All power disappears when lights go on.........

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mattyd72

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Chaps, little problem with my bus.

I've done about 4000 miles this year and have only just started having issues, it runs perfectly during the day, no probs at all. Then as soon as I put my lights on it has started to cut out ( most notably on the Kings Road sunday evening! ) It will drive along and start to cut out then go again and then stall again all while driving along normally, the genny light will flash when it dies and disappear when it gets power again.
Strange thing is that if a car stalls all the iginition lights come on. but it has nothing its like I have a flat battery., but... hazards and side lights still work.

So...

I'm thinking it must be something to do with the ignition breaking down as all constant lives still work, as I have checked all connections including battery and headlights.

Am I just destined to be a daylight driver forever or can someone shed a bit more light on this stoopid problem

Or shall I just buy a new ignition and hope for the best??

So please Earlybay, fix my ride :D
 
I would hazard a guess that the dynamo or regulator is goosed......

during the day after starting how long is the genny light on for?
how soon after the lights are on do you experience problems?
have you checked the battery voltage engine running and not? lights on and off?
 
You have an intermittent electrical fault which is not caused by your alternator/dynamo. You don't say what year or spec it is so follow these general ideas. Check your battery, terminals are clean and tight. Check the battery cables where they attach to the body/starter motor. Check the big red feed to the light switch at both ends, starter and switch. Check the red wire from the light switch to the ignition switch. To check a connection remove it and clean it, looking at is not good enough. Make sure all the connections are clean and tight, replace any that are suspect. Check the gearbox earth strap as well. Good luck.
 
I had the exact same problem with mine about 6 months ago....

Clarkson46 and Aaron both point you in the right direction. I would follow the electrical connection route first, and check everything, as detailed above - it may well be something simple (and cheap :) ). If that doesn't solve it then it all points to Alt/Gen.
My problem sounded exactly like yours and after checking all connections, (and redoing most) it turned out to be a knackered diode in the alternator, so ended up having to get it rebuilt. Problem solved!

Hope you get going again soon
 
If the diodes PN junction in the rectifier are breaking down then you will get symptoms very similar to this.... (Ducati riders will know what I mean bloody italian electrics :x )

also if your isulation on your windings are degrading again as load increases you will not be getting the charge to the battery so the heavier load with the inclusion of lights will mean the battery is doing a lot of work and likely to be boiling (lead sulphate will be produced all the more greatly the deeper discharge you go)....

corroded contacts will give you poor current flow at times of heavy load

sulphated battery will decrease plate area therefore....

the chances are your problem is a combination of several factors.....
 
It's most likely a poor connection on the lighting switch, which goes high resistance when the extra current required by the lights passes through it. In simple terms it gets hot. A PN junction on a semiconductor will not repair its self once short circuit. So check every connection in the circuit to be sure.
 
Thanks for all your ideas guys, i'm hoping its something with the lighting circuit as its the only thing which sets this off, all the other electrics work fine when running i.e stereo with amps, and satnav, all of which have been installed since I rebuilt the bus so I haven't arsed that up!The Genny light goes straight off after ignition and the only flat battery I have had was when I left it hooked up over winter :roll: oh and Clarkson its a 72 microbus :D

I will have a look tomorrow evening and after i've attacked it with some emery paper I will report back

Thanks again

Matt
 
Thats not strictly true, a PN junction always repairs itself on the forward bias and can repair itself on the reverse dependant on why it failed (it is the associated heat that causes the damage and not the reverse bias conductivity), as in the case of the aforementioned Ducati by example, due to the poor siteing of the regulator they got bloody hot and they were thermal pasted to the head stock the paste breaks down leaving the cooling to the air alone (unfortunately Ducati mounted them out of the airflow).... This thermal energy transfers to the diodes N semiconductor and sets off a chain reaction (avalanche breakdown/multiplication, Quantum mechanical tunnelling etc..), a similar reaction to a zenner in that they start to conduct on the reverse (though in a zenner it is a desired result)...

Old diodes often suffer from this as the doping on the semi conductor begins to deteriorate and will for a period appear stable, until high demand/heat pays its toll.... eventually packing up terminally usually taking the battery with it as inevitably your doing a ton when the first signs appear (ok I'm back on the bike here)....
 
I stand corrected. I didn't know that semiconductor devices could repair themselves. 45 years in the electronics industry and I've learned something new today. A short circuit diode that is self repairing. What ever next????
 

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