By Glen Rickerd, NO6W
I’ve been researching reasonably priced Lithium batteries for use in a hidden transmitter “fox box” that I am building. There are several Ham equipment suppliers who sell lithium battery packs, complete with charger in a portable pack, but they can get fairly pricey. Here are some things I have learned:
- The new battery chemistry, Lithium Iron Phosphate (LiFePO4) is much more chemically stable, and unlikely to start fires or explode if abused. My RC aircraft hobby friends who fly locally tell me that nearly every Saturday, some poor soul will have an airplane in flight when it suddenly bursts into flames. Now THAT is an expensive firework!
- Something called “balance charging” is necessary to prolong the service life of these rechargeable packs. The chargers are more expensive, but the overall cost to operate over the total service life is actually lower.
- Cost over service life. a typical LiFePO4 battery can cost as much as double a sealed lead acid battery of the same amp-hour capacity. but since a properly cared for LiFePO4 pack can be recharged as many as 1000 to 2000 times, as opposed to the SLA’s normal 300 cycles, the operating costs over the life of the battery are much lower.
- Energy density, in watt-hours per kilogram, is as much as five times what lead acid technology can provide. In other words, you get the same amp-hour capacity at one fifth the weight.
- When supplying power to a handheld radio, for instance the Yaesu FT-60R that I will be using on low power for this fox-box, more voltage is not necessarily better. The internal NIMH pack on this HT runs at a nominal 8v. When plugged into a 13.8VDC source, the HT has to regulate that down to 8v internally, and just wastes that extra juice in heating up the radio. You can afford to use a lower-voltage pack if you are ONLY powering an HT. The battery will cost less and your rig will run cooler.
Given these factors, I have found some off-the-shelf combinations that won’t break the bank, yet provide reliable and safe portable power.
http://www.hobbyking.com/hobbyking/store/__10310__Turnigy_4500mAh_3S2P_30C_LiFePo4_Pack.html
This battery meter provides a programmable, audible low-voltage warning that could be useful in operational conditions…
There is also a supplier with a good reputation in Richmond, CA that sells individual LiFePO4 cells, AND all the components necessary to roll-your-own pack. Including several cylindrical cells between 10AH and 15AH, rectangular cells up to 20AH, and “prismatic” cells between 20AH and 200AH! Of course it takes considerably more technical savvy to roll your own out of the separate piece-parts, but it is possible to do.
http://www.batteryspace.com/lifepo4rechargeablesinglecells1c-30crate.aspx
Glen Rickerd NO6W