NiMH batteries How do I test?

[Jim GM]

TNX FOR ALL YOUR INPUT ON THIS.

I found that by running the radio until the 8.5V limit is hit on the KX3
and it shuts down I took out the batteries and tested them on a Radio shack
battery tester that I had,  I let the thing load the battery and watch for
the reading drop.  All cells held their voltage and found one bad cell that
the voltage was lower than the rest and fell like a rock under the load of
the tester. Key thing here is leave the meter test the battery for around
10 seconds or so.

Now replaced bad AA cell re charged, For 16 hours. Battery voltage came up
to 11.4V. Tried to recharge for another 4 hours and the KX3 shut down.  Why
did it do that?  I thought 12 volts is where Max charge.  Is the some sort
of algorithm it goes thought to determine if the cells are fully charged??

--
Jim K9TF
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[Jim GM]

What I ment to say I got BAT ERROR when I tried to re charge for another 4
hours. I had to trun the KX3 off and turn it back on to clear the error. So
I used it and ran the battery voltage down to 11 Volts and now still on
charge the BT voltage is at 11.8 and still charging.  So whats with this?
Charger may be smarter than you think.

Jim K9TF


On Sun, Aug 24, 2014 at 3:14 PM, Ray Sills <[hidden email]> wrote:

> HI Jim:
>
> No... there is no real test.  Just a rough guesstimate.  NiMH cells are
> very rugged, and can withstand recharging -many- times (in the thousands of
> cycles, usually).  With the KX3 the charger outputs a mere 200 mA... which
> the cells can tolerate -indefinitely-...  so the charging process is not
> critical at all.
>
> You could -always- set the KX3 charger for 16 hours... although if you had
> only operated for a few hours, the cells might only be depleted by about
> 50% or so.  If you know that, you would just charge for 8 hours.... or 12
> hours.. whatever fits your schedule.
>
> 73 de Ray
> K2ULR
> KX3 #211
>
>
>
> On Aug 24, 2014, at 4:08 PM, Jim GM wrote:
>
>  TNX FOR ALL YOUR INPUT ON THIS.
>>
>> I found that by running the radio until the 8.5V limit is hit on the KX3
>> and it shuts down I took out the batteries and tested them on a Radio
>> shack
>> battery tester that I had,  I let the thing load the battery and watch for
>> the reading drop.  All cells held their voltage and found one bad cell
>> that
>> the voltage was lower than the rest and fell like a rock under the load of
>> the tester. Key thing here is leave the meter test the battery for around
>> 10 seconds or so.
>>
>> Now replaced bad AA cell re charged, For 16 hours. Battery voltage came up
>> to 11.4V. Tried to recharge for another 4 hours and the KX3 shut down.
>> Why
>> did it do that?  I thought 12 volts is where Max charge.  Is the some sort
>> of algorithm it goes thought to determine if the cells are fully charged??
>>
>> --
>> Jim K9TF
>> ______________________________________________________________
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>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
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>>
>
>

--
Jim K9TF
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[Bob N3MNT]

Unfortunately the charger is not that smart, but very effective.  It is a 200 mA constant charger no smarts other than knowing if the battery voltage too low or too close to the supply voltage.  At 200 mA it is difficult to over charge.  If the batteries are fully charged and you ask the charger to start a new charge, you can get the error because the difference between the bat voltage and the supply voltage is too small.  It is not really an error just telling you that it can't charge.  Running them down increases the delta and the charge circuit kicks in again.  

[Elecraft mailing list]

Jim,

Good descriptions from Ray and Bob.  You are also right in that the KXBC3 has some "smarts", but it is constant current temperature monitored charger.

You may also see the display message "Not 0 to 40".  It means the cell temperatures are not within the temperature range of 0 to 40 deg. C.  If it occurs on a cold day at the beginning of a recharge cycle, the cells are probably too cold to be charged, but the most likely time you will see it is near the end of a recharge cycle on a warm day.  As the cells near full charge, they convert more and more of the 200 MA charge current to heat rather than into the chemical process of recharging.  That is how NiMH cells work when recharged with a constant current.  The KXBC3 will suspend charging until the temperature drops below 40 deg. C.  

This is all normal operation, and is the most common method for recharging NiMH cells.

Mark
KE6BB



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[Fred Townsend-2]

Jim I agree with Mark but would like to add one thing. Heat is the enemy of the battery. As Mark says the heat goes up sharply at end of charge. This is how the smart charger knows the battery is fully charged. If you attempt another charge when the battery is hot you may damage the cells. This is why the charger is programed to protect the batteries. The nominal cell voltage is 1.2vdc so for 8 cells it is 9.6vdc, for 9 cells 10.8vdc, or 12.0vdc for 10 cells. The float voltage is 1.25 so the numbers are 10, 11.25, and 12.5 respective. Do not confuse NiMH with SLA which have a nominal voltage of 12.6 and float of 13.85vdc.
73
Fred, AE6QL


-----Original Message-----

>From: "Mark,  KE6BB via Elecraft" <[hidden email]>
>Sent: Aug 24, 2014 4:19 PM
>To: [hidden email]
>Subject: Re: [Elecraft] NiMH batteries How do I test?
>
>Jim,
>
>Good descriptions from Ray and Bob.  You are also right in that the KXBC3 has some "smarts", but it is constant current temperature monitored charger.
>
>You may also see the display message "Not 0 to 40".  It means the cell temperatures are not within the temperature range of 0 to 40 deg. C.  If it occurs on a cold day at the beginning of a recharge cycle, the cells are probably too cold to be charged, but the most likely time you will see it is near the end of a recharge cycle on a warm day.  As the cells near full charge, they convert more and more of the 200 MA charge current to heat rather than into the chemical process of recharging.  That is how NiMH cells work when recharged with a constant current.  The KXBC3 will suspend charging until the temperature drops below 40 deg. C.  
>
>This is all normal operation, and is the most common method for recharging NiMH cells.
>
>Mark
>KE6BB
>
>
>
>______________________________________________________________
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[Elecraft mailing list]

Re:  The float voltage is 1.25 so the numbers are 10 (for 8 cells), 11.25 (for 9 cells), and 12.5 (for 10 cells)…






The voltages Fred lists are correct for a float charger where you are charging at a rate of less than 0.05Cma for an indefinite period of time.  The KXBC3 isn’t really designed to be used as a float charger, so it uses a somewhat higher rate of 0.1Cma (200ma) and is designed for 2000mah or larger cells.  That 0.1Cma is an industry standard constant current rate, and it is meant to be used for a limited amount of time, about 16hr. is what the manufacturers recommend


The datasheets available from most manufacturers don’t always list the voltages you can expect to see when using a 0.1Cma constant current charger, but Ansmann is the exception.  Datasheets for both their 2100mah and 2500mah cells show a sharp voltage increase when reaching the fully charged condition increasing from about 1.35v at hour 10 (assuming you start with a discharged cell), up to about 1.45v at hour 11 where the voltage levels off.  Their charge voltage curves continue nearly level (1.45v) from hour 11 out to hour 16.  That flat curve represents a fully charged cell that cannot accept any more energy for chemical conversion.  The 1.45v is 11.6v for 8 cells.  


As Fred mentioned, heat is the biggest enemy of any battery, so it would be best to stop charging once the voltage reaches about 11.5v, or even 0.3 or 0.4 volts sooner to avoid adding too much heat to the cells.  Hopefully, my cells will last quite a while that way, but I will not hesitate to properly dispose of them and buy new ones if they give me any trouble.  They can become very unreliable (read that as “frustrating”) once they start to deteriorate.


The KXBC3 should protect your cells in most cases, but it is probably best to avoid being too aggressive.  Remember that it limits cell temperature to 40 deg. C which is their specification upper limit, but like most electronic components, they will last longer if the temperature is kept down a bit.


Before retirement, I worked with several battery manufacturers on NiMH technology (and lithium technology as well), and their recommendations were quite similar to the above.  Please heed Fred’s warning, these numbers do NOT have any relation to lead acid (SLA these days) batteries, or lithium cells for that matter!


Mark

KE6BB





From: Fred Townsend
Sent: ‎Sunday‎, ‎August‎ ‎24‎, ‎2014 ‎07‎:‎30‎ ‎PM
To: Mark,KE6BB, [hidden email]





Jim I agree with Mark but would like to add one thing. Heat is the enemy of the battery. As Mark says the heat goes up sharply at end of charge. This is how the smart charger knows the battery is fully charged. If you attempt another charge when the battery is hot you may damage the cells. This is why the charger is programed to protect the batteries. The nominal cell voltage is 1.2vdc so for 8 cells it is 9.6vdc, for 9 cells 10.8vdc, or 12.0vdc for 10 cells. The float voltage is 1.25 so the numbers are 10, 11.25, and 12.5 respective. Do not confuse NiMH with SLA which have a nominal voltage of 12.6 and float of 13.85vdc.
73
Fred, AE6QL
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[Fred Townsend-2]

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