What is a MAL ?
for “Motion Activated Light” of course !
quite popular as outside lights and can be found in various forms.
sense Infra Red radiation at a certain wavelength which matches the
heat radiated by the human body.
These particular units are designed to be installed over
the existing lamp battern, and held in place by the battern and
As no electrician is needed to install them, they prove to be
Some are described as “Oyster Lamps”, as the over all appearance
them suggests Oysters ?
friend approached me with this problem :
His sensor light had stopped working !
the bag he had presented to me, was a familiar looking lamp minus
given me one to fix a long time ago but at that time I couldn’t fix
desperate to get it going as he lives in a semi rural area with no
Having the light come on at night was very convenient for him.
him I would see what I could do …
(Privately though, I didn’t hold
much hope of
overall design was quite clever in so far as ease of installation was
concerned, that was where the cleverness stopped !
within was an
appalling design !
The circuitry was designed to operate directly from
Now, there is nothing wrong with this providing it is done
correctly, but unfortunately, the
whole lot was assembled on cheap phenolic circuit board.
burns and will catch fire quite easily !
To work on
the beasts safely, an isolation transformer is required.
a transformer with a 36V output.
It was just a matter of calculating
value of capacitor required as a voltage dropping element.
reactance of the
capacitor acts like a resistor in this circuit.
A suitable value was to
and temporarily installed.
A suitable lamp was made from three 12Volt 5Watt
automotive lamps in series.
As I had no
circuit available, some tracing out of the circuitry was
that there was no output from the PIR sensor.
There should have been
output as I was sitting right in front of it !
There was a 0.22uF
capacitor stuffing it up !
After replacing that item, the unit began working
Finding that 1N914/1N4148 were being used as mains rectifier diodes was
ridiculous, so I replaced them with 1N4007's !
The original small signal diodes only have a reverse voltage
The nominally 240V RMS mains however peaks at around
340V (excluding common spikes).
volt rating of the replacement diodes meant peace of mind for me!
confident, I then dug
out the other unit that I had given up on a year or so ago.
Now that I
unit working I could make measurements and compare the voltages at
I replaced the tantalum capacitor and the rectifier diodes.
found that tantalum capacitors should only be used as decoupling
higher powered supplies …
They go very leaky in signal circuits or as timing
unit still wouldn’t work.
determined that the LDR or something around it was to blame.
the amount of ambient light and will only allow activation at night
the LDR and that seemed to be the culprit.
The second unit was now
so I thought !
When the lamps were returned to their owner, one of them
It just happened to be the one that I had replaced the LDR
owner then reported the fact that it would still turn on during the
would mean that some juggling of resistor values was going to be
solve that problem. I
told him to use the other one in the mean time.
seen my friend or his MAL for a while now.
I’ll tackle the faulty lamp
I just keep thinking of that appalling design and the many
it there must be out there.
I keep asking myself … HOW DID THEY EVER GET
APPROVED ? Or didn’t they bother!