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U_W v2.0
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PostPosted: 21:23 - 03 Nov 2012    Post subject: electronics question. Reply with quote

i need an ignition activated electrical source on the bike, the thing is i need to take the voltage and current down to no more than 6v @ 750ma.

any ideas how to do this? i dont mind soldering up a small circuit to do the job but would rather an easy option ideally.

mucho thanko.
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The Artist
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PostPosted: 21:27 - 03 Nov 2012    Post subject: Reply with quote

1. It's electrics, not electronics.

2. Just need a transformer like a laptop power supply but find something that uses 6v.

3. Wire it into the loom in the lights power supply pre switch.
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U_W v2.0
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PostPosted: 21:29 - 03 Nov 2012    Post subject: Reply with quote

fair enough, thanks artist. however, if i need a transformer it'd need to be small, i.e "chuck it in the headlamp bowl after coating in heatshrink" small.

would it be possible?
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lihp
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PostPosted: 21:30 - 03 Nov 2012    Post subject: Reply with quote

just use a voltage divider.

google it if unsure. make sure the resistors you use can handle the power that you will be running
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U_W v2.0
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PostPosted: 21:31 - 03 Nov 2012    Post subject: Reply with quote

hum hum, alrighty, i'll google for that, pretty good and condensing circuit sizes hehe.

i dunno, all this for an effing warning light lol.
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The Artist
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PostPosted: 21:32 - 03 Nov 2012    Post subject: Reply with quote

https://www.ebay.co.uk/itm/Waterproof-DC-DC-Converter-12V-Step-down-to-6V-3A-15W-Power-Supply-Module-/221118134791?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item337baafa07
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carvell
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PostPosted: 21:34 - 03 Nov 2012    Post subject: Reply with quote

The Artist wrote:
1. It's electrics, not electronics.

2. Just need a transformer like a laptop power supply but find something that uses 6v.

3. Wire it into the loom in the lights power supply pre switch.

1. Nothing wrong with calling this electronics. Electrics implies domestic / commercial work and high voltage AC.

2. A laptop power supply?! No laptop power supply will ever be 6V. Also, I assume you are referring to a car powered laptop supply? Obviously a mains one won't work.

3. You'd be much better off using a relay from something like the rear brake light. There are guides on this forum on wiring in an ignition controlled relay.

OP: You can get multi-voltage cigerette light adapters, like this:
https://www.ebay.co.uk/itm/Ring-Multi-Voltage-Car-Dc-Power-Adapter-Charger-Rms11-/130468382079?pt=LH_DefaultDomain_3&hash=item1e6085857f&_uhb=1

That'll do you, combined with the relay. Or you could skip the relay step and wire it directly to the rear brake light, but you'd be much better off with a relay.
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U_W v2.0
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PostPosted: 21:35 - 03 Nov 2012    Post subject: Reply with quote

The Artist wrote:


ooo thats interesting, 3amps will probably cause a fire though, although it wont take alot to modify it for a lower ampage.

input values should be suitable for the bike i think.

see how things progress then eh? thanks gents.
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carvell
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PostPosted: 21:38 - 03 Nov 2012    Post subject: Reply with quote

Usually_Wrong wrote:
ooo thats interesting, 3amps will probably cause a fire though, although it wont take alot to modify it for a lower ampage.

Any power supply will only supply what your device draws.

It could be be a 1000 Amp supply - it wouldn't matter, the device will only draw 720 mA.
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U_W v2.0
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PostPosted: 21:39 - 03 Nov 2012    Post subject: Reply with quote

carvell wrote:
The Artist wrote:
1. It's electrics, not electronics.

2. Just need a transformer like a laptop power supply but find something that uses 6v.

3. Wire it into the loom in the lights power supply pre switch.

1. Nothing wrong with calling this electronics. Electrics implies domestic / commercial work and high voltage AC.

2. A laptop power supply?! No laptop power supply will ever be 6V. Also, I assume you are referring to a car powered laptop supply? Obviously a mains one won't work.

3. You'd be much better off using a relay from something like the rear brake light. There are guides on this forum on wiring in an ignition controlled relay.

OP: You can get multi-voltage cigerette light adapters, like this:
https://www.ebay.co.uk/itm/Ring-Multi-Voltage-Car-Dc-Power-Adapter-Charger-Rms11-/130468382079?pt=LH_DefaultDomain_3&hash=item1e6085857f&_uhb=1

That'll do you, combined with the relay. Or you could skip the relay step and wire it directly to the rear brake light, but you'd be much better off with a relay.


ho hum, i was hoping not to reveal this yet but oh well. heres what its for.

im taking a spare brake switch and mounting it to my carb and using 2 leds wired up to the switch with the leds enclosed in a little cube with the choke symbol on which nowhere elysium is kindly doing for me (paid job of course, im not that tight hehe).

idea being, when i forget to turn off the choke there'll be a little display on the cluster to remind me.

just need to sort the power supply, i was just going to use a 9v battery but trying to keep this looking as "OEM" as possible, so a 9v isnt really practical, plus even on 2 leds, well 9v batteries just suck for capacity lol.
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carvell
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PostPosted: 21:41 - 03 Nov 2012    Post subject: Reply with quote

What do you need the 6V supply for?

Why can't you just connect the LED to 12V, with an appropriate series resistor?
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U_W v2.0
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PostPosted: 21:43 - 03 Nov 2012    Post subject: Reply with quote

because the last time i wired leds directly to the 12v source with resistors the wire grew far to hot, so hoping to reduce the voltage and current pre led/switch wiring.

so purely saftey.
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The Artist
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PostPosted: 21:45 - 03 Nov 2012    Post subject: Reply with quote

carvell wrote:
What do you need the 6V supply for?

Why can't you just connect the LED to 12V, with an appropriate series resistor?


Or buy 12v led's...
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carvell
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PostPosted: 21:45 - 03 Nov 2012    Post subject: Reply with quote

You did something wrong then I'm afraid!

An LED is not going to be pulling enough current to get anything hot.

You can connect an LED to 12V perfectly happily, you just need to choose the correct resistor value.
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P.
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PostPosted: 21:46 - 03 Nov 2012    Post subject: Reply with quote

Why don't you just start bike on choke, put jacket, lid and gloves on, ride to the end of the road and turn it off?
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carvell
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PostPosted: 21:47 - 03 Nov 2012    Post subject: Reply with quote

Or buy "12V LEDs", indeed. These have a built in resistor which allows you to connect the LED directly to a 12V battery.
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U_W v2.0
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PostPosted: 21:47 - 03 Nov 2012    Post subject: Reply with quote

i'll look into it, i know this specific wire is good for 1.25 amps as it the same wire i used in the voyager model on a 1.25amp psu.

these should be 12v resistors so it might actually be fine, i'll wire it into the brake light tomorow and check it out.

as for 12v leds, theres no such thing so to speak, the difference is when you buy 12v leds they are pre-wired leds with adequate resistors already in line.
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U_W v2.0
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PostPosted: 21:49 - 03 Nov 2012    Post subject: Reply with quote

carvell wrote:
Or buy "12V LEDs", indeed. These have a built in resistor which allows you to connect the LED directly to a 12V battery.


hehe beat me to it on the 12v led bit.

as for the previous attempt, i think i know what went wrong.

too many led strips wired together with the power leads being under the required rating.

that would explain the hot wires.....
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U_W v2.0
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PostPosted: 21:51 - 03 Nov 2012    Post subject: Reply with quote

##Paddy## wrote:
Why don't you just start bike on choke, put jacket, lid and gloves on, ride to the end of the road and turn it off?


didnt see this, because i usually have to hold the throttle open a little so it doesnt bottom out lol. also, even if i didnt, that would be the smart thing to do and i like to faff around with things.
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kramdra
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PostPosted: 21:51 - 03 Nov 2012    Post subject: Reply with quote

well that was shit. so its just for a switch and couple of leds... use a resistor

and calculate it on 15v, not 12.


Last edited by kramdra on 21:56 - 03 Nov 2012; edited 2 times in total
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carvell
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PostPosted: 21:51 - 03 Nov 2012    Post subject: Reply with quote

There's no such thing as a 12v resistor. What value is it? (in ohms)

The forward voltage of an LED is usually around 2.5V and the forward voltage is usually around 25mA.

Based on this, the resistor needs to be at least 380 ohms.
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U_W v2.0
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PostPosted: 21:53 - 03 Nov 2012    Post subject: Reply with quote

i know theres no such thing as a 12v resistor, i just meant they're suitable for most 12v sources.

also they are around the 500 mark.

blue resistors, colour bands:

yellow brown black? blue brown.
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P.
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PostPosted: 21:54 - 03 Nov 2012    Post subject: Reply with quote

Up your idle.
Wink
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U_W v2.0
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PostPosted: 21:56 - 03 Nov 2012    Post subject: Reply with quote

bah, thats easy.

also, disregard those colors. they're wrong lol. color blind Very Happy
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Islander
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PostPosted: 23:26 - 03 Nov 2012    Post subject: Reply with quote

Just use a resistor. A standard LED on a 12V supply drawing, say 15mA would need a 680 ohm 0.25W resistor. 15mA should be an adequate forward current.

It won't get hot - you're looking at 0.15W or so.
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