Alternator Charging of Lithium Iron phosphate on a travel trailer

[eXodus]

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.

so you are suggesting non linear resistance depending on charging voltage? That's interesting an interesting thesis - so at optimal charging voltage for the cell - almost down to zero resistance - and lower then that we actually got some resistance? That would partial explain the behavior we are observing.

All those alternator overheating concerns are based on the zero resistance in lithium thesis.

How can we measure that?

 

[Jasgeer]

Back in the day (in a prior life) I understood the Nernst equation and electrochemical phenomenon, enough that I obtained a patent. It would seem that if you wanted to investigate such an interaction it would be easiest to test a single cell so that the currents would be correspondingly lower and then scale them up to apply to the battery bank. I would be inclined to start with a regulated power supply which is by definition zero impedance and measure the current flow as you incrementally step the voltage of the power supply. Obviously the time domain will come into play but perhaps manually changing the voltage every 10 seconds would be a place to start.

Another interest I have had is that the output of the alternator is a full-wave rectified signal (it is not regulated DC). Even with the battery connected there is a fair amount of ripple associated with the voltage peaks. The current you read on a meter is just an average or in the worst case a sample at a point in time. If you put a small resistance in series with the cell (or battery) you should be able to see the current on an oscilloscope and observe how it changes. We used to have power supplies where I worked which could be configured to create slow moving ramps (i.e., the voltage could be set to slowly increase over seconds or minutes). Since the cell is a chemical system I would expect the reactions to change somewhat slowly and not instantly, but that is not to say that they would not be effected by voltage excursions.

I worked with an engineer who said it was interesting and sometimes profitable to exchange ignorances.

 

[Zwy]

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,

What year is your GMC? I'm currently installing a second alternator to my 2002 GMC Duramax. The alternator I'm using is an aftermarket 245a that fits into the accessory bracket and uses the original length belt for dual 105a alternators. I also sourced the alternator bracket from GM, I see people spending 2 hours building a bracket when the GM part is only 16 bucks.

I also purchased the alternator lead, it's 2 wire. This is spliced into the 105a alternator harness. The 245a alternator is internally regulated, so basically all it needs is excitement of the windings.

Depending on the year of truck you have, it might be beneficial to swap out the alternator for an internally regulated one instead of trying to circumvent any smart alternator. My current plan is to install DC to DC charger(s) to run off the 245a alternator as my house battery is 24V. Two 24V 50a DC to DC would require 100a at 12V. As was mentioned, if you're on 12V, the resistance of the run would either limit amps or the length creates a situation where voltage drop comes into play. Not such a big problem with 24V in my case, however it will be wired heavy. You could use the resistance to your advantage and not need a DC to DC but you would still want some type of isolation between your starting battery and house bank.

One advantage of running 2 alternators is that it allows you to supply power outside the truck needs on a completely separate circuit. This is why it might be beneficial to run a DC to DC charger, the charging profile can be tailored to your battery type.

 

[NPhil]

I'm testing charging right now, using the cheapest Chinese DC to DC boost converter I saw on Amazon which had:

1. A substantial heatsink.
2. Voltage adjustment _and_ current limiting adjustment.

But not direct from the alternator. I'm boosting 12V (from a backup battery) up to about 30V and connecting it through a heavy duty Schottky diode to the solar controller's panel input, in parallel with my 2X2 series/parallel array of 12V panels. It's only a couple of amps at 30V (more at 12V, of course. Something like 5A, I estimate, although I blew a 7.5A fuse yesterday morning), but hat's enough for me, because I figure that adding load to the alternator means charging batteries with energy from (incrementally) expensive gasoline, as with a generator, except not as efficiently as with a generator, instead of (incrementally) free solar. There are a couple more tricks yet to be added, like a low voltage cutoff board, which cuts it off when the battery drops too low (that's going to be just a little under 13V, I expect), and maybe connecting it to a circuit which is switched by the ignition, probably through a relay). And putting it in a box. Also I will switch, when the panels have fully charged the house batteries, to trickle charging all the 12V batteries via buck converters (to save money on generation costs, and keep the batteries healthier). I think I have all the boards in a box (except the ones I'm already testing with) where I put them after searching them out and ordering them from Amazon, here and there, over the last few months.

The way it is right now, the 24V house batteries trickle charge the backup and starter 12V batteries all the time, except, currently they are a test pack, which is much too small to do that all night _and_ make tea in the morning, before the sun comes up, so I disconnect the trickle charge and connect the boost converter until there is enough stuff to run my electric kettle without the inverter going into low voltage cutoff prematurely, due to voltage sag. Then, since I don't have the panels attached yet, if I'm going somewhere, I leave the boost converter on and let the alternator charge it, otherwise, add the panels, disconnect the boost, and reconnect the buck converter, to charge the 12V batteries back up.

One more thing. Maybe you don't want the _cheapest,_ the one with the largest heat sink I found arrived with electrolytics which had dented cans, Amazon gave me credit, so I bought another, and _it_ has dented cans, and they look like crap capacitors anyway, so I ordered decent ones from distribution, which cost more than the price of the converter, plus, my time to do all that is much more, plus my time to replace the caps when I get around to it (hopefully before one of them pops) is much more, so, I've invested in education (especially if one pops before I get around to replacing it) which I'm now spending non-billable hours sharing here.

And, I guess you could get "free" power from the alternator, if you charged batteries only when decelerating, or descending a hill using engine braking on trips you would have taken anyway. And, save your brake pads!

 

[Jasgeer]

Just to ask: is your solar controller mppt? Keep in mind that solar panels behave like a current source and a mppt controller has the smarts to vary the input load resistance in order to maximize power (V times A). When you the panels are less than the output of the DC to DC it is a low impedance source. The Schottky will prevent the voltage from ever going below approx 30Volts at the input of the controller. It would seem to work with a PWM controller but a mppt is expecting a high impedance which would fight with the output from the DC to DC. Also note that the output of the solar panels and the DC to DC are not summed together. It is strictly one or the other (the one which represents the highest voltage) on the input of the controller.

By the way a DC to DC is a switcher (probably a high frequency) so aluminum electrolytics are not the best to use as they have high series resistant. Tantalum caps are a better choice to smooth ripple from a switcher unless you are just looking for bulk capacitance.

 

[eXodus]

What year is your GMC? I'm currently installing a second alternator to my 2002 GMC Duramax. The alternator I'm using is an aftermarket 245a that fits into the accessory bracket and uses the original length belt for dual 105a alternators. I also sourced the alternator bracket from GM, I see people spending 2 hours building a bracket when the GM part is only 16 bucks.

I also purchased the alternator lead, it's 2 wire. This is spliced into the 105a alternator harness. The 245a alternator is internally regulated, so basically all it needs is excitement of the windings.

Depending on the year of truck you have, it might be beneficial to swap out the alternator for an internally regulated one instead of trying to circumvent any smart alternator. My current plan is to install DC to DC charger(s) to run off the 245a alternator as my house battery is 24V. Two 24V 50a DC to DC would require 100a at 12V. As was mentioned, if you're on 12V, the resistance of the run would either limit amps or the length creates a situation where voltage drop comes into play. Not such a big problem with 24V in my case, however it will be wired heavy. You could use the resistance to your advantage and not need a DC to DC but you would still want some type of isolation between your starting battery and house bank.

One advantage of running 2 alternators is that it allows you to supply power outside the truck needs on a completely separate circuit. This is why it might be beneficial to run a DC to DC charger, the charging profile can be tailored to your battery type.

GM part numbers please.

 

[Zwy]

GM part numbers please.

Bracket- 9735-6246
3 bolts- 11516360
Pigtail- AC Delco PT1383 or GM 15306329
You would need the belt for dual 105a alternators and the extra idler pulley. I sourced these thru parts house.
Alternator- https://www.amazon.com/gp/product/B06VWZQ1FH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Basically pigtail is wired to other alternator connector for field excitement. When the vehicle is on, the alternator would charge as needed. I may or may not run both alternator outputs together. I do run a CFX95 Dometic in the back seat of the truck. But I would prefer running it off the LFP bank when not traveling.

 

[wcsaddict]

2021. Looking at the victron DC to Dc charger.

What year is your GMC? I'm currently installing a second alternator to my 2002 GMC Duramax. The alternator I'm using is an aftermarket 245a that fits into the accessory bracket and uses the original length belt for dual 105a alternators. I also sourced the alternator bracket from GM, I see people spending 2 hours building a bracket when the GM part is only 16 bucks.

I also purchased the alternator lead, it's 2 wire. This is spliced into the 105a alternator harness. The 245a alternator is internally regulated, so basically all it needs is excitement of the windings.

Depending on the year of truck you have, it might be beneficial to swap out the alternator for an internally regulated one instead of trying to circumvent any smart alternator. My current plan is to install DC to DC charger(s) to run off the 245a alternator as my house battery is 24V. Two 24V 50a DC to DC would require 100a at 12V. As was mentioned, if you're on 12V, the resistance of the run would either limit amps or the length creates a situation where voltage drop comes into play. Not such a big problem with 24V in my case, however it will be wired heavy. You could use the resistance to your advantage and not need a DC to DC but you would still want some type of isolation between your starting battery and house bank.

One advantage of running 2 alternators is that it allows you to supply power outside the truck needs on a completely separate circuit. This is why it might be beneficial to run a DC to DC charger, the charging profile can be tailored to your battery type.

 

[wcsaddict]

GM part numbers please.

I do not know the part number. I ordered the truck that way. With this application in mind. It is also why I have an high idle switch. Should allow me to power accessories, and also charge batteries faster. But then I found out about this alternator seeing an almost dead short for bulk charging lithium iron phosphate. Will definitely run a a larger wire to the trailer separate from the 12V charge line through he 7 way.

 

[Jasgeer]

I do not know the part number. I ordered the truck that way. With this application in mind. It is also why I have an high idle switch. Should allow me to power accessories, and also charge batteries faster. But then I found out about this alternator seeing an almost dead short for bulk charging lithium iron phosphate. Will definitely run a a larger wire to the trailer separate from the 12V charge line through he 7 way.

I believe the 7 way is only rated to ~15 Amps (20A Max) which is why some people run a separate connector rated to a higher current. In my case it feeds a 20A DC-DC Renogy charger and thus far I have not overloaded it. I am moving from both alternators being connected together to separating the positive circuits so that the truck does not compete with the trailer needs.

 

[Zwy]

Bracket- 9735-6246
3 bolts- 11516360
Pigtail- AC Delco PT1383 or GM 15306329
You would need the belt for dual 105a alternators and the extra idler pulley. I sourced these thru parts house.
Alternator- https://www.amazon.com/gp/product/B06VWZQ1FH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Basically pigtail is wired to other alternator connector for field excitement. When the vehicle is on, the alternator would charge as needed. I may or may not run both alternator outputs together. I do run a CFX95 Dometic in the back seat of the truck. But I would prefer running it off the LFP bank when not traveling.

And this is what it looks like before install and after.

 

[Zwy]

2021. Looking at the victron DC to Dc charger.

I'd look at Kisae. I'm leaning that way. Victron limited on amps in my situation.

We have a thread here with all the options listed: https://diysolarforum.com/threads/dc-dc-charger-b2b-options-and-general-discussion.17211/

 

[eXodus]

Bracket- 9735-6246
3 bolts- 11516360
Pigtail- AC Delco PT1383 or GM 15306329
You would need the belt for dual 105a alternators and the extra idler pulley. I sourced these thru parts house.
Alternator- https://www.amazon.com/gp/product/B06VWZQ1FH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Basically pigtail is wired to other alternator connector for field excitement. When the vehicle is on, the alternator would charge as needed. I may or may not run both alternator outputs together. I do run a CFX95 Dometic in the back seat of the truck. But I would prefer running it off the LFP bank when not traveling.

thanks!

So you are running 2X 12V alternators. Interesting would be to get a 24V or 48V alternator somewhere.

Alpha Compact 28/150 | Mastervolt

24V/150A Alternator with charge regulator. Optimized for high power output. Compact and up to 40% lighter than conventional alternators.

www.mastervolt.com

Just FYI the Volvo Penta Engine - is just a good old Smallblock 5.7L GM Vortec

 

[Zwy]

thanks!

So you are running 2X 12V alternators. Interesting would be to get a 24V or 48V alternator somewhere.

Yes, 2 12V. I looked for a 24V but not that common. Bolt in with easily sourced belt is another. I wanted the ability to have extra capacity when running various electronics and the Dometic. I don't have a compressor fridge in the camper yet either, I run the fridge on 12V when traveling down the road. I found previously that running air conditioning with blower on high in the truck combined with the Dometic, Weboost, charging phones plus the 12V heater on the absorption fridge and house battery charging is a little hard on alternators after letting the Dometic run all night.

How much I pull off this setup remains to be seen. I always prefer to run everything at 50% duty cycle when possible, 177.5a is 2100 watts. One could add an extra 2000w inverter for those cases where one might need either an emergency backup or need extra power.

If I just use the 250a for the camper LFP pack charging while traveling, even at 50% would require 2 DC to DC chargers. Most I've found is 50a to 60a input of 12v and the same wattage output on 24V. Unless you go with something like this. https://www.safiery.com/3kw-12-48v-canbus-integrated-buck-boost-power-char

That's just a crazy price for the job required. I've even thought about using an inverter up front and running 120v to the back with a AC to DC charger. Might actually be the ticket to transfer all those amps to the rear.

Alpha Compact 28/150 | Mastervolt

24V/150A Alternator with charge regulator. Optimized for high power output. Compact and up to 40% lighter than conventional alternators.

www.mastervolt.com

Just FYI the Volvo Penta Engine - is just a good old Smallblock 5.7L GM Vortec

Not sure it would fit, I have a 6.6L DMax. I also have a larger 12V load in the truck than factory in addition to 24V house system so it may make more sense to stay with the 12V up front.

What does that alternator cost? I've seen prices like this https://megadepot.com/product/mastervolt-46628150-alpha-compact-28-150-charge-regulator and this in Euro https://www.chmarine.com/mastervolt-alpha-compact-alternator-28-150a/ which would be the $3.5K to $4K USD range with the conversion rate and I'll wager customs and shipping would put it at $4K USD.

I think I'll stick with what I have.

 

[Zwy]

I did finish the install, the factory specified belt length for dual 105a alternators fit perfectly. Took me longer to find a bolt for the required extra idler pulley than it did to install the whole thing.

One could install another 250a alternator in place of the 105a currently on the passenger side of the engine, it would bolt right in. That would be 6000w peak output.

 

[12VoltInstalls]

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…

You are missing some important details. The truck with loads could be providing 15+ volts at times. Lithium don’t like that. Plus there’s specific ways a good charger profiles the cycle that’s very different for lead vs lifepo.
You need a DC2DC charger to regulate the lifepo charge imho

I’d ‘settle’ for the 30A supply for truck charging and just look at it as a bonus myself. And just add a few panels at 24V and keep a 12V battery bank. But I’m weird - unless you’re doing consistently high-amp draws or running wire for long distances I’d just go 12V since probably lights and everything are made 12V already.

 

[eXodus]

I did finish the install, the factory specified belt length for dual 105a alternators fit perfectly. Took me longer to find a bolt for the required extra idler pulley than it did to install the whole thing.

One could install another 250a alternator in place of the 105a currently on the passenger side of the engine, it would bolt right in. That would be 6000w peak output.

I think I would go that route. I got a 150A alternator. Just dropping in a 250A would be easy. I recently saw even 320A and 390A single alternator. https://skyhighcaraudio.com/brand-x-gm-320a-alternator-93-04/

320A @12V 3840w
390A @12V 4680W

The truck part needs maybe 500-800w.

 

[Zwy]

I think I would go that route. I got a 150A alternator. Just dropping in a 250A would be easy. I recently saw even 320A and 390A single alternator. https://skyhighcaraudio.com/brand-x-gm-320a-alternator-93-04/

320A @12V 3840w
390A @12V 4680W

The truck part needs maybe 500-800w.

I'm trying to decide how to get that power back to the battery's. I have a 24v Growatt and could feed 120V to the input side if I install an inverter up front. If I'd load two 250a alternators to 50% of both alternators and would have 3000w available. That would give 125a at 24V which the GW only will charge 80a. The GW is limited to 1440w off utility for charging. But I could always just use the transfer switch to power loads if needed.

If instead I use the 355a available at 50% load, that would give me 2100w, still more than the GW can charge at using 120v. Going to a larger alternator doesn't pay unless I was to use multiple DC to DC chargers such as Kisae at a max of 50a 24v.

I'll have to think about this more.

 

[RVLiFe]

Sorry for jumping in here. Quick question. I have 2018 GMC 3500HD Duramax with single 220Amp alternator. I have no interest in re-wiring the truck for DC-DC to my fifth wheel. I just installed 206Ah LiFePO4 battery. Do you recommend that I pull the 30amp fuse to the 7-pin wiring harness that supplies power to the trailer battery or is it such a low trickle that I don’t need to be concerned? Will my truck try to supply 15v to the trailer battery and would this be detrimental to either the LiFePO4 and/or the alternator? Looks like you guys are trying to solve this issue as well but honestly, I don’t really need the power unless I can install a 20 amp dc-dc charger using the same wiring that’s already there.
Between solar, generator and 206Ah battery, installing a charger from the truck just seems overkill for what I need.

 

[time2roll]

Sorry for jumping in here. Quick question. I have 2018 GMC 3500HD Duramax with single 220Amp alternator. I have no interest in re-wiring the truck for DC-DC to my fifth wheel. I just installed 206Ah LiFePO4 battery. Do you recommend that I pull the 30amp fuse to the 7-pin wiring harness that supplies power to the trailer battery or is it such a low trickle that I don’t need to be concerned? Will my truck try to supply 15v to the trailer battery and would this be detrimental to either the LiFePO4 and/or the alternator? Looks like you guys are trying to solve this issue as well but honestly, I don’t really need the power unless I can install a 20 amp dc-dc charger using the same wiring that’s already there.
Between solar, generator and 206Ah battery, installing a charger from the truck just seems overkill for what I need.

I would go as is with no modifications. Worst case the oem fuse will open and stop the charging. Then you can evaluate what you want to do if anything.