chris-g
|
| posted on 1/10/13 at 12:05 PM |
|
|
Battery Charger from Aldi - Repair
Hello All.
Last year I bought one of those battery charger/conditioners from Aldi. A couple of months ago it failed, completely dead but it had a 3 year
guarantee, unfortunately there were no more in stock so I was given a refund and told to throw the faulty one away. I have taken it apart and
discovered a blown fuse, resistor and possibly a FET in the power supply circuit. This is stretching my electronics knowledge so I am hoping some of
you clever people can answer a few questions for me.
The resistor is a reasonable size so I assume its of a low resistance and high wattage. The colours appear to be black, blue, violate (but could be
grey as the resistor is damaged) silver and brown. I make this to be 0.67 ohms, is that correct as it seems a very low value?
The resistor is connected to the source pin of a FET, part no TSF8N60M. I have tested the FET by connecting -ve lead of a multimeter set on diode mode
to the source pin and then measuring with the +ve connected to gate followed by drain. I get a very low reading (1 to 4) and putting a finger across
the pins has no effect on the readings. Is the FET dead? The testing was done with the FET out of circuit and on the bench. Also if it is dead can
someone recommend an equivalent or alternative as this FET is not stocked by RS or Farnell.
Thank you for any help.
|
|
|
|
|
coyoteboy
|
| posted on 1/10/13 at 12:13 PM |
|
|
Resistor is probably a current sense resistor (low resistance, high accuracy used to identify current flow by small voltage drop across it).
FET - not sure without sitting down and thinkin about it but they're normally uber-cheap to replace and may have been stressed so I'd
personally as it's the output stage I'd replace them anyway.
FWIW I found my cheap aldi charger is incorrectly identifying battery voltage - it's reading 13.6v at "float" when the considerably
better multimeter is reading 12.2.
|
|
|
MikeRJ
|
| posted on 1/10/13 at 02:08 PM |
|
|
If the current sense resistor is burnt, then it's probably because the FET has shorted Drain to Source. However, with switching regulators the
actual cause of this failure can be hard to find, FET's don't generally just fail for no reason at all. Very often it's due to
electrolytic capacitors drying out internally, which lowers their capacitance and increases their series resistance. This can upset the dynamics of
the control loop, causing the FET to be either switched on for too long and causing the transformer to saturate, or not being switched fully on which
massively increases power dissipation and causes thermal failure.
|
|
|
britishtrident
|
| posted on 1/10/13 at 03:29 PM |
|
|
Lidl have chargers on sale next week.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
40inches
|
| posted on 1/10/13 at 04:53 PM |
|
|
quote:
Originally posted by britishtrident
Lidl have chargers on sale next week.
I think I may get one, the Bike battery charger doesn't seem to like car batteries.
Lidl
|
|
|
chris-g
|
| posted on 2/10/13 at 10:48 AM |
|
|
Thanks for the info. So when I replace the resistor its important that its as close to the original value as possible? I am happy to replace the FET
but that exact FET doesn't seem to be available here, an internet search brings up data sheets but nowhere that I can purchase one. Any
suggestions for an alternative?
There is a big electrolytic cap but I assumed that was for smoothing. It doesn't seem to have the typical bulging end normally associated with a
duffer. I will replace anyway as they are cheap.
Might have to buy a new charger, I am expecting Aldi to have these in again this month as its nearly a year since I bought the first one and they were
available about the same time as the ones from Lidl.
|
|
|
