what watt bulb ??

SSDD · Post by **SSDD** » Wed Jun 08, 2005 7:16 am

Hi all, What watt bulb can the circuitry handle, im thinking of using a 12v LED & a 21watt 12 volt bulb for the shift light. Would this be ok or would it overload the components \ circuit board

Thanks
Steve

Paratime · Post by **Paratime** » Wed Jun 08, 2005 5:18 pm

The shift light output is controlled by a 2N2222 transistor. It is rated at 800mA max for the metal can style, the plastic are a little less, as I recall. Because it is probably in an enclosed space with no air flow, I wouldn't run more than 400mA through it. With the alternator running, 15 volts is not unheard of. Sooooooo.....

P=I*E
I=400mA
E=15V
P=400mA*15V= 6 Watts

Except for the ones that are brighter than the sun, LEDs use less than 100mA. Should be no problem. The shift light will have to be driven by a small relay, or it will only blink on, followed by a small puff of smoke from the MjLj. I would also use a clamping diode or a resistor on the relay coil, for extra protection against the voltage spike when it gets switched off.

SSDD · Post by **SSDD** » Wed Jun 08, 2005 6:38 pm

Thanks Mate, so what your basicly saying is "NO" shall i just use an LED then ??

Thanks Again
Steve

Post by **brentp** » Wed Jun 08, 2005 6:46 pm

I would recommend using a high brightness LED for your shift light. with a proper current limiting resistor it'll work great.

Josh_b · Post by **Josh_b** » Wed Jun 08, 2005 10:08 pm

hello,
could someone put together a little shiftlight wiring diagram, as it doest just seem to be a simple case attaching an LED to the shiftlight output,
cheers

Paratime · Post by **Paratime** » Thu Jun 09, 2005 1:02 am

You can use pretty much any light you want for the Shift output. All that is required is the addition of a small relay to boost the signal. Any electronics store will have a suitable part. The only specification is a 12 volt input, with a coil resistance of 75 ohms or better. For example, DigiKey has part# Z140-ND for $2.70. The coil is rated at 360 ohms, so it will only draw 42mA, well below the 400mA max. The output contacts are rated at 12 Amps max, so you could run up to a 180 watt bulb. If you don't notice that, you have other problems.

To wire in the relay, attach one side of the coil to Ignition voltage (key on), and one of the two "contacts" to Ignition voltage. Now attach the other side of the coil to the Shift wire (pin 12). Finally, attach one wire from your light to the other "contact" on the relay, and the other wire from the light to ground.

When the shift wire is energized, the relay will turn on, and current will flow through the lamp. The relay protects the MegaJolt from the high lamp current.

As I stated before, I would also put a 300 ohm resistor across the coil terminals of the relay, to suppress any voltage spikes.

Paratime · Post by **Paratime** » Thu Jun 09, 2005 1:14 am

Sadly, there is no single LED diagram, since LEDs come in a variety of voltages and operating currents.

This page:

http://www.superbrightleds.com/led_info.htm

has a web calculator for finding the proper resistor for your particular LED. Use 14 volts for the supply voltage, and then you need the forward voltage (this is the operating voltage for a particular type of LED) and the operating current.

When you get the resistor value, go buy that resistor, and wire thus:

Attach one leg of the LED to Ignition voltage. It has to be the positive leg, but if you get it wrong, nothing will be damaged, but the light, won't.

Next, attach one side of the resistor to the other side of the LED.

Test the LED by momentarily grounding the other side of the resistor with the key on. If no light, switch LED leads.

Finally, attach the other side of the resistor to the Shift (or other Program output) wire.

FUN!

greypride · Post by **greypride** » Thu Jul 14, 2005 11:48 am

im just trying to get my head around this...

So i can use a led shift light using the megajolt output with out a relay if i have

12v> resistor for LED> LED> Megajolt shift light connection

If i want to use a bulb, i must use a relay

is this correct?

Oliver Sedlacek · Post by **Oliver Sedlacek** » Thu Jul 14, 2005 12:13 pm

Yes, that's it. By the way, many LEDs wont take a reverse bias of 12V, so connecting them the wrong way round will blow them. Another option though is to drive two LEDs in series, so you've got 12Ign, resistor (try 560 ohms), LED1, LED2, Megajolt shift pin.

Hey presto, twice the light.

Post by **brentp** » Thu Jul 14, 2005 3:00 pm

Exactly right on the LED.

It can be possible to do the same with an incandescant bulb, you first need to measure it's current draw directly using a meter or, estimate it based on the rated wattage.

Volts X Amps = Watts
Amps = Watts / Volts

So if you have a 5W bulb running at 12v it would draw about .417 Amps. That's right near the capacity of the user defined outputs.

But you should want to use an LED because it's response time is so much faster than a incandescant bulb- no element to heat up.

ZetecXR2 · Post by **ZetecXR2** » Fri Sep 30, 2005 10:55 am

Would a 12v standard LED (One with a resistor built in) be ok? Obviously the in-built resistor is the correct one for a 12v supply, and in a car you can see 14-15v max. Could I still use this type of LED without a resistor, without turning my MJLJ box into a smoldering lump?

Paratime · Post by **Paratime** » Sat Oct 01, 2005 5:34 am

The 12v LED will have a maximum voltage rating from the manufacturer. The actual maximum voltage will be 10-20% higher than this, to allow for manufacturing irregularities. So, counting line loss, and the .3 or so that the CE junction drops, you're probably fine. Of course, just to be safe, I'd put a couple standard diodes in the line, to suck up an extra 1.4 volts.

Autosport Labs

what watt bulb ??

what watt bulb ??

Magic Smoke

Thanks Mate, so what your bas

smoke = bad :)

shiftlight wiring

Lights, camera, thrown rod!

LED 1, 2, 3!

so..

Yes, that's it. By the way,

Exactly right on the LED.

Standard LEDs?

How much too much, is too much?