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Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are

Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are they just difficult to get?

elihu 6y ago
The batteries cost me about six thousand dollars. Lithium iron phosphate is generally recommended for conversions because they're about as safe as you can reasonably expect a battery to be and tolerant of abuse. Used tesla packs have much higher energy density and are actually reasonably inexpensive, but I couldn't really figure out how to make them work in my setup. They're awkwardly long and don't really fit where I wanted to put them, and need liquid cooling. They're also quite a bit more dangerous if they're damaged or catch on fire, which is unlikely in a vehicle carefully designed to protect them but considerably more likely in conversion. So I went with the simpler, safer option. LG Chem has some pretty good batteries as well, but I would have needed multiple series groups connected in parallel, which would have required a pretty complicated battery management system to keep everything balanced.
- phaedrus 6y ago
  I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago for powering a dual motor e-bike project. I ended up also using it to power a mobile robot (rover) project, and sometimes used it for emergency power during blackouts. I went with lithium iron phosphate because it was perceived safer and more durable. Over the past ten years when it wasn't bouncing around inside a rover or e-bike it spent months or years on a shelf when I forgot about it. Most recently I've dusted it back off and use it to power a large shop fan. Because of it's long storage and infrequent charging/balancing the subset of cells that actually power the microcontroller in the BMS were alarmingly low compared to the others, but after a few cycles it seems to have recovered and all but one of the low cells has balanced to the others. The battery still seems to perform well overall.

Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are they just difficult to get?

elihu 6y ago

The batteries cost me about six thousand dollars. Lithium iron phosphate is generally recommended for conversions because they're about as safe as you can reasonably expect a battery to be and tolerant of abuse. Used tesla packs have much higher energy density and are actually reasonably inexpensive, but I couldn't really figure out how to make them work in my setup. They're awkwardly long and don't really fit where I wanted to put them, and need liquid cooling. They're also quite a bit more dangerous if they're damaged or catch on fire, which is unlikely in a vehicle carefully designed to protect them but considerably more likely in conversion. So I went with the simpler, safer option. LG Chem has some pretty good batteries as well, but I would have needed multiple series groups connected in parallel, which would have required a pretty complicated battery management system to keep everything balanced.

phaedrus 6y ago
I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago for powering a dual motor e-bike project. I ended up also using it to power a mobile robot (rover) project, and sometimes used it for emergency power during blackouts. I went with lithium iron phosphate because it was perceived safer and more durable. Over the past ten years when it wasn't bouncing around inside a rover or e-bike it spent months or years on a shelf when I forgot about it. Most recently I've dusted it back off and use it to power a large shop fan. Because of it's long storage and infrequent charging/balancing the subset of cells that actually power the microcontroller in the BMS were alarmingly low compared to the others, but after a few cycles it seems to have recovered and all but one of the low cells has balanced to the others. The battery still seems to perform well overall.