Surge still blows furnace control board out

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  #41  
Old 02-28-16, 05:20 PM
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And so surges blew the old one, and surges blew the new one.........
I am not convinced the surges damaging the boards (if the cause is surges) are coming from the power company. Surges are normal as power is restored after an outage and during normal utility switching, but when the power is restored you are still on generator power and not connected to the utilty power lines. I'd look a little harder at the transfer switch or possibly the generator.
 
  #42  
Old 02-28-16, 05:52 PM
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Hi Geo.....Always had the Genny from since shortly after the house build.

And Westom...you're still analyzing, but not applying analysis or recognition to your own inability to relate properly. And that is FAR more important than anything you could ever know or prove about anything.

Here's a tip...when you admit to being off base or relating poorly...historically people actually wind up liking you better.
 

Last edited by Gen; 02-28-16 at 06:24 PM.
  #43  
Old 02-28-16, 06:26 PM
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Joe, I agree. The line power should be stable by the time the transfer switch decides to cut over. I'm just not familiar with how they accomplish that transfer, relay or some softer approach like syncing the gen to the line first. Doubt if they sync the two.

If it is just a relay and it is generating some sort of spike, wouldn't there be a protection circuit on the output of the generator, in this case that is no longer working?

Bud
 
  #44  
Old 02-28-16, 07:54 PM
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Since you listened to Furd, then what he suggests may be impossible.
I never made any suggestions.

Furd only understands throwing darts.
Citation, please.


While I agree completely in determining the CAUSE of the problem rather than just making non-logical attempts to circumvent the problem, I have yet to see westom give a detailed list of troubleshooting steps, in any of his responses.


It already exists inside every furnace controller and all other appliances. Described is a transient that exceeds what appliances are already designed to withstand without damage. Existing internal protection is robust.
Please explain, in detail, what this already existing device or circuit consists of. I am not aware of any type of TVSS devices or circuits that are routinely built into any appliances.
 
  #45  
Old 02-29-16, 07:05 AM
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I'd look a little harder at the transfer switch or possibly the generator.
Joe brings up an interesting point. If the transfer switch does not switch cleanly back to line power, there could be trouble. This may be exceedingly unlikely, but if L1 switches to line before L2 is released from the generator, I would predict bad things would happen to some loads. Most all double pole relays that I have seen mechanically tie both pole contact sets together.

Is this a 120V furnace; at least at the fan/controller board input?
The problem I have in designing experiments for the owner is that without test equipment, about the only indication of a problem may be more blown boards. Not many of us have differential dual channel, high voltage storage oscilloscopes.
In spite of that, what could be done is use test lamps on each leg of the line. Someone had suggested this before. Furnace OFF, along with any electronics and appliances, stereos, TV all unplugged. Go thru some test cycles on the genset and transfer switch. The transfer switch will have a UTILITY IN breaker. Use that to test the system manually. This is not the PANEL MAIN breaker. Make sure the test lamps switch cleanly, especially with NO BRIGHT pulses. Use some unsophisticated loads, like a couple of space heaters, one on each line.
good luck in the hunt.

ps; I'd use incandescent lamps, and the other transient to look for is a clean turn on to utility power. If the transfer relay is arcing more than usual at the reconnect, you will get very rapid voltage transients during the arc. This can be hazardous to electronics. Called EFT or electrical fast transient in the industry.
 

Last edited by telecom guy; 02-29-16 at 07:14 AM. Reason: clarification, spelling,
  #46  
Old 02-29-16, 08:45 AM
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We still never got the model # of the transfer switch,but I bet it is not really not to sophisticated.
 
  #47  
Old 02-29-16, 09:27 AM
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All of the residential grade transfer switches are ultimately just a double pole relay. They do not sync or co-switch. The two poles are supposed to break-before-make and should be "simultaneous" within the tolerance of a magnetic relay. Most of them have a fixed delay in seconds (usually 10s) between line power restoration (which is measured by RMS voltage +/- 10% of nominal; no fancy waveform analysis) and the transfer action.

A few things are still bounding around my head -- is the relay in the transfer switch really working correctly? Is it chattering, are the contacts arced, are the poles acting independently (perhaps bent/broken internal component)?

If OP is in the country and all or most of his neighors also have transfer switches and automatic generators, then maybe there are big power anomalies happening as all of the neighboring houses cut back on to the utility. The effect would be particularly pronounced if he shares a transformer on the end of a long line.

In any case, this is going to be pretty tough to do any real diagnostics on without quality metering equipment. A standard multimeter is not going to catch anything meaningful in that short of a timespan. Once you've done the basic mechanical inspections of everything, verified good grounding, verified correct wiring, I think the next step is to have the generator and switch inspected by a factory certified tech who can scope it and verify proper electrical operation.
 
  #48  
Old 02-29-16, 08:49 PM
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Hi Ben, Yes this is what I'm doing, my "next step is to have the generator and switch inspected by a factory certified tech who can scope it and verify proper electrical operation."

And thanks Geo but I've run out of bandwidth to deal with this any further...aside from checking if there's actually ground rods outside, then checking for a short between gnd and neutral between furnace and panel....which I know means disconnecting both ends or looking physically.

Also FYI Westom has been banned from the forum.
 
  #49  
Old 03-14-17, 07:32 PM
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Well yes, what we found is that the genny, as measured at its panel, was putting out 160 volts between each leg/phase and neutral instead of the the usual 120v.

So the 160v bypassed the gen panel surge protector and bypassed the dedicated surge protector at the furnace and fried a bunch of stuff in the furnace!!

We have since had the genny output voltage corrected.

It could also be partly a POCO issue too. (power co)

Measure what's coming out of the genny panel, and get sp's installed too. But remember sp's only work well if you have proper grounding, which the other pros will better comment on.
 
  #50  
Old 03-14-17, 08:03 PM
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Surge protectors don't start "turning on" until about 175Volts. They are designed to deal with surges of thousands of volts, that are short lasting.
 
  #51  
Old 03-14-17, 09:05 PM
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Wow, 175 volts? Interesting...meanwhile the furnace slowly simmers and fries at 160v
 
  #52  
Old 03-14-17, 10:39 PM
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The generator was putting out 160vac...... that would be 320vac across the hot legs.

What make was this generator ?
I've installed a lot of them and have never seen that problem. The generator's electronics should have shut that generator down.

Technically, if the 160vac was the problem the furnace board should have fried as soon as it went to generator power. 160v is not a surge..... it is an over voltage problem. A surge protector protects against an instantaneous large spike.

The part that is baffling is why at the transfer point. I'm thinking that maybe the furnace blower was running at the time and the removal of power caused it to spike. Everything was running hot at 160v.

It's hard to believe only the furnace was affected.
 
  #53  
Old 03-14-17, 10:54 PM
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It looks a little confusing. A new member posted here about his problem. In order to not get the two issues confused.... I moved the new member to his own thread which can be found here... http://www.doityourself.com/forum/el...ace-board.html

Sorry for any confusion.
 
  #54  
Old 03-15-17, 08:20 AM
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Generac genny. And we measured continuous 160v at the genny sub panel and at the input to the furnace. This was while the poco power was out and we're only on genny power.

No other things were affected. This condition also fried 2 other SPD outlet strips in the house. But thank fully saved the devices, computer and entertainment center stuff, on the strips. Didn't check voltage at these places though.
 
 

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