Designing a Time Delayed Relay

[chopnhack]

Well... it didn't catch on fire or trip any circuit breakers

LOL, yeah, I was semi confident when I threw the breakers, but you never know

This sounds like the same problem you had earlier with the dust-collector relay operating immediately after power is applied.

Possibly, but it didn't resurface after the programming changes and after much testing so I assumed that it was gone.

It is possible that all those wires are electromagnetically coupling into the PIC's ADC inputs, overriding the Allegro signals.

Negatory - I tested with each removal of a wiring harness and finally again with all harnesses removed, solely Line, neutral and ground. And yes, ground to ground and neutral to neutral not connected to anything else.

At which point I had so many parts removed, I figured I would just pull the board to bench test it again. I have spare connectors which I will rewire again at the bench and see how it behaves. Will let you know!

 

[hevans1944]

Yikes! You removed all that wire and it still misbehaved? Perhaps exorcism followed by Indian sage-burning ritual will help... Murphy is downright persistent but can usually be evicted from the premises with vigorous efforts, some perhaps unconventional. Keep us posted on what you find. Don't forget to probe around with your DSO while looking for artifacts. Ain't electronics Grand?!

 

[chopnhack]

Yikes! You removed all that wire and it still misbehaved? Perhaps exorcism followed by Indian sage-burning ritual will help... Murphy is downright persistent but can usually be evicted from the premises with vigorous efforts, some perhaps unconventional. Keep us posted on what you find. Don't forget to probe around with your DSO while looking for artifacts. Ain't electronics Grand?!

Yes sir, I really liked your idea at first, but when I thought it through I didn't think the wires would present much of an effect on the allegro's - there are so many wires the chances of the lines of force actually lining up in a meaningful way to induce a current seemed unlikely.... but you never know, right Mr. Murphy? I think we can put that one to rest at least since I did the testing in stages and finally with all wires out, still clicking on with the same delay from switch on... - the consistency of that bothers me, since it points to a programming issue again...

I also thought about a field causing the relay to 'click over' and figured that was not likely either. If it was I should have thought about using a SSR instead of an electromagnetic relay.

Bench testing tonight, stay tuned!
(Sorry, have to finish some evaluations today...)

 

[chopnhack]

Ok, back at the bench with the circuit hooked up - the relay is clicking on within three seconds of the circuit being energized with no load on the Allegro's. I reviewed the program and did not see anything that would lead me to believe there is a programming issue, especially since this was working not long ago.

I put the DMM on pin 5 of the pic which is fed off of U3's pin 7 (which is the output of the Allegro sensor) and it reads 4.99VDC

I can only assume that this Allegro chip is damaged and just passing voltage straight through. The chip worked before and then it had some temporary issues which I thought were programming, but ultimately it probably was hardware on its way out. I believe that this is the culprit as the U3 is connected to the 5v+ rail and pins 1-4 are connected to the load, which I don't have one connected (connector not even plugged in) so the only way pin 7 can be outputing Vcc is if it internally failed.

What do you think @hevans1944 , sound logic?

Going to be hard to replace that SMD now with all the tall landscape....

 

[hevans1944]

Are both Allegro chips doing this?

 

[chopnhack]

No, just U3. U2 sits at 2.5vdc.

 

[hevans1944]

I think I would try to make a "desoldering" tool with a vacuum port in the center to simultaneously melt the solder on all the pins and pull the Allegro chip off the board. This could be an "interesting" project in its own right, depending on how long the tool has to be and where the heating element is located. The old candelabra-based heating elements for "pencil" soldering irons that accepted screw-in tips could possible be extended with a socket and a base removed from a lamp. Replace the tip with something customized to fit the chip leads, drill intersecting holes in the center and out one side for the vacuum, and attach to a small pump with Teflon tubing. For extra credit, braze a small brass tube to the hole on the side to allow easy attachment of the Teflon tubing. The Teflon should hold up well at de-soldering (or soldering) temperatures.

Well, that's my story, and I'm sticking with it for now...

Ummm... make sure you remove the correct chip!

 

[chopnhack]

I think I would try to make a "desoldering" tool with a vacuum port in the center

That would be interesting, but I went high tech red neck and got'er done. I saw two videos on desoldering smd's - the first was very interesting in its use of magnet wire to slide under each pin, I had no luck with that method since of the tall connectors nearby preventing getting a good angle to pull from. The next video is pretty much what I had to do to get the chip off, essentially bridge de-soldering.
New chip went on and tested out ok, relay functioning as intended and both inputs to the pic from each Allegro register at 2.5VDC with no loads applied. I think this may be it!
Looks like ME is at FPL

 

[hevans1944]

I liked the second method a lot better, but you do need to pay attention to the temperature of the soldering iron to avoid overheating the PCB and causing traces and (especially) pads to lift off. An SMD workstation with vacuum suction and a hot-air tip are on my shopping list... along with plans to make a re-flow soldering oven.

I might also need to purchase a temperature controlled soldering iron for SMD work, although the tips in my Weller do a fair job of maintaining tip temperature by turning off the heating element when it reaches the Curie temperature of the magnetic switch embedded at the base of the tip... well, actually the switch is a pair of contacts located near one end of the heating element, but it is held closed by a magnet located near the base of, and attracted to, the removable tip. When the tip reaches its Curie temperature it no longer attracts the magnet (which is mechanically coupled to the isolated switch further down in the handle) so the magnet withdraws and de-actuates the switch. Weller offers these in three temperatures: 600 F, 700 F, and 800 F. I mainly use the 700 F tips for 63% tin-37% lead (eutectic alloy) solder. More information here.

Looks like ME is at FPL

Good job, John! Umm... FPL = Full Performance Level? Florida Power and Light? Federal Poverty Level?

 

[chopnhack]

but you do need to pay attention to the temperature

I have a Hakko FX888d that I enjoy using very much - it's temperature controlled, even so I had it up at 800 degrees to do this operation. I felt confident enough to do it because I didn't spend anywhere near as much time as the video demonstrated and the board is 2 oz.

SMD workstation with vacuum suction and a hot-air tip are on my shopping list.

That would certainly be nice! But we don't plan on making anymore mistakes, right .

As for the reflow oven, if you skip the control section, you can use any small toaster oven and a multimeter that has a temperature probe. That is what I used for the DSO. A few test runs with no board to check temp ranges is all I needed to do to learn the ramp up/down. Adding a pic and relay to control this is a nice project too!

Umm... FPL = Full Performance Level? Florida Power and Light? Federal Poverty Level

You may have to ask Ed, lol.

Spoiler: Hint NASA acronyms

Main Engine(ME) at Full Power Level (FPL)