Alternator Charging of Lithium Iron phosphate on a travel trailer

[wcsaddict]

I am upgrading to Lithium iron phosphate batteries in my travel trailer. I understand electricity, and solar pretty well, but I have noticed the videos on this topic of using vehicle Alternators to charge Lithium Iron Phosphate batteries seems to generate a bad response in his videos. He basically said it was too expensive for the special electronics to do it right. So before I knew the lithium iron phosphate batteries were the way I was going to go, I bought a GMC 3500 with dual lead acid batteries and dual alternators 220A primary with 170A secondary. I also had a high idle switch installed on my truck so I can run the RPMs at 1500 to generate more electricity faster specifically to charge the house batteries of the travel trailer when I am hunting off grid for weeks in Montana without having to carry an additional generator (although I have a Honda 2200, but it is a long way to bring gas with me). Anyway, I have noticed in these threads, people are using what I have found which is the Victron Orion TR converter to convert the energy from the standard vehicle to the lithium Iron Phosphate batteries. To complicate this further, I was going to put in the 24V system for all the many benefits of such.

I am not going to change out the alternators on the truck, or do anything like that, so anyone should be able to hook up to this trailer and have some level of charging to the lithium iron phosphate batteries even at 24VDC.

Of course, I like the benefit of getting the batteries charged while driving as well, and I hope this is just to supplement the low solar output I will have in the cold at Northern latitudes of Montana, Idaho, and WA state.

So my main point is this, before I spend $250 on a Victron 12V to 24V DC lithium charging converter to use my alternators to charge my house batteries, have I missed anything that makes this not technically work? Should I build a 12V system out of simplicity instead even though the benefits of 24 seem worth it to me.

Secondly, is it worth it assuming I have a wire large enough from the alternators to the 7 way connector? Will it charge my 4 Lion UT1300 batteries in a series parallel configuration to make 2 24VDC batteries in a reasonable amount of time at 24VDC, assuming I have a 40amp fuse after the alternators and a large enough wire from the alternators to the 7 way connector? I can carry the generator, and the gas, but it is just more stuff people can steal while I am away from the trailer while hunting.

Does this make sense, or am I basically wasting $250 I could spend somewhere else? Should I build it 12VDC, and should I separate the alternators entirely, and use a generator to charge the batteries? Thoughts?

Finally,

 

[eXodus]

So far I hear always that:
"When you use lithium batteries on an alternator you will burn it out"
But I haven't heard about single burned out alternator.

The are some threads, where people just put lead and lithium and parallel charge from the alternator - boaters usually- the alternator seems to do this with no ill effects, and those guys are idling for hours.

One of your questions: The 7 Pin plug provides about 20A @ 12V when it's in perfect condition. Usually those plugs are messed up due to elements and I wouldn't push it past 15A

So it depending how large your battery is - you need a bigger connector. I saw a few people just having a anderson connector dangling from the rear bumper with some more substantial cable.


I mean you have so much alternator power - you could probably get a cheap 12V Pure sinewave inverter - put that on the truck and charge your trailer with 120V. Cheaper then carrying a generator. That would also free up your battery choices in the trailer 24V 48V - no problem. Whatever you want.

The generator will be more fuel efficient - but another headache.

 

[wcsaddict]

I forgot to add, that the GMC has smart alternators too, which means the voltage will not be constant while driving down the road. I wish I understood "smart" alternators better.

 

[eXodus]

I forgot to add, that the GMC has smart alternators too, which means the voltage will not be constant while driving down the road. I wish I understood "smart" alternators better.

that's an easy one

Old alternator just keep one Voltage - while modern (2000 and later) actually measure the what's going to the battery and reduce the voltage when the lead battery is fully charged.
Further like when you hit kickdown or accelerate hard it reduces charging - to free up more engine power for a short period of time.

But nothing of this done by the alternator - those things are still not very smart - but they got a control lead from the Engine Computer. Which lets them tell what to do.

 

[Jasgeer]

I read a report on the Mortons on the Move: Go North webpage that the dual alternators in their F350 would overheat when charging BB 12V Lithium batteries (they had 5 in parallel). They had to cycle them ON/OFF to avoid over heating.
On a Ford the dual alternators became more intelligent ~2012 when they came controlled by the PCM. Also, the wiring on a Ford is relatively easy to separate into two distinct charge circuits.

 

[WhiteHot]

Also, the wiring on a Ford is relatively easy to separate into two distinct charge circuits.

I have dual alternators/LA batteries on my 2020 F250. Would you mind elaborating on the "two distinct charge circuits"?

 

[Jasgeer]

The wiring diagrams on earlier Fords are free to download at https://carmanualshub.com/ford-wiring-diagrams/ I do not know about 2020 versions. I have read that it is fairly easy to separate the feed (battery connection) from the secondary alternator in the wiring harness over the passenger wheel and route it to a second battery. I am toying with converting the secondary alternator to use an external regulator so I can adjust it to a higher voltage (16-16.5V). Internal regulators are available for 6G alternators with Vset up to 14.8V. I even read on a forum of someone who installed a 24V regulator on their 6G alternator to charge their battery bank. You might want to read the comments on the Morton website to gain ideas. Go here: https://mortonsonthemove.com/truck-camper-lithium-alternator-charging/

 

[grizzzman]

I forgot to add, that the GMC has smart alternators too, which means the voltage will not be constant while driving down the road. I wish I understood "smart" alternators better.

I have a "smart Alternator"( I agree that PCM controls the Alternator ) At idle With a Renolgy 40Amp DC to DC charger was pulling 50 Amps at 12.8-12-9 volts, Amps output was 35. This was at idle. ( There is a cost to boosting voltage ) Wire size will play a LARGE roll it to how many Amps gets to the House LFP. Make sure the unit is a buck/boost charger.

 

[time2roll]

With two alternators it there a special accessory connection to get 100 amps off this system?
The existing 12v trailer charge circuit at 40 amps is good for 20/30 amps max into a 12 volt battery. No point in the dual alternators for that.

 

[eXodus]

I read a report on the Mortons on the Move: Go North webpage that the dual alternators in their F350 would overheat when charging BB 12V Lithium batteries (they had 5 in parallel). They had to cycle them ON/OFF to avoid over heating.
On a Ford the dual alternators became more intelligent ~2012 when they came controlled by the PCM. Also, the wiring on a Ford is relatively easy to separate into two distinct charge circuits.

while this cycling on and off is a wise precautions against overheating - It very much depends.

When you got the lithium batteries in parallel to the lead system of the truck - the truck battery will supply the missing amps to the lithium system.

The regulated alternator will just doing it's best and keep charging happy along. Depending on the lithium chemistry you are using. Most alternator systems run at around 13.8V - 14.4V and only supply 14.8V for a short period of time after engine start.

So you LFP battery is fully charged at something like 14.6V

https://sunonbattery.com/lfp-battery-voltage-capacity/

So what happens when your alternator is running at 14V and your batterie sits at 13.60? (50%) There is not much voltage differential - thus not much current is flowing.

You basically only run into those overheating issues - when your LFP batteries is well below 13V (or the alternator is set to a higher voltage) and you got enough voltage drop for current to flow. Water is only flowing fast down the hill when it's step.

Be mindful and run the truck alternator well before you get to 30% DOD.
Further you can always introduce some resistance into the circuit to limit LFP charging - install a shunt, and use the frame of the truck/ trailer as second conductor. You don't need a lot but an Ohm or two would reduce charging quit a bit.

 

[Jasgeer]

If you have everything connected to the same source voltage the current from the alternator will flow to the load (or loads) that draw the most at whatever the voltage happens to be. Some devices in the truck probably start to draw current at very low voltages (like the computer, fuel pump, fans, entertainment, incandescent lights, etc). Other items like batteries only draw current after the voltage achieves a certain threshold voltage which is above where the battery is charged. That is why it makes little sense to connect a wet cell in parallel with a Lithium battery (or anything with a different chemistry). Remember that Ford designed a system with Maintenance Free batteries in mind. The wet cell will likely charge first followed by the Lithium. When you restart the engine the Lithium battery will likely be charging the wet cell and helping to provide current to the truck if the output of the alternator is insufficient at idle. This is part of the justification for separating the two alternator charge circuits so that the primary alternator is dedicated to charging the wet cell and providing power to the truck while the Secondary alternator provides power to the Lithium battery and other loads. By design you could have the Primary and Secondary control at different voltages (assuming you defeat Ford's automatic control of the voltage in recent models).
BTW, I discovered that Ford only turns on the Primary alternator at startup to prevent excessive load on the serpentine belt which would snap the belt. There is a delay of ~45 seconds before the secondary alternator is energized.
A separate DC-DC Converter (like Renogy or other brands) is a good approach as the charging characteristics of the second battery can be configured (typically for more voltage than on the truck's Maintenance Free battery) AND the Lithium will not backflow and try to charge the truck's system.

 

[eXodus]

Oh they do a lot more fancy things with the alternators these days. Many manufactures turn them also off (or reduce to the bare minimum) when you hit kickdown or accelerate hard.

 

[TheBreeze]

I installed this on my motorhome to contain overheating. It may (should?) help. You'll have to translate the guide from motorhome to truck. Motorhome sits on an e450 chassis. I would expect my charge setup to be similar to yours, save the 7-pin. Your call. PC-LiBIM225

 

[Jasgeer]

This would do a good job in preventing the coach battery from supplying energy to the chassis (backflow) but it cannot boost the voltage if the Lithium battery needs more than the alternator provides.

 

[DJSmiley]

Alternator overload can occur, but it's not that common. In theory, yes, the LFP can draw huge amounts of amps, causing the alternator to provide high amps for longer periods. Generally, an alternator isn't designed to run at max load for longer periods.

In reality, this isn't the case that often, primairy due to cable losses. Any cable will cause a voltage drop. This will reduce the current. Especially at high currents, the voltage drop is huge. And with the rather flat curve of a LFP, this will highly limit the max of amps, thus reducing the load on the alternator.
If the battery gets more full, current will drop, voltage drop will decrease, and in the end everything will be all-right.

I did some testing. I've connected an (almost empty) 280Ah EVE set to my alternator (Fiat Ducato - similar to a Promaster, 2.3 Diesel engine). I used 25mm2 jumper cables ( 4AWG) of approx 3m (8ft). The used clamps will cause some additional connection resistance, so keep in mind the current could be higher when properly connected.

I've measured the current: Depending on the RPM (idle: 23A, 3000rpm: 70A). My alternator is capable of 120A. I think, with proper connections and thicker wire, the current could be much higher.

Replaced the 8ft cable with a 8ft 10AWG cable (6mm2): Idle: 21A, 3000rpm: 22A... Proved to me the cabling was indeed limiting the amps.

When using a DC-DC, that compensates for the cable loss. Benefits are faster charging (You're charging at the rated amps of the DC-DC). Downside: the DC-DC compensates for the cable loss by pulling more amps, so the alternator has to provide more power.

When using high-amps DC-DC, especially on an older car with a smaller alternator, or with heavy internal loads on the alternator as well, you're pushing the alternator to it's max. I'm quite sure it won't last long when running at 90+% of its rated capacity.

On the highway, the wind might cool it down, but in a traffic jam, or slowly driving, the wind is less noticable, thus it will get even hotter.

Personally, I won't recommend using more than 30% of the rated alternator power for the secondary battery charging. That will leave some room for its 'regular' jobs and cooling capacities.

I recently noticed a new DC-DC charger from WCS (An German company). They have a 60A DC-DC in their inventory, which also has a temperature sensor to be connected to the alternator. That will cause the charger to lower its output if the alternator gets too hot, preventing the alternator to fry...

https://www.wcs-mobiletechnik.de/

On their Youtube page are some nice interesting clips about this.. (In German tho)

Pretty expensive, but based on the information I've seen, it completely kicks ass compared to a Victron. (Double the amps, alternator temperature based output, works for all setups (12-12, 12/24 and 24/12V setups).

I have installed a Renogy 40A DC-DC in my van. For now, I used it not that much. Generally, my solar panel (315WP) is able to topup the battery fine, so I don't see the need to charge from the alternator (with additional diesel usage) while the sun is free
I've installed a switch on my dash so I can manually switch it on if I really need to.

 

[HRTKD]

I have dual alternators in my Ford F-350 with the 6.7L diesel. I use zero alternator charging to maintain my LiFePO4 battery bank in my RV trailer. I didn't like the problems that have been shown with the standard charge profile coming from the alternator(s). So far, I have no need of the alternator charge, the PV on the roof of the RV is doing a fine job.

However, if I did want a charge from the truck, I wouldn't need much, so I would use the 7-pin circuit and add a DC-DC charger that outputs 15 amps or less.

If I needed more than 15 amps output I would run dedicated cables from the engine bay to the rear of truck and then into the trailer. The challenge here is that the cable for that would have to be quite large if I wanted 40 amps of output to the LiFePO4 battery bank. To use some real world numbers, figure 60' of cable (30' round trip distance), 50 amps input (40 amps output) and 12 volts. To keep under 3% voltage drop, I would need to use 1/0 gauge cable, and I would probably go with 2/0 since I have lugs for that size cable already. That's a lot of weight and expense!

A side note on the Ford alternators. According to what I've read, they rarely run at the same time. They take turns, letting one cool down while the other one runs. So while I have a "rated" 390 amps, it's really much lower.

 

[Jasgeer]

I have dual alternators in my Ford F-350 with the 6.7L diesel. I use zero alternator charging to maintain my LiFePO4 battery bank in my RV trailer. I didn't like the problems that have been shown with the standard charge profile coming from the alternator(s). So far, I have no need of the alternator charge, the PV on the roof of the RV is doing a fine job.

However, if I did want a charge from the truck, I wouldn't need much, so I would use the 7-pin circuit and add a DC-DC charger that outputs 15 amps or less.

If I needed more than 15 amps output I would run dedicated cables from the engine bay to the rear of truck and then into the trailer. The challenge here is that the cable for that would have to be quite large if I wanted 40 amps of output to the LiFePO4 battery bank. To use some real world numbers, figure 60' of cable (30' round trip distance), 50 amps input (40 amps output) and 12 volts. To keep under 3% voltage drop, I would need to use 1/0 gauge cable, and I would probably go with 2/0 since I have lugs for that size cable already. That's a lot of weight and expense!

A side note on the Ford alternators. According to what I've read, they rarely run at the same time. They take turns, letting one cool down while the other one runs. So while I have a "rated" 390 amps, it's really much lower.

I know from experience and observation that on my 2003 F250 7.3L Diesel that the two alternators do not take turns. There is no alternator temperature sensing. They are strictly Primary and then the Secondary is switched on after a delay. There is no voltage control or voltage sensing by the PCM. There is logic but not much you could consider Smart.

 

[HRTKD]

I know from experience and observation that on my 2003 F250 7.3L Diesel that the two alternators do not take turns. There is no alternator temperature sensing. They are strictly Primary and then the Secondary is switched on after a delay. There is no voltage control or voltage sensing by the PCM. There is logic but not much you could consider Smart.

I should have included that my F-350 is a 2017 model. Almost too many smarts in the newer models.

 

[eXodus]

Alternator overload can occur, but it's not that common. In theory, yes, the LFP can draw huge amounts of amps, causing the alternator to provide high amps for longer periods. Generally, an alternator isn't designed to run at max load for longer periods.

In reality, this isn't the case that often, primairy due to cable losses. Any cable will cause a voltage drop. This will reduce the current. Especially at high currents, the voltage drop is huge. And with the rather flat curve of a LFP, this will highly limit the max of amps, thus reducing the load on the alternator.
If the battery gets more full, current will drop, voltage drop will decrease, and in the end everything will be all-right.

I did some testing. I've connected an (almost empty) 280Ah EVE set to my alternator (Fiat Ducato - similar to a Promaster, 2.3 Diesel engine). I used 25mm2 jumper cables ( 4AWG) of approx 3m (8ft). The used clamps will cause some additional connection resistance, so keep in mind the current could be higher when properly connected.

I've measured the current: Depending on the RPM (idle: 23A, 3000rpm: 70A). My alternator is capable of 120A. I think, with proper connections and thicker wire, the current could be much higher.

Replaced the 8ft cable with a 8ft 10AWG cable (6mm2): Idle: 21A, 3000rpm: 22A... Proved to me the cabling was indeed limiting the amps.

When using a DC-DC, that compensates for the cable loss. Benefits are faster charging (You're charging at the rated amps of the DC-DC). Downside: the DC-DC compensates for the cable loss by pulling more amps, so the alternator has to provide more power.

When using high-amps DC-DC, especially on an older car with a smaller alternator, or with heavy internal loads on the alternator as well, you're pushing the alternator to it's max. I'm quite sure it won't last long when running at 90+% of its rated capacity.

On the highway, the wind might cool it down, but in a traffic jam, or slowly driving, the wind is less noticable, thus it will get even hotter.

Personally, I won't recommend using more than 30% of the rated alternator power for the secondary battery charging. That will leave some room for its 'regular' jobs and cooling capacities.

I recently noticed a new DC-DC charger from WCS (An German company). They have a 60A DC-DC in their inventory, which also has a temperature sensor to be connected to the alternator. That will cause the charger to lower its output if the alternator gets too hot, preventing the alternator to fry...

https://www.wcs-mobiletechnik.de/

On their Youtube page are some nice interesting clips about this.. (In German tho)

Pretty expensive, but based on the information I've seen, it completely kicks ass compared to a Victron. (Double the amps, alternator temperature based output, works for all setups (12-12, 12/24 and 24/12V setups).

I have installed a Renogy 40A DC-DC in my van. For now, I used it not that much. Generally, my solar panel (315WP) is able to topup the battery fine, so I don't see the need to charge from the alternator (with additional diesel usage) while the sun is free
I've installed a switch on my dash so I can manually switch it on if I really need to.

I got my 450AH house bank in my VAN directly with connect with a 200A relay to the 180A Chevy Alternator.

The highest I've ever seen had been 100A and that was for like a few minutes after startup, when the battery was fairly empty and the alternator voltage was high (14.8V) then it dropped and was around 50-70A and that's with a massive 0/2 gauge wire. (35mm square)
At the regular 13.8V - 14.4V what the PCM runs the charging system there is not that much current flowing.

I don't think that lithium pull that much current at a low voltage drop. Thesis idea:

That would be a interesting research project - charging different lithium at normal alternator voltages and not optimal charging specification settings.
Sure at a higher Voltage they will pull whatever they can get - but at a lower level they don't

 

[Jasgeer]

I believe the crude equiv circuit of a Lithium cell is that it is a resistance in series with a voltage source of zero impedance. However, since it is a chemical system so it would not be unreasonable to find that the resistance is non-linear and complex in nature. The voltage applied to a cell can determine the chemical response. I base this on some experience with electrochemistry.