LiFePo Batteries: Build or Buy?

[newhaul]

Originally Posted by rgleason

Here is a sketch for the dimensions and config of a battery pack I am considering building.

Dimensions: 4s2p lined up with 5.25" faces parallel against each other, with heavy serial cables on the diagonal 11.5" h x 5.25" w x 12" d (1.5 x 8)

I am thinking of getting or making an aluminum box that would hold these.
I would like to support them at thee sides but have room for air to flow, and have a small computer fan in the side that draws air out (corresponding air holes drilled in the case for good cross air flow) when charge/discharge drives the temperature up. I will have a second fan circulating air from under the double birth (location of battery) as well.

The batteries are going to be strapped to the bottom of the boat and water temperature doesn't generally get above 71F around here.

What material would provide airflow and support for the sides of the batteries?

Am I taking too much "fan" precaution for thermal runaway?

Putting them packed tightly together is just fine however if you wish to charge at a high C rate on a regular basis you may want to space them an 1/8 inch to allow for airflow .

Don't lay them on their sides .stand them up . When removing them you can disconnect and remove each cell individually. Label them and rotate them just like a set of tires .
There is some ( possibly anecdotal ) evidence the inner cells do get a bit warmer than the outer cells when rapid charging which will eventually lead to loss of a couple ah.
Thermal runaway is not really any more of a concern than with good old FLA batteries just install proper short circuit protection.

[CaptainRivet]

Originally Posted by newhaul

Putting them packed tightly together is just fine however if you wish to charge at a high C rate on a regular basis you may want to space them an 1/8 inch to allow for airflow .

Don't lay them on their sides .stand them up . When removing them you can disconnect and remove each cell individually. Label them and rotate them just like a set of tires .
There is some ( possibly anecdotal ) evidence the inner cells do get a bit warmer than the outer cells when rapid charging which will eventually lead to loss of a couple ah.
Thermal runaway is not really any more of a concern than with good old FLA batteries just install proper short circuit protection.

Good tips yes the outer cells loose more AH then inner cells, getting warmer means more energy floating through them but it’s marginal. Rotating them I wouldn’t do, the less you touch them the better. Taking them apart and together is always risky as I assume you don’t have a fully isolated ratchet or similar. short circuiting a lifepo4 is dangerous. My recommendation is only use a wrench and isolate the wrench completely by wrapping it in electric tape, then cut the tape with a razor blade where you place the nut. Like this if it slips out of your hand it cannot shortcut the contacts.

you can lay them on the short side or even upside down. Just avoid to lay them on the “big” sidewall. Yes you can put your house bank together with 100AH, 200Ah would be preferable though, no problem with laying them vertical.
A lifepo4 like to be between 20 and 80% DOD, so that gives you 60AH to work with.

[dnight]

I bought 4 x 300 Ahr Sinoply cells direct from China. A 123Smart BMS and 250A relay from the Czech people. Bought fuses, load and charge bus, Victron charger, built a box and put it all together. All up it cost me about 1800 Euro. That was about 18 months ago and it is still one of the best upgrades I have done on any vessel. We have 160W of solar which needs to be upgraded, but with this setup, in the Med, we get about 5 days on anchor before needing to start the engine to top up. We are full time live aboard, 1983 41ft Moody. Currently hanging out in Ischia, about to head to Ponza. Warm, sunny, no people, long may it last but it's gotta change soon. Until then though.....

[rgleason]

Thanks for all the advice and good tips.
BTW 20% to 80% is 60ah/100th so it would be 120ah which for us I'd fine.
Our need is for 90ah/day cruising and 135-150 ah offshore.

Can you say in more detail where you got the 250a relay and how you wired it?

123BMS is a good adjustible bms.
Does it have no/NC contact to trigger the relay?

[newhaul]

Originally Posted by CaptainRivet

Good tips yes the outer cells loose more AH then inner cells, getting warmer means more energy floating through them but it’s marginal. Rotating them I wouldn’t do, the less you touch them the better. .
A lifepo4 like to be between 20 and 80% DOD, so that gives you 60AH to work with.

Actually its exactly the opposite the inner cells will get a bit warmer and that over time will cause a slight degredation and loss of capacity. Rotating them is considered part of good practice according to the manufacturer. And as always use tools with non conductive coatings on the handles to prevent possible shorting contact just as you should when working with any battery.

Where did you get the 20% to 80% usability information from?
Lfp doesn't care about being charged right up to 100% and for the majority of us as soon as it is fully charged it begins its discharge so no issue .
They just like to be stored when offline between 20% and 80% the closer to 50% the better on the high side.

[dnight]

Hi rgleason, yes the 123smart BMS does have contacts to switch a high current relay. They can also provide the relay, either a 120A or 250A. The ones they sell are actually a double relay, one for the load bus and one for the charge bus. On overvoltage or high cell voltage, it will open the charge relay, on low voltage or low cell voltage, it opens the load relay. In either high or low temp it opens both relays. These relays then close again when everything comes back within the parameters that you set in the software or on the dip switches. Quite a nice system and fairly easy to configure yourself.

[rgleason]

Originally Posted by dnight

Hi rgleason, yes the 123smart BMS does have contacts to switch a high current relay. They can also provide the relay, either a 120A or 250A. The ones they sell are actually a double relay, one for the load bus and one for the charge bus. On overvoltage or high cell voltage, it will open the charge relay, on low voltage or low cell voltage, it opens the load relay. In either high or low temp it opens both relays. These relays then close again when everything comes back within the parameters that you set in the software or on the dip switches. Quite a nice system and fairly easy to configure yourself.

Dnight thank you for the valuable response regarding 123smartBMS which I believe is a reliable system that I looked at a long time ago. This would be a good reliable overall solution!

I have recently seen Franz Valdmen's Hybrid excellent approach
- Github Opensource OpenHybridBMS
- Readme
- Lithium Hybrid Configuration
which makes a lot of sense to me and I would very much like to implement it.


I had also looked into and considered Orion Jr

[newhaul]

Originally Posted by rgleason

.

I measured my cells today and my 250ah cells are 8 inches tall 7.25 inches wide and 2.75 inches thick. But they weigh 6kg each. So the total weight would be 24kg as a 4s1p set.

[rgleason]

I measured my cells today and my 250ah cells are 8 inches tall 7.25 inches wide and 2.75 inches thick. But they weigh 6kg each. So the total weight would be 24kg as a 4s1p set.

That's pretty good. 53 lbs. The height may work, I am looking for my drawings for the height and sections under the bunk. What was the manufacturer?

[newhaul]

Originally Posted by rgleason

That's pretty good. 53 lbs. The height may work, I am looking for my drawings for the height and sections under the bunk. What was the manufacturer?

Here is the spec sheet from XLD I purchased them direct via alibaba b2b

[dalbright1963]

As with anything electrical or electronic, there is a burn-in phase where you learn the viability and personality of your equipment. Typically, the first 30 minutes will let you know if you got a lemon. 8 months in on a complete conversion to LifePo4 batteries from Dakota Lithium and we see nothing but a great value and rock solid performance - so much so that we are converting our auxiliary from diesel to electric and adding eight additional 100ah batteries for a 300ah 48v propulsion bank that will keep the 200ah house bank topped off. These batteries have been a life-changer for our full-time cruising. We rarely get below 85% SOC with our 600ah bank and 1.2k solar array. These batteries are plenty safe for me.

[SV THIRD DAY]

These guys put together a good everything you need Kit for a 280AH battery, comes top balanced and ready for easy assembly.

LithiumBatteryKit.Com / LiFePO4 Battery For Adventures – LiFePO4 12v Boat / RV Battery Solution

[UFO]

Originally Posted by rgleason

Dnight thank you for the valuable response regarding 123smartBMS which I believe is a reliable system that I looked at a long time ago. This would be a good reliable overall solution!

I have recently seen Franz Valdmen's Hybrid excellent approach
- Github Opensource OpenHybridBMS
- Readme
- Lithium Hybrid Configuration
which makes a lot of sense to me and I would very much like to implement it.


I had also looked into and considered Orion Jr

Just finished today installing a 1120Ah system with the 123SmartBMS. Their tech support is excellent and answered all my questions straight away via email All working like a treat. The thing I like about it is that you can connect via Bluetooth and see all the info you need as well as turning off/on charge and load relays to check you have wired them correctly to your relays or controllers - Saves going into a low or over voltage scenario to see if it works!

[TheOffice]

Originally Posted by SV THIRD DAY

These guys put together a good everything you need Kit for a 280AH battery, comes top balanced and ready for easy assembly.

LithiumBatteryKit.Com / LiFePO4 Battery For Adventures – LiFePO4 12v Boat / RV Battery Solution

Rich, Thanks for the link! That's an amazing price for 280 aH. Then I just need to replace my Hitachi knock of alternator with one with an external regulator.

[newhaul]

Originally Posted by TheOffice

Rich, Thanks for the link! That's an amazing price for 280 aH. Then I just need to replace my Hitachi knock of alternator with one with an external regulator.

That or a b2b charger / one way isolator. Just like on my old pickup to charge the trailer batteries.
https://www.etrailer.com/Battery-Cha...BoCNvYQAvD_BwE

95 amp for 65 bucks is a good deal