Testing H4 car bulb with multimeter
Using a multimeter, what resistances would I expect to get from a
working H4 car headlight bulb? Thank you for any info. |
Testing H4 car bulb with multimeter
"Stan" wrote in message
... Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Thank you for any info. If this is a "normal" halogen bulb like this http://www.bestrestproducts.com/cele...4-HP_240-1.jpg then no resistance would mean it is dead. I think the pinouts are, looking at the bottom of the bulb with a terminal on the left, right and top Left terminal is common Top terminal is low beam Right terminal is high beam So you need to measure between the left pin and the top, then the left and the right. Sparks... |
Testing H4 car bulb with multimeter
On Mon, 15 Jan 2007 01:00:21 -0000, Sparks wrote:
then no resistance would mean it is dead. Quick get a patent on it for room temperature super conductivity. B-) Bulbs are either a few ohms (working) or lots of ohms as in open circuit (bust). -- Cheers Dave. pam is missing e-mail |
Testing H4 car bulb with multimeter
"Dave Liquorice" wrote in message
ll.com... On Mon, 15 Jan 2007 01:00:21 -0000, Sparks wrote: then no resistance would mean it is dead. Quick get a patent on it for room temperature super conductivity. B-) Bulbs are either a few ohms (working) or lots of ohms as in open circuit (bust). -- Cheers Dave. pam is missing e-mail Lol, Arse! That's what I actually meant of course! |
Testing H4 car bulb with multimeter
Stan wrote:
Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Very low indeed, and too low to measure with any accuracy with a normal multimeter. Say it's 55 watts at 13.8 volts. Resistance is voltage squared over power, so 13.8^2 / 55 i.e. about 3.5 ohms when hot. When measuring cold you can divide that by about 15, so about 0.2 ohm. HTH -- Andy |
Testing H4 car bulb with multimeter
"Stan" wrote in message ... Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Thank you for any info. provided there is contact between any two pins it will work (because the neutral is common) mrcheerful |
Testing H4 car bulb with multimeter
In article ,
Stan wrote: Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Just measured one - 0.4 ohm. I'd guess it will vary somewhat between makes and depending on ambient temperature. -- *I have plenty of talent and vision. I just don't care. Dave Plowman London SW To e-mail, change noise into sound. |
Testing H4 car bulb with multimeter
Stan pretended :
Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Thank you for any info. Usually you can check them without a meter - just give the lamp a sharp tap with your finger tip and see if the filament vibrates excessively, as if broken. If you really want to test it... One of the three pins is common - connected to both filaments, the other two are the main and dip beam connections. With a multimeter and assuming the lamp is good, you should get a value of a few ohms between any two pins. The two pins which have the higher value between them, means that the third pin is the common. With care you could test the lamp across a 12v battery. Similar to above, the two pins which produce the dimmest light out, means that the third unconnected pin is the common. -- Regards, Harry (M1BYT) (L) http://www.ukradioamateur.co.uk |
Testing H4 car bulb with multimeter
Stan wrote: Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? Zero resistance (short circuit) or as close to it as you're likely to be able to measure with a cheap meter and simple test leads. You might be able to see the diference when you have two filaments in series, but you're unlikely to measure any difference between the high and dipped beams, even though they're of different powers. Resistance of them goes up when they're hot, but a meter won't deliver enough power to notice this. Working resistance of a bulb is v^2/w, so about an ohm or two. They'll be under an ohm when cold. |
Testing H4 car bulb with multimeter
"Stan" wrote in message
... Using a multimeter, what resistances would I expect to get from a working H4 car headlight bulb? See responses below but why would you want to? |
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