Auto electricians

binge · Emo Kiddy Joined: 02 Jul 2004 Karma :

Got a wiring issue I think.

TZR engine, Running without a battery.
All it has to power is a Horn, A 20w Halogen Headlight, And an LED tail light. NO other power drains other than the engine ignition.

I had been running it with no headlight for a while as the bulb had gone, and hadnt got round to replacing it.

Today I bought a bulb, First time its had a headlight bulb since the build. Put it in, Worked fine.

On idle, Its pretty bright, And at very low revs, Its brighter.
But once you wang the throttle open, It goes really dim.

But get this, On the motorway, I was pinned at about 70mph, Full throttle. And when I pressed the horn, The headlight got brighter. Confused

Completely baffled me.

It's as if its working back to front.

Ben

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

Do you have a regulator / rectifier in there somewhere, and are you running the lights etc off the regulated 12V?

If you are, you may need to stick a battery in it, or a big capacitor (sometimes sold as battery eliminators), the battery is quite an important bit of the rectifier's action Smile

f.

binge · Emo Kiddy Joined: 02 Jul 2004 Karma :

I am running everything after the regulator yes.

I thought it was that too. But surely when it revs up, The power output increases, So the bulb should get brighter. Not dimmer.

And then when I use the horn, The bulb goes really bright again.

Ben

mad_revs · Two Stroke Sniffer Joined: 24 Jun 2009 Karma :

mr rip · Scooby Slapper Joined: 24 Jun 2009 Karma :

it sounds like you have an earth problem, ie the earth for the light is running in series with the horn hence it works better with the horn button pressed

check that you don't have the earth & power supply leads to the handlebar switchgear mixed up as that would do it.

the same as the way the alternater light works (by having two positives while alternator is running)

next, try running a new earth lead from the light down to a clean bit of frame

if that doesn't help then try putting a new lead in from the supply to the switchgear
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finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

Problem is the battery acts to smooth all the noise in the regulated supply. It's the noise that is probably causing the bother.

Putting any load on the electrics (like the horn) will also help smooth things out, which is why it's probably having an effect, although I expect there to be additional electrical ju-ju going on because of how horns work.

f.

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

Its behaving exactly as I'd expect! Thumbs Up

If you haven't got a battery in there to suck up some juice and smooth things down, then your poor old reg/rec is having to work overtime mind - poor reg/rec Crying or Very sad

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binge · Emo Kiddy Joined: 02 Jul 2004 Karma :

It shouldnt need a battery. I took the battery off my pit bike engine and it all ran fine.
I've totally re-wired the headlight today, Going directly from, And back to the regulator + and -. And the problem hasn't changed.

Got a multimeter on the Reg/rec output. On tick over it is kicking out around 17 or 18 volts!
And when I rev it, The voltage drops to around 10 or 11 volts.

I've bought a replacement reg/rec off ebay. Hopefully that will sort the problem.

Ben

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

binge · Emo Kiddy Joined: 02 Jul 2004 Karma :

How is it measuring AC after the Reg/Rec? I'm measuring a DC output surely?

Ben

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

To use an analogy - it's like you've taken the dampers off your suspension. It'll still work, it's going to be all over the shop.

f.

the grim reaper · World Chat Champion Joined: 29 Jun 2005 Karma :

This advice above is all correct, the battery acts as a load across the alternator which is required for proper operation. Even though it is effectively downstream and the other side of the reg/rec, having an expected large capacitive load mossing from the circuit will affect all components.

The other possible issue is that you no longer have a common earth. On some bikes you have more than one earth connector going to the battery, if you haven't connected the earths together then certain parts of the bike could be floating, away from 0VDC.

Cheers

Grim
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