Swapping Lead acid for LiPo on my "house" battery, alternator charging questions

[concretejungle]

If this has been covered please link me to the thread!!

As the title says I would like to make the jump from Lead Acid to LiPo for my house battery. I am leaning towards a Battle Born 100 amp hour 12V LiPo battery. this battery is about as "dummy proof" as possible with built in hot and cold sensors as well as BMS. I already have a great Victron charge controller and 120 Watts of solar, but my main question is regarding my current setup with a blue sea ACR in line of the alternator. I want to ensure that my 150 amp alternator is charging the battery correctly.

Do I need a charge controller of some type between my alternator and the ACR or between my ACR and my LiPo battery?

Any help is greatly appreciated.

 

[DirtWhiskey]

DC/DC charger built for Lifepo4. Power cables go from starter battery pos/neg with a proper fuse close to positive. Watch your cable gauges, go over to be safe. Lots of online cable sizing calculators, be sure to calculate for ROUND TRIP wiring length. Verify your alternator and wiring are up to snuff.

 

[dstefan]

⬆ This.

I’ve been running a Battleborn 100ah with a National Luna DCDC 25amp charger and 6gauge cable from my camper/truck bed to the starter battery for 18 mos without any issues. You DO need a DCDC charger to get the proper charge voltage for top balancing, and especially to protect your starter battery and alternator — LiFePos will take all the charge they can get and a typical isolator will leave your starter battery and alternator at the mercy of the LiFePo.

Unless you have a lot of draw or hang in camp for more than 4 to 5 days, I think you’ll find you don’t really need the solar input. I’ve quit using my portable solar altogether to save weight.

 

[DiploStrat]

The voltage settings for the Blue Sea ACR will not work well with a lithium iron battery. The combine voltage is around 13.2v; this is not a problem. But the disconnect voltage is around 12.7vl and most lithium iron batteries will never drop that low, so the ACR may never open. This could lead to your starter battery draining your camper battery.

As noted, even a 100Ah lithium iron battery can pull a lot of amps if deeply discharged - there is a chance of overloading your alternator or wires.

All in all, for a safer retrofit, at battery to battery charger is a better idea.

 

[concretejungle]

thank you all! After a little more research and as suggested here I certainly need a DC-DC charger.

Does the DC-DC charger replace the ACR? Meaning, do I take it out of the line and just replace that with the DC-DC?

 

[concretejungle]

Perfect, so in essence the DC to DC is an upgraded version of an ACR? Just ensuring that my starter battery will also get some juice if needed?

 

[DiploStrat]

No. A DC-DC charger is a totally different animal. (The ACR its a voltage sensing relay; a battery to battery charger is an actual battery charger.) It will NOT allow the camper battery to connect to the starter battery.

You can wire a by-pass, but you probably want something like an Amp-L-Start. They have a lithium compatible product. (N.B. Their website appears to be down. Caveat emptor!)

 

[ConcordCarlos1]

I just replaced the ACR/VSR in my camper with a Victron DC2DC charger. I did this in anticipation of swapping the AGM out for a LifePo4 . in the mean time my AGM will be better off, since it is now getting its 14.7v and 3 stage charging. When i switch batteries I can select the charge profile via the Victron App on the DC2DC and my MPPT.
I set my DC2DC to come on when it sees 13v from the truck side.

 

[concretejungle]

Wanted to update and continue to ask for guidance....

Here is what I've accumulated so far in preparation:
1. 12v battle born lithium 100 amp hour battery
2. Victron non-isolated 30 amp dc-dc charger
3. negative buss bar.
4. Victron BMV-712 smart battery monitor
5. Victron solar charge controller
6. Renogy 100W solar panels.

In preparation to start wiring this up, I've built a wooden box inside my cruiser. I do not want to place this battery under the hood!

First question: The most simple wiring diagram I've found is here. So that is my first question.... do I literally run two positive wires from my alternator; one to my starter battery and the other to the dc-dc charger which then goes to the lithium battery?


Second Question: I would still run my solar charge controller directly to the lithium battery? Currently on my lead acid battery I have the charge controller wired directly to my house lead acid battery so I'm guessing that stays the same only change the charge profile on the charge controller?

 

[ConcordCarlos1]

If I understand Q1 correctly, no. At least on mine, which is similar to yours , positive from start battery to positive in on your DC2DC.

From your DC2DC , positive out to your house battery.

DC2DC , ground to common ground.
house battery negative to common ground.
@DiploStrat (cuz he knows his stuff)

Q2. Yes.

 

[concretejungle]

Your car should already have the wire between alternator and starting battery.
Its sized to carry the expected OEM loads plus a capacity margin of unknown value. (perhaps an industry standard / guideline for that margin exists ? I dunno... )
Yes, connecting DC-DC charger directly to the alternator is better as that keeps the added load of the DC-DC charging off of the existing alternator to starting battery wire.
Said all that..
Lots of guys connect DC-DC input directly to the starter battery with no apparent problems.
Just be aware doing so applies additional 30A (plus or minus) continuious load on the OEM alternator to starting battery wire.

Thanks for your thoughts! Yes, there is an existing wire from my alternator to my starter battery. On my old setup, I had that wire run to my positive starter battery and then had a wire from that positive post on my starter battery run through a breaker to the positive on my House battery (through an ACR). Now that the ACR is out of the equation I will run that wire through my DC to DC charger.

 

[DiploStrat]

Thanks for your thoughts! Yes, there is an existing wire from my alternator to my starter battery. On my old setup, I had that wire run to my positive starter battery and then had a wire from that positive post on my starter battery run through a breaker to the positive on my House battery (through an ACR). Now that the ACR is out of the equation I will run that wire through my DC to DC charger.

If the wiring for your ACR is big enough, simply put the B2B where the ACR was located - electrically if not physically. This ain't hard; even I can do it!

(And if your ACR wiring is not up to snuff, you can simply double it, sometimes this is easier. In the end, copper is copper.)

 

[concretejungle]

If the wiring for your ACR is big enough, simply put the B2B where the ACR was located - electrically if not physically. This ain't hard; even I can do it!

(And if your ACR wiring is not up to snuff, you can simply double it, sometimes this is easier. In the end, copper is copper.)

That's what I was thinking with one exception.... I"m moving the "house" battery back to the cab and out from under the hood. So that means I need to run new wires and relocate stuff.

I also want to continue to use my battery switch that can combine my house battery to my starter battery just in case my starter battery ever get's run down. I should be able to keep that as well, right? Only time it's used is to switch it to combine long enough to start the truck and then switch it back.

 

[DiploStrat]

Being lazy, I was only pointing out the copper is copper. If you are moving stuff, then you will have to rewire, but that doesn't mean you can't reuse some of your existing wire if it is the right size, good condition, etc.

You can certainly wire up a bypass for the B2B with a remote controlled solenoid. Just remember that if you want to use it for actual jump starting, it will have to be starter gauge, not charger gauge.

 

[concretejungle]

OK I think last question. I had a blue sea battery isolator switch in line on my old setup. It's model 6011 https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

Is it safe to use this set-up to jump off my starter battery in an emergency? Making sure my lithium battery will not blow up my lead acid starter battery with to much current?

And if it's OK then I would wire it up the same as my last setup except where it was connected to the ACR it's now connected to the DC to DC charger?

Thanks!