Maha 9000 bypass "HIGH" internal resistance test

[koala]

WARNING: Be aware that the charger may not terminate properly, so melted cell & fire is possible.

Method 1:
Right, I am sick of 'crap' cells and I have lots of them. I know they still work fine, despite slightly higher than normal internal resistance. Sanyo claims the cells to be 20-25miliohm. I need to stop the charger from getting "HIGH". So I inserted the cell, set the charge current, all set and Enter. Immediately after pressing the Enter button, I short circuit the cell with a 12" 30awg wire. I think 3 seconds will do, the charger will start the whining and charging takes place. No more "HIGH"

This fools the charger but beware that this may also blow the mosfets. Also, you are shorting the cell. I am not sure if one should do it but it's a solution for me, if I am stranded on a holiday with my cells turning crap out of a sudden.

Method 2:
There is a second safer method but you need to have very quick reflex. You will need a good cell. Firstly insert the good cell, set the charging stuff then hit Enter. After 10seconds or so, yank the good cell out and insert the 'crap' cell. You need to be VERY quick, have the 'crap' cell ready in your other hand. No more "HIGH"

WARNING: Be aware that the charger may not terminate properly, so melted cell & fire is possible.

 

[TorchBoy]

Have you calculated how much resistance that wire will have? It doesn't sound like a very good idea - as you say, it might blow something - but I think it would have about 25 milliohms resistance. Unfortunately, this chart doesn't include 30AWG wire.

 

[Mr Happy]

Heh

Anything that puts one over on the C9000 is a good idea. The wretched thing is far too sensitive to my liking. I wish it had a switch on the back to bypass the resistance check on cells. I mean, what's the point of selling an advanced charger for expert users, and then including a non-expert U R DUMB feature and refusing to charge cells? It's a complete design failure in my opinion.

 

[MrAl]

Hi,

Unfortunately that happens a lot in todays market. Great
attention to detail is paid in one area and other areas are
almost not thought about at all.
This is why i prefer to design and build all my own chargers
these days. Even if i do overlook something i can always add
it later.

 

[koala]

Please stick to Method 2 it works like a charm for me. Method 1 is dangerous. I have a cell having 0.8ohm internal resistance, it terminates well.

MrAl - Sorry, I haven't get around hooking up the charger that you made, that's mainly because I have access to other chargers but very soon I will, any day now.

 

[mdocod]

just thinking here (and could be wrong)...
Nothing really wrong with using the wire if you ask me, as far as the charger is concerned, a cell is pretty close to a dead short anyways, (it's less than an ohm!) you could use a longer length of wire to increase resistance, and increase surface area of the wire so it doesn't get hot or anything. My only concern is shorting the cell when it may already be quite discharged, could discharge it even more than necessary, but only for a few seconds, I can't see the harm, the cell will likely sag under the load of a dead short to a fraction of a volt temporarily, and since the only cells you would be doing this on are ones with high resistance problems, then I wouldn't expect a lot of current to flow freely from them even into a dead short.

Eric

 

[TorchBoy]

How does the resistance test work? Is it a fixed high current for a short time, to see what happens to the cell voltage?

 

[koala]

Use Method 2

Hi torchboy, I don't know how MAHA test for internal resistance but I know Energizer and Sanyo uses the same 1Khz impedance test in their datasheet.

 

[jtr1962]

Method 2:
There is a second safer method but you need to have very quick reflex. You will need a good cell. Firstly insert the good cell, set the charging stuff then hit Enter. After 10seconds or so, yank the good cell out and insert the 'crap' cell. You need to be VERY quick, have the 'crap' cell ready in your other hand. No more "HIGH"

I've been using this method for a long time. The problem is that the Maha seems to be a little too strict in its internal resistance test. When the cell voltage exceeds a bit over 2 volts in the test it rejects the cell. Not sure what the test numbers correspond to exactly, but I've had cells charge and work perfectly fine when they fail the internal resistance test. I generally consider a cell crap when it's under about 75% of its initial capacity. After that it goes to some kind of low current duty, such as solar garden lights, until it dies completely.

 

[rizky_p]

i hate Maha 9000 resistance test, i have two very capable Sanyo 2100mah which being refused by the charger. They should change it to something like YES/NO question rather then just denied the cell from charging.

Sometimes pusing the cells harder toward the positive charger contact helps to reduce the resistance, can be a different between rejected or accepted by the charger.

Thanks.

 

[WDG]

Have you tried a lower charge rate? I have one Powerex 2700 that gets the "HIGH" message if I try to charge it at 1800mA or higher, but works fine at my normal 1500mA charge rate.

FWIW, the Eneloop charger I have also rejects this same cell with a flashing green light.

 

[WDG]

Thought I'd update regarding my previous suggestion.

Most of my year-old 2700's are now completely rejected by both the MH-C9000 and the Eneloop chargers. Reducing charge rate makes no difference, and they won't even discharge properly, as they sag badly under even moderate loads. Now they can only be charged in my old "dumb" timer-based chargers (glad I kept these around.) They actually seem to have good capacity under VERY light loads, so they are now relegated to duty only in the old analog transistor radios I like to listen to.

Clearly they've grown something internal that's bad. (Meanwhile... my Eneloops of the same vintage and treatment perform essentially as they did when new - I continue to be VERY impressed with these cells.)

 

[jtr1962]

Most of my year-old 2700's are now completely rejected by both the MH-C9000 and the Eneloop chargers. Reducing charge rate makes no difference, and they won't even discharge properly, as they sag badly under even moderate loads. Now they can only be charged in my old "dumb" timer-based chargers (glad I kept these around.) They actually seem to have good capacity under VERY light loads, so they are now relegated to duty only in the old analog transistor radios I like to listen to.

That's what I find with all my "bad" rechargeables. They don't lose capacity at light loads, only at high ones. As such, they're still suited to things like wall clocks or solar lights.

 

[kirby]

Quite a few of my older batteries have the same problem..
However they can still be charged up with the La Crosse 900 charger.

 

[bob_ninja]

That's what I find with all my "bad" rechargeables. They don't lose capacity at light loads, only at high ones. As such, they're still suited to things like wall clocks or solar lights.

I use mine in wireless mouse and other low power apps.
Why all these hacks on C9K?????
BC900 is less strict and will usually accept them.
Also you can find some old dumb charger with a timer.