LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[s/v Jedi]

Originally Posted by Na Mara

Trouble with doing it that way is that it’s really inefficient. I’m planing 800Ah house bank charged off a 250A genmaxx alternator limited to 190A. This will make best use of my limited use of my overpowered engine. But the starter AGM is 110Ah so it can only charge at 50A continuous assuming standard acceptance rates. That would mean I could at most have one 30A DC-DC charger. It would take over a day to charge the house bank like that. I could double up on starter batteries to get 100A charging capacity on them and then I could run 3 parallel 30A DC DC chargers but then it would still take 7-8 hrs to charge from 80% discharge. Moreover those chargers run very hot meaning significant inefficiencies over and above excessive fuel burn.

It’s much more efficient to charge the LFP batteries off a high output alt and DCDC charge the engine battery off the LFPs. But to do that safely requires an external BMS that can talk to the regulator which is a more complex and expensive install.

I’m amazed everyone missed this so here goes: you can charge 100% with this setup. Let’s say your alternator can do a continuous 190A and your start battery can take 50A max. This leaves 140A available for charging your LFP house bank via DC-DC converters. I recommend you buy two 360W Smart Orions that will take 60A (plus… when cold they do more) and see how you like it. You can add a 3rd if you want.

Current from the alternator splits over the battery and the DC-DC converters. The battery does not sit in between alternator and converters. This is why the start battery prevents the transient surge when the BMS would disconnect the house battery.

[Na Mara]

I stand slightly corrected Jedi, but it’s still a very inefficient charging setup that at most allows charging at 90A. This is a poor use of LFP batteries high acceptance rate. Secondly, the problem repeats itself with the Dc Dc chargers, How do they know to stop charging in the event that the house bank BMS’ take the house bank offline? There might be a good answer to that question in which case such a system will at least be safe, but it will still be very inefficient compared to a directly charged LFP bank monitored by an external BMS.

[donradcliffe]

I just finished checking out the electrical system on the 34 ft raceboat I will bring back from Hawaii this summer. Its got a 80 amp dumb hitatchi alternator going to an AGM starting battery, with a battery combiner to a new 200 ahr drop in Lithium house battery. There are about 320 watts of solar, and the main loads will be an isotherm fridge and an autohelm 2000 tillerpilot. The combiner will close at 13.4 volts on either battery, which means the solar can top up the agm, and the alternator can charge the house. The combiner should protect the alternator from a high voltage disconnect on the LFP battery, and the existing wiring switches allow paralleling the house to start the engine and running the house from the start battery/solar if the house fails.

Its not 100% failproof, but it has performed well on 24 hr shakedowns, and looks good enough for me. I can always turn off the reefer and hand steer for a couple of weeks.

I am contemplating bringing a Daly 200 amp BMS I have laying around just in case I have to tear apart the drop in LFP due to BMS failure. Do you think BMS failure or cell failure is more likely?

[s/v Jedi]

Originally Posted by Na Mara

I stand slightly corrected Jedi, but it’s still a very inefficient charging setup that at most allows charging at 90A. This is a poor use of LFP batteries high acceptance rate. Secondly, the problem repeats itself with the Dc Dc chargers, How do they know to stop charging in the event that the house bank BMS’ take the house bank offline? There might be a good answer to that question in which case such a system will at least be safe, but it will still be very inefficient compared to a directly charged LFP bank monitored by an external BMS.

No it is not inefficient. What science do you base that on? You can install any amount of converters but you can also install bigger capacity converters. The reason I recommend to start with just 60A is that when you combine that with the start battery charging, you should check how the alternator is doing temperature wise (measure) as well as how the belt is doing.

If I were in your shoes, I would look into getting away from the alternator being your primary charge source…. Going to solar. I have a brand new 170A Balmar alternator with external regulator and temperature sensors on battery as well as alternator itself. I also have a nice serpentine belt, but I only have two 360W Smart Orion converters and don’t want my alternator to heat up more than it does. The continuous draw generates more heat than you realize.

[newhaul]

Originally Posted by s/v Jedi

I’m amazed everyone missed this so here goes: you can charge 100% with this setup. Let’s say your alternator can do a continuous 190A and your start battery can take 50A max. This leaves 140A available for charging your LFP house bank via DC-DC converters. I recommend you buy two 360W Smart Orions that will take 60A (plus… when cold they do more) and see how you like it. You can add a 3rd if you want.

Current from the alternator splits over the battery and the DC-DC converters. The battery does not sit in between alternator and converters. This is why the start battery prevents the transient surge when the BMS would disconnect the house battery.

Not quite I have posted my setup before a 75 amp alternator fla grp 24 start battery a 60 amp b2b and a 250ah lfp . All I am missing atm is the switch in the exciter wire to shut the alternator off if I need the extra hp for moving the boat in an emergency. Am I missing something ?

[fxykty]

Originally Posted by s/v Jedi

No it is not inefficient. What science do you base that on? You can install any amount of converters but you can also install bigger capacity converters. The reason I recommend to start with just 60A is that when you combine that with the start battery charging, you should check how the alternator is doing temperature wise (measure) as well as how the belt is doing.



If I were in your shoes, I would look into getting away from the alternator being your primary charge source…. Going to solar. I have a brand new 170A Balmar alternator with external regulator and temperature sensors on battery as well as alternator itself. I also have a nice serpentine belt, but I only have two 360W Smart Orion converters and don’t want my alternator to heat up more than it does. The continuous draw generates more heat than you realize.

I don’t know what regulator you have but if it’s a Balmar one then you set the alternator temperature limit and that will cause the regulator to throttle the alternator output when the alternator reaches that temperature.

Your solution with DC-DC converters works but it requires a bunch of extra equipment and doesn’t take advantage of the lithium battery’s charge acceptance rate. That is one of the reasons to direct all charge sources to the lithium battery and use a DC-DC converter or VSR (voltage sensitive relay) to charge the start battery.

Regarding solar as primary charge source, that only works if you only plan to cruise in areas of no clouds. Certainly possible, but not feasible for everyone. Heck, we’ve spent the last 10 months in Australia (and we mostly avoided the rainy season on the east coast), and our solar has only been enough on its own about half of that time. YMMV

An external BMS has many more features to manage your lithium battery investment and generally that system is less expensive than lithium batteries with internal BMS. For alternator control, whether via BMS control or a manual switch, use the ignition wire, not the field.

[s/v Jedi]

Originally Posted by newhaul

Not quite I have posted my setup before a 75 amp alternator fla grp 24 start battery a 60 amp b2b and a 250ah lfp . All I am missing atm is the switch in the exciter wire to shut the alternator off if I need the extra hp for moving the boat in an emergency. Am I missing something ?

I was answering Na Mara as evident from me quoting them.

[s/v Jedi]

Originally Posted by fxykty

I don’t know what regulator you have but if it’s a Balmar one then you set the alternator temperature limit and that will cause the regulator to throttle the alternator output when the alternator reaches that temperature.

Your solution with DC-DC converters works but it requires a bunch of extra equipment and doesn’t take advantage of the lithium battery’s charge acceptance rate. That is one of the reasons to direct all charge sources to the lithium battery and use a DC-DC converter or VSR (voltage sensitive relay) to charge the start battery.

Regarding solar as primary charge source, that only works if you only plan to cruise in areas of no clouds. Certainly possible, but not feasible for everyone. Heck, we’ve spent the last 10 months in Australia (and we mostly avoided the rainy season on the east coast), and our solar has only been enough on its own about half of that time. YMMV

An external BMS has many more features to manage your lithium battery investment and generally that system is less expensive than lithium batteries with internal BMS. For alternator control, whether via BMS control or a manual switch, use the ignition wire, not the field.

Using an alternator to charge LFP does not alter the charge acceptance rate compared to a DC-DC converter. It’s just about how much charge current you can supply and how much the batteries can take. It’s true that you need the dc-dc converters but there isn’t much choice when allyou have is some drop in batteries with internal BMS.

I don’t have that, I’m good, just trying to explain this to those who are limited in options due to their choice of batteries and BMS.

[Maine Sail]

Originally Posted by CharlieJ

Anybody that is installing an LFP bank had best check their alternator temperature carefully with an IR gun at a minimum to ensure that when it is charging a depleted bank its highest temperature is <100C. I am in the business and I use a FLIR IR camera for this purpose and to document the alternator's thermal performance under load.

Some YouTube videos that are germane:
>>

I have a number of images of smoked alternators due to LFP conversions in this article..

LiFePO4 Drop-In Batteries - Be an Educated Consumer (Link)








.

[hjohnson]

Originally Posted by sparrowhawk1

The way I've heard most people charging with an alternator is to keep your starting battery lead and have a battery to battery charger for your lifepo4 house. By choosing a charger that has a lower output than your alternator you will also extend the life of the alternator so it doesn't run full blast the whole time.

Or you do what I did, and use an alternator regulator that actually coordinates with your BMS. My alternator will happily pump out 75A all day long, until the BMS starts ramping down the current limit. While sitting at that 75A, the alternator sits at about 55C. Eventually, it will ramp it down to the point where the current into the battery is zero, and the alternator is powering my house loads. If the regulator loses communications with the BMS, it will flip into a “limp” mode and limit the output voltage to 13.6V.

Modern technology is pretty awesome. With a few hours of motoring, I can easily recharge a couple days use on my house battery.

[CatNewBee]

A normal good stock alternator can do the job without any changes. Neither the alternator nor the LFP will die a sudden death when motoring in a regular setup on a boat with charge distribution diodes and a lead acid start battery.

You will be surprised how low the actual charge current in reality is, that arrives in the LFP through the wiring, a 120A Yanmar alternator on a catamaran can push maybe 40A in the battery bank 5 to 8m away, it will not overheat.

If you want to fry it, use lead acid batteries and run the inverter and watermaker while motoring, that would do the trick.

[hjohnson]

Originally Posted by CatNewBee

You will be surprised how low the actual charge current in reality is, that arrives in the LFP through the wiring, a 120A Yanmar alternator on a catamaran can push maybe 40A in the battery bank 5 to 8m away, it will not overheat.

How so? Designed right, you shouldn’t lose any significant power in the wiring. If you do, that’s putting out significant heat and it’s likely a fire hazard. While I’m not going 5 to 8m, my little 85A alternator puts out a steady 75A after warming up, and according to my BMS, it’s all going straight into my house battery.

[Na Mara]

Originally Posted by hjohnson

How so? Designed right, you shouldn’t lose any significant power in the wiring. If you do, that’s putting out significant heat and it’s likely a fire hazard. While I’m not going 5 to 8m, my little 85A alternator puts out a steady 75A after warming up, and according to my BMS, it’s all going straight into my house battery.

And what Hjohnson can do with an 85A alternator you can just as easily do with a 250A alternator to greater effect. That’s the beauty of LFP’s high acceptance rate. You can really cut charging time, and so fuel burn, way down. Great for people who sail.

[Maine Sail]

Originally Posted by CatNewBee

A normal good stock alternator can do the job without any changes. Neither the alternator nor the LFP will die a sudden death when motoring in a regular setup on a boat with charge distribution diodes and a lead acid start battery.

You will be surprised how low the actual charge current in reality is, that arrives in the LFP through the wiring, a 120A Yanmar alternator on a catamaran can push maybe 40A in the battery bank 5 to 8m away, it will not overheat.

If you want to fry it, use lead acid batteries and run the inverter and watermaker while motoring, that would do the trick.

Stock Yanmar /Hitachi 80A...
..


Stock Yanmar/Valeo 125A

[donradcliffe]

Plan to test the raceboat system with a discharged LFP on Saturday 6/18 and will report back.