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As I wrote above, your figures don't add up.
To put it in other words, if you measured 4 Volt between A & B then Vb - Va should equal 4 Volt.
Thanks for the suggestion but it has a few issues:-
1. the minimum switching current shown in the relay data sheet is 10 mA & the OP measured about 4 mA. See my comments in an earlier post (post #10) re the contact current issues.
2. I don't know if the pulse can be applied immediately the ignition is turned on. A short delay may be necesary.
3. It would be necessary to put a diode across the coil in order to limit the back EMF to about 0.7 Volt.
The life might go down to 10 million cycles at 1 ma at 5 volts, but it will still be chugging long after the beamer. Perhaps, but the data sheet states 10 mA min, so I would not want to make assumptions.
Seems easy enough to check. Is it? The only way I can see to test it is to build the circuit. How else could you simulate the effect?
Yes, good idea.
Regarding the drop out time: Don't forget the load from the GPS is still in circuit on the other side of the cap. Now this may be a problem if this turns out to be the GPS battery voltage. Something that needs to be checked unless you want to use the 12 volts before the power supply.
I looked at the data sheet you pointed me to and I could not see 5 V, 1 mA mentioned. Where did you find this info?I understand your concern over the current. They can't publish all the possible combinations of voltage and current as it pertains to life as it is not a simple matter. But, have a peek at this one which does specify several levels as well as the often mentioned 10 ma min. https://www.mouser.com/ProductDetai...=sGAEpiMZZMv4tz1TW/ArE4mGdvW5WwrPkzLj6m0m3UI=
Turns out the best performance is at 5 volts, 1 ma. See below
As far as the instant on I would just hold down the GPS button then plug it in. You may be right. But I have been assuming that it may be necessary to allow some time for the car systems to stabilise before starting the GPS.
Having said all that I like your circuit. Thanks
The approximate formula is:-Len, that's great! You are right in presuming it would need a delay before starting. A ~2 second delay before starting and a ~1 second pulse would be absolutely ideal - what would you replace C1 and C2 with, with this in mind? Otherwise, that's fantastic and very easy to follow too - thank you You're welcome.
Incidentally, I shall be posting a video of the finished result on the car forum so I shall link you to it too so you can see it in action That will be good to see.
You have to open the actual data sheet. Then it's about 7/8 down the first page on the left.
I think most are now sputtered with Ruthenium because it is inert.
Contact material Ruthenium
Min. recommended contact load 10mV, 10mA
Minimum switching voltage 10mV
Initial contact resistance 200mΩ max. at 10mA, 6VDC
Electrical endurance
form A (NO) and form B (NC), resistive load, +25°C
20VDC, 500mA 1x106 ops.
20VDC, 250mA 20x106 ops.
5VDC, 1mA 100x106 ops. form C (CO) contact, resistive load, +25°C
10VDC, 500mA 1x106 ops.
10VDC, 250mA 20x106 ops.
5VDC, 1mA 100x106 ops.
I always used gold plated contacts for switching audio. They didn't cost more than silver plated contacts that corroded and did not pass dry audio.