Register now to get rid of these ads!

Technical #@&&*$@!!! Jamb Tacts!

Discussion in 'The Hokey Ass Message Board' started by 1great40, May 14, 2015.

  1. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    I hope no one else has had this kind of experience with those nifty little spring loaded electrical contacts that you can use to connect power to your doors or liftgates without the need of installing a wire loom through the jamb.

    I installed a 5 position set of these things in each door jamb of my 40 Pickup. The doors have power windows and electric bear claw latch release motors.
    Although I haven't really had a problem with the windows, the door lock motors were a different story.
    In order to get around the windows and mount the bear claws in the original latch position in the door, I cooked up this idea to actuate the bear claws electrically.The exterior door handles were mounted to a return spring and fitted with a micro switch. The micro switch in turn operated a relay that provided power to the door lock mechanism.
    Years ago, I bought a couple solenoids to attach to the latches. Soon I realized that the solenoids didn't have enough power for the job. So, I grabbed a pair of power lock motors from an Astro van, made up a linkage and voila! I had electrically operated locks. The big advantage of the electrically operated locks was that I replaced the key cylinder in the passenger door with a similar keyed switch, so when the switch was off, the doors were essentially locked.
    Over time, the Astro lock motors wouldn't always pop the bear claws on the first shot, You would need to hit the handle a few times and finally the latch motor would work.
    Marginal power available from the Astro lock motors, I thought. No problem, I just modified the linkage to provide more mechanical advantage and I was back in business.
    Once, I was power washing fake "movie snow" off the truck after I spent a day on the set of a Disney movie (I was an extra with an old truck, I don't even know if I made it into the movie), The power locks died completely! Stupid Jamb Tacts, I thought as I popped out the back glass to get into the truck. I opened the doors manually from the inside, dried off the contacts and all was well.
    As time went on, the door lock situation became annoying. Especially having to explain to passengers the nuances of getting the door to open. I'm fixing this once and for all, I thought to myself and with that, I ordered up a big honkin pair of 50 lb. solenoids. If these things couldn't trip that latch, they would just punch their own hole through the door so you could reach in and open them yourself!
    I decided to test the solenoids "on the bench" by just hot wiring them to the battery. These things had some serious power! I was in door latch heaven,until I realized that the Astro lock motors "pushed" on the latch mechanism and the solenoids "pulled". I figured out how to disassemble the solenoids and turn the armature around and run it out the other end of the solenoid. Now I had a 50 lb. "push" solenoid. I removed the Astro lock motors and the associated linkage and adapted the solenoid in it's place. Then I wired it all up, connected it to the bear claw latch and after a feeble, little girly sort of "click"...nothing!
    All of a sudden, mental block in my head was gone and I realized it was those #$@!!&** Jamb tacts! The power for the electric locks went from the fuse panel, through a set of jamb tacts in the passenger door, through my key switch and then back out through a 2nd set of jamb tacts in the passenger door and over to the driver's door, through a 3rd set of jamb tacts , through the handle switch and to the solenoid. And finally the ground for the solenoid was provided through a 4th set of jamb tacts. So I had 4 jamb tact connections, each adding it's own resistance to the circuit. The solenoid was only seeing about 3 volts by the time I was through pissing away all my power through these spring loaded turds!
    To make matters worse, these solenoids draw more current than any of the previously installed devices and simple Ohm's law math tells us that the more current you try to draw, the bigger the voltage drop at each resistance.
    But, I'm a smart guy, so I finally broke down and made myself a pair of wire looms to provide the current to the relays in the doors that operated the solenoids. With this new design, I was relegating the jamb tacts to handling the low current side of the circuitry and then the major juice would be hard wired to the relay.
    This was pure elegance, I thought. I have hard wired juice being fed by the wire looms and the little stuff is handled by the jamb tacts so even though I had to add the looms, the jamb tacts are still serving a purpose and there is no real major re-wiring going on.
    I got it all wired up, and, wait for it.... nothing! I have a habit of wiring stuff from memory, so I broke out the schematics that I had drawn during the build and tried to figure out how I managed to break it again. From the cartoons, the only way this was not working would be if there was no power being returned from the passenger door to operate the relay that drove the solenoid. I put a meter to the wire that was coming from the key switch in the passenger door and wouldn't you know...4 volts!!!. I got out some 2000 grit wet or dry and polished the jamb tacts and all of a sudden I get 12.3 volts to feed to the drivers door. The !@#%&**! jamb tacts bit me again!!
    I don't know what the plating is on these spring loaded headaches but I'm sure you can't keep polishing them till you wear it all off, the oxidation that causes the poor connections would just return faster.
    Does anyone know of any corrosion inhibiting compound I could coat these things with?
    I don't mind having to clean it off an replace it periodically.
     
    Model T1 likes this.
  2. Dielectric grease... it's clear
     
  3. Katuna
    Joined: Feb 25, 2005
    Posts: 1,823

    Katuna
    Member
    from Clovis,Ca.

    They aren't able to handle the amp draw of the solenoids. The bigger the sol. you use, the higher the amp draw and the fact you're running the signal through a handful of those contacts, you're shooting yourself in the foot. Think of the solenoids just like your starter or horn. Because of the amp draw, the power has to go through a relay. You don't want it going through a switch. A switch is used to close a relay. Same way your ignition switch closes your starter sol.
     
  4. Don't know what they call it (not di-electric grease, because that would inhibit the flow of electricity), but I would think that "Peanut Butter" looking grease the OEM's put in switches and things would be your best bet.

    Well, nevermind! In spell checking dielectric grease, I just found out that it IS what you want to use, and is probably the same thing as the peanut butter stuff, just a different grade. The dielectric grease will not conduct electricity itself, but it also won't prevent the flow of electricity through the jamb contacts when they are touching. It will help insulate the contacts from
    the air, thereby reducing oxidation. Funny, learn something. Ew everyday! See here for more details..... http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

    Posted using the Full Custom H.A.M.B. App!
     
    Model T1 likes this.

  5. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Then dielectric grease it is! I have also figured out that I can actually go back to the Astro van electric lock motors. When they're supplied with enough juice, they seem to work reliably, draw lots less current and are much quieter!
     
    Model T1 likes this.
  6. I have no idea what kind of butter will fix the electrical contact issue or your design issue.

    But having electric doors with electricity being the only way to operate them is just a bad design. As you have seen first hand, one small problem in the chain of wiring and you loose control of the doors. You can't open the doors when you want. You'll lock yourself in, lock yourself out, all at the mercy of electrons.

    Bear claws type latches are a superior latch and keep the doors from popping open over the road, no question. Working out The details of installing them is a pain in the ass. A quick work around is to throw all mechanical actuation out the window and run wires around the windows and other obstacles. I wouldn't do that on my car and if you asked me to do it on your car I'd tell you no.
     
    49ratfink and metlmunchr like this.
  7. I agree with you on the idea that electric only actuation would be bad, I'm doing the same on mine, but only for outside actuation, the stock inside door latches will still be hooked up. The secondary method of opening from the outside will be to roll down the electric windows, and reach in and pull the inside door release. For dead battery issues, I have a trunk mounted battery with auxiliary posts mounted under the trunk to allow jumping.
     
    Last edited: Jun 9, 2015
  8. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    You guys bring up good points. Most of which I have addressed in the initial design. The dead battery issue is no problem as the battery is in the lower part of the front passenger fender, easy to connect to for a jump. The inside door handles are strictly mechanical and I designed them to work completely independently of the electrical locks. I determined early on that the only thing dumber than getting locked out of your car is to get locked into your car! In the event of an accident, I'm not dependent on power to open the doors from the inside. Someday, when I have everything else worked out, I plan to add a mechanical release that's hidden so the doors are fail safe. In the meantime, as I mentioned, it only takes a minute to pop the back lite and a couple more to re-install it. So while the glass popping is my ace in the hole right now, I believe I have covered everyone's concerns. They were my concerns as well and completely valid.
     
    Model T1 likes this.
  9. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    I just saw an ad the other day from a hot rod parts supplier that sells a bell crank type of mechanism that takes the mechanical movement from the door handle, down to the bottom of the door via a rod and then the other side of the bell crank has a rod that goes up to the bear claw latch to actuate it. No electrons required! I also had designed something along these lines when building the truck but opted for the electric approach because the substitution of the key operated switch, in place of the lock cylinder gave me the ability to lock both doors with the turn of a key, very handy!
     
    Model T1 likes this.
  10. This is the only part that confused me, why is your power going through the jamb tacts so many times. The actual explanation doesn't make sense to me. It makes it sound like your ignition switch is in the door? I'm guessing that isn't true. And if power goes through the ignition switch first, does it have to be on for the doors to open? The power "should" only go through the jamb tacts once per accessory. You "should" get a plenty good ground through the door hinges. For mine I'll have a hot lead in for the popper, and a hot lead in for the power windows, and I have speakers in the doors, so the other two contacts are the pos. and neg. for the speakers.

    Posted using the Full Custom H.A.M.B. App!
     
    Last edited: Jun 9, 2015
  11. If you want to "up" the current capacity of one of these jamb contacts, you can wire 2 or more of the contacts in parallel.
     
  12. That could add twice as many problems easier than correcting the one.

    Mechanical issues/problems shouldn't be treated symptomatically.
    If a tire is flat, treating the symptom of no air would be to put air in it. When it's flat again tomorrow, putting in 2x the amount of air in an attempt to prevent a flat the day after next will cause additional problems.
     
  13. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Blown, I realize that describing things gets a little complex. I have a fused circuit for the power door lock motors. In order to "lock" the doors, I need to be able to switch that power. The switch for the power to the door locks motors is in the passenger door. I removed the lock cylinder and replaced it with a keyed switch that is weather proof and is almost a dead ringer for the original lock cylinder.
    So, to get the power to that keyed switch, it runs into the door through the jamb tact and then once inside the door, over to the keyed switch. The switched power lead now supplies power to the lock motor circuits, one of which is in the passenger door, the other one is in the drivers door. To get that switched power over to the drivers door, it has to come back out of the passenger door via another set of jamb tacts and then over to the drivers door. Once it gets to the drivers side, it goes through another set of jamb tacts to get into the drivers door. Once inside the drivers door, it feeds the power lock motor circuit in the drivers door. An additional issue here is that the cab of the truck is fiberglass, so I need to utilize a set of jamb tacts to provide the ground for any circuitry in the door. I had originally considered grounding the doors through the hinge, since I could simply attach a ground lead to the cab side hinge leaf but I thought a dedicated ground would be better plus I had enough contacts available in the jamb tact device, each jamb tact has 5 connections available.
    So, that explains the convoluted routing of power for the door lock motors. And of course, each one of those connections has a certain amount of resistance associated with it, so the more current you attempt to draw through the jamb tact, the more of a voltage drop you get across the resistance associated with the connection.
    My biggest problem was that I under estimated the resistance of the jamb tacts and the fact that that the resistance changes as the surface of the contacts oxidizes.
    The current for each door lock motor is switched by a relay in the door with the primary of the relay controlled by a micro switch attached to the exterior door handle.
    The new scheme brings the power for the door lock motors directly into the door through the wire looms I made, eliminating the voltage drops associated with the jamb tacts. The primary side of things, that is to say the power that runs through the micro switch and the coil of the relay is still supplied by the jamb tacts. However this is very low current ( milliamps compared to the 15 amps that the solenoids draw).
    To respond to the suggestion posted by 36 Roadster, you are correct, putting 2 or more jamb tacts in parallel will lower the resistance, but I am also clean out of jamb tacts! :)

    31Vicky, I understand your concerns, but electrically operated accessories can be made to operate quite reliably and are a great way to put the features you want into your hot rod. In this case, the circuit allows me to lock both doors of the truck at the same time by the use of the key in the passenger door. The circuitry employed here is of the most basic type, my mistake was not actually verifying the contact resistance and the associated voltage drop and designing around it when I built the truck. A second mistake I made was not actually verifying the force required to operate the bear claw latch. If I had done that and measured the force generated by the Astro van lock motors, I would have known that the motors did in fact develop sufficient force for the latches and that my wiring scheme was the culprit all along.
     
  14. 49ratfink
    Joined: Feb 8, 2004
    Posts: 18,129

    49ratfink
    Member
    from California

    having doors that only open electrically is a disaster waiting to happen. :eek:
     
  15. IF a guy was going to use the jamb contacts on a build, might be good to source them from one of the OE applications. Seems like I've seen them in use on GM suvs. I would ASSume that the OE quality would be significantly better than a typical offshore-sourced accessory, as the OEs generally know that they'll have to live with them for at least the duration of the new vehicle warranty period.
     
    slack likes this.
  16. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Ribbed, you hit the nail on the head
     
  17. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    describe disaster :)
     
  18. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    NO fair...those are real contacts, I got mine at a swap meet, no specs, no warranty :)
     
  19. 49ratfink
    Joined: Feb 8, 2004
    Posts: 18,129

    49ratfink
    Member
    from California



    how about a car fire that kills the battery? there was a 34 Ford on here some time back, got in a accident and was on fire, the doors were jammed shut from the wreck and lucky for the guy inside some bystanders were able to get him out.
     
  20. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Well it would be helpful to know if the doors were physically jammed from the wreck, or the wouldn't open as a result of an electrical failure. In an accident, anything can and does happen and it's more likely that a failed electrically operated door wouldn't stand a chance against a first responder.

    I understand your concerns, they're not unfounded. And to that point we have history to show us that guys with your engineering skills were the ones that kept putting cranks and crank holes in the grilles of cars into the mid 40's.

    I originated this post to poke a little fun at myself for overlooking the some of the basics of my design thinking it may help others to avoid the same pitfall. No one died, the whole door operating scheme is not inherently dangerous, I gave an example of an instance where it got the best of me and showed that I could still get into the car in a matter of seconds.

    What is this tremendous fear of electricity and how to apply it?

    Sometimes I get the distinct feeling that a lot of guys literally hide behind the word "Traditional" because it keeps them from having to understand anything that was invented after 1932.

    Now was I supposed to yank up on that crank, or push down??? oh, and don't forget to retard the timing, but you guys already knew that, after all, it's electrical, er, mechanical.
     
    Last edited: Jun 8, 2015
  21. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Just got around to installing the wire loom on the passenger door and reworking the wiring for that door motor. Both doors work like a champ now with the jamb tacts only handling the low current side of the circuit. I polished the jamb tacts and put a little dielectric grease on them. The drivers side was actually starting to pit where the contact was touching the pad...not good.
     
  22. ISweet, glad it's working better. We had a little show here two weeks ago and it rained (well, sprinkled) and we had a friend who was all upset because his window wouldn't roll up. He had jamb tacts and forgot so he was sitting in the car with the drivers door open. He turned really red when we reminded him the door had to be shut for them to work! I still want to put them in my Plymouth, but I haven't had a chance to hit the junkyard and check out the GM SUV's to see how many contacts the ones they use have. Think I could get by with 4 contacts (one for hot lead to the windows, one for the door solenoids, and two for the door mounted speakers), but a fifth one would be nice to run a dedicated ground through. Can you post a picture of the loom you made to carry the high current supply to the door? Did you go the flexible route or one of those hard tubes that slides in and out when the door is opened? I think this is probably a (really) good idea, but the whole reason I wanted to use the jamb tacts was to get away from this. I'm hoping the OEM jamb tacts will carry enough current (and have enough contacts) to skip that part. If not, I'll probably try the Ron Francis ones.

    Posted using the Full Custom H.A.M.B. App!
     
    Last edited: Jun 9, 2015
  23. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Here's the wire loom I made. The tubing itself is a discarded 3/8 water supply tube with the wire loom.jpg braided plastic covering. I made bushings for each end out of some scrap cycolac. The end in the door jamb is glued in with RTV gasket maker. The end in the door is anchored with a couple 4-40 screws through the flange. The end of the tube is anchored to the door side flange by pressing a bushing into the I.D. of the tube. The door jamb side lets the tube slide in and out of the jamb. After I drilled the hole in the door jamb, I glued in the bushing and then I made a pointed, shouldered pilot that pushed into the door jamb bushing. I put a little ink on the point of the pilot and then slowly closed the door. This transferred a dot to the door, which is the exact center of where I needed to drill the door for the door side bushing.
     
    Ed Angel and loudbang like this.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.