Author Topic: Widening Hole on strip-board?  (Read 4747 times)

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Offline RedOwen1177

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Widening Hole on strip-board?
« on: October 27, 2016, 09:02:47 pm »
So I'm making a simple board, with a relay (8a, 250v), transistor (http://www.digikey.com/product-detail/en/sanken/2SC2921/2SC2921-ND/3929386), base resistor, and a flyback diode. My goal is to switch on and off an electrical outlet with an Arduino. Now, before anyone says, "Why didn't you just buy a relay board from Amazon?", I didn't want to. I already had the parts (salvaged from an audio amp that killed itself), and I wanted to get better at soldering. My problem is this: the relay's NC/COM pins are too wide to fit into the holes on the strip-board. Do I drill out the holes more? I can't file down the pins, because I don't have a file. So I'm kind of stuck. Can anyone help?
 

Offline setq

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Re: Widening Hole on strip-board?
« Reply #1 on: October 27, 2016, 09:11:43 pm »
Please go and buy a relay board. There are about a million reasons you don't want to do this on stripboard.
 

Offline RedOwen1177

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Re: Widening Hole on strip-board?
« Reply #2 on: October 27, 2016, 09:47:32 pm »
Could you please outline the benefits of a pre-made relay board versus one I make myself?
 

Offline Buriedcode

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Re: Widening Hole on strip-board?
« Reply #3 on: October 27, 2016, 10:15:18 pm »
Did you read what setq said? 'millions reasons you don't want to do this on stripboard'

Unless the relay is switching low voltage and relatively low current, buy a relay board that is designed for mains.

Stripboard is *not* meant for mains voltage  - just look at the distance between the tracks. I won't even mentioned current capacity because the voltage thing means its out.
 

Online Alex Eisenhut

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Re: Widening Hole on strip-board?
« Reply #4 on: October 27, 2016, 10:22:06 pm »
Yes, by all means, set your house on fire because of some sort of hobbyist stubbornness.
*Except AC/DC adapters on eBay. Avoid them all!
 

Offline Zero999

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Re: Widening Hole on strip-board?
« Reply #5 on: October 27, 2016, 10:23:14 pm »
The main reason not to use stripboard for mains is the numerous copper tracks make it difficult to achieve the minimum creepage distance required for safety. If you do opt for a pre-built board, then you still need to be sure there's a large enough gap between the control and mains side.
 

Offline RedOwen1177

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Re: Widening Hole on strip-board?
« Reply #6 on: October 28, 2016, 12:46:46 am »
Got it. Ordering one from amazon right now.
 

Offline setq

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Re: Widening Hole on strip-board?
« Reply #7 on: October 28, 2016, 08:22:05 am »
Good outcome. thanks for listening. Many people end up hurting themselves with the mains.

Stripboard is fine for sub-50v stuff. Zero problems there that aren't logistical or longevity related. I use it myself occasionally myself if it's a one shot and not too complicated and low frequency but for mains, the problems are:

1. It's flammable
2. The tracks peel off easily when it gets hot
3. No creepage
4. Low current capacity
5. Wrong hole sizes
6. Difficult to securely mount wire
7. Difficult to mount safely
8. SRBP is hygroscopic
9. Solder bridges
10. Fragile
11. No ground plane.
 

Online blueskull

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Re: Widening Hole on strip-board?
« Reply #8 on: October 28, 2016, 08:28:39 am »
Good outcome. thanks for listening. Many people end up hurting themselves with the mains.

Stripboard is fine for sub-50v stuff. Zero problems there that aren't logistical or longevity related. I use it myself occasionally myself if it's a one shot and not too complicated and low frequency but for mains, the problems are:

1. It's flammable
2. The tracks peel off easily when it gets hot
3. No creepage
4. Low current capacity
5. Wrong hole sizes
6. Difficult to securely mount wire
7. Difficult to mount safely
8. SRBP is hygroscopic
9. Solder bridges
10. Fragile
11. No ground plane.

I've never used one since my first day playing with electronics. I started with kits that use "buttons" (literally, jeans buttons with nickel plating) to do interconnection, then moved to soldering parts floating in air without a substrate. Then, without and bread boards, I moved directly to 4 layer PCBs.
 

Offline setq

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Re: Widening Hole on strip-board?
« Reply #9 on: October 28, 2016, 08:36:53 am »
I tend to do deadbug as well these days.

When I did use it regularly I turned it copper side up and used it deadbug as well. Makes it quite quick to prototype digital circuits then without piddling around with kynar etc. Can use wire that mere mortals can handle. You get an IC socket, bend the leads out, drill holes to stop leads shorting and solder it to the board from the top. Looks like crap but works.

Dolby used this method for prototypes:

« Last Edit: October 28, 2016, 08:38:40 am by setq »
 

Offline Ian.M

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Re: Widening Hole on strip-board?
« Reply #10 on: October 28, 2016, 10:25:59 am »
+1 to Setq's list of why not to use stripboard for mains.

Been there, done that, a long time ago.  Its too much work peeling strips off to get enough creepage distance,  and now cheap FR4 PCBs are so easy to order, attempting it just proves you are dangerous and crazy.

However the world of cheap relay boards for the maker community isn't all sweetness and light either.  Too many don't have the required creepage and clearance distances.  As you are USA based, there is also the significant risk of loss of neutral causing your nominally 120V supply to surge to up to 240V depending on the ratio of the loads on the two legs of the installation downstream of the neutral fault.  Therefore if there is *ANY* risk of direct contact with the Arduino circuit, it either needs to be robustly grounded or the relay board needs to have reinforced insulation rated for 240V operation.

Its difficult to robustly ground an Arduino board to allow you to use the basic creepage distances - there's nowhere to bolt on a ground terminal, and a soldered on connection needs to be through-hole for reliability and of adequate CSA to carry the potential fault current so that means desoldering the power in jack to expose a suitable hole and pad.

The basic minimum creepage distance (from UL table 2L) for 125V operation is 1.5mm.  That assumes worst case PCB materials and pollution degree 2 - i.e. a clean office environment.  In a domestic environment, if there is a significant risk of conductive contamination e.g. cooking fumes,  heavy smokers, wood fires, proximity to the coast or a major highway, it would be advisable to go up to pollution degree 3, which for the same 125V operation is 2.4mm.

For 250V operation the creepage distances are 2.5mm and 4.0mm respectively.

If the Arduino side is to be treated as a touch-safe SELV circuit, you need reinforced insulation - basically double the distances above.  Assuming you can avoid the risk of significant contamination so you can use the pollution degree 2 column of the table, 5mm should be satisfactory. 

If it turns out you need >5mm creepage distance this may be difficult to meet with an off-the-shelf relay board (though a very good sign is a routed slot between the coil and common terminals, or the use of a relay that has coil and contact terminals at opposite ends of the package), you may have no choice but to use off-board relays and more 'industrial' parts:

e.g DIN rail mounted relays and low voltage transformer to feed the Arduino in a DIN rail equipped enclosure, or a chassis mount transformer and chassis mount screw terminal relay bases with plug in relays, then carefully sleeve, loom and secure all low voltage wiring and loom and secure all mains wiring so no single fault can allow them to come into contact.
« Last Edit: October 28, 2016, 11:34:08 am by Ian.M »
 

Offline setq

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Re: Widening Hole on strip-board?
« Reply #11 on: October 28, 2016, 11:06:31 am »
Good points there. Velleman/Cebek ones are well designed in this respect. Chinese ranom crap, not so much. I've seen a few that use live/neutral as a ground plane!
 


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