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Thread: Maha MH C808M Charger

  1. #61

    Default Re: Maha MH C808M Charger

    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,

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  2. #62
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    Default Re: Maha MH C808M Charger

    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
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  3. #63
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    Default Re: Maha MH C808M Charger

    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?
    Last edited by wptski; 01-24-2006 at 07:58 AM.
    Bill

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    Default Re: Maha MH C808M Charger

    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!

  5. #65
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    Default Re: Maha MH C808M Charger

    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.

    Bill

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  6. #66
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    Default Re: Maha MH C808M Charger

    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?

  7. #67
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    Default Re: Maha MH C808M Charger

    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 .

  8. #68
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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by 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?
    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.
    Bill

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  9. #69
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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by wptski
    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.
    Last edited by bcwang; 01-24-2006 at 09:53 PM.

  10. #70
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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by bcwang
    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.
    Bill

    I'm a retired mechanic not a electronic/electrical engineer!

  11. #71

    Default Re: Maha MH C808M Charger

    Quote Originally Posted by bcwang
    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

  12. #72
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    Default Re: Maha MH C808M Charger

    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.


    Bill

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  13. #73
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    Default Re: Maha MH C808M Charger

    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.

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    Default Re: Maha MH C808M Charger

    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

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    Default Re: Maha MH C808M Charger

    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.
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    Default Re: Maha MH C808M Charger

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

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    Default Re: Maha MH C808M Charger

    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!
    Bill

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  18. #78
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    Default Re: Maha MH C808M Charger

    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.

  19. #79
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    Default Re: Maha MH C808M Charger

    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
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    Default Re: Maha MH C808M Charger

    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
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  21. #81
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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by 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
    I'm definitely going to try to figure out if this was a fluke or completely repeatable. I just wish I had a better way to test capacity quickly than the BC900. I do notice the capacity coming out of the 808m after a 30 minute wait before testing in the bc900 is much less than letting the bc900 do a charge and test cycle which has no wait time. I wonder how much that 30 minute wait hurts capacity. I'm talking about the difference between 2250mah against 2550mah which is quite significant.

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    Default Re: Maha MH C808M Charger

    bcwang:

    I wonder if that's what I'm seeing also? I charged four cells in the C808M and then D/C the four as a pack on the Triton.
    Bill

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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by wptski
    bcwang:

    I wonder if that's what I'm seeing also? I charged four cells in the C808M and then D/C the four as a pack on the Triton.
    Tried these two tests with the same set of batteries. The 808M after 8 hours on the charger at the normal setting (around 7 hrs is trickle), I got around 2230-2370mah depending on the cell or charge position. Only waited 5 minutes or so between pulling the batts out of charger and placing in bc900 tester.

    With the C204W, after 8 hours on the charger ( around 5 hrs is with the light green), I got 2510-2540mah depending on the cell. Waited 1 hour between pulling batts out of charger and putting in tester. I had to drive take it to work to monitor the discharge.

    So it seems the 808M doesn't charge as fully. My cell imbalance is more of a concern though, the different slots are not performing the same. I did a test of the voltage after coming off the charger last night. The cells ended at 1.39v on the first two slots, 1.40v on 3-4. The last 4 some were 1.40 and some 1.39v but I didn't pay too much attention on the order, but it was mixed. The C204W comes off at 1.41v

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    Default Re: Maha MH C808M Charger

    Hello Ben,

    I just pulled 8 cells off of the charger. Most of them were at 1.44 volts. The lowest was 1.43 volts, and the highest was 1.46 volts.

    Your cells at 1.39 and 1.40 volts do not seem to be fully charged.

    Tom
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    Default Re: Maha MH C808M Charger

    Quote Originally Posted by SilverFox
    Hello Ben,

    I just pulled 8 cells off of the charger. Most of them were at 1.44 volts. The lowest was 1.43 volts, and the highest was 1.46 volts.

    Your cells at 1.39 and 1.40 volts do not seem to be fully charged.

    Tom
    I should bring my multimeter home to test with, I was actually using the bc900 to test the voltage, it might load the cell a bit dropping it from the resting voltage. If not, it could be from testing the cells after they were out of the charger for 30min-2hrs. My BC900 was in progress at the time so I was waiting for it to free up to measure the voltage coming off my maha chargers. But my cells that measured 1.41v did test out to around 2550mah at 500ma discharge.

  26. #86

    Default Re: Maha MH C808M Charger

    I have the c801d version of this charger, it only charges AA/AAA. I have a problem, it has on 3 seperate occasions overcharged my cells. It just happened now, I inserted 2 AAs and clicked the soft mode and condition mode. First it charges before discharges. Problem is, it never quit charging and the batteries got extremely hot. When I pulled them out, the voltage was 1.52 and quite uncomfortable to touch. They were Rayovac 1800 AA NiMH.

    Do you think I have a defective charger?

  27. #87

    Default Re: Maha MH C808M Charger

    Quote Originally Posted by tareed69
    I have the c801d version of this charger, it only charges AA/AAA. I have a problem, it has on 3 seperate occasions overcharged my cells. It just happened now, I inserted 2 AAs and clicked the soft mode and condition mode. First it charges before discharges. Problem is, it never quit charging and the batteries got extremely hot. When I pulled them out, the voltage was 1.52 and quite uncomfortable to touch. They were Rayovac 1800 AA NiMH.
    tareed69,

    A quick way to check if the charger is working properly:

    1) Unplug
    2) Plug in power and watch the power up diagnostic... you should see all the symbols go on from right to left (DONE, CHARGE, 3-level battery etc).
    3) After that's done, the screen should remain off with NO symbols at all. You might want to wait for about 10 sec to make sure no symbol pops up by itself.

    William

  28. #88

    Default Re: Maha MH C808M Charger

    Quote Originally Posted by tareed69
    I have the c801d version of this charger, it only charges AA/AAA. I have a problem, it has on 3 seperate occasions overcharged my cells. It just happened now, I inserted 2 AAs and clicked the soft mode and condition mode. First it charges before discharges. Problem is, it never quit charging and the batteries got extremely hot. When I pulled them out, the voltage was 1.52 and quite uncomfortable to touch. They were Rayovac 1800 AA NiMH.
    tareed69,

    Assuming the power up diagnostic is good, here are some possibilities:

    1) 1.50V is a reasonable voltage for NiMH if you tested them immediately off the charger. The charger's absolute cutoff (Vmax) is at 1.60V.

    2) How long have you had the cells? Are these recently purchased? If so, your "new" cells may not be new at all. I would bet the Rayovacs are at least 18-24 month off the production if you'd just purchased them. Cells like these develop a extremely high impedence due to prolonged storage and would cause high temperature (~130F) when first charged. If the cells are manufactured well, then the impedence should drop after a few cycles.

    Hope this info helps!

    William

  29. #89

    Default Re: Maha MH C808M Charger

    Thanks for the response, the batteries are ancient, that probably is the problem.

  30. #90
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    Arrow Re: Maha MH C808M Charger

    willchueh : Please help ..........

    For the first 3 weeks my MaHa C-808-M charger worked just fine ................

    But now :

    I'm having problems too .
    When I insert the first AA battery in the far left slot - and within 2 to 8 seconds press the soft charge button - it won't go into soft charge mode . The word softcharge won't appear on the display . I am pressing and holding the button for 5 seconds - but still nothing .

    If I press condition - the word condition will appear - so that function seems o.k.


    I have un-plugged *AC* power - and the *DIN* connection cable , waited 5 minutes - then plugged all back in so it would re-set and go thru *self test* - all batt. symbols blinked from right to left . I wait 5 minutes after selftest has finished B-4 inserting battery and pressing softcharge button . I have done this whole proceedure several times , but still can't get it to go into softcharge mode . The word won't appear in the display. The first batt. icon on left will register and start blinking as it normally does and the white display light is working......but no softcharge .

    Also have tried several different AA batteries - they are all 2600 MiAh's - 2 months in use - and have been thru at least 6 charges on this charger in 3 weeks and all was fine till now .

    Have done ALL I know to do - can you offer any advice , thanx willchueh , for you help.





    Last edited by TooManyGizmos; 02-16-2006 at 03:16 PM.
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