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p-mo

Trouble with relays

Question

Hello,

 

Been trying to install a relay and fusebox in the boot of my Celica (Gen7 if you care!).

 

I have installed as the attached picture shows.  However It seems that power is going to the fusebox whether the signal line (86->85) is sitting at 12v or not.  The line from the interior fusebox seems to work as expected (VAcc off= no led, VAcc on= lit LED).  However whether or not the LED is lit power gets to the fusebox- I've ran an amplifier off the the fusebox (along with the signal line for the amplifier) and I still get sound through the amp at all times.

 

Do I need something on 87a? Do I have this hooked completly wrong? Do I have a dodgy relay?

 

(oh and sorry for the slightly weird depiction of ground- sure you know what I mean)

 

59513fb35d0a3_relaysetup.jpg.6a76268b4930e745acd69a1e471bf16d.jpg

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continuity test the relay contacts, see if they do open and close when the coil is energised.

 

Most relays are multi-pole and some even have commoned contactors - double check you are correctly wired across them to open close the circuit when the coil is energised

 

I am curious why you have the LED in series with the coil though, you will get a little voltage drop because of that and it may not make the contactors move fully into position.

 

If you want and indicator LED, instead put it across 30 and ground with its own current limiting resistor

Edited by G.Lewarne

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2 hours ago, G.Lewarne said:

I am curious why you have the LED in series with the coil though, you will get a little voltage drop because of that and it may not make the contactors move fully into position.

 

If you want and indicator LED, instead put it across 30 and ground with its own current limiting resistor

 

Yes, if that is what the diagram means, the LED will not allow sufficient current for the coil to pull in.

 

As suggested, the LED needs to be wired in series with a resistor (~1000 ohms is about right) and the LED/resistor combo wired in parallel with the coil. A single LED will only take about 10mA current, whereas the relay will need ~300mA (?) for the initial pull in. Also, when the relay drops back out, it will produce a voltage spike and the LED may not like that. Additional components could be used to protect it... but do you really need it ? Can you get a relay with a LED built in?.

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Your diagram looks wrong as the relay is not earthed

 

Here is how I wire in relays and have done for years

 

Permanent live > Fuse > 30

Earth (negative) 85

Ignition based live > fuse > Switch > 86 (You can change this so that its permanent live, or remove the switch so that it comes on wiith igntion)

Output to accessory > 87

 

87A is not needed in most setups

 

What is that you are trying to run through the relay? And how do you want it to come on?

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also, to be honest its risky having a long cable run from battery positive, through a relay contact and then into a fuse - the fuse should be as close to the battery end of your new supply line as possible otherwise, say if your wire chafes through the insulation, you potentially have a big-ass amp supply cable unfused shorting to ground witch is definitely a fire risk

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There are many types of LED. An old fashioned pure LED would probably go pop with the current passed by a relay coil, but nowadays many leds come with series resistors (which would stop the relay pulling in) or high power/high brightness which would probably work in the diagram shown. The safest bet is to get an LED rated for 14V (12V) or an old fashioned led plus a series 1K ish resistor and wire in paralell with the relay coil.

 

As far as permanent power, you may have wired to the normally closed contact, and then not have sufficient current topull in the relay. It is also possible that the relay is wired correctly but has insufficient current for the load and the contact has welded together. Amplifiers usually have large capacitors which pull a very high current for a short time at power on, this is renowned for weldingrelay contacts.

 

Another safety issue is that you should have a fuse next to the battery with a rating no higher than the wiring it is feeding. i.e. if you have used 50A wire, then the fuse should be rated 50A or less. This is so that if you get a short in the wiring or any other sort of overload, the fuse will blow before the wire catches fire. You can use lower rated fuses in the fusebox and then run thinner wires from there.

 

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This is what I would do .  The indicator LED is in parallel with the new load so to actually give an indication if the load is receiving power or not.  Put it anywhere else, such as in parallel with the relay coil and all you are getting is an indication that the relay is getting power - the load fuses might be blown but the LED would still light up, which is useless.  Also, you may not need the back EMF diode, a lot of automotive grade relays already have them built in

circuit.png

 

 

Edited by G.Lewarne

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Thanks guys. I originally didnt have the LED in place I just wanted to check the state of the indicator line to check I hadnt accidently hooked to an always on line. It is a new style LED I just hooked a 501 that Id bought spares of for sidelights, etc. Oh and I did have a fuse right at battery terminal- I just neglected to add that to diagram. The wiring from the battery->fuse->Relay->Fusebox is of a very high gauge so no issues with that overheating.

 

The Amplifier itself has a 20Amp fuse (both at amplifier and new fusebox) and my relay is rated 30/40Amp.  All Im running off it is the Amplifier power and signal line.

 

I guess maybe having the LED in series could have pulled too much power through the signal line.  Ill remove LED try a different relay and get back to you.

 

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22 minutes ago, p-mo said:

I guess maybe having the LED in series could have pulled too much power through the signal line.  Ill remove LED try a different relay and get back to you.

 

quite the opposite.

 

When you had the 501 led in series it was only allowing a handful of miliamps to flow through that circuit (and hence the coil) because of its built in current limiting resistor.  That would have stopped the coil being energized properly and the contacts pulling in.  Always put indicator LEDs in parallel with a load, not in series for this reason

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