Charging LFP dropin questions

[chowdan]

Hey all,

My firefly batteries from 2019 are starting to show signs of ending their life. I've probably got another season out of them. Being a full time liveaboard on a mooring ball in the PNW, I'm guessing I will likely replace them before next winter.

I've got pretty much all victron onboard for most things except the alternators which are externally regulated via a MC-614 and the generator(belt driven alternator) is driven by a MC-618, both are capable of LFP.

Currently the house bank is directly charged via alternator/solar/shore and the start batt is charged via an ACR. I do NOT want to do DC-DC charging when switching to LFP because the alts have temp sensors to save themselves.

My big question is handling surge spikes in voltage in the even that the BMS cuts off the power during charging. Seems like most people recommend a FET such as the Victron Argofet to handle the voltage spike.

Since all charging sources lead to the unswitched distribution block(including ACR) which is also what my house bank runs to, wouldnt the ACR function as a load dump in the event that the BMS shuts down charging?

In an ideal world I'd be buying a wakespeed, LFP's that communicate, and what not but thats not happening as budget is quite limited currently.

[wholybee]

It isn't the normal setup, but yes, I think it will work fine. As long as the ACR has the start battery connected when the alternator is running, I don't see any issues. The start battery will be charging at the LFP voltage, and I don't see that as an issue either.

[CaptainRivet]

Originally Posted by chowdan

Hey all,

My firefly batteries from 2019 are starting to show signs of ending their life. I've probably got another season out of them. Being a full time liveaboard on a mooring ball in the PNW, I'm guessing I will likely replace them before next winter.

I've got pretty much all victron onboard for most things except the alternators which are externally regulated via a MC-614 and the generator(belt driven alternator) is driven by a MC-618, both are capable of LFP.

Currently the house bank is directly charged via alternator/solar/shore and the start batt is charged via an ACR. I do NOT want to do DC-DC charging when switching to LFP because the alts have temp sensors to save themselves.

My big question is handling surge spikes in voltage in the even that the BMS cuts off the power during charging. Seems like most people recommend a FET such as the Victron Argofet to handle the voltage spike.

Since all charging sources lead to the unswitched distribution block(including ACR) which is also what my house bank runs to, wouldnt the ACR function as a load dump in the event that the BMS shuts down charging?

In an ideal world I'd be buying a wakespeed, LFP's that communicate, and what not but thats not happening as budget is quite limited currently.

I assume acr means automated charging relay and that is not sufficient to use with LFP and lead as it let current flow in both directions.
The easiest solution is to connect to your distribution block the argofet as input and output goes to LFP and your lead charger. So in case the BMS cuts off the lead starter is always there. That this is not happening in normal operation configure your 2 balmar accordingly so that absorption starts earlier at eg 13.6V and when then 13.8V is reached its at 2-5A charge and a cutoff of field wire doesn't create any spike as the LFP is still connected or I case you mean dumb drop ins without any communication nothing is happening then too as charge current when cut of is low but that will be then be in 14,4-14.6V area.

A Wakespeed doesn't make sense as you have perfectly capable external regulators to protect your alternator/generator and a wakespeed cannot protect you from spikes in case of a sudden disconnect.

[Ixium]

I have a very very similar setup. With mc-614. My firefly’s are toast now. So I’m dropping in lifepo4’s this spring.

I’m going to be setting the alt regulator to a lower charge voltage. It’ll never top up the batteries, but also won’t over volt. Not the end of the world.

I’m also adding an alternator protector device . Striking makes one.

[chowdan]

Originally Posted by CaptainRivet

I assume acr means automated charging relay and that is not sufficient to use with LFP and lead as it let current flow in both directions.
The easiest solution is to connect to your distribution block the argofet as input and output goes to LFP and your lead charger. So in case the BMS cuts off the lead starter is always there. That this is not happening in normal operation configure your 2 balmar accordingly so that absorption starts earlier at eg 13.6V and when then 13.8V is reached its at 2-5A charge and a cutoff of field wire doesn't create any spike as the LFP is still connected or I case you mean dumb drop ins without any communication nothing is happening then too as charge current when cut of is low but that will be then be in 14,4-14.6V area.

A Wakespeed doesn't make sense as you have perfectly capable external regulators to protect your alternator/generator and a wakespeed cannot protect you from spikes in case of a sudden disconnect.

Yes, ACR is automatic charge relay from Blue Seas. It will only function as a pipe in both directions if the voltage is high enough(ie combined). This is the part that i've been trying to think through, mainly with zero lithium experience I've been trying to understand the voltage profiles.

The ACR i've got will cut the pipe at 12.75V(for 30 sec), but is combined at a minimum 13.0V(for 2 mins). I dont think it'd really matter much if i draw on my start bank for 2-5 minutes after charging sources are shut down AS LONG AS the voltage does drop quick enough on the LFP bank - this is where i'm not fully convinced will happen.

That said I do not want to put full faith in the BMS regardless of how rare it would be for it to cut power. In some sense, the ACR would totally work for saving an alternator, but if the pipe remains open for tooo long after shut down, then ACR will definitely have go.

Personally I am probably jaded by the career path i've taken - software tester - and so anything software based to me ALWAYS has failure points in the code. Nothing is perfect and as such, this makes me incredibly resistant to the idea of LFP on a boat. That said, I am overcoming that resistance by thinking through faults and designing a way(with what i've got) to handle them. But it does appear that a FET is probably the best option to handle it as it seems like voltage on the LFP will likely stay quite high for an extended period of it's charge

[chowdan]

Originally Posted by Ixium

I have a very very similar setup. With mc-614. My firefly’s are toast now. So I’m dropping in lifepo4’s this spring.

I’m going to be setting the alt regulator to a lower charge voltage. It’ll never top up the batteries, but also won’t over volt. Not the end of the world.

I’m also adding an alternator protector device . Striking makes one.

It's an unfortunate, fortunate thing to happen. I am looking at being able to do 600ah LFP rather than 440ah fireflies which will be nice for us.

How are you handling your start bank? Are you going to use the APD as a means to handle potential BMS shutdowns?

I am leaning mroe and more towards the FET device from victron but its just another $ to spend and another thing to install

[CaptainRivet]

Originally Posted by chowdan

Yes, ACR is automatic charge relay from Blue Seas. It will only function as a pipe in both directions if the voltage is high enough(ie combined). This is the part that i've been trying to think through, mainly with zero lithium experience I've been trying to understand the voltage profiles.

The ACR i've got will cut the pipe at 12.75V(for 30 sec), but is combined at a minimum 13.0V(for 2 mins). I dont think it'd really matter much if i draw on my start bank for 2-5 minutes after charging sources are shut down AS LONG AS the voltage does drop quick enough on the LFP bank - this is where i'm not fully convinced will happen.

That said I do not want to put full faith in the BMS regardless of how rare it would be for it to cut power. In some sense, the ACR would totally work for saving an alternator, but if the pipe remains open for tooo long after shut down, then ACR will definitely have go.

Personally I am probably jaded by the career path i've taken - software tester - and so anything software based to me ALWAYS has failure points in the code. Nothing is perfect and as such, this makes me incredibly resistant to the idea of LFP on a boat. That said, I am overcoming that resistance by thinking through faults and designing a way(with what i've got) to handle them. But it does appear that a FET is probably the best option to handle it as it seems like voltage on the LFP will likely stay quite high for an extended period of it's charge

You don't have to think that through with ACR as its simply forbidden be ABYC to combine to different chemistry with lithium what you do with ACR and its also the wrong way. You want insurance or insurance not to simply bail out of any battery related damages for US vessels, then exclude the ACR solution.
Argofet is best solution as simple, cheap and reliable.

Search for jedi reference diagramm and have a look at them, they are your best source how things are done correctly and as lithium beginner I highly advise to follow them as there are many use/fault cases you are not aware off while very experienced people like jedi are.

[wholybee]

Originally Posted by CaptainRivet

I assume acr means automated charging relay and that is not sufficient to use with LFP and lead as it let current flow in both directions.
The easiest solution is to connect to your distribution block the argofet as input and output goes to LFP and your lead charger. So in case the BMS cuts off the lead starter is always there. That this is not happening in normal operation configure your 2 balmar accordingly so that absorption starts earlier at eg 13.6V and when then 13.8V is reached its at 2-5A charge and a cutoff of field wire doesn't create any spike as the LFP is still connected or I case you mean dumb drop ins without any communication nothing is happening then too as charge current when cut of is low but that will be then be in 14,4-14.6V area.

A Wakespeed doesn't make sense as you have perfectly capable external regulators to protect your alternator/generator and a wakespeed cannot protect you from spikes in case of a sudden disconnect.

No problem with current flowing both directions. The ACR will only be closed when charge current is detected on the LFP. (i am assuming all charge sources connect to the LFP) So current flow will only be from LFP to Start. Never from Start to LFP.

It could be an issue if there is a shore charger on the start battery.

[CaptainRivet]

Originally Posted by wholybee

No problem with current flowing both directions. The ACR will only be closed when charge current is detected on the LFP. (i am assuming all charge sources connect to the LFP) So current flow will only be from LFP to Start. Never from Start to LFP.

It could be an issue if there is a shore charger on the start battery.

That's simply wrong, which direction current flows depends on the SOC of each battery as soon as they are combined. The ACR is not protecting when an empty LFP get connected to a full lead and vice versa. ACR are developed for lead batteries, not LFP.

[witzgall]

Chris from Balmar here.
My 2 cents:
1 - use a DCDC from the house to charge the start batt. Simple, inexpensive
2- Use our APM on each alternator

Chris

[chowdan]

Originally Posted by CaptainRivet

You don't have to think that through with ACR as its simply forbidden be ABYC to combine to different chemistry with lithium

I totally over looked this - good call out. Perfect reason for everyone to ignore my initial post and for me to go with a argoFET or a dc-dc charger from house to start.

Pure isolation, withing spec and chemistry not combined. Cheap insurance for being in allowance

[chowdan]

Originally Posted by witzgall

Chris from Balmar here.
My 2 cents:
1 - use a DCDC from the house to charge the start batt. Simple, inexpensive
2- Use our APM on each alternator

Chris

Chris - Thanks for this. I am not opposed to running a dcdc from house to start, but i still am hesitant about a BMS failure(or just it shutting down). The APM will protect the alternator in this instance, however it seems it'd be better to have a solution that we could rely upon that absorbs output in the event that the house bms is shut down?

[Paradox111]

In lieu of Victron argofet, I have been using Sterling 'ProSplit-R Zero Volt Drop Marine Battery Isolator', for several years now, connecting Lead to LiFeP04 with my external Balmar regulator with temp sensors. (programing Balmar voltage for LFP)

https://www.sterling-power-usa.com/P...olator-12.aspx

[CaptainRivet]

Originally Posted by chowdan

Chris - Thanks for this. I am not opposed to running a dcdc from house to start, but i still am hesitant about a BMS failure(or just it shutting down). The APM will protect the alternator in this instance, however it seems it'd be better to have a solution that we could rely upon that absorbs output in the event that the house bms is shut down?

Balmar prefers the APM+DC2DC route where you can also replace the starter with lithium or LTO and can even skip the DC2DC to get completly rid off lead which start to really make sense if you see how far the cell prices went down. And delivers the most current from the alternator. The APM protects the system and works.

But if you wanna keep lead (I personally hate it) its also the more expensive and complex way while other way is the cheaper and more simpler with argofet and lead starter.
Both methods work.
Your boat, your choice.

[sailorboy1]

Originally Posted by chowdan

Hey all,

My firefly batteries from 2019 are starting to show signs of ending their life. I've probably got another season out of them. Being a full time liveaboard on a mooring ball in the PNW, I'm guessing I will likely replace them before next winter.

Didn't read thread as I have read lots of the others and even started the same 14 months ago.

I would, and do, charge my LFP batteries exactly like I did the Firefly batteries before. Just changed the setpoints of the charging sources