On 14 Oct 2006 08:41:08 -0700, wrote:

Based on positive reviews here and elsewhere, and deciding I could live
with its ergonomic idiosyncracies, I just bought a new Kaito KA1103.
So far, I like it well enough, and the ergonomics are even a little
charming. But I have a question about using the radio itself to charge
the included NiMH batteries. It's not clear to me how long to set the
charging timer for, nor whether there is a risk of damage if the
batteries are charged for too long. The spartan "manual" gives a
formula of battery mAh / 100 for the # hours to charge, which in this
particular case of 4 x 1300 mAh batteries is 52 hours? But the maximum
charge time you can set is 23 hours. Does anyone have prior experience
charging the KA1103? After playing with the radio for an hour, the
battery indicator hit the 25% full mark, and I decided to charge them
for 10 hours, based on nothing in particular. Is this too long? Too
short? Anyone know?
First of all it isn't 4 x 1300mah, the batteries are charged in
series. Figure the charginig process isn't 100% efficient, so you
need to charger to about 120% of capacity, however you rarely run the
batteries flat. Long term overchargiing converts water to oxygen and
hydrogen which are vented from the battery, resulting in battery
failure. You need to estimate how far down you are going to run the
battery, Without knowing how it evaluates battery charge, it is hard
to know what 25% really represents. NiCd and NiMh have pretty flat
discharge characteristics, so at the point at which you notice a
significant voltage drop, the battery is pretty much flat already.
I.E. by the time you get from 1.25V per cell to 1.1 volts per cell,
the battery is probably down to about 5% of capacity. Immediately
after recharge you can see voltages as high as 1.7 volts per cell, but
it doesn't last long.

In any case, figure out how far you run down the batteries, and
re-charge to about 120% of that. However if you use the latest high
capacity NiMh cells, 2600-3000mah, at 100ma, you may NEVER fully
charge the batteries. It is very hard to reach full charge if you
charge at less than C/25....

matt weber wrote:

First of all it isn't 4 x 1300mah, the batteries are charged in
series. Figure the charginig process isn't 100% efficient, so you
need to charger to about 120% of capacity, however you rarely run the
batteries flat. Long term overchargiing converts water to oxygen and
hydrogen which are vented from the battery, resulting in battery
failure.

I was under the impression that Potassium Hydroxide was the electrolyte
being used, not water...I may be wrong.

You need to estimate how far down you are going to run the
battery, Without knowing how it evaluates battery charge, it is hard
to know what 25% really represents. NiCd and NiMh have pretty flat
discharge characteristics, so at the point at which you notice a
significant voltage drop, the battery is pretty much flat

It is better to think the NiMh batteries have a rapid discharge rate and
a flat 'running' range. They hold their rated voltage longer than a lead
acid, but near the end of the capacity, suddenly drop. That is why they
are a bad idea for smoke detectors. You might not be around when they
give the warning beeps.

nimh discharge:

http://snipurl.com/z3f3

Dry cell types have a longer slope of discharge and it starts WAY
earlier in the charge life of the battery. They give you lots of warning
as they approach an inoperative state.




mike

m II wrote:
matt weber wrote:

First of all it isn't 4 x 1300mah, the batteries are charged in
series. Figure the charginig process isn't 100% efficient, so you
need to charger to about 120% of capacity, however you rarely run the
batteries flat. Long term overchargiing converts water to oxygen and
hydrogen which are vented from the battery, resulting in battery
failure.

I was under the impression that Potassium Hydroxide was the electrolyte
being used, not water...I may be wrong.

Water by itself is miserable at carrying charge. You need the addition
of ions and, in this, case potassium hydroxide is used the alkaline
electrolyte. In other words, you are right!

JB


You need to estimate how far down you are going to run the
battery, Without knowing how it evaluates battery charge, it is hard
to know what 25% really represents. NiCd and NiMh have pretty flat
discharge characteristics, so at the point at which you notice a
significant voltage drop, the battery is pretty much flat

It is better to think the NiMh batteries have a rapid discharge rate and
a flat 'running' range. They hold their rated voltage longer than a lead
acid, but near the end of the capacity, suddenly drop. That is why they
are a bad idea for smoke detectors. You might not be around when they
give the warning beeps.

nimh discharge:

http://snipurl.com/z3f3

Dry cell types have a longer slope of discharge and it starts WAY
earlier in the charge life of the battery. They give you lots of warning
as they approach an inoperative state.




mike

On Sun, 15 Oct 2006 23:34:01 GMT, m II wrote:

matt weber wrote:

First of all it isn't 4 x 1300mah, the batteries are charged in
series. Figure the charginig process isn't 100% efficient, so you
need to charger to about 120% of capacity, however you rarely run the
batteries flat. Long term overchargiing converts water to oxygen and
hydrogen which are vented from the battery, resulting in battery
failure.

I was under the impression that Potassium Hydroxide was the electrolyte
being used, not water...I may be wrong.
The KOH is dissolved in water. When you over charge, it is the Water
that dissociates, ultimately there isn't enough water to keep the KOH
dissolved and the battery is finished.

You need to estimate how far down you are going to run the
battery, Without knowing how it evaluates battery charge, it is hard
to know what 25% really represents. NiCd and NiMh have pretty flat
discharge characteristics, so at the point at which you notice a
significant voltage drop, the battery is pretty much flat

It is better to think the NiMh batteries have a rapid discharge rate and
a flat 'running' range. They hold their rated voltage longer than a lead
acid, but near the end of the capacity, suddenly drop. That is why they
are a bad idea for smoke detectors. You might not be around when they
give the warning beeps.

nimh discharge:

http://snipurl.com/z3f3

Dry cell types have a longer slope of discharge and it starts WAY
earlier in the charge life of the battery. They give you lots of warning
as they approach an inoperative state.




mike

matt weber wrote:

Immediately after recharge you can see voltages as high as 1.7 volts per cell, but
it doesn't last long.

Which is why it's a good idea to let a freshly charged NiCd or NiMH
stand for a while to normalize the voltage before using it. This is
especially important for certain voltage sensitive devices. For example,
zapping an incandescent bulb in a flashlight with too much voltage can
shorten it's life. If you have to use the battery immediately after
charging it, you can reduce the over voltage by briefly shorting it with
a wire connected between both terminals.

HFguy wrote:


If you have to use the battery immediately after
charging it, you can reduce the over voltage by briefly shorting it with
a wire connected between both terminals.


Now that could be a good way to damage the battery.

craigm wrote:
HFguy wrote:



If you have to use the battery immediately after
charging it, you can reduce the over voltage by briefly shorting it with
a wire connected between both terminals.



Now that could be a good way to damage the battery.

Thus the word 'briefly'.