Homemade car relay tester

[Cmjl67]

Anyone built one of these? I'm considering doing so, (a) to refresh my knowledge of electronics and circuitry, and (b) because the car is a near 20 year old jag and has about a million fuses and relays and a tester would be easier than faffing about with crocodile clips and multimeter

I've the relay socket already so reckoning a box with 9v battery, sounder, led indicator and push to make switch to power up for test for the standard 4 prong relays

I think I've the circuitry worked out for this and will give further thought to dealing with the five prong relays where I think the centre prong is connected except when relay powered up

Any thoughts

cheers

chris

 

[bareass172]

Check this out:
http://www.garagejournal.com/forum/showthread.php?t=241265

 

[signcrafter]

I've thought about making one to test the relay. The thing that has stopped me is the amount of different relays used on today's vehicles and the lack of cheap relay sockets for those different relays. For now it's easier for me to just replace the relay with a know good and then test out the relay circuits.

But if all you want to do is test the standard bosch type 4 and 5 pin relays that is easy. Get a 5 pin relay socket. Wire up pins 85 to the battery negative. Wire pin 86 to battery positive but put a switch between the battery and the relay socket. Wire pin 30 to battery positive. Pin 87 and 87a would each go to a different LED light on the anode(+) side. The cathode(-) side of the LEDs would go to the battery negative. So when you plug a relay in the 87a LED would light up right away if the relay is a 5 pin. If it's only a 4 pin relay then nothing will happen. Then when you press your button the 87a LED would go off and the 87 LED would light up.

That link above is something I made to test the whole relay circuit and works pretty nice. I've used it a few times now. More complicated but does more.

 

[APEowner]

Making a relay tester is a cool potentially fun project but for troubleshooting it's often quickest to just plug in a known good relay. If you own a 20 year old Jag then you'll need to have a bunch of them on hand anyway.

 

[larry_g]

I would suggest that you have a good load for the contacts. Lighting an LED can be done with a bad contact but it will not carry a real load. Also for good checking you need to check the voltage drop across the contact points. If there is a voltage drop across the points what do you consider acceptable?

Just thinking, do modern relays have contact points or are they all solid state these days?

lg
no neat sig line

 

[hackwelder]

I would suggest that you have a good load for the contacts. Lighting an LED can be done with a bad contact but it will not carry a real load. Also for good checking you need to check the voltage drop across the contact points. If there is a voltage drop across the points what do you consider acceptable?

Just thinking, do modern relays have contact points or are they all solid state these days?

lg
no neat sig line

+1 on using a real load for testing, like an incandescent bulb.
Electromechanical and SS relays are still made and many hybrid ss/mechanical types too.

 

[cowboy73]

What about this: http://www.amazon.com/dp/B0054WGSD2/?tag=atomicindus08-20
This isn't real expensive and would probably be a lot easier.

 

[Vegaman_Dan]

I have found that the most common failure of relays are the points not making clean contact. They'll click just fine, but too much pitting or arcing at the contacts will kill them off over time.

Replacement with a known good relays is the quick and easy maintenance. I wouldn't bother buying them at the local store though, and just get them online in bulk for around $2 each. If you spend $4, you can get them with the pigtail harness too which is useful in projects. Amazon and Ebay are both good sources.

 

[Danglerb]

I have two Porsche 928's, both full of relays, some of which aren't just expensive, they are Porsche expensive, as in $200 each. Functional test of a relay is NOT worth the time or effort, for exactly the reason above, many will fail flaky so a "practical" test would need real world loads and many cycles over perhaps weeks.

Simple go/no go tests are better done with a couple jumpers and a test light, such as testing a brand new relay before installing it to see if that fixes the problem.

Lisle sells a set of modified relay extension sockets, pull the relay, insert relay in Lisle socket, insert socket where the relay came from, check operation via handy tabs.