Question on my planned car electrics - please see diagram
- Thread starter David Womby
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vance.dykes
Well-Known Member
a/c clutch is 12 volt
OK that makes sense
Remember I trigger fans on diagram via ground. So the 30 terminal takes the ground input and the 87 the ground output to splice into the relay which actually will make work the relay to feed the fan. So the A/C relay takes the clutch signal which is positive just to close the ground path to trigger later the fan relay, just like the override switch, but automatically when A/C is on. That relay is not for load like the one being use to feed the fan but to become the positive trigger onto a ground trigger. 85 and 86 will be the relay solenoid to close the path and are the only sources that need the + signal to activate the relay
about the override switch notes... sorry, is a board resizing problem... hosting it on a diff service and post the link so you can click the link to a better view
https://i.postimg.cc/Dzpmm5y6/dual-fan-option-FULL.jpg
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but between + and - on relay ? Noises are supressed by condensers no diodes. From my point of view, there will get a short when fan is activated
vance.dykes
Well-Known Member
OK then what dose it suppressed ?
well, I'm not electronic components expert, just the basics on this, but I can't find the logic. Anyway, No need for that for the fan operation
The diagram I made is pretty much similar to that one but with more details and options.
One difference is That diagram shows a pilot light after the relay and I optioned before the relay using the switch itself. Will depend about prefferences and if you really want a pilot light for it. After the relay will test for good the relay and Thermo switch signal and before the relay just will test the thermo signal itself, no test for relay operation. But the pilot light after the relay requires one more wire to the cab and can't be used a lighted switch on the way it is
One difference is That diagram shows a pilot light after the relay and I optioned before the relay using the switch itself. Will depend about prefferences and if you really want a pilot light for it. After the relay will test for good the relay and Thermo switch signal and before the relay just will test the thermo signal itself, no test for relay operation. But the pilot light after the relay requires one more wire to the cab and can't be used a lighted switch on the way it is
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vance.dykes
Well-Known Member
i found this
The Transient Voltage Suppressor diode (also known as a TVS Diode) is a protection diode designed to protect electronic circuits against transients and overvoltage threats such as EFT (electrically fast transients) and ESD (electro-static discharge).
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Why Put a Diode Across a Relay Coil?
When the power supply is connected to the relay, the inductance coil’s voltage builds up to match that of the power source. The speed at which current can change in an inductor is limited by its time constant. In this case, the time it takes to minimize current flow through the coil is longer than the time it takes for the power supply to be removed. Upon disconnection, the inductive load in the coil reverses its polarity in an attempt to keep current flowing according to its dissipation curve (i.e., % of maximum current flow with respect to time). This causes a huge voltage potential to build up on the open junctions of the component that controls the relay.
This voltage built up is called flyback voltage. It can result in an electrical arc and damage the components controlling the relay. It can also introduce electrical noise that can couple into adjacent signals or power connections and cause microcontrollers to crash or reset. If you have an electronics control panel that resets each time a relay is de-energized, it’s highly possible you have an issue with flyback voltage.
To mitigate this issue, a diode is connected with reverse polarity to the power supply. Placing a diode across a relay coil passes the back electro magnetic field and its current through the diode when the relay is energized as the back EMF drives the flyback protection diode in forward bias. When the power supply is removed, the voltage polarity on the coil is inverted, and a current loop forms between the relay coil and protection diode; the diode again becomes forward biased. The freewheeling diode allows current to pass with minimal resistance and prevents flyback voltage from building up, hence the name flyback diode.
Tiny flyback diodes prevent huge flyback voltage from damaging your components.
Flyback Diode Wiring for Relay Noise Suppression
The placement of a flyback protection diode is rather simple; it should be placed directly across the relay's coil. A schematic for a freewheeling diode circuit in a relay is shown below. In this schematic, the resistor R in parallel with the flyback diode wiring represents the coil's intrinsic DC resistance.
Flyback diode wiring in a relay circuit.
Note that the placement of the diode does not prevent a voltage spike from travelling to some downstream load. Instead, it provides a path with low resistance that reroutes the current, thus the voltage spike at the downstream load will be much lower. Using a simple 1N4007 diode is sufficient to suppress large voltage spikes in a 24VDC relay with a diode protection circuit.
The current path in the diode depends on whether the switch in the relay is closed or opened. As the switch is initially closed, the inductor load generates a back electro magnetic field as its transient response, and the voltage slowly rises to the supply voltage value. Once the switch is opened, the back electro magnetic field created by the inductor switches direction and points towards ground, creating a transient response that slowly dies off. Thanks to the low resistance loop created by the freewheeling diode in forward bias, current is diverted through the diode rather than creating a large voltage spike elsewhere in the circuit.
Current flow through the flyback diode wiring in a relay circuit.
For automotive applications having decent stereo systems, relay “popping” noise can be picked up in the audio from relays without a “flyback” diode across the primary coil. Some OE high end automotive relays have them built in. Pictured, diodes installed on headlamp relays.
Another approach
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cool... as I told, I'm not an component expert on this for every application available, just the basics applications! thanks for the info!
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David Womby
Well-Known Member
Guys, my head is spinning like crazy with all the knowledge showing up on here. Don't stop on my account though. 
David
David
vance.dykes
Well-Known Member
Guys, my head is spinning like crazy with all the knowledge showing up on here. Don't stop on my account though.
David
on to each is given a talent and to shear it is how to have it carries on.
451Mopar
Well-Known Member
All I can add is the relays with the flyback diodes are polarized. The trigger supply and ground can not be reversed.
Thank you for posting this, I learned something useful today
. I got halfway through your post and thought.... Wait a minute here, now I know what that damn noise is!!! Now to find the culprit.
Derwud
Well-Known Member
Must be English and hate back feeds..
David Womby
Well-Known Member
Thanks for all the help on this one.
David
Cool!! ( never better said! LOL )
No need for fuse at the 86 terminal. That wire is not holding a significant load, just triggs the positive side of the solenoid, being ready for the negative side from the temp sensor.. the load is actually on 30-87 lines.
Fan can be grounded anywhere on chassis-sheetmetal. No need to run to batt.
If your car got ammeter, the 30 circuit should be sourced from alt stud, not from batt.
No need for fuse at the 86 terminal. That wire is not holding a significant load, just triggs the positive side of the solenoid, being ready for the negative side from the temp sensor.. the load is actually on 30-87 lines.
Fan can be grounded anywhere on chassis-sheetmetal. No need to run to batt.
If your car got ammeter, the 30 circuit should be sourced from alt stud, not from batt.
David Womby
Well-Known Member
Fair points but that diagram shows the actual physical wiring locations that were already there (wired in by previous owner) and that I adapted to work the way I want. I didn't see any harm leaving the fuse in the circuit that activates the relay and the ground wire from the fan was already in place running back to the grounding stud attached to the battery -ve. So I used it.
David
David
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