Electrical question
Discussion
So for starters this is not on a TVR ... A Noble M10 so not far off.
It's quite common to wire an ignition switch so that when switched on it only powers the coil of an Ignition Load Relay so that large amounts of current are not being drawn through the switch. Sometimes the switch does power some other circuits. On a Chim it is Relay 5.
So that is how this car is wired with the relay and the wipers being the only circuits powered direct from the ignition switch.
But........... there is a diode in the line just after the switch.
I can't think of a reason for this so any ideas would be good.
Thanks
Steve
It's quite common to wire an ignition switch so that when switched on it only powers the coil of an Ignition Load Relay so that large amounts of current are not being drawn through the switch. Sometimes the switch does power some other circuits. On a Chim it is Relay 5.
So that is how this car is wired with the relay and the wipers being the only circuits powered direct from the ignition switch.
But........... there is a diode in the line just after the switch.
I can't think of a reason for this so any ideas would be good.
Thanks
Steve
Yep, I’d say it’s there to protect from back EMF.
From my old house alarm days, I was always taught to fit them when using relays, electro magnetic locks etc
I’m 99% certain, that the lack of diode leading from the immobiliser to the starter motor relay on the Cerbera, is what knackers that output up, on the immobiliser.
From my old house alarm days, I was always taught to fit them when using relays, electro magnetic locks etc
I’m 99% certain, that the lack of diode leading from the immobiliser to the starter motor relay on the Cerbera, is what knackers that output up, on the immobiliser.
Stops engine running on due to Alternator Diode Trio D+ supplying the ignition when ignition is switched from engine run to off
Or
Stops chattering relay/relays or relay/relays hold-in due to Alternator Diode Trio D+ supplying the ignition when ignition is switched from engine run to off
Or
Same as above but possibly happening when hitting the master switch if car has one and it isn't of FIA specification or is of FIA spec but has been incorrectly wired
Or
Stops chattering relay/relays or relay/relays hold-in due to Alternator Diode Trio D+ supplying the ignition when ignition is switched from engine run to off
Or
Same as above but possibly happening when hitting the master switch if car has one and it isn't of FIA specification or is of FIA spec but has been incorrectly wired
?
Edited by Penelope Stopit on Friday 30th July 08:57
GreenV8S said:
Where is the diode relative to the split feeding the two circuits? If the diode is on the branch feeding the wiper motor, it's possible the diode prevents the wiper motor back emf from holding the ignition switched relay closed. Otherwise I can't see any reason for it.
The diode is between the switch and the split which, like you, confuses me as any Back EMF will just arrive at the switch which will be off.On a Chim the switch feeds the Ignition Load relay, reverse lights, ECU, door locking, alarm, immobiliser & the fuel pump relay but has no diode.
Steve
Steve_D said:
Penelope Stopit said:
.......Any pics of the diode?........
No it is nicely done in heat shrink which I don't want to touch at this time. It's a customers car so I need to convince myself before binning it.It measures about 9mm long and about 5.5mm in diameter.
Steve
Is the ignition relay a big one without a resistor or diode across its coil and the diode has perhaps been fitted for that reason instead of doing the job a better way ? Guessing though
Would be nice for you and the customer if it could be proven that the HT spark had been increased by removing the diode
Steve_D said:
GreenV8S said:
Where is the diode relative to the split feeding the two circuits? If the diode is on the branch feeding the wiper motor, it's possible the diode prevents the wiper motor back emf from holding the ignition switched relay closed. Otherwise I can't see any reason for it.
The diode is between the switch and the split which, like you, confuses me as any Back EMF will just arrive at the switch which will be off.On a Chim the switch feeds the Ignition Load relay, reverse lights, ECU, door locking, alarm, immobiliser & the fuel pump relay but has no diode.
Steve
Suspect the switch’s contacts are rated 12vdc and 5A or less ?
Given this more thought because it's a goodun
The diode is causing a volt-drop in the coil supply circuit because that's what diodes do
The diode has supposedly been fitted to prevent back EMF yet whoever fitted it must surely have known that there was an ignition relay already in the circuit and that the relay should have a resistor in parallel with its coil
Bearing in mind ignition switches don't normally have a diode anywhere in their circuits and they cope very well with back EMF from starter solenoids and ignition coils
When the ignition switch is turned to off, any back EMF is dumped to ground through the ignition relay coil and its resistor due to its circuit now being in series with the ignition coil supply
Bin It Innit - Keep the faith Steve_D, you find it odd and it is well odd, somebody got it wrong
The diode is causing a volt-drop in the coil supply circuit because that's what diodes do
The diode has supposedly been fitted to prevent back EMF yet whoever fitted it must surely have known that there was an ignition relay already in the circuit and that the relay should have a resistor in parallel with its coil
Bearing in mind ignition switches don't normally have a diode anywhere in their circuits and they cope very well with back EMF from starter solenoids and ignition coils
When the ignition switch is turned to off, any back EMF is dumped to ground through the ignition relay coil and its resistor due to its circuit now being in series with the ignition coil supply
Bin It Innit - Keep the faith Steve_D, you find it odd and it is well odd, somebody got it wrong
Gassing Station | General TVR Stuff & Gossip | Top of Page | What's New | My Stuff