New LFP House Battery

[SycloneDriver]

I just replaced two group 34 AGM batteries with one LFP. I saved about 20 pounds and have about 6 times the usable capacity.

The install isn't finished yet. I need to buy some hardware and strap the battery down. I also need to add a DC to DC charger.

I have reprogrammed the charge and float settings on my Pronautic P1230 charger. I set it at 14.2 charge and 13.2 float. I verified that it stopped charging when the battery was full.

The alternator is presently connected to both the house and start battery though an isolator. With the charger on and the engine running the charge current was at about 45 amps. I ran the engine for about 5 minutes at cruise rpm and the alternator barely got warm. The charger is only connected to the house battery. It pumped out 30 anps for hours, it got very warm.

I will probably add a DC to DC charger. It with draw from the starter battery and feed the house battery while the engine is running. I am also considering adding a trickle charger for the start battery.

I also have a Victron Smart Shunt to help keep an eye on things.

 

[dlochner]

I will probably add a DC to DC charger. It with draw from the starter battery and feed the house battery while the engine is running. I am also considering adding a trickle charger for the start battery.

No need to add the trickle charger for the start battery. Start batteries recharge very quickly and the rest of the alternator's out put will go to the house batteries.

 

[Tally Ho]

I just replaced two group 34 AGM batteries with one LFP. I saved about 20 pounds and have about 6 times the usable capacity.

The install isn't finished yet. I need to buy some hardware and strap the battery down. I also need to add a DC to DC charger.

I have reprogrammed the charge and float settings on my Pronautic P1230 charger. I set it at 14.2 charge and 13.2 float. I verified that it stopped charging when the battery was full.

The alternator is presently connected to both the house and start battery though an isolator. With the charger on and the engine running the charge current was at about 45 amps. I ran the engine for about 5 minutes at cruise rpm and the alternator barely got warm. The charger is only connected to the house battery. It pumped out 30 anps for hours, it got very warm.

I will probably add a DC to DC charger. It with draw from the starter battery and feed the house battery while the engine is running. I am also considering adding a trickle charger for the start battery.

I also have a Victron Smart Shunt to help keep an eye on things.

What is the “isolator” that allows you charge both banks from the alternator?

I am keeping my old Guest charge to charge the start battery, and I bought a new Victron charger for the LFP bank. But right now, my alternator is charging the starter battery. That is fine I guess, unless I am out in the hook for more than a few days and want to charge the house bank some. I don’t have solar.

Greg

 

[Johann]

I have reprogrammed the charge and float settings on my Pronautic P1230 charger. I set it at 14.2 charge and 13.2 float. I verified that it stopped charging when the battery was full.

The alternator is presently connected to both the house and start battery though an isolator. With the charger on and the engine running the charge current was at about 45 amps. I ran the engine for about 5 minutes at cruise rpm and the alternator barely got warm. The charger is only connected to the house battery. It pumped out 30 anps for hours, it got very warm.

When you leave the boat do you leave loads on that will discharge the LFP? If so, the 13.2V float will allow the SOC to drop to about 70%. That’s not a problem unless you want a full battery when you show up. It will take a few hours for the 30A charger to get the house back to 100%.

Also is your alternator externally or internally regulated? If it is internally regulated you could end up overcharging your LFP on a long motoring run if you start at a high SOC.

 

[heritage]

I would put a safety cover over the positive start battery terminal or put it in a battery box. It looks like an accident waiting to happen in that location below the engine.

 

[SycloneDriver]

I would put a safety cover over the positive start battery terminal or put it in a battery box. It looks like an accident waiting to happen in that location below the engine.

The start battery is in another location and it is in a box.

If I can find reasonable covers I'll add them to the house battery, the one in the picture. I don't have room for a box, the battery barely fits as it is.

 

[SycloneDriver]

No need to add the trickle charger for the start battery. Start batteries recharge very quickly and the rest of the alternator's out put will go to the house batteries.

I basically get my lead acid batteries for free but they are already 5 years old when I get them. I usually get an extra 3 years out of them. I attribute this long life to the care they received before and after they are installed on the boat. A temperature compensated trickle charger is all I use at work and a temperature compensated 30 amp on the boat. I like to think that makes a difference.

You are correct about the start battery recharging very quickly. My engine starts quickly with little cranking or glow plug.

If I ever actually get to take the boat cruising I'll purchase a new AGM start battery.

 

[SycloneDriver]

What is the “isolator” that allows you charge both banks from the alternator?

I am keeping my old Guest charge to charge the start battery, and I bought a new Victron charger for the LFP bank. But right now, my alternator is charging the starter battery. That is fine I guess, unless I am out in the hook for more than a few days and want to charge the house bank some. I don’t have solar.

Greg

The isolator is a transistor based unit. Its the original type that Beneteau installed. I did have to replace it once, the voltage drop was higher than it was supposed to be. I think the drop was 0.7 volt at very litte current if i remember correctly. It's supposed be something like 0.2 volt at 20 amp and 0.5 at 50.

At this time my alternator is internally regulated. I do have a new Balmar external unit that I can install if temperature becomes an issue.

My plan is to add a Victron 50 amp dc to dc charger. That may or may not keep the alternator happy. I'll do a little more testing and post my results.

 

[SycloneDriver]

I feel like I'm shooting down everyone's suggestions, don't let that stop you from posting. I really do appreciate your input.

 

[jssailem]

Doing the same type of install. Following the diagram worked up by Maine Sail.

 

[SycloneDriver]

When you leave the boat do you leave loads on that will discharge the LFP? If so, the 13.2V float will allow the SOC to drop to about 70%. That’s not a problem unless you want a full battery when you show up. It will take a few hours for the 30A charger to get the house back to 100%.

Also is your alternator externally or internally regulated? If it is internally regulated you could end up overcharging your LFP on a long motoring run if you start at a high SOC.

I do leave the fridge on, I want cold drinks on the boat without having to bring them with me. I do need to adjust the float voltage, I set it too low. Thanks for pointing that out.

 

[Scott T-Bird]

When you leave the boat do you leave loads on that will discharge the LFP? If so, the 13.2V float will allow the SOC to drop to about 70%.

I wasn't aware of this and my monitor always shows 100% charge (with AGM batts). Is this relevant only to LFP? What is explanation? Perhaps I need to do some detailed reading?

 

[dlochner]

I wasn't aware of this and my monitor always shows 100% charge (with AGM batts). Is this relevant only to LFP? What is explanation? Perhaps I need to do some detailed reading?

AGMs want to be kept at 100% SOC, LFP batteries like to be stored at around 50-70% SOC.

Since I have solar, I always leave something on. When I was away from the boat for 2 months over the winter I left the AIS on. Now I just leave the refrigerator on. The batteries will cycle.

 

[Johann]

I wasn't aware of this and my monitor always shows 100% charge (with AGM batts). Is this relevant only to LFP? What is explanation? Perhaps I need to do some detailed reading?

Yes, this is only relevant to LFP. The resting voltage of LFP being higher than AGM, if you want to maintain 100% the float voltage will be higher. I use 13.4V if I need to and that keeps about 99.5%. But as Dave said, while AGMs stay healthier if kept at 100% (to prevent sulfation), LFP will age slower when held at a lower SOC. When away for a long period I set 13.15V, and when aboard and on shore power I use 13.25V, then charge to full prior to departure. This takes time with a large bank so that is why I mentioned it.

 

[Davidasailor26]

My plan is to add a Victron 50 amp dc to dc charger. That may or may not keep the alternator happy. I'll do a little more testing and post my results.

I presume you have either a 60A or 80a alternator? I have the 80A and routinely see 40A going into my AGM house bank when they’re at a low SOC. If I ever upgrade to lithium I’d probably get an Orion XS that can be current-limited and set it to 40A.

 

[SycloneDriver]

I presume you have either a 60A or 80a alternator? I have the 80A and routinely see 40A going into my AGM house bank when they’re at a low SOC. If I ever upgrade to lithium I’d probably get an Orion XS that can be current-limited and set it to 40A.

I have a 100A Balmar alternator. I liked the output vs RPM curve.

 

[SycloneDriver]

I got back to the boat today. I've definitely got to set the float voltage a little higher.

Think I'll go for a sail. The weather is great. I will check the alternator output while I'm motoring out.

 

[SycloneDriver]

Check out the date code on my start battery, November 2014. I just tested it at 800 CCA with a cheap but reliable tester. I had to replace my mower battery this spring and it was from January 2016, I thought that was impressive.

I'm sure it will fail at the worst possible time. I do have a jump pack on board.

 

[SycloneDriver]

Out on the lake today i saw a maximum of about 45 amp flowing from the alternator into the house battery, it tapers off to about 13 amps at idle. I think that's good. I'm gonna wait to purchase the DC to DC charger.