Designing a Time Delayed Relay

[chopnhack]

Do you think the leads are tall enough for me to bend the transistor and heat sink back over the other components? "If so, with careful layout, its possible to have the transistor bend over other parts after they are installed."

In other words, lay out some of the low lying items, smd caps, diodes, resistors where applicable and then bend the heatsink and transistor so it lays on top of these components, parallel to the board? Maybe use a nylon bushing to keep a specific distance off of the board and bolt it together through the board so that it cant short out on the other components.

I don't know if there is enough height on the leads to do it, but its a thought!

 

[KrisBlueNZ]

I think that would be OK if you use a standoff between the heatsink and the PCB. Either nylon or metal. Or could you mount it on the underside of the PCB? Either with a short standoff, or flat against the board if you can avoid tracks on the underside in that area.

 

[chopnhack]

I think that would be OK if you use a standoff between the heatsink and the PCB. Either nylon or metal. Or could you mount it on the underside of the PCB? Either with a short standoff, or flat against the board if you can avoid tracks on the underside in that area.

I figured on the component side, the bottom I envision mounting some low profile nylon bushing to keep the board from grounding out against the metal box or perhaps some threaded standoffs (like the ones used in pc pcb mounting to cases) with a nylon washer and nylon screw or just ensure no copper where the screw head will touch pcb.

Do you think this design is buildable at this point? Any other quirks that need to be ironed out?

 

[KrisBlueNZ]

I don't know. What are the maximum allowable PCB dimensions?

 

[chopnhack]

I don't know. What are the maximum allowable PCB dimensions?

The PCB has to fit inside a 10cm square box, there are some internal protrusions at the corners so, figure 8.8cm square.

I was wondering more along the lines of the circuitry. I know the fitting will be trial and error with the layout.

 

[KrisBlueNZ]

You mean you're concerned that there won't be enough PCB area for the components? My gut feeling is that 8.2 x 8.2 cm will be big enough, but I'll have to check. Can't work on it right now though.

 

[chopnhack]

You mean you're concerned that there won't be enough PCB area for the components? My gut feeling is that 8.2 x 8.2 cm will be big enough, but I'll have to check. Can't work on it right now though.

No, you have done more than enough Kris!! Thank you, I will need to do some more leg work from here on out until I become utterly confused and befuddled, which may not be long from now

I will create a BOM and start on a new layout if you think the schematic is good enough to work from. I do recall you mentioned that the change to the TIP29 may require a different resistor value for the base-emitter or was that only for the Darlington if used?

 

[KrisBlueNZ]

That was only for a Darlington. OK, go for it

 

[KrisBlueNZ]

BTW what connectors are you using? If you're using the Phoenix type that I suggested, you can save space by using 6-pin connectors for the current circuits. Or even 4-pin.

 

[chopnhack]

BTW what connectors are you using? If you're using the Phoenix type that I suggested, you can save space by using 6-pin connectors for the current circuits. Or even 4-pin.

I think back in post 77 you used a 8 pin and a 6 pin header with plug assembly - 4 pins per leg of the current circuit to the allegro chip. I don't know what space I will have, but if I run into constraints those certainly will help! I was think of using the phoenix combicon compact screw termination blocks, they are very economical and still fairly small. I haven't started a layout yet, but two banks of these plugs has me thinking about maybe a two tiered option.

 

[KrisBlueNZ]

Sure, sounds fine apart from "screw termination blocks" - are these pluggable? Or do you screw the wires into the board-mounted connector? Pluggable is a lot better, although more expensive.

 

[chopnhack]

The connector itself is soldered to the board, while the incoming wires are fed into the channel below and a screw (from above in this picture) forces a bar down onto the wires. Fairly small units, but there are of course other options.

 

[KrisBlueNZ]

I really recommend pluggable Combicon, unless you're really trying to minimise cost. They are much more convenient, safer, and they don't take up any more board area than the wire-to-board type.

 

[chopnhack]

I really recommend pluggable Combicon, unless you're really trying to minimise cost. They are much more convenient, safer, and they don't take up any more board area than the wire-to-board type.

The header might save some space, the cost is probably around 3x more.
Why were you saying to switch to 6 or 4 pin now? The current to the Allegro's is still the same.

 

[KrisBlueNZ]

Because compromises! Each pin of a pluggable Combicon is rated for 16A, I think, so strictly speaking a 2-pin or 4-pin connector would be adequate. But experience tells me to use more pins than are needed, i.e. to engineer conservatively. But if another factor makes the whole project unworkable, then compromises must be made.

 

[chopnhack]

Because compromises! Each pin of a pluggable Combicon is rated for 16A, I think, so strictly speaking a 2-pin or 4-pin connector would be adequate. But experience tells me to use more pins than are needed, i.e. to engineer conservatively. But if another factor makes the whole project unworkable, then compromises must be made.

LOL, indeed! If the darn thing won't fit in the boot, it doesn't come home!

Perhaps the 6 pin per Allegro, if it will fit, that should give us some headroom for full load when the motor is turned on. I think this should be a very interesting layout. I will try to workout on that tomorrow!

 

[chopnhack]

Is it ok to substitute this bridge rectifier in place of the 4 1n4004 diodes? D1-D4
http://www.digikey.com/product-detail/en/DF04S-G/641-1345-5-ND/2074810

Also, what is the value of R9? I can't quite make it out - either 8.2 or 9.2k?

 

[KrisBlueNZ]

Is it ok to substitute this bridge rectifier in place of the 4 1n4004 diodes? D1-D4
http://www.digikey.com/product-detail/en/DF04S-G/641-1345-5-ND/2074810

Yes, sure. It doesn't need to be 1A 400V. These ones are 0.5A 100V which is plenty, and I think they're smaller:
http://www.digikey.com/product-detail/en/MB4S-TP/MB4S-TPMSCT-ND/722465
http://www.digikey.com/product-detail/en/MB1S/MB1SCT-ND/2094421

Also, what is the value of R9? I can't quite make it out - either 8.2 or 9.2k?

8k2. Save the image and view it with an image viewer, and you'll see it 1:1 and it will be easier to read.

 

[chopnhack]

Awesome!
I did use a separate viewer for the schematic, but it was still blurry, thanks for confirming that.
The bridge diode is smaller and certainly more compact than the individual diodes. The additional smt components decreases the layout flexibility some as there are fewer opportunities to use a through hole as a means of getting to the other side of the board! Not a bid deal, just interesting the things you pick up as you go along.
I have a new BOM completed - just missing the connectors. I will start on that tomorrow.
Thanks!

 

[chopnhack]

Temporarily picked a few connectors to finish the schematic. Could you look it over for any errors? I had a bit of a struggle with the bridge rectifier until I started to think of the nodes! Please let me know if you see errors, I will start on board layout next. Thanks!!
Sorry - the quality is so poor, the only thing I was able to do was add a better copy at google drive - they don't seem to play with the size or resolution!

https://drive.google.com/file/d/0B1P01SzcMubrLXMza3J2dnFxU2s/edit?usp=sharing


http://i279.photobucket.com/albums/kk143/jmansphotos/Electrical/schematic2_zpsa1d71cab.jpg