How do you test 12v spotlights?

[Rednadnerb]

I was trying to figure out whether a 50w 12 volt spotlight bulb had blown and used the multimeter to see what voltage there was at the contacts, nothing registered, I tried it on another known working spot and still nothing. I thought the multimeter might be faulty so tested it on the 12 car battery. It registered 12.7 volts so it is OK.
What is going on?

Thanks

Brendan.

[Chris Bartram]

Put the meter on a resistance or continuity range and measure the bulb
out of circuit. It should read quite low when cold.

[Graham.]

I am guessing you had your meter set to measure DC volts instead of AC
volts.
Why don't you pull the bulb out and test it with the resistance or
continuity range?

--
Graham.

%Profound_observation%

[ARW]

Graham. wrote:
> On Thu, 4 Jul 2013 14:04:34 -0700 (PDT), Rednadnerb
> <bhar...@hotmail.co.uk> wrote:
>
>> I was trying to figure out whether a 50w 12 volt spotlight bulb had
>> blown and used the multimeter to see what voltage there was at the
>> contacts, nothing registered, I tried it on another known working
>> spot and still nothing. I thought the multimeter might be faulty so
>> tested it on the 12 car battery. It registered 12.7 volts so it is
>> OK. What is going on?
>>
>> Thanks
>>
>> Brendan.
>
> I am guessing you had your meter set to measure DC volts instead of AC
> volts.

:-)

It happens.

Life is a learning curve.

--
Adam

[Dave Plowman (News)]

In article <c6cb93fe-2950-4c9e...@googlegroups.com>,

You were checking the socket to see if there was 12 volts present? If it
is a SMPS rather than transformer, it may not switch on unless the minimum
load is present, and a DVM presents virtually no load.

However, it's easier to check the bulb - simply set the DVM to resistance.
You will get a very low reading on a good bulb - perhaps 5 ohms or so.

--
*Also too, never, ever use repetitive redundancies *

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[harryagain]

"Rednadnerb" <bhar...@hotmail.co.uk> wrote in message
news:c6cb93fe-2950-4c9e...@googlegroups.com...

Flat battery in your multimeter.
Needed to measure resistance but not voltage.

[Rednadnerb]

Thank you everyone.

I know how to test the bulbs for continuity, that bit is not a problem.
The answer that it is SMPS rather than transformer seems the most likely explanation for why I cannot test the connectors. I am assuming that it is 12v DC not AC but I think I tested for AC as well.

[Muddymike]

Test the bulb on the car battery, simple!

Mike

[The Natural Philosopher]

12V AC at several KHz (electronic transformer) or 50Hz (real toroid)
wont register on a DC meter


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.

[Rednadnerb]

I guess my question should have been 'How do I use a multimeter to test that there is power at the place (bayonet?) where you insert the spotlight bulb pins?'

[John Williamson]

Rednadnerb wrote:
> I guess my question should have been 'How do I use a multimeter to test that there is power at the place (bayonet?) where you insert the spotlight bulb pins?'

If it's supplied by a SMPS, then you may need a load to circumvent any
safety cut-off. So, I would suggest first checking the bulb, and using
that or another identical one to confirm power. Otherwise, you need to
gain access to the back of the socket.

You *could* possibly make up an extension lead with the right plug and
socket combination and use that as a break-out to check for power with
the bulb connected. It is, though, possible that the frequency of the
output on the SMPS is too high to register on your meter, even on the AC
ranges. Try putting a transistor radio on AM or FM nearby to check for
RF interference.

Or a damp finger... Give Darwin's law a chance. :-?

12 volts *shouldn't* do any damage.

--
Tciao for Now!

John.

[John Rumm]

and even with the meter on AC you might get odd results on those modern
SMPSU style "transformers", since the waveform out is unlikely to be
very sine like.


--
Cheers,

John.

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