A Different Battery Question

I did pretty much what you said except for the recording and measuring
part.Â* My ClearNav and my Dynon D10a each have a volt meter displayed
and, though they had slightly different readings, they seemed to track
pretty well as I turned each device in turn.

For now, I'm gonna go with charging the lithium battery for a longer
period after the green light comes on, probably over night each time.

Thanks for all the good advice!

On 10/16/2019 1:50 PM, Charlie M. (UH & 002 owner/pilot) wrote:
Good thoughts posted thus far.....

My $0.02....with even an inexpensive DMM/DVM.....start at the "common buss" on/near the panel with all batteries fully charged.
Measure D.C. Voltage at the buss main input with a battery connected....
Switch things on, read voltage....write it down....
Key mic and do other load things...record voltage under load.
Repeat with the other battery.....
If the large battery shows a bigger voltage drop.....work through connections back towards battery with same test....see where the voltage drops lessens....in between good vs. bad/poor voltage drop is likely a poor or bad connection.

Could be a bad crimp, poor solder joint, loose/poor screw connection, maybe even small wire gage (although not likely unless waaayyyyy tiny...).

--
Dan, 5J

Dan Marotta wrote on 10/16/2019 9:48 AM:
I've been using a 20 AH LiFePO4 battery as a backup in the Stemme. It's portable
and secured behind the passenger seat.* I charge it outside of the aircraft.* When
used, it is connected through an DPST switch (only one half used) and switches the
tail battery out of the system as it's switched in.

The problem:* Even when fully charged it comes on line at around 11.4 volts or
below and, if I key the radio, the radio display flashes and the vario gives a Low
Voltage warning.* When the tail battery is at 11.4 volts (it's an SLA battery),
the radio works fine.

I've tested the lithium battery using a pair of 2.5 ohm power resistors in
parallel and measuring with a Watts Up power meter and it seems to perform just
fine, starting with voltage in the high 13s.* I ran it for several hours that way,
burning up about 15 amp hours without the voltage ever dropping below the mid 12s.

Any ideas?* Everything seems to work just fine except for the low voltage as
measured at my ClearNav and at the Dynon D10a.* I'm using good quality Tefzel wire
of sufficient diameter, Power Pole connectors, and the battery is properly fused.
I'm at a loss.

I'm guessing you did the test with the 2.5 ohm resistors in series (5 ohm total),
for about 2.5 amp draw. In parallel (1.25 ohms total) the draw would be 10 amps.

How much current is needed to run your instruments?

Disconnect the battery, short the connector, and select the backup battery with
your switch. Measure the resistance of the wiring with an ohmmeter on the (+) and
(-) of the 12 volt buss at the panel. It should read less than 0.5 ohms.

If that wiring (panel to battery box through the switch) is OK, look closely at
the connectors (glider side and battery side). Check the ohms for each lead from
battery post to battery side connector. It should less than 0.1 ohms (essentially
a short circuit). If the (+) lead is high, maybe the fuse is bad, too small, or
the wrong kind, or the fuse holder is faulty.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

On Wednesday, October 16, 2019 at 1:01:35 PM UTC-7, Eric Greenwell wrote:
Dan Marotta wrote on 10/16/2019 9:48 AM:
I've been using a 20 AH LiFePO4 battery as a backup in the Stemme. It's portable
and secured behind the passenger seat.Â* I charge it outside of the aircraft.Â* When
used, it is connected through an DPST switch (only one half used) and switches the
tail battery out of the system as it's switched in.

The problem:Â* Even when fully charged it comes on line at around 11.4 volts or
below and, if I key the radio, the radio display flashes and the vario gives a Low
Voltage warning.Â* When the tail battery is at 11.4 volts (it's an SLA battery),
the radio works fine.

I've tested the lithium battery using a pair of 2.5 ohm power resistors in
parallel and measuring with a Watts Up power meter and it seems to perform just
fine, starting with voltage in the high 13s.Â* I ran it for several hours that way,
burning up about 15 amp hours without the voltage ever dropping below the mid 12s.

Any ideas?Â* Everything seems to work just fine except for the low voltage as
measured at my ClearNav and at the Dynon D10a.Â* I'm using good quality Tefzel wire
of sufficient diameter, Power Pole connectors, and the battery is properly fused.
I'm at a loss.

I'm guessing you did the test with the 2.5 ohm resistors in series (5 ohm total),
for about 2.5 amp draw. In parallel (1.25 ohms total) the draw would be 10 amps.

How much current is needed to run your instruments?

Disconnect the battery, short the connector, and select the backup battery with
your switch. Measure the resistance of the wiring with an ohmmeter on the (+) and
(-) of the 12 volt buss at the panel. It should read less than 0.5 ohms.

If that wiring (panel to battery box through the switch) is OK, look closely at
the connectors (glider side and battery side). Check the ohms for each lead from
battery post to battery side connector. It should less than 0.1 ohms (essentially
a short circuit). If the (+) lead is high, maybe the fuse is bad, too small, or
the wrong kind, or the fuse holder is faulty.

That should be "short the plane side connector"! I know Dan wouldn't short the battery side connector and waste fuse, but somebody might on their system...

Hi Eric,

The two power resistors were in parallel for a total of 1.25 amps. Yes,
I should get around 10 amps (they sure got hot!) but I'll have to do the
measurement again to be sure, but I want to keep it charged up right now
to try a flight now that it's been on a charger for some time.

On 10/16/2019 2:01 PM, Eric Greenwell wrote:
Dan Marotta wrote on 10/16/2019 9:48 AM:
I've been using a 20 AH LiFePO4 battery as a backup in the Stemme.
It's portable and secured behind the passenger seat.Â* I charge it
outside of the aircraft.Â* When used, it is connected through an DPST
switch (only one half used) and switches the tail battery out of the
system as it's switched in.

The problem:Â* Even when fully charged it comes on line at around 11.4
volts or below and, if I key the radio, the radio display flashes and
the vario gives a Low Voltage warning.Â* When the tail battery is at
11.4 volts (it's an SLA battery), the radio works fine.

I've tested the lithium battery using a pair of 2.5 ohm power
resistors in parallel and measuring with a Watts Up power meter and
it seems to perform just fine, starting with voltage in the high
13s.Â* I ran it for several hours that way, burning up about 15 amp
hours without the voltage ever dropping below the mid 12s.

Any ideas?Â* Everything seems to work just fine except for the low
voltage as measured at my ClearNav and at the Dynon D10a. I'm using
good quality Tefzel wire of sufficient diameter, Power Pole
connectors, and the battery is properly fused.Â* I'm at a loss.

I'm guessing you did the test with the 2.5 ohm resistors in series (5
ohm total), for about 2.5 amp draw. In parallel (1.25 ohms total) the
draw would be 10 amps.

How much current is needed to run your instruments?

Disconnect the battery, short the connector, and select the backup
battery with your switch. Measure the resistance of the wiring with an
ohmmeter on the (+) and (-) of the 12 volt buss at the panel. It
should read less than 0.5 ohms.

If that wiring (panel to battery box through the switch) is OK, look
closely at the connectors (glider side and battery side). Check the
ohms for each lead from battery post to battery side connector. It
should less than 0.1 ohms (essentially a short circuit). If the (+)
lead is high, maybe the fuse is bad, too small, or the wrong kind, or
the fuse holder is faulty.


--
Dan, 5J

On Wednesday, October 16, 2019 at 12:48:29 PM UTC-4, Dan Marotta wrote:
I've been using a 20 AH LiFePO4 battery as a backup in the Stemme. It's
portable and secured behind the passenger seat.Â* I charge it outside of
the aircraft.Â* When used, it is connected through an DPST switch (only
one half used) and switches the tail battery out of the system as it's
switched in.

The problem:Â* Even when fully charged it comes on line at around 11.4
volts or below and, if I key the radio, the radio display flashes and
the vario gives a Low Voltage warning.Â* When the tail battery is at 11.4
volts (it's an SLA battery), the radio works fine.

I've tested the lithium battery using a pair of 2.5 ohm power resistors
in parallel and measuring with a Watts Up power meter and it seems to
perform just fine, starting with voltage in the high 13s.Â* I ran it for
several hours that way, burning up about 15 amp hours without the
voltage ever dropping below the mid 12s.

Any ideas?Â* Everything seems to work just fine except for the low
voltage as measured at my ClearNav and at the Dynon D10a.Â* I'm using
good quality Tefzel wire of sufficient diameter, Power Pole connectors,
and the battery is properly fused.Â* I'm at a loss.
--
Dan, 5J

Dan, if you put two 2.5 ohm resistors in parallel the total resistance would be 1.25 ohms. By Ohm's law the current draw with 12 volts would be 9.6 amps. The nominal voltage on LiFeP battery is around 13.6 volts which would be an even higher draw.

CTEK makes a specialized LiFePO4 charger with 8 stages. Not cheap, but helps preserve your LiFePO4 investment.

It comes with clamps and ring connectors. I chopped the ring connectors and put in terminals to match my batteries