Building a 48V system - 4x12V in series or a larger 48V, and help with BMS

[jdy2kgt]

I've been trying to read everything I can on these forums but I'm also starting to go cross eyed so I'm hoping you don't mind me asking some basic questions. I want to build a 48V 100AH system. This is for an electric pontoon boat. Currently the boat uses 4x12V SLA's in series and 440W solar with Victron MPPT and shunt. I've never gotten close to running the SLA down to 50% which is why I want to just stick with 100ah. From everything I've read I feel confident I can put this together. My thought is to use EVE 105AH A cells. Here's my questions:

1) Should I do one 48V (16S) or do four 12V(4S)? The one reason I'm considering the 12V way is because that makes it alot easier for me to get the batteries on and off the boat. But should I do the 48V so I only have one BMS and it keeps all the cells balanced?

2) Speaking of balancing. I was all set on the JK BMS because of the active balancing but then I started reading multiple recent threads about issues people are having with them. And the same sort of thing being said about Daly. Can someone just tell me which BMS to choose? The electric motor pulls 83amps at full power, but other motors pull 96amps. So I was thinking of going with a 150A BMS in case I ever change out the motor in the future.

3) As far as building these I was planning on using screw top battery boxes from Ali and fibatape to hold the cells together with the thin plastic in between them. I've also seen Topbms brackets/intermediate bracket and wanted to know what you thought of those.

Please share your thoughts on the this build and ask any questions.

Thank you,
James

 

[sunshine_eggo]

1) that's the trade off. If you make sure you properly prep and monitor the individual 12V, it generally works fine. If you have a 48V marine charger that's designed to charge the individual 12V in series, that's even better.

2) They all have their issues from time to time. The JK seems to be the most versatile and has the 2A active balancing, which is great. I have a couple JBD I'm happy with.

3) no opinion.

 

[chrisski]

2) Speaking of balancing. I was all set on the JK BMS because of the active balancing but then I started reading multiple recent threads about issues people are having with them. And the same sort of thing being said about Daly. Can someone just tell me which BMS to choose? The electric motor pulls 83amps at full power, but other motors pull 96amps. So I was thinking of going with a 150A BMS in case I ever change out the motor in the future

I’m not sure how a 150 amp BMS will handle a surge from an 83 amp constant draw. I just dont run my BMSs at so close to max capacity when I run my AC.

I chose an Overkill, which is a rebranded JK BMS supposedly used on medical equipment for my large 8s 280 ah BMS, and would do so again.

I chose Daly for tiny capacity in the 25 ah range, because that was the only branded BMS I could find, but that is not programmable like the 150 amp size Daly you are looking at.

 

[sunshine_eggo]

I’m not sure how a 150 amp BMS will handle a surge from an 83 amp constant draw. I just dont run my BMSs at so close to max capacity when I run my AC.

I chose an Overkill, which is a rebranded JK BMS supposedly used on medical equipment for my large 8s 280 ah BMS, and would do so again.

JBD, not JK.

 

[nasko]

HI jdy2kgt and all other DIYers!
Would you share which route did you take?

I am in the same boat with you (pun intended).
I want to build a 48V/280Ah bank for an electric outboard and I want to be able to unload the batteries on shore for charging.
The motor will pull 200A maximum with 100A or less consistently.
I am considering building four 12V banks and to connect them in series for a total of 48V with the following parts:
16pcs EVE EF280K distributed in four 4s banks
4pcs JK-B2A8S20P for each of the 12V packs
4pcs battery boxes
My intention is to charge the 4 packs simultaneously with individual chargers 12V/20A
I still have some doubts whether it will be more easy to buy ready 12V/280A banks but the price difference is substantial - 1000USD in favor of DIY.

Any advice will be highly appreciated.

 

[chrisski]

My intention is to charge the 4 packs simultaneously with individual chargers 12V/20A
I still have some doubts whether it will be more easy to buy ready 12V/280A banks but the price difference is substantial - 1000USD in favor of DIY.

Any advice will be highly appreciated.

If you are not charging with solar, You can get an Aims 120 VAC to 75 amp 12 volt charger converter for about $300.

I don’t like the idea of individually charging the batteries that are in parallel. Since they are in parallel, you’re actually charging all the batteries. If you do go the individual charger route, just make sure thay can be stacked in parallel to 4. A different converter I do is limited to stack three in parallel.

Also, with the DIY, take into account all the costs. I was surprised at how much BMS prices and cases added up. I made my own case, but you can get 4S 280 ah cases, but it is pricey. As a boat build, you probably want something watertight.

 

[nasko]

If you are not charging with solar, You can get an Aims 120 VAC to 75 amp 12 volt charger converter for about $300.

I don’t like the idea of individually charging the batteries that are in parallel. Since they are in parallel, you’re actually charging all the batteries. If you do go the individual charger route, just make sure thay can be stacked in parallel to 4. A different converter I do is limited to stack three in parallel.

Also, with the DIY, take into account all the costs. I was surprised at how much BMS prices and cases added up. I made my own case, but you can get 4S 280 ah cases, but it is pricey. As a boat build, you probably want something watertight.

Thank you for the reply.
As I said the whole unit will be 48V/280Ah - 16pcs x 6kg(13lbs) = 96kg(211lbs) and probably 10kg(22lbs) for BMS, cases, wires, etc. in total around 110kg(242lbs). For charging I have no option alongside a pier or a berth.
So I am left with only two options:
- remove the battery and charge it, or
- tow the boat with the battery in it and charge it.
I would rather stick with the first option, but a 110kg(242lbs) battery is out of my league for moving around. I consider starting Crossfit but still it's a future project.
This is the reason I preffer to connect four 12/280Ah batteries in series on the boat and to unload them on shore for charging. And the charging to bre done simultaneously but not in parallel with four individual chargers for each battery.
As for the prices so far:
16 pcs - EVE280k x 95usd=1520usd,
4 pcs - JK-B2A8S20P x 69=276usd
4 pcs - cases x 18usd=72usd
shipping cost: 322usd, DDP price, door to door, tax and custom has been included
Total: 2190usd / 2738usd (+ VAT and duties)
Or by pack - 548usd / 684usd for one 12V/280Ah pack
There is no better price for a comparable 12V/280Ah pack. And with the all complains about packs full of rocks and used cells I preffer to have more control over the battery internals.

 

[chrisski]

As I said the whole unit will be 48V/280Ah - 16pcs x 6kg(13lbs) = 96kg(211lbs) and probably 10kg(22lbs) for BMS, cases, wires, etc. in total around 110kg(242lbs). For charging I have no option alongside a pier or a berth.

I have the same cells set up 8s2p, and I figured I’d need a forklift to remove and install from 4 feet high. Not an option.

This is the reason I preffer to connect four 12/280Ah batteries in series on the boat and to unload them on shore for charging.

Your overall plan seems valid, just ensure the BMS you choose can go 4s 48 volts. If you need that much power and the only way to charge it is removing four 60 lbs batteries, that’s what you have.

There’s many places to get battery cases for 4s 280ah cells, but all I’ve seen are pricey, not for the cost of the item itself, but 70% or more is shipping. I’d like to see what you decide on. I found no 8s 280ah cases.

Also, although many manufacturers say lithium batteries can be put in series, the problem is when one BMS trips, what happens to the other three?

I would think since you are not charging in the boat this would only be for under voltage in a single cell or under voltage in a single battery, or perhaps over amps in a single battery and this would cause the circuit to open and all three batteries shut off.