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

[sailingharry]

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.

It is true that the BMS will disconnect if the voltage gets too high, but the thought makes me shudder. We often hear about BMS disconnects, usually in regard to alternator damage. In my mind, a BMS disconnect should be such an incredibly uncommon event that we should never see it in the life of the battery. Remember, a BMS disconnect for any reason leaves you with a boat with no electricity for any systems!

[boatpoker]

You seriously need to have a Certified Marine Electrician look at what you are doing. A decent claims investigator will find this thread.

I'd still like to know what make/model battery charger you have.

[SaylorMade]

Originally Posted by wholybee

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/

Hmm all the "cheap" BMS's I have seen, has a setting for max cell voltage and also pack voltage, and will disconnect when the first cell reaches the set cell voltage.
Pack voltage is just another back-stop if the first doesn't work for some reason.

I don't see why you would raise the disconnect pack voltage to 14,7 or 14,8 as you write??
Surely no BMS comes with that as standard.

[Rohan]

Originally Posted by sailingharry

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.

Thanks, I'll switch to copper washers instead then. Short battery cables are not very flexible, and due to the space and alignment of the batteries involved, I have to put something between the cable and the battery surface.

However, just testing on the tips of the bolts I used with a multimeter, the current reads very strong as it is.

[Rohan]

Originally Posted by boatpoker

You seriously need to have a Certified Marine Electrician look at what you are doing. A decent claims investigator will find this thread.

I'd still like to know what make/model battery charger you have.

I already went into that in this thread. I didn't want to re-hash that here.

https://www.cruisersforum.com/forums...es-278038.html

[ixnax]

Originally Posted by boatpoker

You seriously need to have a Certified Marine Electrician look at what you are doing. A decent claims investigator will find this thread.

I'd still like to know what make/model battery charger you have.

That's assuming there is an insurance policy for the op's boat or attachable assets were an unapproved installation be the cause of a neighbors boat burning to the waterline.

Having a Certified Marine Electrician approve the installation, even if one is super confident, is just the right thing to do and it's not that much money.

[sailingharry]

Originally Posted by ixnax

Having a Certified Marine Electrician approve the installation, even if one is super confident, is just the right thing to do and it's not that much money.

Interesting concept. I do nearly 100% of the work on my boat (as mentioned in another thread, even when I want to hire tradesmen, I can't get them to respond).


I'll be building my own LFP this winter, from bare cells. I'll be mostly or completely ABYC compliant (ie, maybe my battery cable will be 10" before the first fuse, not 7" -- not a current intention, but an example of what I mean by "mostly"). I do keep a current set of ABYC standards, read them, and understand them.


It might be nice to get a "Certified Marine Electrician" (I assume you mean an ABYC electrician, since I don't think there is any legal certification) to review and provide a statement on compliance.


So, the question. Have you (or others on the thread) been able to find ABYC electricians willing to provide this service? I'm skeptical that technicians are willing to do this. But to be honest, I've never tried. I do know that riggers do provide a similar service (rigging inspection) so perhaps it is a viable way forward.


On the lines of "mostly compliant," virtually all boats are partially non compliant. My boat came to me with a battery bank that looks very professionally installed. Knowing the boat's history, they poured money into it using top tier vendors. The 4 batteries have a moderate cable (maybe 1/0 or 2/0?) going to a terminal post, each about 2' long. From the battery post is a 4' long 4/0, terminating at 400A fuse. This is horribly not to standard -- more than 7" (and not in sheath), 5 lugs on one post, 2/0 cables protected (downstream, no less!) by a 400A fuse. But the non-compliant work is very professionally installed -- solid mountings, neat wire runs, battery hold-downs are exceptionally robust, etc.

[wholybee]

Originally Posted by SaylorMade

Hmm all the "cheap" BMS's I have seen, has a setting for max cell voltage and also pack voltage, and will disconnect when the first cell reaches the set cell voltage.
Pack voltage is just another back-stop if the first doesn't work for some reason.

I don't see why you would raise the disconnect pack voltage to 14,7 or 14,8 as you write??
Surely no BMS comes with that as standard.

Most cheap drop-ins do not allow user configurable settings, and yes, most of them actually have the cut-off at 3.7V per cell (14.8 pack) or higher. The reason is because the BMS is NEVER supposed to stop charging. It is a last ditch effort to save the battery if the charger is set at too high a voltage. So, the BMS will allow a charge to 14.6V without disconnecting, to give the charge a chance to do it's job.

Also, if a BMS disconnect at full charge while charging from an alternator, you risk blowing up the alternator, and all other electronics on board. A BMS disconnect should never actually happen. If you are relying on a BMS to stop charging, you are asking for all kinds of problems.

[boatpoker]

Originally Posted by Rohan

I already went into that in this thread. I didn't want to re-hash that here.

https://www.cruisersforum.com/forums...es-278038.html

How have you modified the alternator to charge the batteries ?

[Rohan]

Originally Posted by boatpoker

How have you modified the alternator to charge the batteries ?

The alternator isn't connected to the batteries directly, it runs through the battery charger. I set the charger to 14.1 max voltage.

[boatpoker]

Originally Posted by Rohan

The alternator isn't connected to the batteries directly, it runs through the battery charger. I set the charger to 14.1 max voltage.

That makes no sense to me, sending the DC output from the alternator to an AC charger that takes an AC input to put out DC to the batteries ????

I'd really like to see a schematic of how thats done

[flightlead404]

Originally Posted by wholybee

A BMS disconnect should never actually happen. If you are relying on a BMS to stop charging, you are asking for all kinds of problems.

The way I started to think about BMS disconnect was essentially the same as a breaker trip or a fuse blow.

That is, it should never happen as you say, and if it does its a last ditch effort to save the battery (and possibly the boat), and finally that it should trigger a Root Cause Analysis. Like tripping a breaker, it doesn't get reset until I fully understand why it tripped/blew/disconnected and have corrected not just the immediate condition that caused the trip/blow/disconnect but the systemic problem I likely introduced in the first place.

[Rohan]

Originally Posted by boatpoker

That makes no sense to me, sending the DC output from the alternator to an AC charger that takes an AC input to put out DC to the batteries ????

I'd really like to see a schematic of how thats done

OK, I'm really confused now. Serious question, but why wouldn't it be to the battery charger? How else would the boat stop power from the alternator from charging the batteries after they are full? It's not like the alternator has switches or settings on it.

Unfortunately I don't see the alternator listed anywhere on the wiring diagrams.

Here's what I do know. I have removed and reinstalled all the batteries twice on this boat and the only wires to the batteries, other than the solar wires I added myself, are the Pos+ cables from the battery selector switch, and then Neg- cables going to the engine ground. That's it. Maybe the alternator power is instead going directly to the battery selector switch? But then how would it regulate the power? If the regulator is hard wired into the alternator itself, then how would anyone ever adjust it?

[Flod]

Originally Posted by Rohan

OK, I'm really confused now. Serious question, but why wouldn't it be to the battery charger? How else would the boat stop power from the alternator from charging the batteries after they are full? It's not like the alternator has switches or settings on it.



Unfortunately I don't see the alternator listed anywhere on the wiring diagrams.



Here's what I do know. I have removed and reinstalled all the batteries twice on this boat and the only wires to the batteries, other than the solar wires I added myself, are the Pos+ cables from the battery selector switch, and then Neg- cables going to the engine ground. That's it. Maybe the alternator power is instead going directly to the battery selector switch? But then how would it regulate the power? If the regulator is hard wired into the alternator itself, then how would anyone ever adjust it?

Rohan, no offence but I don’t think you have enough knowledge to mess around with lithium batteries. There is really so much that can go very wrong and you don’t seem to have done your homework. My advice is to either switch back to AGM or hire someone to help you.

[Stu Jackson]

Originally Posted by Rohan

OK, I'm really confused now. Serious question, but why wouldn't it be to the battery charger? How else would the boat stop power from the alternator from charging the batteries after they are full? It's not like the alternator has switches or settings on it.

Unfortunately I don't see the alternator listed anywhere on the wiring diagrams.

Here's what I do know. I have removed and reinstalled all the batteries twice on this boat and the only wires to the batteries, other than the solar wires I added myself, are the Pos+ cables from the battery selector switch, and then Neg- cables going to the engine ground. That's it. Maybe the alternator power is instead going directly to the battery selector switch? But then how would it regulate the power? If the regulator is hard wired into the alternator itself, then how would anyone ever adjust it?

OEM 1-2-B Switch Wiring History http://c34.org/bbs/index.php/topic,4....html#msg30101

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 )
https://marinehowto.com/1-2-both-bat...onsiderations/




Rohan,


I agree with others, you need to be doing some serious research and homework if these are the things you "believe."


A basic boat electrical book would help.


There's also my Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html


Maine Sail did this on lith systems: https://marinehowto.com/drop-in-life...ated-consumer/


Please do a lot more reading.