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the12volt`s installbay - Mobile Electronics Forums the12volt's install bay / General Discussion

Subject Topic: wiring, fuse box, lights, wiper

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turboturtlee
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Posted: November 08, 2012 at 11:21 AM - IP Logged
Link to Post  Post Reply Quote turboturtlee

Hi.

I have some quick questions for you guys.

1. Is correct if you wire the right side of a fuse box with 12v wires and from the left side you take them to the relay?

2. Can you wire the front and rear lights on a single 40A relay? The lights will work properly? Is the switch wired good?

3. When you are wiring the wiper motor and the brake light is it recommended to use a relay? Or a simple fuse will work just fine?


Made this in paint to give you an idea about what im talking! Please excuse me if the questions are stupid but i dont have any training and I want to learn .

posted_image


Cheers!
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shortcircuit161
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Posted: November 08, 2012 at 2:30 PM - IP Logged
Link to Post  Post Reply Quote shortcircuit161

Anytime you connect an accessory or lights or anything to 12v, it should ALWAYS be fused no matter if a relay is used or not.

A relay is used when the switch you are using is not capable of handling the amperage or power needed for that device. Or to reverse the polarity needed (from negative to positive) such as in your picture.


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oldspark
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Posted: November 08, 2012 at 6:06 PM - IP Logged
Link to Post  Post Reply Quote oldspark

Well said shortcircuit161.

turboturtlee - don't confuse "protection" like fuses and circuit breakers with switching - eg, relays.

A fuse is there to protect its downstream distribution (wiring) in case of short circuits etc.
The fuse must therefore be rated equal to or less than the cable/wire and switch/relay etc rating. (EG - if a 50A fuse protects a 40A cable and a 30A relay, the cable or relay may melt or cause a fire before the fuse blows.)

As shortcircuit161 wrote, relays are used to take the "load" off the switch(es).
Relays also mean that smaller switches (or less powerful electronics) can be used as well as more direct heavy-current cabling.
For example, older cars had wiper and light switches in the cabin/dash. That meant a heavy cable to the switch and back to the load (wiper, lights), and a heavy-rated switch.
These days relays are used instead. Hence the heavy current-carrying cable need only run from the battery (thru fuses!!) etc thru the relay to the load. Only a small switch is needed with smaller wires to the relay coil.
Hence also lower voltage drops to the load due to shorter power runs or because heavier cable can be used, and relay contacts usually stay cleaner than mechanical cabin switches (dirt & wear = resistance, hence heat and failure).



FYI - by convention the more +ve goes to relay coil #86 - ie, +12V to #86 and the 0V/earthed/ground wire to #85.
But that is by convention and only important if you have a relay with inbuilt diode snubber to prevent voltage spikes. Most relays don't have internal diodes though many these days have an internal snubber resistor, but they don't care about their polarity. (I prefer normal (non-diode) relays and instead add my own external diode if needed.)   


And incidentally, your relay circuit is a classic horn-relay circuit - a grounded button triggers the relay which connects +12V to the horn.   3-pin horn relays that internally joined #30 to the coil were once common.
Also wipers were often the opposite - their motor was connected to +12V and the relay connected motor winding(s) to ground, usually from a +12V switch.

Stick to shortcircuit161's reply if this has confused you. Your circuit is quite ok (provided you don't use a relay with internal diode).


PS - "distribution fusing" like yours is separate to "equipment protection fusing" as used in amplifiers etc. You may have a 30A fuse and relay and wiring to a 10A amplifier or HU and that's fine. The equipment protection fuse will be at the equipment end - ie, the 10A fuse in the radio/HU/amp, or just before it. [Though it could also be the same wiring with a 10A fuse "up front" (ie, at the battery end instead of at the load/equipment end) that replaces the 30A fuse. But that's provided no-one ever changes the size of that front 10A fuse assuming the load doesn't have its own, but then a bigger 20A or 30A fuse should be used instead - ie, blow one fuse, not both.]
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turboturtlee
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Posted: November 09, 2012 at 8:21 AM - IP Logged
Link to Post  Post Reply Quote turboturtlee

Thanks for replays!

I had a feeling that the relay was some kind of safety feature who takes power and lets it flow smoothly through the entire circuit.

Wired the switch that way because I thought is a lot better if you don't have 12v constantly at the button or through the circuit.

Here is a previous diagram that I was working on,any advice?
http://img528.imageshack.us/img528/2314/dswd1v1.jpg




Cheers!
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howie ll
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Posted: November 10, 2012 at 2:39 AM - IP Logged
Link to Post  Post Reply Quote howie ll

Your link just sends us back to this thread.
In at right side, out left?
Never heard of that one before.
Neatness, weather and corrosion protection are far more important.
SS and Oldie called it correctly in fact ex factory most side light circuits have TWO equipment fuses after the relay output, one for left and one for right OR one for front and one for rear.
The question about coil pins on a relay;
When they are dioded ex OEM, 86 is ALWAYS the positive side by ISO convention/standards therefore I always use it as the POS.
Frankly unless you're using a 5 pin (87a) relay as a changeover in practise it doesn't matter which way round 30 and 87 go.
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Read the installation manual, do a search here or online for your vehicle wiring before posting.
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turboturtlee
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Posted: November 10, 2012 at 9:22 AM - IP Logged
Link to Post  Post Reply Quote turboturtlee

howie ll wrote:
Your link just sends us back to this thread.
In at right side, out left?
Never heard of that one before.
Neatness, weather and corrosion protection are far more important.
SS and Oldie called it correctly in fact ex factory most side light circuits have TWO equipment fuses after the relay output, one for left and one for right OR one for front and one for rear.
The question about coil pins on a relay;
When they are dioded ex OEM, 86 is ALWAYS the positive side by ISO convention/standards therefore I always use it as the POS.
Frankly unless you're using a 5 pin (87a) relay as a changeover in practise it doesn't matter which way round 30 and 87 go.


yep,sorry I'm not that good expressing my self. Just copy/paste the link in the search bar and it will work I've wiried the relay correctly I think, pin 86 is POS.

Instead of putting one fuse for front and one for rear , can you just put one fuse after the relay for the entire circuit?

Cheers!
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howie ll
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Posted: November 10, 2012 at 9:44 AM - IP Logged
Link to Post  Post Reply Quote howie ll

Yes its a throwback to those wonderful(?) old days of the 50s and 60s when cars had non-halogen headlights and drove on sidelights.
you still had some lighting if one side or end failed.
Even today the left and right headlamps have individual fuses.
___________________________________
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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howie ll
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spacespace

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Posted: November 10, 2012 at 9:46 AM - IP Logged
Link to Post  Post Reply Quote howie ll

BTW what are you doing?
Are you trying to build a roadworthy vehicle because in that case you'd damn will better fuse everything.
And your relay was quite correct.
___________________________________
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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turboturtlee
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Posted: November 10, 2012 at 10:07 AM - IP Logged
Link to Post  Post Reply Quote turboturtlee

Thanks!

Well not exactly roadworthy, for rallycross to be exact, I want to remove all the OEM wiring and replace it with this basic layout.

Ok, so two more 4way fuseboxes for front/rear.

Another question, what should I use between the bat. and fuse box? an 80A Maxi fuse or 150A Mega fuse, how do you calculate what kind of fuse do you need?
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howie ll
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Posted: November 10, 2012 at 10:41 AM - IP Logged
Link to Post  Post Reply Quote howie ll

You won't need it.
The fuse box should cover all your consumables plus alternator and say 70 amps for the starter motor.
Oldspark may have some answers when he comes back on line later tonight our time.
The calculation is worked out from the known load + up to 5 amps depending on distance from source.
Back in our audio days, a rear mounted amp with a 30 amp inbuilt fuse got a 40 amp at the battery.
Fusebox rule, not to exceed 12" (30cm) from the battery +.
___________________________________
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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