DC to DC Charging for LifePO4 battery bank.

[dbhost]

I probably got the wrong thing, but here goes.

My truck shell camper build. I need to provide power to...

#1. Alpicool APLT60 60 liter / 63 quart LG compressor fridge. 45w rated, this obviously cycles on and off so not a constant draw, but it draws on and off 24x7.
#2. Z2 Travel CPAP. Only runs when I am trying to sleep, so 8hr / overnight, no solar coming in. 35w on ramp up, 20w running.
#3. Asus Rog Strix G17 laptop. 100w USB C charging, or 240w 110v through the inverter.
#4. Samsung Galaxy Note 9 phone / camera / wifi hotspot etc... I have a separate solar charger for this though.

My charging circuit looks like this.

#1. Atem Power 20 amp DC to DC charger / mppt solar controller. Does NOT have a specific profile for LifePO4, but does for Lithium Ion. Both Atem Power on their website, and several sellers say it can be used for LifePO4, allegedly by using the AGM profile. Need to verify this.
#2. Obviously, or a least I hope it is obvious, High output alternator, TBD at the moment for my 2004 F150 5.4L 3V, yes new engine been bulletproofed as much as these can.
#3. Dokio 300w portable solar panel kit. This is to be deployed when in camp. The charge controller that came with this DOES support LifePO4.

So I have a dilema. I would like to go with Lifepo4, but don't think my DC to DC charger will do the job, I can charge with solar no problem and have more than enough power with a 200 amp hour battery, but that also poses a physical storage problem. I was originally planning on a Group 31 AGM battery in a Ford E series cab and chassis mount under the cab of my truck. I am not super skilled with metal fabrication so making my own larger under body mount is not exactly an option... What can I do for battery / battery bank?

And what can I do for a charger that will handle from the alternator charging AND solar AND Lifepo4?

 

[Alloy]

What are the specifics of the charging programs/algorithms that Atem Power uses for AGM and Lithium Ion?

Are you thinking of a DIY Lifepo or factory assembled?

Atem sells factory assemble Lifepo which might (should) work with the DC-DC on a AGM program. Worth a call to find out.

 

[DiploStrat]

20A is so low, it almost doesn't matter what profile you use. All of their voltages are way high, but they is how they compensate for the low output. You should be fine. (This does not look like the greatest bit of kit, but it should work.)

Drop in two 100 Ah Lithium camper batteries, or one of the new 280Ah combo batteries, and you will be happy.

12V 20A DC to DC Battery Charger MPPT System Kit Isolator Dual Battery

If you’re planning an off-grid camping, a DC-DC charger by ATEM POWER will be your perfect companion for a dual battery setup when you cannot access main power. This device, which is designed to do a full charge cycle with the ability to choose either Lead Acid, AGM, Gel, calcium, LiFePO4...

atempower.com

 

[dbhost]

20A is so low, it almost doesn't matter what profile you use. All of their voltages are way high, but they is how they compensate for the low output. You should be fine. (This does not look like the greatest bit of kit, but it should work.)

Drop in two 100 Ah Lithium camper batteries, or one of the new 280Ah combo batteries, and you will be happy.

12V 20A DC to DC Battery Charger MPPT System Kit Isolator Dual Battery

If you’re planning an off-grid camping, a DC-DC charger by ATEM POWER will be your perfect companion for a dual battery setup when you cannot access main power. This device, which is designed to do a full charge cycle with the ability to choose either Lead Acid, AGM, Gel, calcium, LiFePO4...

atempower.com

I am trying to avoid straight lithium ion. Those have a tendency to catch fire, and I want to mount under the cab of the truck. . 20amp is what the MFG of the solar panels calls for which is why I went that way. I am not running a heater or anything like that off of it. If I pulled full load at once, which I will never do, I am looking at just under 12 amps load, fridge, CPAP, and laptop. And of course mind you, I also have a 1KW gas inverter generator to work with as well...

 

[dbhost]

And a breakthrough. Just talked with a friend of mine that is helping me with the engine swap. He's got some Chen Lifepo4 100 amp hr batteries, a pair of them, in his RV. We are going to test on them and will go that way if it works. He is using some kind of truck battery box on the RV frame for his house batteries. We may have a solution! Not sure if 2 100 amp hour, or 1 200 amp hour is a better idea, but will decide later.

 

[DiploStrat]

Not talking lithium ion, but lithium iron. I was thinking Battle Born, Lithionics, or similar. Your choice. (FWIW, you probably can't buy a lithium ion battery in a standard sized case.

Something like this would be very easy. https://battlebornbatteries.com/product/270ah-12v-lifepo4-deep-cycle-gc3-battery/ This one happens to be stupidly east to install, but there are lots of options on the market.

FWIW: The Atem claims a lithium iron profile, but it looks a bit hot to me. Not a real issue as the charger is so small.

N.B. Mount them inside the heated camper. If not, consider heated batteries if you live in cold climes.

 

[dbhost]

Not talking lithium ion, but lithium iron. I was thinking Battle Born, Lithionics, or similar. Your choice. (FWIW, you probably can't buy a lithium ion battery in a standard sized case.

Something like this would be very easy. https://battlebornbatteries.com/product/270ah-12v-lifepo4-deep-cycle-gc3-battery/ This one happens to be stupidly east to install, but there are lots of options on the market.

FWIW: The Atem claims a lithium iron profile, but it looks a bit hot to me. Not a real issue as the charger is so small.

N.B. Mount them inside the heated camper. If not, consider heated batteries if you live in cold climes.

Pickup truck shell camper 6.5ft bed with a twin mattress. Gulf coast of Texas is my home base but I range up into snow and sub freezing temps periodically. I can build a box to enclose the battery next to the bed and make up a nightstand of sorts. I need a place to set the CPAP anyway... I'm just not flush with extra space. My plan for heat is a 3K Coleman catalytic heater OR a Buddy Heater, but the Buddy heater on low is still pretty high, have to keep a window open... just to keep from baking it there...

 

[jonyjoe101]

Just make sure and measure all the voltages directly from the battery terminals. For lifepo4 you want to get them up to 14.4 volts (max for a 4s lifepo4 is 14.6 volts). The atempower charges the lifepo4 to 14.4 volts which is adequate for the type of battery, but just verify the battery terminals. If you have voltage drop from the charger to the battery, the charger will think the battery is full at 14.4 volts (and reduce amps) while in reality the battery terminals are reading only 14.2 volts.

IF the dc-dc charger/mppt controller isnt getting the terminals up to 14.4 volts, the battery will never reach max charge. If you don't have a coulomb meter, you need one for lifepo4. The resting battery voltage on lifepo4 settles at about 13.1 volts when its between 20 and 100 percent, only way to verify the SOC is by counting amps going in and out of battery.

I recommend this coulomb meter to everyone, I been using for years on my 220ah lifepo4 battery bank, it reads the voltage directly from the terminals so you will be able to bounce that voltage with whatever the charger claims its reading. It will also show you how many amps the charger is charging at, you want to get the max 20 amps from the charger to keep the battery fully charge.

tk15 coloumbmeter (cost around 40 dollars for the 50amp model on ebay).

 

[dbhost]

Something interesting I just noticed. From the Atempower website it actually shows a Lifepo4 profile on the control pad and a SKU number of VABG007A-VOR.

The one I got from Amazon has a SKU number of ‎VABG007A-UFA and shows lion not lifepo4.

Wonder what the differences are...

 

[DiploStrat]

Sorry, getting ready for OEXPO East but, at 120 kph:

-- There is little if any difference between the "profile" for lithium ion and iron. Indeed, there is really little profile for lithium at all. Most call for a constant voltage/constant current charge at the target voltage and a complete shut off when the trailing amps drop to around 0.5A per 100Ah of battery. It is not hard to find a profile that is close to that.

-- With a six foot bed, I would drop a single case 280Ah battery under the bed.

-- One advantage of lithium is that it does not suffer if not fully charged, and indeed, most of the old line lithium gurus preach a target voltage of around 13.9v. The charger manufacturers like higher voltages because: 1. Their chargers are already set there, and 2. with a smaller charger (e.g. 20A) you can get a faster charge with no damage to the battery. (The bigger the battery, the safer it is.)

-- All of these batteries are made up of lots of smaller cells wired in series/parallel to get the desired voltage and capacity. The better manufacturers overbuild and undersell, and then set their BMS to fully protect the battery. That way they can claim "100%" discharge and/or "never die". Basically, the BMS keeps the battery from discharging below, say, 10-20% or charging above, say, 80-90%. With a good battery, these beasts are near bullet proof, hence the long warranties.

Good luck!

 

[jonyjoe101]

3s Li-ion is fully charged at12.6 volts and 4s lifepo4 is fully charged at14.6 volts. For your lifepo4 just set it to lead acid 14.4 volts, thats good for lifepo4. All the batteries lead acid, li-ion, gel, agm, lifepo4 are charged by the CC/CV method which the charger does, the profiles only changes the bulk voltage. The only thing that bothers me is that it does equalization automatically, where it pulses voltages above 14.4 volts, its not needed for lithium, if you can find a setting to disable equalization I would do it.

 

[DiploStrat]

Probably much more geek than dbhost wants but:

-- All chargers have a "profile", even a constant voltage/constant current is, technically, a profile, especially if the charger has a logic to shut itself off automatically.

-- Many (most?) lithium gurus preach that lithium batteries don't need the classic, multistage profile of bulk>absorb>float, but, assuming that the voltages are about right, the battery will not be damaged. And a slower ramp up in the bulk stage can't hurt.

-- The "target" voltage, the voltage at which we say the battery is fully charged is usually defined as the absorb voltage, but, of course, it would also be the voltage at the end of the bulk stage. Chargers vary; Some hit the target voltage immediately while others ramp up through the bulk stage.

-- Scholars debate absorb. For lead acid, a long absorb stage is essential. For lithium, the conventional wisdom is that you don't want a long absorb stage. Victron, for example, tends to limit it to an hour or so. Again, the conventional wisdom is that the only purpose in holding the battery at full voltage is to allow balancing.

-- Agree completely on the equalization stage. You don't want that at all, if only for the same reason that you don't want a long absorb. Once a lithium battery hits its target voltage, shut off the charger.

-- Float is another discussion. My personal take, open to challenge, is that you do want some float when you are actually in the camper, running things all day. When the camper is in storage, you want the battery at about 50% with little or not charge. (I actually turn off my main solar array.) N.B. Again, this is the exact opposite of lead acid. My starter batteries are in float all the time.

Hope this is:

A: Accurate, and,

B: Helpful.

As always, when in doubt, listen to the folks who warranty your battery, not you charger.

 

[Alloy]

A missing piece in this thread is the BMS.

 

[dbhost]

...-- Float is another discussion. My personal take, open to challenge, is that you do want some float when you are actually in the camper, running things all day. When the camper is in storage, you want the battery at about 50% with little or not charge. (I actually turn off my main solar array.) N.B. Again, this is the exact opposite of lead acid. My starter batteries are in float all the time.

Hope this is:

A: Accurate, and,

B: Helpful.

As always, when in doubt, listen to the folks who warranty your battery, not you charger.

Yes, very helpful, and seems to be right in line with the info I am finding online on my own research...

You mentioned earlier a larger battery under the truck bed / cab, which is great. Budget could certainly handle for example a Chins 200 amp hour Lifepo4. But this leaves the question of how to mount under the bed / cab of the truck. I am figuring I might have to have a custom mount box or bracket made. Being as I am coastal TX, I am not terribly worried about too cold of temps, however I will be travelling to see snow as my wife hated the stuff, but I miss it.

Now for the reason I am picking the specific bits I am to reply to... You mention when the camper is in storage.

My plan, at least for now, is to, since I will be working hybrid, be working semi nomadically, as it the camper should in theory be in use at least 1.5 weeks / month. Which is why I am was shooting for ability to keep the laptop topped up... I am using my personal laptop as a control as I know it is power hungry. Latest / fastest processor and big honkin GPU, not meant for energy efficiency, but for gaming. I actually got it for fast clean audio / video editing... My work laptop charger is actually only 50w, not a powerhouse by any means...

WIth that bit of knowledge, do I need to worry about how charged the battery is between trips?

It would be a stretch, but I could probably find a way to make the Chins 300 amp / hour swing... Seems like the rest of the setup would be kind of undersized at that point though...

 

[DiploStrat]

Couple of comments:

-- I was thinking of a battery inside the actual pickup bed, under the sleeping bed. There are batteries, like Battle Born's "Gamechanger", that come with mounting tabs which would make this very easy. You could cobble up a plywood (or similar) box as the base for your sleeping bed, put the battery inside, and mount your B2B, inverter, fuses, etc. on the side. (You might need to vent it.)

-- If you are using the camper for a week every month, I would not worry about "storage." Use your solar panel if you need to.

Updating my reference stuff for OEXPO East here: https://diplostrat.net/documents/

You might enjoy the "Planning" document.