How about the brand and model number of the charger. Perhaps we could determine from manufacturer’s literature whether it automatically senses and corrects polarity.

 

Can the charger be opened non-destructively, to identify the internal control IC?

 

Does the top part of this holder come off? Maybe it fell down, came off and was put back the other way......... (the spring may be part of the top part)

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Pictures 1 to 3 - These are photos of the charger (model number MTLC-04200-1000)
Picture 4 - I took off 4 rubber feet from the bottom to reveal some crosshead screws holding the charger together.
Picture 5 - Testing and checking the meter.

I have not yet opened the charger.

 

I wonder if the regulator chip inside the charger has failed, and what you see is some "leakage" of voltages passing through the controller chip. The charger must be rectifying the AC to DC and have a floating DC circuit.
Can't explain how this (reversal) could all happen, but if everything you say is true, then I would suspect the chip inside the charger has gone wonky.

 

I cannot understand what has happened but I have a single 18650 mains operated battery charger which I've used for several years to charge the 18650 battery

Several faithful years of service - now in failure mode; are they that expensive? It may be time to buy new.

I believe some batteries can be charged in reverse, especially if they are dead, though I don't know about Lithium cells.

I've seen that first hand. Back in the early 80's I came across some mercury cell batteries that were old and no longer useful. Not fully understanding their nature, I took some of them home. Sure enough, they wouldn't charge. However, one I accidentally connected in reverse polarity and the darn thing took a charge. A REVERSE charge. The positive end had a negative voltage on it. I don't know how that happened, but it did. So I tried another. It charged reverse polarity. Tried a third, fourth, fifth and sixth, and they all gave plenty of power. They were on the order of size of a D cell battery. And I used them as such until I accidentally shorted one. Darn near started a fire. The wife insisted I get rid of them. Wish I had them now. Those suckers had some darn kick to them.



There's the problem! You plugged it in upside down.



Just kidding.

 

Have you tried charging any other batteries with it in the correct position and in reverse? If so, what have been the results?

And finally, since I am no expert on this, when the charger was functioning normally one could assume it was charging FULLY correctly. But now if it's charging reverse, is there any protection for over voltage or over current? If something has failed, it's conceivable that the safety circuitry may also be in failure, thus presenting a fire hazard. Or worse.

I still think it may be a better / safer bet to just retire the old unit and get a new one.

 

It is interesting that in your first photo of post #24 the "Charging" light is on, though there is no battery inserted in the charging position. Has it always done that?

Do you know the brand name of the manufacturer?

 

It is interesting that in your first photo of post #24 the "Charging" light is on, though there is no battery inserted in the charging position. Has it always done that?
Do you know the brand name of the manufacturer?

Yes, it always shows a green light when connected to the mains and without a battery.
If an uncharged battery is inserted (in this case the reverse way round), a red light shows until the battery is fully charged then the green light shows indicating the battery is fully charged.

If the battery is inserted the correct way, the green light shows all the time and the battery will not charge.

I do not know the manufacturer's name but if you look up MTLC-04200-1000 on the internet there is lots of results.

I can provide more photos of the 18650 battery (I only have one 18650 battery) showing you what happens if anyone wants to see.
I have not seen anything like this before so I'm at a loss as to why this is happening. I wouldn't normally post a thread if I could work why this is happening but I can't work it out.
I'm just hoping that someone had a cogent explanation and can close this thread.

 

Follow-on question: And now does it work that way but with the battery installed backwards?

 

I think he would have noticed if the battery charged in reverse. That is not what he is saying. He is saying the + terminal on the charger has become the negative and it charged normally when the battery is reversed, and not when it is inserted normally.

 

It is possible to reverse charge a charge depleted battery effectively changing its polarity.
So what the battery looks like is important.
Is the + terminal originally labeled?? Is it mechanically obvious which is + terminal.
Now, knowing positive terminal, what is voltage/polarity of the battery?

 

It is possible to reverse charge a charge depleted battery effectively changing its polarity.
So what the battery looks like is important.
Is the + terminal originally labeled?? Is it mechanically obvious which is + terminal.
Now, knowing positive terminal, what is voltage/polarity of the battery?

I was thinking earlier, I want to have another look at the battery but it's in the torch at the moment and it's getting late here now and dark so soon bedtime. I will look at it tomorrow morning.
I would like to measure the voltage using the meter and take some photos then reduce the charge in the battery then put it in the charger and take some more photos. The mystery continues tomorrow.....please stay tuned.

 

Are we digressing? The issue is not about whether a battery can be reverse charged.
The charger has changed its output polarity. How? That's the mystery.

 

Are we digressing? The issue is not about whether a battery can be reverse charged.
The charger has changed its output polarity. How? That's the mystery.

Agree.

I have proposed two possible explanations, both of which seem unlikely.

1. Someone has pulled a prank on him by opening it up and switching the wires. There could be evidence of this tampering if this is correct.

2. The charger is capable of sensing polarity and correcting it, and it has failed when the battery is in correctly but still works when the battery is reversed. A board with an H-bridge driving the connections to the battery would partially confirm this.

 

Agree.
I have proposed two possible explanations, both of which seem unlikely.
1. Someone has pulled a prank on him by opening it up and switching the wires. There could be evidence of this tampering if this is correct.
2. The charger is capable of sensing polarity and correcting it, and it has failed when the battery is in correctly but still works when the battery is reversed. A board with an H-bridge driving the connections to the battery would partially confirm this.

Firstly number 1 is an utterly ridiculous accusation and should be ignored and erased. I am the only one who uses the charger no one else is here to touch it.
Number 2 - I do not know, maybe.

Below are photos of the charger that I have taken over the past day. For some bizarre reason the charger is now for back to normal. There is something about this charger which is very mysterious. It seems I have to check which end is positive and negative before I put a battery on charge.

Photo 1 - Checking the battery before charging
Photo 2 - Checking the charger before charging - the positive and negative connections are now correct
Photo 3 - Checking the charger before charging but the positive and negative leads to the meter are reversed.
Photo 4 - Placing the battery into the charger and checking the battery voltage that is now 3.184v and the charger red light is on showing that the charger is charging.
Photo 5 - Checking the battery voltage after the green light has appeared.

 

Hmm. "Curiouser and curiouser" said Alice.
As an aside, I do admire the battery manufacturer's bravery in naming the brand UltraFire.

 

Am I missing something? I thought you were finding a positive voltage at the negative end of the charger. Your photos show a negative charge at the negative end. I'm confused.

 

Am I missing something? I thought you were finding a positive voltage at the negative end of the charger. Your photos show a negative charge at the negative end. I'm confused.

The spring should be negative and it only shows up as negative in the photos. There must be something missing...

 

The spring should be negative and it only shows up as negative in the photos. There must be something missing...

@Tonyr1084 1084 Oh, the TS is saying it is back to normal! That's what was missing.