 Voltage drop on relay circuit?, 12v down to 10.5v |
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| IronHillRestorations |
 Jul 11 2017, 11:46 AM
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I. I. R. C.  Group: Members Posts: 6,731 Joined: 18-March 03 From: West TN Member No.: 439 Region Association: None 
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I'm making a harness that needs a power circuit switched via relay.
I've got generic Bosch style 5 pin relays, and I'm seeing a voltage drop on the power out side of the relay. It's rare that I make a harness that needs a relay, and in the few that I've done with a relay circuit, this has never been reported as a problem. I'm not an electrical engineer, but I always thought a relay was just an electro-mechanical switch and I should be getting the same voltage on the output. Just to be clear for those who do know more about this than me, none of the wires that I'm using to test this are more than 24" long and none are less than 14 gauge wire. The relay power is for a coil pack, so I'm sure that needs a good 12+ volts. |
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| Spoke |
Jul 11 2017, 02:16 PM
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Jerry Group: Members Posts: 6,991 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None
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It is possible that the battery charger is full-wave rectified with no filter caps, not pure dc.Not good if used by itself.
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| Dave_Darling |
Jul 11 2017, 05:59 PM
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#3
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914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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QUOTE(Spoke @ Jul 11 2017, 01:16 PM)  It is possible that the battery charger is full-wave rectified with no filter caps, not pure dc.Not good if used by itself. Could that show a voltage drop across a switch like in a relay? PK could try using a battery instead of a charger/voltage supply box. I'd be tempted to pry open a relay to see WTF is really going on in there--but I've got bit of the old "destructo" still in my soul. The round Bosch relays literally have contacts like a set of points do. Should be zero resistance or voltage drop across them unless there is contamination/corrosion of the contacts. --DD |
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Posts in this topic
Perry Kiehl Voltage drop on relay circuit? Jul 11 2017, 11:46 AM
914Sixer Are all the relays showing the same test? Jul 11 2017, 12:03 PM Perry Kiehl Yes, Mark they do. I currently have only cheap on... Jul 11 2017, 12:14 PM Bartlett 914 If you can, measure at the relay input and output.... Jul 11 2017, 12:27 PM danschy Pretty hard to get a significant voltage drop acro... Jul 11 2017, 12:54 PM jd74914 Do you know the circuit load (current)? How are yo... Jul 11 2017, 12:55 PM Perry Kiehl This is all bench testing. I'm using a batter... Jul 11 2017, 01:36 PM Spoke What voltage do you measure at the output of the c... Jul 11 2017, 02:19 PM Perry Kiehl I feel sooo stuuupid! It's the battery ch... Jul 11 2017, 08:50 PM
914_teener
I feel sooo stuuupid! It's the battery c... Jul 12 2017, 07:06 PM Spoke It's called "fog in the cockpit". Ha... Jul 11 2017, 08:52 PM Perry Kiehl
It's called "fog in the cockpit". H... Jul 12 2017, 08:31 AM Perry Kiehl The smart guys figured it out right away. Jul 12 2017, 07:44 PM |
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