Current from a Boch relay
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=30125
Printed Date: May 11, 2024 at 10:21 AM
Topic: Current from a Boch relay
Posted By: kaffeene
Subject: Current from a Boch relay
Date Posted: April 10, 2004 at 6:52 PM
Typically how much current is drawn from a Bocsh relay coil? Is it safe to use on a remote output of a headunit or should I look for a relay that draws less current?
Replies:
Posted By: Mad Scientists
Date Posted: April 10, 2004 at 8:57 PM
Just measure it with your meter.. What are the specs on the head unit? Regards, Jim
Posted By: kaffeene
Date Posted: April 11, 2004 at 7:07 AM
I want to know how much amperage the coil is going to use? 12V and I dont know what the coil resistance is. I have nothing hooked up, just wanted to know what they typically use as far as current .
Posted By: sparkyssb
Date Posted: April 11, 2004 at 12:27 PM
The current draw by the coil of a bosch relay is ~0.160 amps. Most amplifiers draw at the most 1/3 of this just to turn them on. Also, they Bosch relay has low resistance. (Usually ~75ohms) So... a different relay will probably be your best bet just so you don't accidentally damage the headunit's transistor for the remote out.
Look for a relay from Radio Shack. Its stock number is 275-248. It has a coil resistance of ~400 ohms which means that it will draw ~1/5 the amount of current of the Bosch relay.
Also, look at protecting your head unit with a diode soldered on the relay. You can use Radio Shack part #s 276-1101, 276-1102, 276-1103, or 276-1104. You need to put this inline with the coil or the power terminals. Just make sure the positive terminal and the striped end of the diode are together before you solder. Do not connect the positive terminal and anode together.
Hope this helps!
Eric Lucas
Posted By: kaffeene
Date Posted: April 11, 2004 at 4:49 PM
I looked at that part number on the Radio Shack site. How can you tell how many Ohms it has? It doesn't say. Its ok to use it in an automotive application?
Posted By: JasonL
Date Posted: April 11, 2004 at 5:52 PM
The coil impedance should be listed on a product datasheet, though I don't see one for the Rat Shack relay. Or simply measure with a multimeter.
Look at your headunit manual and see if there is a max current for the remote turn-on. I'd be surprised if it can't supply the ~160mA to activate a Bosch relay.
Posted By: JasonL
Date Posted: April 11, 2004 at 5:53 PM
Sometimes the coil impedance will be listed on the packaging as well.
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