Power surge every time the blower starts

Hang out, sip some ice tea, and shoot the breeze with TR regulars.

Moderators: emkubed, Captain Ned

Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 12:50 am

From what I've seen in threads about UPSs, PSUs, and even motherboards, you guys seem to know quite a bit about Power. So here's one for you.

I'm spending the first winter in a new (to me) house. It's freezing out, so the furnace is cycling frequently. I've noticed that every time the fan kicks on, about half of the lights in the house increase in brightness for a split second. It's the only appliance that produces a surge every time it fires up. The other large appliances cause the lights to dim, which seems a little more normal to me. It's a 180k BTU monster from the 70s, so it's probably not very power efficient. Still, it is on a 20A breaker, which I don't believe is being shared with anything else.

I asked the HVAC guy about this when he was cleaning it out. His response: "That's normal for these old belt driven fans."

So, I am wondering just how big of a surge this thing is producing, and if it can shorten the life of other appliances and electronics? Our electronics are plugged into standard (cheap) surge protectors, but ~25 surges a day can't be very good for the surge protectors. Would a line conditioner be a better idea?
setaG_lliB
Gerbil
 
Posts: 41
Joined: Wed Mar 03, 2010 6:02 pm

Re: Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 2:04 am

In all honesty to answer your question completely I would need to know the type of breaker, wiring configuration and a few other things, but generally speaking:

It's not really common to see something on a dedicated circuit to affect a different circuit at all. A circuit is a group of physical wires that runs through your house, It is tied to your main via the circuit panel which was designed specifically to insulate your house from spikes on the main line. I'm not saying it isn't happening, but it isn't right.

Here is what is happening: the motor kicks on and draws a lot of power for like a milisecond (usually just under 20A which is why usually they will put HVAC on its own circuit), then once the belt gets going it doesn't need nearly as much power, so the draw has to equalize. This causes the surplus. Power grids can't store power efficiently, so the extra energy seeks the easiest path to ground it can and the open light circuits provide a good escape and the flow equalizes after a second or so.

The way a surge protector works is it offers a bridge between hot and ground that can siphon excess voltage while maintaining nominal current flow. think water through a pipe and think pressure relief valve on a spring. When the voltage is over 120v household current something like a metal oxide varistor or a tube of inert gas shunts power to ground until the pressure drops and the spring on the valve closes back up. its not really very likely to wear out if you use it a lot because its just a resistor which has certain physical properties.

IF your HVAC is on the same circuit as anything that you want to keep, computer, tv, whatever, get a mid range surge protector ($10-30) or move them to a different circuit. other than that, I don't worry too much. it shouldn't be a problem. If/when you do shop for power strips, always look for the magic words transient voltage surge suppressor which means that it isn't just a multi outlet extension cord like the $3 daisy chain special at walmart.

To check whether your HVAC is on its own circuit, simply turn off that circuit and walk around your house with a nightlight or lamp to see what outlets are affected.
Diplomacy42
Gerbil
 
Posts: 63
Joined: Sat Sep 01, 2012 2:56 pm

Re: Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 12:46 pm

I do agree that it is hard to know the exact cause without knowing more about how things are connected, however it is most likely an imbalance in current draw on the two 120V feeds combined with a bad neutral connection. There are two 120V legs to the breaker panel that are 180 degrees out of phase. 220V appliances use both 120V feeds. 120V circuits will use one or the other. If you have exactly the same current both 120V legs, there will be no current on the neutral line. This, of course, never happens and you get some current on the neutral line. If the blower is a 120V blower, then you will suddenly have a nearly 20A imblance when it starts. Where things get strange is if you have a poor neutral connection back to the power transformer. This will cause a voltage drop as the current will see a higher resistance path back to its source (potentially through the ground -- the actual ground).

Assume that under normal circumstances, you have an imblance with lights being on leg A and the blower and other stuff being on leg B. Leg A current is 10A total and leg be current is 2.5A (the number don't matter and are simply for explanation). In this state, the neutral line is carring 7.5A of return current to the transformer, all from leg A. Also assume that the neutral connection is bad and this current is enough to cause a 20V drop. Leg A is 100V and leg B is 120V. This would mean that your lights are normally running off of 100V, which looks normal to you since that is how things normally are. Now, kick on the blower on leg B. All of the sudden, leg B is pulling 22.5A (we assume the blower pulls 20A startup current to make it easy). This means that the entire current of leg A is now being returned through leg B so the leg A voltage drop is removed and the voltage jumps to 120V. This makes the light bright. In fact, the voltage on A may go above 120V due to the fact that lights are a resistive load and the blower is an inductive load, but that is more math than I want to do on a Sunday morning. Once the motor is running, its load drops way down, to say 2.5A. This means that leg A is now pulling 10A and leg B is pulling 5A. The 5A imbalance is returning down the neutral line. The voltage drop is now something like 13V and the lights are running off of 107V.

This is only one of the scenarios possible. There are others too. To troubleshoot this, you need a voltmeter, a clamp on ammeter and access to your breaker box, with the front panel removed. At this point, since you can kill yourself with a mistake, my advice is to call an electrician and ask him how much it will cost to troubleshoot a load imbalance on the two 120V phases and a high resistance neutral return. Actually, I would describe the same thing you did to us and if he can't hit on the possibility of imbalance/high resistance, then try another electrician.

Patrick M
SecretSquirrel
Gerbil Jedi
Gold subscriber
 
 
Posts: 1715
Joined: Tue Jan 01, 2002 7:00 pm
Location: The Colony, TX (Dallas suburb)

Re: Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 2:02 pm

The above all is very important.
But while you are at it, you might want to think about replacing the blower.

It's a 180k BTU monster from the 70s,


Something like 1/4 of your heating bill is going to the blower pushing the air around your house.
Newer models are indeed quite a bit more efficient.

Yeah, if your heating season is only 4 months, the payback will be longer...but in general these things pay for themselves over the long run...10+ years. :wink:
mdk77777
Gerbil XP
 
Posts: 346
Joined: Fri Dec 12, 2008 3:42 pm

Re: Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 2:14 pm

Belt driven, wow that's gotta be old. On fuses or breakers? Newer houses is usually code for a furnace to be on its own breaker/circuit. If your furnace is belt driven, it could mean that is 30+ yrs old, and if you house is fuses, there very well could be 20 things on a circuit.

I recently (may 2013) installed an ECM motor in my furnace as a PSC direct replacement. Very happy with it so far, smooth, soft start, soft ramp between speeds and a low recirc speed to save power. I would say it payed for itself in 6 months, however I recirc 24/7 and electricity up here (after all taxes, delivery, etc.) is about 18 cents/kw.hr!!

http://www.usmotors.com/Our-Products/HV ... owner.ashx

http://www.usmotors.com/Our-Products/HV ... oTech.ashx

I got a 5532et, and I am not a rep or shill, there are other options, but I was able to get this the easiest for a good price ($350) after tax.
Life doesn't change after marriage, it changes after children!
anotherengineer
Gerbil Elite
 
Posts: 563
Joined: Fri Sep 25, 2009 1:53 pm
Location: Timmins, ON Canada, Yes I know, Up in the sticks

Re: Power surge every time the blower starts

Postposted on Sun Dec 08, 2013 5:09 pm

1970s furnace? I wouldn't bother upgrading or retrofitting it. Just keep getting the heat exchanger inspected and save for the replacement.

In the meantime, a "floating neutral" condition sounds like the best explanation and likely indicates a significant problem forming at either the box or the transformer neutral connection. DO have it inspected soon.
He who laughs last, laughs first next time.
ludi
Gerbil Elder
 
Posts: 5439
Joined: Fri Jun 21, 2002 10:47 pm
Location: Sunny Colorado front range

Re: Power surge every time the blower starts

Postposted on Mon Dec 09, 2013 2:57 am

SecretSquirrel wrote:

Diplomacy42 wrote:

I always learn something new here. Thanks for the explanation. I actually understood most of that.
Looks like I was wrong. The furnace, washer, and dryer all share that 20A circuit. I've never noticed it before, but the washer and dryer also cause a bit of a surge when they start up; just not as severe as when the blower motor starts. As luck would have it, the living room seems to be the most affected area (where the lights brighten up most), and that's where the TV and stereo stuff is. :roll:
anotherengineer wrote:Belt driven, wow that's gotta be old. On fuses or breakers? Newer houses is usually code for a furnace to be on its own breaker/circuit. If your furnace is belt driven, it could mean that is 30+ yrs old, and if you house is fuses, there very well could be 20 things on a circuit.

Built in 1978. It uses 15, 20, and 50A breakers.

ludi wrote:1970s furnace? I wouldn't bother upgrading or retrofitting it. Just keep getting the heat exchanger inspected and save for the replacement.

In the meantime, a "floating neutral" condition sounds like the best explanation and likely indicates a significant problem forming at either the box or the transformer neutral connection. DO have it inspected soon.

None of the other appliances in the house produce voltage spikes. It just seems to be the one 20A breaker that's acting up. Is this still a "floating neutral?"
setaG_lliB
Gerbil
 
Posts: 41
Joined: Wed Mar 03, 2010 6:02 pm

Re: Power surge every time the blower starts

Postposted on Mon Dec 09, 2013 9:20 am

A natural gas furnace usually only requires a 15amp circuit, forced air electric furnaces can draw big time power. Washer is usually a 15amp dedicated circuit and a dryer is usually a 30amp dedicated circuit.

Is your furnace forced air electric?

A floating neutral means the neutral line has not been grounded. In the panel, the neutral is tied to ground and that ground connector should have a cable running to the nearest earth ground (usually copper water line coming in through floor)
Which could be a possibility. Still sounds like an overloaded circuit to me.

Residential panels have 240VAC, black to red = 240, red to neutral = 120, black to neutral =120. Panels usually stagger the red and black lines in regards to the breakers so to keep the load between them 'balanced'
If you have multiple loads on 1 circuit, what ends up happening, for example is having 60amps drawing from the black and 20 amps from the red.

Like another user said, either get a qualified electrician to check it out, or an electrical building inspector - which might be cheaper, at least to identify an issues.
Life doesn't change after marriage, it changes after children!
anotherengineer
Gerbil Elite
 
Posts: 563
Joined: Fri Sep 25, 2009 1:53 pm
Location: Timmins, ON Canada, Yes I know, Up in the sticks

Re: Power surge every time the blower starts

Postposted on Mon Dec 09, 2013 11:20 am

setaG_lliB wrote:Looks like I was wrong. The furnace, washer, and dryer all share that 20A circuit. I've never noticed it before, but the washer and dryer also cause a bit of a surge when they start up; just not as severe as when the blower motor starts.


Electric or gas dryer? What circuit is the refridgerator connected to?

If it really is only on circuit that is affected by the blower, then the problem could be within the breaker box. Could be a loose or corroded connection there. I can come up with several ways that it would only impact those two circuits. You would be suprised the crazy things that get done when building a house, that technically pass code.

All the items you have said cause the problem have large motor in them that have a high starting current and then drop down to a much lower running current. I asked about the refridgerator as it is the other large inductive load that would show up in most houses.

--SS
SecretSquirrel
Gerbil Jedi
Gold subscriber
 
 
Posts: 1715
Joined: Tue Jan 01, 2002 7:00 pm
Location: The Colony, TX (Dallas suburb)

Re: Power surge every time the blower starts

Postposted on Mon Dec 09, 2013 9:52 pm

Furnace and dryer are both gas.
The fridge is connected to a different, 15A breaker. When it, or any other appliance upstairs turns on, the lights dim.

Yeah, I guess I'll get an electrician in to look at it. The increase in brightness in the living room is quite high, even if just for 1/4 sec.
setaG_lliB
Gerbil
 
Posts: 41
Joined: Wed Mar 03, 2010 6:02 pm

Re: Power surge every time the blower starts

Postposted on Mon Dec 09, 2013 11:07 pm

Have it looked out, definitely sounds like an imbalance issue pretty much exactly as SecretSquirrel described.

Note there's also some other weird scenarios if you are in a mixed residential/commercial area where you get 4 wire service - ultimately it depends on the service that's provided to your box. (I honestly never ever ever understand why power companies do this stupid stuff, there's just no reason the transformers they are using cannot provide traditional 120/240 single phase service.) However if you have those situations, the electrician should know right of the back AND be totally familiar with it unless you live in BFE.

Speaking of exotic service, my parents lived in a house once that had true 120/1ph wire service. This was because we lived on a ranch in the middle of nowhere and they saved on aluminum.
keltor
Gerbil First Class
 
Posts: 177
Joined: Thu May 10, 2012 4:29 pm

Re: Power surge every time the blower starts

Postposted on Tue Dec 10, 2013 7:06 am

setaG_lliB wrote:Furnace and dryer are both gas.
The fridge is connected to a different, 15A breaker. When it, or any other appliance upstairs turns on, the lights dim.

Yeah, I guess I'll get an electrician in to look at it. The increase in brightness in the living room is quite high, even if just for 1/4 sec.


I'd lay pretty good money that you have a faulty neutral return then. The other appliances being on the higher load side would cause a further voltage drop when they turn on an the lights would dim. Please report back and let us know what you find.

--SS
SecretSquirrel
Gerbil Jedi
Gold subscriber
 
 
Posts: 1715
Joined: Tue Jan 01, 2002 7:00 pm
Location: The Colony, TX (Dallas suburb)

Re: Power surge every time the blower starts

Postposted on Tue Dec 10, 2013 8:35 am

I can't add anything to the discussion about your electrical issues that hasn't already been said. But, I feel I should say something about your furnace. Don't bother with trying to put in a new blower or a new motor on your existing blower. It's not worth the money on a furnace that old.

I was in the Heating and Air business for several years. The best advice I can give you is to replace that old gas furnace, its costing you more than you realize. Assuming it was new in 1978, its probably only 60%, and possibly only 50%, efficient. That means for every dollar you paying for gas your only getting 50 to 60 cents worth of heat out of it. The rest goes up the flue pipe with the exhaust gases. Today's furnaces are any where from 80 to 96 percent efficient depending on how much you want to spend for one.

Lets be generous and say your existing furnace is 65% efficient. For every $100 your spending for gas you could be saving any where from $20 to just over $30 with a new furnace. Again, those savings numbers depend on how efficient the new furnace is. That $20 to $30 can add up making it really easy for a new furnace to pay for itself in less than ten years.
Khali
Gerbil XP
 
Posts: 336
Joined: Thu Dec 20, 2012 5:31 pm

Re: Power surge every time the blower starts

Postposted on Thu Dec 12, 2013 2:07 am

Khali wrote:Lets be generous and say your existing furnace is 65% efficient. For every $100 your spending for gas you could be saving any where from $20 to just over $30 with a new furnace. Again, those savings numbers depend on how efficient the new furnace is. That $20 to $30 can add up making it really easy for a new furnace to pay for itself in less than ten years.

Depends how often it runs. US natural gas prices have gone down in recent years, while most of the tax credits for efficiency improvements have dried up. The initial investment in a high-efficiency furnace in his size range can easily be $1500+ installed, while the added complexity makes repairs both more likely and significantly more expensive.

The unit in my house, roughly a 7yo $2k Amana purchased by the previous owners, had a motor burn out last February that dominoe'd a control board. Net trouble: three visits by the repair service including special-order parts for $650 (thanks, Amana, for using a custom motor bracket that defies all universal replacement kits), four hours of lost workday, and two oil-filled electric heaters for $80 plus $10 of electricity to prevent pipes from freezing.

One failure like that, and the cost savings have returned to break-even.
He who laughs last, laughs first next time.
ludi
Gerbil Elder
 
Posts: 5439
Joined: Fri Jun 21, 2002 10:47 pm
Location: Sunny Colorado front range

Re: Power surge every time the blower starts

Postposted on Thu Dec 12, 2013 10:36 am

Unless your insulation is really great, the money is probably better spent there. Gas prices are just so damn low.
keltor
Gerbil First Class
 
Posts: 177
Joined: Thu May 10, 2012 4:29 pm

Re: Power surge every time the blower starts

Postposted on Thu Dec 12, 2013 12:15 pm

Though I'd like to replace it with something quieter and more efficient (was told I'd be able to replace this 180k BTU gas guzzler with a 100K BTU and feel just as warm), I'm just too poor at the moment. The HVAC guy did say that the heat exchanger in this thing would probably last another 25 years. It's an Airco furnace, which were apparently built like tanks. Might explain why they're no longer in business.
setaG_lliB
Gerbil
 
Posts: 41
Joined: Wed Mar 03, 2010 6:02 pm

Re: Power surge every time the blower starts

Postposted on Thu Dec 12, 2013 1:22 pm

setaG_lliB wrote:Though I'd like to replace it with something quieter and more efficient (was told I'd be able to replace this 180k BTU gas guzzler with a 100K BTU and feel just as warm), I'm just too poor at the moment. The HVAC guy did say that the heat exchanger in this thing would probably last another 25 years. It's an Airco furnace, which were apparently built like tanks. Might explain why they're no longer in business.

Actually Airco is still around but not in the Gas Furnace business. They merged or were bought by Olsen, a Canadian company. Your correct in saying they were built like tanks. Airco gas furnaces were in fact built with a heat exchanger designed for a oil furnace, hence thicker metal. Airco got out of the gas furnace business because they could not compete with the more efficient gas furnaces that started showing up in the late 80's. I am not sure why this choice was made. It could have been they did not have the expertise to do it and they did not have the money to hire the expertise. It wasn't long afterwords that Olsen took them over and now they are exclusively into oil furnaces. But the Airco name is still around, you just have to go north to find it.

OK, you can't afford a new furnace, fair enough. Then I second the other suggestion. Spend a little at a time and add insulation to your new to you home. Another layer in the attic, to start with, will show the biggest benefits.
Khali
Gerbil XP
 
Posts: 336
Joined: Thu Dec 20, 2012 5:31 pm

Re: Power surge every time the blower starts

Postposted on Thu Dec 12, 2013 2:14 pm

http://web.ornl.gov/~roofs/Zip/ZipHome.html

Good calculator to figure out what you need and where - you can estimate you R-values with a ruler for your attic.

Get your neutral fixed ASAP since that "could" result in a fire.
keltor
Gerbil First Class
 
Posts: 177
Joined: Thu May 10, 2012 4:29 pm


Return to The Back Porch

Who is online

Users browsing this forum: Bing [Bot] and 7 guests