Maha MH C808M Charger

[john2551]

William,

Thanks for answering my question. I think your charger is superb for charging these very very high capacity D cells in just 7 hours, the Ansmann Energy-16 takes more than double that time.

Regards,

John

 

[SilverFox]

Hello William,

Thanks so much for stopping by, and welcome to CPF.

Now the final pieces of information are falling into place...

Brilliant work on designing the conditioning algorithm. This allows all the cells to be balanced and become ready for use at about the same time. For multi cell applications, this is very convenient.

I did not mean to stir things up by not following standard protocol, but I was curious as to how this charger worked. Now the conditioning cycle makes perfect sense, and if I only want to discharge cells, I may be able to figure out how to do that and skip the initial charge.

I have some C and D cells that I like to do a discharge cycle on every so often. Since they are almost empty, I am just interested in discharging them, then charging them back up. Kind of a mini conditioning cycle. I think I can figure out how to do that now...

It looks like I was off on the discharge rate. I will go back and edit my comments to reflect reality...

Tom

 

[wptski]

willchueh:

You stated in your first post:
>>>
. The first stage PWM is a high-frequency one (several hundred KHz) and establishes a fixed 2.0A current. This is done all in the AC adapter.
>>>
Now that's a continous output, not something that happens at the start of every cycle, or on each seperate channel, right?

 

[bcwang]

Hi William,

I thought of one other question about this charger. What kind of charge termination methods are used?

I know -delta V is one
Probably over temp protection is another

What about delta T/delta time, 0 delta V, or any others such as time limit? I've seen moving window deltaV mentioned on the maha website before, what does that mean?

Thanks again!

 

[wptski]

Here's a superimposed screen in the same time scale using a current probe. The top trace is a AAA cell and the bottom is a AA cell. You can see that the AA cell is pulsed much faster.

 

[bcwang]

Nice graph Bill.

Does the time division say 5 seconds?

What charge mode were you using for the AA and AAA to produce this graph?

 

[nickz]

Thanks for this one!! I have been looking for a decent charger for some time. Ordered my C801D today. Went with it since I only need to charge the AA batteries. I can come up with something if battery removal is tough. I figure putting a ribbon around each cell before putting them on to charge will do just fine and saves me $30 to boot :rock: .

 

[wptski]

Nice graph Bill.

Does the time division say 5 seconds?

What charge mode were you using for the AA and AAA to produce this graph?

bcwang:

Yes, it's 5 sec. divisions. They both were in Soft Mode. I have problems with picture size when posting. I try to get it big enough but not so big that one must scroll over to see all. Not sure if it's the forum or what, one day, one byte size works but the next day it doesn't.

 

[bcwang]

bcwang:

Yes, it's 5 sec. divisions. They both were in Soft Mode. I have problems with picture size when posting. I try to get it big enough but not so big that one must scroll over to see all. Not sure if it's the forum or what, one day, one byte size works but the next day it doesn't.

Interesting, it looks like for AAA in soft mode, it applies a 2 sec charge pulse every 12 seconds or so. I always thought pulse chargers pulse at a much higher rate, like multiple times per second. But this graph seems to conflict with your earlier graph which shows a pulse of only around 8 milliseconds long. I wonder why they're so different.

Do you notice any pulse behavior at all when charging AA's in normal mode? William mentioned that although it charges at 100% duty cycle, there are special pulses and pauses still.

 

[wptski]

Interesting, it looks like for AAA in soft mode, it applies a 2.5 sec charge pulse every 12 seconds or so. I always thought pulse chargers pulse at a much higher rate, like multiple times per second. But this graph seems to conflict with your earlier graph which shows a pulse of only around 8 milliseconds long.

Do you notice any pulse behavior at all when charging AA's in normal mode? William mentioned that although it charges at 100% duty cycle, there are special pulses and pauses still.

bcwang:

That earlier one was done in the One Shot Mode, maybe not the proper way and was also in Regular Mode too!

I did a AA and AAA cell in Regular Mode charging but the battery in my scope was about to die, so I quickly plug it in the charge before it lost memory. I had to change the settings to see the pulses, so it's a bit different than the Soft Mode. I'll post them tomorrow evening.

 

[willchueh]

I thought of one other question about this charger. What kind of charge termination methods are used?
Thanks again!

bcwang,

The charger uses quite a few cutoff techniques. While I am not able to discuss some of our proprietary technology in great depth, I can say that the algorithm is a lot more complicated than Negative Delta V.

The combination of algorithms we use is responsible for the low battery temperature given such a high current.

One thing to point out is that the ASIC used in the charger has an effective voltage step size (voltage resolution) of 1mV. Most chargers use microcontrollers (including many of Maha's other chargers) have resolution in the range of 3 to 5mV. This level of resolution is needed to run some of our algorithm. At the same time, such high resolution also require a superb amount of noise reduction and signal conditioning to avoid misreadings.


William

 

[wptski]

Here's another scope screen of a AA and AAA cell in regular charge mode. More visible in the AAA trace, there is a variable PWM going on. I think in the AA trace there is a variable PWM where I have it marked as "false peak". There were also times were there was no pulse at all but you can't see it in the traces but I could tell from the scope. This variable PWM happens while that third and last segment is flashing in the battery icon at the end of the cycle. The scale is 2A by 2 sec.

 

[bcwang]

Looks like some of Maha's advanced charging algorithms at work. It's nice to have a scope, you can learn a lot about how things work.

I wonder if this thread should be in the "batteries" forum. I only caught this one because I searched for this charger model. I guess I've never thought of looking in the reviews for discussion about battery chargers.

 

[bcwang]

Hi Tom,

Any chance of posting results of this charger in your "battery charger" sticky? I'd be nice to see how fully charged the cells come off this charger compared to the ones currently in the graph.

Or are the cells you used for the previous test no longer available to make comparison meaningful?

Ben

 

[BVH]

Noticed something unusual about my 808. It sits by my PC with the power supply unplugged most of the time. The charger body does a awful lot of creaking and poping with minor temp changes. Nothing else in the entire room makes any noises.

 

[bcwang]

Noticed something unusual about my 808. It sits by my PC with the power supply unplugged most of the time. The charger body does a awful lot of creaking and poping with minor temp changes. Nothing else in the entire room makes any noises.

That is pretty strange. I haven't heard any noises from mine yet, but I"ll be sure to pay more attention.

 

[wptski]

Tom:

You stated that the cells coming off the C808M have somewhat lower voltage than others. I have some new Energizer 2500mAh, rebranded Sanyo HR's cells.

They don't have that many cycles on them so at first I blamed it on that. The cells charged in Slow Mode(1A) and discharged at 1A on my Triton are 200mAh lower than when they are C/D at 1A on the Triton. The cells still don't have that many cycles on them but this has repeated twice!

 

[bcwang]

My feeling on this charger is that it doesn't seem to charge to as high a capacity as my MH-C204W, but it comes off cooler. I think I'm going to spend some time in the next few weeks to do a controlled experiment to see which of my chargers produces what charge results on my batteries.

A thing I find a little concerning is that it seems slot 3 and 4 seem to charge to a higher capacity than slot 1 and 2. I can only say this is true when charging 4 batteries at once as that is my only test scenario right now. I thought it was the batteries at first, but I swapped the positions and it happened again, so then I mixed the batteries up, and it still came out the same way. Slots 3 and 4 came out with higher capacity than slot 1 and 2. They were about 50mah apart. I have to do more testing to verify, and try out the other slots as well.

Tom, when you tested to make sure all the slots in your unit charged evenly, was that charging with all of them at the same time, or did you use one slot at a time and test the capacity after each charge? I've seen a couple of slots go from charging to complete at the exact same time which seems odd. I notice this with a few other independent cell chargers too. I wonder if the signal from one battery completing causes the other ones to trigger finished even if they're not. This needs some more investigation.

 

[SilverFox]

Hello Bill,

It is my understanding that the Maha C808M is designed to get the most cycle life from your cells. The cost for this is slightly less capacity. This charger does not overcharge cells at all, not even a little bit. Thus the increase in cycle life.

Tom

 

[SilverFox]

Hello Bcwang,

My charger is very consistent from slot to slot. I tested this with 2 cells, 4 cells, 6 cells, and 8 cells. I know this is not "exhaustive," but it gave me a pretty good indication of its operation.

I have been using some very good Powerex 2500 cells for this testing. They seem to handle hard use (and some abuse ) very well. A few more cycles in my Mag85, and I will add them to the NiMh shoot out thread.

Tom