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Generator noise suppression - Printable Version

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Generator noise suppression - VK2ZIW - 06-06-2017

Has anybody investigated the HF noise problems from the generic chinese 1-2Kw generators?

I have a GMC 850W and a Dingo 900W 2-Stroke. Both have the same alternator.
Looking at the waveform (after a 240 to 24V transformer) it's horrible with obvious
PWM of the field excitation an maybe 1000Hz.

Ignition noise (spikes at a regular 25 or 50Hz) most noise blankers are designed for.

Anybody looked?

Alan VK2ZIW

RE: Generator noise suppression - VK4ADC - 08-06-2017

I was given a GMC 850 (or 900 watt?) genny earlier this year and fired it up into 300W of light bulb loads but haven't looked at the waveform.  Maybe a LPF inserted in the 240VAC mains output is a reasonable solution. A multisection LPF (Fc < 150Hz) rated at more than 300V would also round out spikes as well as make the AC waveform a little more sinusoidal.

My FD setup is to use only the 12V output to charge the 300AH battery bank, the 240V AC output is simply ignored in the field, the battery is thus effectively a very large capacitor so any spikes could be ignored.  If it is a sunny day, 2 x 80W solar panels plus regulator are used and they produce much the same charge current as the genny - though not very effective at night  Cool

I don't get much impulse noise off my little genny even on HF with the NB off and I suspect that is the case because the spark plug lead is resistive and quite short.

I will put a CRO on to have a look at the waveform when I pre-test the genny in  the next week or two in prep for the Winter Field Day.


73 Doug VK4ADC

RE: Generator noise suppression - VK2JDS - 09-06-2017

Be very wary of the mains output of those gmc and similar 850 watt generators. I have one and on a field day last year it destroyed a HP laptop power supply.
The multimeter showed 265 volts, but who knows what spikes and crap were also present.
Voltage regulation is very poor, drifts randomly and also according to changing load, with major surges.
The worst overvoltage is when the fuel runs out and the generator runs fast as the mix goes lean just before it stops.
All they are good for (and probably designed for) is to run power tools.
Just use it as a battery charger and for lighting.
73 Dave

RE: Generator noise suppression - VK3YCQ - 09-06-2017

At the least, have a small 240v incandescent bulb as a load, connected at all times. Added Filters on the 240V output would be good too, made using decent high voltage capacitors and ferrites from discarded computer power supplies. Definitely get a battery and solar setup like Doug has, just use the cheapie gen to charge the battery up and/or absorb the spikes. Better still, get something decent as a generator. At a pinch the cheapies do work but you get what you pay for. You also get added extras for free, like lots of smoke and noise.

Ian
VK3YCQ

RE: Generator noise suppression - VK2ZIW - 15-07-2017

Come on guys. Isn't there somebody out there with a CRO and some nouse?
When the weather warms up, I'll setup my two (GMC and Dingo) in my back yard and do some testing.


I just did a Google search of "Chinese generator radio noise suppression" and all I find
is this exact thread!!

Does this mean, nobody else has any issues??

Sorry, advice to buy a "better" generator is not helpful.

Alan VK2ZIW

RE: Generator noise suppression - VK3QI - 16-07-2017

Alan,

Hopefully Doug will allow cross posting of the following:

http://www.vklogger.com/forum/viewtopic.php?f=61&t=13683

This is the archive of the previous forum where your problem was dealt with in quite some detail.

Within that topic is a reference to another posting:  viewtopic.php?f=31&t=13534&start=20#p60419

which outlines the importance of considering all possible paths that RFI can take.

One common problem seems to be where the operator is using a vertical antenna.

If you think about it, in a portable situation, obtaining a reliable RF earth is often difficult  (rocks etc.)    The earth lead from the generator actually becomes part of the radiating antenna.

So one has to somehow isolate the earth lead from the generator.

(Way 1)   a decent earth stake at the generator (difficult)

(Way 2)   suitable ferrite filtering in the earth lead as well as the active and neutral leads.

If you look at most powerline filters available commercially, they only filter the active and neutral leads and maintain an DC earth path through the metal case.    It is only when you go to the more sophisticated power line filters that are often used in medical rated equipment, that you find the earth lead being filtered as well.

So the trick is to introduce ferrite filtering of the earth lead as well.   From a safety point of view you still maintain a DC connection, but at the RF frequencies, the signal does not pass.

Ideally a decent earth stake at the generator as well will always assist the situation.    Note that on may of the Inverter generators available, the 240 volts is developed between Active and Neutral, rather than between Active and Earth as in our domestic  M.E.N.S.  system.

Cheers

Peter  VK3QI    (FD contest station VK3ER/p)
Alan,

I should have added that just disconnecting the earth lead from the generator is a big NO NO.  

Cheers

Peter  VK3QI

RE: Generator noise suppression - VK4ADC - 16-07-2017

Maybe I have been slack but I haven't yet had the need to fire up my genny.  However I will do so shortly so that I can have a look at the waveform - as promised in an earlier post.

I think Peter's comments are valid and earth lead filtering is probably a good idea.

Cross posting ?? No issues here provided the source is attributed (eg weblink address shown).

73 Doug

RE: Generator noise suppression - VK5ZD - 08-08-2017

(06-06-2017, 10:24 PM)vk2ziw Wrote: Has anybody investigated the HF noise problems from the generic chinese 1-2Kw generators?

I have a GMC 850W and a Dingo 900W 2-Stroke. Both have the same alternator.
Looking at the waveform (after a 240 to 24V transformer) it's horrible with obvious
PWM of the field excitation an maybe 1000Hz.

Ignition noise (spikes at a regular 25 or 50Hz) most noise blankers are designed for.

Anybody looked?

Alan VK2ZIW

I have a cheaper (i.e. not Honda) inverter generator which produces some HF noise, most of which is radiated from the extension lead. I use one of Jaycar's EMI filters in a diecast box which has a short lead with a plug in the input site and an outlet socket mounted on the box. The input lead has 6 ferrite sleeves on it.

https://www.jaycar.com.au/240v-ac-emi-filter/p/MS4001
https://www.jaycar.com.au/large-ferrite-suppression-sleeves-pk-6/p/LF1260

This combination pretty much eliminated the interference. Using an earth stake makes no significant difference.

73
Iain