More grist for the battle of the battery

Probably OK. However, if you are really concerned, one option is to put
a Schottky diode (of sufficient current capacity) in line. It will
introduce approximately 0.5v of voltage drop over the whole range of
supplied voltage.



Larry





"Bill Daniels" wrote in message
:

Lithium Ion rechargeables seem to have recently seen a 50% or so price drop.
A 4-cell, 14.8V, 8AH with charger and mounting plate can be had for $169.99
(USD). These are basically long endurance laptop batteries.

This is still too much for me given that a SLA with the same capacity is
around $25 but the downward price trend is hopeful. Someone contemplating a
transponder, electric T&B and other juice hungry gadgets in a $100,000+
glider might see Li-Ion as a possibility now.

Beyond price, my concern is voltage. 4-cell Li-Ion packs produce 14.8V and
a detail in the spec sheet admits that a new, fully charged pack might
produce 16.2V into a high resistance load. My avionics manuals say 16V max.
Is that 0.2V overvoltage likely to be a problem?

Bill Daniels

I have two NiMh packs in my Nimbus.

One replaces a 7.5 Ah SLA, its 2/3 the size of the SLA, half the weight
and its capacity is nominally 9 Ah but it delivers more like 10.5 given
my discharge curve. The other is a replacement for the lead brick of an
18 AH SLA in the nose, weighs 1/2 the 18 AH, nominally rated at 13 Ah
and delivers about 16.

Yes I have a switchable diode to ensure I don't over volatage the panel
when the cells are topped right off. I did have a small problem with a
Colibri logger that went haywire on 17 volts ( in spite of what the ,
now corrected, manual said )

Charging also requires a microprocessor controlled specialised charger.

The batteries perform extremely well over a wide temperatire range.
I have saved about 5 kg of weight right in the nose of the ship.
The extra voltage is good for the radio range.
The current capacity and voltage of the system spins up my 14v Horizon
in about 90 seconds ( 3 turns before going into cloud if left late )