Battery Upgrade for the LittleHouse
Over the past year or so, our batteries for the solar power system have been deteriorating. This winter, I replaced just one of the eight 6 volt lead-acid batteries, in the hopes that it would improve operation until I could apply a fix in the spring.
It worked for a while, but then other batteries in the string began losing their capacity to the point of the system going down nearly every day for a few hours before the sun rises each morning.
I decided to bite the bullet and install a whole new string of batteries.
On researching, it appeared that it would make sense to replace the old lead-acid battery technology with newer Lithium Iron Phosphate technology. Not only are the new batteries considerably more compact and lightweight for a given capacity, they should also last much longer and require little maintenance.
I decided the replace the eight batteries comprising the 48 volt, 200 amp hour lead acid string with two Lithium Iron battery packs of 100 amp hours each. This matches the nameplate ratings of the existing system, while in reality nearly doubling my usable capacity.
You see, while it is inadvisable to discharge a lead acid pack lower than 50% (100 amp hours in my case), the LifePo4 batteries may be discharged over 7000 times to 20% capacity (a discharge of 160 amp hours) without adversely affecting the packs. That's nearly 20 years of very hard discharge/charge every single day without damage. They are rated to still have 80% of their initial capacity after that time.
In our case, we very lightly discharge our system from day to day. Only about 20 - 30 amp hours each day. Under this type of use, I would expect these batteries to last the rest of our lives at the ranch (27 years, if I live to be 100!)
So, I ordered the batteries from Signature Solar in Texas. They arrived a few days later by freight. It cost about $200 to ship them to our door in Mesa. They weigh 200 pounds for the two packs.
They are rack mounted 48 volt Server Batteries, meant for the computer industry. It is reported that these work very well in off-grid solar power systems.
After receiving the packs, I powered them up and hooked up the included RS-485 cable adapter from the packs to my laptop computer. I was able to run the diagnostic program and check their operation on thew floor of my house, before hauling them up to the LittleHouse for installation.
I also developed a controller to turn off and turn on my old inverter at the LittleHouse at appropriate voltage levels. Because this old inverter was developed before the newer battery technologies available now, it had different low voltage cutoff and restore voltages that were not compatible with the new batteries. This converter solves that problem.
I could have paid the $400 for a programming box from Outback to change the parameters as needed, but my little controller cost about $100 and provides additional functionality. In addition to controlling my inverter cutoff, it also reports the battery status back to one of my computers in Mesa every 30 seconds. I can then display the state of the batteries on my computer screen 200 miles south of the LittleHouse.
The first step of the battery upgrade was to remove all of the old batteries from the battery box.
Once this was done, I spent the rest of the day cutting and installing foam insulation inside the box. One of the disadvantages of the new technology batteries is that they do not allow charging at a temperature below freezing. It is hoped that with the new insulation, I will be able to add a very small thermostatically controlled heater to the box to keep the temperature in a comfortable range. I also hope that this will take little energy, as the box is very well insulated.
Once the insulation was in, I set the battery packs inside, and wired them in. I was hoping to be able to reuse the existing wiring, and was able to do so, but I need to get one longer cable on the negative lead from the battery on the left, and one longer cable on the positive feed to the fuse. I will order these and get them installed in the next few months.
I had a problem with getting the stainless steel nuts off of the fuse holder on the left. It was galled, and messed up the threads. So I attached the cable straight over the fuse, rather than beside it. I don't think it will hurt anything.
Next, it was time to tackle the battery monitoring system. You can see from the before picture, that I have a home-built fan controller on the left side, being fed from a 12 volt wall wart next to it. That wall wart was replaced with a 12 volt supply that works straight off of the 48 volt batteries, so that my circuit will still work, even when the inverter is turned off.
I mounted the 48 volt -to 12 volt converter, the Junctek Battery Monitor and the 400 amp shunt to read current into and out of the batteries.
On the other side of the charge controller, I mounted the Inverter Cutoff/battery status monitoring control that I constructed down in Mesa.
I then ran a communication line into the LittleHouse, so that I could mount the display unit for the Battery Monitor. The picture below shows the unit temporarily mounted, but not full programmed yet.
After programming (changing settings) on the battery monitor, I set about linking it up to the computer in Mesa, via the internet. That went well, and soon it was happily talking.
I made a display in Mesa to show on my computer, the state of the batteries, updated every 30 seconds.
You can see the details of developing the inverter cutoff controller at my ham radio blog: www.wb0smx.net
That's about all for now. I'll post again in a few months to report on how it is working out.