Lithium batteries and alternator protection.

[N6WT]

The six 6 volt lead-acid house batteries in my class A DP have gone bad. I am looking to replace them with 6 Battleborn 100Ah 12v LiFePO batteries. Eventually I will be adding solar.

I am not looking for recommendations on what batteries and components to buy, I have made up my mind so please don't try and change it.

The reason for this post is, I am reading that in class A motorhome when you switch batteries you should install a DC to DC charger to protect the alternator of the motorhome from overheating. I would like to know if anyone here has done this to their motorhome, what did you use to do it and where inline did you install it?

[otrfun]

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.

[otrfun]

oops

[BFL13]

"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.

[N6WT]

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?

[shelbyfv]

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.:?

[BFL13]

"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! 🙂

[pianotuna]

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.

[time2roll]

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.

[otrfun]

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.

[time2roll]

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

[S_Davis]

time2roll wrote:

S Davis wrote:
I have monitored alternator voltage on all my trucks and they never have gone below 14.2, my 2013 used to run a little higher at about 14.4. Same voltage when I start the truck and the same voltage over a seven hour drive. I have a volt meter on the dash.

Still not an issue for a truck charging a trailer LFP through the 7-pin connector.

I agree, depending on the voltage drop in the 7-pin circuit. You could still over charge the LifeP04 if the 7- pin doesn’t have enough voltage drop.

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.

[time2roll]

S Davis wrote:
I have monitored alternator voltage on all my trucks and they never have gone below 14.2, my 2013 used to run a little higher at about 14.4. Same voltage when I start the truck and the same voltage over a seven hour drive. I have a volt meter on the dash.

Still not an issue for a truck charging a trailer LFP through the 7-pin connector.

[S_Davis]

StirCrazy wrote:

S Davis wrote:

theoldwizard1 wrote:

CA Traveler wrote:
Also 13.2V would not be a issue for me as it indicates a charged battery and the alternator is only supplying chassis and converter loads. A higher voltage indicates the chassis battery is drawing amps so at least the DC-DC converter has less conversion losses.

Almost all vehicles for the past 15-20 years or so, use some kind of a smart charging system. The voltage from the alternator is controlled by the engine computer and can vary over a wide range.

Not on 2009, 2013, 2019 GM 2500HD diesels, my last three trucks all have had steady voltage at about 14.2 no matter what. They must be in the almost none category.

One of my Redarc 50 amp chargers pulls 50 amps from the alternator and output is about 46 amps to the batteries, so on Redarc it looks like the rating is what is pulled from the alternator.

Im not sure when GM started doing it but your 2013 and 2019 should have smart altanators, but may not. you would have to look for the shunt as GM did it differently and it should be part of your negitive batery post atachment.

GM uses a shunt system whil ford uses a two wire bus.. as well other things might be different as in the voltage setting and such but ventualy when your battery is full in your truck and if your not using a ton of other power hungry stuff it will go down to a maintance voltage. this is to both give longer life to the altanator and the batteries. as for dc to dc chargers a lot of the input output power descrepencies are from wire size also.

I have monitored alternator voltage on all my trucks and they never have gone below 14.2, my 2013 used to run a little higher at about 14.4. Same voltage when I start the truck and the same voltage over a seven hour drive. I have a volt meter on the dash.

[pianotuna]

Nice clean install.

What are the input amps when output is 25 amps?