Balanced Power Supply

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Dr Bunsen Honeydew
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#151 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

I took it direct to earth, obviously not through me and the consumer unit tripped every time.
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Ali Tait
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#152 Re: Balanced Power Supply

Post by Ali Tait »

Mine tripped the CU recently. Unbeknownst to me, the plug on the cable feeding my system from the BPS only had a 3A fuse in it. Been like that since I built the BPS. I flubbed switching off the amp running the bass - big 500w class ab, it didn't switch off and went straight back on, which blew the fuse and took out the RCD in the CU. not what I'd have expected to happen. No harm done though, replaced fuse and all well, except the usb ports started playing up on the media pc. Strange thing, some worked, some didn't. All still had power as a usb TT light I have worked in all of them, but any peripheral plugged in wouldn't show up on the pooter on the dodgy ones. Tried all the usual fixes, nowt worked. Still scratching my head..
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Nick
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#153 Re: Balanced Power Supply

Post by Nick »

Dr Bunsen Honeydew wrote: Thu Aug 17, 2017 9:50 pm I took it direct to earth, obviously not through me and the consumer unit tripped every time.
Fair enough. With a smallish resister I assume to emulate a person?
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#154 Re: Balanced Power Supply

Post by Ant »

Dac is now powered off it. Wasnt the dac psu, it was the switch on the socket itsself. Cycled the switch a couple of times and its fine. I'd stood it on its face when i bolted the tx in. Maybe that caused the problem
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Dr Bunsen Honeydew
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#155 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

Nick wrote: Thu Aug 17, 2017 10:00 pm
Dr Bunsen Honeydew wrote: Thu Aug 17, 2017 9:50 pm I took it direct to earth, obviously not through me and the consumer unit tripped every time.
Fair enough. With a smallish resister I assume to emulate a person?
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#156 Re: Balanced Power Supply

Post by jack »

Nick wrote: Thu Aug 17, 2017 9:47 pm Touch one of the secondary connections while holding a water pipe. Afaik consumer units don't measure earth current directly.
Most people here will know this, so apologies, but for those that don't:

It's certainly not usual - RCD/RCCBs only trip on L/N current imbalance, typically around 30mA and normally in under 100ms - they do not provide over-current protection like MCBs but will trip in the above scenario on the LN imbalance.

ELCBs measured the earth current but they are no longer used as they only detect faults via the earth wire, not any other fault condition, e.g L to the kitchen sink :)

RCBOs are RCCBs with an integral MCB - "residual current breaker with over-current protection".

Neither RCDs or ELCBs detect L/N faults, i.e if you grab L in one hand and N in the other, you're not protected obviously.

Note that all these devices generally only work with a proper sine wave input so use on an inverter with care as they often produce pretty shitty quality sine wave output.

If you have a consumer unit MCB that keeps tripping and you have a big transformer on it or other inductive load that causes inrush current on turning on, change the MCB for a "C" or possibly even a "D" rated one. Only do this for that circuit, no others; normal domestic MCBs should be "B" rated.
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Dr Bunsen Honeydew
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#157 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

Blimey, I wish you had been around when all the shite was flying around the forums about the NVA BMU. Are you reading Jacks post Ali Tate !!!!!!!!!!
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#158 Re: Balanced Power Supply

Post by Ant »

The ring that the bmu is on is the ring for all the downstairs sockets so i couldnt change the rated rcd on it hence the thermistor. The dual rcd on the secondary has the same 30ma rating as the ones on the cu, so if one of the 115v windings pulls more or less current than the other one it will cut off both secondaries from the sockets on the bmu. So if for example a fuse blows in the equipment plugged into it, (in the live side) you won't be left with 115v sat on the neutral if the cu rcd doesnt trip.

I wasn't sure if the cu rcd would see a fault on the secondary side, as that kind of fault wouldn't create a current imbalance between l and e on the primary side of the tx would it?
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Ali Tait
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#159 Re: Balanced Power Supply

Post by Ali Tait »

Dr Bunsen Honeydew wrote: Fri Aug 18, 2017 10:28 am Blimey, I wish you had been around when all the shite was flying around the forums about the NVA BMU. Are you reading Jacks post Ali Tate !!!!!!!!!!
Oh ffs don't start all that crap again, and if you're going to have a go at least spell my name correctly.

There were perfectly valid reasons I built mine the way I did. End of.
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Dr Bunsen Honeydew
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#160 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

You building it that way is no problem, what is a problem is the lies and shit that it created at AoS that got passed around other forums, DUE to what you said about it being ESSENTIAL FOR SAFETY, taken up by other nob heads and passed to other forums mostly by the mad boss eyed accountant Pinky.

How would you like being told you make unsafe product, when you know you don't, and are having to put up with eeeeeeediots per usual saying it and having NO RIGHT OF REPLY. At least here thanks to Nick I have a right of reply. So come on tell me I produce unsafe products AGAIN!!!!!!!!! this time I have a right of reply.
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Ali Tait
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#161 Re: Balanced Power Supply

Post by Ali Tait »

Show me the post where I said that.

Don't put on to me what others may or may not have said on the back of what I expressed as my opinion. That is neither my fault or my problem. Speak to the people that made the posts.

As I got tired of saying, I built mine the way I did because it was made with the intention of being portable so could be used at Owston or other bake offs and also due to the fact that there are regularly young children in our house. I therefore wanted belt AND braces safety.

I built mine with safety first in mind, not sound quality.
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Dr Bunsen Honeydew
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#162 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

The posts are in the archive at AoS just search under your name and BMU.

OK so explain what is more safe about the one you built compared with the NVA one.
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Ali Tait
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#163 Re: Balanced Power Supply

Post by Ali Tait »

The posts are all there in the AOS archive under my name.
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Nick
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#164 Re: Balanced Power Supply

Post by Nick »

Well, AFAIKS, a CB that only monitors the L+R for imbalance and doesn't actively monitor earth current wont see the fault condition I mentioned. The fault current will pass from the secondary of the transformer, through the user, to the water pipe, to the PG of the house, back through the earth to the transformer and to the centre tap of the secondary. Never altering the L + N current so not being seen by the CB.

If you DO have a CB that monitors earth current, then it will trip, but then your household is not protected with a live to water pipe condition (as they weren’t before with wire fuses).
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Dr Bunsen Honeydew
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#165 Re: Balanced Power Supply

Post by Dr Bunsen Honeydew »

OK lets look at some daftness. Ant has done a good job, if all the primary and secondary wires dropped off and touched everywhere around inside the case would the case become live, NO because it is built of wood and the construction is largely double insulated classII. APART from one thing, the thing that is supposed to give you more safety, the RCB, it is not rated for classII regs. So the thing you include for safety is the only thing that is potentially unsafe !!!!!!!!!!!!!!!

If you are daft enough to build one of these in a steel or other conducting material case, then probably the only thing to make them completely safe would be to embed them in concrete.
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