Voltage ratings of connectors AC and DC?

[bikerhifinut]

I have been looking at some options for umbilical power connectors for a project.
RS online sell some 5pin XLR jobs that are rated at 250VAC and some more expensive ones at 500VAC.
Now my question is this:
What would the DC rating be? I am thinking it has to be at least 1.4 x the AC rating to allow for peak voltage, but as an AC waveform goes from positive to negative, should this be 2.8x the AC waveform? or has my maths and understanding gone slightly awry? This could save me a bit of money as I am looking at a 450V DC feed and obviously the 500V AC jobs are well adequate, but would a 250VAC fitting also work?
XLR's are a good fit into the Chassis at the amps as they already have a correct sized mounting hole for XLR Chassis plug.

I've got a nice solution for the PSU side of things.



A.

I would go for the 250vac ones, most things like this are flash tested to loads more. As long as the feed can cope (blow a fuse) with a short just in case.

[bikerhifinut]

Thanks Merlin.
I will have to go with the 500V chassis socket as there isnt a 250V one in RS online, unless I can find one from a REPUTABLE source elsewhere. I'm wary of chinese eBay shops.
None of this kit is destined for use other than by myself so no liability issues arise.
A.

[bikerhifinut]

I have a couple of these in the toybox and I wondered if they would be ok at 450V DC @ 250mA max. I'm thinking they would make quite good umbilical connectors.
https://www.maplin.co.uk/p/bulgin-6a...onnector-hl40t

Can anyone think of a reason why not? They have an AC breakdown voltage of 5.2kV between poles which suggests they'll be fine for my needs.

Andy

[russell_w_b]

Looks OK to me. That means the d.c. breakdown voltage is 7.35kV. As long as they'll handle the current you require.

Once over, you'd've used a B9A valve base and a matching plug (can't remember the name) for such-like.

[bikerhifinut]

Thanks Russell. I have a couple of the panel sockets and a single plug so i just need to bag another plug before maplin run out of them as they are discontinuing them. I did use it in the past for one of my first preamp DIY projects but at a humble 250V DC. They are just a lot easier to solder up to, having a good spacing between pins.
Rated at 6 amps so that should be plenty.
I'll still need to use XLRs on the power amps due to height restriction on the chassis but that's the easy bit if I can find some 250V or better chassis plugs at a better price than RS online. Otherwise I will have to bite the bullet.

Andy.

[Herald1360]

Just be beware of connecting/disconnecting on load with DC. Arcs can't go out every 10mS!

[llama]

Do you need 5 pole or would 4 pole do? I've just looked at Rapid and the difference is £7+ to £4+
Graham

[russell_w_b]

Originally Posted by Herald1360

Just be beware of connecting/disconnecting on load with DC.

If you're worried about that sort of thing, you could always wire a couple of spare pins as an interlock loop to a relay to bring off the mains if the plug gets yanked out inadvertently. Or use a Jones-type plug with a clamp.

Your chosen plug looks like a modern version of the Octal socket / plug supplies arrangement on our Leak TL12/Plus amplifiers (granted only 400V d.c. at 40mA).

If you had money to burn, you could always look at what F. C. Lane has to offer with their 'BA' connectors. Bit OTT, perhaps, but would offer extra shrouding and surface path clearance between pins. And the pins are easily changed (been there; done that...).

[G6Tanuki]

The Bulgin types are OK: in the past I've used them to handle interlinks between amplifiers/modulators and valve transmitters, where the insulation needs to cope with both the standing DC of the HT supply along with the peak-to-peak audio modulation (hence peak of 2x the standing HT) and never had a problem.

I wouldn't want to put too much current through them though - a couple of amps max. And no plugging/unplugging if powered-up!

[Interlocks are a pet thing of mine]

[mole42uk]

I’ve used the Lane BA connectors between my power supply and radio chassis. Quite effective, easy to use, not cheap.

[daviddeakin]

Originally Posted by bikerhifinut

What would the DC rating be? I am thinking it has to be at least 1.4 x the AC rating to allow for peak voltage

It doesn't work like that. The (official) DC ratings are often much, much less than the AC ratings, beecause DC can arc for longer. It's common to see 250VAC / 30VDC, but that is often combined with a high amperage rating that we never need. Of course, the DC leakage (insulation) will be at least as good as the RMS AC rating, so for us low-current DIYers we can get away with any sensible looking, heavy-duty connector, even though it might not pass a commercial compliance certification when so used. I've used Bulgin and the ‘Cliffcon’ ZC (miniature multi-pole) series before. The Cliff S (loudspeaker) series also look like likely candidates.

[julie_m]

If you are not going to be connecting or disconnecting them while energised, then you can usually take some liberties with ratings.

If in doubt, use a Megger.

[bikerhifinut]

Thanks for the many and varied responses.

Julies suggestion of a megger is interesting, but as i do not possess such a thing and an ordinary ohm meter wouldnt give me any idea of insulation breakdown voltage then I'll have to regretfully miss that one.

Its for the transmission of around 9V DC at around 3.5 amps plus 450V DC at NO MORE THAN 200mA for the circuits in question. I have every confidence that the Bulgin multi pins I have will work more than adequately in the application in mind. So its just the other end where I need a smaller diameter socket (Panel mounting plug, male socket). I know I can get some 500V rated XLRs at a price so I'm going to be ok. XLR plugs must be ok for low voltage high current jobs because we have a lead acid battery charger here at home that plugs into the battery pack with a 3 pin XLR.

I will also be insulating the solder pins on the XLRs with heat shrink sleeving to avoid bare contacts in close proximity, I hope that helps reduce danger of arcing or whiskers of wire getting too close to another live point.

Oh I have no intention of plugging and unplugging these things in a "Live" condition, I'd like to avoid life threatening and property damaging experiences!

5 pin was chosen so that I can have a chassis safety earth wire integral with the power plugs, it strikes me as safer and less fiddle than separate earth bonding wires between units.

Thanks to all.

Andy.

[dseymo1]

I'd be slightly concerned about using the XLRs if the HT supply is referred to earth. Ensuring that a stray wire within breaking loose and touching the shell could cause no injury might prove a problem. Bonding between the shell and the earthy terminal is adequate for audio and LT signalling, but may not be so under high voltage fault conditions.

[bikerhifinut]

Just going off at a slight tangent, if I used 4 pin locking connectors, which I have a small stock of, would that be ok if I also did add chassis bonding points and used a separate wire for the mains safety earth connections? As stated previously, I normally raise the signal 0V above mains/chassis earth with a 10 ohm resistor and 0.1uF HV capacitor in parallel and if i didnt interconnect the mains earth the chassis of the power amps would only have a return path to earth via the power amps earth lift (currently 2.2 ohm) and then via the PSU earth lift resistor. Or do I really only have to worry about the actual PSU case being at mains earth? Doing it this way will ensure that the mains earth wires will not be close to the HT and heater supplies in case of any shorting issues.
At this rate I might end up rebuilding the amps onto a single chassis but the weight of it would be a real nightmare to lift safely.
Thanks in advance for your considered thoughts.
I have some commercial (kit) preamps that use an offboard PSU that feeds a valve phono pre and a valve line level preamp and that happily uses 4pin power umbilicals, admittedly at low currents. So in theory at least, I should be ok with 4 pin connectors and a separate earth bonding wire?
Andy.

[ex 2 Base]

Re a Megger, and not having an 500 volt DC tester. There are Insulation Testers on the usual site VC 60B for around £20. I've compare mine against my Megger and found it to be reliable. Ted

[G6Tanuki]

Originally Posted by dseymo1

I'd be slightly concerned about using the XLRs if the HT supply is referred to earth. Ensuring that a stray wire within breaking loose and touching the shell could cause no injury might prove a problem. Bonding between the shell and the earthy terminal is adequate for audio and LT signalling, but may not be so under high voltage fault conditions.

In any "common" connector like this you really need to arrange that the earth-conductor pin mates first and separates last when plugging/unplugging.

[That;s why on pretty much all mains connectors, from the old 2/5/15A BS546 round-pin stuff, through BS1363 13A plugs/sockets to the modern IEC309 'kettle-lead' PC power leads, the earth-pin is always longer so it's the first-to-mate amd last-to-break]