LiFePO4 Battery installation for mobile use in RV or camper van
The AGM house batteries in my Sprinter based RV are starting to perform very poorly. It's time for an upgrade, and I don't want to go the AGM lead acid route again. I've been keeping an eye out on LiFePO4 batteries because 4 cells in series works well with a standard 12V DC system. An ebay seller had an interesting packaging for a 12V 100Ah pack. He was putting them into metal ammo boxes PA-19, and including a balancer and a battery voltage meter. Specs for the PA-19 ammo cans
8140-00-145-0051 PA-19
Interior Dimensions: 11 x 5-9/16 x 9-8/16
Exterior Dimensions: 12-1/32 x 6-3/32 x 10-5/16
The GB 100Ah cells are a perfect fit in these, and there's still space left over for a balancer, maybe a breaker, and hopefully an exit for the wires. It's waterproof, so the batteries can potentially be mounted on the underside of the vehicle. It's also fire resistant, even though that's less of a concern with LiFeP04 batteries than regular lithium ion, there are still incidents where they catch on fire.
Here's one source for the cells:
http://elitepowersolutions.com/faq.html
http://www.batteryspace.com/lifepo4-prismatic-battery-12-8v-100ah-1-28-kwh-10c-rate---un38-3-passed-3-2vx4-dgr.aspx
http://www.batteryspace.com/Smart-LED-Balance-Module-for-3.2V-LFP-Cell-with-
250mA-Balance-Current-for-L.aspx
Wiring
Wire Gauge Here's a good chart for the gauge of wire to select. Looks like I will want 2 AWG extra flexible for a short length. (individual strands are 30 guage.) http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg Crimped on eyelets need to be used to terminate and attach the wire.
The eyelets can be crimped or soldered, but in my experience soldering is time consuming because the copper is such a good heat conductor. Crimping will be faster, and less chance of melting the wire insulator. Here's the crimp tool I chose.
Two holes are drilled in the side of the box to run the wires out. Two waterproof sealing grommet glands are used to pass the wire through and provide a tight seal.
Circuit Breaker
It may be tempting to use a self resetting breaker that fits inside the box, but do not use this. A self resetting breaker (the type that resets automagically when the load falls below the trip point) is not suitable for use as a short circuit safety device. It's only use is for over current protection. Only use a manual reset circuit breaker or fuse in this application.
Connectors
Outside the individual battery boxes, I plan to use some Anderson SB120 connectors, that way each battery pack can be easily removed. There are also waterproof boots available for these connectors, which is great if you're installing this anywhere that could get wet, like in my case under the vehicle. Here's the pdf info on the boots. These are the parts that I purchased from Online Components:
Anderson SB120 Housings Red (Blue and Grey also avaiable) - 6810G3-BK
Anderson SB120 Contacts for 2 gauge wire x 2 per connector - 1319-BK
Anderson SB®120 Environmental Boot, Load 3-6035P1-BK
Anderson SB®120 Environmental Boot, Source 3-6034P1-BK
Battery Low Voltage Protection
Two 12V packs will be connected in parallel and pass through a Low Voltage Disconnect relay. This will cut off the power if it drops below the threshold voltage to prevent permanent damage to the batteries.
