Post by thread:[PICLIST] Turn signal Lightbulbs

I have a 12V 27W light bulb in my car turn signals. The bulb measures 1 Ohm. So I think theirs about 2.2 Amps current flowing. 1) I cant even get them to light outside my car using my power supply. I am using some regular alligator clips and touching them to the light bulb. The supply is set to 12 Volts and im measuring 3 amps. I am a little hesitant to increase the current because I dont know what im doing...Whats a safe way to get them to light? Shouldnt they be slightly lit if I only supply 1 Amp of current? 2) Whats a cheap way to increase the resistance on the line so they will blink faster. I havent seen pots that can handle 30W and I hear they are quite expensive ($45). Is there some other ways that I can vary the resistance (variably by hand or digitally) on the line? Greg ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

Greg Wrote > I have a 12V 27W light bulb in my car turn signals. > The bulb measures 1 Ohm. So I think theirs about > 2.2 Amps current flowing. > > 1) I cant even get them to light outside my car > using my power supply. I am using some regular alligator > clips and touching them to the light bulb. The supply is set to 12 Volts > and im measuring 3 amps. I am a little hesitant to increase the current > because I dont know what im doing...Whats a safe way to get them to > light? Shouldnt they be slightly lit if I only supply 1 Amp of current? > 1. Alas a light bulb is a non-ohmic conductor, like you measured, the cold resistance is 1 ohm, if it stayed 1 ohm then 12 amps would flow at 12 volts = 144 watts, as it gets hotter the resistance increases and bulb settles at 27 watts or (volts x volts / watts) 5.3 ohms. So youre 3 amp supply just cant persuade the bulb to get hot enough to increase its resistance. The second part about more resistance to change the flashing rate... I would be tempted to remove the flasher unit and put an electronic one in its place, there have been many such units published in electronic hobbiest magazines, with clever little bulb failure warnings etc.. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________

Lightbulbs have an extremely nonlinear resistance- they will draw much more than their rated current on turn-on. If you want to be really careful- add a large capacitor to the output of the power supply, turn on the supply, and then attach it to the lightbulb, the capacitor should absorb the initial high current demand of the lightbulb to get it to the ~2.5A steady state condition. One way to effectively increase the resistance would be to PWM (pulse width modulate) the light bulb- using a transistor to rapidly cycle the lightbulb on and off. Though you aren't really increasing the resistance (unless you look at the circuit over time in terms of power delivered to the bulb), this should do what you want. Matt Bennett {Original Message removed}

> I have a 12V 27W light bulb in my car turn signals. > The bulb measures 1 Ohm. So I think theirs about > 2.2 Amps current flowing. > > 1) I cant even get them to light outside my car > using my power supply. I am using some regular alligator > clips and touching them to the light bulb. The supply is set to 12 Volts > and im measuring 3 amps. I am a little hesitant to increase the current > because I dont know what im doing...Whats a safe way to get them to > light? Shouldnt they be slightly lit if I only supply 1 Amp of current? > > 2) Whats a cheap way to increase the resistance on the line so they will > blink faster. I havent seen pots that can handle 30W and I hear they are > quite expensive ($45). Is there some other ways that I can vary the > resistance (variably by hand or digitally) on the line? > > Greg > If your car uses a bi-metalic type flasher unit, then they can be carefully tweaked to flash faster or slower by judicious bending of the bimetalic arm inside. Adding resistance just to speed up the flashers is not the way to go. The lamps will be dimmer and therefore less easily seen in bright light, and the resistor will have to dissipate a lot of power. We have 22 Watt flasher lamps over here in the UK, wonder if they are the same fitting? (Bayonet cap type) That would speed up the flashers without signifgicantly reducing light output. Mike

Add another 12v load to the line...maybe a 10W bulb. Install it in some enclosure with holes to let heat escape and tuck it in the trunk. BTW, don't you decrease the resistance (increase current) to make it blink faster? Greg Hastings wrote: {Quote hidden}> > I have a 12V 27W light bulb in my car turn signals. > The bulb measures 1 Ohm. So I think theirs about > 2.2 Amps current flowing. > > 1) I cant even get them to light outside my car > using my power supply. I am using some regular alligator > clips and touching them to the light bulb. The supply is set to 12 Volts > and im measuring 3 amps. I am a little hesitant to increase the current > because I dont know what im doing...Whats a safe way to get them to > light? Shouldnt they be slightly lit if I only supply 1 Amp of current? > > 2) Whats a cheap way to increase the resistance on the line so they will > blink faster. I havent seen pots that can handle 30W and I hear they are > quite expensive ($45). Is there some other ways that I can vary the > resistance (variably by hand or digitally) on the line? > > Greg > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com -- Salaam. --- Jason Erik Muhammad ======================================== E-Mail: spam_OUTmilsumaiTakeThisOuTexecpc.com ICQ # : 12978762 ======================================== .:::. ,,, _(- -)_ / ( ) \ \_/ : \_/ |_/ \_| | | | -TRY PRAYER-

If you have access to Electronic Design, June 12,2000 look at page 135. The author used a 7555 to drive a pair of FET's to toggle the rate of 50W bulbs. ____________________________________________________________________ Get free email and a permanent address at http://www.netaddress.com/?N=1