Baxi 105e emitting interference

Radioman · 17 Jul 2006

If anybody knows how to cure the radio interference from a Baxi 105e (about 3 years old) I would be forever in their debt.

Details: emits intereference peaks every 15kHz on 14MHz band.

I don't know whether the newest control board does this (P/N 5112380)

Baxi-Remeha · 17 Jul 2006

whats it interfering with????

Agile · 17 Jul 2006

Since you only have 350 kHz of amateur band at 14 MHz I can understand that signals at 15 kHz spacing are rather intrusive.

I dont know what process within the pcb produces that signal, it seems rather low to be a processor timebase.

Can I assume that it is exactly 15 kHz and not 15,625 Hz ?

Have you determined how the interference is leaving the boiler? What about ferrite rings on the mains supply?

Have you tried disconnecting the room stat connection?

Tony Glazier

ChrisR · 17 Jul 2006

When does it do it? All the time?

Ferrite rings pinched from dud low voltage lighting transformers are quite good.

Radioman · 18 Jul 2006

Thanks for the suggestions.

I have placed a substantial ferrite on the mains input. I suspect that the 15kHz (and it seems to be exactly that) is the cycle time for the switch mode psu on the control board.

I await some more ferrites from Maplin to put on the line to the thermostat which is on the dc side.

Thanks for your help,
Mike.

Agile · 18 Jul 2006

If the problem is caused by the SM power supply and the signals are harmonics then I would not expect them to be at multiples of 15 kHz because the SM frequency is not very exact. They would also drift.

It seems more likely to me that the 15 kHZ itself is getting into the receiver and modulating the oscillator or directly into the mixer or something similar.

RF Ferrites will have little attenuation at only 15 kHz so I would suggest something more suitable for 15 kHz. What about a torroidal mains transformer core with a few turns of the mains cable? It might well need a seperate core on each conductor!

I suggest you disconnect the thermostat connection first to see if thats the main exit point.

Tony

Radioman · 18 Jul 2006

Agile, you know your onions obviously and I appreciate your input.

Well I haven't tried disconnecting the thermostat yet but I did put 5 ferrites on that cable. The ferrites are the ones about 1/2 inch diameter, 1/3 inch long, clip on style. Result: nothing and as you predicted.

I don't think it will be practical to put a large toroid on each conductor due to cost. I think I will wait for the Baxi R&D (laugh) department to get back to me. Another idea is that the board, due to its age, has a known problem and could be replaced. I do know that the 105h board is fitted to the newer examples. Maybe they know about this problem. Maybe this board will have an "accident" and be replaced under maintenance contract. Hopefully the new board is better EMC tested!

Another idea is to have a remote switch via those Byron type units and just switch the bl***y thing off as required. Not much use for the winter and the other half.

Tell me, Baxi, have you heard of BS EN 55011?????!!!!!

Cheers,
Mike.

Agile · 18 Jul 2006

The RF ferrites in the small clip on package ( which we sell ) come in several types and the ones we have give most attenuation about 1 MHz up to 24 Mhz but very little, just 1-2 dB below 400 kHz.

You do not need to pay much if anything for a suitable ferrite because most old computer SM power supplies have a few inside and they are all for SM power supplies although most are probably rather higher than 15 kHz I think.

Strip one down and try one of those AFTER you have tried disconnecting the stat first! Its essential to know the interference source first.

Good luck

Tony

Radioman · 18 Jul 2006

Thanks for that Tony.

I will try disconnecting the thermostat cable (nice antenna NOT!).

If I can locate on the board where the dc power runs in I could get a linear psu and feed from that instead perhaps. Then I will discover its the on board circuitry...

Might be time to get a new condensing boiler anyway..

All the best,
Mike.

croydoncorgi · 18 Jul 2006

Presuming that this PCB does NOT conform to EN 55011, the interference is presumably bad enough to interfere in neighbouring houses as well as where the boiler is sited.

I wonder whether there are lots of Radio Amateurs with this particular problem. There are certainly lots of these boilers still installed!

Radioman · 18 Jul 2006

I think in the last few years before CE really got going their was a rather cavalier attitude to EMC by the manuafacturers.

There must be lots of Hams with this and I have asked the RSGB EMC committee if they know of a fix. Fortunately (?) there are no other hams near me and the interference is mainly noticeable in the Hf area only which would not impact on most households. Who listens to SW these days except us anyway? No one, they are too busy messing about with their iPods and mobile phones or whatever.

Fed up? Me? Yeah I am a bit..

Agile · 18 Jul 2006

Its far worse than that!

Radio amateurs have no legal protection from interference at all.

The only legal protection to interference is when its caused to standard UK broadcasting providing the installation is up to the best standard for the local signal level.

Its even more frustrating because the radio enthusiast has no right to minimise the interference from a neighbours equipment and most people would not let a radio ham into their house let alone allow them to modify their computer etc.

Tony

Radioman · 18 Jul 2006

Tony,

On another forum (4m website) they tell me that the valve modulating circuit may well be thyristor controlled referenced to neutral. Since I have pme earth arrangement I guess I have got radiated AND conducted interference. Not bad eh! May be their designers should work for HMG in electronic warfare - they would be star performers.

Another suggestion is to fit a 1k pf cap across the bae and emitter of the drive transistor on teh board. Without a cct diagram of the 105e I don't think I will be that brave yet.

Yes, that's right we do not have protection from interference as we are not static services as you say. We are not even primary users on some bands as well. We are abused by all and blamed by all when their telly suddenly starts talking Swedish to them in the summer..

Frustrating isn't it!

Cheers,
Mike.

ChrisR · 18 Jul 2006

It depends whether your radio's susceptibility is due to conducted (wires borne) or radiated (air borne) emissions from the boiler. If the troublesome 15kHz spikes are only getting out as modulations of the 14MHz then it's the 14MHz band you need to attenuate.
The lighting smps toroids I mentioned would be big enough to wind the mains conductors through, but I would have a look at the board first.

I have just checked an earlier baxi 105 pcb (248074) and notice that the mains filtering components around A4, that's 3 caps and an inductor, are not fitted. Good, eh?

Looks like a linear power supply to me - presumably they changed it in the redesign, but see if your board has similar unemployed "provisions"!
I have a couple of the older boards - could flog you one ... email in profile.

Radioman · 18 Jul 2006

Yes,

I note L1 C20, C22 and C23 all missing!! What was that saying about some tar?

I cannot get the board part no. as the poxy plastic lugs at the back near the hinge refuse to let me take it off despite removing the two screws.

That's why we hate designers and their project managers

Mike.

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Baxi 105e emitting interference

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