Electronics help

[whisky-dave]

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.

[Harry Bloomfield]

[e-mail] has brought this to us :

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.

[Roger Hayter]

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

[Brian Gaff]

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

[Terry Casey]

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.

[Archibald Tarquin Blenkinsopp]

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

[ss]

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.

[Andy Burns]

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

[tabbypurr]

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

[tabbypurr]

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

NT

[ss]

No they were fixed to the casing.

[Harry Bloomfield]

ss formulated on Thursday :

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.

[Archibald Tarquin Blenkinsopp]

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

[Harry Bloomfield]

[e-mail] submitted this idea :

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.

[ss]

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.

[Archibald Tarquin Blenkinsopp]

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

[tabbypurr]

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

NT

[Fredxx]

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.

[Archibald Tarquin Blenkinsopp]

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

[tabbypurr]

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