Is it important to have pin 85 to ground and 86 to the power supply (in this case a draw from the headlights to energise the coil). I thought I’d didn’t matter unless the relay was diode protected.
I have power in to 30, and out from 87a to the DRLs and that works fine, but I have grounded 86 and am seeing 7.5 volts between 85 and earth. The Relay is unused, but has been in the shed for maybe 15 or 20 years, it is Maplin branded, so not likely to be the most expensive. Not sure if it is faulty, or if this OK. Reluctant to connect it to earth when I am seeing a voltage.
So just set up now as ‘always on’ with power feed into pin 30 and 87a feeding the DRLs.
Questions:
Is the relay goosed, or would you expect to see 7.5v on pin 85 when the only powered input was coming from pin 30?
Does it matter which of the coil terminals 85/86 is grounded?
Current in the coil causes a magnetic field and the armature closes.
Red Herring here. There are things like bi-polar relays, I’ve used them at work, where a + pulse is used to close it and a - pulse opens it, and it remembers state after the pulse has gone. Expensive!
DIN 72552 defines contact numbers in relays for automotive use;
85 = relay coil -
86 = relay coil +
87 = common contact
87a = normally closed contact
87b = normally open contact
DIN 72552 says pin 30 is from Battery + direct
Where is this pin 30 you refer to? Do you have the normal five pins labelled on the relay?
It’s a mechanical relay yeah. You need to ground 85 and put 86 to your switch live. If you’re using your side lights etc 86 should be exactly the same voltage as that wire. Check you have a good earth. How did you connect to the sidelights? Scotch locks or a decent connection? Scotch locks are the worst thing I have ever seen!
Test between battery + and 85 to see it the earth is good. Test between 86 and battery - to make sure live feed is good.
30 should go to a live, the battery eg. Via a fuse. Then 87 to the DRL’s.
I have :
12v connected to 30
87a goes to an led light the other end of which is to ground
87 not connected
86 not connected
If I measure between 85 and gnd, I am seeing a voltage of 7.5v.
85 and 86 will come into play when I wire them up, but I am reluctant to wire them up when I am seeing 7.5v between 85 and ground. Looks like a relay fault to me, but I really don’t know if this is maybe normal?
Ah I see. You’ll find it’s just induced voltage. Your meter has such a minuscule resistance when measuring volts so it doesn’t become a load thus altering the readings that it won’t ‘pull down’ or ‘pull up’ induced voltages. Research resistance networks it saves me a lot of typing if you want to know more, am happy to help or explain if you want tho. Induced voltage is more of an AC issue but with LED drivers it’s common for them to invert or chop the DC to get the LUX level they want it causes the same induction as such.
Here’s what I suggest. Get a common car bulb and solder a wire on the main body, or go Heath Robinson and tape it on WITH CARE. Hold the other end of the wire on 30 and the tip of the bulb (it’s a lamp but…) on ground. It will illuminate if 30 is live. Next hold the wire on 85 or 86 and put the tip of the bulb to earth. It will not illuminate even faintly. If you test at the same time voltage will show zero there now. If not there’s more to it but I’m 99.9% sure it will act as I explained.
When I was trying to work out why my Ducati wouldn’t run a couple of winters ago, I was advised to make or buy a test-bulb. I bought one from Halfords and it was a huge help.
(Eventually, after all sorts of red herrings, I traced the fault to the wiring for the in-tank fuel pump, which had broken inside the insulation.)
Had a look this morning, and yes happy that the relay is OK.
I will move the ground to 85, just to be ‘tidy’.
Need another breakout fuse which I will get today from Halford to finish the job off.
Will then have proper E marked DRLs that dim on headlights going on, possibly not mounted in the correct place (too narrow) but will feel a lot safer on the shady country lanes.
I have a made up a set of meter leads with a built in potentiometer, turn the setting to ohms, set it to 10k then back to voltage. That pulls down floating voltages nicely. I don’t use a fixed resistance because some times I like to lower the resistance but you have to be cautious, you’re introducing a load. That will effect accuracy and load up the power supply in question, too low a resistance is going to do damage. You need to know where and when to do that sort of thing, current rating and flow have to be adhered to for the resistor too. Luckily there’s lots of people online who will normally help out. I love forums for this reason.
WITH CARE. Hold the other end of the wire on 30 and the tip of the bulb (it’s a lamp but…) on ground. It will illuminate if 30 is live. Next hold the wire on 85 or 86 and put the tip of the bulb to earth. It will not illuminate even faintly. If you test at the same time voltage will show zero there now. If not there’s more to it but I’m 99.9% sure it will act as I explained.