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Heljan motor buzz before moving off


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I have a Heljan and the motor buzzes while on slow starting from standstill....I think cv's can be adjusted on this but would like advice first..TIA

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What Heljan model, what decoder, have the mechanisms been well run in?

 

The big Heljan motor is generally pretty much silent with the Lenz Standard without any adjustment, only decoder I have used on these for my own operation. (23, 26/0, Parcels car)

 

The little Heljan motor in the narrow body diesels like 15, 16, 17 and steam models Garratt and O2 2-8-0 buzzes slightly very briefly at start, might be helped by removing any capacitors you can see. Same with both Lenz and Zimo MX63. Might quiet with a 40Hz output from a more recent Zimo, but it's so little noise I cannot be bothered, you have to be right on top of the model to hear it.

 

The mechanisms quiet noticeably with running, several hours often necessary, as the lubricant is properly distributed in a thin film over the working surfaces. I don't start assessing locos until through this phase. If the motor is having to overcome a draggy gear train still fighting top operate smoothly with much grease on the teeth, it may well buzz. A 'big motor' model running on 12VDC before decoder fitting will coast over a metre on straight and level track once properly run in. The small motor models not so much, but should come to rest silently.

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the motor output from most/all decoders is PMW (Pulse Width Modulated)

At full speed the voltage is on most of the time (top graph)

At low speed the voltage is on for a small percentage of the time

Each drawing shows about 4 cycles & IIRC the frequency is in the low kHz range

At low speed the motor gets a small kick each cycle, as these kicks are in the kHz range the motor looks to be rotating smoothly 

Some of the energy is lost in this jerky motion & is dissipated as sound

My explanation may not be 100% correct but should give an insight into where the sound is coming from

 

PMW.png.59b230b283ff4fb10c3d3d82a7763ee1.png

John 

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On ‎20‎/‎06‎/‎2020 at 16:13, 34theletterbetweenB&D said:

...The little Heljan motor in the narrow body diesels like 15, 16, 17 and steam models Garratt and O2 2-8-0 buzzes slightly very briefly at start, might be helped by removing any capacitors you can see. Same with both Lenz and Zimo MX63. Might quiet with a 40Hz output from a more recent Zimo, but it's so little noise I cannot be bothered, you have to be right on top of the model to hear it...

The 'buzziest' of the small motor Heljan's I have is an example of class 16. That's actually running on an old Bachmann 36-544, because movement performance was excellent, indistinguishable from that produced by a Lenz Silver, and I always use the cheapest decoder available that will do the job, and my old stash bought at £8.50 a throw isn't exhausted yet.

 

Thought the noise aspect was interesting (although it doesn't bother me as I have to be within twelve inches of the model to hear it when the layout is being operated, drowned out otherwise by wheels on rails) and having just had an order of decoders delivered decided to try the Zimo MX638, before it went in the steam model it was intended for. Same excellent movement performance in the class 16, same slight buzzing noise on starting and stopping. So tried it on the 40kHz option (CV112, bit5 set) and it is slightly quieter. Still some audible sound though. So there's an option to try if the buzz really annoys.

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