Any reason not to use lifepo4 batteries rather than agm on a very small boat at these prices?

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steve yates

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This is aimed at the specific circumstances in my 18foot boat. She currently has a 50w solar panel charging two 120ahr leisure batteries. This set up allows about a weeks cruising before requiring a marina to charge up the batteries. Bit less in winter and I will cruise in winter.
It runs lights/ ipad/iphone/gps dongle ( the dongle and ipad are plugged in all day when sailing) / deisel heater/ autohelm/ vhf/anchor light/nav lights.)
The batteries have a b121 switch I use solely to switch the loads to a different battery each day allowing a modicum of recharge from the solar to the other battery.
It works well, but I am very close to low voltages by the end and I would like be able to have two weeks marina free cruising.
I am going to add another solar panel, (might even manage a 100w one ) to the new sprayhood, as the original is on the companionway hatch and will often be shaded by the hood.
I also have a new tohatsu outboard, which has a charging coil and was intending to wire that up to the 121 switch.

So far so good, one of the batteries is pretty old and when I looked at replacement prices,
I found 130ahr agms at £150. Then out of curiosity, I checked lithium and found 100ahr life4po at £155.

It seems to me that if I replace my dual battery 10a pmw solar charger with a 20a mppt one, which would be required anyway with addition of extra solar, and got a shore charger that could handle lithium, the would be a much better bet for extending my cruising time and range outwith marinas?

I understand I couldn’t use the tohatsu as a charge source but not running the outboard is a good thing :)

Am I right in thinking I effectively go from a starting available useable 120ahr with mycurrent agm to 180ahrs with lithium, with a faster recharge and recovery process that will put more ahrs back in the bank faster than with the agm’s?

Last question, is cold dangerous to life4po batteries? As the boat would be out or on a mooring in winter when its below freezing.

So what does the jury think, worth swapping to lithium when ugrade time comes? Or are there good reasons not to bother!

Thanks.
 
I had the same thought process as you earlier this winter. I’ve now got 3x renology lifepo4 batteries and associated wiring / dc:dc charger to install next time I’m over at the boat….

at the current pricing it seems a bit of a no- brainer imo. A bit of thought required to connect them all up, but that should be a one time job.
 
As I understand it, the cold only affects whether the battery can take charge. It doesn't destroy the battery just by being cold.

In your shoes, Lithium would be a no-brainer really and one with a BMS that shuts off when it has reached charge (or a pre-defined % such as 90%) is what you need so you can just leave it under solar all the time you are away.
 
Poecheng said:
As I understand it, the cold only affects whether the battery can take charge. It doesn't destroy the battery just by being cold.

In your shoes, Lithium would be a no-brainer really and one with a BMS that shuts off when it has reached charge (or a pre-defined % such as 90%) is what you need so you can just leave it under solar all the time you are away.
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A programmable BMS should allow you to set that.
 
On the store at 80% thing - do you set it like your central heating thermostat in that mon - fri it sits at 80%, then come Friday it accepts more solar to be 100% for when we arrive after work?
 
Minerva said:
On the store at 80% thing - do you set it like your central heating thermostat in that mon - fri it sits at 80%, then come Friday it accepts more solar to be 100% for when we arrive after work?
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No. You set the cutoff to whatever and that's it. You have to change it when you get onboard.
 
Two, slightly conflicting, factors at play:
- the cells need to spend some time at the top of the voltage range in order to balance. Doesn't have to happen on a schedule, and certainly not daily, but it does need to happen at some occasionally. So you don't want to just set your max SOC to 95%.
- cells shouldn't be stored at 100% for a prolonged period of time. It will reduce their capacity.

For cells in daily use, it's not a problem. You'll charge up during the day and then discharge a bit in the evening/overnight.
For a boat that is not being used, you don't have these loads so if you don't do anything, you end up with the cells at 100% for a long time. So you either change your charge settings, or disconnect everything with the batteries sitting at 50-70%. Reconfigure when you use the boat. It's just just toggling a setting in the app.

To be honest, LFP batteries are so cheap now that maybe some of the previously accepted wisdom isn't really that important. They no longer represent an investment that must last a decade to make financial sense. So if you can't be bothered doing any of the above, it's not exactly a crime, and your batteries will likely still prove a better buy than any flavour of lead acid, in terms of performance and lifespan.
 
As I understand it a lithium battery which includes a charge control circuit should be ok with solar connected without a charge controller. Likewise any charge from the outboard should be OK provided it gives enough voltage under load. A very crude shore charger giving a high voltage should also be able to charge the lithiun battery relying on the BMS in the battery to cut off at a specific charge level. ol'will
 
William_H said:
As I understand it a lithium battery which includes a charge control circuit should be ok with solar connected without a charge controller. Likewise any charge from the outboard should be OK provided it gives enough voltage under load. A very crude shore charger giving a high voltage should also be able to charge the lithiun battery relying on the BMS in the battery to cut off at a specific charge level. ol'will
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Sorry, this is totally wrong.

My solar panels sit at around 100V, that isn't going to do anything much good. The BMS will cut the charge when the battery reaches the set voltage, but trying to push excess voltages into the batteries will end in tears.
 
William_H said:
As I understand it a lithium battery which includes a charge control circuit should be ok with solar connected without a charge controller.
Click to expand...
If by 'charge control circuit' you mean BMS, then... I don't think that will work. A 12v nominal panel will actually produce around 17v. I'm not really sure what would happen if you tried directly hooking up a panel to a LFP battery, with no charge controller involved- the BMS could shut down because of the high voltage.
The only system design I've heard of which uses a direct connection is the Electrodacus BMS, which is designed to work with 12v panels and no charge controller. But we're firmly in to geek territory now.

William_H said:
Likewise any charge from the outboard should be OK provided it gives enough voltage under load.
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I don't think that's a good idea. A battery shut off (e.g. because the battery is full) will leave the alternator with no load, which they do not like at all.

William_H said:
A very crude shore charger giving a high voltage should also be able to charge the lithiun battery relying on the BMS in the battery to cut off at a specific charge level. ol'will
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Yes, you can use a normal charger to charge a lithium battery... but on some systems the battery will go offline once it is full.

The BMS is there as a failsafe. Relying on it to shut off charging isn't really a good idea.
 
fredrussell said:
The 100 a/h one has a claimed 200 amp max discharge which is twice what you would normally expect BUT may still not be enough to start your engine, depending on size of engine and other factors.
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2C probably isn't going to give the batteries a long life.

So many of these companies making big claims, but short warranties.
 
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