Advice Requested re Conversion to LFP House Bank

[john61ct]

Again, with a 75A alt, even if I carry an 800Ah bank, but

only use 150Ah most days, and my motor runs 3hours on average, then I'd be silly to go to a bigger one.

With a few panels even more so.

In a different scenario maybe I'd want a 500A alt, my point is just that bank size has little to with it.

[newhaul]

Originally Posted by john61ct

Again, with a 75A alt, even if I carry an 800Ah bank, but

only use 150Ah most days, and my motor runs 3hours on average, then I'd be silly to go to a bigger one.

With a few panels even more so.

In a different scenario maybe I'd want a 500A alt, my point is just that bank size has little to with it.

you are correct however experience has taught me if you have the power you will find a use for it..

[Sailor 99]

Originally Posted by Stu Jackson

I'd ask myself: Why bother? Get rid of ther 8Dsand go golf carts.


Good luck.

^^^^^ This.


Unless there is a big change in chemistry I will not be putting any Li Ion batteries on my boat or any place were I live. Certainly not under my bed.


Li Ion are great until they start on fire and then they burn until they completely consume themselves. These fires can not be put out. If you submerge them in water they still burn. As each cell consumes itself it looks like the fire is going out until the next cell catches and so on.



Thanks but no thanks. I have 900 ah of flooded golf carts and 1120 watts of solar. No need to add in a potential catastrophic fire hazard.



IMHO Li Ion has absolutely no place on a boat. If it was anything other than the coolest new battery tech you would not even consider something this dangerous on a boat. Imagine if your flares started to spontaneously fire themselves off. You would not accept that. Why accept that behavior in a battery.

[senormechanico]

Originally Posted by newhaul

alternator reduce the output amperage not the voltage.

Ah, no to both you and john.
The alternator heats up, increasing its internal resistance which lowers the current output and also the voltage at the output terminal.
The lost voltage and resultant output goes up in heat from the increased INTERNAL RESISTANCE of the alternator. This is what cooks the alternator if it's run to destruction. The stator windings will short out from cooked insulation and / or the diodes will fry from over temperature.

[senormechanico]

Originally Posted by Dark Horse

^^^^^ This.


Unless there is a big change in chemistry I will not be putting any Li Ion batteries on my boat or any place were I live. Certainly not under my bed.


Li Ion are great until they start on fire and then they burn until they completely consume themselves. These fires can not be put out. If you submerge them in water they still burn. As each cell consumes itself it looks like the fire is going out until the next cell catches and so on.



Thanks but no thanks. I have 900 ah of flooded golf carts and 1120 watts of solar. No need to add in a potential catastrophic fire hazard.



IMHO Li Ion has absolutely no place on a boat. If it was anything other than the coolest new battery tech you would not even consider something this dangerous on a boat. Imagine if your flares started to spontaneously fire themselves off. You would not accept that. Why accept that behavior in a battery.

The OP is talking about LFP. Not Li Ion.

[newhaul]

Originally Posted by Dark Horse

^^^^^ This.


Unless there is a big change in chemistry I will not be putting any Li Ion batteries on my boat or any place were I live. Certainly not under my bed.


Li Ion are great until they start on fire and then they burn until they completely consume themselves. These fires can not be put out. If you submerge them in water they still burn. As each cell consumes itself it looks like the fire is going out until the next cell catches and so on.



Thanks but no thanks. I have 900 ah of flooded golf carts and 1120 watts of solar. No need to add in a potential catastrophic fire hazard.



IMHO Li Ion has absolutely no place on a boat. If it was anything other than the coolest new battery tech you would not even consider something this dangerous on a boat. Imagine if your flares started to spontaneously fire themselves off. You would not accept that. Why accept that behavior in a battery.

you are correct in that lithium ion has no place on a boat.
However as I'm sure you would notice from the title of the thread we are talking about Lfp or lifepo4 not Li ion.
There is actually more fire risk from the 900ah of gc2 Fla due to hydrogen offgassing during charging .
Your boat your choice.
Personally I would prefer Lfp better charging profile than Fla as well as a 70% weight reduction . Not to mention the longevity issue. ( 10k + cycles expected with how we use them wrt house banks. )

[john61ct]

Yes, no more fire risk from LFP than from a lead bank.

Likely far less in fact.

[john61ct]

Originally Posted by senormechanico

The alternator heats up, increasing its internal resistance which lowers the current output and also the voltage at the output terminal.
The lost voltage and resultant output goes up in heat from the increased INTERNAL RESISTANCE of the alternator. This is what cooks the alternator if it's run to destruction. The stator windings will short out from cooked insulation and / or the diodes will fry from over temperature.

Aaargh.

I was referring to stock alt / VRs that have over-temp protection to prevent this, but in such a way they do not keep charging properly.

As opposed to current de-rating VRs like MC-614, that **keep putting out the voltage setpoint** just at a reduced current rate.

[Q Xopa]

Originally Posted by john61ct

No the de-rating is exactly the point, actually pulling the max rating from 99% of alts out there for more than a couple minutes in high temp conditions either destroys them, or their protection measures effectively ends charging.

With all current-limiting solutions, it is up to the owner to determine how high a rate to pull given the current conditions, and set that as a maximum.

No need to fully refill in just an hour anyway, ICE's usually running for other reasons anyway.

Anyway, I'm not saying spending tons of money on just that one alt is never worth it, just that B2Bs are often a better value due to their flexibility, used with multiple sources, even other vehicles or in your home, whatever.

And finally, B2Bs can be stacked as needed.

Derating 25% off the top seems crazy. Whats the point of having LFPs that you can charge quicker?

Derating all the time is not the point. Derating when the Aternator gets hot is the point.

With a B2B trying to suck 60A, or even worse 120A from a stacked B2B pair, in a hot engine room you might still melt your alternator.

Yes you can stack them. At around $400 each thats getting expensive to loose 25% power.

Which happens to be what I paid for my large case 200A alternators.

But feel free to do yours the way you want.

[Q Xopa]

Originally Posted by john61ct

Again, with a 75A alt, even if I carry an 800Ah bank, but

only use 150Ah most days, and my motor runs 3hours on average, then I'd be silly to go to a bigger one.

With a few panels even more so.

In a different scenario maybe I'd want a 500A alt, my point is just that bank size has little to with it.

What?

[Q Xopa]

Originally Posted by Dark Horse

^^^^^ This.


Unless there is a big change in chemistry I will not be putting any Li Ion batteries on my boat or any place were I live. Certainly not under my bed.


Li Ion are great until they start on fire and then they burn until they completely consume themselves. These fires can not be put out. If you submerge them in water they still burn. As each cell consumes itself it looks like the fire is going out until the next cell catches and so on.



Thanks but no thanks. I have 900 ah of flooded golf carts and 1120 watts of solar. No need to add in a potential catastrophic fire hazard.



IMHO Li Ion has absolutely no place on a boat. If it was anything other than the coolest new battery tech you would not even consider something this dangerous on a boat. Imagine if your flares started to spontaneously fire themselves off. You would not accept that. Why accept that behavior in a battery.

You do know that GCs and all Lead acid batts produce Hydrogen which is highly flamable?

I have had a FLA top blown clean off from a spark from a dodgey terminal. It was on a truck I went to start very early one morning before daylight in a jungle camp. I was not very awake before I turned the key. But I was instantly awake a second after, along with everyone else in the camp.

I can assure you this can happen and it is spectacular.

They are also filled with a deadly acid. I have the powdered remnants of my work clothes to prove it.

Just saying, seeing you seem to like some dramatics.

[jmardiat]

Thanks again for everyone’s input.

In addition to adding a solar panel, I’ve been planning on keeping my original 75 A alternator for the time being and keeping track of the SOC of the LFP house bank when off shore, in order to see if I really need more charging capability. I just don’t want to burn up my alternator during the trial period. Is that really a risk?

[john61ct]

Yes it really is.

LFP high current "acceptance" means a small bank actually demanding, **pulling** much higher amps than even an 800Ah lead bank ever could, and for much longer. Not what they're designed for.

You could do controlled testing with a thermal gun, see how your amp handles it, some stock setups can have effective overtemp protection.

But say that kicks in after 5-10min, does not mean the bank gets charged after that, just that the alt didn't get toasted.

The two choices for solutions are outlined above.

[john61ct]

Originally Posted by Q Xopa

Derating 25% off the top seems crazy. Whats the point of having LFPs that you can charge quicker?

The point is, a stock alt rated for 75A is never going to actually output anywhere near that for any length of time.

In hot weather it might get to 50 or 60 actual continuous. Or maybe just 40A.

One way or another, the key to effective charging will be finding that number, for those conditions and effectively limiting the output at that level.

Yes a good VR will do that for you too as I said, but there is no solution that magically enables higher current output than what the alt is capable of doing.

And going to a bigger alt may or may not even be needed, that is a solution to a completely different problem.

[AndyEss]

I don't remember if you said your alternator was internally or externally regulated. Most newer external regulators include alternator temperature sensing, so this should take care of any over output issues. As others have discussed, internal regulators limit outputs by temperature also.

I bought William Thomason's external regulators for my setup, but health reasons have prevented me from completing my charging system upgrades to the higher output commercial truck externally regulated alternator I bought. His regulators support LFP charging, have both alternator and battery temp sensing, and are considerably less expensive than more well known brands. I have no durability comments as that part of my system isn't implemented yet.

I do know that because of my v-belt drive system (which luckily you don't have) going from LA to LFP with my internally regulated 45A automotive type alternator has resulted in the belt stretching, dusting and breaking issues.

As for surface area to mount solar panels, in addition to my dodger and bimini tops, I have several smaller semi-flexible panels fixed on my cabin top in low traffic areas. I often single hand so traffic by definition is usually pretty low.

The panels, being dark, get very hot on bare feet, and are extremely slippery when wet. I will be judiciously adding some very narrow traction tape at the cell joints (so as not to shade the active cells) to improve wet traction (not that I often need/want to step on the panels).The semi-flexible panels conform to the cabin top surface extremely well, so I am not concerned with excess panel flexure.