Battery Charger Repair ?

[raden]

In message , the_constructor writes

Where are you, and how heavy are they ?

I can take a look if you want

[raden]

In message , George writes

No - I would say that he's talking about the fuse, wouldn't you if you'd actually read what he wrote

[Alang]

How?

[Pete C]

Often the output caps, a TV repair shop should be able to check and replace them.

If DIYing remember to put new ones in the right way round ;)

cheers, Pete.

[Andy Dingley]

A _what_ shop ?

[Owain]

Is "the right way" defined as "the way they don't pop", ir is it more technical than that?

Owain

[Palindrome]

Sealed lead acid batteries can gas during charging. If the battery is charged incorrectly, the gases produced may not be recombined back into water as fast as they are being produced. Pressure valves will eventually trip and the gas vented - resulting in permanent loss of electrolyte. Allow this to continue and there will be no electrolyte left..so one incorrect recharge *can* kill the battery.

Charging at much too high a current can lead to the internal structure of the battery deforming. If this leads to a short between plates, the result can be catastrophic.

Pressure relief valves are often non-resettable - they are there only to stop the battery exploding under fault conditions. Once such non-resettable valves have tripped*, gases will not be contained and further recombination will not happen. Even correct charging can result in gassing and loss of more electrolyte.

etc.

*They can do so with enough force to send the the valve cover 20 foot or more across the room. BTDTGTTS.

[Dave Plowman (News)]

Could be but not exclusively.

And equally important make sure they are low ESR ones.

[Dave Plowman (News)]

Most electrolytics are polarised and have the negative marked. Unlike other types of caps which aren't polarity sensitive.

[The Natural Philosopher]

You forget that I=Vdiff/R..drive from a low voltage and the current reduces as the battery charges. However in theory at least, and rather horrendously in practice sometimes, a low power supply impedance will ultimately end up in I tending to infinity with the usual result..

[Palindrome]

Nope. The I decreases because the Vdiff decreases - not because R increases. R remains constant. Even cheap chargers usually limit Imax for high VDiff - too many people connect chargers to car batteries with the 6v12v slide switch set incorrectly. Things have moved on from selenium rectifiers and moving iron meters..

However, the basic point is that "cheap and cheerful" car battery chargers should not be used with batteries of the type normally fitted to mobility scooters. It certainly can end up with things heading towards infinity - such as bits of the battery. ;)

[Pete C]

Hi,

One of these should do if you can change the battery connector over:

Poss a bit cheaper on Ebay.

cheers, Pete.

[Pete C]

Or try here:

cheers, Pete.

[Owain]

I knew that :-)

But if you put it in the wrong way round does it just pop or would something else bad happen? I.e. would trial and error with one spare capacitor suffice?

Owain

[Pete C]

Be sure to plug the uncased supply into a hard-to-reach socket just before putting it down on your lap...

Not usually a pop, more 'this power supply will self destruct in FIVE seconds' c.f. James Bond.

cheers, Pete.

[Owain]

The last time I played with electrolytics and a 9v battery they swelled and elongated gently until finally squeezing some fluid out in a little dribble.

Owain

[Palindrome]

Life is full of disappointments.. ;)

Electrolytics have weakened fracture lines in the top now - in the past it was entirely possible for the case to detach and literally rocket off the board..especially with valve equipment using high voltage capacitors.

A 9v battery will have a fairly high internal impedance and won't be able to dump a lot of energy very quickly into a faulty component. Hence the result of a fault will be a little tame.

Similarly, a well-designed switch mode power supply will sense that an overload is present and shutdown - before a lot of energy has been transferred from the mains side of the hf transformer. There are mains side capacitors that can fail fairly dramatically.

However, for real excitement, try a UPS... A lot of 12v lead acid batteries in series, a lot of stored energy, a very low source impedance. It can sometimes be difficult to actually *find* the capacitor..

[FKruger]

Thats the Maplin one but £11 cheaper. Doesn't supprise me ;)

[Palindr☻me]

Thanks for the link, Pete and "F". I hadn't come across this company before. They seem to ahve some good kit at a reasonable price.