I finally got the BMS and I’ve hooked up all of the batteries. I’ve even done a few impromu equipment safety tests.

The lowest my BMS will allow a cell to go is 2.45. This isn’t ideal as it is lower then 2.6. A second test and it went to 2.55. Whatever the case may be, I’d prefer my BMS never allow a battery to get to 2.60 volts on the low end. I’ll be looking for a different one, but for the budget this one will do okay. I just fear that it will greatly harm the lifespan. It also allows the batteries to get slightly over the recommended charging voltage. So far I’ve seen 3.68. Again, not dramatic, but I’d prefer if we never went above 3.60 volts. This BMS doesn’t balance unless it is between 3.60-3.65 from what I gather from reading. So long as we don’t get much higher I’m not that worried.

After assuring myself that the battery won’t be seriously harmed with the BMS on duty I decided to do a capacity test. Keep in mind the pack wasn’t 100% charged and even though my meter says it is 13.33 volts, the pack voltage was in the 44-46v range. The specific issue here is that the BMS is dropping power. The voltage is actually coming from a capacitor in something else on the circuit.

Speaking of capacitors. I was tired when the battery first failed. Thinking the BMS was going to kill my battery I decided to bottom balance the cells. This means that at the top of the charging cycle the BMS will be cutting back power. The line of reasoning was that I would find out what is near the top (the highest cell approaching 3.50 volts) and I would take a few bits off of that to keep everything safe. I never actually did this. While doing that though I got confused. The black terminal ring is positive, not negative. My sleep deprived mind decided it should be ground and all the capacitors decided to jump into action….

Casulaties include:

  • My pride
  • My phone screen which caught a section of molten copper and it melted and cracked the screen.
  • A section of skin on my finger (toasty, and painful but not much worse)
  • A piece of molten copper was caught by my foot.

On the brighter side of things, I’ve reached a new record with my solar array.

That’s right folks 1.47kWh coming in!

It hasn’t stopped being cloudy here and I’ve been struggling to get 3kWh of power stored every night. I have noticed I use between 2-3kWh of power running my AC. This is with it on “Eco” mode, and with everything “pre chilled” by running both AC’s on maximum while driving to my sleeping spot.

In order to have some reserves I’m seriously contemplating ordering another battery. I may get the same capacity of 4.4kWh for $1,000. I’ve also found another one that is 6.1kWh for $1470. Not only is it a better deal I can get them wholesale. I’ve been seriously thinking of offering a pack building service using my ability to find good deals. While most people wouldn’t want such a huge pack I’m thinking slightly smaller pack sizes if the quality of them is as good or better then what I’m currently using. 🙂

So far to date the following is the total “AC” expense list:

  • $1,000 4.4kWh lifepo4 pack
  • $40 16s Lifepo4 BMS
  • $785 Victron 150/100
  • $150 Walmart Window AC
  • $700 1.3kW Solar array
  • $250 3,000W Inverter
  • $330 Victron 100/50
  • $1400 Previously purchased 12v battery pack~ 1.8kWh (Currently in use)
  • $500 – Wires, connectors, etc. (yes, seriously)

I’ve just recently purchased a DC-DC charging solution using an MPPT/DC-DC boost converter. I’ll use that to charge the 48V side from the alternator. It looks like 600watts max each, so that is 1.2kWh assuming I can and decide to pull that from my alternator. More likely I’ll set it to something more reasonable to keep it on the safer side of things. They were about $50 each. I still need to purchase a $250 48V Inverter, and the BMS I’d like to try next is $130.

This post is so I can point to people who MUST have AC, now they can get a quick look at what it takes. I’m still building my system so more work is required.

Usage notes:

I can only run my AC for 8-10 hours at night. That is it. During the day I can run it as long as the sun is shining, but if I don’t get enough sunlight I wouldn’t be able to run it later that night! I’m still waiting on good sun to see exactly where this level is. I’ve had these batteries for a week now and I’ve yet to have a full sun day to charge them. With the 12v pack I was able to run the AC on high and keep them charged for a good portion of the day, but there were sections I was missing.

Sorry for the scrambled writeup. This is just a “Real quick in the moment” type of post. I plan to do a better job later documenting what I have, what it is like and what one can expect of it. 🙂

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