Irony
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| posted on 6/6/11 at 11:57 AM |
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What items to use a relay with?
Starting to think about the electrics in my V8 viento (with Megajolt and Carbs). I have been looking over the wiring loom that came with the car and
it seems to be in good order (except for everything in the fuse box is labelled back to front,  ). The brief manual that came with the loom
doesn't mention the use of any relays in the system at all apart from a flasher unit. It just seems to say 'wire it all up'. This
worries me, as for example the wiring loom cooling fan cables are very thin, about 1.5mm squared and the cables from the fan are 3 times that thick,
surely I will need a relay????
What items in a standard kitcar setup would you guys suggest the use of a relay?
[Edited on 6/6/11 by Irony]
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steve m
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| posted on 6/6/11 at 12:30 PM |
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I havnt got any relays except the flasher ones, the main beam could really do with a relay, but is never on for long enough to worry about
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Strontium Dog
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| posted on 6/6/11 at 12:31 PM |
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You only need a relay in normal use if the switch you have does not have a high enough current rating to handle the load!
Amps is volts divided by resistance, you know the voltage so only need to measure resistance to find the Amperage! Then check to see if the switch you
are using has a sufficient rating. If not then you can use a relay or a heavier rated switch!
Hope that helps!
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bbwales
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| posted on 6/6/11 at 12:42 PM |
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Hi,
I use smaller wires to my dash and switch gear so I use 5 relays, these being:
70 amp for all ignition controlled circuits
40 amp for Main beam
40 amp for dip beam
40 amp for Horn
40 amp for fan.
Regards
Bob
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iank
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| posted on 6/6/11 at 01:37 PM |
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Switches usually have a number of loads specified.
AC, DC resistive and DC inductive. With both having specified max current at some voltage.
If you are switching a motor (or a solenoid, horn) then use the DC inductive figure, if a lamp then DC resistive if your switch can't cope with
the load then you need a relay.
The trick is usually finding the specifications for the switch you are using. Farnell and RS catalogues can help for aftermarket switches. For OEM
switchgear follow what they have done.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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Chippy
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| posted on 6/6/11 at 03:25 PM |
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I would add that the wire size is also critical for safety, you MUST keep the smoke in the cable and not out of it. Use a low amp cable on a high amp
item and flames are what you will be looking at, but you can use a low amp cable to feed a relay, which will be fed by the correct amp cable. You pays
your money and takes your choice, (or chance). Cheers Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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Irony
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| posted on 6/6/11 at 03:58 PM |
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I will just find out what ampage each component draws then use a reply if the wiring doesn't seem up to spec. I have a sierra steering column.
Does anyone have a cable diagram for it anywhere?
[Edited on 6/6/11 by Irony]
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wilkingj
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| posted on 7/6/11 at 10:10 AM |
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quote:
Originally posted by Irony
I will just find out what ampage each component draws then use a reply if the wiring doesn't seem up to spec. I have a sierra steering column.
Does anyone have a cable diagram for it anywhere?
[Edited on 6/6/11 by Irony]
Sierra Stalk Wiring....
Linky
Remember there are two versions of stalk switches / wiring, One switches an earth to fire the headlight relay(s), (main or dip).
The other switches 12v to fire the relay(s).
Its just a question of which stalk you have, and then putting the correct bit on the other side of the relay coil. ie if the switch is putting out
12v, then the far side of the coil needs to be put to earth, or if the switch is putting out an earth, the far side of the coil needs to go to 12V.
Simples... <Chk>
As said above, you need a suitable sized (amps) relay to switch the circuit, if the switch cannot handle the full current of the circuit. eg 2 x 65W
headlights = 130Watts, P=IV, therefore the headlights take 130/12=Amps ie about 11 Amps. The sierra switches cannot carry that sort of current , so a
Relay is necessary to prevent you destroying the switches in the steering column. (and to prevent a probable FIRE)
Take your time and get this RIGHT FIRST TIME. You would not want your beloved car to go up in flames as you go it wired incorrectly, and more to the
point unsafely.
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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Irony
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| posted on 7/6/11 at 10:12 AM |
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Thanks WikingJ, you are legend as always.
That switching problem seems quite complex. Let me get this straight.
If my steering column outputs a earth for the headlights I need to have them wired perminantly into 12v. Then the switch in the steering column
outputs a earth to a relay which then turns the headlights on.
Or
The switch in the steering column outputs 12v as normal which goes to a relay and the headlights are just earthed to chassis.
I was planning on not using the majority of the switching stalks in the column and having a switch on the dash for most things. I think however I
will use the indicators and the hazard switch (which is on top of the column).
Have I got this right??
[Edited on 7/6/11 by Irony]
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