ARB fridge with LiFePO4 in a dual battery setup

[soul]

My new ARB 50 quart should be in tomorrow, and am planning to use a dual battery setup in my SUV.
The goal is to run the fridge on battery for 3 days, without recharging, so minimum 120Ah lead battery will be necessary.

Problem is, my SUV has not much of space for a 120Ah battery. It will be big and very heavy. My experience with LiFeP04 (used them in RC Heli) has been very good. They are half the weight of Lead batteries, twice the life, very stable and safe, fast charging and useful capacity is over 80% (compared to 50% of Lead). Nowadays they are not very expensive compared to Lead acid battery, if the life and cycles are factored in.

I am thinking of battery isolator pushing current to the LiFeP04 via protection circuit (meeting LiFePO4 requirements). But would also like to keep Solar as an option in future. Anyone tried this before? There are not any isolator+LiFePO4 chargers like the ones CTEC has for Lead packs.

 

[Xterabl]

Well, you might also be interested in this kind of setup:
http://www.expeditionportal.com/forum/threads/100585-80W-Solar-350-Wh-li-ion-TI-BQ24650

 

[kevint]

I'll be interested in what you come up with. I've been intrigued with the capabilities of LiFePO4 batteries since obtaining a Sherpa 120. I have wondered what a replacement for my 2 Trojan T-105s would look like (with charger). I had read they are popular with the RC world.

 

[Ramjet]

I'll be interested in what you come up with. I've been intrigued with the capabilities of LiFePO4 batteries since obtaining a Sherpa 120. I have wondered what a replacement for my 2 Trojan T-105s would look like (with charger). I had read they are popular with the RC world.

Kevin, this is what happens with those older Sherpa Batteries. Just keep an eye on it. Mine exploded about 3 weeks ago. The smell is so hard to get rid of. They will replace it if this happens with the newer model if you ask nicely. So I would not recommend those types of batteries for a dual battery system. My .02

 

[soul]

Not all Goal Zero Sherpa's use LiFePO4 (only the Elite series), normal Lithium Oxide or Lithium Polymer (common in RC) are not stable. The LiFePO4 are proven to take abuse, and more commonly used in Electric and Hybrid Vehicles.

 

[soul]

Thanks!, that is the path am considering.

Instead of 12V packs, with built in BMS I am thinking of using 3.3v 100Ah x 4 packs and use a LiFePO4 protection circuit ($26) to balance the cells. I can stack them or place side by side to easily fit in the vehicle.

LiFePO4 - http://www.all-battery.com/32v100ahlifepo4lithiumironphosphaterechargeablebattery.aspx
BMS Protection - http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=41
Solar Panel - http://www.sunpowerlink.com/120w folding solar panel/120W_folding_solar_panel.html
MPPT for Lithium - http://genasun.com/all-products/sol...ium/gvb-8a-li-lithium-solar-boost-controller/
Battery Isolator - http://www.amazon.com/WirthCo-20090...8?s=automotive&ie=UTF8&qid=1368552361&sr=1-68 - Returned



UPDATE

The Battery Isolator did not work, as it is a dual sensing one. Firstly it needs both batteries to be directly connected to it, so that it can sense voltage. It simply will not bridge if the Aux battery is absent or if its not able to sense the Aux battery voltage (so cannot put LiFePO4 charger or step up converter in-line). Secondly, the LiFePO4 has higher operating voltage than Lead battery so once the isolator connects the two it will not disconnect until both the batteries are below 13V. The the full capacity of LiFePO4 will be never utilized because of this. So the battery isolator is returned.

Here is another option for battery isolator, to be tried out

1) Simple relay isolator ($15 - http://www.amazon.com/gp/product/B001EAWS6O/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1)
2) Voltage sensing Relay control ($32.5 - PST-SBC1120-Module (battery isolator control module without the relay) http://www.powerstream.com/battery-isolator.htm )

This will be a single sensing isolator, so will not care what am putting on the Aux side of isolator.


The second problem identified is the charging current, the alternator cranks between 13.4 to 14.4v and considering the wiring drop the effective charging voltage on LiFePO4 is lower. Typically the charging current is between 4amp to 8 Amps, which is good enough to replenish ARB consumption but not the best. So my plan is to add a dc-dc step up converter, which will boost the voltage to say 17 or 18V and use it with a in-line LiFePO4 charger

1) DC DC Step up converter ($22 - http://www.amazon.com/DROK-Converte...DC+Converter+Buck+Adjustable+4-32V+to+1.2-32V). I can also add 2 in parallel, for a peak capacity of 30A.
2) LiFePO4 Solar Charger ($49 - http://store.bioennopower.com/colle...oducts/12v-24v-30a-lifepo4-solar-controller-1)

Now I already have a DC supply, that can provide 15vdc 30A from 110VAC. So at home, it can be linked to the LiFePO4 charger, to charge a full empty pack within 3-4 hours. When the engine is running, I should get charging current of 12 amps or more. Using100w Solar panel connected to the LiFePO4 charger, I should get 6-7Amps.

All good in theory, lets see how it works in reality

 

[kevint]

Not all Goal Zero Sherpa's use LiFePO4 (only the Elite series)

Hmmm? I believe the Sherpa 120s are marketed as LiFePO4. If that's not what I have, I'm not happy. I'll check my documentation when I get home tonight.

Just did a little googling. The Sherpa 120 is listed as an Elite model.

I am aware of the Sherpa 120 failures. My first one had a performance issue. GoalZero replaced it.

 

[kevint]

Thanks!, that is the path am considering.

Instead of 12V packs, with built in BMS I am thinking of using 3.3v 100Ah x 4 packs and use a LiFePO4 protection circuit ($26) to balance the cells. I can stack them or place side by side to easily fit in the vehicle.

LiFePO4 - http://www.all-battery.com/32v100ahlifepo4lithiumironphosphaterechargeablebattery.aspx
BMS Protection - http://www.evassemble.com/index.php?main_page=product_info&cPath=6&products_id=41
Solar Panel - http://www.sunpowerlink.com/120w folding solar panel/120W_folding_solar_panel.html
MPPT for Lithium - http://genasun.com/all-products/sol...ium/gvb-8a-li-lithium-solar-boost-controller/
Battery Isolator - Still searching, any recommendations?

Great information. When I first became aware of LiFePO4 batteries, I figured I must be missing something since I didn't hear of anyone using them in their vehicles (for auxillary devices like lights and fridges). It has been in the back of my mind to research further one day,

Following with great interest.

 

[soul]

The dual battery setup is complete

These are the 3.2V 100AH x 4 LiFePO4



4 cell 30A BMS board, all connected and ready to be attached to the battery




Battery isolator and fuse in the engine compartment



Everything else goes in the small footboard compartment in the rear hatch



The ARB 50 Quart




Will be testing this rig for few days, the solar panel will be added in future !

 

[Rando]

Very cool!

 

[soul]

The setup is working great, maintained -3 deg (on panel) on a 3 day camping trip. The only concern I have is around the battery isolator (Battery Saver).
After the engine is shut down, the Battery Saver needs to isolate the Aux from the Main but I do see the Aux charging the Main battery till the voltage equalizes.

It could be a faulty unit, maybe should have gone with a simple solenoid.

 

[madmax718]

very cool! I likey.

 

[Andy@AAV]

The setup is working great, maintained -3 deg (on panel) on a 3 day camping trip. The only concern I have is around the battery isolator (Battery Saver).
After the engine is shut down, the Battery Saver needs to isolate the Aux from the Main but I do see the Aux charging the Main battery till the voltage equalizes.

It could be a faulty unit, maybe should have gone with a simple solenoid.

Not sure about the battery saver but the National Luna I use only disengages when the voltage on the Aux battery drops below a certain threshold (I think 12.5 volts). If the LiFePO4 battery has a higher standing voltage (~13.2 volts if my math is correct) it will not shut off and the LiFe battery will slowly charge the main (which I assume is a standard lead-acid ~12.5 volts) until they equalize and thereby discharging your LiFe battery. You would need to have the automatic shut off set for a higher voltage threshold or manually disconnect the two.

 

[soul]

ARB also has disengage level (High, Medium, Low). The problem is the voltage difference between the two batteries. I tried putting in a LFE charger in series between Isolator and Aux, that prevents Aux being discharged (no reverse current). But the Battery Protector then fails to operate at engine on, as it cannot see the Aux battery connected.

It looks like automatic isolation for two different battery types (Pb and LFE) is not possible with solenoid or electronic isolators. This is because once the isolator bridges the two batteries, the effective voltage will be the higher one of the two batteries. Unless that goes down below the threshold the isolator will not disconnect.

Some options to think of -

1) Manual switch (don't really want to go this route)
2) Simple relay linked to ignition ON, so the batteries will be connected when ignition is on otherwise seperate
3) Voltage triggered Isolator, with disconnect based on reverse current (never seen any, so may have to be developed)

 

[dwh]

4) DC-DC charger