Charging NiMH problem with MC3000

Recently I got a MC3000 charger. It is good for lithium-ion based batteries. But there is some problem when charging NiMH.
First problem is charger can't stop charging (HKJ's review also mentioned that). I used standard AA Eneloops. They always stop correctly on c9000 or BT-C2000 charger (when charging capacity reaches 1900-2000mAH. Current is 0.2A). But MC3000 will not stop even at 2500mAH (Current 0.2A, DeltaV set to -3mV & -2mV). Battery is already about 40°C and MC3000 seems will continue forever.
Second problem is the battery voltage. On MC3000, battery voltage rises to 1.53-1.54V when charging capacity is1900mAH (This is the position where c9000/BT-C2000 stop). As I remember, on c9000/BT-C2000, battery voltage never went above 1.5V (typically 1.47-1.48V when stop).
So my question for the first problem is, why MC3000 fails to detect the -deltaV? How to let MC3000 correctly stop when charging Eneloop (some other NiMH brands which correctly stop on c9000/BT-C2000 also have same problem).
For the second problem, the voltage difference may not be important, but I wonder why. Why there is such voltage difference? Is it because MC3000 uses constant current instead of pulsed current? If yes, why pulsed current leads to lower voltage? Which is better?

[edit]
Thanks HKJ. I've read his article on charging NiMH. It contains convinving experiment data/chart. Now I know why MC3000 is a good charger. I will make voltage termination program for NiMH.
The left question is pulsed charge VS CC charge, CC charge seems lead to higher off load voltage at same charge level. It is interesting.

no problems here

Post a list of all program settings or just your changes from default nimh program so others can try them.

I have had no problems with Eneloop 2000mah myself.

John

What rate are you charging at? Is it .2a or is that the rate towards the end of the charge cycle. Around 1a rate is good for eneloops, if it is 0.2a then its too low and may cause charging issues(generally) .

ven said:

What rate are you charging at? Is it .2a or is that the rate towards the end of the charge cycle. Around 1a rate is good for eneloops, if it is 0.2a then its too low and may cause charging issues(generally) .

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I agree. I think that 200mA on a 2Ah Eneloop is just too low. Maha throws out the number .3C, so that would be 600mA, at least.

Chris

Is there a capacity termination setting on the MC3000, If so set it to 2400mah for 2000mah battery that`s 20% extra for charging inefficiency, maybe even higher.

John.

The setting is: (Eneloop, standard AA, charge, 200mA, -3 or -2mV). I have to use time or capacity limit now since -deltaV detection does not work.
For the 0.1C rate, I did see Maha says on its booklet to recommend 0.3C or higher to let c9000 stop correctly.

But fact is:
(1) I have no problem using 0.1C rate on c9000/BT-C2000 for most batteries (they always stop at right charging capacity, including Sanyo's 10/7.5AH NiMH D cell and 5AH NiCD D cell).
(2) On MC3000, I ever tried Sanyo 10AH D cell at 3A rate, it could not stop when capacity was over 11AH. Battery temperature was already very high at that time (For c9000 or BT-C2000, they always correctly stop at about 9.5-10.5AH, current is 1A-2A). I also tried 1A current on MC3000, result was same.

I will try charging Eneloop at 0.3c or higher rate. But I think the result will be same.
I will post result later.

tbx8192 said:

I will try charging Eneloop at 0.3c or higher rate. But I think the result will be same.
I will post result later.

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Let's just keep it simple.

Discharge Eneloops, place them on the MC3000 and charge them up at 1A, each.

See what you see.

Then charge them up at 800mA, repeat and rinse.

Chris

ChrisGarrett said:

I agree. I think that 200mA on a 2Ah Eneloop is just too low. Maha throws out the number .3C, so that would be 600mA, at least.

Chris

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For NiMH, I recommend 0.1-0.2C rate for better battery life. I think Eneloop can not last 1800 or 2100 cycles when using high charge rate.

tbx8192 said:

For NiMH, I recommend 0.1-0.2C rate for better battery life. I think Eneloop can not last 1800 or 2100 cycles when using high charge rate.

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I don't think that you can quantify that empirically.

They can be fast charged at 2A if need be and will probably develop higher IRs before you get anywhere close to even 1000 cycles.

Or put another way, what's worse for a battery? Missed terminations that aren't caught immediately, or regularly charging a battery up at say .5C?

My money has been on the latter for the past 4+ years.

Chris

Ideal charge rate for Eneloop AA is 600mA. I think the standard Eneloop charger is at 350mA. You could go as high as 1000mA and the cells don't get hot. Also the amount of mAh from the charging cycle is lower the higher the charge rate is. If the cells are depleted a slower charge rate may be more ideal. C9000 will charge to about 90% and top off the cells for 2 hours to prevent premature wear from increased temps. Generally the higher the charge rate the more likely the cell will reach 1.47v so the C9000 doesn't really depend on the delta cutoff.

You can't really go under 350mA on AA cells and 200mA on AAA cells because smart chargers have issues reading the delta that cells give off to prevent overcharge due to the low charge rate. Higher charging will allow the chargers to detect the delta.

If you want to be totally sure of correct termination using delta in the mc3000, do not charge at a rate less than 0.3C.....in other words, charge your 2000mAH Eneloops at a minimum of 667mA. This rate will not hurt the batteries.

There is no charger, that I am aware of, that can correctly terminate on delta at 0.1C charge rate.

You are not alone my new charger BT-C3100 has done the exact same thing,stuck 4 eneloops in the other night from my bathroom radio ,3 charged within the hour and the 4th would not stop charging at all.I did a full discharge and put it back in charge and all seems ok now.

ChrisGarrett said:

I don't think that you can quantify that empirically.

They can be fast charged at 2A if need be and will probably develop higher IRs before you get anywhere close to even 1000 cycles.

Or put another way, what's worse for a battery? Missed terminations that aren't caught immediately, or regularly charging a battery up at say .5C?

My money has been on the latter for the past 4+ years.

Chris

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As I know, 2A charge will leads to over 0.2ohm IR (ten times of a new one) before 200 cycles.
I understand people may prefer time to money. But for me, I do not need fast charge because I usually prepare 2 battery sets (or more) for a device. After replacing with a new set, old ones will do an overnight charge then become backup. There is plenty of time to charge.

Devon said:

If you want to be totally sure of correct termination using delta in the mc3000, do not charge at a rate less than 0.3C.....in other words, charge your 2000mAH Eneloops at a minimum of 667mA. This rate will not hurt the batteries.

There is no charger, that I am aware of, that can correctly terminate on delta at 0.1C charge rate.

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I already tried 0.3C rate for 10AH D cells: same result. I will try Eneloop later.

For a charger to terminate on delta at 0.1C rate, BT-C2000 is one (since c9000 is not assumed -deltaV termination). As I tested, it worked for many batteries (2AH Eneloop, 10AH/7.5AH NiMH D cell, 5AH NiCD D cell and many other brands). There are ones it fail to terminate correctly. But for these, it always works.

Why not set the capacity cut-off before charging? I use this feature a fair bit and it does work, lets use use whatever charge rate you like with no worry about overcharge. If I am not sure how full a cell is I set the cycle to discharge, rest, then charge with capacity cut-out.

If you want use very low charging current you can configure the MC3000 to perform like the C9000

tbx8192 said:

I already tried 0.3C rate for 10AH D cells: same result. I will try Eneloop later.

For a charger to terminate on delta at 0.1C rate, BT-C2000 is one (since c9000 is not assumed -deltaV termination). As I tested, it worked for many batteries (2AH Eneloop, 10AH/7.5AH NiMH D cell, 5AH NiCD D cell and many other brands). There are ones it fail to terminate correctly. But for these, it always works.

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For your information, most D cells I have disassembled, including Eneloops, have been made up of 3 AA batteries in parallel.

It is impossible to terminate a D cell constructed in this manner as all 3 batteries will never achieve delta at the same time, so typically not possible.

The method used to charge this type of battery is either terminating on time and charge rate, or on voltage, and both using a slow charge rate.

Never hear this before so verification by other members would be helpful, Though i have never noticed any problem with termination myself on lower priced smart chargers, though i could not tell without disassembly if the D cells were made up of multiple cells in parallel.

John.

Devon said:

For your information, most D cells I have disassembled, including Eneloops, have been made up of 3 AA batteries in parallel.

It is impossible to terminate a D cell constructed in this manner as all 3 batteries will never achieve delta at the same time, so typically not possible.

The method used to charge this type of battery is either terminating on time and charge rate, or on voltage, and both using a slow charge rate.

Click to expand...