BMW K bikes (Bricks)

You are not connected. Please login or register

View previous topic View next topic Go down  Message [Page 1 of 1]


club_c

club_c
Life time member
Life time member
I want to test my Hall sensor and injectors with an LED light. I know the recommendation has been a 3.3v LED and 470 ohm resistor in series, but all I could get was a 2.2v light. What resistor am I going to need? I picked up a 40 pack of assorted resistors, so I sure hope in there will be the one that someone here is going to recommend.

    

Crazy Frog

Crazy Frog
admin
admin
This is not rocket science.

A 2.2v LED is rated for 0.02 amps. you have to drop the voltage by 10v. To calculate the value of the resistance, use the ohm law formula: Resistance = Volts divided by Amps = V/I = 10/0.02 = 500 ohms.
Your source of power being the battery, the voltage is not exactly 12v. If the engine is running, the alternator will deliver up to 13.5v.
At 13.5v, you should drop the voltage by 11.3v. The value of the resistance will be 11.3/0.02 = 565 ohms
In practice, anything between 470 or 560 ohm will work for the common LED requiring 2.2 volts

The two leads are called: a (or +) for anode and k (or -) for cathode (yes, it really is k, not c, for cathode). The cathode is the short lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not an official identification method). The resistor has to be installed on the anode (+).

Calculating LED light and resistors - How To? Ledak10


__________________________________________________
Calculating LED light and resistors - How To? Frog15Calculating LED light and resistors - How To? Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

club_c

club_c
Life time member
Life time member
How do you know all this stuff?

    

phil_mars

avatar
Life time member
Life time member
Should we go into colour codes for the resistors Smile although the multimeter should put you in the ballpark.


__________________________________________________
Regards,
Phil
    

club_c

club_c
Life time member
Life time member
The kid at 'The Source' where I bought the resistors showed me how to read them, but I like Phil's idea better. I just have to go through 40 of them to find the one I want (40 for $4)...

    

Crazy Frog

Crazy Frog
admin
admin
Here is a very nice small free software to give you the color code for a resistor.

Bert


__________________________________________________
Calculating LED light and resistors - How To? Frog15Calculating LED light and resistors - How To? Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

K-BIKE

avatar
Life time member
Life time member
One minor issue it does not matter which lead the resistor goes on the LED will not be affected. One can also purchase for very little money a 12 volt regulated LED intended for car use which is tolerant of the voltage swings on a car or bike which needs no resistor and can be incorporated into a voltage test light instead of a filament lamp usually inside them. The LED can also be put across the injectors and because the turn on and off so quickly one can easily see if the injector is receiving a stream of firing pulses. All in all a handy diagnostic tool to carry on the bike. As is a cheap digital meter.
Regards,
K-BIKE

    

robmack

robmack
Life time member
Life time member
Or the old fashion way, memorization.

Politically incorrect diddely

When I was taking electrical engineering, we used a rather politically incorrect diddely to remember the order of colours. It probably is less used nowadays. It was a very male oriented profession in the day. It worked because I've remembered the colour code to this day using it.



Last edited by robmack on Fri Aug 20, 2010 8:47 pm; edited 1 time in total


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

club_c

club_c
Life time member
Life time member
It's 2010, do we still say this stuff?

    

Rickmeister

Rickmeister
Life time member
Life time member
Also, Wattage might need to be considered...
20mA through say 470 Ohms (P=I squared x R) approx = 200mW
My 2 Ohms worth!...

    

Crazy Frog

Crazy Frog
admin
admin
Ulrich_Grabau wrote:My 2 Ohms worth!...

And what would be the color of your resistance? faded? Twisted Evil

Lets not confuse people. 470 to 560Ohms is what you need.


__________________________________________________
Calculating LED light and resistors - How To? Frog15Calculating LED light and resistors - How To? Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

Crazy Frog

Crazy Frog
admin
admin
@robmack wrote:Or the old fashion way -- memorization

I'd love to comment, but this is a public forum and I would have to moderate myself!
This is just a 'funny' way to remember the order of the color code. We cannot always take statements to the first degree.

To reply to K-Bike, you are right about the resistance being installed on any lead.
Using the Anode is just the way that I always use to regulate the voltage. Just my choice.
Sorry about this 'misinformation'


__________________________________________________
Calculating LED light and resistors - How To? Frog15Calculating LED light and resistors - How To? Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

Crazy Frog

Crazy Frog
admin
admin
Here is the basic of electricity. It applies to your bike, car, house........
Electricity is something that you cannot see, but if you touch it you feel it. Why is that?

Using the following triangle makes an easy way to determine the relationship between voltage, current and resistance when making Ohm's law calculations. Just cover the unknown quantity to determine the needed calculation.
As Ulrich_Grabau stated, we could go further, but these basic formulas should be enough for everybody's needs:

E = Voltage (pressure) in volts
I = Current (flow rate) in amperes
R= Resistance (friction) in ohms.

Calculating LED light and resistors - How To? Ohmtri10

The interpretation of this triangle is:
E=IxR
I= E/R
R=E/I

alles klar? (Yes we are riding a panzer and when I talk to my bike, I sometimes speak German to her -she's a lady-) Alles Klar means "all clear" in German.


__________________________________________________
Calculating LED light and resistors - How To? Frog15Calculating LED light and resistors - How To? Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

Dennis

Dennis
Platinum member
Platinum member
Ah yes, the old Ohm's Law. In Oz industry we (Fitters) have a saying about electricians - What's the difference between a computer and an electrician ? Answer - you only have to punch the information into a computer once.

    

charlie99

charlie99
VIP
VIP
Calculating LED light and resistors - How To? 44271


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OCalculating LED light and resistors - How To? Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

RicK G

RicK G
admin
admin
@Dennis wrote:Ah yes, the old Ohm's Law. In Oz industry we (Fitters) have a saying about electricians - What's the difference between a computer and an electrician ? Answer - you only have to punch the information into a computer once.

Now Now that is unkind as I am both. I did an apprenticeship (for want of a better word) with the old PMG as a tech and then an Adult apprenticeship with Hornibrooks as a fitter in marine engineering from 73 to 76 so who ya gonna punch now Razz Razz Razz Nah nah nah nah nah nahhh Laughing Laughing

    

View previous topic View next topic Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum