On Thursday, 1 February 2018 10:36:22 UTC, Harry Bloomfield wrote:
ss wrote on 01/02/2018 :
Hopefully final question :-)

Would it be a fast blow or slow blow fuse?

My guess would be a slow blow, to allow for the initial in rush surge.

It could be anti-surge :-) or time delay.

RS have eleven (11) different speed ratings for fuses.

although as stated something with a delay of some sort would be best.

has brought this to us :
well be something on the scooter that is at fault although I doubt that

that can't be the cause

It would be trivially easy for someone not very careful with a tendency
to fiddle with things, to reverse the connections between battery and
charger.

Harry Bloomfield wrote:

ss presented the following explanation :
As for the 3A fuse, looking at the remains of the old one would I be
correct in saying it was in the form of an upside down U shape, as I see
there are 2 points of damage, the remains of a glass fuse and then the
longish wire with just a cap on it, I presume these were connected at
one point and I basically bridge that gap with the fuse.

It looks as if the wire ended fuse was mounted vertically, with the
upper wire folded over and back down to the PCB. Often they design
PCB's with component options. In this case it looks as if it might have
been designed for a fuseholder, but to save a few pennies they used a
wire ended fuse direct to the PCB.

It doesn't only save money. It also increases reliability, especially
for something that may work in a corrosive or damp atmosphere.

--

Roger Hayter

I'm still very sus of the bridge rectifier, I had this happen on the psu in
my sub woofer which blew the fuuses as well. The bridge was only rated at
the max current expected as a steady state, not peaks, two legs went short
and blew the fuse.
Brian

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This newsgroup posting comes to you directly from...
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"The Natural Philosopher" wrote in message
news
On 01/02/18 10:25, wrote:
On Thursday, 1 February 2018 09:14:01 UTC, ss wrote:
On 01/02/2018 08:33, Harry Bloomfield wrote:
ss used his keyboard to write :
Charger for a mobility scooter. One charger not working, I opened it
up and as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to
solder this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse
which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Could it be that if the batteries on the scooter were goosed that the
charger was trying to draw too much power and blew the fuse?

very unlikely. The huge current required to do that must have come from
the batteries, the charger would not be able to supply it.



Which would be why the fuse blew?

NT



--
Microsoft : the best reason to go to Linux that ever existed.

In article ,
says...

I have ordered a fuse from ebay, Yes I will try that Harry
as it may well be something on the scooter that is at fault
although I doubt that as the scooter was being used until
the batteries failed, who knows.

The scooter itself works ok as I replaced with new batteries.

You might not have ordered the correct fuse, I'm afraid.

I've just been taking another hard look at the picture and I'm
now convinced that there *is* a fuseholder, though not like
anything I've ever seen before.

If you look carefully, the botton end cap appears to be
sitting in a cup and I think that that is the other cup on the
end of the wire - look at the height of it compared to the
width - its much less than the length of a fuse cap!

It isn't easy to scale, but I reckon it is a 20mm fuse so a
mains fuse is too fat to fit the cups. It might also be useful
to know excactly what is engraved on the remaining end cap if
I'm right, you should be able to just pull it out.

Oh, and measure the diameter of the cap as well.


--

Terry

---
This email has been checked for viruses by AVG.
http://www.avg.com

On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:

ss used his keyboard to write :
Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

On 01/02/2018 19:29, Terry Casey wrote:
In article ,
says...

I have ordered a fuse from ebay, Yes I will try that Harry
as it may well be something on the scooter that is at fault
although I doubt that as the scooter was being used until
the batteries failed, who knows.

The scooter itself works ok as I replaced with new batteries.

You might not have ordered the correct fuse, I'm afraid.

I've just been taking another hard look at the picture and I'm
now convinced that there *is* a fuseholder, though not like
anything I've ever seen before.

If you look carefully, the botton end cap appears to be
sitting in a cup and I think that that is the other cup on the
end of the wire - look at the height of it compared to the
width - its much less than the length of a fuse cap!

It isn't easy to scale, but I reckon it is a 20mm fuse so a
mains fuse is too fat to fit the cups. It might also be useful
to know excactly what is engraved on the remaining end cap if
I'm right, you should be able to just pull it out.

Oh, and measure the diameter of the cap as well.


Ok here some images of the caps, back of board and front of board. The
cap wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

ss wrote:

Ok here some images of the caps, back of board and front of board

I presume those earth crimp-ring terminals were *not* dangling around
inside like that until you took it apart?

On Thursday, 1 February 2018 11:19:58 UTC, Harry Bloomfield wrote:
tabbypurr has brought this to us :

well be something on the scooter that is at fault although I doubt that

that can't be the cause

It would be trivially easy for someone not very careful with a tendency
to fiddle with things, to reverse the connections between battery and
charger.

that would do it. So it depends whether any wires have been messed with - the usual connectors won't go in the wrong way. And the scooter wouldn't function with its batteries wired in reverse - unless it's really ancient.


NT

On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

On 01/02/2018 20:32, Andy Burns wrote:
ss wrote:

Ok here some images of the caps, back of board and front of board

I presume those earth crimp-ring terminals were *not* dangling around
inside like that until you took it apart?



No they were fixed to the casing.

ss formulated on Thursday :
Ok here some images of the caps, back of board and front of board. The cap
wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

A much better idea of what we are looking at and it is a switch mode
type. The fuse is on the mains input side. If that is really intended
to be a fuse-holder, it is not one I have ever come across before. I
cannot see any obvious signs of damage, apart from the seriously
damaged fuse. Are there any obvious blast marks on the earthed casing
etc.?

I suspect there is no fault, apart from the obvious one, that your FIL
was messing about with it live and managed to short the fuse to earth/
metal casing. With that sort of blasted fuse, if there were a fault on
the PCB, the likelihood is that those diodes would also be well blasted
too - they are not.

On Thu, 1 Feb 2018 12:45:45 -0800 (PST), wrote:

On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

submitted this idea :
I'm puzzled by your comments. What sort of lead acid charger is not voltage
regulated?

I didn't actually mention it not being voltage controlled. I had in
mind it might have been a very basic simple charger, using basic
voltage sensing to switch a relay when a set voltage was reached across
the battery. I have one such in my workshop, which charges an emergency
starter battery/ min compressor type thing. You plug it into the mains,
it charges until the battery reaches a set voltage then switches the
charge circuit off. It then remains off/ not charging until the next
time the mains supply is cycled. It is rather a neat way to do it and
proving the mains supply is cycled very occasionally, such a battery
will be kept in good condition for decades, with little electrolyte
evaporation.

On 01/02/2018 20:50, Harry Bloomfield wrote:
ss formulated on Thursday :
Ok here some images of the caps, back of board and front of board. The
cap wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

A much better idea of what we are looking at and it is a switch mode
type. The fuse is on the mains input side. If that is really intended to
be a fuse-holder, it is not one I have ever come across before. I cannot
see any obvious signs of damage, apart from the seriously damaged fuse.
Are there any obvious blast marks on the earthed casing etc.?

I suspect there is no fault, apart from the obvious one, that your FIL
was messing about with it live and managed to short the fuse to earth/
metal casing. With that sort of blasted fuse, if there were a fault on
the PCB, the likelihood is that those diodes would also be well blasted
too - they are not.

The earths are ok, no burn marks.
I dont think the blasted fuse is in a fuse holder as such as when I
check on ebay they look similar ie as if they are in a holder.

On Thu, 01 Feb 2018 21:07:39 GMT, Harry Bloomfield
wrote:

submitted this idea :
I'm puzzled by your comments. What sort of lead acid charger is not voltage
regulated?

I didn't actually mention it not being voltage controlled. I had in
mind it might have been a very basic simple charger, using basic
voltage sensing to switch a relay when a set voltage was reached across
the battery. I have one such in my workshop, which charges an emergency
starter battery/ min compressor type thing. You plug it into the mains,
it charges until the battery reaches a set voltage then switches the
charge circuit off. It then remains off/ not charging until the next
time the mains supply is cycled. It is rather a neat way to do it and
proving the mains supply is cycled very occasionally, such a battery
will be kept in good condition for decades, with little electrolyte
evaporation.

But the givaway would be the rectifiers. A FW bridge in close physical
proximity yo the mains input would not be likely at all. The bridge
would be after the TX, unless of course the battery was of such small
capacity there would be little excess power to dissapate. But of
course you would have a supply derived directly from the mains using a
bridge, so you could not then rely on the polarity of the incoming
mains to provide "safe" terminal Voltages.

The fact that the driven device is a scooter makes your interpretation
of the circuit extreemely unlikely.

AB

On Thursday, 1 February 2018 21:05:05 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 12:45:45 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

I can only conclude you don't understand lead acid charging.


NT

On 01/02/2018 21:14, ss wrote:
On 01/02/2018 20:50, Harry Bloomfield wrote:
ss formulated on Thursday :
Ok here some images of the caps, back of board and front of board.
The cap wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

A much better idea of what we are looking at and it is a switch mode
type. The fuse is on the mains input side. If that is really intended
to be a fuse-holder, it is not one I have ever come across before. I
cannot see any obvious signs of damage, apart from the seriously
damaged fuse. Are there any obvious blast marks on the earthed casing
etc.?

I suspect there is no fault, apart from the obvious one, that your FIL
was messing about with it live and managed to short the fuse to earth/
metal casing. With that sort of blasted fuse, if there were a fault on
the PCB, the likelihood is that those diodes would also be well
blasted too - they are not.

The earths are ok, no burn marks.
I dont think the blasted fuse is in a fuse holder as such as when I
check on ebay they look similar ie as if they are in a holder.

I have known a suppression type capacitor to go short and the the
corresponding fuse to go in an old TV. In my case there was little left
of a conventional holder.

In this case the fuse is in series with the thermister.

I suspect the problem is whatever was plugged into CN3.

On Thu, 1 Feb 2018 13:28:38 -0800 (PST), wrote:

On Thursday, 1 February 2018 21:05:05 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 12:45:45 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

I can only conclude you don't understand lead acid charging.


NT
What aspect?

I must admit the chemistry is not something that I have dealt with for
some considerable number of years.

I am however keen to learn, just how would an expert such as your good
self approach charger design?

AB

On Thursday, 1 February 2018 21:52:28 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 13:28:38 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 21:05:05 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 12:45:45 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

I can only conclude you don't understand lead acid charging.


NT
What aspect?

I must admit the chemistry is not something that I have dealt with for
some considerable number of years.

I am however keen to learn, just how would an expert such as your good
self approach charger design?

AB

Lead acids are charged with voltage regulated chargers. There are 1 stage or better chargers have more stages. The charger must of course have overcurrent limit too, but it is the battery itself that limits i much of the time.

As opposed to NiCd & NiMH which require current controlled chargers.


NT

Fredxx expressed precisely :
In this case the fuse is in series with the thermister.

I suspect the problem is whatever was plugged into CN3.

You might be correct, but I couldn't think of anything representing a
load that might be part of a PSU. Without trying to trace out the
tracks, might CN3 be a mains on/off switch, or even a mains powered
neon warning light?

I have a scooter and its SMPSU in the hut. That PSU has a cooling fan,
I wonder if this unit also has one? The fan only runs when the unit is
doing a rapid charge.

wrote :
I can only conclude you don't understand lead acid charging.

As so often you are in the NG, you are wrong yet again. You have done
little to help the OP in this thread, other than try to wind those up
who are trying to help him - much more noise than signal.

On Thu, 1 Feb 2018 21:14:55 +0000, ss wrote:

snip

I dont think the blasted fuse is in a fuse holder as such as when I
check on ebay they look similar ie as if they are in a holder.

I think the general observation has been that the PCB may have been
designed to take a surface mounted / traditional fuse holder (that
would accept a std 20mm / 1-1/4") fuse, or (for cost savings), a wire
ended fuse, soldered directly to the PCB, possibly in alternative /
smaller holes.

Cheers, T i m

On Thu, 1 Feb 2018 14:21:39 -0800 (PST), wrote:

On Thursday, 1 February 2018 21:52:28 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 13:28:38 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 21:05:05 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 12:45:45 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

I can only conclude you don't understand lead acid charging.


NT
What aspect?

I must admit the chemistry is not something that I have dealt with for
some considerable number of years.

I am however keen to learn, just how would an expert such as your good
self approach charger design?

AB

Lead acids are charged with voltage regulated chargers. There are 1 stage or better chargers have more stages. The charger must of course have overcurrent limit too, but it is the battery itself that limits i much of the time.

As opposed to NiCd & NiMH which require current controlled chargers.


NT
That's deep!

So you have Voltage regulation?

Why do you need an overcurrent limit? You already have Voltage
regulation, so how can the current become excessive?


When you say the battery limits the current "much of the time", just
how much of the time?

At what point does the battery stop limiting the current and why
doesn't your Voltage regulation just reduce the Voltage to the point
where you are not reliant on the environmental variables of the
surroundings to influence current consumption?

AB

On 01/02/2018 21:34, Fredxx wrote:
The earths are ok, no burn marks.
I dont think the blasted fuse is in a fuse holder as such as when I
check on ebay they look similar ie as if they are in a holder.

I have known a suppression type capacitor to go short and the the
corresponding fuse to go in an old TV. In my case there was little left
of a conventional holder.

In this case the fuse is in series with the thermister.

I suspect the problem is whatever was plugged into CN3.

CN3 connects to the on/off switch on the outer casing.

On 01/02/2018 22:31, Harry Bloomfield wrote:
I suspect the problem is whatever was plugged into CN3.

You might be correct, but I couldn't think of anything representing a
load that might be part of a PSU. Without trying to trace out the
tracks, might CN3 be a mains on/off switch, or even a mains powered neon
warning light?

I have a scooter and its SMPSU in the hut. That PSU has a cooling fan, I
wonder if this unit also has one? The fan only runs when the unit is
doing a rapid charge.

might CN3 be a mains on/off switch...correct

Yes it has a cooling fan.

On 01/02/2018 22:34, Harry Bloomfield wrote:
wrote :
I can only conclude you don't understand lead acid charging.

As so often you are in the NG, you are wrong yet again. You have done
little to help the OP in this thread, other than try to wind those up
who are trying to help him - much more noise than signal.

Out of interest a previous poster mentioned a fuse holder, I googled
that and the one in the link appears to match the solder joints where
the blown fuse is.

https://www.cricklewoodelectronics.c...SABEgIEHPD_BwE

On Thu, 1 Feb 2018 20:22:21 +0000, ss wrote:

snip

Ok here some images of the caps, back of board and front of board. The
cap wont pull out but then it may have welded when it exploded.

I think you will find they were made like that and were actually
'welded' (spot) in the factory. ;-)

Cheers, T i m

ss wrote:

On 01/02/2018 20:50, Harry Bloomfield wrote:
ss formulated on Thursday :
Ok here some images of the caps, back of board and front of board. The
cap wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

A much better idea of what we are looking at and it is a switch mode
type. The fuse is on the mains input side. If that is really intended to
be a fuse-holder, it is not one I have ever come across before. I cannot
see any obvious signs of damage, apart from the seriously damaged fuse.
Are there any obvious blast marks on the earthed casing etc.?

I suspect there is no fault, apart from the obvious one, that your FIL
was messing about with it live and managed to short the fuse to earth/
metal casing. With that sort of blasted fuse, if there were a fault on
the PCB, the likelihood is that those diodes would also be well blasted
too - they are not.

The earths are ok, no burn marks.
I dont think the blasted fuse is in a fuse holder as such as when I
check on ebay they look similar ie as if they are in a holder.

Do you think they make the wire-ended fuses by crimping these caps with
leads to standard fuses? I can see that soldering directly to standard
fuses might affect their construction in unpredictable ways.



--

Roger Hayter

Harry Bloomfield wrote:

submitted this idea :
I'm puzzled by your comments. What sort of lead acid charger is not voltage
regulated?

I didn't actually mention it not being voltage controlled. I had in
mind it might have been a very basic simple charger, using basic
voltage sensing to switch a relay when a set voltage was reached across
the battery. I have one such in my workshop, which charges an emergency
starter battery/ min compressor type thing. You plug it into the mains,
it charges until the battery reaches a set voltage then switches the
charge circuit off. It then remains off/ not charging until the next
time the mains supply is cycled. It is rather a neat way to do it and
proving the mains supply is cycled very occasionally, such a battery
will be kept in good condition for decades, with little electrolyte
evaporation.

I think that would only work for trickle charging. If you want to
charge at a decent rate then the battery has to be charged at a somewhat
higher voltage, overlapping what would be the fully charged voltage.

--

Roger Hayter

On Thu, 1 Feb 2018 20:22:21 +0000, ss wrote:

snip

Ok here some images of the caps, back of board and front of board. The
cap wont pull out but then it may have welded when it exploded.

https://imgur.com/vCG2M8O

https://imgur.com/KhigJP1

https://imgur.com/71nQ3Pa

Do you have access to a DMM? If it has a diode test range on it it
might be interesting (and as I believe has been mentioned elsewhere)
to measure the 4 diodes to see if one (or more) are short circuit?

I recently repaired a multi-port battery charger that had two dead
diodes around the same area and similar on a PSU board for a big LCD
TV.

You might need to lift one end of any diode that appears to be short
circuit in case it's other components showing up as a short.

Cheers, T i m

On Thursday, February 1, 2018 at 5:32:16 AM UTC+11, ss wrote:
Charger for a mobility scooter. One charger not working, I opened it up
and as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to
solder this part if I can find a replacement.

https://imgur.com/a/QTZ0e

Looks like it is a time lag fuse; T denotes time lag fuse. F denotes fast acting fuse.

On Thu, 01 Feb 2018 19:29:19 +0000, Terry Casey wrote:

In article , says...

I have ordered a fuse from ebay, Yes I will try that Harry as it may
well be something on the scooter that is at fault although I doubt that
as the scooter was being used until the batteries failed, who knows.

The scooter itself works ok as I replaced with new batteries.

You might not have ordered the correct fuse, I'm afraid.

I've just been taking another hard look at the picture and I'm now
convinced that there *is* a fuseholder, though not like anything I've
ever seen before.

If you look carefully, the botton end cap appears to be sitting in a cup
and I think that that is the other cup on the end of the wire - look at
the height of it compared to the width - its much less than the length
of a fuse cap!

It isn't easy to scale, but I reckon it is a 20mm fuse so a mains fuse
is too fat to fit the cups. It might also be useful to know excactly
what is engraved on the remaining end cap if I'm right, you should be
able to just pull it out.

Oh, and measure the diameter of the cap as well.

I've been following this thread, not having followed the link to the
posted photo until now, and two things have become rather obvious from
that rather restricted view of the PCB showing the fuse and its close
proximity to what appears to be a mains voltage rectifier diode bridge.

Firstly, that fuse *is* a standard wire ended glass fuse[1] intended to
be soldered onto the PCB of a SMPSU and secondly, the small section shown
of the PCB looks typical of the mains input section of a cheap SMPSU
(there were no EMC filter components in evidence).

In theory, even cheap SMPSUs include overload protection so shouldn't
need to rely on a user replaceable fuse for such protection. However,
since even the best quality SMPSU can't be guaranteed against failure of
its high voltage switching transistor(s) which tend to go spectacularly
short circuit rather than go silently open circuit like a fuse, such
soldered in fuses are a mandatory requirement in all such SMPSUs
regardless of the expense of their manufacture simply to ensure that they
don't go up in flames and set light to whatever premises they're located
in.

Very few manufacturers would be willing to take the risk of a criminal
prosecution of Arson or Manslaughter (although it would seem that when it
comes to cheap knock off USB phone chargers, there are some who take a
more relaxed attitude to the risk of Manslaughter by electrocution).

In short, the reason for the soldered in fuse protection is to protect
against the fire hazard when (rather than if) another soldered in
component, the mains voltage rated switching transistor, blows short
circuit. The mains voltage fuse is deliberately made a non user
serviceable part simply because there's no point in replacing it without
replacing at least one or more other soldered in parts.

If the OP does go ahead with his plan to try testing it by powering it
up after soldering in a replacement fuse, all he's going to get for his
pain is a repeat fuse blowing event.

[1] Such glass wire ended fuses are typically wrapped in heat-shrink
sleeving to prevent glass shards being sprayed around the interior of the
PSU due to the very high fault current that is produced when a switching
transistor goes short circuit.

--
Johnny B Good

On Thu, 1 Feb 2018 23:31:45 +0000, (Roger Hayter)
wrote:

Harry Bloomfield wrote:

submitted this idea :
I'm puzzled by your comments. What sort of lead acid charger is not voltage
regulated?

I didn't actually mention it not being voltage controlled. I had in
mind it might have been a very basic simple charger, using basic
voltage sensing to switch a relay when a set voltage was reached across
the battery. I have one such in my workshop, which charges an emergency
starter battery/ min compressor type thing. You plug it into the mains,
it charges until the battery reaches a set voltage then switches the
charge circuit off. It then remains off/ not charging until the next
time the mains supply is cycled. It is rather a neat way to do it and
proving the mains supply is cycled very occasionally, such a battery
will be kept in good condition for decades, with little electrolyte
evaporation.

I think that would only work for trickle charging. If you want to
charge at a decent rate then the battery has to be charged at a somewhat
higher voltage, overlapping what would be the fully charged voltage.

It's interesting, not something that I have come across.

Not sure exactly how it would be done, probably using the terminal
voltage after a small load resistance and then using a timer to ensure
that charging was maintained for a significant period.

The terminal Volts alone couldn't be used as 12V batteries seem to be
happiest being charged at 13.8V, settling to 12.6- 12.7 V on removal
of the charger.

Although it,s a fair while since I played with batteries, I seem to
recollect that 13.8V was the voltage measured at almost every state of
the recharging process.

'Couldn't find anything via Google, one or two curves but really the
charge Voltage is to a great extent dependent on the source resistance
of the charger.

AB

On Wed, 31 Jan 2018 18:32:08 +0000
ss wrote:

Charger for a mobility scooter. One charger not working, I opened it
up and as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to
solder this part if I can find a replacement.

https://imgur.com/a/QTZ0e

As a temporary test you could just clean up the toasted bit of wire and
wrap some fuse wire between the two, with a dab of solder if you want.
If that vapourises there's probably no point sourcing and fitting the
proper fuse.

On Fri, 2 Feb 2018 03:08:49 +0000, Rob Morley
wrote:

On Wed, 31 Jan 2018 18:32:08 +0000
ss wrote:

Charger for a mobility scooter. One charger not working, I opened it
up and as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to
solder this part if I can find a replacement.

https://imgur.com/a/QTZ0e

As a temporary test you could just clean up the toasted bit of wire and
wrap some fuse wire between the two, with a dab of solder if you want.
If that vapourises there's probably no point sourcing and fitting the
proper fuse.
Someone suggested earlier that a 100W lamp could be wired across the
open ends.

That seemed a far more practical solution.

Not quite as practical as a minute or so with a DMM, but a reasonably
sound approach to the problem.

Faffing about with bits of burnt wire isn't the best approach. When
the cobble up fails to produce results its not going to be certain
that the connections to the burnt bits were reasonably Ohm free.

Even in a valid circuit a high resistance connection can produce
emsisions in the visible parts of the electromagnetic spectrum!!

AB

On Thursday, 1 February 2018 22:34:22 UTC, Harry Bloomfield wrote:
tabbypurr wrote :
I can only conclude you don't understand lead acid charging.

As so often you are in the NG, you are wrong yet again. You have done
little to help the OP in this thread, other than try to wind those up
who are trying to help him - much more noise than signal.

wrong on both points as usual

On Thursday, 1 February 2018 22:58:47 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 14:21:39 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 21:52:28 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 13:28:38 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 21:05:05 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 1 Feb 2018 12:45:45 -0800 (PST), tabbypurr wrote:
On Thursday, 1 February 2018 20:12:30 UTC, Archibald Tarquin Blenkinsopp wrote:
On Thu, 01 Feb 2018 08:33:20 GMT, Harry Bloomfield
wrote:
ss used his keyboard to write :

Charger for a mobility scooter. One charger not working, I opened it up and
as per image below it looks like some kind of fuse has blown.
Text on the board looks like 3A/2500AR.

Can anyone confirm and identify what I would need to replace.
I have limitations on electronic stuff but could probably manage to solder
this part if I can find a replacement.

https://imgur.com/a/QTZ0e

From what I can see in the image, it looks like a wire ended fuse which
has exploded. That suggests a serious fault.

Also from what I can see, it looks like a fairly crude charger.
transformer, bridge, then possibly a relay switching the charge current
on and off, driven by a basic voltage across the battery sensing
circuit.

Cobblers!

One does not need an NTC thermistor in a "crude" charger.

I would have serious doubts that terminal Voltage plays a big part in
the control feedback. The control is via current monitoring so a more
stable source of reference would be needed.

There would be no piddly little rectifiers in a "crude" charger
either, they would be after the tranny and would need to handle a few
Amps, assuming the charge process was to take less than 24 hours.

Incidentally an exploded fuse is a fairly minor fault from a
diagnostics perspective. Generally a few seconds with a DMM will find
the problem.

As to what happens when the little plastic thing with legs = 3 is
found to be S/C, is a completely different story.

AB

I'm puzzled by your comments. What sort of lead acid charger is not voltage regulated?


NT

The statement was "terminal Voltage".

Direct Voltage regulation isn't really an option. Have you tried
charging a 12Volt lead acid battery from 12Volts?

Have you tried charging from 14Volts?


Can you suggest a few drawbacks to using a supply regulated to give
either Voltage, or even one in between those values?

The internal resistance of a battery is dependent on a number of
things, age, temperature and the amount of charge stored, therefore
the terminal Voltage of the battery isn't the best starting point for
control.

AB

I can only conclude you don't understand lead acid charging.


NT
What aspect?

I must admit the chemistry is not something that I have dealt with for
some considerable number of years.

I am however keen to learn, just how would an expert such as your good
self approach charger design?

AB

Lead acids are charged with voltage regulated chargers. There are 1 stage or better chargers have more stages. The charger must of course have overcurrent limit too, but it is the battery itself that limits i much of the time.

As opposed to NiCd & NiMH which require current controlled chargers.


NT
That's deep!

So you have Voltage regulation?

Why do you need an overcurrent limit? You already have Voltage
regulation, so how can the current become excessive?


When you say the battery limits the current "much of the time", just
how much of the time?

At what point does the battery stop limiting the current and why
doesn't your Voltage regulation just reduce the Voltage to the point
where you are not reliant on the environmental variables of the
surroundings to influence current consumption?

AB

the keywords you're looking for a lead acid battery charging


NT

In article ,
says...


Out of interest a previous poster mentioned a fuse holder, I googled
that and the one in the link appears to match the solder joints where
the blown fuse is.

https://www.cricklewoodelectronics.c...SABEgIEHPD_BwE


Yes, they are quite common.

In the days before printed circuits became widely used,
similar clips were fastened to a sheet of insulating material.

The design of the clip included a solder tag that the
connecting wired were soldered to.



--

Terry

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In article ,
says...

Someone suggested earlier that a 100W lamp could be wired
across the open ends.

That seemed a far more practical solution.


Yes - a lamp limiter - common practice for enthusiasts
renovating old radios and TVs - especially TVs.

They usually have a bulb and bulbholder mounted on their work
bench in series with the mains supply with a bypass switch to
short out the lamp when they are satisfied that no damage will
result.

--

Terry

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