EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: accesscontrolforum on August 03, 2021, 08:10:39 pm
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https://youtu.be/XenYR0CoGyU (https://youtu.be/XenYR0CoGyU)
Been installing these types of gate openers for almost 20 years (see video). Never took the control boards out before welding.
Recently had a friend who installed two new gates. Prior to the installation, the gates were working and after the installation, they were not.
The manufacturer says the boards had a surge.
It seems to me, err on the side of caution And take the control boards out.
It seems that there are several articles on welding to automobiles. I can't find any information related to welding around this type of electronics.
- Does the manufacturer's explanation seem correct?
- Isn't the potential ground on the generator the same as the chassis? If so how would current flow through the control board back to ground if there's no potential difference?
- Some welders, like my Miller 140, operate at less than 50 VDC. Is this low enough to where some input protection would not apply?
- In addition to never seeing this problem before, we often ground our insulation testers to chassis ground when testing inground inductance loops. Sometimes these output up to 1000 V DC. It would seem to me that that would also cause issues. But it never has.
Also, I'm not worried about physical damage to the control board we take plenty of precautions.
any input or articles that I can read would be appreciated.
Example welder( Rated Output 90 Amps at 18.5 VDC, 20% duty cycle): https://www.millerwelds.com/equipment/welders/mig-gmaw/millermatic-141-mig-welder-m00486 (https://www.millerwelds.com/equipment/welders/mig-gmaw/millermatic-141-mig-welder-m00486)
Example gate opener (pg 10 shows welding the arm but doesn't show how to ground): https://max.us.com/wp-content/uploads/2016/03/Max-Megatron-UL-325-2016-V10.3.16.pdf (https://max.us.com/wp-content/uploads/2016/03/Max-Megatron-UL-325-2016-V10.3.16.pdf)
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An electric arc is a powerful source of broadband RF energy, a lot more energy than an insulation tester (assuming that the insulation holds up at 1kV DC).
There are all sorts of potentially complicating factors, for instance maybe you use a generator on rubber tyres while you friend was using a mains powered welder (with associated common common return). It's hard to know if one particular setup is going to cause a problem without looking at it in detail, but it's entirely feasible that he did fry the electronics as the manufacturer said.
Isolating the electronics would be the safest practice though - as you say it's a common thing to do in automotive welding. There was a problem recently with new Hitachi trains in the UK. Their Aluminium lifting points were cracking and needed reinforcement welding. Not a long job you'd think, but they were having to strip out / isolate all of the electronics first which took an age!
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Thanks for the information!
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An electric arc is a powerful source of broadband RF energy, a lot more energy than an insulation tester (assuming that the insulation holds up at 1kV DC).
There are all sorts of potentially complicating factors, for instance maybe you use a generator on rubber tyres while you friend was using a mains powered welder (with associated common common return). It's hard to know if one particular setup is going to cause a problem without looking at it in detail, but it's entirely feasible that he did fry the electronics as the manufacturer said.
Isolating the electronics would be the safest practice though - as you say it's a common thing to do in automotive welding. There was a problem recently with new Hitachi trains in the UK. Their Aluminium lifting points were cracking and needed reinforcement welding. Not a long job you'd think, but they were having to strip out / isolate all of the electronics first which took an age!
sound like an extreme case of belt and suspenders
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Depending where things are grounded and where you are attaching the welder ground, the 90 amps you're pumping through the metal could create quite a potential difference and could lead to current flowing through ground points.
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Depending where things are grounded and where you are attaching the welder ground, the 90 amps you're pumping through the metal could create quite a potential difference and could lead to current flowing through ground points.
absolutely, but you'd think professionals are smart enough to pick a sensible grounding point
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Depending where things are grounded and where you are attaching the welder ground, the 90 amps you're pumping through the metal could create quite a potential difference and could lead to current flowing through ground points.
absolutely, but you'd think professionals are smart enough to pick a sensible grounding point
I've only got a hobby type welding course under my belt, but simple experiment and observation teaches the importance of having the current path set up so that there are minimal losses leaving all the energy to do work in the arc. If your ground is bad, the welds look like shit. Move the ground clamp (electrically, mostly) closer, and you immediately become a better welder.
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Not obvious to everyone, avoid having the welding current flow through any type of bearing like wheel bearings.
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Welding currents usually melt PCB traces if (weld) ground current gets pulled through two places. OP has vehicle sensing induction loops which surely pick up strong magnetic fields- but the board's inputs should be protected. Were the boards dead afterwards?
The gate controller board connects to a literal planet of devices, so hard to guess - welders will usually clamp ground to the gate/fence I imagine, unless it's painted then he's going for the gearbox or housing which would be bad.
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Welding current isn't a problem, like, if there were an obvious path through low current wires, they'd have melted and burned up long ago. You'd barely be able to strike an arc before noticing the problem. Or be able to hold an arc once the traces/wires fuse...
It's the sparking that's a problem, and also HF start if applicable. The voltage drop along a rigid metal beam can be massive when it's done very quickly, and the time frame can be as short as single nanoseconds, for fast sparks through air. HF start typically consists of microsecond bursts, at high energy (some ~mJ doesn't sound like much energy in general, but in such a short time frame, it's a lot of peak power!), which can in turn be sharpened by sparking action to the nanosecond scale.
And even if the structure is grounded (it certainly should be -- in the very literal sense, being buried in post holes!), and the welder is grounded (through power cable or otherwise), these are all pathways with substantial length -- grounding doesn't exist at high frequencies, these are only galvanic (mains / DC) paths. They might as well be open circuit, at high enough frequency.
But on the flip side, these should all be environmental stresses the controls are built to handle. Cables routed through air are subject to ESD where people may be in contact, and induced lightning when subject to nearby strikes; buried cables are additionally subject to lightning ground-return surge. (Which might not be a big deal; the control cables can be insulated inside of whatever box they terminate in, no need to make a ground loop; it does need to be insulated well enough not to spark under those conditions.)
Not that most of these are very frequent -- they might simply not design for nearby lightning strikes. And like, direct strike might seem promising (consider a gate at the edge of a flat field!), but is just too immensely destructive to bother trying to protect (~100kA surge!).
(There's also mains surge, which is typically induced or direct lightning strike, conducted on the mains distribution network -- which is not as destructive because there are surge arrestors and transformers between the strike and most any customers. It's also isolated from the control by its power supply. So this seems an unlikely route to be affected by welding.)
So, it could be poor design, but there's still possibility it's due to unexpected paths. And like xavier mentioned, maybe something went through (or didn't) the bearings/guides, maybe the designers made a faulty assumption about those being good grounds so didn't bother putting protection on some connections across them, etc.
Tim
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It's the sparking that's a problem, and also HF start if applicable.
I was going to post this but did not find the right words, so thanks.
We had a customer that did a milling error in one of the machines we sell.
To fix it up he decided to weld the area of the part so he could mill it again to the correct shape.
Bad idea, exactly as you said the moment the HF appeared the machine died.
Was quite an extensive repair required for the machine!
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When I first started work in a private company, one of the junior electronic engineers was also capable of welding aluminum. Before welding, he would first notify everyone, after numerous problems were reported on computer systems, etc. during his arc welding. He described his situation and their reaction as "Baron von Frankenstein, as the peasants stormed his castle with pitchforks."
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Also these gates often have sensor loops buried both sides of the gate that are directly connected to the control board. The manufacturer may not have included protection for unusual circumstances of welding cables lying across these loops.