When to charge Eneloops?

[AMD64Blondie]

I just got my new Fenix TK40 on Friday,Dec.11,2009.It's now Dec.13,2009.I haven't charged my new Eneloops yet(took them straight out of the package -2/3 charged-and installed them in my new TK40).When should I put my Eneloops on to be charged?

Here's my charger,just FYI:
http://www.batteryjunction.com/8800.html

Titanium M8800.

[SilverFox]

Hello AMD64Blondie,

When your cells read 1.0 volts under load it is time to charge them back up...

Tom

[BigBen]

Hello AMD64Blondie,

When your cells read 1.0 volts under load it is time to charge them back up...

Tom

Hi Tom (SilverFox),

How do you test a cell under load?

Can you simply put a meter on it when it's out of the light, and test it that way?

Thanks again for your help,
BigBen

[Mr Happy]

It's hard to measure the voltage on a cell when it is in a light.

With Eneloops you can make a fairly good estimate of the state of charge by measuring the open circuit voltage after removing the cells from the light. 1.20 V is empty, 1.20 - 1.30 V is between empty and two thirds full, above 1.30 V is on the way to being fully charged.

I would normally recharge my eneloops once the resting voltage is below 1.22 V.

[BigBen]

It's hard to measure the voltage on a cell when it is in a light.

With Eneloops you can make a fairly good estimate of the state of charge by measuring the open circuit voltage after removing the cells from the light. 1.20 V is empty, 1.20 - 1.30 V is between empty and two thirds full, above 1.30 V is on the way to being fully charged.

I would normally recharge my eneloops once the resting voltage is below 1.22 V.

Thanks Mr. Happy.
So you just put the meter on them after you remove 'em from the light, correct?

Thanks again,
BB

[Mr Happy]

So you just put the meter on them after you remove 'em from the light, correct?

Yes, but the exact readings I gave are for batteries that have been sitting for a while at room temperature. Bear that in mind when taking the measurements.

[45/70]

Keep in mind that the voltage drops faster the lower the voltage is. eg. it will take a lot longer for the rested voltage to go from 1.30 Volts to 1.25 Volts, than from 1.25 Volts to 1.20 Volts.

Dave

[BigBen]

Excellent, now I understand perfectly!
Thank you Gentlemen.

BB

[TooManyGizmos]

But back to one of his questions .....

"How do you test a cell under load?"

Do all DMM meters with "batt. test" functions put a load on the batt, to obtain a reading , or should you use a resistor to load the battery? Or does it depend on the price and quality of the meter ? Some meters have both a "V" function selection and also individual function selections for various battery ranges such as : 9v , 3v , 1.5v etc. strictly for battery testing. So does that function load the battery ? And will it accurately test a 1.2v Eneloop on the 1.5v setting ? ( 1.5 normally for Alkaline)

If a resistor is used , what value to use and exactly where in the circuit should the resistor be placed ? (series or parallel ?)

It would be nice to have this discussed - but I don't feel qualified to give details or comprehensive comments ........

So I will ask if our qualified members could address these questions to enlighten the entire membership please . (including me)

Thanks

[Mr Happy]

The battery test function on a DMM is really designed for primary cells like carbon/zinc or alkaline. The load and the voltage range is tuned for that kind of battery.

It is quite difficult to test a NiMH cell under load because such cells are quite load tolerant. You would have to put a much heavier load on them to get a meaningful result, but even then there can be a lot of variation between cells caused by the age, usage and specific type. That's why battery testers like the ZTS are not very reliable when used on NiMH.

When you discharge a NiMH cell under test conditions or in normal usage, you typically wait until the voltage under load drops to 1.0 V or 0.9 V and then you remove the load. Once you do that the voltage of a healthy cell will gradually climb back up to about 1.2 V. It is important to stop discharging at that point. You must not keep applying the load until the voltage drops to 0.9 V and stays there. That will over discharge the cell and weaken it.

For practical purposes, the best thing to do with NiMH cells is to become familiar with the characteristics of the particular cells you have, and then just measure their open circuit voltage. It doesn't take long to learn what voltage your favorite cells have when fresh off the charger, when stored for a week or two, and when partially used. Any time the cell reads 1.2 V open circuit, consider it fully discharged and do not drain it any further.

[TooManyGizmos]

Mr. Happy ,

So you are saying on a DMM , to NOT use the Battery test function setting . As the load is not compatible to the rechargeable NiMh batteries we are using. I got it. Only use the D.C. variable voltage function setting appropriate to the Max. voltage of the battery. And test "open-circuit" with no load .

[Conan]

Currently available "load testers" that I've become aware of due to reading CPF are the Ansmann Energy Check LCD and the ZTS Pulse Load tester.

http://www.ansmann.de/cms/en/consumr...check-lcd.html



http://www.ztsinc.com/index.html

[Locoboy5150]

AMD64Blondie,

Since I seem to be the only CPF member that has that same Titanium Innovations M-8800 charger that you just bought, here is some information on how to read the nice LCD display. The information in the instruction manual isn't too descriptive.

The LCD bar graphs blink sequentially to show what's going on:
* Blink upward - charging.
* Blink downward - discharging.

If you use the refresh mode, the cells will be discharged and then the charger will automatically start charging them immediately. The charger will not shut off or stop and wait for you to do something after the batteries are discharged.

Unlike when the batteries are being charged, there is no way to tell how far along the discharging process is. All four segments of the LCD bar graphs will blink downward throughout the discharge cycle. That will not change if there is one minute left in the cycle or three hours.

To stop the discharging process and begin charging, just press the refresh buttons again. The LCD bar graphs will change from blinking downward (discharge) to blinking upward (charge.)

When the batteries are fully charged, the LCD bar graphs will stop blinking and all four segments of the bar graphs will be lit up completely.

I hope that helps out.

[Apollo Cree]

I just got my new Fenix TK40 on Friday,Dec.11,2009.It's now Dec.13,2009.I haven't charged my new Eneloops yet(took them straight out of the package -2/3 charged-and installed them in my new TK40).When should I put my Eneloops on to be charged?

Here's my charger,just FYI:
http://www.batteryjunction.com/8800.html

Titanium M8800.

Since the TK40 uses 8 AA's, I'd be sure to charge new Eneloops right out of the box to be sure you don't have one weak cell that gets reverse charged. I'd also be more than usually careful not to discharge it deeply, especially if the batteries haven't been charged recently.

An 8 cell device has a lot more chance of getting a reverse charge than a device with fewer cells.

[gtwace]

Isn't there a Eneloopy that checks the eneloops for u ? http://www.gadget3.com/node/882

[arodaz]

Eneloopy?!?!? I gotta find one

[WDG]

Because readiness is an important consideration, I make a habit of swapping a charged cell into my EDC once a week. In my usage, that means I rarely have less than 3/4 of the cell capacity left. If i find myself using it more than normal, I'll do this more often. YMMV.

FWIW, considering the ease of refilling rechargeables, I just don't see the point of ever letting them get to where I don't have plenty of emergency reserve, especially in a multi-cell light.

P.S. That TK-40 looks nice! I think I'll put it in the upper half of the list of things I'd like to get.

[mfm]

My Eneloopy is giving a red nose to 1.26V open voltage... (yellow at 1.30, green at 1.37). These are examples and not the limits.

[AMD64Blondie]

On my Titanium Innovations M-8800 charger,when it's flashing "F" and all 8 bar graphs are completely full..this means the batteries are fully charged,right?

Thanks,Mike

[Locoboy5150]

On my Titanium Innovations M-8800 charger,when it's flashing "F" and all 8 bar graphs are completely full..this means the batteries are fully charged,right?

See my post above:

"When the batteries are fully charged, the LCD bar graphs will stop blinking and all four segments of the bar graphs will be lit up completely."

If the bar graphs are blinking, then it's still charging.

[TyJo]

Bump. So an Eneloop at an open resting voltage of 1.2 volts or lower should be recharged... correct? Also, I just checked some Eneloops I rotate in my lights (they only go in 2 cell lights and are marked and matched, charged properly, rotated, new cells, etc.). They were charged and stored properly about a month ago, or slightly longer. I tested them and 2 different, cheap voltmeters gave me readings of 1.27 and 1.29v on the same cell, so 1.28 average (I accept the slight variation between the cheap volt meters). I am assuming this is a normal voltage for the eneloops... just making sure. Cells were charged using a Powerex (maha)MH-C9000 after a 1000 ma charge.

[Mr Happy]

Hmmm, even the cheapest voltmeter should read accurately to the 10 mV level. One or other of your voltmeters is broken. Does the battery need replacing?

Assuming the voltage readings are correct (doubtful), your Eneloops are under charged. They should be reading in the 1.33 to 1.38 V range. Did you leave them to do the 2 hour top off in the C9000 after "Done" appeared?

[Lynx_Arc]

Personally I think voltage (not under load) is a good indicator of charge level once you get attuned to your nimh batteries. If what you are using the batteries in you (under average use) only get 1-2 hours of runtime you will want to charge batteries at higher voltage than if your runtime is 10-15 hours because capacity left is related to runtime and if you only have 25% left on a 2 hour runtime that means only 30 minutes while 25% of a 10 hour runtime equals 2.5 hours which unless you plan on being away from a charger or a battery swap is typically useful. I typically charge batteries below 1.28v (no load test) as there is less than 50% left and charging and/or swapping batteries is just as easy as pulling dead batteries out of something and charging them at that time. Nimh are meant to be used and charged often so even a top off charge is worth the effort over endlessly testing batteries and just putting them back in. If you get 500 cycles out of batteries that would be one charge a week for 10 years.

[TyJo]

Hmmm, even the cheapest voltmeter should read accurately to the 10 mV level. One or other of your voltmeters is broken. Does the battery need replacing?

Assuming the voltage readings are correct (doubtful), your Eneloops are under charged. They should be reading in the 1.33 to 1.38 V range. Did you leave them to do the 2 hour top off in the C9000 after "Done" appeared?

I rechecked my batteries. There is a small possibility that I had measured partially used batteries since I just changed my rotation system. The readings are within 1/100 decimal, or only vary by 1/100. I doubt that I left the batteries in after it said done. I checked some other batteries and 2 different sets read 1.40 and 1.43. I will leave the batteries in for 2 hours after charging from now on.