Roy Lewallen wrote:

The end discharge voltage (generally 1.0 volt per cell for NiCd and NiMH
cells) is measured under load. After disconnecting the load, the voltage
will typically rise substantially, but its value isn't of any significance.

It's usually not recommended to discharge below 1.0 volt, but it doesn't
seem to cause any harm, at least if it's not done really often. I think
a cell is more likely to grow dendrites and short if it's left in an
extreme discharged state for an extended period, so it's probably a good
idea to put at least some charge back in before too awfully long if
you've discharged it particularly deeply. What is harmful is reverse
charging of the cell. But that happens only when you have an external
source of current, like other cells in a series connected battery.

Roy Lewallen, W7EL

=======================================

Thanks for your help Roy. See you at the Dayton QRP Suite.

Bruce AF8F

"Bruce W.1" wrote:
The only problem
I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.

There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

"Bruce W.1" wrote:
The only problem
I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.

There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

Run the power to an old style electric clock or an analog
battery-powered clock through another set of contacts, and you've also
got the time it took.

All you've gotta do is find the relay. . .

Roy Lewallen, W7EL

wrote:

"Bruce W.1" wrote:
The only problem

I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.


There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

Run the power to an old style electric clock or an analog
battery-powered clock through another set of contacts, and you've also
got the time it took.

All you've gotta do is find the relay. . .

Roy Lewallen, W7EL

wrote:

"Bruce W.1" wrote:
The only problem

I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.


There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

wrote:

"Bruce W.1" wrote:
The only problem
I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.

There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

================================================== ====

I like that idea. Thanks.

This one drops out at 0.6 volts:
http://www.radioshack.com/product.as...5Fid=275%2D248

wrote:

"Bruce W.1" wrote:
The only problem
I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.

There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

================================================== ====

I like that idea. Thanks.

This one drops out at 0.6 volts:
http://www.radioshack.com/product.as...5Fid=275%2D248

Roy Lewallen wrote:

Run the power to an old style electric clock or an analog
battery-powered clock through another set of contacts, and you've also
got the time it took.

All you've gotta do is find the relay. . .

Roy Lewallen, W7EL

Very good idea, Roy. You can also build a little more into it,
sacrificing some simplicity. For example, a comparator can
be used to energize a second relay whose closed point is in
the coil circuit for the first relay, or the coil of the
relay can be fed from a voltage divider using only 1 relay,
or any other variation one cares to cobble together to create
the precision needed. The key is to have all current paths
opened by the relay dropping out.


wrote:

"Bruce W.1" wrote:
The only problem

I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.


There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.

Roy Lewallen wrote:

Run the power to an old style electric clock or an analog
battery-powered clock through another set of contacts, and you've also
got the time it took.

All you've gotta do is find the relay. . .

Roy Lewallen, W7EL

Very good idea, Roy. You can also build a little more into it,
sacrificing some simplicity. For example, a comparator can
be used to energize a second relay whose closed point is in
the coil circuit for the first relay, or the coil of the
relay can be fed from a voltage divider using only 1 relay,
or any other variation one cares to cobble together to create
the precision needed. The key is to have all current paths
opened by the relay dropping out.


wrote:

"Bruce W.1" wrote:
The only problem

I have is remembering to disconnect the battery from the resistor after
it hits one volt, Doh! Some of them were pulled down to 0.4 volts
(under load) but they recover to about a volt at rest.


There is a simple way to do that automatically. Find a relay
whose dropout voltage equals the voltage you want to discharge
the battery to. Discharge the battery through the relay coil and
the normally open point on the relay. You'll need to operate
the relay manually or via an external power source to start
the discharge cycle. When the battery discharges to the dropout
voltage, the relay drops and all current flow stops.