Battery Update 10/2008
A lot has happened in the past few years with battery technology. At Pacificon I picked up a 4S2P LiFePO4 pack from www.Buddipole.com. This pack has 8 A123Systems cells wired in series-parallel (4 in series, two in parallel) for 13V 4.6AH. This pack can easily deliver enough current to operate an HF radio at 100 watts and it is small and very light. Let's compare it to similar rated but other technology batteries that I have on hand:
1) Sealed Lead Acid (VRLA) AGM type 12V 3.4AH
type - Valve Regulated Lead Acid
size - 5.25x2.75x2.25 - largest
weight - 3lb 2oz - heaviest
max current - 5C or 17A - insufficient for 100W operation
discharge voltage - 12.6-12.0 - voltage sags at high currents
self discharge - a few percent per month
charging regimen - constant voltage current limited
maintenance - recharge every few months, should not be left discharged
life - 4-6 years
hazards - acid, lead
comment - failing to keep up on the charging ruins these batteries
application - cost sensitive applications that don't mind the weight
2) NiMH 12V 4AH 10 cell
type - Nickel Metal Hydride
size - 5x2.5x2 - medium size
weight - 1lb 15oz - medium weight
max current - approx 4C or 16A - insufficient for 100W
discharge voltage - 12.6-12.0?
self discharge - high, a few percent per day, not harmful to leave discharged
charging regimen - constant current to zero delta V
maintenance - recharge every month or two
life - 5 years?
hazards - nickel, etc
comment - always dead when I need it, requires recycling to get capacity back
application -
3) A123Systems LiFePO4 13V 4.6AH 8 cell
type - Lithium Iron Nano-Phosphate / LiFePO4
size - 4.25x2.75x2 - smallest
weight - 1lb 7oz - lightest
max current - 30C which is 138A!! WOW!
discharge voltage - 13.3-12.5 - better voltage for radios (do not overdischarge)
self discharge - very low, a few percent per month, longest lifet at 50-70% charge
charging regimen - charge to 3.7-3.8v per cell, balancing recommended
maintenance - recharge every year or two
life - 10 years
hazards - expansion, steam; LiFePO4 does not burst into flames as some other lithium technologies
comment - always ready to go, two of these in parallel can start your car.
comment - the high output voltage is excellent for radio equipment.
applications - electric cars are all switching to this technology
How long will a 4AH battery operate an HF radio? Of course this depends on the radio, the power level and the duty cycle. Most of the time is receiving, so the receive current is the major factor. Receive only with a K2 might be 12+ hours, with an IC706 it will be more like 3 hours. The Yaesu FT857 or FT897 are popular due to their low current receive drain. Oliver KB6BA gets about 3 hours per pack from a 4.6 AH pack with the FT857 doing SSB. Adequate for an outing, and it is not hard to carry a second battery for longer ops at under 1.5 pounds.
Digital modes consume a lot more power (due to duty cycle) than SSB so runtimes will be less.
Balancing Chargers are recommended for Lithium Ion technology batteries (including Lithium Iron). They monitor and adjust the voltage across each cell to maintain equal voltages. See FMA Cellpro and others.
AlanB
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