Hello, I have a couple of what are probably very basic questions that hopefully someone can help me with. They are:
Is there a limit to the current that can pass through the coil (terminals 86 to 85) on a standard 40A relay?
Is it safe to connect terminals 87 and 86 together if different power sources are connected to terminals 86 (with a low current) and 30 (a higher current)?
I added auxiliary lighting to my motorcycle and used a relay so that the lights can be wired direct to the battery, but will only work when the bike is powered. As the bike provides a switched socket for accessories, I used a plug with the positive pin connecting to terminal 86 of a relay, terminal 85 then goes to a switch, which returns to the negative pin of the locker to ground it. The power to the lighting then coming from the positive terminal on the battery through terminals 30 and 87 of the relay. Obviously I also have fuses coming from both positive sources to protect the cabling,
I am sure that is a pretty standard layout, and it works perfectly. I cannot remember precisely why the switch was placed after the relay, but I read something which made it sound like a better choice. But the reason for using a relay was firstly so only a minimal current would go through the switch which is fastened to the handlebars, and secondly because the accessory circuit is shared, so it seemed better to power a relatively high current use directly from the battery.
The reason for my questions is that what I would like to do now is make it so that when the bike's power is turned off, the lighting will remain on until the switch is turned off to break the circuit. Essentially making the relay power the coil itself once engaged. I know that this can be achieved by connecting terminals 87 and 86 together. My concerns are that the current required by the lighting would go through the coil, which will be several amps rather than the milliamps the coil itself draws on its own circuit. So would this be too much or does it not matter? And it also means the coil, once engaged, would have both the switched connection and direct battery connection powering it. Is that safe? Both in terms of how it would affect the current they draw, but also it effectively means the battery's positive terminal will be connected to the positive pin of the accessory socket.
I realize that just connecting the terminals on a single relay would undermine my requirement for only a small current goes through the switch, as the current drawn by the lights will also be connected to terminal 86 and therefore go through the switch too. So I would look to use two relays, the one described above to only active the coil of a second relay, with a direct battery connection on terminal 30 to power the lighting.
Incidentally, I can see how three relays can be used to avoid all the things I am asking about, but I am sure there must be a simpler solution with two relays.
I hope that makes sense. I gave the full context of what I am trying to achieve to explain my questions, but I would like to understand the general principles rather than just get an answer to the specific problem.
Thank you.