Classic cars forum & vehicle restoration.
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ukdave2002
Joined: 23 Nov 2007
Posts: 4105
Location: South Cheshire
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 Posted: Fri Jul 01, 2022 5:56 pm Post subject: |
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| Ray White wrote: | I guess it wouldn't light up at all..?
I suppose what I am asking is why there isn't a resistor on BOTH sides of the bulb? |
Correct , re your question; What would a resistor on either side achieve over a single resistor on ether side? |
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Ray White
Joined: 02 Dec 2014
Posts: 6318
Location: Derby
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| Posted: Fri Jul 01, 2022 6:05 pm Post subject: |
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| ukdave2002 wrote: | | Ray White wrote: | I guess it wouldn't light up at all..?
I suppose what I am asking is why there isn't a resistor on BOTH sides of the bulb? |
What would that achieve over a resistor on ether side? |
I don't have the answers. It all seems contradictory to me.
For example, why won't a fuse blow if it goes after a relay (rather than before it) yet a resistor can protect a bulb if it does.? |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4105
Location: South Cheshire
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| Posted: Sat Jul 02, 2022 6:36 am Post subject: |
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| Ray White wrote: | | For example, why won't a fuse blow if it goes after a relay (rather than before it) yet a resistor can protect a bulb if it does.? |
Ray, a fuse can go either side of the relay contacts.
If the fuse is in the relays coil circuit (which is electrically completely separate to the circuit that the contacts are in) , it wont be protecting anything except the low current relay control wiring, something that is not usually fused.
Dave |
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Ray White
Joined: 02 Dec 2014
Posts: 6318
Location: Derby
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| Posted: Sat Jul 02, 2022 9:01 am Post subject: |
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| ukdave2002 wrote: | | Ray White wrote: | | For example, why won't a fuse blow if it goes after a relay (rather than before it) yet a resistor can protect a bulb if it does.? |
Ray, a fuse can go either side of the relay contacts.
If the fuse is in the relays coil circuit (which is electrically completely separate to the circuit that the contacts are in) , it wont be protecting anything except the low current relay control wiring, something that is not usually fused.
Dave |
Thank you Dave. I have been struggling with this for a while now ... but you have made things MUCH clearer for me.
I now have the supply to the relay contacts fused (not in the relay coils circuit)
The ignition warning light will have a 2.5V low wattage torch bulb with a resistor.
I think I have got this right now. |
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