I live at the end of 8 miles of dirt road, and that'show far away the nearest utility line is. This December, my four-year-old Deka GC-15 12V 230Ahbattery bank wasn't cutting it near the solstice, and I looked at my options, determined not to be in the dark next winter.
For starters,I upgraded from the Morningstar TS-45 (PWM)without the optional RTS, which I never bought, becauseof themismatchbetween the two24V GT panels and the 12Vbattery bank,to the TS-MPPT-60 with RTS and remote Battery Sense. I figure the Lead Weight could last a few months or even more than a year, but even withthe new charge controller assembly, it's obvious that it's days are numbered.
When I asked my sister's boyfriend for some feedback about my strategy, he suggested a DIY powerwall and offered that he knows someone who could get me salvaged 18650s at no cost. I wasn't comfortable with using used laptop batteries, due to both the chemistryand the headache of matching used cells. After doing some digging, learning everything that I could about LiFePO4 and finding some discounted new, old stock,5500mAh 32650 cells from a liquidation company on ebay, I decided to go for it.
UPS was very confused about my address, because it wasn't in their system, so after the packages had been in town for almost two days, I drove through the mud to pick up the 320 cells in town.
The battery bank will be 72p4s until I get around to shopping for a 24V inverter, at which point I'll rewire it for 36p8s.
I've tested a sample of cells for capacity individually and in parallel, and I'm pleased with the results. I'm going to run one more capacity test at C/20, to confirm a theory that I have about the Peukert exponent of these cells vs. their rated capacity.After I run to town for some hardware and order fuses and contacts, itwill then be time to put it together.
I'll use the Lead Weight as a buffer for the Powerlab 8. I could charge directly from the TS-MPPT-60. However, sunlight isn't constant, and since I already have the Powerlab for testing the cells, I might as well use it for charging.
I have tested the electrical contact resistance of Keystone Electronics 1016-1 gold-plated battery contacts in my test bed, and I'm comfortable that the resistance can be balanced well enough to use them for the battery assembly. Having removable cells will make me more comfortable, by making it easier to tinker with the battery.
Here's my 10p test rig.
This photo shows the balanced parallel wiring, which is something that I haven't seen or discussed regarding DIY battery packs.
The battery bank will be wired for at least 125A. I'm going to experiment with a mostly solderless assembly, because sordering almost 600 battery contacts to bus bars doesn't sound like fun to me. It will have fuses onindividual cells, parallel modules and the pack. It will also have a Trimetric TM-2030 battery monitor to monitor the charge. I bought the TM-2030 when I bought the TS-MPPT-60, so I already have that, too.
I only use about 30Ah at 12V daily and don't have any high-power electric appliances, so I'm considering charging the battery intermittently and using the solar power for other things, such as a hot water heater.
When I was shopping for the new charge controller, I didn't imagine that I would be building anything like this, but I'm very excited about it.
For starters,I upgraded from the Morningstar TS-45 (PWM)without the optional RTS, which I never bought, becauseof themismatchbetween the two24V GT panels and the 12Vbattery bank,to the TS-MPPT-60 with RTS and remote Battery Sense. I figure the Lead Weight could last a few months or even more than a year, but even withthe new charge controller assembly, it's obvious that it's days are numbered.
When I asked my sister's boyfriend for some feedback about my strategy, he suggested a DIY powerwall and offered that he knows someone who could get me salvaged 18650s at no cost. I wasn't comfortable with using used laptop batteries, due to both the chemistryand the headache of matching used cells. After doing some digging, learning everything that I could about LiFePO4 and finding some discounted new, old stock,5500mAh 32650 cells from a liquidation company on ebay, I decided to go for it.
UPS was very confused about my address, because it wasn't in their system, so after the packages had been in town for almost two days, I drove through the mud to pick up the 320 cells in town.
The battery bank will be 72p4s until I get around to shopping for a 24V inverter, at which point I'll rewire it for 36p8s.
I've tested a sample of cells for capacity individually and in parallel, and I'm pleased with the results. I'm going to run one more capacity test at C/20, to confirm a theory that I have about the Peukert exponent of these cells vs. their rated capacity.After I run to town for some hardware and order fuses and contacts, itwill then be time to put it together.
I'll use the Lead Weight as a buffer for the Powerlab 8. I could charge directly from the TS-MPPT-60. However, sunlight isn't constant, and since I already have the Powerlab for testing the cells, I might as well use it for charging.
I have tested the electrical contact resistance of Keystone Electronics 1016-1 gold-plated battery contacts in my test bed, and I'm comfortable that the resistance can be balanced well enough to use them for the battery assembly. Having removable cells will make me more comfortable, by making it easier to tinker with the battery.
Here's my 10p test rig.
This photo shows the balanced parallel wiring, which is something that I haven't seen or discussed regarding DIY battery packs.
The battery bank will be wired for at least 125A. I'm going to experiment with a mostly solderless assembly, because sordering almost 600 battery contacts to bus bars doesn't sound like fun to me. It will have fuses onindividual cells, parallel modules and the pack. It will also have a Trimetric TM-2030 battery monitor to monitor the charge. I bought the TM-2030 when I bought the TS-MPPT-60, so I already have that, too.
I only use about 30Ah at 12V daily and don't have any high-power electric appliances, so I'm considering charging the battery intermittently and using the solar power for other things, such as a hot water heater.
When I was shopping for the new charge controller, I didn't imagine that I would be building anything like this, but I'm very excited about it.