generator power quality

[nizak]

Has anyone here run across an issue where a generator used to power a residence has caused a circuit board in a furnace to go bad? Was in a box store today and overheard a customer telling the associate that his furnace was damaged by his generator. He said the HVAC tech that came out told him that generators produce "dirty power" and that all warranties are voided when the furnace is being operated on anything but utility power. Could a cheap portable unit produce a lesser quality grade of power then say a Generac or Kohler whole house gen set?

 

[dfmischler]

I think I once burned up a microwave oven while running on a portable generator. I guess it might have been coincidence. I think the voltage was probably a bit low, and who knows what the waveform looked like.

Here is an interesting page showing waveforms from various small UPS and generators. Some are much better than others.

 

[dfmischler]

Application note from Fluke that discusses furnace power requirements.

 

[electrofelon]

Has anyone here run across an issue where a generator used to power a residence has caused a circuit board in a furnace to go bad? Was in a box store today and overheard a customer telling the associate that his furnace was damaged by his generator. He said the HVAC tech that came out told him that generators produce "dirty power" and that all warranties are voided when the furnace is being operated on anything but utility power. Could a cheap portable unit produce a lesser quality grade of power then say a Generac or Kohler whole house gen set?

I would say nonsense. Practically all electronics rectify the ac immediately and rectified ac is "dirty" anyway

 

[PatM]

Rectified AC isn't "dirty" unless the board manufacturer really cheaps out on smoothing capacitors then uses voltage drops instead of regulators for the proper DC voltage.

What can get weird is an inverter powering electronics: If it's not true sine wave then some switching power supplies can get messed up (laptops etc). I highly doubt someone would buy an inverting genny large enough for whole house use though - the cost would be staggering.

All of the HVAC control boards I've seen use pretty basic AC conversion, just a transformer, full or half wave scheme diodes, and regulation/smoothing. Can't say I've seen one using a switching regulator but there probably is one somewhere.

Of course there could be unknown oddities with the way the genny was connected etc. Big arcs/spikes, reverse wired, no overcurrent protection, no auto switchover so mains and genny supply at the same time etc.

 

[ron]

I had a tough time buying a small generator for myself that had a voltage regulator. Many small ones (5kW and smaller) do not have one.

 

[nizak]

If I do a service changeout I use a portable Honda 2000W to power essential circuits in the owners home. I can't count the # of times I've powered a furnace over the years and never once had an issue.Many were newer H/E (90%+) furnaces.

 

[qcroanoke]

I have watched my Samsung 52 inch tv and surfed the net while on my generator. without a problem.
It is a 7200 watt Troybilt.

 

[just the cowboy]

I recommend to people that they don't run their electronic type devices off of a generator unless they have a constant fuel supply, when the generator is running out of fuel that is when I have seen the surge because of the way it is shutting off.

 

[qcroanoke]

I recommend to people that they don't run their electronic type devices off of a generator unless they have a constant fuel supply, when the generator is running out of fuel that is when I have seen the surge because of the way it is shutting off.

Very good point.

 

[electrofelon]

Rectified AC isn't "dirty" unless the board manufacturer really cheaps out on smoothing capacitors then uses voltage drops instead of regulators for the proper DC voltage.

What can get weird is an inverter powering electronics: If it's not true sine wave then some switching power supplies can get messed up (laptops etc). I highly doubt someone would buy an inverting genny large enough for whole house use though - the cost would be staggering.

Filter capacitors help but still dont leave you with pure DC. Intuitively I would think a voltage regulator circuit set below the lowest ripple would take it all out but I am not sure. I think the more you are willing to pay, the more pure your DC will be. I have always been curious about those warnings about MSW inverters not working or potentially damaging certain loads. I was initially nervous plugging in my cordless tool chargers to one because they say those are often problematic, but I
have never had a problem. Never had a problem running laptops or hard drives off them either (I am off grid with a pretty cobbed up electrical system at the moment - Ill be getting a nice sine wave inverter soon).

 

[goldstar]

With respect to what has already been mentioned, we don't know what type of generator was used and whether or not it had a voltage regulator. However, I've found that many service people who service equipment with electronic controls will immediately tell a customer that they will not warranty their equipment if a generator was used, irrespective of whether the generator was a quality unit or not. There's no investigation as to what caused the damage, it's just a flat out statement that lets them off the hook so they can replace the circuit board and charge their customer an exorbatant amount of money

By the same token, if the customer used a 30 year old, rusted bucket of bolts for their generator they deserve what they get.

 

[PatM]

Filter capacitors help but still dont leave you with pure DC.

Electronics is my hobby and I've built many power supplies, sometimes with caps 1/10th the size a regulator's datasheet recommends and not had any ripple problems. Of course at high loads (or very low depending on the regulator) undersizing can cause some problems, particularly if any analog parts are in use. For analog the worst culprit is lack of bypass caps at the analog part but even that just means jumpy outputs.

If they use a cheap linear regulator (78xx) and go real small on the transformer then use half-wave with small caps the voltage drops could cause the regulator to drop out but it wouldn't destroy anything.

 

[GoldDigger]

I think that for incorrect operation problems as opposed to component destruction use by the board circuitry of 60Hz line frequency for timing could be a real problem.
If the noise or even harmonics are at a high enough level a zero crossing detector could see additional spurious counts. In a poorly designed timing pickup circuit the results could be much worse

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