ARB fridge with LiFePO4 in a dual battery setup

[soul]

Actually yes ! thanks! and the one which will step up the voltage. The battery has BMS and protection circuit, so if I manage to charge the LiFePO4 to 14.6V then am good.
I found a good dc-dc step up converter @15Amps http://www.amazon.com/gp/product/B00C9UUFHC/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

The Battery Protector is going back, as it is not useful in this situation.

 

[soul]

The setup now has a DC DC charger which converts 12v to 15vdc @15Amps to charge the LiFePO4 battery. It has been working flawlessly for over a month now, with 2 - 3 day camping trips under the belt.
I am keeping the fridge in the vehicle itself, normal driving is keeping the batteries fully charged.

Overall choosing LiFePO4 turned out better for me, in terms of size, weight and hopefully the longevity.

 

[sCir]

So it's been a few months since you posted about your LiFePO4 setup. Still working well? Assuming I'm skipping solar charging for now and will only be going off the alternator, my shopping list would be the following:

3x 3.2v LiFePO4 cells
BMS Protection board
DC DC Step Up Converter
30a Fuse
Battery Isolator (in my case I'll use just a simple relay and switch)

Does this seem right? I'm not sure where the step up converter goes in the circuit as your original schematic doesn't show it. I would assume between the fuse and the BMS Protection? Could I skip the step up converter and BMS if I used a more sophisticated off the shelf DC Charger, something like this: http://www.kulkyne.com/au/CTEK-D250S-Dual.html? This unit seems to be specific to led acid or AGM batteries, but I'm not sure I understand why it should matter so long as the output voltage is high enough to fully charge the LiFePO4 packs..

My end goal here is to run a fridge and possibly charge some portable electronics.

 

[mib1392]

Hi,
this might be interesting for you to play with. I can't quite convince myself to start playing with the LiFePo...I have a nice Pb setup (CTEK dual) in my European camper and not really a need for a 2nd battery in the US car. But 35h left to rethink it.

https://www.kickstarter.com/projects/electrodacus/open-source-programmable-solar-bms-development-boa

Best,
Mike

 

[coolfeet]

This set up looks great! I am wondering if someone could provide the final schematics? I was considering buying Apsect Solar's Power Bar with the optional 50 W solar panels. This looks like a great project for less money plus it can be connected to the main battery of my van.

 

[soul]

I don't think the CTEK has BMS feature built into it. Basically the BMS will 1) Prevent overcharge 2) low voltage cutoff 3) Balance cells 4) monitor in/out current, etc. The CTEK may cover 1), but not sure of the rest.
Also to your point, CTEK has voltage booster but if its designed for Lead Acid will not advise it to use for LiFePO4. The voltage characteristics which help the charger adjust current when batteries are full are very different between battery chemistries. LiFePO4 are sensitive to under and over voltage during load and charging.

 

[soul]

Will post my updated schematic, it has been working flawless since May 2013 to the point I rarely remove my fridge from the SUV.

 

[JK Driver]

Very cool.
Please post your schematic.
Regards,
Jim

 

[BigSwede]

This tech is exciting. A 50 ah LiFePO4 like this should be at least equal or better than a 100 ah AGM for our purposes, and look at the size/weight savings!

http://store.starkpower.com/12V-50A...ttery-LiFePO-Energy-Storage-Battery_p_42.html

May need to figure out charging issues:
"It is best for the "UltraEnergy" battery not to be trickle charged but to use advance chargers that turns OFF charging current when the battery is completely charged at 14.6V. ...Using lead acid chargers that charges up to 16V, along with leaving them ON, will damage the Lithium battery over extended time."

 

[Xterabl]

Mr. Soul, that schematic would definitely be nice!
Did you use the same DC-DC charger that you linked to on Amazon?
Looking around on the web, LiFePo's don't seem to be getting any cheaper. Probably it'll be another few years before that kicks in?

 

[BigSwede]

I think demand has outstripped supply for the moment, the cells he used are all sold out. I figure by the time my current fairly new AGM battery craps out the LiFePOs will be affordable.

 

[ebnelson]

Hi,
this might be interesting for you to play with. I can't quite convince myself to start playing with the LiFePo...I have a nice Pb setup (CTEK dual) in my European camper and not really a need for a 2nd battery in the US car. But 35h left to rethink it.

https://www.kickstarter.com/projects/electrodacus/open-source-programmable-solar-bms-development-boa

Best,
Mike

Thanks, I've pre-ordered one of these from Dacian.

Eric

 

[randy h]

This is an interesting thread. I am subscribing.

My 48ah yellow top was abused and is getting old. My Solar Charge Controller is fairly configurable. Mating it up to an internally managed Stark battery like BigSwede linked should be a no brainer.
But what about letting your vehicle alternator charge a Stark battery. Not starting the car with the Stark, but topping off while driving, or helping out on extended cloudy days?

 

[soul]

1) LiFePO4 - http://www.all-battery.com/32v100ahl...lebattery.aspx or http://www.batteryspace.com/lifepo4...v-100ah-10c-rate-320wh-un38-3-passed-dgr.aspx
2) BMS Protection - http://www.evassemble.com/index.php?...products_id=41 or http://www.batteryspace.com/pcbpcmfor128vlifepo4pack4inseries.aspx
3) LiFePO4 Charger 30A - http://www.bioennopower.com/collect...oducts/12v-24v-30a-lifepo4-solar-controller-1
4) DC DC Converter - http://www.amazon.com/gp/product/B00C9UUFHC/ref=wms_ohs_product?ie=UTF8&psc=1
5) Isolator - http://www.powerstream.com/battery-isolator.htm
6) Solar Panel & Diodes - Searching for Flexible Monocrystal Panel, which can be mounted on rooftop and/or at campsite
7) Box for batteries- Currently batteries are kept in a small floor compartment in the SUV, planning to make it portable using 14.5 x 12 x 4 inch box. The batteries are light, so easy to move around.

This unit is running extremely well over a year now, I have taken it to campsites that had day temp of 108 deg (Millerton Lake on 4th July 14). Based on ambient temperature and how many times the fridge is opened during the day, it provides 3 to 4 days of use without running the engine.

 

[soul]

@Xterabl The DC charger was from Amazon, just ensure its the boost type with 15A rating. I ordered the wrong one from the same company, so had to return. I also tested with a DC DC doubler @30A, but it loads the alternator too much (Alternator voltage drops significantly, which will affect main battery charging). In my case, a 2 hour engine run will charge the LiFePO4 battery enough to run the fridge for additional 24hours (15A x 2 hours = 30 AH, ARB 50q uses between 16 to 30 AH per day in my case)

In theory the 100w Solar panel with good sunlight over 3-4 hours/day will keep the fridge running for extended period, without requiring to start the car engine. I will test that soon.