Arlec BC58112 v battery charger

[Roger Dewhurst]

I have an Arlec 12 volt battery charger which I accidentally blew up when
the 3 pin plug touched the chassis of my truck while the leads were clipped
to the battery. The circuit contains three resistors, what I think is a
small Zener diode, two large diodes and a peculiar elongated glass tube with
two wires leading in at one end. It has been glued in place between the two
diodes and connects to the input from the transformer. The glass tube is
about 30mm long and 5mm in diameter, It appears to be either gas filled or
evacuated. It reminds me slightly of a diode valve. Could it be some form
of capacitative device to smooth the waveform? Since the transformer
appears to be OK I suspect that it is either this tube device or the Zener
diode that has blown. Can anyone offer any suggestions? The Zener, if that
is what it is would be about 12.5 volts, would it not? The charger cost
less than $20 and a technician would charge twice that just to open the box!

R

 

[Phil Allison]

"Roger Dewhurst"

I have an Arlec 12 volt battery charger which I accidentally blew up when
the 3 pin plug touched the chassis of my truck while the leads were
clipped
to the battery.

** 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" ??

The circuit contains three resistors, what I think is a
small Zener diode, two large diodes and a peculiar elongated glass tube
with
two wires leading in at one end. It has been glued in place between the
two
diodes and connects to the input from the transformer. The glass tube is
about 30mm long and 5mm in diameter, It appears to be either gas filled
or
evacuated.

** Sounds like a fuse that has blown.



........ Phil

 

[Roger Dewhurst]

"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.

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

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" ??

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.

** Sounds like a fuse that has blown.

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

 

[Phil Allison]

"Roger Dewhurst"

"Phil Allison"


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

** 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.

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.

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

The unit is Double Insulated - right ?

Has the double square symbol on it.

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.

** 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 there are only two diodes instead of four
seems a little odd.

** 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

 

[Roger Dewhurst]

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

** What crazy drivel is this ???

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.
*******************************************

There is no circuit between those pins and anything else.

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.

You need to work out what actually happened - cos your explanation is

not right.

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

The unit is Double Insulated - right ?

Has the double square symbol on it.

It does carry the double square symbol.

** 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.

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?

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

El cheapo came to mind!

Roger

 

[Homer J Simpson]

I have an Arlec 12 volt battery charger which I accidentally blew up when
the 3 pin plug touched the chassis of my truck while the leads were
clipped
to the battery. The circuit contains three resistors, what I think is a
small Zener diode, two large diodes and a peculiar elongated glass tube
with
two wires leading in at one end. It has been glued in place between the
two
diodes and connects to the input from the transformer. The glass tube is
about 30mm long and 5mm in diameter, It appears to be either gas filled
or
evacuated. It reminds me slightly of a diode valve.

Can you post a picture on ABSE?

Could it be some form
of capacitative device to smooth the waveform?
No.

Since the transformer
appears to be OK I suspect that it is either this tube device or the Zener
diode that has blown. Can anyone offer any suggestions?

Do you own a multimeter?

 

[Phil Allison]

"Roger Dewhurst"
"Phil Allison"

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.

** So no current can flow and no damage can happen that way.

not right.

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

** Then your first para is pure fantasy.


BTW

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



......... Phil

 

[Peter Bennett]

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


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.

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?

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.


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.

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).

R

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

 

[Phil Allison]

"Peter Bennett"

A three wire output sounds strange - is it intended to charge two
batteries with a common ground?

** 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

 

[Roger Dewhurst]

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?

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

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.

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.

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).

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.

 

[Roger Dewhurst]

Can you post a picture on ABSE?

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

Do you own a multimeter?

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

 

[Phil Allison]

"Roger Dewhurst"

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.

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

Also known as Polyswitches.

Jaycar sell them.

A diode rectifier would only need a two wire input. What is the third
(black) wire from the secondary coil doing?

** Oh dear.

Look up " full wave rectifier " on Google.




......... Phil

 

[Phil Allison]

"Roger Dewhurst"

And what is ABSE?

** " alt.binaries.schematics.electronic "

Most news servers have it in their list.

Great for schems, JPEGs etc.




...... Phil

 

[Roger Dewhurst]

"Roger Dewhurst"



** " alt.binaries.schematics.electronic "

Most news servers have it in their list.

Great for schems, JPEGs etc.

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

R

 

[Ross Herbert]

I have an Arlec 12 volt battery charger which I accidentally blew up when
the 3 pin plug touched the chassis of my truck while the leads were clipped
to the battery. The circuit contains three resistors, what I think is a
small Zener diode, two large diodes and a peculiar elongated glass tube with
two wires leading in at one end. It has been glued in place between the two
diodes and connects to the input from the transformer. The glass tube is
about 30mm long and 5mm in diameter, It appears to be either gas filled or
evacuated. It reminds me slightly of a diode valve. Could it be some form
of capacitative device to smooth the waveform? Since the transformer
appears to be OK I suspect that it is either this tube device or the Zener
diode that has blown. Can anyone offer any suggestions? The Zener, if that
is what it is would be about 12.5 volts, would it not? The charger cost
less than $20 and a technician would charge twice that just to open the box!

R

The Arlec BC581 is a current model
http://www.arlec.com.au/pdfs/battery_chargers.pdf

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.

 

[Phil Allison]

"Roger Dewhurst"

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

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

** 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

 

[Homer J Simpson]

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.

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


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--

 

[jasen]

I have an Arlec 12 volt battery charger which I accidentally blew up when
the 3 pin plug touched the chassis of my truck while the leads were clipped
to the battery. The circuit contains three resistors, what I think is a
small Zener diode, two large diodes and a peculiar elongated glass tube with
two wires leading in at one end.

It has been glued in place between the two
diodes and connects to the input from the transformer. The glass tube is
about 30mm long and 5mm in diameter, It appears to be either gas filled or
evacuated. It reminds me slightly of a diode valve. Could it be some form
of capacitative device to smooth the waveform?

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)

Since the transformer appears to be OK

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

 

[Roger Dewhurst]

The Arlec BC581 is a current model
http://www.arlec.com.au/pdfs/battery_chargers.pdf

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?

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.

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.

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

 

[Peter Bennett]

"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.

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
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca