INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Suitable transient voltage suppression diode

Suitable transient voltage suppression diode

(OP)
I have a 1992 Dodge Stealth with a relay that no longer works, The circuit is fused for 15 amps and is 12 volts. After some investigation I have determined that a transient voltage suppression diode, which was soldered into the relay, is open. This very tiny diode has the number 77 on it and also has the number 1 then a dot followed by what appears to be the capital letter I (eye). Can a replacement diode suitable for this circuit be recommended? Any help is appreciated

RE: Suitable transient voltage suppression diode

Any 1n4001 series or higher should work. Is this in series with the relay? Just wondering because an open suppression diode would not prevent the relay from operating. Ford has a diode in series with a relay to prevent damage to electronics should a battery be connected in reverse. Many automotive relays now just use resistors in parallel with the coil for suppression.

RE: Suitable transient voltage suppression diode

You probably already did, but just to make sure...

Did you confirm the price of a new relay. Some common types are not very expensive, under $3 shipped.

RE: Suitable transient voltage suppression diode

You seem to be going down the path that the transient voltage suppressor is causing the relay to fail. Unless it's a dead short, that should not be the case. It.s more likely that the relay itself is fubar, and replacing the suppressor will not change the situation. Does the relay try to engage? If not, then you probably have an open coil as well. If the relay does engage, but doesn't make contact, then your contacts are trashed. Either way, you probably need a new relay.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

RE: Suitable transient voltage suppression diode

An open free-wheeling diode seldom causes a relay malfunction.

But it can, and does, cause the relay drover Circuit to fail. If it is Electronic (a transistor for example) it will be hurt by the inductive overvoltage that the diode is supposed to handle.

You may need to look a bit further. Finding and replacing the diode is OK, but there could be more to look for.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Suitable transient voltage suppression diode

(OP)
Thanks to all who responded. The diode is in series with the coil. I have purchased 2 new replacement relays which also tested bad and were returned. I am testing the relay per the instructions in my service manual. The relay does make the audible clicking noise indicating closure of the contacts but 12 volts is not found across the appropriate terminals. This relay actually has 2 separate coils and the other coil works as it is supposed to. The cost for this particular relay is $96 and up depending on supplier. This and the problems with the new relays is why I have pursued attempting to repair my relay. Testing all other internals of the relay has found only the diode to be malfunctioning. All testing that I have done takes place inside my house so nothing in the circuit itself is in play. Just as an aside the other coil is actually double wound to provide its suppression. Thanks again to everyone

RE: Suitable transient voltage suppression diode

"...this particular relay is $96..."

Ouch! Good luck with the diode repair.

RE: Suitable transient voltage suppression diode

"In series" - sounds very special. Why would that be so? Is it a polarized relay?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Suitable transient voltage suppression diode

I have never seen a relay like this in automotive use. That explains the $96. Could you explain the function? Just how are you testing this? a diode in series with a relay coil may show as an open on many testers and the diode may be a zener. I have a strong suspicion that the problem lies elsewhere and the relay is fine.

RE: Suitable transient voltage suppression diode

(OP)
The coil with the double winding runs the fuel pump. The coil with the diode runs the idle control servo motor, the purge control solenoid, and the air temperature sensor. I have the factory service manual for this car and in it there is a very detailed description on how to test this relay. The particular check that this relay fails is: Connect the positive pole of the voltage source to pin #10, connect the negative pole of the voltage source to pin #8 and use a voltmeter across pins #4 and #5. The volt meter should show the source voltage. When I connect pins #10 and #8 The contacts can be heard as a "click" but the volt meter reads Zero volts. I perform this and the other checks inside my house using connectors I assembled. I purchased 2 brand new relays and both failed this very same check and were never installed in the car. They showed up bad. The relay has a cover which is not all that securely attached so I removed it from my relay to see what was inside just for the heck of it. I used an ohm meter to check the coils and all other possible junctions inside the relay and appropriate resistance was found. I then decided to remove the diode and measured its resistance in both directions. I found resistance way 1.5 million ohms indicating an open diode. That is my story and pretty everything I know about this relay. What problems there were with the 2 new relays I purchased I do not know for sure other than zero volts across pins #4 and #5 when there should have been 12 volts. Many thanks once again for all the responses. Ultimately I hope to repair this relay as there is only 1 company still making them, Standard Motor Parts and they are getting them out of China.

RE: Suitable transient voltage suppression diode

There seems to be something wrong in your description. Assuming that the contacts are 4 and 5, if they are closed, you should not be able to measure 12V across them because they should be shorted. It's extremely unlikely that you would get 2 brand relays that can't operate correctly. The fact that the contacts are moving basically says they're working correctly. Therefore, the test procedure is not correct, or the interpretation is not correct.

Do you have a schematic drawing of the relay along with the test procedure in PDF form?

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

RE: Suitable transient voltage suppression diode

I understand this is frustrating for you, but I would bet what little reputation I have here that the three relays you tested are good. I rebuilt an automatic transmission and that manual had several errors. I would take a step back and rethink this.

RE: Suitable transient voltage suppression diode

Hi

Any time you connect probes across a closed contact you will see voltage drop, 0V is good.
Black test probe to neg. supply and red probe to either pin 8or10 to read source voltage maybe.

Chuck

RE: Suitable transient voltage suppression diode

Note that some DMMs do not generate sufficient voltage necessary to read diodes. The typical DMM has a specific test range for diodes, usually marked with the diode symbol. ONLY that range will give the correct reading for a diode.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

RE: Suitable transient voltage suppression diode

(OP)
I do not have the schematic or instructions for testing in PDF form. I tested the diode in the proper selection on my DMM. Pins #4 and #5 are continuous with each other so reading 12 volts across is proper. About a year ago I had another electrical issue with this car and during my investigation I tested this relay and, at that time, it tested good doing the very same tests I have described. I found it hard to believe that 2 new relays would both test bad, but this is a double relay with 2 coils and the other coil tests just like it is supposed to. I am confident in my findings but not comfortable telling a manufacturer the problems I have encountered. This relay is not your usual situation. Again, thank you for replying and efforts to help me. I can scan the pages in my factory service manual and save them as a jpeg. Would that help?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close