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Aug 24th, 2023
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Joined: Jun 2015
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Talk Morgan Enthusiast
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Talk Morgan Enthusiast
Joined: Jun 2015
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Could well be a fly-back diode to the pcb relay has gone up the swanny then? I replaced mine recently with beefier diodes just on the chance that they'd fail at some point in the future. Agree. I have never had a close look at one, but typical wiring diagrams suggest that the only electronic components on the pcb are diodes. No hi tech microprocessors or anything like that. A fly-back diode is only there to supress sparking across the switch terminals when an inductive load is switched off. Simple and cheap to replace if you are handy with a soldering iron. If not, i would be tempted to seek out “a man that can” (oops, or woman!) rather than wait for ever. A friend of mine with a similar issue simply wired the lamp direct to a new separate switch .
Doug
2011 Plus 4 in Rich Maroon
1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900
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Joined: May 2010
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Needs to Get Out More!
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Needs to Get Out More!
Joined: May 2010
Posts: 9,285 Likes: 69 |
I will try to dig out the photos I took of the control box innards.
I remember a small pcb with more than diodes. I think there was an eprom in there to manage the logic of resetting the lights to require them to cancel when headlamps were switched off.
Plus Four MY23 Furka Rouge
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Talk Morgan Regular
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Talk Morgan Regular
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A fly-back diode is only there to supress sparking across the switch terminals when an inductive load is switched off.
[/quote
Just a thought - if that's the bit that's failing would the fitment of non-inductive load bulbs ( LED upgrade bulbs opposed to filament bulbs) not solve the issue from happening?
2015 Morgan 4/4 (Wolf fettled) previously 2014 M3W
MINI Cooper S and numerous BMC/BL relics.
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Joined: Jun 2015
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Talk Morgan Enthusiast
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Talk Morgan Enthusiast
Joined: Jun 2015
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No. Bulbs are resistive load rather than inductive loads. An inductive load is typical of relay coils, motors, etc where electro-magnetism comes into play. When you try to Interrupt the current flow by switching off, the inductive winding will try to oppose and as no current can flow, a voltage acrues instead and you end up with a fat spark across the switch contacts.. The flyback diode acts as a sort of relief valve by giving a conducting path for the reverse current to flow and stop a build up of volts across the switch contacts.
As I said, I have never had a close look at what’s there and why. Maybe it’s only because they use crappy switches (surely not, Morgan??) and are trying to prolong their life. Only a guess!
Think “miligoons” advice from earlier post is sound, as are others who found it was just poor soldering of connections in the first place. If its done proper, it should last!
Doug
2011 Plus 4 in Rich Maroon
1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900
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Joined: Apr 2014
Posts: 6,830 Likes: 59
Talk Morgan Sage
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Talk Morgan Sage
Joined: Apr 2014
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No. Bulbs are resistive load rather than inductive loads. He did say LED as opposed to filament.
Best Regards
Lang may yer lum reek
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Talk Morgan Guru
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Talk Morgan Guru
Joined: Feb 2016
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The issue is due to relays where fitted and their coils, not the bulbs they feed. When controlled by sensitive electronics its important diode protected relays are used, not to protect their contacts but to quench the back emf pulse and its effects on associated electronics from the relay control circuit.
I had a demonstration of this phenomena on a new canal boat build. There was some confusion with the polarity coding of wires on tiny indicator LED's I used on several plain relay controlled circuits. The control switches and relays all functioned correctly but no LED indications. I noticed though when switching any of the circuits off I got a brief flash on the corresponding LED caused by the back (reverse) emf from the collapsing field of relay coil. Reversing the LED indicators polarity fixed the problem.
Last edited by Richard Wood; 27/11/18 11:33 PM.
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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Talk Morgan Enthusiast
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Talk Morgan Enthusiast
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I'm a total novice when it comes to electronics although I have skimmed through a few basic articles.
I understand that a diode is a one way none return valve to protect against spikes going back into sensitive electronics. That was a concern when I ripped out the old ECU and wired in the new Omex ECU.
But how do you know for sure whether there will be a problem?
Dumb question maybe but why not always use diode protected relays other than cost?
As I recall, they come in the exact same sizes and do the same switching job so why not play safe and use them as standard?
If that question is actually dumber than dumb, please enlighten me gently but comprehensively.
It would appear that I still need to learn a bit about electronics even on my turn of the century model.
Last edited by IvorMog; 28/11/18 08:48 AM.
Bob
2009 Black Roadster
1999 4/4 2 litre Zetec
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Talk Morgan Guru
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Talk Morgan Guru
Joined: Feb 2016
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A sensible argument Bob especially as they cost little more. On the M3W wiring schematic (maybe others) it clearly states diode relays should be fitted.
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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Joined: Nov 2015
Posts: 7,914 Likes: 243
Just barreling along Talk Morgan Guru
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Just barreling along Talk Morgan Guru
Joined: Nov 2015
Posts: 7,914 Likes: 243 |
No. Bulbs are resistive load rather than inductive loads. An inductive load is typical of relay coils, motors, etc where electro-magnetism comes into play. When you try to Interrupt the current flow by switching off, the inductive winding will try to oppose and as no current can flow, a voltage acrues instead and you end up with a fat spark across the switch contacts.. The flyback diode acts as a sort of relief valve by giving a conducting path for the reverse current to flow and stop a build up of volts across the switch contacts.
As I said, I have never had a close look at what’s there and why. Maybe it’s only because they use crappy switches (surely not, Morgan??) and are trying to prolong their life. Only a guess!
Think “miligoons” advice from earlier post is sound, as are others who found it was just poor soldering of connections in the first place. If its done proper, it should last! Interesting info on electrics, emf, etc But in defence of the Factory the current push switches are made by a high end pukka control switch / auto parts manufacturer and cost upwards of £50-£60 each !
Jon M
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Joined: Jun 2015
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Talk Morgan Enthusiast
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Talk Morgan Enthusiast
Joined: Jun 2015
Posts: 1,961 Likes: 43 |
No. Bulbs are resistive load rather than inductive loads. He did say LED as opposed to filament. Ok Bob, perhaps I missed his point by focussing on the function of a flyback diode. Having said that, the reactive effect of a filament lamp is negligible and I would think so is a LED, when connected to D.C. (a.c. of course is a different kettle of fish with LEDs as many may have found when trying to dim them using a conventional dimmer...but I digress) So, changing to LEDs should certainly place less current switching duties on the switch contacts and circuitry in general but not convinced the diodes would notice any difference in duty called upon. What we don’t know is why the pcb has failed. Diode failure may well be a red herring; it is just as likely to be poor construction/soldering of joints, vibration, water ingress, etc.
Doug
2011 Plus 4 in Rich Maroon
1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900
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