12" #2 cables going from + to -, nine of them overall. I then connected the three strings in parallel, all the -'s on the left and all the +'s on the right, four 23" cables overall. The charge controller and the inverter were connected to opposite corners of the bank, two cables of the same length - each.
Now I would get four 36" cables to provide more flexibility for moving things around.

The cables to the inverter should be as short as possible to minimize line loss. I had originally placed the inverter on the wall top left of the battery bank. That put the inverter lugs 12" from the top left of the bank and 68" from the bottom right, meaning both cables would have to be 68". I then moved the inverter down with its lugs centered left of the bank. The distances then became 34" and 39" so I purchased two 40" cables.
Now I would get two 60" cables to provide more flexibility for moving things around.

Autozone did not have the correct pair of cables but they had one twice as long so I took that to a local alternator repair shop where they cut it in half and clamped on new connectors. The guy did a nice clean solid job and they work fine. However, I have since read that such cables will gradually deteriorate over time; that you have to use the factory compressed and sealed cables; custom made jobs just don't last.

Still on my to-do list is to obtain relevant 'set point' (Current Limit, Absorb, Float) specs on the Optima Bluetop D34M battery so that I can reprogram the MX60 Charge Controller for optimum interaction with same.





2012: I have replaced these with a new bank of 16 Deka AGM 12V Batteries.





Copyright © 2008, Van Blakeman