How does a battery charger stop charging

[Kal_B]

I can not determine cathode from anode.

In diode mode:

Positive to small wire and negative to big wire = direct short/ zero resistance
Reverse polarity of above test = same result

Any another tes/ connection of leads results in no meter reading at all. That means placing one probe on small wire and other on bolt connection and reverse or one probe on big wire and one probe on bolt and reverse.

Thanks
Kal

 

[chemelec]

It Should be Tested OUT OF CIRCUIT.
But it Sounds like it is SHORTED and BAD.

 

[Kal_B]

Thanks chemele. I tested both of the out of circuit and got the same result. I will get new ones and see the difference.

It Should be Tested OUT OF CIRCUIT.
But it Sounds like it is SHORTED and BAD.

 

[spec]

Hi Kal,

You can't test high power components the same way that you test low power components.

The reason is leakage current which the meter will just see as a short circuit. Some high power diodes for example, have leakage currents of tens of miliamps.

The measure of a diodes rectification efficiency is its back to front ratio (BFR), which is the ratio between the forward current and reverse current. Some of the early automobile alternator diodes were incredibly leaky; not sure what modern alternator diodes are like.

Schottky diodes are fast and have a much lower forward voltage drop than normal silicon diodes, but Schottky diodes are very leaky.

What you need to do is connect a 5V battery/power supply in series with a 47 Ohm, or so, resistor across the terminals of high power components and measure the current that flows with your multimeter.

spec

 

[Kal_B]

Thanks spec. Across which terminals? I still haven't been able to determine with any certainty which is which.

And I can not see anywhere anything resembling a rectifier. How could that be?


Kal

 

[spec]

Thanks spec. Across which terminals? I still haven't been able to determine with any certainty which is which.

And I can not see anywhere anything resembling a rectifier. How could that be?


Kal

Hi Kal,

I will detail a test procedure when I wake up.

It is possible that the battery charger uses a center-tapped transformer/transformers so, with that arrangement, only two SCRs would be required: the SCRs in that arrangement would not only be controlling the average charge current, but also doing the rectification.

spec

 

[Kal_B]

Thanks spec. The transformer is a Lester E81749 - 180h which I was able to find pictures of on Google but no data sheet.
I will keep digging though.


Kal

 

[spec]

POST ISSUE 1 of 2017_02_23

Hi Kal,

Below is a schematic as promised this morning (UK).

The circuit on the left is the two SCR rectifier/current controller that I mentioned, an elegant topology, but it does require a center-tapped transformer secondary.

The circuit on the right is for testing SCRs.
(1) With the switch open the ammeter should show zero current or a low current (1 mA?).
(2) When the switch is closed the ammeter should read around 50 mA.
(3) When the switch is then opened the current reading should still be 50mA.
(4) When the battery is removed and reconnected the ammeter current reading should be essentially zero, as (1) above.

The small sized terminal on your SCRs will definitely be the gate.

With a 5V battery, as shown, or power supply, you will do no damage whatever way you connect the SCR to the test circuit.

spec

 

[john1201]

Hello everyone,

I couldn't login for some reason so I had to re-register.

I have an old (very old) pallet lift battery charger that I think is overcharging the batteries and took it apart to see what's going on inside and couldn't find how the charger knows that the batteries are charged. It basically has transformers, circuit board, contactor, a fuse (T-Tron JJN-80) , a breaker and a charge gauge.

In general, what kind of sensing devices are used with theses kind of chargers.

Thanks
Kal

How the battery Charger works?
Microchip-based electronic circuits to sense how much charge is stored in the batteries, figuring out from such things as changes in the battery voltage. The main componemt Diode is used in series with the battery .. so when the battery is fully charged, it stops charging

 

[Kal_B]

Thanks spec. I will try it this weekend.

John,

There is a circuit board and it's sealed with some resin that its very difficult to determine, even by eye, if any component is burnt.
It may very well be the circuit board but I am guessing there has to be something else that senses the current change for the board to make the decision.

Kal

 

[john1201]

Thanks spec. I will try it this weekend.

John,

There is a circuit board and it's sealed with some resin that its very difficult to determine, even by eye, if any component is burnt.
It may very well be the circuit board but I am guessing there has to be something else that senses the current change for the board to make the decision.

Kal

Yes you can check the current with the ampere meter at the input of the circuit and the output of the circuit. If the circuit is break from inside then we do not get the correct output or may not get the any output.

If the circuit board is sealed and the circuit is break than that circuit is not of any use. You have open it and if possible try to correct the circuit.

 

[Kal_B]

Thanks everyone. I changed the two SCRs and the charger works very well.

Thanks a lot.
Kal

 

[john1201]

I have one question.
If we do not remove the charger after the battering being fully charge then there may be the chances of explosion of Lithium batteries?

because i heard the many cases of explsion of lithium batteries in the **broken link removed**.

Is this true.

 

[alec_t]

It is true, if the charger is not smart enough to recognise that the battery is fully charged and switch itself off (or into standby mode).