Beomaster 8000

[Michael Maurice]

Those of you who know this tuner/amplifier will be aware that it uses a massive toroidal transformer which is switched on softly by a couple of relays and resistors in the primary of the transformer.

The problem is that when you bring it out of standby it trips the circuit breaker in the customers home.

It doesn't trip in my home or in the workshop. This receiver is not earthed and trips when brought out of standby whether connected to the turntable, or cassette deck.

Does anyone know what causes this and what can be done to stop it tripping the breaker?

[Boater Sam]

Most likely is that the client has some other appliance/s that have small leakage and that these are adding up. I assume a 30mA trip RCD? Or is it tripping a miniature circuit breaker, MCB?
The fact that the 8000 has no earth is irrelevant, RCD's trip on the imbalance of live and neutral. MCB's have a current surge tolerance, class B is usual, C is higher tolerance, D is known as never trip. It will produce a spike on either side of the supply when it powers up.
We need to know exactly what trips and if it's an MCB whether it is the same on another circuit.
It is also very likely that the RCD, if that is what is tripping, is failing.

[dseymo1]

...Or that there's another faulty device on the same circuit, making the RCD's margin marginal, if you see what I mean.

[Michael Maurice]

I was wondering whether the huge inrush of current was causing the breaker to trip.

[ronbryan]

Michael

I would check that relay RL1 is sequencing correctly, rather than operating immediately. This relay shorts out the surge limiting resistors R1 and R2. Capacitor C21 times the delay for RL1 and this could have dried out. There is also a 330nF C1 across the primary of the main transformer 30T2 which may be worth checking.

Ron

[dave cox]

You didn't say if this was an RCD or overcurrent device only?


Without any earth on the applience (deliberate or accidental, and I'm sure you have checked for inadvertant leakage) an RCD should not trip unless it's a bit faulty. RCD's I've seen rely on mangnetic flux cancellation so if they were not wound quite right, or not have enough damping in the sensor, the edge of a fast transient might not get cancelled fully and trip the circuit. Given the current pulled through the circuit, and that a 30mA difference trips it, the cancellation has to be very good - probably > 99.9%

dc

[Bookman]

Transformer magnetising inrush currents are as we all know one the most annoying problems not just for a breaker designer but also system protection characteristics. They also cause problems when switching off transformers that are off load or lightly loaded owing to the inability of breakers to extinguish the arc at low current values.

I believe your situation may be "not fit for purpose" somewhere along the way in terms of IEC boundary definition criteria. In this I am referring to the ability of the RCD or otherwise to withstand the inrush and its consequent usage or B&O own test criteria to determine the use of their product in compliance with power supply characteristics.

You may wish to contact B&O or the breaker manufacturer direct and let them know of the problem or indeed Trading Standards owing to the possibility of circuit monitoring.

There is of course the possibility that B&O may employ an NTC Thermistor to reduce the magnitude of the inrush and this may now be shorted?

Incidentally, most if not all breakers relay on the pressure/thermal characteristics caused by the arc to assist with the mechanics and dialectrics employed to extinguish it.

Certainly an interesting topic?
Joe

[Beobloke]

Originally Posted by Bookman

I believe your situation may be "not fit for purpose" somewhere along the way in terms of IEC boundary definition criteria. In this I am referring to the ability of the RCD or otherwise to withstand the inrush and its consequent usage or B&O own test criteria to determine the use of their product in compliance with power supply characteristics.

You may wish to contact B&O or the breaker manufacturer direct and let them know of the problem or indeed Trading Standards owing to the possibility of circuit monitoring.

I have a Beomaster 8000 and I know of 4 other people who do also. None of us have ever had any problems with our units tripping breakers so I suspect the design is absolutely fine.

[Hartley118]

My workshop lighting is protected by an MCB. It was fine until I installed a 300W toroidal transformer to feed the LV halogen spotlights because the interference from the previous switch mode converter was just too severe. Then I found that the inrush current into the transformer would often trip the MCB - no doubt depending on the residual magnetisation of the toroid at the time.

I cured this completely by simply adding a suitably rated NTC thermistor in series with the mains input to the transformer. Of course it gets pretty warm in use, so needs to be properly and safely mounted.

It does sound, though, that B&O have tried to design round their inrush problem and, as suggested already, it would be as well to check that the original protection is still working.

Martin