Arlec BC58112 v battery charger

"Roger Dewhurst"

** That should not happen !

The DC output terminal of a car battery charger should have NO connection to the AC supply ground conductor.

You just found out the reason.

Sure that Arlec charge was built like that or was it modified by some zealot to make it "safer" ??

** Sounds like a fuse that has blown.

....... Phil

That makes sense. I should have written 2 pin, not 3 pin plug.

zealot

No. I bought in new and can see no signs of modification. I had only used it two or three times.

There is a two wire power supply to the primary of the transformer but a three wire output, two blue and one black. The two wire supply should be safe enough because the only metal parts that can be touched are the output clips. Everthing else touchable is plastic.

When the power is on and the clips are on the battery none of the lights go on, but two should. Whe a clip is pulled off the battery, with the power still on, all the lights go on! That suggests to me that transformer is OK and the fault lies elsewhere. The LEDs are OK, the resistors appear to be OK and there is no reason for them not to be. The big diodes should be as tough as old boots. That just leaves the Zener (?) and the glass tube device.

is

It does not look like any fuse that I have ever seen! It is a fixture and obviously not intended to be changed. It seems to be part of the rectifier section of the circuit. That there are only two diodes instead of four seems a little odd. It would have been easy enough to put in a four diode rectifier.

R

"Roger Dewhurst"

** What crazy drivel is this ???

There is no circuit between those pins and anything else.

You need to work out what actually happened - cos your explanation is not right.

** Shame if the insulation in the tranny ever fails.....

The unit is Double Insulated - right ?

Has the double square symbol on it.

** A "last line of defence " fuse would NOT be fitted to allow user replacement.

One often sees a bi-metal over current trip in the same spot.

** That is how nearly all battery chargers are made - makes for lower cost and less diode voltage and heat loss.

Shame the AC tranny is under utilised.

....... Phil

But it did. A bunch of sparks and now a dud charger.

I should have put a couple of lines between the two statements above.

******************************************* Thus:

You: The DC output terminal of a car battery charger should have NO connection to the AC supply ground conductor.

Me: That makes sense.

*******************************************

Indeed the resistance between the power supply plug pins and the secondary coil outputs appear infinite i.e there appears to be no connection between the primary circuit and the secondary and thus no connection between the power plug and the output clips.

not right.

I do not have an explanation merely a bunch of symptoms of the thing blowing up!

It does carry the double square symbol.

and

Is this a glass tube with both wires going at one end?

If it is a 'last line of defence' fuse and the output is rated at 2.5 amps should I try replacing it with a 3.0 amp fuse?

What are the chances that it is the Zener that has blown?

cost

El cheapo came to mind!

Roger

Can you post a picture on ABSE?

No.

Do you own a multimeter?

"Roger Dewhurst" "Phil Allison"

** So no current can flow and no damage can happen that way. ** Then your first para is pure fantasy.

BTW

Try replacing that glass tube thing with a 5 amp thermal cut out.

........ Phil

A three wire output sounds strange - is it intended to charge two batteries with a common ground? How are you supposed to connect the three leads to the battery?

Is this glass device 1.25 inches long by .25 inch diameter - if so, it sounds like a common North American fuse. The appearance of the thing inside the glass can vary depending on whether it is a fast-blow or slow-blow fuse.

Two diodes sounds like a full-wave rectifier - a perfectly reasonable and common design. Four diodes are required for a bridge rectifier (also reasonable and common).

--
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
new newsgroup users info : http://vancouver-webpages.com/nnq
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"Peter Bennett"

** Err - the AC tranny has three output wires.

The third ( black) one is the centre tap of the winding - allowing use of a two diode, full wave rectifier.

...... Phil

Three wires from the secondary coil to the electronics but two wires from the electronics to the battery clips.

go

power

OK

be

as

tube

the

tube

filled

and

rectifier

diode

My estimate was a bit on the low side! It is 40mm x 9mm exactly. That is a bit bigger. The white glue smeared over the glass makes it difficult to see what is inside. The tube is pointed at the end with no wires and flattened at the end with the wire inputs. Just inside the tube there is a dark coloured bead which appears to keep the wires separate. The battery charger is almost certainly made in China.

A diode rectifier would only need a two wire input. What is the third (black) wire from the secondary coil doing? It does connect to one side of the tube device. The other side of the tube connects to the negative output and to one of the LEDs.

My wife has the camera at the moment! And what is ABSE?

Yes, and a soldering iron but I am not ready to start de-soldering wires until I have a better clue about what I am doing!

R

"Roger Dewhurst"

** Ok - now it sounds like a PTC = positive tempco thermistor.

Also known as Polyswitches.

Jaycar sell them.

** Oh dear.

Look up " full wave rectifier " on Google.

........ Phil

"Roger Dewhurst"

** " alt.binaries.schematics.electronic "

Most news servers have it in their list.

Great for schems, JPEGs etc.

..... Phil

Subscribed to that but I have to wait for the camera.

R

when

clipped

is a

tube with

the two

tube is

filled or

some form

Zener

if that

cost

the box!

The Arlec BC581 is a current model

With these cheap and nasty chargers a common method of charge control is to use a thermal current switch, which is what I suspect the elongated glass tube is. Does it appear to have a metallic contact in it?

To avoid any fancy regulation circuitry the idea was that the transformer operated at maximum voltage output up to its VA rating at all times and when the current exceeded a set value the thermal switch operated to cut off the charge current. After many successive cycles the battery voltage would gradually rise to the rectified output voltage of the transformer (which hopefully would be in the region of

14V) thus the charge current would no longer be sufficient to operate the thermal switch. This is where the danger of these cheap chargers lies - they keep charging as long as the battery is connected and if not disconnected after a full charge is reached they will lead to the demise of the battery.

"Roger Dewhurst"

** What you did was this:

The AC plug was resting on the car body with the two pins in contact with bare metal - no conduction until YOU connected the leads to the car battery IN REVERSE !!

Large current pulses flowed in the secondary winding as you attached the battery clips generating large primary voltage spikes and hence the visible sparks at the AC plug pins.

Then the glass tube thermistor device failed from the over current ituation - it is the only protection the charger has from reversed leads.

..... Phil

It's a center tapped transformer with two diodes for full wave output. Quite normal.

--
.

sounds like a self-resetting thermal, fuse. it's unlikely to be the problem if the cause was as you describe, if it works it shouls read as a low resistance (less than 0.1 ohm)

does it hum when you plug it in? can you light up a small 12V lamp by connecting it to the output side of the transformer?

Bye. Jasen

There appear to be two parallel strips of metal terminating in something looking a bit like the points in an ignition system. The two strips of metal are separated by a bead at the input end. The 'points' appear to be fully closed.

I see now that the two main outputs from the secondaty coil supply the two diodes and the centre tap supplies one side of this thermal current switch. The other side of the TCW is connected to the negative battery clip. The outputs from the two diodes are connected together and to the positive battery clip. The rest of the circuit, which is hard to follow, is in the middle somewhere. If the TCW is closed the charger should work as long as the secondary coil is OK? But the secondary should be protected against reverse current by the diodes and against excessive forward current by the TCW? That seems to leave the thing which looks like a Zener. Would that be a 12.5 volt Zener? On reading all the comments and thinking about it some more I think that I may have just connected the clips to the battery the wrong way round! I have been using a battery charger for years and have never made this mistake before, but I suppose that there is always a first time. Assuming that is what I have done which elements in the circuit would you expect to be destroyed?

Roger

Oops - I somehow read that as three wires out of the charger. Three wires from the transformer to the full-wave rectifier makes sense...

--
Peter Bennett, VE7CEI  Vancouver BC, Canada
peterbb4 (at) interchange.ubc.ca  
new newsgroup users info : http://vancouver-webpages.com/nnq
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Vancouver Power Squadron: http://vancouver.powersquadron.ca