Pulled the trigger on the cheapest LiFePO4 batteries anywhere. And I have a question.

[Rohan]

Pulled the trigger on the cheapest LiFePO4 batteries anywhere, these Ecoworthy LiFePO4 12V 100Ah.

https://www.eco-worthy.com/products/...sphate-battery

They are already cheap, and I got 4 of them on Amazon prime day for insanely cheap to replace my AGMs.

So I tried them over the weekend - installation was harder than I expected because the battery posts are flush with the battery instead of raised like they are on AGMs so it didn't line up well with my existing cables which each has a bend to accommodate that raised portion.

And instead of a screw post built into the battery like on AGMs, instead you line up the cable and thread a screw down into it. Problem is, the screws they provided are so freaking short that they can only accommodate one battery cable at a time, but I need to attach more to connect multiple batteries together.

I solved both problems by going to the hardware store, getting longer screws (M8 1.25 metric), and some washers and nuts to act as spacers. I chose zinc instead of steel since zinc has better connectivity (hope that was correct decision, my multimeter seems to show a good connection).

I loved the fact that by swapping out I was removing over 100lbs weight. And for a few days anyway, the batteries worked flawlessly with one exception and I'm wondering if the forum can explain this.

I have been using 4 batteries in 2 battery banks. I rigged it so bank 1 has a single battery that I treat as the starting battery. Bank 2 has the other three batteries which I switch to when I'm going to be anchored for awhile. This arrangement worked well with my AGMs.

When I installed LiFePO4 battery #1, it was reading 13.3v right out of the package, so I decided to test it and see if it would start the motor (Yanmar 29hp). It couldn't. In fact, it basically went dead immediately and read only 5v! I thought maybe it wasn't ready right out of the box, so I charged it up for a couple hours, and then it bounced back and was able to start the engine on it's own. However, after being out on the water for awhile, I tried again, and same problem, it wouldn't start and basically flatlined. I had to use my other 3 batteries on bank 2 to start the motor instead. So it seems like one LiFePO4 can't start the engine by itself unless it's been bumped up a bit from recent charging.

So what gives? My AGMs could start the engine no problem even when they were drained down to 12v. But the LiFePO4 showing 13.3v can't do it? My AGMs had 900 marine cranking amps (These are the AGMs I was using). I don't know the MCA/CCA of the lithium batteries because that's not listed.

Is this a typical problem with LiFePO4s or did I get a bad one?

[jcapo]

Others will delve more deeply but the battery internal BMS disconnected the battery due to current load. The website says 100A max load but they lied or the starter current exceeded 100A.

Parallel all 4 batteries for the house bank and retain one AGM, or buy another, for the starting battery.

LFP batteries are not drop in direct replacements for lead acid batteries. You have a lot of studying to do re: LFP on boats.

[Tin Tin]

The website link you provided says specifically not to use these batteries as starter battery.https://www.eco-worthy.com/products/...sphate-battery down the bottom of the description tab.

[boatpoker]

What BMS do you have ?
How are you charging them ?

[Rohan]

Originally Posted by Tin Tin

The website link you provided says specifically not to use these batteries as starter battery

True, although from the photo and description I thought it meant for cars. If it can't handle the starting load by itself, that's fine, I'll use 2 or 3 as starting batteries. I was just curious. Not going to hook up an AGM as the starter. I don't like the weight and I don't want to add more complications with a different type battery in the mix.

[Rohan]

Originally Posted by boatpoker

What BMS do you have ?
How are you charging them ?

A battery charger set to the max voltage of the LiFePO4s, but much more of the time I charge by solar only, with the charge controller on lithium setting.

[boatpoker]

Originally Posted by Rohan

A battery charger set to the max voltage of the LiFePO4s, but much more of the time I charge by solar only, with the charge controller on lithium setting.

What model charger is that ?
What model controller ?
So no BMS ?
No charging from engine alternator ?

[wholybee]

Congratulations on the upgrade.

You really should use a lead acid for starting. FLA is fine, it doesn't need to be AGM, but it should not be LFP, for a variety of reasons. Including the possibility of permanent damage, leaving you stranded without being able to start your engine, and also no power to be able to call for help.

Your alternator should be connected to the lead acid battery, not the LFP, unless you are planning some upgrades there. A stock alternator can be damaged from charging and LFP. This is one of the less obvious reasons to keep lead acid for starting. You can use a DCDC charger to connect the 2 banks together, so the LFP will charge while the engine is running.

All other charge sources (solar, etc.) can go to the LFP.

You should not use washers on the battery terminals. Steel isn't a great conductor, so they will overheat and cause a voltage drop. If you _must_ use washers, then need to be copper.

It is quite important to only use a charger made for LFP. A basic charger "set for the max voltage of LFP" will kill them in short order. A very important fact to realize is that with LA you always wanted them to be fully charged. With LFP the opposite is true. Keep them around 50%-80%, and give them a full charge just before you leave for the weekend.

If your current charger doesn't fit the bill, then connect it to the LA battery, and allow the LFP to charge through the DCDC charger.

Safely starting from an LFP is possible, but you need to use a higher end drop in battery especially designed for it, or use a battery built from cells with an appropriate BMS.

[Rohan]

Originally Posted by wholybee

Congratulations on the upgrade.

You really should use a lead acid for starting. FLA is fine, it doesn't need to be AGM, but it should not be LFP, for a variety of reasons. Including the possibility of permanent damage, leaving you stranded without being able to start your engine, and also no power to be able to call for help.

I'm actually not worried about being stranded. I have a separate jump starter made for trucks that works on my Yanmar even if my battery is totally drained (I have tested it), or if worst comes to worst, I can use my portable generator to recharge the batteries. But obviously that's all a hassle I want to avoid.

Your alternator should be connected to the lead acid battery, not the LFP, unless you are planning some upgrades there. A stock alternator can be damaged from charging and LFP. This is one of the less obvious reasons to keep lead acid for starting. You can use a DCDC charger to connect the 2 banks together, so the LFP will charge while the engine is running.

OK, that's a lot to take in. My battery is a house bank, there is no starter battery that's separate from the rest, although I simulated that on my own by switching between two battery banks. So if I have an AGM battery in the mix I would need to add an isolator or possibly a DC to DC charger? I would prefer to keep the system as simple as possible though.

The alternator runs through the battery charger, it's not directly connected to the batteries.

My solar panels are directly connected to one battery bank.

You should not use washers on the battery terminals. Steel isn't a great conductor, so they will overheat and cause a voltage drop. If you _must_ use washers, then need to be copper.

The washers, bolts and nuts I used are all zinc, not steel.

It is quite important to only use a charger made for LFP. A basic charger "set for the max voltage of LFP" will kill them in short order

I actually have it set quite a bit lower, to 14.1 when the max is 14.6. Also, I use solar charging more often, and that just has a default lithium setting. Several sources have told me I should be good with that, hopefully that's correct.

If your current charger doesn't fit the bill, then connect it to the LA battery, and allow the LFP to charge through the DCDC charger.

That is something I will consider.

Safely starting from an LFP is possible, but you need to use a higher end drop in battery especially designed for it, or use a battery built from cells with an appropriate BMS.

Thanks, I'll consider instead getting a lithium battery optimized for starting. That might be simpler in the long run. I really do want to keep the system as easy to handle as possible.

Although my literature for my current batteries says don't mix different kinds of LiFePO4 batteries together! Although I can't help thinking that's a bit of CYA.

[SaylorMade]

Originally Posted by wholybee

Congratulations on the upgrade.

It is quite important to only use a charger made for LFP. A basic charger "set for the max voltage of LFP" will kill them in short order.

Could you please elaborate on this?
Any power source outputting a "flat" max 14.6v should charge a LFP battery just fine, since the BMS will disconnect when the first cell reaches the set max voltage. You can go lower on the voltage, but 14.6 is the max.

I am not saying that you are wrong, but I've never heard this before, and would like to know how and why it would damage an LFP battery in short order.
We assume here that the OP's battery has an internal BMS. (Drop-in batt)

[GILow]

You are getting some good advice here,.

These things and the setup you have is a disaster waiting to happen.

FLA for the starter is waaaay smarter. There are a million posts on this and an equal number of smart ways of keeping the FLA charged.

I've got a clean battery slate for the new boat and there are two things all my reading here and elsewhere made clear.

1. FLA for the starter.

2. Cheap lithium is one thing, but the cheap BMSs in cheap lithium are the real issue, and you don't want to be dependant on them.

In your position I'd combine the lithium batteries for the house bank, buy a single suitable FLA for the engine and keep the two banks well away from any dumb battery combiner switch. There are all manner of simple, cheap and clever ways of keeping everything charged, and all are documented well on CF.

[Tupaia]

FWIW I recently replaced 2 banks of 3 AGM's with one bank of 4 Lithiums. I got round the start issue by using a couple of Racing Series batteries these are very small, weight approx 6kg and are designed for starting so have excellent cranking ability.

[wholybee]

Originally Posted by SaylorMade

Could you please elaborate on this?
Any power source outputting a "flat" max 14.6v should charge a LFP battery just fine, since the BMS will disconnect when the first cell reaches the set max voltage. You can go lower on the voltage, but 14.6 is the max.

I am not saying that you are wrong, but I've never heard this before, and would like to know how and why it would damage an LFP battery in short order.
We assume here that the OP's battery has an internal BMS. (Drop-in batt)

If the battery is in balance, and it really should be, then a single cell will not cause the BMS to disconnect. So, assuming the BMS is set to disconnect at 14.7V-14.8V, then a charger that charges to 14.6V will never cause the BMS to disconnect. Holding an LFP at 14.6V will overcharge it. After 14.6V is reached, charging must be terminated. LFP batteries do not need a charger to "float" like lead-acid do. After an LFP battery is charged, holding any voltage over 13.8V will over charge them.

Rod at marinehowto has a nice LFP primer that anyone considering LFP should read.
https://marinehowto.com/lifepo4-batteries-on-boats/

[krid2000]

Originally Posted by Tupaia

I got round the start issue by using a couple of Racing Series batteries these are very small, weight approx 6kg and are designed for starting so have excellent cranking ability.

What chemistry are they?

Dirk

[sailingharry]

You already have good comments on the lfp part of the problem, and you will get more I'm sure.

But a comment on the terminal posts. Your choice of bolt material, and an up thread comment on washers. On a wiring terminal post or connector strip or almost anywhere else we put wires on a boat, the important thing to remember is the bolt and washer do not and should not ever conduct electricity (of course it will conduct small amounts, but they should be considered irrelevant). The concept is the flat surface on the device you are connecting to is where the electricity needs to go. The cable lug lays on that surface and provides the electricity. The bolt (and a washer if you use one) serve one function -- to provide sufficient pressure between those two conducting surfaces. It is absolutely critical that you put nothing between those surfaces, -- it is not uncommon for people to put a washer there which is extremely bad.

And a small detail. You said you used zinc instead of steel. Zinc is a pretty awful material for something like a bolt, and so bolts are not made of zinc. You probably meant zinc plated steel (a very common household fastener). I assume when you said steel, you meant stainless. With the information in the paragraph above, it follows that a stainless bolt is perfectly acceptable.