Charging lithium batteries direct from an alternator and why you shouldn't
T1 Terry said
11:39 AM Oct 4, 2019
This is a Victron video demonstrating what I have been says for the last 8 yrs, trying to charge a lithium battery without a DC to DC charger inbetween and the correct size cabling to carry the required current will destroy either the very expensive alternator or result in either the failure of the DC to DC charger if the supply cable is too small, or the actual cable melting and shorting out if the type of DC to DC charger used wasn't smart enough to reduce its output current when the voltage was too low.
Thanks for the link. The alternator would run even hotter in the engine bay.
I might swap over my Victron dumb DC to DC for a smart one.
-- Edited by Whenarewethere on Friday 4th of October 2019 12:02:40 PM
Noelpolar said
12:15 PM Oct 4, 2019
Most alternators are geared up by 2x to 2.5x.... only saying this to make sense of their rpm statements. I certainly am to CS (Chicken Sh##) to run largish capacity lithiums off a standard vehicle alt.... also pulling out a run of 6B&S from the van this week end to replace it with 2B&S to jelp the 40 amp DC2DC to get past it's 27amp issue... the Enerdrive unit current limits at about 11.6v.... 13 meters from car battery.
T1 Terry said
12:20 PM Oct 4, 2019
Noelpolar wrote:
Most alternators are geared up by 2x to 2.5x.... only saying this to make sense of their rpm statements. I certainly am to CS (Chicken Sh##) to run largish capacity lithiums off a standard vehicle alt.... also pulling out a run of 6B&S from the van this week end to replace it with 2B&S to jelp the 40 amp DC2DC to get past it's 27amp issue... the Enerdrive unit current limits at about 11.6v.... 13 meters from car battery.
Yeas, the smart alternators are making the old standard of 6B&S cabling being sufficient to supply the DC to DC charger out dated. $ B&S or even 2 B&S might become the norm for these applications and an upgrade from the traditional 50 amp Anderson plug because it can not handle the bigger cable.
Which is the better option, increase the alternator voltage and risk problems there, or increase the size of the supply cable all the way back to the DC to DC charger, not just to the tow bar.
T1 Terry
Whenarewethere said
12:40 PM Oct 4, 2019
If I got a cold climate pack for my car, ie heated seats, steering wheel, windscreen. The car would get a larger alternator with an extra 30amps.
T1 Terry said
01:58 PM Oct 4, 2019
Whenarewethere wrote:
If I got a cold climate pack for my car, ie heated seats, steering wheel, windscreen. The car would get a larger alternator with an extra 30amps.
The alternator in a car is not rated for a 100% duty cycle so you can't expect it to run anywhere better than 50% in the engine bay heat for long periods of time without failing. Is pushing the continuous output voltage up from 13.6v to 14.1v or higher adding strain to the alternator? Depends if you are also increasing the continuous current draw at the same time.
Use watts to calculate the results, an alternator pushing out 100 amps @ 13.6v = 1360w. Now increase that to 14.1v and the total is now 1410w. If the efficiency is 50% as Victron suggest, that is now 1410w of heat that needs to be removed from an alternator that was designed to put out 1360w and need to displace 1360w of heat for a short period to recharge the start battery, then just drop back to the load the accessories require.
think about what will happen if you boost the output voltage to 14.1v, this drops to 12.8v as it passes through the various relays and plug as well as the cable length. The DC to DC charger is set to put out 14.4v @ 40 amps, 14.4 x 40 = 576w and the alternator must supply this along with the accessory load and the initial starter battery recharging .... do you need to add the recharging requirements for any aux batteries in the back of the car or under the bonnet? Odds are the alternator will handle this fine because the additional load was only 45 amps x 14.1v, but if that lithium battery was close by of connected with heavy cable so the voltage drop was minimal and no DC to DC charger was fitted inbetween to act as a current limiter? Until the lithium battery reaches that 14.1v it will take everything the alternator can put out by holding the voltage lower than the 14.1v it is trying to reach, how long do you think it will take for the alternator to overheat?
Those temperature rises shown in the video have ambient temperature air being pumped through and alternator mounted in a clear air flow region. Now look at where the alternator is in your engine bay and just how hot it gets in there when dragging the RV along .... how hot do you reckon that alternator will get even if it is spinning at 5,000rpm? Now imagine that same alternator at idle engine revs ....
T1 Terry
Noelpolar said
02:19 PM Oct 4, 2019
I've recently become a fan of 120A Andersons..... they are easier to plug and unplug than the 50s.... good for old hands.... don't need your glasses either. Another 10 years and I'll be doing everything in 175s.
-- Edited by Noelpolar on Friday 4th of October 2019 02:21:08 PM
T1 Terry said
02:27 PM Oct 4, 2019
Noelpolar wrote:
I've recently become a fan of 120A Andersons..... they are easier to plug and unplug than the 50s.... good for old hands.... don't need your glasses either. Another 10 years and I'll be doing everything in 175s.
-- Edited by Noelpolar on Friday 4th of October 2019 02:21:08 PM
:lol: Those 50 amp Anderson plugs can become a real tug of war without a handle attached. The bigger plugs give a much better contact area as well so less heat build up across the faces. Not too many of the copy cat manufacturers have the bigger plugs so you are more likely to buy the quality Anderson manufactured plugs if you do go for the bigger plugs, so a bit of a bonus there as well, but they cost a bit more than the 50 amp units and are a bit harder to locate when you need one after it dragged up the road for a few hundred kms.
T1 Terry
Whenarewethere said
04:35 PM Oct 4, 2019
The starter motor current in my car is 238amps & charging increases & settles normally to 80amps after 30 seconds.
Looking through list of fuses for the 3 fuse boxes in my car it is pretty frightening what current the car needs to power everything & I only have a semi pauper model! The hi-fi has a 40amp fuse.
A lot of things are only an intermittent load but I am still surprised that the alternator can keep up with everything. For example last year in Mildura at 47°C, AC running & internal fan on high, second radiator fan running, hi-fi plus all the other requirements.
The 3 power outlets in my car each have 20amp fuses. Typically my two 9amp DC to DC chargers are well within this capacity.
Tony LEE said
04:04 AM Oct 5, 2019
I am a member of a couple of US fora on RV solar power, and I have occasionally warned about the dangers of charging Li from older alternators, and invariably get the usual "oh, I've been doing that for yonks and had no problems" with the implied "Tony Lee is an idiot" (which might be true but in this case they will have to declare whether Victron is also stupid.
Tony LEE said
04:05 AM Oct 5, 2019
BTW, pretty sure Collyn used to give the same warnings about split charging big AGMs
Tony LEE said
04:45 AM Oct 5, 2019
https://www.amazon.com/Battle-Born-Batteries-Lithium-Isolation/dp/B07DY8S815/
Battleborn is a bit of a fad in the US because they are drop in replacements with a pretty good warranty, but while they are confident in their BMS they are obviously aware of alternator limitations
T1 Terry said
01:21 PM Oct 5, 2019
A topic taken very seriously on the blue water cruising forums because they recharge very big battery banks via alternators when they have the engines running. Either they fit very expensive Balmar alternators with 2 or 3 cooling fans and a Balmar regulator that senses alternator heat and belt slip, or they use DC to DC chargers to limit the current and save the standard automotive alternator that came with the motor. It really depends if the motor is the only method of recharging the battery pack or if it is just an aux charging method.
T1 Terry
Aus-Kiwi said
08:46 PM Oct 5, 2019
One of those things that can work for long time ? As long as you dont flatten battery too much . I guess its up to the regulator
If it was me ? I would fabricate another alternator, voltage reg ( whatever ) as seperate dedicated charging system..
.
T1 Terry said
01:09 PM Oct 6, 2019
Aus-Kiwi wrote:
One of those things that can work for long time ? As long as you dont flatten battery too much . I guess its up to the regulator If it was me ? I would fabricate another alternator, voltage reg ( whatever ) as seperate dedicated charging system.. .
Have you looked under the bonnet of many of the vehicles towing the big vans these day? Where would you put a dedicated alternator and where would you squeeze in the drive belt to run it? Remember, if that alternator is going to be capable of pumping out hundreds of amps 100% of the time it is running, it will be big and it will need big drive belts. The belts used now on the average newer vehicle aren't up to the job of running what is there now, most of use have heard that alternator squeal when we first start up, the alternator is cold and attempting to put out 125% of its rated output and the belt can't get enough grip to keep turning it at the speed required .... can you imagine the size of the belt and pulleys and tensioners required to put out twice that much power from the alternator full time?
T1 Terry
Aus-Kiwi said
10:30 PM Oct 6, 2019
Done em drive off the drive shaft . Kiss !!! Simple
Tony Bev said
01:04 AM Oct 8, 2019
Thanks for that link, T1 Terry This is something I was unaware of
T1 Terry said
11:48 AM Oct 8, 2019
Aus-Kiwi wrote:
Done em drive off the drive shaft . Kiss !!! Simple
Only simple for a rear wheel drive, not a front wheel drive vehicle, and simple is a stretch of the terminology when you think about it compared to adding a DC to DC charger, now that is simple. It might even come to adding a DC to DC charger up front to charge both the aux battery that runs the fridge in the rear of the vehicle and has a parallel output that goes to the Anderson plug. From there it's a relatively short run to the DC to DC charger in the van so the van DC to DC is supplied at a higher voltage than just a cable run from the start battery all the way back to the van DC to DC. A Schottky diode at the aux battery in the rear of the vehicle would mean the aux battery could be charged via the DC to DC but the van DC to DC could not drain the aux battery.
T1 Terry
Jaahn said
01:57 PM Oct 8, 2019
Hi :)
I do not disagree with the overall ideas shown regarding the draw on the alternators and heating. It would be wise to use a DC-DC charger that will limit the current to safe levels for both batteries and the alternator.
However just for general information as Noelpolar has already said, the alternators on normal vehicles do run at least 2x and usually more, ~2.5x than the engine RPM.Those tests in the video were done using what looks like about 1to1 ratio drive from the motor. So the lowest rpm test of 1500 actually would be over 3000 alternator RPM on a real motor, which was OK in their tests. Just pointing out that fact. Not looking for an argument.
Suggesting that people can fit another alternator to a modern engine bay in the currently used 'tugs' is not realistic for sure as Terry said. And driving off the driveshaft of one is also almost too silly to say, I regret to say. With some vehicles it could be done but ignores the practicalities I believe.
Jaahn
Scubadoo said
08:21 AM Oct 9, 2019
Terry
I have been following Jono and his narrow boat videos for a while and note with interest that he is now a narrator for Victron.
You may well guess where my initial interest LiFePO4 batteries originated.(-;
Our 4 cell 300Ah Sinopoly battery pack installation has now reached the 5 year mark of fulltime travelling and still performing way beyond our expectations powering our 6.8m 3.9l turbo Canter cab over MH. Unlike most (all?) other installations it is the only battery in the vehicle. It both starts the truck and powers the house behind. 800W solar (Victron MPPT) , 100A (current limited to 70A) direct charging alternator and as yet unused 30A Victron mains charger have kept it all operating including the Samsung DI 255l fridge.
Back to the video. I note with interest that the alternator managed the load perfectly at 3000rpm. The standard pulley ratios on our truck during my very occasional 1200rpm fast idle emergency bad weather battery top up will spin the alternator beyond 3000rpm. I am happy with that and also note that our setup could never spin the alternator at the video smoke producing 1000rpm anyway.
T1 Terry said
01:54 PM Oct 9, 2019
Generally the alternator spins at up to x 2 for a normal revving motor and up to x 3 for a slow revving motor that doesn't see much above 2,000 rpm. At 2,000rpm engine speed the alternator would be spinning at 6,000rpm, so upper rpm limits also apply. An engine that spun out to 4,000rpm regularly wouldn't generally have the alternator at x 2 rpm as that would have the alternator spinning at 8,000 rpm and getting into the fly apart range.
This means a diesel engine idling at 500rpm yet capable or revving to 4,000rpm, the alternator would be spinning at maybe 1,000 rpm, just like in the test. This might only be happening when idling, but every so often the engine is running at idle speed. If the engine run at a higher speed then probably less problems as long as it can cool sufficiently. This very much depends where it gets its cooling air from and just how shrouded in the alternator is as to just how effective the cooling will be. Alternators that have the blades just behind the pulley are most likely drawing the air in through the back and displacing it out through the fan. The open case type alternators that have 2 internal fans pull the air in from the centre each end and out through the slots in the casing and these cool much better if there is cool air being fed into them.
T1 Terry
Jaahn said
08:15 PM Oct 9, 2019
Hi Terry
I think your ideas might be a bit behind the times. I thought I would measure the pulleys on both my vehicles to determine the ratio as you can see they are high geared.
One is a Renault 1.2 turbo petrol that does almost 6000 RPM peak. The other is a Mercedes Sprinter 2.9L turbo diesel that does 3800 RPM max. By my measurements they are both well more than 2.5 and close to ~2.7 to 1 geared up, both almost exactly the same ratio.
Again not to be argumenitive but to actually measure some real world figures. The Merc alternator is fixed voltage 110 A dual fan type. The Renault is unknown amps (perhaps ~70) and also dual fan type, with "smart" control.
Cheers jaahn
-- Edited by Jaahn on Wednesday 9th of October 2019 08:22:33 PM
T1 Terry said
01:48 PM Oct 10, 2019
Could be right there Jaahn, most of my figures were based on bigger engines used in heavier equipment and vehicles. 6,000rpm x 2.7 ratio, 16200rpm at the alternator, dual fan so cooling must have been an issue with the single fan design. No idea of the diameter of these two alternators, but the tip speed of the core must be approaching the sound barrier.
T1 Terry
Reed said
03:41 AM Oct 12, 2019
We run any line/generator power through 2kW battery charger at 48 V
Reed said
10:15 PM Oct 12, 2019
Forgot to mention that our LFP battery bank is 48 V
This is a Victron video demonstrating what I have been says for the last 8 yrs, trying to charge a lithium battery without a DC to DC charger inbetween and the correct size cabling to carry the required current will destroy either the very expensive alternator or result in either the failure of the DC to DC charger if the supply cable is too small, or the actual cable melting and shorting out if the type of DC to DC charger used wasn't smart enough to reduce its output current when the voltage was too low.
https://www.youtube.com/watch?v=jgoIocPgOug&feature=youtu.be&fbclid=IwAR2PGH9e93AnpYjnokoNkJBGXXCGDCSjv8YhTC3145i_hG-vdDIMCRTfqpA
T1 Terry
Thanks for the link. The alternator would run even hotter in the engine bay.
I might swap over my Victron dumb DC to DC for a smart one.
-- Edited by Whenarewethere on Friday 4th of October 2019 12:02:40 PM
Most alternators are geared up by 2x to 2.5x.... only saying this to make sense of their rpm statements. I certainly am to CS (Chicken Sh##) to run largish capacity lithiums off a standard vehicle alt.... also pulling out a run of 6B&S from the van this week end to replace it with 2B&S to jelp the 40 amp DC2DC to get past it's 27amp issue... the Enerdrive unit current limits at about 11.6v.... 13 meters from car battery.
Yeas, the smart alternators are making the old standard of 6B&S cabling being sufficient to supply the DC to DC charger out dated. $ B&S or even 2 B&S might become the norm for these applications and an upgrade from the traditional 50 amp Anderson plug because it can not handle the bigger cable.
Which is the better option, increase the alternator voltage and risk problems there, or increase the size of the supply cable all the way back to the DC to DC charger, not just to the tow bar.
T1 Terry
If I got a cold climate pack for my car, ie heated seats, steering wheel, windscreen. The car would get a larger alternator with an extra 30amps.
The alternator in a car is not rated for a 100% duty cycle so you can't expect it to run anywhere better than 50% in the engine bay heat for long periods of time without failing. Is pushing the continuous output voltage up from 13.6v to 14.1v or higher adding strain to the alternator? Depends if you are also increasing the continuous current draw at the same time.
Use watts to calculate the results, an alternator pushing out 100 amps @ 13.6v = 1360w. Now increase that to 14.1v and the total is now 1410w. If the efficiency is 50% as Victron suggest, that is now 1410w of heat that needs to be removed from an alternator that was designed to put out 1360w and need to displace 1360w of heat for a short period to recharge the start battery, then just drop back to the load the accessories require.
think about what will happen if you boost the output voltage to 14.1v, this drops to 12.8v as it passes through the various relays and plug as well as the cable length. The DC to DC charger is set to put out 14.4v @ 40 amps, 14.4 x 40 = 576w and the alternator must supply this along with the accessory load and the initial starter battery recharging .... do you need to add the recharging requirements for any aux batteries in the back of the car or under the bonnet? Odds are the alternator will handle this fine because the additional load was only 45 amps x 14.1v, but if that lithium battery was close by of connected with heavy cable so the voltage drop was minimal and no DC to DC charger was fitted inbetween to act as a current limiter? Until the lithium battery reaches that 14.1v it will take everything the alternator can put out by holding the voltage lower than the 14.1v it is trying to reach, how long do you think it will take for the alternator to overheat?
Those temperature rises shown in the video have ambient temperature air being pumped through and alternator mounted in a clear air flow region. Now look at where the alternator is in your engine bay and just how hot it gets in there when dragging the RV along .... how hot do you reckon that alternator will get even if it is spinning at 5,000rpm? Now imagine that same alternator at idle engine revs ....
T1 Terry
I've recently become a fan of 120A Andersons..... they are easier to plug and unplug than the 50s.... good for old hands.... don't need your glasses either. Another 10 years and I'll be doing everything in 175s.
-- Edited by Noelpolar on Friday 4th of October 2019 02:21:08 PM
:lol: Those 50 amp Anderson plugs can become a real tug of war without a handle attached. The bigger plugs give a much better contact area as well so less heat build up across the faces. Not too many of the copy cat manufacturers have the bigger plugs so you are more likely to buy the quality Anderson manufactured plugs if you do go for the bigger plugs, so a bit of a bonus there as well, but they cost a bit more than the 50 amp units and are a bit harder to locate when you need one after it dragged up the road for a few hundred kms.
T1 Terry
The starter motor current in my car is 238amps & charging increases & settles normally to 80amps after 30 seconds.
Looking through list of fuses for the 3 fuse boxes in my car it is pretty frightening what current the car needs to power everything & I only have a semi pauper model! The hi-fi has a 40amp fuse.
A lot of things are only an intermittent load but I am still surprised that the alternator can keep up with everything. For example last year in Mildura at 47°C, AC running & internal fan on high, second radiator fan running, hi-fi plus all the other requirements.
The 3 power outlets in my car each have 20amp fuses. Typically my two 9amp DC to DC chargers are well within this capacity.
T1 Terry
If it was me ? I would fabricate another alternator, voltage reg ( whatever ) as seperate dedicated charging system..
.
Have you looked under the bonnet of many of the vehicles towing the big vans these day? Where would you put a dedicated alternator and where would you squeeze in the drive belt to run it? Remember, if that alternator is going to be capable of pumping out hundreds of amps 100% of the time it is running, it will be big and it will need big drive belts. The belts used now on the average newer vehicle aren't up to the job of running what is there now, most of use have heard that alternator squeal when we first start up, the alternator is cold and attempting to put out 125% of its rated output and the belt can't get enough grip to keep turning it at the speed required .... can you imagine the size of the belt and pulleys and tensioners required to put out twice that much power from the alternator full time?
T1 Terry
Thanks for that link, T1 Terry
This is something I was unaware of
Only simple for a rear wheel drive, not a front wheel drive vehicle, and simple is a stretch of the terminology when you think about it compared to adding a DC to DC charger, now that is simple. It might even come to adding a DC to DC charger up front to charge both the aux battery that runs the fridge in the rear of the vehicle and has a parallel output that goes to the Anderson plug. From there it's a relatively short run to the DC to DC charger in the van so the van DC to DC is supplied at a higher voltage than just a cable run from the start battery all the way back to the van DC to DC. A Schottky diode at the aux battery in the rear of the vehicle would mean the aux battery could be charged via the DC to DC but the van DC to DC could not drain the aux battery.
T1 Terry
Hi :)
I do not disagree with the overall ideas shown regarding the draw on the alternators and heating. It would be wise to use a DC-DC charger that will limit the current to safe levels for both batteries and the alternator.
However just for general information as Noelpolar has already said, the alternators on normal vehicles do run at least 2x and usually more, ~2.5x than the engine RPM.Those tests in the video were done using what looks like about 1to1 ratio drive from the motor. So the lowest rpm test of 1500 actually would be over 3000 alternator RPM on a real motor, which was OK in their tests. Just pointing out that fact. Not looking for an argument.
Suggesting that people can fit another alternator to a modern engine bay in the currently used 'tugs' is not realistic for sure as Terry said. And driving off the driveshaft of one is also almost too silly to say, I regret to say. With some vehicles it could be done but ignores the practicalities I believe.
Jaahn
This means a diesel engine idling at 500rpm yet capable or revving to 4,000rpm, the alternator would be spinning at maybe 1,000 rpm, just like in the test. This might only be happening when idling, but every so often the engine is running at idle speed. If the engine run at a higher speed then probably less problems as long as it can cool sufficiently. This very much depends where it gets its cooling air from and just how shrouded in the alternator is as to just how effective the cooling will be. Alternators that have the blades just behind the pulley are most likely drawing the air in through the back and displacing it out through the fan. The open case type alternators that have 2 internal fans pull the air in from the centre each end and out through the slots in the casing and these cool much better if there is cool air being fed into them.
T1 Terry
Hi Terry
I think your ideas might be a bit behind the times. I thought I would measure the pulleys on both my vehicles to determine the ratio as you can see they are high geared.
One is a Renault 1.2 turbo petrol that does almost 6000 RPM peak. The other is a Mercedes Sprinter 2.9L turbo diesel that does 3800 RPM max. By my measurements they are both well more than 2.5 and close to ~2.7 to 1 geared up, both almost exactly the same ratio.
Again not to be argumenitive but to actually measure some real world figures. The Merc alternator is fixed voltage 110 A dual fan type. The Renault is unknown amps (perhaps ~70) and also dual fan type, with "smart" control.
Cheers jaahn
-- Edited by Jaahn on Wednesday 9th of October 2019 08:22:33 PM
T1 Terry