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Technical Help Forum
Started by NIEDS at 07-14-2010 10:48 AM. Topic has 8 replies.
  
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 07-14-2010, 10:48 AM
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NIEDS
Joined on 03-26-2010
Rochester, NY
Posts 8
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not being to electrical savy i might have a stupid question to ask.
im redoing the idiot lights into my gauges and using leds instead of incandescent bulbs.
ive read somewhere that there is a 7v regulator off the battery going into the controls area
and the bulbs for the idiot lights say 12v 3.4w.
in order to wire the leds with proper resistors i need to know the amount of volts coming out of these wires.
is it safe to assume its 12v as per the bulbs read? or is it 7v because of the regulator?
i know a multimeter should be able to tell me exactly what volts are coming out of there but i cant seem to figure
the damn thing out. i keep getting (-) readings and numbers bouncing all over. ive checked my grounds and used
the batterys neg terminal.
any help would be appreciated, id like to get the right #s before i start soldering
nieds
1980 CX500C
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07-14-2010, 2:32 PM
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bobbrumby
Joined on 12-30-2007
Australia
Posts 80
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the 7v regulator afaik is only for the temp guage. any 12v led should do but remember these are a light emiting diodes and the negative leg must be connected to the negative on the bike. You may aswell need resistors in paralell with the indicator idiot light leds to get the right current draw to opperate the flasher relay but i am not sure about that one.
83 cx500 custom (Australian Spec) 70,000km
05 vtr250 20,000km (Daily Ride)
82 xr200
04 xr400r
ct110 postie bike
"you meet the nicest people on a honda"
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07-14-2010, 2:45 PM
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Marty J.
 
Joined on 01-17-2008
Hammel, Denmark
Posts 158
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I've never tried it and this is pure guesswork, but I would imagine using an LED instead of an incandescent bulb for an indicator idiot light would not require adding a resistor. The change in current with an LED would be very small compared to the current draw of the two indicator bulbs, so the flasher relay would hardly be affected. It might blink very slightly more slowly but you would hardly notice the difference.
- Marty
'81 CX500A, '85 CX650E
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07-14-2010, 3:10 PM
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NIEDS
Joined on 03-26-2010
Rochester, NY
Posts 8
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the only thing is for an LED the voltage is way less than the incandescent. if the LED gets over loaded then it will blow, which is why you need resistors.
also, i couldnt find LED bulbs that were screw in replacements to the current bulbs, so im just cutting that sh*t out and splicing in LEDS.
1980 CX500C
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07-14-2010, 3:26 PM
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Shep
Joined on 01-30-2007
UK.2x1980CX500A
Posts 7,647
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07-14-2010, 5:03 PM
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BillRod
Joined on 11-09-2009
Richton Park, IL 33 miles SW of Chicago
Posts 350
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That resistor needs to be IN SERIES with the LED. Not parallel.
71 years old (April 1939)
Richton Park, Illinois
Just bought 1982 GL500 Naked 13,000 miles
Never worry about theory as long as the machinery does what it is supposed to do.
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07-14-2010, 8:33 PM
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marshallf3
Joined on 01-12-2009
Oklahoma City
Posts 1,542
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Also most LEDs draw around 20 ma, the voltage drop across them varies but it's usually 1.7 or 1.9V for Red, Orange and Yellow but higher for Green, Blue and White.
Any LED you buy should give you these specs. I buy all my LEDs from http://www.mouser.com
REmember that your +12V isn't always +12V, it's a bit higher when the battery is charging but LEDs are fairly forgiving.
Just use ohms law to figure out what value of resistor to place in series with any LED that doesn't already have an internal dropping resistor.
Let's say you want to use an LED that has a typical forward voltage of 1.9V and an average operating current draw of 20 mA. (0.02 Amps)
To run this LED off, say, 13.2V (alternator cranking a decent output) you need to drop 11.3V (13.2V - 1.9V) at 0.02 A
R = E/I (voltage drop divided by current)
R = 11.3V / 0.02 A = 565 ohms.
560 ohms is a commonly available value, however a 470, 510, 620 or 680 ohm would also work without much difference in brightness.
They don't need to be high wattage either, P= I^2R = (0.02)(0.02)(560) = 0.224 watts meaning I'd use a 1/2 watt or better resistor.
Be careful, some of the newer LEDs can crank out a ton of light with only 20 mA driving them, I doubt you'd want anything more than around 200 - 400 mcd at a decent viewing angle so the light is somewhat diverted instead of just coming out as a spotlight.
1979 CX500C
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96 & 98 GTP, 78 Chevy G30 400V8, 78 Gremlin 304V8, 65 Barracuda 273V8
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07-14-2010, 10:07 PM
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NIEDS
Joined on 03-26-2010
Rochester, NY
Posts 8
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thanks dude, i did however research all that stuff, my original question was just how much voltage is coming to those wires.
so from wat i gather is 12v +/- is a good bet
1980 CX500C
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07-14-2010, 11:41 PM
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vern401
Joined on 05-23-2010
Vass, NC
Posts 197
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Yes that is a good bet. I use a meter with a light that tells me when the voltage is 12-13VDC and it glows green for the indicator lights on my CX.
79 CX500 Custom
72 SL350 K2
78 CB750F
91 Kawasaki ZX600C4
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Honda CX500 & G... » CX500 GL500 Tra... » Technical Help ... » Re: electrical inquiry
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