Question for the experts.

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marcl
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Question for the experts.

OK I have a question for anyone who understands this stuff. I have 3 of these chargers:

http://www.fasttech.com/products/1421/10000436/1046800-portable-digital-...

Now they all terminate at slightly different voltages 1 at 4.16v, 4.22v and the last one at 4.25v. Now when I put a DMM across the contacts of the charger, with no cells of course 1 of them is reading 600ma another 800ma and the one that reads 4.16v is reading 000ma, nothing! But this is what I don’t understand, it charges my cells perfectly to 4.16v. So why is it not giving a reading?

Thanks,

Marc.

Eagles may soar, but weasels don't get sucked into jet engines!

scaru
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You were shorting the charger... If you want to measure charge current place a battery in it so the - side of the battery connects with the - contact plate. Then using a DMM on the 10 amp setting finish the circuit going from + on the battery to the positive contact plate. That number will be your charge current. 

marcl
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scaru wrote:

You were shorting the charger… If you want to measure charge current place a battery in it so the – side of the battery connects with the – contact plate. Then using a DMM on the 10 amp setting finish the circuit going from + on the battery to the positive contact plate. That number will be your charge current. 

Surely that will blow the fuse and read the discharge of the cell? How come the other two chargers read right but the last one doesn’t?

Marc.

Eagles may soar, but weasels don't get sucked into jet engines!

scaru
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marcl wrote:
scaru wrote:

You were shorting the charger... If you want to measure charge current place a battery in it so the - side of the battery connects with the - contact plate. Then using a DMM on the 10 amp setting finish the circuit going from + on the battery to the positive contact plate. That number will be your charge current. 

Surely that will blow the fuse and read the discharge of the cell? How come the other two chargers read right but the last one doesn't? Marc.

No, because what I described is simply measuring the charge current. What you described could easily kill the charger though, you were shorting it with your method. 

marcl
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scaru wrote:

marcl wrote:
scaru wrote:

You were shorting the charger… If you want to measure charge current place a battery in it so the – side of the battery connects with the – contact plate. Then using a DMM on the 10 amp setting finish the circuit going from + on the battery to the positive contact plate. That number will be your charge current. 

Surely that will blow the fuse and read the discharge of the cell? How come the other two chargers read right but the last one doesn’t? Marc.

No, because what I described is simply measuring the charge current. What you described could easily kill the charger though, you were shorting it with your method. 

Ok, i will try that. But it still doesn’t explain why 2 of them give readings and the last one doesn’t. Have you any idea?

Marc.

Eagles may soar, but weasels don't get sucked into jet engines!

moderator007
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Scaru is correct. You read current with the DMM in the circuit. It has to pass through the meter to be able to read it.

Vieplis
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marcl wrote:
Surely that will blow the fuse and read the discharge of the cell? How come the other two chargers read right but the last one doesn’t?

Marc.


You are wrong. Read again what scaru wrote. You can not measure “right” at 0V.
I have another question. I have a charger which terminates at more than 4.35V (Don’t buy cheap chargers!). An unmarked DIP-8 chip is responsible for this value, does anybody know what chip this might be?
marcl
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scaru wrote:

marcl wrote:
scaru wrote:

You were shorting the charger… If you want to measure charge current place a battery in it so the – side of the battery connects with the – contact plate. Then using a DMM on the 10 amp setting finish the circuit going from + on the battery to the positive contact plate. That number will be your charge current. 

Surely that will blow the fuse and read the discharge of the cell? How come the other two chargers read right but the last one doesn’t? Marc.

No, because what I described is simply measuring the charge current. What you described could easily kill the charger though, you were shorting it with your method. 

Good stuff Scaru! 400/450ma from two of them the one that reads 4.16v however is only giving 250ma.

@Vieplis these may be cheap but they are very good little chargers!

Thanks,

Marc.

Eagles may soar, but weasels don't get sucked into jet engines!

Vieplis
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I would expect a 0.6A charger to give 0.6A… My 4.35V is certainly not good.
I have also one 14500 with exactly the same label as yours, this one gives 0.3A, 4.2V.

marcl
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Vieplis wrote:
I would expect a 0.6A charger to give 0.6A… My 4.35V is certainly not good.

Depends on the cells get some Samsungs Wink But you are right unless it’s supposed to, yours sounds knackered!

Marc.

Eagles may soar, but weasels don't get sucked into jet engines!

RedForest UK
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Remember to measure with a cell at a low voltage, if the charger is a good one it will user a CC/CV type algorithm. That means it would charge at it’s max charge current until the cell gets near fully charged before slowly decreasing charge current by inputting a certain voltage instead of a set current. The charge then terminates when the cell accepts less than a set minimum current threshold in that CV phase. (That’s how I understand it anyway, I may be wrong.)

This means that you can only read the max charge current of well-designed chargers when the cell being charged still has some way to go to reaching max capacity. It also means that as a cell gets older it won’t get blindly pumped up to the same voltage each time, but the charger can effectively tell to stop charging when it can’t take any more.

marcl
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RedForest UK wrote:
Remember to measure with a cell at a low voltage, if the charger is a good one it will user a CC/CV type algorithm. That means it would charge at it’s max charge current until the cell gets near fully charged before slowly decreasing charge current by inputting a certain voltage instead of a set current. The charge then terminates when the cell accepts less than a set minimum current threshold in that CV phase. (That’s how I understand it anyway, I may be wrong.)

This means that you can only read the max charge current of well-designed chargers when the cell being charged still has some way to go to reaching max capacity. It also means that as a cell gets older it won’t get blindly pumped up to the same voltage each time, but the charger can effectively tell to stop charging when it can’t take any more.

I think thats why I am getting 400/450ma. All my cells are around 4.1v. I need to run one down a bit and try again. But if what your saying is right then it add credence to these little chargers. As it seems to be lowering the current as the voltage goes up.

I shall do more tests. Thanks for you input everyone.

Marc.

(I’ll have to change that sore now, Red Wink )

Eagles may soar, but weasels don't get sucked into jet engines!