Charging lithium from the Alternator

[mistericeman]

From memory Average tick over speed of the alternator is usually around 2500 rpm

Most are rated to spin up to 15,000

 

[colinm]

Isn't that what he said Colin?

Yes, I was halfway through posting when I got a phone call and hit reply too early, soo to finish my post.

A smaller pulley on the alternator turns it at a higher speed, to work out the speed differance you need to compare the circumference, next time I'm under the bonnet if I remember I'll measure the pulley's to get an idea of speed.

 

[merl]

Having done the research rather than relying on widespread belief I can say that charging a lithium battery via an alternator or lead acid mains charger in your motorhome is usually completely OK.
It's widely touted that
'Lithium could cause excessive current because the internal resistance is massively lower than lead acid'
This is completely false, a 100Ah LFP battery is typically only around half the resistance of a new 100Ah lead acid, this means that 2 new 100Ah lead acid batteries would have a similar internal resistance of a 100Ah LFP battery, do people question or fear their alternator or wiring burning out when fitting 200Ah of new lead acid batteries into their MH? NO! It's been done thousands of times.
Secondly the difference in internal battery resistance is massively outweighed and swamped by the wiring resistance because MH wiring resistance is typically at least 10 times higher than battery resistance.
Thirdy, whilst charging, lithium battery voltage is nearly always higher than LA, this voltage increase actually reduces charge current in LFP compared to LA, so typical alternator charging currents are lower for lithium than new lead acid.
WRT damaging lithium by leaving them connected to a charger or alternator while they are fully charged (float charging lithium). Again the widely held belief and 'expert' advice is in fact massively overblown and inaccurate and 'floating' lithium with an alternator or mains charger would have very little negative effect over time considering typical MH use.

 

[Geek]

Thirdy, whilst charging, lithium battery voltage is nearly always higher than LA, this voltage increase actually reduces charge current in LFP compared to LA, so typical alternator charging currents are lower for lithium than new lead acid.

Although I think your other points and your conclusions are correct, this point is not, according to my experience.
I have a li-ion battery running in parallel with two agm batteries. They are charged by the same b2b charger, but I monitor the battery terminal voltages and the currents in and out of each battery bank separately.

Typically, when they are on charge, the Li-ion battery takes the lion's share of the charge, but due to voltage losses in the charging cables (they're only 25mm) the li-ion battery is at a lower voltage than the other two, not higher.

When the charger gets past the bulk stage, the Li-ion BMS starts to have an influence and the battery voltages tend to even out.

After the charging stops, there is generally a bit of current flowing from the Li-ion into the AGMs, and when charging resumes, the Li-ion gets more current again.

They work really well together. The Li-ion tends to do almost all of the day-to-day work, but after a long time (several days) of draining with no charge, when the Li-ion is getting empty, its voltage drops to where the AGMs are able to help.

Note that my 12v use is all low current loads. Nothing big. The biggest is probably the water pump, which doesn't run often.
It might be different if I used a big inverter or a 12v fridge.

 

[marchie]

Having done the research rather than relying on widespread belief I can say that charging a lithium battery via an alternator or lead acid mains charger in your motorhome is usually completely OK.
It's widely touted that
'Lithium could cause excessive current because the internal resistance is massively lower than lead acid'
This is completely false, a 100Ah LFP battery is typically only around half the resistance of a new 100Ah lead acid, this means that 2 new 100Ah lead acid batteries would have a similar internal resistance of a 100Ah LFP battery, do people question or fear their alternator or wiring burning out when fitting 200Ah of new lead acid batteries into their MH? NO! It's been done thousands of times.
Secondly the difference in internal battery resistance is massively outweighed and swamped by the wiring resistance because MH wiring resistance is typically at least 10 times higher than battery resistance.
Thirdy, whilst charging, lithium battery voltage is nearly always higher than LA, this voltage increase actually reduces charge current in LFP compared to LA, so typical alternator charging currents are lower for lithium than new lead acid.
WRT damaging lithium by leaving them connected to a charger or alternator while they are fully charged (float charging lithium). Again the widely held belief and 'expert' advice is in fact massively overblown and inaccurate and 'floating' lithium with an alternator or mains charger would have very little negative effect over time considering typical MH use.

Neil Cooper, who used to own KS Energy, made a video initially refuting the need for a B2B, saying that the Lithium was a drop-in replacement [he fitted mine on this basis!] and that the fire risk from the alternator was more theoretical than real. Whether it was in response to customer doubts/falling sales [always a powerful motivation to recheck one's claims!], I don't know, but he subsequently issued a revised video recommending the use of a B2B to avoid any fire risk

Steve

 

[Pudsey Bear]

All work of the Divil, anything to do with elecktrickery needs a certain mindset I believe, and while some of it trickles in, I am very grateful to know we have a few chaps on the forum who do have a clue.

 

[merl]

Although I think your other points and your conclusions are correct, this point is not, according to my experience.
I have a li-ion battery running in parallel with two agm batteries. They are charged by the same b2b charger, but I monitor the battery terminal voltages and the currents in and out of each battery bank separately.

Typically, when they are on charge, the Li-ion battery takes the lion's share of the charge, but due to voltage losses in the charging cables (they're only 25mm) the li-ion battery is at a lower voltage than the other two, not higher.

When the charger gets past the bulk stage, the Li-ion BMS starts to have an influence and the battery voltages tend to even out.

After the charging stops, there is generally a bit of current flowing from the Li-ion into the AGMs, and when charging resumes, the Li-ion gets more current again.

They work really well together. The Li-ion tends to do almost all of the day-to-day work, but after a long time (several days) of draining with no charge, when the Li-ion is getting empty, its voltage drops to where the AGMs are able to help.

Note that my 12v use is all low current loads. Nothing big. The biggest is probably the water pump, which doesn't run often.
It might be different if I used a big inverter or a 12v fridge.

Hi, from your brief description of your system what you're experiencing seems sound and as I'd expect. I guess you've got the two battery types quite close with relatively short interconnects compared a much longer run of common cable supplying them from the B2B?
What you're seeing playing out is the relative differences between the resistance in the battery interconnects and the internal resistances of the two types of batteries, this is manifesting as the differential between the LA and the LFP terminal voltage. (After all if the batteries were TRULY in parallel then the terminal voltages must be identical).
In your case the relatively short length of the interconnects means the relative differences in the internal resistance of the two battery types ISNT swamped by wiring resistance (between battery and alternator) as it would be in a typical MH setup and therefore becomes significant and the LFP battery MUST receive a greater current than your LA as dictated by ohms law.
Please also bear in mind that the internal resistances I referenced were for new LA and LFP batteries (LFP approx 4mΩ, lead acid approx 8mΩ) were manufacturers figures for brand new batteries, those figures will rise faster for LA than LFP as the batteries age and this will also contribute to the figures you're seeing.

 

[Fisherman]

Neil Cooper, who used to own KS Energy, made a video initially refuting the need for a B2B, saying that the Lithium was a drop-in replacement [he fitted mine on this basis!] and that the fire risk from the alternator was more theoretical than real. Whether it was in response to customer doubts/falling sales [always a powerful motivation to recheck one's claims!], I don't know, but he subsequently issued a revised video recommending the use of a B2B to avoid any fire risk

Steve

All new vehicles now have smart alternators to reduce power consumption and reduce emissions. They supply more power as required say when you are running headlights, heated seats etc, but on low use they cut back current. The B2B optimises the charge current to habitation batteries allowing them to run equipment such as your fridge whilst keeping your habitation and starter batteries charged. My victron 50a B2B has three stage charging to prevent overcharging and protect the alternator. I find that with my fridge running one hours driving adds around 40amps to my two 100ah lithium batteries, that’s 20%. In winter with less solar and less need for the fridge to be running whilst travelling I will try leaving the fridge off and hope to increase this to 50a and 25%.
Whilst not essential with a standard alternator it’s recommended that a B2B is fitted.
They’re not cheap but with my smart alternator vital. I had a 30a victron B2B installed prior to this which struggled when my fridge was on, the 50amp version has improved things enormously.

 

[Fisherman]

Hi, from your brief description of your system what you're experiencing seems sound and as I'd expect. I guess you've got the two battery types quite close with relatively short interconnects compared a much longer run of common cable supplying them from the B2B?
What you're seeing playing out is the relative differences between the resistance in the battery interconnects and the internal resistances of the two types of batteries, this is manifesting as the differential between the LA and the LFP terminal voltage. (After all if the batteries were TRULY in parallel then the terminal voltages must be identical).
In your case the relatively short length of the interconnects means the relative differences in the internal resistance of the two battery types ISNT swamped by wiring resistance (between battery and alternator) as it would be in a typical MH setup and therefore becomes significant and the LFP battery MUST receive a greater current than your LA as dictated by ohms law.
Please also bear in mind that the internal resistances I referenced were for new LA and LFP batteries (LFP approx 4mΩ, lead acid approx 8mΩ) were manufacturers figures for brand new batteries, those figures will rise faster for LA than LFP as the batteries age and this will also contribute to the figures you're seeing.

I think I see your point merl, resistance being not only measured via internal batteries but wiring circuitry also. Therefore a lithium battery with lower internal resistance than a lead battery can be balanced out by the lithium batteries either being further away from the alternator, or if using a smaller cable than the cable used for lead batteries.
So with this in mind can the internal resistance differential be balanced with use of different cable sizes, by upping the resistance of one cable against the other.

Cheers.

 

[merl]

Neil Cooper, who used to own KS Energy, made a video initially refuting the need for a B2B, saying that the Lithium was a drop-in replacement [he fitted mine on this basis!] and that the fire risk from the alternator was more theoretical than real. Whether it was in response to customer doubts/falling sales [always a powerful motivation to recheck one's claims!], I don't know, but he subsequently issued a revised video recommending the use of a B2B to avoid any fire risk

Steve

Indeed Steve and in my comments above I did say that drop in is USUALLY ok, not ALWAYS ok! There's a gazillion ways to wire the electrics on a gazzilion different sort of vans, the variations are too great for a manufacturer to make a blanket statement of proclaiming their batteries are ALWAYS drop in replacements.
If one of those gazzillion set ups involves someone who's wired/rewired their van with extremely short fat cables (Just as the infamous Victron video Kev posted) without an appropriate fuse then that manufacturer/seller/installer is potentially in big trouble. In a litigious world with current day social media it's important to cover your ass and Mr Cooper quickly decided that the financial benefits of providing a LFP battery that was a 'drop in replacement' was outweighed by the potential of harm from the an unusual setup and backtracked to recommending a B2B.
I've currently got a setup that includes a 40A B2B. If I keep the van and install more solar, a bigger controller and more lithium then I'll probably remove the B2B because I need the space for another controller and charge direct from the alternator. I KNOW and am absolutely confident that I can size the cables to give me SAFE and effective charging without ruining my LFP batteries or alternator. Would I do the same for a customer if I were a commercial installer?? Absolutely NOT!

 

[merl]

All new vehicles now have smart alternators to reduce power consumption and reduce emissions. They supply more power as required say when you are running headlights, heated seats etc, but on low use they cut back current. The B2B optimises the charge current to habitation batteries allowing them to run equipment such as your fridge whilst keeping your habitation and starter batteries charged. My victron 50a B2B has three stage charging to prevent overcharging and protect the alternator. I find that with my fridge running one hours driving adds around 40amps to my two 100ah lithium batteries, that’s 20%. In winter with less solar and less need for the fridge to be running whilst travelling I will try leaving the fridge off and hope to increase this to 50a and 25%.
Whilst not essential with a standard alternator it’s recommended that a B2B is fitted.
They’re not cheap but with my smart alternator vital. I had a 30a victron B2B installed prior to this which struggled when my fridge was on, the 50amp version has improved things enormously.

Yes, B2B needed for smart alternator vehicles. I should have included that

 

[exwindsurfer]

My 4 Relion 100amp lithiums batteries are over 6 years old now and only get charge from my alternator or my solar no b to b so I guess I must be doing something right .I do have a mains charger but have never used it.

 

[merl]

I think I see your point merl, resistance being not only measured via internal batteries but wiring circuitry also. Therefore a lithium battery with lower internal resistance than a lead battery can be balanced out by the lithium batteries either being further away from the alternator, or if using a smaller cable than the cable used for lead batteries.
So with this in mind can the internal resistance differential be balanced with use of different cable sizes, by upping the resistance of one cable against the other.

Cheers.

Yes it can Bill.
There's only one equation that's relevant and that's ohms law, Current equals voltage divided by resistance. It's a law not a guide AND it applies to motorhome wiring too
The voltage we're using at isn't 12V or 14.4v. It's voltage differential between alternator (source) and battery (load).
The DUMB alternator voltage is essentially constant and relatively stable whereas the battery voltage varies quite a lot by comparison according to it's state of charge, charge current also has a smaller but relevant affect. Here's a chart showing Voltage VS SOC, it's cell voltage so you have to multiply the voltage by 4 .

Understanding the LiFePO4 Voltage Chart

Discover the LiFePO4 voltage chart and how voltage affects power delivery, energy storage, and lifespan. Optimize device performance and longevity.

www.evlithium.com

Using the 0.3C line (30A charge for a 100Ah battery) at approx 5% SOC the terminal voltage is 13V, at 95% the voltage rises to 13.65v. Ohms law states that current will therefore be higher at the lower end because there's more voltage differential available to drive current, below the 5% figure current will shoot up considerably so we want to avoid charging at such low levels directly from the alternator, just in case there should be a correctly sized fuse to protect from accidental charging in this zone.
If we decide a max charge current of 30A @ 5% SOC is a suitable UPPER limit for our charge current we then have a voltage differential of 1.4V (alternator voltage minus battery voltage) We now have the voltage (1.4) and the current (30) for our equation, from this we can now calculate the required TOTAL resistance needed in the charge circuit, this is 0.047 ohms. or 47mΩ,
We know that the maximum charge current is 30A so we'll help our cause of introducing enough resistance to limit current by using the thinnest cable permissible and use 4mm cable.
Cable resistance for 4mm copper is 7.4mΩ,/metre so at first glace we need 6.3m of cable in the WHOLE circuit including the negative (47 over 7.4) to meet the requirement. however there are other resistances in our circuit that we didn't factor in.
Battery resistance. (4mΩ),
Fuse resistance. Use 2, 1 at each end of the positive. ( approx 7mΩ, each at 25A) so around 14mΩ, total)
Contact resistance on terminal posts etc. (not huge but significant)
Because actual charge current will be supplied by the alternator and typically the wiring will be sourced at the starter battery NOT the alternator then the resistance in the circuit between the alternator and starter battery will also play a part in the equation as will the true alternator voltage. Both of these factors are highly system dependant.
In practice you'd probably end up using about half the cable so about 3-4m or if the distance between alternator and battery is sufficient then go up a cable gauge to 6mm but you'd obviously have to discharge the battery to a low level of around 5% and measure the current in real life and adjust the cable length accordingly, adding another fuse would be an option to tweak the resistance.
We now have 30A flowing at 5% capacity, the current will now fall gradually as the battery charges and it's voltage increases, at 95% charge the current will drop off to around half of what we had at 5%. From 95% to 100% the battery voltage rises and hence current drops off quickly and obviously at 14.4v the current essentially stops.

 

[molly 2]

Mine looks like a 240v incomer with a red illuminated switch for the charger. There is another box of goodies under the rear seat/bed, but all you see are fuses. But there is zero way to change settings, so I have to assume it's a dumb charger.

Is that a sargent system

 

[molly 2]

We do tend to drive most of the day, less so in the UK though.

Not found a single battery so far labelled as Lead Carbon.

I got mine from alpha battery's

 

[Pudsey Bear]

Is that a sargent system

I don't think so Barrie, it seems to be all Nordelletro, I'll take a pic next time I go in the van.

 

[Pudsey Bear]

I got mine from alpha battery's

I stuck with LA Barrie, if a knackered one can almost keep up, who needs more?

 

[exwindsurfer]

No Sargent just 2 blocks of fuses

 

[exwindsurfer]

Yes it can Bill.
There's only one equation that's relevant and that's ohms law, Current equals voltage divided by resistance. It's a law not a guide AND it applies to motorhome wiring too
The voltage we're using at isn't 12V or 14.4v. It's voltage differential between alternator (source) and battery (load).
The DUMB alternator voltage is essentially constant and relatively stable whereas the battery voltage varies quite a lot by comparison according to it's state of charge, charge current also has a smaller but relevant affect. Here's a chart showing Voltage VS SOC, it's cell voltage so you have to multiply the voltage by 4 .

Understanding the LiFePO4 Voltage Chart

Discover the LiFePO4 voltage chart and how voltage affects power delivery, energy storage, and lifespan. Optimize device performance and longevity.

www.evlithium.com

View attachment 145356
Using the 0.3C line (30A charge for a 100Ah battery) at approx 5% SOC the terminal voltage is 13V, at 95% the voltage rises to 13.65v. Ohms law states that current will therefore be higher at the lower end because there's more voltage differential available to drive current, below the 5% figure current will shoot up considerably so we want to avoid charging at such low levels directly from the alternator, just in case there should be a correctly sized fuse to protect from accidental charging in this zone.
If we decide a max charge current of 30A @ 5% SOC is a suitable UPPER limit for our charge current we then have a voltage differential of 1.4V (alternator voltage minus battery voltage) We now have the voltage (1.4) and the current (30) for our equation, from this we can now calculate the required TOTAL resistance needed in the charge circuit, this is 0.047 ohms. or 47mΩ,
We know that the maximum charge current is 30A so we'll help our cause of introducing enough resistance to limit current by using the thinnest cable permissible and use 4mm cable.
Cable resistance for 4mm copper is 7.4mΩ,/metre so at first glace we need 6.3m of cable in the WHOLE circuit including the negative (47 over 7.4) to meet the requirement. however there are other resistances in our circuit that we didn't factor in.
Battery resistance. (4mΩ),
Fuse resistance. Use 2, 1 at each end of the positive. ( approx 7mΩ, each at 25A) so around 14mΩ, total)
Contact resistance on terminal posts etc. (not huge but significant)
Resistance in the van wiring between alternator and battery because actual charge current will be supplied by the alternator and typically the wiring will be sourced at the starter battery NOT the alternator. ?? (System dependant)
In practice you'd probably end up using about half the cable so about 3-4m or if the distance between alternator and battery is sufficient then go up a cable gauge to 6mm but you'd obviously have to discharge the battery to a low level of around 5% and measure the current in real life and adjust the cable length accordingly, adding another fuse would be an option to tweak the resistance.
We now have 30A flowing at 5% capacity, the current will now fall gradually as the battery voltage increases, at 95% charge the current will drop off to around half of what we had at 5%. From 95% to 100% the battery voltage rises and hence current drops off quickly and obviously at 14.4v the current essentially stops.

You do realize all that is right over my head Merl lololol

 

[merl]

You do realize all that is right over my head Merl lololol

Shhh, it's all bollox, I made it all up! It's amazing what you can get away with if you just act confident and look like you know what you're doing.