Replace AGM house battery to LifePO4?

[MobileAndMonitoring]

Hello Expo,

We decided to go full time in our 2005 Toyota Tundra 3 months ago and have been on the road since. We've had 3 months of using our electrical system on the truck 24/7 and are considering upgrading our 4 year old AGM house battery to lithium (LifePO4) rather than replacing the AGM. According to the battery monitor we average around 65ah draws but we do draw about 100ah a couple times a month so I think we could use more capacity. Also the battery is getting old and I'm assuming it doesn't have the capacity that it used to have. And finally with winter coming I know the solar will not be producing what it is now. Anyways I thought I'd draw up a basic diagram of my electrical system with only the charging portion shown to simplify the diagram below. The LifePO4 battery we are considering is the Aims Power 200ah LifePO4 battery. It's a group 4D just like what we have now so as far as dimensions go it will be a drop in replacement. Haven't seen much online about them but thinking of taking the leap. Specs are here.


So the main thing I'm trying to understand is what I need to change to my on board charging system. Our Victron Energy solar controller supports lithium batteries but I assume our alternator does not? After some basic internet reading it seems we need a DC to DC charger aka battery to battery charger? (On a separate note I wonder if we should have had one this whole time for our AGM). Is this true? If so there seem to be a few offerings out there. A couple concerns I have below:

-The alternator seems to never get above 13.5-13.8v. Does this fact alone require a DC to DC charger because the voltage is too low (battery requires 14.4-14.6)?
-We have 2 gauge wire between the staring battery and house battery. It seems most DC to DC chargers do not support such large wire
-I presume the National Luna Battery Isoloator will not be an issue? Would this DC to DC charger go between the battery isolator and house battery?
-We also have a AC to DC charger we hardly ever use (haven't used it since we left our house). Would we wire this behind the DC to DC charger as well?
-Are below freezing temperatures an issue? How about extreme hot temps? Battery warmer or cooler needed?
-How to determine what amp draw would be suitable? We have a large overpowered alternator and would like to know how you might calculate which one to choose.

Any help in this would be awesome. We have 2 weeks coming up next week in Portland and I think I can get most of this done if I can fully understand what goes along with these new Lithium batteries.

 

[dwh]

Good discussion that covers a lot of issues here...

https://www.expeditionportal.com/fo...battle-born-through-d250s-b2b-charger.173120/

It all depends on the voltage they set it up to run at. For instance the BattleBorn has a full charge resting voltage of 13.4v, and is dead flat drained at 12.7v.

So for that, the preprogrammed voltage setpoints of a normal ACR (The National Luna in your diagram) are all wrong.

The Iota might be a problem if it's one with the built-in IQ/4 brain. If it's got the plug-in IQ/4 that's good, because Iota now makes a slew of different plug-in IQ units with different charge profiles for different things.


Voltage matters, and the manual for the battery you linked says it is 12.8v nominal. Which sounds good until you see they list AGMs at 12v nominal. So...WTH does 12.8v nominal actually mean?

I'd want to know the full charge resting voltage and the "It's dead, Jim" voltage to be able to figure out exactly what will and will not work with it.

Especially before dropping 1800 clams on a battery.

 

[MobileAndMonitoring]

Good discussion that covers a lot of issues here...

https://www.expeditionportal.com/fo...battle-born-through-d250s-b2b-charger.173120/

It all depends on the voltage they set it up to run at. For instance the BattleBorn has a full charge resting voltage of 13.4v, and is dead flat drained at 12.7v.

So for that, the preprogrammed voltage setpoints of a normal ACR (The National Luna in your diagram) are all wrong.

The Iota might be a problem if it's one with the built-in IQ/4 brain. If it's got the plug-in IQ/4 that's good, because Iota now makes a slew of different plug-in IQ units with different charge profiles for different things.


Voltage matters, and the manual for the battery you linked says it is 12.8v nominal. Which sounds good until you see they list AGMs at 12v nominal. So...WTH does 12.8v nominal actually mean?

I'd want to know the full charge resting voltage and the "It's dead, Jim" voltage to be able to figure out exactly what will and will not work with it.

Especially before dropping 1800 clams on a battery.

Thanks @dwh for your reply. I agree they have some weird things listed on their site. I too saw the 12v nominal voltage for AGM listed. I was hoping that was just the marketing department. It's a shame their manual is also lacking on information and that they do not have a full spec sheet with say a discharge profile or any real helpful graphs or details specs. They do however boast a 10 year warranty and have a group 4D which would make this a easy drop in replacement dimensionally for me.

The thread you linked to is great. Nice seeing a manufacturer interact on a forum with some real answers. It would be nice if Battle Born had a larger battery available. I don't think I have enough room for two of their batteries in parallel.

I emailed them for more information but lets just say for a second that this Aims Power battery has a full charge resting voltage at 12.8v and is fully dead at 12v. The battery needs 14.4 -14.6V to charge. My trucks alternator voltage never gets above 14v so a DC to DC charger would be required. I would imagine one where I can program in the unique charging voltages since these voltages are not standard across LiFePO4. Any ideas on what I should do since I have 2 gauge wire going into the house battery? It seems that the Sterling Power 60 amp unit they recommend 4-6 gauge. So I'm assuming 2 gauge will not work.

Also that thread you linked to never really directly answered any questions about charging both the AGM and the LiFePO4 at the same time. I imagine that's because it doesn't matter as long as you have the DC to DC charger feeding the house battery you can have different charging profiles? And as long as there is a battery isolator they cannot be discharged together?

I'm glad I came here first. I had no idea how different and sensitive batteries really can be. And like you said when dealing with this new lithium technology you don't want to mess up with a $1700 battery! Thanks again for all your help.

 

[luthj]

What voltage is your alternator? Depending on that, you may be totally fine with your current isolator. Folks like the Dc-DC for the bling, and for the "correct profile". The reality is that most drop in lithium packs will charge readily to the mid 90% range on 14.1V. And quite quickly to boot. With that 370A alternator, you could recharge a 100A battery in under 2 hours.

Take note that many lithium packs cannot be charged (or have reduced charge rates) below 40F. So take that into account. You may find that you need an insulated battery box, with ~100W heater (with thermostat) depending on where your battery is mounted.

If you only draw down 100AH on a worst case scenario, you probably only need a 100AH lithium pack. Essentially a lithium pack almost never needs to be more than 50% of the lead pack it replaces. That is because it doesn't need regular full charges, and charges much faster (and more efficiently). Thus is takes advantage of normally wasted solar/alternator charging.

 

[MobileAndMonitoring]

What voltage is your alternator? Depending on that, you may be totally fine with your current isolator. Folks like the Dc-DC for the bling, and for the "correct profile". The reality is that most drop in lithium packs will charge readily to the mid 90% range on 14.1V. And quite quickly to boot. With that 370A alternator, you could recharge a 100A battery in under 2 hours.

Take note that many lithium packs cannot be charged (or have reduced charge rates) below 40F. So take that into account. You may find that you need an insulated battery box, with ~100W heater (with thermostat) depending on where your battery is mounted.

If you only draw down 100AH on a worst case scenario, you probably only need a 100AH lithium pack. Essentially a lithium pack almost never needs to be more than 50% of the lead pack it replaces. That is because it doesn't need regular full charges, and charges much faster (and more efficiently). Thus is takes advantage of normally wasted solar/alternator charging.

With the National Luna battery monitor I almost never see above 14v. More like 13.8 max. I believe when I swapped out the alternator the voltage had dropped by a bit. It also doesn't charge at idle when in drive but that's a whole other matter. I totally get the bling factor especially with overlanding but I know how batteries can get toasted without much notice (ive done it myself). If I'm going to invest in an expensive battery I want to give it exactly what it wants.

The cold does worry me a bit. This last winter it got down to 15 degrees in area the battery was stored. This particular battery shows 32 degrees as it's lowest temp for charging but I'd like to figure out a way to wrap the battery in a heated blanket or something. Haven't gotten that far yet. I imagine they make a DC powered small heated blanket I could attach to a temp controlled relay (which I think my victron battery monitor has actually).

Finally in regards to maybe only needing 100ah I'd rather overkill the power bank. That figure I mentioned is our max in one day and that's monitoring it closely and turning off the devices early when we hit 100ah. I have a powerful laptop that when editing videos or photos the CPU is maxed out and the laptop pulls 350w continuous. So the battery can be exhausted quickly. When we are in colder more overcast climates I know we will need more. Also the form factor is exactly what I have now and would make it an easy swap. Since we are living on the road that goes a long way!

 

[MobileAndMonitoring]

@luthj Wow just noticed you have 2 LifeLine 8Ds??

 

[dwh]

The glaring issue in the linked thread regarding ACRs, is that the Blue Sea (for example) disconnects at 12.7v.

Which for a Battle Born, represents a dead battery. So tying a lead-acid and a Battle Born with a Blue Sea ACR is a nogo; the ACR would basically never disconnect.

Hence a DC-DC charger, rather than an ACR, is the obvious answer.

Will the National Luna have the same problem with the Aims battery?

Dunno. Insufficient data.

 

[luthj]

Yes I do. Soon to be replaced with lithium pack.

 

[MobileAndMonitoring]

The glaring issue in the linked thread regarding ACRs, is that the Blue Sea (for example) disconnects at 12.7v.

Which for a Battle Born, represents a dead battery. So tying a lead-acid and a Battle Born with a Blue Sea ACR is a nogo; the ACR would basically never disconnect.

Hence a DC-DC charger, rather than an ACR, is the obvious answer.

Will the National Luna have the same problem with the Aims battery?

Dunno. Insufficient data.

Seems the National Luna is the same 12.7v. So with the 2 AGM configuration the 12.7 works just fine since almost any load will put the batteries at 12.7 and disconnect. But with the Battle Borns (for example) that doesn't work becuase their resting voltage is so much higher?

Yes I do. Soon to be replaced with lithium pack.

Do you have a non lithium starting battery? What kind of configuration do you have you current battery bank in terms of supporting electronics? Also care to elaborate on the lithium pack?

 

[dwh]

The 14v from the alternator will charge the Aims, but slower. To deal with that either DC-DC charger, or raise the truck's voltage...or just live with it.

Of course, if it turns out that your LiFePo4 + ACR has the same issue that I just described, then it's gonna end up a DC-DC charger.


As to wire size question...Sterling might recommend #4-#6, what is the actual max that the terminal can accept? Is it a type where you stick the wire in a hole and tighten a screw, or a post that accepts a ring terminal?

Either way, there's a workaround to get your fat wire connected to the thing.

 

[dwh]

But with the Battle Borns (for example) that doesn't work becuase their resting voltage is so much higher?

No, it doesn't work because their fully depleted voltage is the same as the ACR disconnect voltage. So the lithium just ends up constantly acting as a float charger for the lead-acid.

 

[Rando]

I am really not sure why everyone seems to think that lithium batteries need DC-DC chargers. Relative to lead acid batteries lithiums care a lot less about 'correct charge profiles' give them a voltage between 13.6 - 14.4 and they will charge, shut it off if it goes over 14.4 (or the BMS will do it for you). They don't care about multi stage charging or float charging or any of the rest of that lead acid nonsense.

If your alternator outputs 13.8v, that would get your LiFePO4 battery up to 80-90% SOC and stay away from the 'knee' in the charge profile which can cause balance issues. I have my Victron MPPT solar controller set at 13.8 for my LiFePO4 bank, and it works well. Even with my anemic 13.6V output alternator and a long run of skinny wire my 150Ah lithium will still charge at ~10A from the alternator, which is plenty for me.

The easiest option for charging from your alternator would be an ignition controlled relay (you can probably rewire your National Luna to work this way) so that the lithium charges with the car running and is isolated when it is off. However you should add a battery monitor and the Victron BMV-712 has a fully configurable relay output that could be used to control the solenoid between the starting and house batteries then you can set the combine/isolate voltages to what ever you want. Also note that if you add the Victron Smart Battery Sense to your battery, then the Victron MPPT can be configured not to charge below a certain temperature.

 

[dwh]

Yes, an ignition controlled relay (a.k.a. dumb solenoid or split-charge relay) will work.

However, the OP has a different setup. He doesn't have a long run of skinny wire, he's got fat wire. So there is certainly the potential there to overheat the alternator. The DC-DC charger provides current limiting, which the split-charge relay won't.

The OP is also full-timing, with a 200ah house battery, and concerned with a lack of solar during winter - so a 10a charge rate probably ain't gonna cut it.

He needs to strike a balance...a charge rate high enough to get it done in a reasonable time, without burning out his alternator. He's talking about a 60a Sterling, but depending on the alternator, I might say go with a 30a instead.

It could be done with a split-charge relay by carefully planning out the wire size/resistance, but he's already got the fat wire installed in an existing system. The Victron setup you described will limit voltages, but I dunno if it will limit current.

Since the NL probably (can't say for sure without knowing the precise voltage range the Aims battery is built to operate at) will be a problem, and have to be reolaced with something else...then a DC-DC charger will likely be the best solution - for THIS guy in THIS situation.

It is what it is.

 

[luthj]

The op lists a 370A alternator, so overloading seems like a minor concern.

 

[Rando]

I doubt that overloading a 370 amp alternator is going to be a problem, particularly as the max current for this battery is 160A.

Anyway, the smartest option would be to hook this up to the alternator using the existing wire and see what happens. If the issue is drawing too much current and having the BMS shutdown, adding a section of smaller gauge wire or an extra fuse may fix that for only a few $. Most likely a DC-DC charge will not be needed, but on the off chance it is, it can be added later. It would seem silly to spend (a lot) of money in a charger when there is a good chance it is not needed and it may actually slow the charging of the battery.