Charging Li-ions with Maha 777PlusII

[LitFuse]

I just got a PlusII recently, and have been using it on all manner of bare Li-ion cells. I'm concerned that it is overcharging the cells though. If I let the charger do it's thing till the display says "Full" and terminates the charge, my cells are reading 4.3+ on my Fluke meter. The PlusII shows 4.1V, but after resting the cell for 24 hours, the Fluke reads 4.31V. This example is with a 650mA R123.

I'm no battery Guru, but I'm pretty sure 4.3+V is not healthy for these Li-ion cells. Does anyone else have the same issue with the Maha? Should I be pulling the cells out when the Maha reads 4V? Do I have a defective charger?

Any and all insight appreciated. /ubbthreads/images/graemlins/smile.gif

Peter

 

[vacuum3d]

I face the same exact problem. There's another thread somewhere where people have reported to not see this overchanging problem. I thought my problem was unique. I tried calling the Tech Support number that came with the package, but the number is no longer in service.

ernest

 

[SilverFox]

Hello Peter,

4.3 volts is a bit on the high side. The results of charging to that high a voltage is that you will probably get more capacity from the cell, but at the same time get fewer cycles. I had one cell that I charged up to 4.5 volts and got 4 cycles. After that it was dead.

For maximum capacity I believe you want to stay close to 4.2 volts. For maximum cycles (at the cost of some capacity) 4.1 volts is where you want to be.

I believe 4.2 volts will yield about 500 cycles and 4.1 volts will yield about 1500 cycles. Of course 4.5 volts yields 4 cycles...

Tom

 

[Lux Luthor]

You might want to take a look at some eham.net reviews. Overcharging is a common complaint with this charger. here

 

[LitFuse]

[ QUOTE ]
Lux Luthor said:
You might want to take a look at some eham.net reviews. Overcharging is a common complaint with this charger. here

[/ QUOTE ]

I had perused that site before buying the Maha. Most of the issues were not relevant to my intended use of charging Li-ion cells. I saw lots of bitching about the pin system and hot NiMH cells, but not much about Li-ion batts. Perhaps I didn't dig deep enough?

At any rate, is anyone else seeing 4.3+V in cells charged on the Maha? Those last couple tenths of a volt take a long time, and there is certainly a window of opportunity to manually terminate the charge at that time, but I'd really like to be able to charge these things without babysitting them. Is this going to be possible?

Peter

 

[LitFuse]

[ QUOTE ]
SilverFox said:




I believe 4.2 volts will yield about 500 cycles and 4.1 volts will yield about 1500 cycles. Of course 4.5 volts yields 4 cycles...

Tom

[/ QUOTE ]

Thanks for the reply Tom. That is some interesting information, that I have not seen before. I understand where the 4.5V data came from /ubbthreads/images/graemlins/grin.gif, but what about the dramatic cycle life differential yielded by the .1V voltage difference. Is that anecdotal information, or is it supported by testing etc.?

Peter

 

[andrewwynn]

that's very interesting.. are there any diodes with a .1V drop? /ubbthreads/images/graemlins/wink.gif.. the charger looked awesome, but i don't want to charge over 4.2V either.

-awr

 

[LitFuse]

That was going to be my next question Andrew. Is there a way to "tweak" the charger to eliminate the overcharging?

That sure is a troublesome tenth of a volt. /ubbthreads/images/graemlins/help.gif

Peter

 

[koala]

Can you return it? get a Triton instead!

I read rcgroups some people say that older Maha777Plus has this problem and it is corrected in the later version.

I think you should email the support people. They are very helpful and replies quickly. Let us know the result.

-vince.

 

[KevinL]

I would definitely ask their support about it if mine did that. Mine's a very new one, and I notice that it slows down the charge rate as the cell goes above 4.0V. Approximately 2-3 hours fast charge (for large 1800mAH cells), the last 2 hours are very slow. I wait till the beep, pull them off, DMM them, and I've never seen anything beyond 4.18V.

Except for the time I didn't set my battery type selector switch properly.. that's the only thing you gotta watch.

 

[nonbox]

How do you tell the difference between the old model Maha777Plus and the new one?

Can you use any R123 in the Maha777Plus?

 

[LitFuse]

[ QUOTE ]
koala said:
Can you return it? get a Triton instead!

[/ QUOTE ]

I considered the Triton, but I just wasn't keen on having to use a separate power supply to run it. I have also heard that the Triton has it's own issues with Li-ions (undercharging IIRC). I think I heard that there is some new software to fix the glitch though. I may end up with the Triton yet, but I'm gonna start by contacting Maha tech support.

Peter

 

[koala]

Yes it's a pain to use a seperate power supply. Triton is design as a field charger, means you can run it off 12v car battery. I use a modified 200watts AT power supply. Now you have three units to watch for fire. /ubbthreads/images/graemlins/smile.gif PSU-Charger-LiIon /ubbthreads/images/graemlins/rolleyes.gif

Triton undercharging problem was a some time ago. The newer version is ok. Mine is a faily new unit so I don't have a problem with it. Do you read rcgroups.com? there are many happy users there /ubbthreads/images/graemlins/grin.gif.

However, the Maha is a *more affordable unit which does the job, I think you should contact Maha tech asap and see what they will do about it. There are also alot of photography enthusiastic who swear by the Maha777PlusII. Maha reply my emails(about sales) very fast and precise.

There are alot more chargers out there. Like the Schulze, Supernova, Swallow, Prolux, etc. They all are very specialized hobby charger.

Vince.

 

[wptski]

[ QUOTE ]
nonbox said:
How do you tell the difference between the old model Maha777Plus and the new one?

Can you use any R123 in the Maha777Plus?

[/ QUOTE ]
The new is a C777PLUS-II with a RESET button and another button you press so you can discharge only!

 

[Lux Luthor]

[ QUOTE ]
KevinL said:...Mine's a very new one, and I notice that it slows down the charge rate as the cell goes above 4.0V. Approximately 2-3 hours fast charge (for large 1800mAH cells), the last 2 hours are very slow. I wait till the beep, pull them off, DMM them, and I've never seen anything beyond 4.18V....

[/ QUOTE ]

That's good news.

Would you happen to know if there's a way to vary the charge rate down to 10ma or less? I would need it to be able to charge button cells also.

 

[KevinL]

I doubt it. The Maha is as automatic as it gets, in fact the old versions only had one button to select discharge mode. The new one has two buttons, discharge and reset.

Maha strongly discourages any attempt to charge any cell smaller than 400mAH on this charger because it's going to toast it. For a 40mAH button cell that would be 10C... /ubbthreads/images/graemlins/ooo.gif rechargeable 9V is an absolute NO as well, according to the papers they supplied with it.

 

[Lux Luthor]

Bummer.

 

[koala]

How a bout a suitable resistor in series to drop the current? Just a suggestion I hope this won't cause fire.

 

[Lux Luthor]

Thanks for the suggestion. I'm sure it would work - atleast with another LiIon, although I don't have a clue as to how the charger would respond. You could also just float it with another battery, once it gets close to being fully charged.

I did want this process automated, though. I will probably end up getting one of the Linear chips, and building my own.

 

[wptski]

I charged a Pila 168S on my MAHA C777PLUS-II which finished sometime during the night but check at 4.24V this morning.