15 min fast charger will not charge selected batteries?

[Haz]

Hi there,

I just purchased a Varta 15 minute Ready2Use charger, i tried to insert some Eneloop NiMh batteries AAA into the charger, but it will not charge it. The light is suppose to stay on red to indicate charging, but it simply continued to blink to indicate the battery may be around the wrong way, which it isn't. Does anyone know why it will not charge it?

I also tried some other Eneloop AA, AAA, it didn't charge it either at first. However, after changing it to another slot, it eventually started charging it. Seems to be quite difficult to get it to charge.

The original batteries (AA) that come with the charger managed to charge and are somewhat similar to the Eneloop too, being low discharge batteries, so i cannot understand why some of the Eneloop will not charge.

I did a google search and it seems sometimes the Energizer 15 minute charger doesn't charge some batteries too, so i wonder if it's because fast chargers can only charge some batteries and why is that the case?

 

[MrAl]

Hi there,


15 minute chargers are very sensitive to the internal resistance of
the cell. If it detects that the internal resistance is too high,
it will not charge the cell.
What can cause this is either an old cell, a defective cell, or
even if the contact resistance is too high. To reduce the
contact resistance you should make sure the terminals of
the cell are cleaned very well and make sure the contacts
on the charger are clean also. If you think they are not,
use an eraser to clean them. It also helps sometimes to
rotate the cells as they sit in the bay, using your thumb
to make them rotate along their cylindrical axis. This helps make
a better contact too.

If you happen to have an Energizer 15 minute charger you can
make my modification shown elsewhere on this forum (for AA
cells only).

 

[Haz]

thanks for the detailed information MrAl.
I think is the thread that you are referring to, thanks very much.
I was starting to think the charger was faulty, your explanation really clears it up.

http://www.candlepowerforums.com/vb/showthread.php?t=157139

 

[BrianChan]

Hi Haz,

I assume that you are using the Varta 4 cell 15 minute charger as the 2 cell version does not do an internal resistance check.

Well there's a workaround for this if you insist on charging your rejected cells on the 15 min. charger, with the 7.5A charge rate. Open up the casing, look to the upper left of the PCB and you'll see a blue 'device' that you can adjust using a Philips screwdriver. Turning it fully clockwise/counter clockwise will either remove the internal resistance check or make the charger reject all but the newest cells. My guess is that it sets the resistance threshold for rejecting cells.

Another way to do it is to perform Mr Al's mod on the charger as the internals are very similar to the Energizer 15 minute. Bear in mind that there's a timer, which turns all leds green after 20 minutes if you use the lower charge rate.

Since I have both E15 and Varta15 minute chargers I'll post my observations for them:

1) You can use an E15 adapter on a V15 and vice versa.
2) V15 has 4 leds while the E15 has one.
3) The fan on the V15 is ridiculously powerful but a bit noisy. Get a tool from Bunnings and cut all the vents on both the front and back of the fan, leaving the fan exposed and your cells will actually be cool throughout the charge cycle.

 

[Haz]

Hi Haz,

I assume that you are using the Varta 4 cell 15 minute charger as the 2 cell version does not do an internal resistance check.

That's right, i have the 4 cell one. Thanks for your advice, i tried what you told suggested, and it works. The AAA cells that originally did not charge are now charging. I'm always amazed at the wealth on knowledge on this forum, and you proved it once again. Thanks.

Haz

 

[SilverFox]

Hello Haz,

Keep in mind that the reason these 15 minute chargers reject cells is because higher internal resistance translates to higher cell temperatures.

High cell temperatures kill NiMh cells. I would recommend that you keep track of the cell temperature while charging to make sure you are OK.

Also, by reducing the reject limit, it may be possible to blow up an Alkaline cell with the charger if someone accidentally tries to charge one. I think these chargers have other safeguards against charging Alkaline cells, but it is worth consideration if others, besides you, have access to use the charger.

Tom

 

[MrAl]

Hi again,


Tom, some good points there. With my Energizer mod the charger still looks at internal
resistance and the mod also forces a lower charge current for the cells with higher
internal resistance, so the charge is still safe.

On the other hand, with the Varta mod bypassing the internal_resistance_check
mechanism without reducing the current also is a little risky. If there was some way
to lower the current a bit too that would be nicer.

I know it also bites when you buy a nice new charger that is supposed to be so
good and then you find out it wont charge some of your cells. This led me to the
Energizer mod because i just didnt like that (and i paid 30 dollars for mine).