LiFePO4 and auto alternator concerns...

HiPlains

New Member
Greetings. I am planning on replacing the 100 amp hr AGM house battery in my 2000 VW camper. I have a single remaining concern with the variety of Lithium batteries that advertise Plug and Play status. Because the BMS in a good lithium battery will shut the battery off when fully charged, what happens to the alternator circuit? It is my long held belief that in boats and cars/vans that one does not ever want to experience an open circuit with regard to the alternator. I do have a 160 watt solar panel on the camper, ( AGM) and it is connected to the alternator charging circuit. I have changed nothing in that circuit.

I would appreciate input regarding this issue. Most cars come with some form of lead acid battery and the charge tappers off but does not stop and lead acid batteries are reasonably forgiving and accept a trickle charge.

One well known Lithium provider simply said that this issue should be taken up with folks that manufacture 12 volt alternators... I think there must be better answers out there from knowledgable battery folks.

Any educational tips here are welcome.
 

ianganderton

Covid free in NZ
Because alternators are designed to work with lead acid and there are a number of problems when connecting a lithium battery house battery directly it seems the best option is instead to use a DC to DC charger

A properly set up dc to dc charger from the starter battery/alternator to lithium house battery will control the load on the alternator and make sure the lithium house battery recieves the correct voltage to fully charge it
 

boondox

Chief Engineer, RedNeckTech Industries
Part of this depends on what size alternator you have. In my van I used a 50 amp DC to DC charger. That limits how much I pull from the alternator. It also depends on your use profile. IN my case I want to be able to idle some in place and charge. Pulling too much off an alternator at idle will overheat it for sure. As well, stock alternators do not have the correct charge profile for lithium. So you really need a charge controller i the middle.
 

HiPlains

New Member
Hi and thanks for the input and the DC to DC suggestion.

Rephrasing... What do people that have a camper and simply drop in say, a 100 amp hr Battle Born battery in and take off face as risks? ie not everyone is going to fiddle with the existing wiring and converters etc.
 

smoothJoey

SmooJo
As @ianganderton said a dc2dc charger is highly recommended.
The idea that a lifepo4 battery is a drop in replacement isn't absolutely correct.
A lifepo4 battery can draw enough charge to hurt itself but more likely it will hurt your alternator first.
The other important thing to consider is your bms is not intended to be used for charge termination.
Its to be used as a "reserve parachute" to keep your lifepo4 battery from being harmed.
A typical BMS won't disconnnect from the charge source untils > 3.65 volts per cell.
 

HiPlains

New Member
Part of this depends on what size alternator you have. In my van I used a 50 amp DC to DC charger. That limits how much I pull from the alternator. It also depends on your use profile. IN my case I want to be able to idle some in place and charge. Pulling too much off an alternator at idle will overheat it for sure. As well, stock alternators do not have the correct charge profile for lithium. So you really need a charge controller i the middle.
 

ianganderton

Covid free in NZ
Have you see the Victron video where they show the problems with lithium pulling high loads on the alternator and causing over heating?

Not sure if battle born have measured that protect against thins in their bms
 

smoothJoey

SmooJo
Have you see the Victron video where they show the problems with lithium pulling high loads on the alternator and causing over heating?

Not sure if battle born have measured that protect against thins in their bms
Your alternator is not battleborn's concern.
 

ianganderton

Covid free in NZ
Your alternator is not battleborn's concern.
No but Battle Born do seem to be a good technology company that would want to provide Problem free products that customers Are happy with

Customer satisfaction is something that battleborn are concerned with and burning alternators might not be good for that 😜
 

HiPlains

New Member
Greetings and thank you for the useful advice. The ability of a Lithium based replacement for the house battery could indeed draw a lot of current if the battery pack is down say 60 amp hours after running the12 volt fridge for say three or four cloudy days.

So far the car is "stock" likely a 50 amp hour alternator. SO... Do you have any suggestions for a voltage charge controller the I might put in the middle.

A plan B for me, could be to simply remove the charging wire to the house battery, effectively isolating a new Lithium battery for house use, to the 160 watt moveable solar panel on the camper roof. That would leave the alternator circuit to the starter battery as a "stock" factory system.

Help with either issue is appreciated.
 

ianganderton

Covid free in NZ
Moving to only solar charging is one of the best solutions if you are using the system in an environment where that’s possible.

E.g someone using their camper as a base for skiing may struggle with solar only

The renolgy mppt and dc charger combining solar and alternator charging is a good option


Kisae have versions too

 

smoothJoey

SmooJo
No but Battle Born do seem to be a good technology company that would want to provide Problem free products that customers Are happy with

Customer satisfaction is something that battleborn are concerned with and burning alternators might not be good for that 😜

Let me know how that works out for ya. ;)
 

boondox

Chief Engineer, RedNeckTech Industries
Greetings and thank you for the useful advice. The ability of a Lithium based replacement for the house battery could indeed draw a lot of current if the battery pack is down say 60 amp hours after running the12 volt fridge for say three or four cloudy days.

So far the car is "stock" likely a 50 amp hour alternator. SO... Do you have any suggestions for a voltage charge controller the I might put in the middle.

A plan B for me, could be to simply remove the charging wire to the house battery, effectively isolating a new Lithium battery for house use, to the 160 watt moveable solar panel on the camper roof. That would leave the alternator circuit to the starter battery as a "stock" factory system.

Help with either issue is appreciated.

For starters, replace the 50 amp alt with as big a one as you can fit. In my case I have 150 amp alt so I figured 50 amps of charge would be OK. Never forget that there are vehicle loads and that you want a good amount of margin in your alt rating. I figured 50 amps for the house batts, 50 amps for the vehicle and 50 for overhead. Once you have decided what you think the charge rate should be, Then look around at the various chargers and find one that will suit your needs.

While you can do some solar as you outline, you have to have a way to charge when the sun don't shine.
 

CascadeOffGrid

Off Grid Design and Installer
I regularly install lithium batteries for my customers and am a Battleborn dealer. I will not do a straight lead acid to lithium swap out with an alternator tie in anymore. There is a high probability of burning up your battery isolation device and/or alternator. DC-DC chargers are the way to go.
 

HRTKD

Boondocker
I regularly install lithium batteries for my customers and am a Battleborn dealer. I will not do a straight lead acid to lithium swap out with an alternator tie in anymore. There is a high probability of burning up your battery isolation device and/or alternator. DC-DC chargers are the way to go.

Are you running a separate line from the tow vehicle battery to the DC-DC charger? Or are you using the feed from the 7 pin cable?
 

CascadeOffGrid

Off Grid Design and Installer
Are you running a separate line from the tow vehicle battery to the DC-DC charger? Or are you using the feed from the 7 pin cable?

For trailers I run a separate power and ground line and try to use Victron products. Anderson powerpole connectors are very nice for this application. The Victron products have adjustable turn on/off voltage set-points. This avoids running a separate ignition wire to turn on/off the DC-DC charger or installing an automatic charging relay.

I typically only use the Renogy products in vans and motorhomes because the ignition wire signal is easily accessible.
 
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