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.
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
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.
Wow you are really coming along with this. I must have missed part 2. after doing two of these, i found that getting the full speed amps dialed in requires replacing the prop with less pitch to prevent overheating or to increase the pitch to get more amps and power. My 3.5 Nissan needed a bigger prop from a Yamaha 8 to get nearly rated power out of my 1000W 36v motor. the evinrude fisherman 6 needs a flatter prop. right now the 1000 W motors is pulling 44 Amps at 48 volts. It gets hot pretty fast. muffin fan has no chance to cool it. My motors are rated at 3000 RPM. A guy on youtube,
"emily and clark's adventure" does a really good job testing and reviewing batteries. I am building the Evinrude with a High School class and essentially took the summer off. If I can find a nice flat prop for it, We will test again. Otherwise we will need to build a reduction system with little timing belts.
I haven't had any overheating issues...yet! But then again I'm not running at my motor's max rated power. Operating at the highest voltage that you can is going to reduce the current (at a given power level)...and heating. My motor has enough thermal mass that it takes a while to heat up, and a long time to cool down using fan cooling. So I can see some advantages from re-installing the impeller and trying water cooling -- if temperature does become a problem. I've been using the prop that came with the motor; I'm going to (hopefully) test one with a bigger diameter and see what the difference (if any) is. More data is coming in the next project installment.
You got the brushless motor that i wanted for the high school class, but was too worried about controlling a brushless. I read that you can't just throw X amount of volts at them and have them run like a brushed motor. I use a PWM controller for speed control, but in a pinch i could just hot wire it and go full voltage and turn it on and off with a switch to get home or off the rocks. I have never had any heating with the tohatsu based setup with the 1000W 36V motor, but to get 20 amps, i needed to increase the load with a larger prop than standard. It now pushes my 3000 lb full keel Bristol Corinthian to about 4 knots. My 20AH LiFePo battery has only gone flat once. The 1000W 48 volt brushed motor (I think it is the same actual motor as th e36V one) Got pretty hot with 44 Amps. That is twice the motor's rating, so it figures. I could just dial down the PWM and keep it under 20 Amps. It is still 48 volts, just shorter ON pulses. I just need to figure a way to keep the High School kids from over riding the limit. Let me know if you want to see photos, i can't attach them here.
PWM controllers are cheap. Higher power PMDC motors are not...there's just not a lot of demand for them, compared to brushless 3-phase motors. If you're really worried about a student override, install a lower amp fuse. And keep a couple of spares close by ; )
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.
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!
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.
Wow you are really coming along with this. I must have missed part 2. after doing two of these, i found that getting the full speed amps dialed in requires replacing the prop with less pitch to prevent overheating or to increase the pitch to get more amps and power. My 3.5 Nissan needed a bigger prop from a Yamaha 8 to get nearly rated power out of my 1000W 36v motor. the evinrude fisherman 6 needs a flatter prop. right now the 1000 W motors is pulling 44 Amps at 48 volts. It gets hot pretty fast. muffin fan has no chance to cool it. My motors are rated at 3000 RPM. A guy on youtube,
"emily and clark's adventure" does a really good job testing and reviewing batteries. I am building the Evinrude with a High School class and essentially took the summer off. If I can find a nice flat prop for it, We will test again. Otherwise we will need to build a reduction system with little timing belts.
I haven't had any overheating issues...yet! But then again I'm not running at my motor's max rated power. Operating at the highest voltage that you can is going to reduce the current (at a given power level)...and heating. My motor has enough thermal mass that it takes a while to heat up, and a long time to cool down using fan cooling. So I can see some advantages from re-installing the impeller and trying water cooling -- if temperature does become a problem. I've been using the prop that came with the motor; I'm going to (hopefully) test one with a bigger diameter and see what the difference (if any) is. More data is coming in the next project installment.
You got the brushless motor that i wanted for the high school class, but was too worried about controlling a brushless. I read that you can't just throw X amount of volts at them and have them run like a brushed motor. I use a PWM controller for speed control, but in a pinch i could just hot wire it and go full voltage and turn it on and off with a switch to get home or off the rocks. I have never had any heating with the tohatsu based setup with the 1000W 36V motor, but to get 20 amps, i needed to increase the load with a larger prop than standard. It now pushes my 3000 lb full keel Bristol Corinthian to about 4 knots. My 20AH LiFePo battery has only gone flat once. The 1000W 48 volt brushed motor (I think it is the same actual motor as th e36V one) Got pretty hot with 44 Amps. That is twice the motor's rating, so it figures. I could just dial down the PWM and keep it under 20 Amps. It is still 48 volts, just shorter ON pulses. I just need to figure a way to keep the High School kids from over riding the limit. Let me know if you want to see photos, i can't attach them here.
PWM controllers are cheap. Higher power PMDC motors are not...there's just not a lot of demand for them, compared to brushless 3-phase motors. If you're really worried about a student override, install a lower amp fuse. And keep a couple of spares close by ; )