Realistic Capacity Margin for DOY LiFePo4 Setup?

[monkeyodeath]

I've decided to take a crack at building a DIY LiFePo4 battery setup for my rig.

My current setup is a 300W solar panel and a Group 34 lead acid battery. I'm running an ARB fridge and occasionally a diesel heater. No real plans to add anything else aside from maybe a 12v oven for giggles at some point.

I'm going LiFePo4 because the battery doesn't seem to have the capacity to run the fridge all night on really hot days. Solar doesn't appear to be an issue -- battery is generally fully charged within a couple hours of sunrise. I realize that dual golf-cart batteries are the economical option here, but I'd rather not load that much extra weight into my first-gen Tacoma and I'd like to be able to easily remove the battery pack when it's not needed.

I'm trying to decide between a 280ah or a 160ah setup. Seems like these are the most commonly available cells right now.

Was leaning towards the 160ah because the price is about half ($264 vs $440 for the cells) and because, based on my (admittedly sketchy) math, 160ah should be plenty for my needs. Vast majority of my camping is in the Southwest, where sun is pretty reliable, and my solar panel is a full-size 300w residential panel feeding into an MPPT. So I can't imagine my battery going any more than a couple days without getting a decent charge.

But I wanted to double-check with the experts here to make sure I wasn't omitting any considerations or doing my math wrong.

 

[DiploStrat]

OK, I'll help spend your money.

As to capacity, guesstimate 80% usable and you will be fine. I am so lazy that I assume that my 280Ah cells are about 250Ah usable. ("Good" companies [as opposed to those that are simply misleading you] that advertise "100%" usable capacity simply oversize their battery and then advertise the safe capacity as determined by the BMS. You can do the same thing - set your BMS conservatively and your battery will outlive you.)

Buy the 280's. You will never regret the extra capacity. (I actually bought two extra cells as I ordered directly from China, back when shipping was cheaper.)

Compared to the size and weight of lead acid, four 280Ah cells are tiny. Just be sure to get a decent BMS, that has:

-- High/low voltages.
-- High/low cell voltages.
-- High/low temp shutoff.

I bought mine from Overkill Solar - good product and great hand holding.

Get the bigger cells, you will never regret it.

Overkill Solar

More is Better...

overkillsolar.com

 

[jonyjoe101]

Get the larger batteries you can get. I have a 220ah lifepo4 and a 312ah li-ion battery banks. I use the 312ah just for my 26 liter 12 volt fridge.

One thing I notice is that your group 34 is fully charged the following day within a couple of hours from sunrise. I suspect the mppt controller is not reading the correct voltage from the battery terminals and undercharging your battery. From 300 watts you should be getting a max of about 14 amps of charge power when the sun is overhead and the battery is depleted. Even with full sunlight it will take most of the day to get a full charge especially in the winter.

I used to run a 43 liter edgestar fridge 24/7 on a 120 watt panel and 75ah agm, Your 300 watts and group 34 should easily keep up with your ARB fridge (more efficient than the edgestar) even in the hottest months of summer.

I would verify that your group 34 is getting fully charge (check voltage at battery terminals , they should reach 14.4 volts) . It should stay at 14.4 volts (absorb) for at least an hour. If the mppt is switching to float to soon, you probably have voltage drop from the mppt to the battery.

If battery terminals isn't reaching 14.4 volts, you need to adjust the bulk voltage on the mppt controller upwards, until you reach 14.4 volts on the terminals. On my ecoworthy 20a mppt, I had to adjust the bulk voltage to 15.5 volt just to get the battery terminals to 14.6 volts. Anything less than 15.5 volts and the battery wouldnt get a full charge. Go up slowly on the bulk setting go to 14.8 volts check the terminals, and keep adjusting until you reach 14.4 volts.

Also in the summer, vent the fridge compressor to the outside of the van. I have a 120mm fan that exhausts the hot air (over 120 degrees) that the compresser put out and this air goes outside. This reduces the heat inside the van and also around the fridge. The fridge compressor runs less the cooler it is. It's a simple technique that helps alot.

 

[dstefan]

FWIW, I ran my ARB 50 qt fridge last summer for 5 days/4 nights in 70 to 85° daytime temps along with charging multiple devices, but no laptop, other 12v draws for lights, a heating pad and some low draw inverter use at one point. We ran our Maxxair fan often and all night on low. My fridge has the ARB insulated cover and a little extra I added. we were in and out of it relatively often, but not excessively. We went from 100% when we parked to 40% when we pulled out (measured on a Victron shunt)

This was on a 100 ah Battleborn that’s DcDc charged from the starter battery/alternator. We did not move or turn on the truck at all, nor did we use our portable solar panel as I was really trying to test the system.

It all depends on your loads and you use patterns of course. Seems like if you’re not trying to run high draw 120v appliances on an inverter, 100ah is plenty.

For my use DCDC charging and 100ah is overkill almost. I had thought about roof top solar at one point, but have abandoned the idea, and quit hauling the portable solar too. For some situations, certainly mine, I think the DCDC charger may be more cost effective and reliable.

Hope that helps. YMMV!

 

[monkeyodeath]

Appreciate all the advice.

Thanks to jonyjoe101 for the tip about checking the charge voltages. I myself was surprised that the group 34 battery wasn't cutting it -- figured it would be enough.

I'm also seeing the wisdom of going for the higher AH rating despite the cost. That much overkill would give me a nice cushion in case solar isn't cutting it on a particular trip and plenty of capacity to add stuff on.

Figure it will end up in a longer useful life for the battery -- even as capacity over time starts to degrade, I'll still have plenty of headroom for quite a while.

 

[Willsfree]

FWIW, I ran my ARB 50 qt fridge last summer for 5 days/4 nights in 70 to 85° daytime temps along with charging multiple devices, but no laptop, other 12v draws for lights, a heating pad and some low draw inverter use at one point. We ran our Maxxair fan often and all night on low. My fridge has the ARB insulated cover and a little extra I added. we were in and out of it relatively often, but not excessively. We went from 100% when we parked to 40% when we pulled out (measured on a Victron shunt)

This was on a 100 ah Battleborn that’s DcDc charged from the starter battery/alternator. We did not move or turn on the truck at all, nor did we use our portable solar panel as I was really trying to test the system.

It all depends on your loads and you use patterns of course. Seems like if you’re not trying to run high draw 120v appliances on an inverter, 100ah is plenty.

For my use DCDC charging and 100ah is overkill almost. I had thought about roof top solar at one point, but have abandoned the idea, and quit hauling the portable solar too. For some situations, certainly mine, I think the DCDC charger may be more cost effective and reliable.

Hope that helps. YMMV!

I'd like to use a DC/DC charger; what brand/model charger did you end up using and what other components are needed to make it work?

 

[DiploStrat]

Scholars differ.

I like Redrac and Sterling Power.

Redarc units are nice, epoxy sealed bricks. (Nice if you have to mount under the hood/outside of the camper, etc. But don't do it if you can avoid it, even with a sealed unit that doesn't have a fan.) All programming is connecting and disconnecting wires. Dead easy to install.

Sterling Power have a wider range and a few bigger units. Their units typically need a bit more air, but can be programmed to the gnat's eyelash, should you wish.

Victron are getting into the game, and since a DC-DC charger is really just an MPPT front end with a charger at the back, basically the same as a solar controller, I suspect that their units are fine. They also have the advantage of plugging into their ecosystem, allowing nifty remote control/monitoring, etc.

(Scholars debate the importance of programming for lithium iron, but that is another story.)

 

[wicked1]

I've got 175Ah batteries, and never use their capacity. I've got a 12v fridge.
The sun keeps the fridge running and gets the batteries charged fully, on the shortest day of the year, mid US latitude.

Other than the fridge, there's a minimal amount of light, fan or blower, and charging things usage. I don't think I've ever dropped below 70% charge. And, these aren't like lead.. you can actually use their full capacity.
But.. I'd still get more than you expect to need. They're small and light compared to lead. Get the 280's. (I've seen 200's, 220's, and 250's as well).

-Edit to say.. If you want to go as light and inexpensive as possible, I do think the 160's will be enough for you, based on your usage and where you camp. Now that I think about it, I'm not sure why I suggested to get more than you need.. As I said, I've never needed my 175Ah. It will keep everything running for a few days w/out any charge. Technically, I think I could go 5-6 days, based on my average usage. (But OTOH, one unaverage situation, like if I needed to run the blower furnace all day/night, could drain me in a day.. I've got a non blower heater, too, tho, so that shouldn't be an issue for me.. Just mentioning you might want to consider other circumstances)

I built mine a few years ago, and there seems to be no change in performance.
A brief description of my build...
I've got two aluminum plates, which are the size of the large side of a cell, on each end. The 4 cells in the middle. All 'clamped' together w/ a few heavy zip ties. (you could obviously do a more professional job w/ threaded rod, but I think this is sufficient). It's all wrapped in kapton tape, too. (The aluminum plates are basically just to stop the zip ties from crushing the corners of the cells.)
From the bottom it's a piece of foam board insulation. Next is heating pads glued to an aluminum plate (plate to spread the heat). Then the 4 cell battery. All the sides are insulated as well. I used 2" (or maybe 1.5") foam board for the insulation. I do a lot of winter camping, and find I usually need to plug the heater in the first morning I'm out. But then it doesn't ever turn back on..The insulation and usage of the battery keeps it above freezing for the 20-30 degree temps I'm usually in. (The heater is automatic (temperature controller), but I leave it disconnected when I'm not camping).
Let me know if you have any questions while building it.


Edit 2: I initially said some things about RedArc (they're great), but, if your panel is a higher voltage panel, redarc won't work.. It has 32v max, peak.. Home panels usually reach higher voltages than that.. Then I'd probably go Victron, but haven't looked into controllers for a few years.

 

[dstefan]

I'd like to use a DC/DC charger; what brand/model charger did you end up using and what other components are needed to make it work?

Its the National Luna DC25 because I decided to go with their Powerpack to keep things simple and be able to easily remove the battery in the Phoenix summer heat as well as use it in two different vehicles. It also has a good MPPT solar controller built in. Been very happy with it for two years and many trips.

One other recommendation is that the NL is what Mario at ATOverland used in his builds either in the Powerpack or as a stand-alone DCDC charger.

 

[rruff]

Was leaning towards the 160ah because the price is about half ($264 vs $440 for the cells)

Where are you buying from? This place has gotten good reviews and has US stock of Eve and CATL cells. Prices are less than 1/3 what you are stating for the larger batteries.

DOCAN POWER

Brand New High Quality LiFePO4 Battery Cells SupplierDocan is TOP10 battery and battery suppliers in China. We supply TOP1 service of Lifepo4 Prismatic Cell and Battery Pack for variouse area, 12 years+ focus on high capacity, high wattage, high voltage, high dicharge current battery cells and...

www.docanpower.com

 

[monkeyodeath]

Where are you buying from? This place has gotten good reviews and has US stock of Eve and CATL cells. Prices are less than 1/3 what you are stating for the larger batteries.

DOCAN POWER

Brand New High Quality LiFePO4 Battery Cells SupplierDocan is TOP10 battery and battery suppliers in China. We supply TOP1 service of Lifepo4 Prismatic Cell and Battery Pack for variouse area, 12 years+ focus on high capacity, high wattage, high voltage, high dicharge current battery cells and...

www.docanpower.com

Oh, price I was quoting was for a bank of 4 of those batteries to get to 12v.

 

[rruff]

Oh, price I was quoting was for a bank of 4 of those batteries to get to 12v.

Well, that's a really *good* price! Source?