Alternator charging LiFePO4 ?

[Seven30]

I am interested in the same inquiry, of charging lifepo4 (battle born gc3 270ah , 300A bms) with my vehicle alternator. I have a '15 Roadtrek Adventurous which is a sprinter and it has a dedicated 2nd alternator (Nations Mercedes-280-XP) which outputs 280A@12v. BB says the GC3 will take 170A continuous charge and based on the info I provided them, that I dont need an external regulator. That would be a blessing but want to make sure I'm going about this right. When I called Nations about instructions on Balmar connection to my existing alternator, they said that it isn't configured for external regulator therefore I'd have to do a $500 modification service or buy a new one $1100. I figure if there is no value in the old one , I might as well give it a try without any regulation and simply replace it with the correct solution if and when it burns out.

Since its designed for auxiliary duty and has an intergrated regulator the details should be available to find out where it gets its startup power(some are self exciting) and if it has a temperature sensor as well as its output voltage at various currents and temperatures. It may have a remote enable/disable and/or regulator power connector which would be convenient.
That 4ga wire has to dissipate the 170Ax2V=340W so keep it isolated from anything else. Nice opportunity for a fire.

 

[justinm001]

My alternator is oil cooled, no fan. and it puts out full power at idle. 600RPM
Its on a prevost bus.

Hey Rickety just came across this. I have a Prevost too with the 50DN but 12V and a couple 12V lithium battery packs (EG4-LL). Just setup a wakespeed WS500 regulator with a lithium profile and it works amazingly. Has a temp sensor to keep the alternator from getting too hot. Had first trip with it yesterday and 2nd today and it works great. Charges 2500+watts in bulk. I'm thinking about switching to 24V, adding 2 more batteries and replacing the 50DN with a 50DN+ which does 450amps

 

[ImAnIdiotPleaseBePatient]

Hey Rickety just came across this. I have a Prevost too with the 50DN but 12V and a couple 12V lithium battery packs (EG4-LL). Just setup a wakespeed WS500 regulator with a lithium profile and it works amazingly. Has a temp sensor to keep the alternator from getting too hot. Had first trip with it yesterday and 2nd today and it works great. Charges 2500+watts in bulk. I'm thinking about switching to 24V, adding 2 more batteries and replacing the 50DN with a 50DN+ which does 450amps

Would you still need to keep some 12v to run some of the bus's functions?

 

[justinm001]

Would you still need to keep some 12v to run some of the bus's functions?

So the chassis/starter has 4 12v batteries in series/parallel for 24v start and it uses a 100amp vanner to also run 12v and pull loads from one battery then the vanner equalizes the batteries.

The house side still needs 12v for a bunch of things like lights and I could either use a Vanner like the chassis does or just get a 24 to 12 victron charger and run all off that.

 

[OhmsLawyer]

I know this is an old thread but many people will read it when google searching for insight into charging lithium battery chemistry using a car, bus, or truck alternator. I've read through the entire thread and have determined that there is one piece of information that everyone here seems to have missed. I believe that this comment will put a definitive end to the argument.

That piece of info is that there is a PROFOUND difference between the ESR (equivalent series resistance) of lead acid batteries verses the ESR of LiFePO4 or lithium ion, especially when comparing ESR at a discharged state. This is why standard car, bus, or truck alternators cannot be directly connected to any kind of lithium battery.

Standard alternators are designed to charge lead acid batteries that have a high ESR when discharged, thus providing a voltage drop through the battery itself when charging. That voltage drop adequately limits the charging current from the alternator. In this scenario, the battery ESR is much greater than the alternator "ESR" so very little heat is generated in the alternator. The alternator runs cool and is never overloaded.

On the other hand, any type of lithium battery will have a relatively constant low ESR, even when 50% discharged, and this low ESR means the alternator will attempt to match the regulator voltage to the battery voltage, which will be impossible, so the alternator is then forced to dissipate an intense amount of power in an attempt to make up for the voltage difference.

If this is difficult to understand- please read this simplified case example:

A typical lead acid car battery that is 50% discharged may have an ESR around 50 milliohms. The resting voltage of this 50% discharged battery will be around 12.0 volts. When the car is started, the alternator will put out around 14.4 volts max, regardless of what the battery voltage is, because its output voltage is regulated to 14.4 volts. However, since the battery is sitting at 12.0 volts, there will be a 2.4 volt difference in voltage between battery and alternator. Therefore, due to the ESR of 50 milliohms, the charging current will be around 2.4 volts divded by 0.05 ohms = 48 amps. The actual charging current will be less, however, since lead acid batteries exhibit some hysteresis between the resting voltage and charge voltage, but that is another discussion and this calculation gets you into the ballpark. 48 amps is totally fine for most car alternators. Truck alternators need to be larger because they use more batteries in parallel- so the parallel ESR will be proportially less according to parallel resistance rules.

Now, replace that car battery with a 100Ah LiFePO4 battery with a relatively steady ESR of about 1 milliohm. Discharge the battery to 50% and the ESR stays around 1 milliohm! This is actually one of the biggest reasons why lithium batteries are superior to lead acid- it's all about the low and steady ESR. However, since the ESR is so low, it will not self-regulate charging current like lead acid batteries do. Working through the same calculation as above, given that we discharge the LiFePO4 battery down to 12.0 volts as in the previous example, we get a charging current of 2.4 volts divided by 0.001 ohms = 2400 amps! If the alternator could actually produce that much current it would attempt to be fed into the battery but the battery's internal BMS current protection would trip off. If the alternator can't produce that current, then it will be overloaded and either overheat or the alternator's regulator will fry out or trip.

This is all because standard car and truck alternators are voltage regulated, not current regulated. When you are charging your ebike or something, your AC wall charger has current regulation as well as voltage regulation. Vehicle alternators do NOT have current regulation because they assume to be connected to lead acid batteries.

This is why you need to add some kind of current regulating circuit between the vehicle alternator and any sort of lithium battery. The field control loop needs to be closed around either current or temperature or both, to keep both the battery and the alternator from being overloaded by excess current.

As the popularity of adding lithium batteries to automotive, RV, truck, and bus vehicle systems increases, manufacturers may develop new types of alternators designed to be compatible with lithium battery charging. They would incorporate both current and temperature regulation in addition to voltage regulation. But for now, we are stuck with having to DIY this kind of stuff.

Cheers, everyone, and happy DIYing.

BTW I am a retired NASA spacecraft avionics engineer, not that it matters.

 

[mikefitz]

we get a charging current of 2.4 volts divided by 0.001 ohms = 2400 amps!

Not quite, when you take into account the alternators source resistance and the series resistance of connecting cables, fuses, connectors, the current Into the lithium battery is limited to around 100 amps typically.
The alternator may still fail, the rectifier pack being the weak link.

 

[MisterSandals]

Therefore, due to the ESR of 50 milliohms, the charging current will be around 2.4 volts divded by 0.05 ohms = 48 amps.

This is great, i learned something today!

I would like to know how the ESR number relates to the "resistance" (internal resistance i presume?) number on my capacity tester. I am doing a LiFePO4 305Ah 4 wire discharge at 30A and it shows "resistance .128 ohms".

??
30A x .128ohms = 3.84V (is this meaningful?)

Thanks for any info.

 

[Crowz]

I'm wondering how car companies are getting away with equipping cars with lifepo4 batteries if this is such a problem.

BMW has a lithium battery option for one.



I am planning on running lifepo4's in my x5 the next time it needs a battery. One thing I have planned is using 2 batteries to make sure cranking amps won't be an issue and hopefully it will eliminate the bms disconnecting and driving the alternator nuts.

 

[OhmsLawyer]

Not quite, when you take into account the alternators source resistance and the series resistance of connecting cables, fuses, connectors, the current Into the lithium battery is limited to around 100 amps typically.
The alternator may still fail, the rectifier pack being the weak link.

Thanks, I appreciate your comment, and you are correct.

Of course my calculation was theoretical and assumed zero resistance in the alternator circuit (including cables etc).

However, since the voltage regulator is sampling at the output of the alternator, the alternator resistance and rectifier drop are difficult to account for because the field current will increase to make up for the voltage drop in that resistance and across the rectifiers. The result is that the alternator output at the terminal will raise back up to 14.4V or whatever the set voltage is, or until the alternator overloads. Once you max out the regulator and field current, the alternator and rectifiers are already operating well outside of their capacity.

Therefore you can only really consider the cables, fusible link, terminals, etc. in the circuit to support your argument for resistive current limiting. If the total resistance of those components is around 24 milliohms, then, yes, your estimate that current would be limited to around 100 amps would be correct, but that would mean 240 watts of power is being dissipated by the cables and connectors, and something is going to get hot and burn. If you are getting any voltage drop at the alternator output, then again, the alternator and rectifiers are grossly overloaded and as you say, the alternator would likely fail with the rectifier pack being the weak link.

And assuming there really is 24 milliohms of resistance in the alternator cables and terminals- that amount of resistance is actually very high, and if you were to charge a lithium battery through that resistance, as the battery voltage approaches full charging voltage, the charging current would drop off quite dramatically. For instance, if the battery is at 14.2 volts and the alternator is putting out 14.4 volts, the 24 milliohm resistance in the cables and terminals would limit the charging current to only 8 amps. If you had any loads greater than 8 amps on the house battery at that time, the battery would be drained instead of charged!

When a lead acid battery is being charged, however, the voltage drop in the battery is significantly larger than the drop through the cables and through the alternator windings, so nothing burns up, nothing is overloaded, and there is very little dissipation in the cables.

 

[OhmsLawyer]

I'm wondering how car companies are getting away with equipping cars with lifepo4 batteries if this is such a problem.

BMW has a lithium battery option for one.

View attachment 170174

I am planning on running lifepo4's in my x5 the next time it needs a battery. One thing I have planned is using 2 batteries to make sure cranking amps won't be an issue and hopefully it will eliminate the bms disconnecting and driving the alternator nuts.

My guess is that their new cars have alternators equipped with current and temperature limiting (foldback regulation). That would make them compatible with both lead acid and lithium batteries.

 

[scubadoo]

Theory does little for me. If it did our battery would have died years ago according to a few doomsayers.

A recent post of mine on this forum:
I'm still waiting for an "expert" to inform us wether the alternator or battery will die first and when.

"The "non smart" original 100A rated alternator in our Mitsubishi Canter 3.9l turbo diesel truck based motorhome has survived 9 years of full-time travel direct charging the 4 cell 300Ah LiFePO4 Sinopoly battery at 70-80A without releasing any smoke yet.
No standard "BMS" circuitry involved.
I recently paralleled a 4 cell 280Ah LiFePO4 EVE battery.
As well as powering our house it has also started the truck perhaps a few thousand times over the years. Perfect performance so far.
The "BMS" involves no charging source exceeding 14.1V at which point the battery is always at 100% SOC regardless of charge current. 80A alternator, 50A solar and 30A battery charger.
20% SOC alarm and Victron BatteryProtect disconnect at 12.5V. Never triggered.

I'm guessing that the alternator must have some form of temperature control?
Charge current starts at c95A and drops to nearer 70A over about 30 minutes."




Reply

Report Edit

 

[fratermus]

Of course my calculation was theoretical and assumed zero resistance in the alternator circuit (including cables etc)

Relay-charging typically routes NEG return through the chassis, introducing large amounts of resistance.

My last few observations of charge acceptance with bank voltage and SoC before cranking the engine. 180A alt @ 14.2v, 150Ah LiFePO4 bank:

1. 0.245C, 13.07v, 60% SoC
2. 0.13C, 13.15v, 72%
3. 0.12C, 13.13v, 69%
4. 0.27C, 12.95v, 27%
5. 0.15C, 13.29v, 80%
6. 0.24C, 13.27v, 80%
7. 0.17C, 13.30v, 81%
8. 0.165C, 13.22v, 77%
9. 0.26C, 13.03v, 39%

Solar contribution and loads varied at the time of measurement.

and if you were to charge a lithium battery through that resistance, as the battery voltage approaches full charging voltage, the charging current would drop off quite dramatically

Yes, that is what I observe.

I believe that this comment will put a definitive end to the argument.

I am reminded of the saying that "people who say it cannot be done should not interrupt those who are doing it."

 

[mikefitz]

the alternator resistance and rectifier drop are difficult to account for because the field current will increase to make up for the voltage drop in that resistance and across the rectifiers

The alternator ' internal resistance effect' at high current.
When the field current reaches maximum, driven by alternator output voltage, the available power at a given RPM reaches a limit. Due to the heavy load current, the alternator output voltage falls, thus the field current falls and the alternator enters a steady state where its developing maximum power but at a lower voltage than the regulator is demanding.
This effect of a lower alternator voltage than nominal clearly shows in testing.

It's probable there will be a number of posts in reply to this discussion that state no issues with direct alternator charging.
My short term tests on a number of van conversions with alternators rated at 150 to 180 amps with direct connection, vehicle battery to lithium battery with cable rated for 110 amps, showed a maximum current 60 to 90 amps at engine idle speed.

A battery to battery charger is recomended for long term reliability, correct termination of charge, keeping within the manufactures maximum ancillary loading. The latter is important to avoid possible litigation if things go wrong.

Mike

 

[TimE]

I know this is an old thread but many people will read it when google searching for insight into charging lithium battery chemistry using a car, bus, or truck alternator. I've read through the entire thread and have determined that there is one piece of information that everyone here seems to have missed. I believe that this comment will put a definitive end to the argument.

That piece of info is that there is a PROFOUND difference between the ESR (equivalent series resistance) of lead acid batteries verses the ESR of LiFePO4 or lithium ion, especially when comparing ESR at a discharged state. This is why standard car, bus, or truck alternators cannot be directly connected to any kind of lithium battery.

Standard alternators are designed to charge lead acid batteries that have a high ESR when discharged, thus providing a voltage drop through the battery itself when charging. That voltage drop adequately limits the charging current from the alternator. In this scenario, the battery ESR is much greater than the alternator "ESR" so very little heat is generated in the alternator. The alternator runs cool and is never overloaded.

On the other hand, any type of lithium battery will have a relatively constant low ESR, even when 50% discharged, and this low ESR means the alternator will attempt to match the regulator voltage to the battery voltage, which will be impossible, so the alternator is then forced to dissipate an intense amount of power in an attempt to make up for the voltage difference.

If this is difficult to understand- please read this simplified case example:

A typical lead acid car battery that is 50% discharged may have an ESR around 50 milliohms. The resting voltage of this 50% discharged battery will be around 12.0 volts. When the car is started, the alternator will put out around 14.4 volts max, regardless of what the battery voltage is, because its output voltage is regulated to 14.4 volts. However, since the battery is sitting at 12.0 volts, there will be a 2.4 volt difference in voltage between battery and alternator. Therefore, due to the ESR of 50 milliohms, the charging current will be around 2.4 volts divded by 0.05 ohms = 48 amps. The actual charging current will be less, however, since lead acid batteries exhibit some hysteresis between the resting voltage and charge voltage, but that is another discussion and this calculation gets you into the ballpark. 48 amps is totally fine for most car alternators. Truck alternators need to be larger because they use more batteries in parallel- so the parallel ESR will be proportially less according to parallel resistance rules.

Now, replace that car battery with a 100Ah LiFePO4 battery with a relatively steady ESR of about 1 milliohm. Discharge the battery to 50% and the ESR stays around 1 milliohm! This is actually one of the biggest reasons why lithium batteries are superior to lead acid- it's all about the low and steady ESR. However, since the ESR is so low, it will not self-regulate charging current like lead acid batteries do. Working through the same calculation as above, given that we discharge the LiFePO4 battery down to 12.0 volts as in the previous example, we get a charging current of 2.4 volts divided by 0.001 ohms = 2400 amps! If the alternator could actually produce that much current it would attempt to be fed into the battery but the battery's internal BMS current protection would trip off. If the alternator can't produce that current, then it will be overloaded and either overheat or the alternator's regulator will fry out or trip.

This is all because standard car and truck alternators are voltage regulated, not current regulated. When you are charging your ebike or something, your AC wall charger has current regulation as well as voltage regulation. Vehicle alternators do NOT have current regulation because they assume to be connected to lead acid batteries.

This is why you need to add some kind of current regulating circuit between the vehicle alternator and any sort of lithium battery. The field control loop needs to be closed around either current or temperature or both, to keep both the battery and the alternator from being overloaded by excess current.

As the popularity of adding lithium batteries to automotive, RV, truck, and bus vehicle systems increases, manufacturers may develop new types of alternators designed to be compatible with lithium battery charging. They would incorporate both current and temperature regulation in addition to voltage regulation. But for now, we are stuck with having to DIY this kind of stuff.

Cheers, everyone, and happy DIYing.

BTW I am a retired NASA spacecraft avionics engineer, not that it matters.

Nice explanation of how it works.
I would add that nobody seems to mention what happens to the alternator diodes should the lithium BMS do a shut down. Even with an expensive after market external regulator, such as a Wakespeed, unless is connected to a Victron BMS/battery combo or a Lithionics, the diodes will fry. If you install a Sterling alternator protection device, its just another set of diodes in a little box. Those diodes will fry instead of the ones in your alternator. You have to spend £80 to buy a new one after you have had a BMS shut down whilst charging with your alternator. How many spares should you carry?

 

[fratermus]

I would add that nobody seems to mention what happens to the alternator diodes should the lithium BMS do a shut down

The lead starter battery is still in the circuit. The radiator cooling fans on my van pull more current than my LiFePO4 pack and shut on/off frequently. I also don't charge my pack to BMS shutoff.

 

[TimE]

The lead starter battery is still in the circuit. The radiator cooling fans on my van pull more current than my LiFePO4 pack and shut on/off frequently. I also don't charge my pack to BMS shutoff.

Mixing lead and lifepo4 is a whole new thread. It's not something I will do

 

[OhmsLawyer]

Thank you to those who challenged my comment and gave real life examples of installations that are directly charging lithium type batteries from alternators (or charging via isolator relays) without excessive charging current and without overheating the alternators. None of that negates my comment, however, it just shows that there is some resistance in the charging circuit somewhere, as one commenter noted there is often resistance in the chassis negative connections, or it's possible newer alternators have regulators that feature voltage foldback upon reaching maximum allowable current and use of such alternators to charge lithium batteries could be perfectly fine as a result of having built-in current regulating circuits.

My comment was assuming the use of old classic alternators (in my example I tried a 1980s vintage Leece Neville ambulance alternator) without current regulation.

If you could specify what vehicle make/model/year and/or alternator part number I would be interested in repeating your setups to see if those particular alternators use current limiting regulators in them.

This actually gives me hope because I would like to experiment with direct charging of lithium batteries using alternators, and would measure the voltage drops, regulator output, and charging current for different setups and report back here my findings. This would allow DIYers the opportunity to set up lower cost mobile installations by not requiring a DC-DC converter for charging.

Therefore, the trick to doing this successfully and reliably would be dependent upon the make/model of alternator used.

Best regards!

 

[RV8R]

Thank you to those who challenged my comment and gave real life examples of installations that are directly charging lithium type batteries from alternators (or charging via isolator relays) without excessive charging current and without overheating the alternators. None of that negates my comment, however, it just shows that there is some resistance in the charging circuit somewhere, as one commenter noted there is often resistance in the chassis negative connections, or it's possible newer alternators have regulators that feature voltage foldback upon reaching maximum allowable current and use of such alternators to charge lithium batteries could be perfectly fine as a result of having built-in current regulating circuits.

My comment was assuming the use of old classic alternators (in my example I tried a 1980s vintage Leece Neville ambulance alternator) without current regulation.

If you could specify what vehicle make/model/year and/or alternator part number I would be interested in repeating your setups to see if those particular alternators use current limiting regulators in them.

This actually gives me hope because I would like to experiment with direct charging of lithium batteries using alternators, and would measure the voltage drops, regulator output, and charging current for different setups and report back here my findings. This would allow DIYers the opportunity to set up lower cost mobile installations by not requiring a DC-DC converter for charging.

Therefore, the trick to doing this successfully and reliably would be dependent upon the make/model of alternator used.

Best regards!

I value your input here & find it interesting. As you are well aware, there are big differences between;

Theory & Real World Experience
A Specific Part & An Entire System
Dumb Alternators & Smart Ones ( I am unaware of unregulated alternators )


This topic interests me. I have done both with AGMs ,,, “Direct Charged” & “DC2DC”

As LFP has a BMS & AGMs don’t, I recently purchased a Kisae 1250 to “custom charge” my 250Ahr AGMs. This DC2DC does a much getter job than the direct charge method I originally put into my van. 3 Stages with voltage & amperages “user programable”.


Modern vehicles have computers that control the alternators. I had to go down a rabbit hole years ago while attempting to sort out an “alternator issue” on one of my airplanes, & as it wasn’t “Rocket Science” I still came across the internal regulator for my particular alternator & researched the letter destinations on these internal regulators which is;


C = Computer
S = Sensor
D = Dummy


It was over a decade ago, but in specifics the internal regulator I installed on my airplane alternator was a Transpo IN256 “Sensor”;











I would assume, most RVs vehicles “these days” have alternators which are controlled by computers & computer regulators “C” type.


The Days of Yore are past. Everything has a computer(ish) feel these days.


My point is, where I can read & understand what you have posted & it is all great information ( in theory ), it might not be relevant when you cnsider “the entire system” & all the computer control.


For Me; With LFP “Direct Charge” or “DC2DC” there are Pros & Cons to both choices, but it comes down to the choice of;

Direct Charge “Better Power” typically

DC2DC “Less Power” but “Might Be Easier on the Equipment”


Either way, IMO it falls under the “Experimental“ classification.


Voltage with my Kisae 1250 ( newly installed on my Van )






Typical voltage “Direct Charge” AGMs;





My AGM battery specs @ bulk charge is 14.7v & I am only able to “typically” get this with a DC2DC.

 

[Reed Cole]

Thank you to those who challenged my comment and gave real life examples of installations that are directly charging lithium type batteries from alternators (or charging via isolator relays) without excessive charging current and without overheating the alternators. None of that negates my comment, however, it just shows that there is some resistance in the charging circuit somewhere, as one commenter noted there is often resistance in the chassis negative connections, or it's possible newer alternators have regulators that feature voltage foldback upon reaching maximum allowable current and use of such alternators to charge lithium batteries could be perfectly fine as a result of having built-in current regulating circuits.

My comment was assuming the use of old classic alternators (in my example I tried a 1980s vintage Leece Neville ambulance alternator) without current regulation.

If you could specify what vehicle make/model/year and/or alternator part number I would be interested in repeating your setups to see if those particular alternators use current limiting regulators in them.

This actually gives me hope because I would like to experiment with direct charging of lithium batteries using alternators, and would measure the voltage drops, regulator output, and charging current for different setups and report back here my findings. This would allow DIYers the opportunity to set up lower cost mobile installations by not requiring a DC-DC converter for charging.

Therefore, the trick to doing this successfully and reliably would be dependent upon the make/model of alternator used.

Best regards!

I have a 2018 ram pro master, gas engine, standard option 180 amp alternator. I have been charging 2x 100ah Battleborn batteries for two years now directly from the alternator, via a relay with over voltage protection. Seems to work fine. It puts out more current when the batteries are more depleted, tapering dramatically as it nears 100% charged. I use the batteries and drive almost everyday, though in the summer solar can be enough and I might leave the alternator disconnected.

Edit: it's actually been three years now