LinkBack URL
About LinkBacks
Reply With QuoteThere will be a brief moment of no voltage as the relay switches. I assume you're looking for a seamless switch; you could achieve this with a capacitor to supply the current during the switch duration.
Assuming you're working with a standard SPDT relay:
I'd like to place a +12v source on the N/O (87a) terminal. I'd also like to place another +12v source on the N/C (87) terminal. When the coil activates/deactivates, will the device attached to the common (30) terminal see a voltage change? Will there be a brief moment of no voltage? Will there be a voltage spike or dip? Or will it be a seemless switch from being powered by one +12v source to another?
Thanks in advance.
There will be a brief moment of no voltage as the relay switches. I assume you're looking for a seamless switch; you could achieve this with a capacitor to supply the current during the switch duration.
Yes. I'd like to switch the 12v ignition lead for my P1900 from an actual 12v ignition lead over to a 12v battery lead with an inline switch. This way the PC will continue running as there will still be 12v on the P1900's ignition lead when I turn the car off, but I could then kill the PC by flipping the inline switch on the 12v battery feed to simulate the ignition going off.
How would I know what size capacitor I'd need?
The capacitor size you need depends on the amount of current being drawn, and the time it takes to switch (ie how long the capacitor needs to supply the power). If this is for a turn-on signal, it's likely both these values are quite small, and you don't need a very large capacitor.
Once you have rough values for time (s, seconds) and amps (A), the rest is some basic math*:
Caps are measured in farads (F). F = C/V. C = A * s. So F = (A * s) / V. Plug in your values and you get the minimum capacitance you need to supply the current you need. Real-world caps are not perfect though and have a voltage dropoff, so double or quadruple that number.
*disclaimer: IANAEE, I'm just whinging it, so I may have some errors.
Or, y'know, you can just use a 100uF cap and see if it works (which is what I'd do)
What exactly are you trying to do? If what you want is to turn on with ignition but then not turn off until you hit a switch, I can think of better ways to go about it.
Posting Permissions
Bookmarks