I'm working on a similar project for my boat. I think with all the little e-foil and e-bike components cheaply available and the excellent qualities of lifepo4 this is the way to go and as you noted much cheaper than a production electric outboards with proprietary connectors and heavily marked up batteries with very limited charging capabilities. Thanks for documenting it! -Alan
Thanks Jerry for describing your project so well. I would like to add some more information on LiFePO4 batteries ( I talked about this at the Port Townsend Wooden Boat Festival a few weeks ago). As you mention, there is a wide price difference between the "drop-in" batteries and this is where one needs to read the fine print on the product descriptions. The cells used are graded as Grade A , B, and C. Grade B cells may only have 1/4 the life span of Grade A cell. If the product description does not specify Grade A I would suspect that they are Grade B.
As you mentioned, the BMS is a critical part of the Li battery and the one most prone to have problems in the long run. Most of the negative comments I have found on-line talk about problems with the BMS. In addition to shutting the system down if an individual cell starts overcharging or reaches full discharge, it balances the cells. The current that shunts the charging power when one cell in the series reaches its maximum voltage before the others is usually 1000 mA or less. What I have found is that after 5-6 years of use the balancing current is no longer adequate ( I have some LiFePO4 cells in use now for 12 years!). It is important therefore to be able to monitor the voltage of each individual cell. The more expensive batteries have a bluetooth option that lets you monitor each cell as it charges. If an individual cell is out of balance enough that it does not fully charge, I use a bench top power supply and keep charging at a rate (Amps) that is lower than the balancing current of the BMS. That way I can fully charge the one or two cells that fail to fully charge.
You also mention the waterproof rating of a battery. I consider that a very important factor in my choice. Most batteries are rated to IP65, but I do not consider this adequate protection. The last sentence on the description of IP65 is "some ingress (of water) permitted." And that is under the light spray that is the rating for this level. I consider IP66 much better since it protects against water from a 3" hose at 3ft.
Finally, I have found that battery chargers that have internal fans with a grill to the outside fail very quickly in the marine environment. They also need to have an IP66 or IP67 rating. Chargers with internal fans succumb to humidity very quickly. I learned this the hard way as the ones I tried never lasted more than one year. I finally tracked down the specs on some of them and found out they are rated only to a humidity of 80-90%. However, the older tech ferro-resonant chargers from outfits like QuickCharge are pretty much bomb proof, though less efficient, and need to be special ordered for Li batteries.
Thanks for all of your comments, Tom, especially those about the grade of the cells used. It seems quite possible that "old" cells get used in the cheapest "drop-in" LFP batteries. As usual, it pays dividends to do the homework. Thanks also for pointing to QuickCharge chargers...they're new to me, and now we've all got another really useful data point from someone who's been there and is doing it.
My son did the same, bought low cost lithium batteries directly from China for his solar power bank, which cost about one quarter of what buying in the U.S. would have cost.
I'm working on a similar project for my boat. I think with all the little e-foil and e-bike components cheaply available and the excellent qualities of lifepo4 this is the way to go and as you noted much cheaper than a production electric outboards with proprietary connectors and heavily marked up batteries with very limited charging capabilities. Thanks for documenting it! -Alan
Thanks for the comment, Alan. Based on your previous exploits with CoreSounds and tris, I'm looking forward to reading more about what you're up to!
Thanks Jerry for describing your project so well. I would like to add some more information on LiFePO4 batteries ( I talked about this at the Port Townsend Wooden Boat Festival a few weeks ago). As you mention, there is a wide price difference between the "drop-in" batteries and this is where one needs to read the fine print on the product descriptions. The cells used are graded as Grade A , B, and C. Grade B cells may only have 1/4 the life span of Grade A cell. If the product description does not specify Grade A I would suspect that they are Grade B.
As you mentioned, the BMS is a critical part of the Li battery and the one most prone to have problems in the long run. Most of the negative comments I have found on-line talk about problems with the BMS. In addition to shutting the system down if an individual cell starts overcharging or reaches full discharge, it balances the cells. The current that shunts the charging power when one cell in the series reaches its maximum voltage before the others is usually 1000 mA or less. What I have found is that after 5-6 years of use the balancing current is no longer adequate ( I have some LiFePO4 cells in use now for 12 years!). It is important therefore to be able to monitor the voltage of each individual cell. The more expensive batteries have a bluetooth option that lets you monitor each cell as it charges. If an individual cell is out of balance enough that it does not fully charge, I use a bench top power supply and keep charging at a rate (Amps) that is lower than the balancing current of the BMS. That way I can fully charge the one or two cells that fail to fully charge.
You also mention the waterproof rating of a battery. I consider that a very important factor in my choice. Most batteries are rated to IP65, but I do not consider this adequate protection. The last sentence on the description of IP65 is "some ingress (of water) permitted." And that is under the light spray that is the rating for this level. I consider IP66 much better since it protects against water from a 3" hose at 3ft.
Finally, I have found that battery chargers that have internal fans with a grill to the outside fail very quickly in the marine environment. They also need to have an IP66 or IP67 rating. Chargers with internal fans succumb to humidity very quickly. I learned this the hard way as the ones I tried never lasted more than one year. I finally tracked down the specs on some of them and found out they are rated only to a humidity of 80-90%. However, the older tech ferro-resonant chargers from outfits like QuickCharge are pretty much bomb proof, though less efficient, and need to be special ordered for Li batteries.
Tom Hruby
Thanks for all of your comments, Tom, especially those about the grade of the cells used. It seems quite possible that "old" cells get used in the cheapest "drop-in" LFP batteries. As usual, it pays dividends to do the homework. Thanks also for pointing to QuickCharge chargers...they're new to me, and now we've all got another really useful data point from someone who's been there and is doing it.
My son did the same, bought low cost lithium batteries directly from China for his solar power bank, which cost about one quarter of what buying in the U.S. would have cost.