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Double Relay Explained. . . In Color!
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Mal evolent
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PostPosted: Fri Jun 13, 2014 7:14 am    Post subject: Reply with quote

the lower diode goes to connection 86, relay coil, and ground. when a connection is made to a coil, that coil generates a magnetic field. when the connection is opened, that magnetic field collapses. the inward collapse of the magnetic field is in the opposite direction of the previous expansion of the field. this causes a stupendous reverse voltage spike. 321 volts from a 12 VDC coil, by actual measurement. Hence the fat blue spark when you unplug a motor.

the diode absorbs that spike and shunts it to ground. when used in this way, it is a commutating ( switching ) diode. get a diode rated for 400 PIV ( Peak Inverse Voltage )

It must be connected to the coil, or the side of a switch connected to the coil, to be effective.

good for starter solenoids - Ford uses Diode Suppressed solenoids - , wiper and fan motors, et cetera. you would need a vast diode for a starter motor.
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telford dorr
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PostPosted: Fri Jun 13, 2014 9:24 am    Post subject: Reply with quote

[Oops - typed too slow.]
Above post is correct. The lower end of the diode goes to ground.

When power to the relay coil is turned off, the switched end of the coil will try to go very negative, in an attempt to keep its coil current flowing (it's the nature of an inductance). When it goes more than 0.6 volts negative, the lower diode conducts, allowing the energy from the collapsing coil magnetic field to dissipate. Otherwise, an extreme negative voltage would be developed (think: ignition coil - same effect), which could over-voltage the upper diode, causing it to fail. Two solutions: (1) use a really high voltage diode (e.g. 1N4007) for the main diode and hope you stay lucky, or (2) add the second diode and guarantee you stay lucky...
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01capevwnut
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PostPosted: Fri Jun 13, 2014 3:36 pm    Post subject: Double relays Reply with quote

I did not get to the car today or get to test the relays. I will reassert myself on Monday. This has been a nightmare. The fun is fast out the door here. I will walk away and start fresh another day. I will keep you all posted as to the test of the progress. Thank you all for the advise & input.

John

I must check to see if my hose/pipe from the oil fill to the s boot is loose. see the photos. It cost $1.48 for the elbows and the pipe was free.
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PostPosted: Fri Jun 13, 2014 3:56 pm    Post subject: Reply with quote

Shocked Confused sigh........................
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PostPosted: Fri Jun 13, 2014 4:10 pm    Post subject: Reply with quote

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01capevwnut
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PostPosted: Sat Jun 14, 2014 5:30 am    Post subject: Double relays Reply with quote

I hate a silly fix and real stupid modifications as well, but it is painted black at this point and has proven itself in my other FI S/B for over six months of daily use. For $1.48 I think it is a well worth the permeant replacement of the hose that would cost me $25 with shipping. Advanced Auto don't know what I am talking about. unfortunately I don't have any current photos of it painted black but I will post them. when I put it all back together. In fact I made another for a friend and his mechanic in Hilton Head through he purchased it at a parts store.
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PostPosted: Sat Jun 14, 2014 9:42 am    Post subject: Reply with quote

Quote:
from the oil fill to the s boot
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any idea why it is plumbed this way? You also have a free air alternator. What engine is in this bus? Normally on a T4 FI engine the S-boot goes to the breather, which has a diaphragm designed to not let the case become a huge vacuum can, and to the decal valve, and AAR. That leaves the S-Boot a sealed unit where all air coming into it comes through the AFM so it can be monitored.
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Randy in Maine
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PostPosted: Sat Jun 14, 2014 10:50 am    Post subject: Reply with quote

Is that 76-79 FI Type 1?

I was trying to figure out where I could get that hose fromt he oil fill to the S boot, but have not found one. Anyone know?
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PostPosted: Sat Jun 14, 2014 8:19 pm    Post subject: Double relays Reply with quote

That is the motor on my 78 Super beetle. The AFM and filter box was not yet installed. I wanted to get a clear photo in case anyone wanted to copy/make it for their beetle. Some one else thought I had a bus, but no such luck on my part, it's a super beetle.

Airhead parts has the correct hose, but again not wanting to spend the money on the part + shipping I saw $1.48 for the making of my part better than the $25 for the part + shipping.

My apologies to those who want to stay pure. I painted it black after the fitting in the photos and it looks great. I did not want to lose this opportunity of the photos thinking I had something here so that is why it is white in the posted photo. This is the only mod I have made to this vehicle. Otherwise it is bone stock. I have had three FI S/Bs and all were missing this correct hose. P/Os substituted straight hose in stead of the real Mccoy. This is usually a mess that falls off at the most inopportune of times. I see this hose replacement as permeant fix that will never need correction again. I have photos of all the pipe length and elbows should anyone care for them.

Again Thanks for all the help to all who have answered my questions on the relays and of course I will post my findings on the relays tested once I get back into the garage after the 16th.
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busdaddy
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PostPosted: Sat Jun 14, 2014 8:59 pm    Post subject: Re: Double relays Reply with quote

01capevwnut wrote:
That is the motor on my 78 Super beetle. The AFM and filter box was not yet installed. I wanted to get a clear photo in case anyone wanted to copy/make it for their beetle. Some one else thought I had a bus, but no such luck on my part, it's a super beetle.

Airhead parts has the correct hose, but again not wanting to spend the money on the part + shipping I saw $1.48 for the making of my part better than the $25 for the part + shipping.

My apologies to those who want to stay pure. I painted it black after the fitting in the photos and it looks great. I did not want to lose this opportunity of the photos thinking I had something here so that is why it is white in the posted photo. This is the only mod I have made to this vehicle. Otherwise it is bone stock. I have had three FI S/Bs and all were missing this correct hose. P/Os substituted straight hose in stead of the real Mccoy. This is usually a mess that falls off at the most inopportune of times. I see this hose replacement as permeant fix that will never need correction again. I have photos of all the pipe length and elbows should anyone care for them.

Again Thanks for all the help to all who have answered my questions on the relays and of course I will post my findings on the relays tested once I get back into the garage after the 16th.

I completely understand where you are coming from and applaud your enginuity in fabricating a replacement. But at the same time once stuff like that starts what will get hacked next?, that seemingly expensive hose lasted for almost 36 years so if you look at it on a $ per year basis it's almost free. Adding things like that often interferes with other components and sooner or later things will have to be bent or moved to get along with it, stuff like that disturbs the VW mojo that worked on milliions of those cars for many years, good temporary fix but I'd still get the real hose when I can.
Another point to consider is how many other 38 year old cars still have the parts support yours does? Yes your crafty fix does the job but in 10 or 20 years when it's time to make it as original as possible will Airhead or similar suppliers still be around and still have the part?, support the sellers who are making an effort to produce a quality correct part because they may not last without you. If you find the price of repro VW parts hard to swallow you should shop for parts for makes and models with much lower production numbers, it's essentially the same pricing but with another zero added, jump on the parts when you can.
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PostPosted: Sun Jun 15, 2014 10:39 am    Post subject: double relays Reply with quote

You know what? That is an excellent and intelligent argument with regards to supporting the parts suppliers & industry at the same time, not to mention the fact of the car remaining as close as close as possible to original for the future generation of collectors.
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PostPosted: Mon Jun 16, 2014 11:13 am    Post subject: Double relays + hose from oil fill neck to s boot Reply with quote

Relay test:

relay 1: 85 to G, power to 86c I get a click, then power to 86 i get a click.

relay 2: the same as relay 1

relay 3: 85 to G, 86C to power I get a click, NO click on 86

Now for anyone who needs a oil breather hose:

Is that 76-79 FI Type 1?

I was trying to figure out where I could get that hose fromt he oil fill to the S boot, but have not found one. Anyone know?

This is the correct hose to use that is fitted for the job part # 181 129 651. Airhead parts has it :

https://www.airheadparts.com/vintage-vw-parts/air-...81129651-c

Bughaus has it also:
http://www.bughaus.com/air_cleaner_hose_-_181129651c.htm

One is a dollar cheeper than the other. Hope this helps I will be replacing mine to stay stock.
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01capevwnut
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PostPosted: Mon Jun 16, 2014 11:15 am    Post subject: Reply with quote

Randy in Maine wrote:
Is that 76-79 FI Type 1?

I was trying to figure out where I could get that hose fromt he oil fill to the S boot, but have not found one. Anyone know?



This is the correct hose to use that is fitted for the job part # 181 129 651. Airhead parts has it :

https://www.airheadparts.com/vintage-vw-parts/air-...81129651-c

Bughaus has it also:
http://www.bughaus.com/air_cleaner_hose_-_181129651c.htm

One is a dollar cheeper than the other. Hope this helps I will be replacing mine to stay stock.
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01capevwnut
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PostPosted: Mon Jun 16, 2014 11:18 am    Post subject: Reply with quote

telford dorr wrote:
Yes, you can, but I doubt it will fix the problem. Consider: there is no reason the relays should fail, unless they're driving something which is pulling way too much current.

I'd do an analysis on the 'failed' relays and determine (1) which relay is failing, and (2) what is the failure mode. Bench testing is easy if you have a 12 volt source (battery, battery charger, power supply, etc.). You should be able to apply 12 volts to each coil, activate each relay individually and observe them pull in. Inspect the contacts on each relay and look for signs of failure or overheating. Post the results.

I'm betting there's an intermittent short in the system somewhere...

p.s. here's a corrected schematic from the first page showing a double relay equivalent built from standard cube relays. Note my version has two diodes. The second diode protects the first diode from back EMF from the relay coil. The diodes allow the starter and the airflow meter to both drive the fuel pump relay, but they keep the airflow meter from trying to drive the starter:
Image may have been reduced in size. Click image to view fullscreen.


Relay test:

relay 1: 85 to G, power to 86c I get a click, then power to 86 i get a click.

relay 2: the same as relay 1

relay 3: 85 to G, 86C to power I get a click, NO click on 86
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telford dorr
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PostPosted: Mon Jun 16, 2014 5:02 pm    Post subject: Reply with quote

So: relay #3's diode is probably blown, making it a candidate for permanent retirement.

As far as the other two go, next you want to inspect the contacts on the relays to see if any are burnt. If you can get the relay cover off, make a note of any obvious damage.

If nothing obvious noted, run your test above again, this time with +12 on terminals 88Z (relay section A) and 88Y (relay section B), and a test light from 88A / 88B (relay section A) or 88C / 88D (relay section B) to ground. When the appropriate relay activates, the lamp should light.

If you want to get crazy about it, here's a test fixture circuit for bench testing double relays:
Image may have been reduced in size. Click image to view fullscreen.

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'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
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Same thing happens when you're stupid. - Philippe Geluck
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Last edited by telford dorr on Mon Jun 16, 2014 5:59 pm; edited 3 times in total
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01capevwnut
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PostPosted: Mon Jun 16, 2014 5:51 pm    Post subject: double relays Reply with quote

If nothing obvious noted, run your test above again, this time with +12 on terminals 88Z (relay section A) and 88Y (relay section B), and a test light from 88A / 88B (relay section A) or 88C / 88D (relay section B) to ground. When the appropriate relay activates, the lamp should light.[/quote]

Ok will do tomorrow on the testing.

I am beside myself I took a running engine out now it won't start. I was quite cocky when it came to starting and trouble shooting this kind of problem. I am down to using the Muir book I went through the tune up procedure. I re pulled the distributor re set TDC. All for not. I must be missing something. I am fried, tomorrows starts the new attack.

JV signing off...
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PostPosted: Thu Jul 03, 2014 2:32 pm    Post subject: Double relays Reply with quote

I stayed away from the car for a few days to give myself a break. I got the car back together Monday the 30th. (little things I was testing) I found no gas going to or through the fuel rail. So I checked my lines they were inverted. Six more times of getting under the car (I put them on wrong each time, I can only imagine I was laying down at a different angle each time when I went under the car.) Anyway my foolishness. Got the car running. I will test those extra relays and post some findings as time permits.

Thanks to all who shared,

John
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PostPosted: Sat Aug 05, 2023 8:03 am    Post subject: Re: Double Relay Explained. . . In Color! Reply with quote

My OEM double-relay failed so I cut it open and took pictures of the guts so people can see what it looks like inside that li'l black box Think

Note: The removed case is in the correct orientation in each picture.
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PostPosted: Sat Aug 05, 2023 4:04 pm    Post subject: Re: Double Relay Explained. . . In Color! Reply with quote

Cool, thanks! That’s helpful for diagnosing weird shit that seems to be popping up more frequently Smile

Robbie
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PostPosted: Sat Aug 05, 2023 4:16 pm    Post subject: Re: Double Relay Explained. . . In Color! Reply with quote

strange. Mine came apart without any cutting. The sides just had to be spread apart a little to take the cover off. It was a genuine Bosch too. If a diode is bad it can be replaced, and if the points are burned they can be filed.

Thanks for the photos.
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