Experiences charging LFP from alternator WITHOUT a DC-DC charger

[Dzl]

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring safe methods and hoping for the best.

Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

 

[beanbaggs]

Ford Transit 3.2L 150a Alternator -> Sterling Pro Alt C 210A-> 2x 300Ah BYD LFP w/100a BMS
-> 2x 780CCA Starter Battery

The Pro Alt C is really just a fancy starter battery isolator that also boosts the charging voltage going to the house bank to run a 3 stage lead acid charging profile. Sterling's website says that it is compatible with LFP, but there is no specific setting for that battery chemistry, and the SLA profile is the closest one to the charging requirements LFP. In practice, it works fine. Just make sure your setup is top balanced so that the BMS isn't constantly going into single cell overvoltage protection when the unit tries to bulk charge up to 14.4V.

In theory, you could do without the pro alt c and use a battery isolator between the starter and house batteries to ensure that the starter battery doesn't get overcharged (Victron makes some nice ones). The starter battery should be fine sitting at the ~14.4V that your LFP bank would sit at towards the end of the charge cycle. The LFP will then disconnect and from there, your vehicle's charging system should float the starter battery at 13.6V.

These are used cells, and I run this system relatively hard. High rate charging (80-130A), partial charges, deep discharges, holding the house bank @ 14.4V for hours on end, and high rate discharges (100-200A for 10-30min), and it is holding up great.

At the end of the day, I am happy to have included the Pro Alt C in my design, because it simplifies the whole system, combining multiple components (isolator, DC smart charger, and external alternator regulator) into one. It also has temp monitoring on the alternator, and house batteries to limit current if things get too hot. It's a nice unit, expensive, but easy to install. It is the one component of my electrical system that I have not needed to troubleshoot, set it and forget it, worth the $$$.

 

[Reed Cole]

I'm trying to motivate myself to install this soon.

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It has over voltage protection, and cycles the charging on and off to prevent over heating of the alternator, though you can override that with a switch for continuous charging. I'm just hemming and hawing over what size cable to use since I don't really know how many amps the alternator will actually push, my van has 180A rated alternator but I'm not sure how that translates to real world use. The voltages I've seen from the van's charging system seem reasonable.

Hopefully this thread will motivate me and I will report back with some results soon.

 

[beanbaggs]

Which van do you have?
If it's newer, the ecu should be able to control the load on the alternator so that it won't overheat. Mine constantly runs between 80-100% capacity, and it holds up fine. An alternator has around 200k before it needs to be rebuilt. The last one in my 2015 Transit went for 183k before the regulator and diodes gave up, but the armature contacts were just about shot, so it didn't have much life left regardless of how hard it'd been run. It's a relatively cheap part (< $300) that you can replace in your driveway in under an hour with basic auto tools.
If the van is older and doesn't have current and temp feedback to maintain control over the alternator voltage/duty cycle, then you may have to invest in an alternator to battery charger that will ensure that the alternator doesn't overheat.

 

[Reed Cole]

Which van do you have?
If it's newer, the ecu should be able to control the load on the alternator so that it won't overheat. Mine constantly runs between 80-100% capacity, and it holds up fine. An alternator has around 200k before it needs to be rebuilt. The last one in my 2015 Transit went for 183k before the regulator and diodes gave up, but the armature contacts were just about shot, so it didn't have much life left regardless of how hard it'd been run. It's a relatively cheap part (< $300) that you can replace in your driveway in under an hour with basic auto tools.
If the van is older and doesn't have current and temp feedback to maintain control over the alternator voltage/duty cycle, then you may have to invest in an alternator to battery charger that will ensure that the alternator doesn't overheat.

It's a 2018 Promaster. I already have a sterling 30A B2B becuase I started out with a single 100ah battery, now I have a second and it would be nice to be able to charge at a higher rate at times. Hard to find any solid information but I think the alternator will push less than 100A most of the time.

Currently the batteries are about 10ft from the starter battery but I suppose I can bring the batteries closer to test it out before I buy 20ft of heavy guage cable.

 

[beanbaggs]

It's a 2018 Promaster. I already have a sterling 30A B2B becuase I started out with a single 100ah battery, now I have a second and it would be nice to be able to charge at a higher rate at times. Hard to find any solid information but I think the alternator will push less than 100A most of the time.

Currently the batteries are about 10ft from the starter battery but I suppose I can bring the batteries closer to test it out before I buy 20ft of heavy guage cable.

I'd be surprised if you ever pulled more than 60A. I have a diesel and even with all its glow plugs, def heater, and headlights on, it only draws 60A. You might be able to find the generator output current with an OBDII scan tool, but I'm not sure what PIDs are available for your vehicle. You could also put a DC Amp Clamp meter on the alternator output to see how much current it's providing.
In this post, the charging method is described, which would indicate that the generator is controlled by the PCM and should limit the max output current. You'll be running your alternator hard, but it shouldn't overheat.

 

[Reed Cole]

I'd be surprised if you ever pulled more than 60A. I have a diesel and even with all its glow plugs, def heater, and headlights on, it only draws 60A. You might be able to find the generator output current with an OBDII scan tool, but I'm not sure what PIDs are available for your vehicle. You could also put a DC Amp Clamp meter on the alternator output to see how much current it's providing.
In this post, the charging method is described, which would indicate that the generator is controlled by the PCM and should limit the max output current. You'll be running your alternator hard, but it shouldn't overheat.

Thanks, I found another post on the Promaster forum where someone documented the the amps going to their 200ah lithium battery and the total amps being pushed by the alternator. They didn't say what size wire they used over what run, but they were seeing about 50A when their battery bank was at 85% soc but they were seeing 80-90A when their battery bank was at about 35% Soc.

Alternator output gauge?

www.promasterforum.com

 

[Reed Cole]

I did it, got some 2 awg cable, ($$$ not sure why I felt compelled to buy cable at the marine store, at least they are a local business), and installed the LI-BIM 225 yesterday as well as a selector switch so I can choose between using the Sterling B2B or the LI-BIM. Actually they only had a combiner switch so if I want to get wild I can try charging with both.

With my 200ah battery bank at about 50% soc I was seeing ~60A going into the battery just letting it idle for 10-15 minutes. That's almost 3x what the Sterling puts out, should come in handy over the winter.

Of course I did things like forget to put the auxiliary voltage sensing wire for the BMV back on the starter battery. Always something to redo.

 

[Dzl]

I did it, got some 2 awg cable, ($$$ not sure why I felt compelled to buy cable at the marine store, at least they are a local business), and installed the LI-BIM 225 yesterday as well as a selector switch so I can choose between using the Sterling B2B or the LI-BIM. Actually they only had a combiner switch so if I want to get wild I can try charging with both.

With my 200ah battery bank at about 50% soc I was seeing ~60A going into the battery just letting it idle for 10-15 minutes. That's almost 3x what the Sterling puts out, should come in handy over the winter.

Of course I did things like forget to put the auxiliary voltage sensing wire for the BMV back on the starter battery. Always something to redo.

Thanks for the feedback Reed.

So your testing so far has been for periods less than or equal to 15 minutes? Did you observe alternator temperature at all during this period?

Can you briefly explain what the Li-Bim is?

And briefly explain your reason for direct connecting the lithium house bank to the vehicle charging system considering that you already have a B2B charger?

 

[Reed Cole]

I linked to the LI-BIM in a previous post on this thread, is just a battery isolator relay that will connect the starter battery and the lithium battery bank for 15 minutes then disconnect for 20 to prevent overworking the alternator. It also has over voltage protection and you can force it to stay connected for as long as you want.

I ordered it mistakenly thinking it would work with just one 100ah battery and never returned it, now that I have two batteries they can handle the current and living in the PNW we don't always get a lot of sunshine and I don't always want to have to drive for hours to keep my batteries charged as the Sterling only puts out 22 amps.

I haven't really had time to test it much other than to see that it works.

 

[Reed Cole]

So far so good, I discharged my batteries to 36% soc last night and drove for about 2 hours this morning. After an initial surge the batteries began receiving about 60amps and slowly decreased to about 50amps as approached 80% soc. I don't have a good way to monitor alternator temperature but the alternator itself is rated for 180A, although what that means isn't exactly clear, but I don't feel like I'm stressing the alternator, and I know it's not uncommon for people to use 60a b2b chargers in their Promasters.

For the Promaster at least I am beginning to believe a b2b charger is not really needed for a smaller battery bank.

 

[HRTKD]

So far so good, I discharged my batteries to 36% soc last night and drove for about 2 hours this morning. After an initial surge the batteries began receiving about 60amps and slowly decreased to about 50amps as approached 80% soc. I don't have a good way to monitor alternator temperature but the alternator itself is rated for 180A, although what that means isn't exactly clear, but I don't feel like I'm stressing the alternator, and I know it's not uncommon for people to use 60a b2b chargers in their Promasters.

For the Promaster at least I am beginning to believe a b2b charger is not really needed for a smaller battery bank.

What voltage are the batteries seeing for that charge?

 

[Reed Cole]

I have this screen shot of BMV app showing voltage and watts from the other day, I think it would have been 60%-80% SOC somewhere in there.

 

[HRTKD]

I have this screen shot of BMV app showing voltage and watts from the other day, I think it would have been 60%-80% SOC somewhere in there.

Not too bad of a float voltage. But if you're at 60-80% SOC, I would think you would want to be in bulk/absorb, not float.

 

[Reed Cole]

Well the voltage taken at the starter battery terminal of the li-bim relay when the batteries are connected is about 14.10-14-12, when they are disconnected the starter reads 14.44-14.46

 

[Reed Cole]

Here are some more data points. All these screenshots were taken on different days. I let it charge up to 100% today.

 

[Reed Cole]

 

[Reed Cole]

 

[jwelter99]

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring safe methods and hoping for the best.

Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

I have and the recommendation is don't do it; Lithium has such low internal resistance it can put extremely high loads on an alternator.

The challenge is you can not limit or regulate this load without putting something in between to do so.

 

[Marinepower]

Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring safe methods and hoping for the best.

Whatever the case I would like to hear about your insight, experience, and lessons learned. Especially if you have used an external regulator.

Dzi,

much of the marine world uses alternators for charging LFP banks in conjunction with an external regulator, like the Balmar models. See for eg. the Marine How To lifepo4 articles or search "Stan Honey's Observation on lifepo4. "

Seems to work fine for years for many if you limit bulk charging to 13.8v - 14.1v or so and limit absorb and float to 13.4v or below. As the regulator can only read pack level voltage, you really need a BMS to cut power to the regulator if anyone cell goes out of voltage. The Balmar has the ability to reduce the current out put of the alternator as well - which is the other problem with alternator charging of LFP.

MP