Test results LiFePO4 glider batteries after 6 years

On 08/08/2018 10:08 AM, George Haeh wrote:
I've had my K2's for about five years now. Last spring I bought a CTEK LiFePo4 charger, which has 8 stages and ran the batteries through several recharges. Each time the batteries seemed to absorb a bit more.

Last week I flew one battery for over 7 hours on two flights. The Air Glide S showed the voltage flipping between 11.9 & 12.1. Note that the Air Glide S seems to underread by about 0.6V compared to the Tasman. Poking around with probes showed no drop in voltage between the battery and the Air Glide.

Back on the charger it took over three hours to get the battery back up to float. The charger was quite warm for the 2.5 hours in stage 2.

The other battery flown for three hours charged back up in a little over an hour.

I suspect that the batteries need heavier usage than just 3-4 hours of flight before accepting a full recharge.


You've got two old batteries, with two different state of charges.
Rather than speculating on some memory effect, it might be more likely
that the batteries are no longer equivalent, perhaps one has a few weak
cells and needs a bunch of balancing.

That was an interesting thread you bumped, didn't realize just how much
misinformation got crammed into that one. Someone stated that you don't
charge a LI-PO battery with a SLA charger, certainly a true statement.
Multiple people responded by saying that it's fine to charge an LFP with
a SLA charger. It's almost as if they don't know the difference. With
all the discussion about how typical BMS boards need high voltage
applied for a long period of time in order to balance cells, some people
still think the SLA charger works fine for LFP. I guess it's fine as
long as you don't care about the lifetime of your battery, and if you
don't care about getting a full charge.

Then there was another discussion about how radios supposedly last
longer with higher voltage, because someone's 37 year old radio just
died. I really don't think it would have lasted any longer no matter
what voltage was used. Similarly, radios that we use don't draw less
current with higher voltage, the only instrument in your panel that
might draw a bit less current is a transponder.

-Dave

"the only instrument in your panel that
might draw a bit less current is a transponder"

I seriously doubt it. All modern avionics are designed to operate over a wide input voltage range; they have internal dc-dc conversion circuits that transform the supply voltage to a regulated, operating voltage. Trig, for instance, specifies an input voltage of 11 to 33 V.

Tom

On 08/08/2018 11:30 PM, 2G wrote:
"the only instrument in your panel that
might draw a bit less current is a transponder"

I seriously doubt it. All modern avionics are designed to operate over a wide input voltage range; they have internal dc-dc conversion circuits that transform the supply voltage to a regulated, operating voltage. Trig, for instance, specifies an input voltage of 11 to 33 V.

Tom


So does an LX9000 count as a piece of modern avionics? 12 volts
nominal, 10-16 volts min to max. How about a Becker 4201 radio? 12.4
min, 15.1 max, 13.8 nominal. There's very little avionics used in
gliders that have dc-dc converters, they're included in transponders
because you can't generate 300 watt pulses using battery voltage, you
have to step it up with a converter.

Dave