Lithium batteries and alternator protection.

BFL13 wrote:
. . . worst threat to alternator is if the LFP's BMS cut out, leaving the alternator in the lurch --forget the name for that.

Explanation here.

oops

"This thread is about damaging your MOTORHOME alternator and using a DC to DC charger to protect it. Not sure your comment is relevant?"

Thread drift. You also need to protect the LFPs from the alternator. The DC-DC (isolation type) saves them from each other in a MH too seems like.

AFAIK worst threat to alternator is if the LFP's BMS cut out, leaving the alternator in the lurch --forget the name for that.

BFL13 wrote:
"Ref overcharging via the 7-pin, a lifepo4 (with a properly functioning BMS) would have to be subjected to =>14.6v continuously for days/weeks at a time to be overcharged"

According to at least one article on LFPs, any time at Vabs past when the batt is "full" reduces its expected number of cycles. This might be in dispute by the various experts. No info on how many cycles lost. Longer time = more lost?

Usual? story is wait the 20 minutes like BB says for balancing but no real harm done by leaving it at Vabs for ? time days/weeks.

With alternator charging, drive time keeps time at Vabs short. If the batt is not run down much overnight and you drive more next day, does that add more hours at Vabs, which would be reached quickly after starting off?

That same article says Vabs can be anything like 14 vs 14.6 it just means it takes longer to get the batt full, so hard to know when it is full and you are now into overtime? I don't know. It is all a mystery how it really works.

He also mentioned the rated "3,000 cycles" was done by running the batt up to full and immediately discharging it so there was no time ever sitting at Vabs when full. He claims that if you did the rating like a real RVer would using some time at Vabs when full, you would have fewer cycles as a result.

IMO that does not matter if you only get 2,000 instead of 3,000 because many Rvers will only do 500.

Oops I forgot--I am not allowed to talk about LFPs on here because I don't own one. Sorry! :)

This thread is about damaging your MOTORHOME alternator and using a DC to DC charger to protect it. Not sure your comment is relevant?

Has anyone come across input from a vehicle manufacturer as to whether or not their alternator/charging system could be damaged by using a Lithium battery in a trailer? Maybe on one of the truck forums? There has been chatter and speculation for several years now, it would be nice if one or more had provided a definitive answer.:?

"Ref overcharging via the 7-pin, a lifepo4 (with a properly functioning BMS) would have to be subjected to =>14.6v continuously for days/weeks at a time to be overcharged"

According to at least one article on LFPs, any time at Vabs past when the batt is "full" reduces its expected number of cycles. This might be in dispute by the various experts. No info on how many cycles lost. Longer time = more lost?

Usual? story is wait the 20 minutes like BB says for balancing but no real harm done by leaving it at Vabs for ? time days/weeks.

With alternator charging, drive time keeps time at Vabs short. If the batt is not run down much overnight and you drive more next day, does that add more hours at Vabs, which would be reached quickly after starting off?

That same article says Vabs can be anything like 14 vs 14.6 it just means it takes longer to get the batt full, so hard to know when it is full and you are now into overtime? I don't know. It is all a mystery how it really works.

He also mentioned the rated "3,000 cycles" was done by running the batt up to full and immediately discharging it so there was no time ever sitting at Vabs when full. He claims that if you did the rating like a real RVer would using some time at Vabs when full, you would have fewer cycles as a result.

IMO that does not matter if you only get 2,000 instead of 3,000 because many Rvers will only do 500.

Oops I forgot--I am not allowed to talk about LFPs on here because I don't own one. Sorry! :)

Hi,

I know my v-10 does nothing near 14 volts. It is in a class C E-450.

Fortunately I have a dc to DC charger to install this spring.

S Davis wrote:
What I don’t agree on is the blanket statement that most all newer vehicles have smart alternators systems. If the Chevy diesels have it my last two trucks have been broken.

I believe the 3/4+ trucks are not subject to fuel economy ratings and so the alternator is not programmed to run at the minimum.

Ref alternator voltage, our 2016 Ram 3500 produces 14.3v - 14.4v about 95% of the time. However, there are times when it drops to 13.9v when the batteries are discharged and the alternator is under high load charging the batteries. This typically happens when we have to repeatedly start/stop the engine in very hot weather after the truck had been sitting for a few weeks.

On the flipside, while operating in very cold weather, typically less than 20f, alternator voltage on our Ram can ramp up as high as 15v. The first time I saw this happen, I was envisioning all kinds of over-voltage damage throughout the truck. However, according to Ram this is normal operation. The higher voltage is needed to properly charge lead-cell batteries in very cold weather.

Ref overcharging via the 7-pin, a lifepo4 (with a properly functioning BMS) would have to be subjected to =>14.6v continuously for days/weeks at a time to be overcharged. Odds of a vehicle producing that high of a voltage at the 7-pin connector (after flowing through a 10-20 ft run of small gauge wire with high voltage drop) are very low. Odds of a vehicle running continuously for days/weeks at a time . . . practically zero.

Drop in batteries allow and recommend 14.6 volts. If it is DIY the max battery voltage and be limited at your choice.