LiFePO4 Battery Build

[dtfeld]

As a winter upgrade project, going to build and add 2 12V 304 Ah Lithium Iron Phosphate (LiFePO4) batteries to power my inverter/charger and supplement the house bank. Parts starting to arrive, including the 8 cells today. Lots of thought planning and design going into this, but still pretty basic, as these will be a separate system from the standard 12V system on the boat.

Still waiting on the BMSs and a few more pcs and parts to start getting this put together.

The inspiration come from here --> https://panbo.com/building-a-diy-lifepo4-battery/

 

[ocgrant]

Cool.. Following this stuff on Pambo and now here. Going to FLIBS next week to see more of this stuff.

 

[JC3]

DIY Solar with Will Prowse on You Tube. Everything you will need to know and more about Solar, Lith etc...

 

[importmonkey]

still pretty basic, as these will be a separate system from the standard 12V system on the boat.

What is their primary use if not used in the boat's standard 12V system?

 

[dtfeld]

What is their primary use if not used in the boat's standard 12V system?

Only purpose is to run a 12V Inverter/charger, and run the galley and possibly the Vberth AC over nite, no generator, but for now will not be charged from the main engine 12V. Basically the inverter draws power out of this bank, and when shore or generator AC power is available, it will recharge this bank.

Lots of other ways to charge these up, high output alternators, and solar, but that gets expensive. For that type system, look at what Ttmott is working on

As for a reason, big loads like inverters kill lead acid type batteries pretty quickly, and I’d like not to kill my expensive AGMs, and I needed a winter project!

 

[Tucker K5]

Only purpose is to run a 12V Inverter/charger, and run the galley and possibly the Vberth AC over nite, no generator, but for now will not be charged from the main engine 12V. Basically the inverter draws power out of this bank, and when shore or generator AC power is available, it will recharge this bank.

Lots of other ways to charge these up, high output alternators, and solar, but that gets expensive. For that type system, look at what Ttmott is working on

As for a reason, big loads like inverters kill lead acid type batteries pretty quickly, and I’d like not to kill my expensive AGMs, and I needed a winter project!

A couple of questions if I may?

1. Will there be less corrosion at termination points around the electrical system with lithium batteries as opposed to lead acid?

2. What does it take to convert from lead acid to lithium on the main engine 12v system?

 

[dtfeld]

A couple of questions if I may?

1. Will there be less corrosion at termination points around the electrical system with lithium batteries as opposed to lead acid?

2. What does it take to convert from lead acid to lithium on the main engine 12v system?

1.. Hydrogen gas from standard lead acid batteries is what causes the corrosion. Since these don’t outgas, should be no corrosion.

2. Difficult to answer as it depends on a lot of factors, but you can not just drop in Lithium and use your standard alternator/ charging system with out some modifications. Lithium batteries have very low internal resistance , and will accept all the current an alternator can produce, and they are not meant to do that for long. You will burn them up pretty fast.

Tom (Ttmott) is switching out and doing and entire re-engineering of his system that is quite elaborate.

 

[GnrlPatton]

Thanks for starting this thread, I am looking at doing similar and replacing my house bank (currently 4x 6v GC batteries at 205aH) with a DIY 2x 304aH (608aH total) LiFePO4 bank. That should give me almost 3x my current capacity. I already have 2x 100W solar panels and a 2kw inverter, so I'm just trying to determine what charging options (new charger that can push 40+A, DC-DC charger for alternator use, etc) that I want to include. Ideally it would be a shore charger, solar charger, alternator charger combo, but it gets more complex and costly the more you add to it.

+1 to the Will Prowse YT channel, been watching him for a year while I plan out this build. So many things change so quickly with this technology, it's tough to keep up!

 

[km1125]

1.. Hydrogen gas from standard lead acid batteries is what causes the corrosion. Since these don’t outgas, should be no corrosion. ....

Just a little correction/clarification here... It's not the hydrogen gas that causes the corrosion, it's the H2SO4 (sulfuric acid) vapors that come off the battery that does this. Sometimes it comes from just leaking around the base of the post, and sometimes it's just the vapors that are part of the off-gassing during charging.

Lithium shouldn't have these problems, but can have problems associated with using different materials for the connectors (galvanic corrosion) or hardware that might be mistaken for the lead-acid issues.

 

[Skybolt]

@dtfeld Dave, what are you going to use to charge/maintain these? The balancing is quite an issue if not planned for correctly.

Nice little project, will be following this one.

 

[dtfeld]

@dtfeld Dave, what are you going to use to charge/maintain these? The balancing is quite an issue if not planned for correctly.

Nice little project, will be following this one.

Using 2x 200A 4s BMS w/ high and low temp cut out. This was the hardest decision as 200A BMSs are not as common and much more expensive. I considered going to a 24v inverter/charger, but expense of new inverter outweighed benefits, so stuck with 12V and 200A BMSs.

I found a generic version of the Radio B 200A that checked all the boxes in one of the DIY Solar forums. Yep..Will Prowse…thank you!


https://radiobtech.com/products/sma...th-module-4-cells-12-8-volts-diy-programmable

 

[dtfeld]

Here is the link where I found my 304Ah cells… good price, good service. So far very happy. You can send Jenny an email.

https://diysolarforum.com/threads/our-new-go-to-lifepo4-vendor-09-20-21.28696/page-6#post-352169

 

[Skybolt]

Using 2x 200A 4s BMS w/ high and low temp cut out. This was the hardest decision as 200A BMSs are not as common and much more expensive. I considered going to a 24v inverter/charger, but expense of new inverter outweighed benefits, so stuck with 12V and 200A BMSs.

I found a generic version of the Radio B 200A that checked all the boxes in one of the DIY Solar forums. Yep..Will Prowse…thank you!


https://radiobtech.com/products/sma...th-module-4-cells-12-8-volts-diy-programmable

Really cool Dave (@dtfeld) This looks like a really cool project, can't wait for the rest of the post's on how this is working out! Looks like no more generator for you. Very nice!

 

[dtfeld]

I contemplated getting rid of the genny and putting a bunch of these in its place…but beyond my project scope for now. I still need the generator to charge this up.

 

[Skybolt]

I contemplated getting rid of the genny and putting a bunch of these in its place…but beyond my project scope for now. I still need the generator to charge this up.

Thats actually funny, your trying to replace the generator use with this battery/inverter setup but need the generator to charge it. But I get it, quite time is priceless on a boat.

How are you tying the inverter in to the panel? With a 2nd cross over switch with the generator?

 

[JC3]

Will put up a new video of a really good plug and play system. (

). The technology is changing almost daily.

 

[dtfeld]

Thats actually funny, your trying to replace the generator use with this battery/inverter setup but need the generator to charge it. But I get it, quite time is priceless on a boat.

How are you tying the inverter in to the panel? With a 2nd cross over switch with the generator?

Basically, I added a breaker to the existing AC panel, and wired it so that the 4 circuits I want inverter power on are fed thru the inverter. As long as shore or generator power is available, everything is powered. If neither is available, then the inverter powers the 4 circuits. I’ll have to put up the diagram…

 

[dtfeld]

BMSs showed up over the weekend. Expected to take much longer as I ordered from Aliexpress. I need to get this power up and make sure the features I need are indeed onboard.

 

[ttmott]

Hi Dave - I assume you are going to make a compression box for the prismatic cells; make sure you install an insulating material between them with good thermal insulating properties like micarta or fiberglass sheet. Don't trust the shrink wrap around the cells to isolate; one little rip in that thin wrap and you will have a cell to cell short. I am suspect that that black battery box will serve you well to hold compression on the cells...
Those BMS will get hot so they also need to be able to dissipate heat through the heat sinks to air.
Also, what are you planning to get the cells top and bottom balanced?
Tom

 

[dtfeld]

Hi Dave - I assume you are going to make a compression box for the prismatic cells; make sure you install an insulating material between them with good thermal insulating properties like micarta or fiberglass sheet. Don't trust the shrink wrap around the cells to isolate; one little rip in that thin wrap and you will have a cell to cell short. I am suspect that that black battery box will serve you well to hold compression on the cells...
Those BMS will get hot so they also need to be able to dissipate heat through the heat sinks to air.
Also, what are you planning to get the cells top and bottom balanced?
Tom

Lots of opinions and controversy on compression, and compression is going to be most difficult part of this as the battery boxes have limited space for a typical DIY compression system (threaded studs).

My current planning is a sandwich construction with insulation between cells and taped together just as the commercially available batteries are constructed (use materials just as you have listed above). I would term this a limited compression build. One of the pros to compression is it limits the stress imparted on the terminals due to the expansion and contraction especially when cells are connected with rigid bus bars. I'm looking to eliminate this aspect by using braided bus bars if i can find them premade and reasonable in cost.

One of the other ways to improve the cycle life is to limit the SoC and discharge cut off (cycle between 90% and 20% SoC), and I've sized this system to stay within those bounds.

BMS placement likely to be in the battery box but I'll have to test that. I'm looking for a (mostly) watertight system. We shall see if that is possible or if I have to abandon this approach and try something else. The BMS has onboard programmable temp monitoring and cut off capabilities, so I'll know pretty quick if this will work. The BMS I purchased has high temp cut off, low temp cut off and I can add heater if I want to be able to charge it in the winter (which right now I'm not planning to install as we don't do to much in the winter, but it was a $5 add to the BMS, so I bought that option. For now low temp cut off will just prevent charging below 1C.

As for Top balancing I purchased a variable power supply to do that job...may take a while lol.