Cordless Phone Charger

[Larry B]

I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
pretty quickly. I measured the voltage to the charging contacts and it is 11
VDC. Seems like a quick-charging, short battery life scenario. Please
confirm.

I put a potentiometer on the + side of the charging leads and found that it
took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
is it reasonable to put in a dropping resistor?? If so, what kind of
resistor can I use to drop the voltage without turning the phone into either
an expensive space heater or even a plastic-melting fire danger?? Is there
another way to do this??

Thanks!! LarryB

 

[gothika]

I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
pretty quickly. I measured the voltage to the charging contacts and it is 11
VDC. Seems like a quick-charging, short battery life scenario. Please
confirm.

I put a potentiometer on the + side of the charging leads and found that it
took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
is it reasonable to put in a dropping resistor?? If so, what kind of
resistor can I use to drop the voltage without turning the phone into either
an expensive space heater or even a plastic-melting fire danger?? Is there
another way to do this??

Thanks!! LarryB

This is a bit crude and probably not the most scientific way to
correct overcharging cell phone batts.
I use a wall wart rated at 3.6 volts with a charge rate of from 50-100
milliamps.
I rigged the handset with a dc coaxial jack and jusr plug the wall
wart into the handset whenever the battery runs down.
I've noticed my batteries last much longer than when I used the base.
I have one cordless that uses nicads and they require alot more care
when charging, hence the wall wart.
I also have a cordless that uses lead acid rechargables.
It tends to be much more durable and memory free as well.

 

[Jerry G.]

The opened end voltage from the phone charger will be in the 10 to 12 volt
range. It is current limited to be proper for your battery. The problem is
that your battery is no longer able to hold the charge. Get a new battery,
and it will charge properly. The life span of these batteries is about 2
years under ideal conditions in these cordless phones.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
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I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
pretty quickly. I measured the voltage to the charging contacts and it is 11
VDC. Seems like a quick-charging, short battery life scenario. Please
confirm.

I put a potentiometer on the + side of the charging leads and found that it
took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
is it reasonable to put in a dropping resistor?? If so, what kind of
resistor can I use to drop the voltage without turning the phone into either
an expensive space heater or even a plastic-melting fire danger?? Is there
another way to do this??

Thanks!! LarryB

 

[JM]

quoting:

I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
pretty quickly. I measured the voltage to the charging contacts and it is 11
VDC. Seems like a quick-charging, short battery life scenario. Please
confirm.

I put a potentiometer on the + side of the charging leads and found that it
took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
is it reasonable to put in a dropping resistor?? If so, what kind of
resistor can I use to drop the voltage without turning the phone into either
an expensive space heater or even a plastic-melting fire danger?? Is there
another way to do this??

Thanks!! LarryB

I've got a Uniden phone that ate batteries in 6 months. I replaced the Nicad
with a NiMh version, still going strong 3 years later.

This works because cordless phone chargers are often slow dumb type. NiCad
"shake and bake" overcharge on these chargers, kills them fast. NiMh does
not overcharge when charged constantly at a slow rate.

 

[Larry B]

quoting:


I've got a Uniden phone that ate batteries in 6 months. I replaced the Nicad
with a NiMh version, still going strong 3 years later.

This works because cordless phone chargers are often slow dumb type. NiCad
"shake and bake" overcharge on these chargers, kills them fast. NiMh does
not overcharge when charged constantly at a slow rate.

Thanks everyone. My next one will be NiMH but I already have a new NiCad.
The first one lasted about 6 months. I just put in a resistor that dropped
the charging voltage (under load) to 7.7vdc. We'll see what happens.

Larry

 

[Larry B]

is that
Thanks everyone. My next one will be NiMH but I already have a new NiCad.
The first one lasted about 6 months. I just put in a resistor that dropped
the charging voltage (under load) to 7.7vdc. We'll see what happens.

Larry

Well, the resistor messed with the charging circuit so we'll just have to
burn out another battery and go for the NiMH next time.

Larry