i guess i will start right off. i have several projects going right now and have a pretty good understanding of them. i however am new to diy Lifepo4 batteries. i have a new project that i am working on that is not solar, but uses many of the same components so i feel i could reach out here. i want to build a 36v 100ah lifepo4 battery bank. this if for a trolling motor for my boat that will pull a max of 40-50 amps continually. is there a bms made to allow me to do that. i was thinking about using the fortune batteries. other then that i have no clue of how to wire or what other components i would need to build the battery. after the battery i am ok with. btw i am very handy and have no issue in doing any of the work. i just do not have the knowledge of lifepo4 stuff. . i do not have tons of time to research as i normally do so i am asking for help. I work for the utility company here in San Diego as an emergency responder and have had little time due to this mess of the virus. i am very fortunate to be working but have had little time to spend on anything else. that is not a complaint, i'm just saying, that's why i need help. thank you so much !
Greetings from Poway,Ca./SanDiego, great to be a part of this awesome community. so glade there is a place like this around.
- Thread starter Gasman760
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Welcome to the nuthouse err I mean forum. If someone here can't answer your questions I would be surprised.
So, jumping in, for 100Ah @ 36 volt you will need 12 cells. The fortune cells are expensive but a good choice for something that is going to get banged around. However, even with the fortune cells you should plan on building a box to hold the battery and the BMS.
The logical wiring for the cells would look like this.
When you add the Balancing Harness it looks like this
However, you may want to physically arange them in two groups of 6 side by side like this.
At
So, jumping in, for 100Ah @ 36 volt you will need 12 cells. The fortune cells are expensive but a good choice for something that is going to get banged around. However, even with the fortune cells you should plan on building a box to hold the battery and the BMS.
The logical wiring for the cells would look like this.
When you add the Balancing Harness it looks like this
However, you may want to physically arange them in two groups of 6 side by side like this.
At
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
50 amps is not very demanding on a BMS. The 7S-16S version of this would work for you:
https://www.aliexpress.com/item/33014476298.html?
The 100A version would probably work, but for the price difference I would go with the 320A version.
https://www.aliexpress.com/item/33014476298.html?
The 100A version would probably work, but for the price difference I would go with the 320A version.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
BTW: At 50A, you will only get ~ 2 hrs on the battery.
Meanwhile, what are you planning to do for charging it?
Meanwhile, what are you planning to do for charging it?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Some other practical things to consider:
You will want to put a fuse or circuit breaker on the system. Perhaps on the battery box. That could also act as a disconnect. Since you only need 50 Amps, go with a 60-70 Amp breaker.
How long do the leads to the trolling motor need to be? If it is less than 5 feet, you could get away with 6AWG cable, but I would recommend 4AWG.
You will want to put a fuse or circuit breaker on the system. Perhaps on the battery box. That could also act as a disconnect. Since you only need 50 Amps, go with a 60-70 Amp breaker.
How long do the leads to the trolling motor need to be? If it is less than 5 feet, you could get away with 6AWG cable, but I would recommend 4AWG.
Thank you so much FilterGuy. This has helped out so much. Unfortunately at this time 100ah is all I can afford or should I say my wife will let me spend at this time. I do plan on a good box to put it in and a breaker at the battery for sure. I like the idea of a higher amp rated bms. the run from the battery is about 10 or so feet but I already have 4/0 cable I can use so I will be ok with that. Again thank you. If you or anyone has any suggestions they may feel i can additionally benefit from please feel free to give your opinion.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Out of curiosity.... what is the connection to the tolling motor? Is there some kind of high-amp connector to the motor?
As far as charging I plan on using house power from home, after I get home from fishing. I do not have a charger in mind. As far as boat charging I would love to be able to charge using main motor, but not really sure if I could. I have a new Victron three outlet 300amp battery isolator I am hooking up. I am in the middle if rewiring my boat when I got the hair brain idea to install the bow trolling motor so things are in a flux as to exactly how I’m going to wire everything. Not sure if it would be possible to use the third outlet on the isolator to go onto a charger or go directly to the lifepo4? I know you can’t go directly from the alternator to lithium batteries due to over demand on the alternator but im not sure if the isolator would limit amps to outlets of the isolator. I will need to look that up. Any thoughts are welcome. Thank you.
No it is not done yet. I will likely install some kind of lug.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
You should look at using a heavy duty Anderson connector or something like that. This would make it easy to plug and unplug and make it difficult to accidentally get a short or get it backwards.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
You should definitely do some research on that *before* you buy anything. Finding a LiFePO4 charger for a 36V bank may be a challenge
Tell us more about your 'main motor'. Is it running 36Volt off it's alternator?
Sorry I wasn’t very clear on that. No main motor is my drive motor and I would use my alternator connected to the isolator. Alternator is 12v and the isolator charge profile is taken from battery connected to outlet one on the isolator, which is a carbon foam AGM by firefly. So unless I could find a charger with a transformer to convert to 36v and limit the amps I don’t think I can go that route.i think I will be limited to charging at home by extension cord.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yup... Finding a charger that would boost from 12V would be a challenge.
How do you like the firefly?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I just did a quick search of "36V LiFePO4 charger". There are a bunch out there for the scooter market. They all appear to be 10A or less. It would take 10 Hours to charge at 10A..... but maybe that is ok.
BTW: Look closely at them before you buy. Some of them don't shut off when the charging is complete..... and that would be a hasel. You want to be able to plug it in and forget it till your next escape.
BTW: Look closely at them before you buy. Some of them don't shut off when the charging is complete..... and that would be a hasel. You want to be able to plug it in and forget it till your next escape.
So question on that bms. It looks like that same bms can be used for 12v, 24v,36v? Is it just how many cells that are put in series and that the bms can be connected to In series that determines your voltage? So a bms with four balancing lines can only be used for 12v, but a bms with let’s say 12 balance wires an be used for 12,24, and 36v? Thanks for your patience. I have been trying to find the strait answer on this and haven’t been able to.
I just bought the firefly so I haven’t used it yet. I have been in the purchasing mode so I can put it all together when things slow down . Since I’m so busy right now I have only been able to work a little at a time on the boat. I hope firefly batteries work good. I think I left my marine radio on the last time I went fishing and that is a none switched load and it drained my last battery so bad that I could not keep a charge on it. Sucks to loose a $300 battery for letting it die just once. I tested voltage on the old AGM and it was at 0v. I guess they Don’t like that?.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
That is mostly correct. Each one will say what it can do. The one I pointed to is advertised as a 7S to 14S. That tells you it can be configured for as few as 7 cells in series and as many as 14 cells in series. However, it can not do 4 cells. The instructions for each one will say how to do the wiring for the cells.
Excellent, that is exactly what I needed to know. I didn’t want to buy something that isn’t going to work for what I needed, or I need multiples of the same thing. It’s hard to find any real info on some of these parts and as I said I am new to this battery building so I am very unfamiliar with these components. This will not be my last battery build though. I look forward to updating my solar system on my travel trailer and out building.
