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Old 10-15-2019, 11:18 AM   #101
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Default Re: DPS5020 dual power supply build

You are switching AC to the AC load so a NO NO to put diode across the load, you will see nice fire works when that diode conducts. You will put diode across the RELAY DC winding with proper DC polarity to the relay winding.
RC snubber of for the switch contact.
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Last edited by budm; 10-15-2019 at 11:22 AM..
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Old 10-15-2019, 11:21 AM   #102
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Default Re: DPS5020 dual power supply build

Quote:
Originally Posted by budm View Post
You are switching AC to the AC load so a NO NO to put diode across the load, you will see nice fire works when that diode conducts.
Yes, I know that That's why I mentioned DC as a separate topic.
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Old 10-16-2019, 02:21 PM   #103
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Default Re: DPS5020 dual power supply build

To suppress back EMF from an inductive load, an RC snubber is commonly used. A DC inductive load usually has a diode across it to clamp the back EMF.

You can guess a snubbers value based on the transformer's size.
I would use 33-47nF and 22-100 ohms 1-3W as a ballpark for a 1,500VA transformer. The film cap needs to be HV rated, a junkbox X-cap is OK but if the cap fails short, the resistor burns up.

Leakage current from the cap doesn't matter, the transformer might have 1mA flowing all the time but it will stay asleep. Although some loads will still have weak ghost power from that.
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Old 11-30-2019, 11:13 AM   #104
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Default Re: DPS5020 dual power supply build

This is great info. Sorry for replying so late, but it's only recently that I started working on the project again

If I use a double-gang switch to cut both the L and N AC lines, should BOTH sides of the switch get a snubber across them ? Silly question perhaps.....
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Old 11-30-2019, 01:25 PM   #105
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Default Re: DPS5020 dual power supply build

It turns out dual-switch contacts are never identical, so one will close last (power-on inrush current) and another will open last (power-off arc). I had a boss yell at me that it would not last any longer than using one switch contact, when I tried them in parallel.

Electrical codes here in NA forbid switching both line and neutral in a device. You can only switch line or hot. But I see your breaker panels and motor contactors seem to disconnect both.

I would use two snubbers, one across each switch contact if you want to open both line and neutral. That is the best way to have no spikes when you switch off. I tried a MOV across the transformer primary but still got a spike.
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Old 11-30-2019, 01:30 PM   #106
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Thumbs up Re: DPS5020 dual power supply build

Quote:
Originally Posted by redwire View Post
It turns out dual-switch contacts are never identical, so one will close last (power-on inrush current) and another will open last (power-off arc). I had a boss yell at me that it would not last any longer than using one switch contact, when I tried them in parallel.
Ah yes, now that you mention it, I remember hearing about this before (including the boss part ), so you probably answered somewhere in the earlier posts.

Quote:
Originally Posted by redwire View Post
Electrical codes here in NA forbid switching both line and neutral in a device. You can only switch line or hot. But I see your breaker panels and motor contactors seem to disconnect both.
I think this is because EU plugs are not polarized, so either conductor can become hot at one time....just a thought. I, as an ordinary do-it-yourselfer, always choose to cut both wires whenever possible "around the house", like if I wire up a simple power strip for instance...
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Old 12-01-2019, 02:05 PM   #107
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Default Re: DPS5020 dual power supply build

That is right that dual contact switches one will make/break before the other and that one will die first, but I was wondering about that electrical code requirement for switch both line and neutral at the same time... Switching protective ground is clearly very bad, but would think that neutral would not be so bad...

I've seen a lot of computer equipment that has both line and neutral switched, and seen/have some DPST wall toggle switches. Is this really against code? The most I saw in the electrical code rules is that if neutral gets disconnected, line MUST be disconnected at the same time, which implies DPST are OK.

On the other hand, I also saw that "grounded" conductors must not be switched, and whether neutral, which is "ground" also counts as "ground" that must not be switched. Now that remains a curiosity for me...
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Old 12-01-2019, 05:31 PM   #108
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Default Re: DPS5020 dual power supply build

neutral is not considered grounded in the device or even a building - it would be a dangerous asumption.
any bonding is at the power company's side - either at the box or the transformer.
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Old 12-02-2019, 06:45 PM   #109
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Default Re: DPS5020 dual power supply build

That would agree with what I see so far - meaning a DPST is okay since neutral is not ground, but I still don't quite understand the statement in post 105...
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Old 12-05-2019, 03:16 PM   #110
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Default Re: DPS5020 dual power supply build

Quote:
Originally Posted by eccerr0r View Post
That would agree with what I see so far - meaning a DPST is okay since neutral is not ground, but I still don't quite understand the statement in post 105...
Iím not aware of the electric regulation on Canada.

Nevertheless, itís a common mistake wrong labeling and interpretation about Earth connection.
While the Line is sometimes referred as Hot without raising any problems,
the Neutral is often mislabeled or referred to as Ground leading to wrong assumption and confusion with Earth .

Therefore, with exception for the electric house panel where Neutral, and Earth (off course), must always remain connected (only the Line can be switched),
itís very common to switch both Line and Neutral.
In contrast switching Earth is totally forbidden.
.

Last edited by megaraider; 12-05-2019 at 03:19 PM..
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Old 12-06-2019, 08:20 PM   #111
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Default Re: DPS5020 dual power supply build

I'd imagine Canada have much similar rules as USA which is described in the NEC. However even https://en.wikipedia.org/wiki/Electr..._North_America has some wording implying that neutral switching is taboo in most circumstances:
Quote:
Originally Posted by wikipedia Electrical wiring in North America
North American standards state that the neutral is neither switched nor fused except in very narrowly defined circumstances.
Agree that it should not be fused, but should be okay to be switched IFF hot is switched off first, and hot is on last.

Need to find the explicit rule, and then again whether this is only for building wiring or does it apply to end run pluggable equipment as well...
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Old 12-07-2019, 06:55 AM   #112
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Default Re: DPS5020 dual power supply build

end equipment often has double-pole switching - it just makes sense once you understand that earth-neutral bonding cant be assumed.

what if it's an old building with earth on a gas-pipe or just non-existant?
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Old 12-07-2019, 12:54 PM   #113
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Default Re: DPS5020 dual power supply build

So is there a difference between end equipment and building code rules and hence is why post 105 is confusing?
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Old 12-07-2019, 02:15 PM   #114
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Default Re: DPS5020 dual power supply build

yes, there is a plug and socket or a atleast a junction-box for fixed / industrial stuff.
the supply side is "infrastructure" the thing connected is an "appliance"

different rules apply to each.
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