Author Topic: inverter doesn't like my coffee maker  (Read 19034 times)

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Offline birdhouse

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Re: inverter doesn't like my coffee maker
« Reply #30 on: May 02, 2012, 11:53:56 pm »
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There's obviously nothing wrong with the inverter.

if it will run an air compressor while cutting a 2x6 on my chop saw, i'd like to hope that's the case!

adam

Offline ChrisOlson

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Re: inverter doesn't like my coffee maker
« Reply #31 on: May 03, 2012, 01:37:48 pm »
if it will run an air compressor while cutting a 2x6 on my chop saw, i'd like to hope that's the case!

Adam, your description of what else you run with the inverter, with no problems at all, made me decide that.  There is nothing inherently "weird" about coffee makers that should cause any big current spikes to trip out the inverter.  I have run many, many coffee makers on inverters and have never yet seen a properly functioning coffee maker that even small inverters will not power.

That leaves a ground fault problem in the coffee maker, by process of elimination.  Based on what I've seen blow up in those, my best guess is an intermittent short from hot to frame, or hot to neutral in the brewing heating element.  Like you say, plugged in to a true 20 amp circuit, the thing would probably function OK - for awhile.  It depends on what the problem is in it.  I'll bet you could find the problem by taking it apart and ohming it out to find the leak.  But to my way of thinking, the thing is defective and should be replaced by the store where you bought it from.
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Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #32 on: May 03, 2012, 05:39:57 pm »
if it will run an air compressor while cutting a 2x6 on my chop saw, i'd like to hope that's the case!

Adam, your description of what else you run with the inverter, with no problems at all, made me decide that.  There is nothing inherently "weird" about coffee makers that should cause any big current spikes to trip out the inverter.  I have run many, many coffee makers on inverters and have never yet seen a properly functioning coffee maker that even small inverters will not power.

That leaves a ground fault problem in the coffee maker, by process of elimination.  Based on what I've seen blow up in those, my best guess is an intermittent short from hot to frame, or hot to neutral in the brewing heating element.  Like you say, plugged in to a true 20 amp circuit, the thing would probably function OK - for awhile.  It depends on what the problem is in it.  I'll bet you could find the problem by taking it apart and ohming it out to find the leak.  But to my way of thinking, the thing is defective and should be replaced by the store where you bought it from.
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Chris

It's just odd for a gfci to trip due to a 2 prong plug device which didn't have some of the fault current returning to say an earth ground by way of water contact.  My understanding is a gfci monitors the current leaving one terminal and returning on the other.  If a difference of ~6mA is monitored out but not returned, the gfci is tripped.  With 3 prong plugs, if that ~6mA is returned on the earth ground plug, the gfci is tripped. 

I did read where the maker alone plugged in worked fine ( for a while anyway ).  This could be a combination of multiple device current leaks but not one of the items alone is enough to trip his gfci. 
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Offline ChrisOlson

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Re: inverter doesn't like my coffee maker
« Reply #33 on: May 03, 2012, 09:19:00 pm »
My understanding is a gfci monitors the current leaving one terminal and returning on the other.  If a difference of ~6mA is monitored out but not returned, the gfci is tripped.

It measures the current differential on the hot and neutral.  There is no real "return" like DC because the hot and neutral alternate 60 times/second (or 50 if you live overseas).

But GFCI is not foolproof.  Wiring two of them on one circuit will cause one to trip even though there's not a ground fault.  Neutral is bonded to ground at the service entrance (or inverter).  So with a polarized two-prong plug on an appliance - you still have a grounded neutral.  But if you touch neutral to ground anywhere else in the system, even though they are bonded, it will trip a GFCI.  The reason is because in a situation where the load side neutral is grounded and a ground fault also occurs, a parallel path through the GFCI for the ground fault current could exist.  The portion of the ground fault current returning on the neutral conductor will not be sensed as differential current.  This has the effect of desensitizing the GFCI.  So the UL standard requires that GFCIs trip with a 6mA ground fault even when the neutral and ground are connected.  To meet the requirement, GFCIs trip when the load side neutral and equipment grounding conductors are joined, even if there is no ground fault.

So there's several things that could be wrong in that coffee maker, causing the inverter to spit out.  But it all points to a problem in the device, and not the inverter.  The inverter is doing what it's supposed to do.
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Offline birdhouse

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Re: inverter doesn't like my coffee maker
« Reply #34 on: May 03, 2012, 09:40:40 pm »
chris-
i fully agree with your thoughs on GFCI's and the defunk coffee maker.  worst part is, now i have to buy a new one next weekend to be able to make coffee, then return the old one on the way home.  two trips to the same store for the same issue...   >:(

maybe i'll try a different model!  hopefully it work the way it's supposed to work!

adam

Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #35 on: May 03, 2012, 10:00:55 pm »
My understanding is a gfci monitors the current leaving one terminal and returning on the other.  If a difference of ~6mA is monitored out but not returned, the gfci is tripped.

It measures the current differential on the hot and neutral.  There is no real "return" like DC because the hot and neutral alternate 60 times/second (or 50 if you live overseas).

But GFCI is not foolproof.  Wiring two of them on one circuit will cause one to trip even though there's not a ground fault.  Neutral is bonded to ground at the service entrance (or inverter).  So with a polarized two-prong plug on an appliance - you still have a grounded neutral.  But if you touch neutral to ground anywhere else in the system, even though they are bonded, it will trip a GFCI.  The reason is because in a situation where the load side neutral is grounded and a ground fault also occurs, a parallel path through the GFCI for the ground fault current could exist.  The portion of the ground fault current returning on the neutral conductor will not be sensed as differential current.  This has the effect of desensitizing the GFCI.  So the UL standard requires that GFCIs trip with a 6mA ground fault even when the neutral and ground are connected.  To meet the requirement, GFCIs trip when the load side neutral and equipment grounding conductors are joined, even if there is no ground fault.

So there's several things that could be wrong in that coffee maker, causing the inverter to spit out.  But it all points to a problem in the device, and not the inverter.  The inverter is doing what it's supposed to do.
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Chris

So, where is that current going that is missing to cause the gfci to trip?  It's not going through the counter top or the plastic case of the device.  With a two prong device, there is clearly not a return path to ground.  If it's a very simple coffee maker, it will have a heating element for the pot warmer, a coil for heat tube up to the coffee grounds, some kind of heat limiting device and a switch to turn if off and on.  Also, a neutral with alternating current is nothing more than a " bond " to help protect from a voltage potential.  What if: " the sock, where the coffee maker is plugged in, is wired with the taller prong ( neutral ) ' hot ' and the smaller of the two prongs ( hot ) wired with the ' neutral '?"  The coffee maker will work fine and honestly just as if plugged into a properly wired plug.  Will the coffee maker still trip a gfci?  Sure it will if there is a current differential or a return on the earth ground conductor to the inverter in a certain amount of time.  He is dealing with alternating current, from one prong back to the other and so forth and so on.  Does the gfci trip while the current is flowing from the ' hot ' leg or does it trip when the current is flowing from the ' neutral ' leg?

Here is a statement similar to the training I have had regarding these devices. 

GFCI Limitations

The use of GFCI devices is obviously not a substitute for using good common sense. If you have your hairdryer, toaster or other electrical apparatus powered through GFCI receptacles or GFCI-protected extension cord, this doesn’t mean you can do dangerous things. It is possible to have an AC-operated tool or other device powered through a GFCI and still get electrocuted. GFCI’s only operate when they sense a ground fault (short through to ground). If the operator puts himself between the hot wire and neutral without any current flowing to the earth, the GFCI will not open the circuit. As a rule, DO NOT use any AC-powered tool while you are standing in water. NEVER use any electrical tool if you or the tools are wet.

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Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #36 on: May 03, 2012, 10:09:10 pm »
chris-
i fully agree with your thoughs on GFCI's and the defunk coffee maker.  worst part is, now i have to buy a new one next weekend to be able to make coffee, then return the old one on the way home.  two trips to the same store for the same issue...   >:(

maybe i'll try a different model!  hopefully it work the way it's supposed to work!

adam

I certainly hope you can make it through your next RE project with a pot of coffee by getting that coffee maker replaced.  ;D  However, if the next maker doesn't cause the gfci to trip, I hope it wasn't due to a different underlying cause. 

Good luck and best wishes. 
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Offline oztules

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Re: inverter doesn't like my coffee maker
« Reply #37 on: May 03, 2012, 10:50:04 pm »
Watt,
That is exactly as iIunderstand it , and always have. Previously they were a core balanced relay, where the incoming current had to balance the outgoing current. If any current found a way to circumvent this circuit, it unbalanced the circuit and a fault was sensed.

They can only then find a way out of the active-neutral circuit,if the electrons can find some other/alternative way home... can only be via an earth fault.

Neutral and ground bonded at the switchboard, and separately distributed thereafter. A 2 pin appliance sitting on a plastic tray cannot trip any remotely decent leakage detector... and no current can leak out of the circuit.

If you step up to the tray and grab the 2 pin appliance with any part live or leaking, then the core/relay will trip.

A three pin appliance can trip on it's own, as there is now an earth point in that frame of reference on the plastic tray. The track to ground then can be as small as spider web across the active to earth at any point, mixed with moisture and dust.... or you grab the active bits.....

It cannot trip without an earth return of some kind as I understand it.


............oztules

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Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #38 on: May 03, 2012, 11:05:24 pm »
Watt,
That is exactly as iIunderstand it , and always have. Previously they were a core balanced relay, where the incoming current had to balance the outgoing current. If any current found a way to circumvent this circuit, it unbalanced the circuit and a fault was sensed.

They can only then find a way out of the active-neutral circuit,if the electrons can find some other/alternative way home... can only be via an earth fault.

Neutral and ground bonded at the switchboard, and separately distributed thereafter. A 2 pin appliance sitting on a plastic tray cannot trip any remotely decent leakage detector... and no current can leak out of the circuit.

If you step up to the tray and grab the 2 pin appliance with any part live or leaking, then the core/relay will trip.

A three pin appliance can trip on it's own, as there is now an earth point in that frame of reference on the plastic tray. The track to ground then can be as small as spider web across the active to earth at any point, mixed with moisture and dust.... or you grab the active bits.....

It cannot trip without an earth return of some kind as I understand it.


............oztules

oztules, we use a similar scheme to help protect our folks in the field when we use delta generators.  We have master electrician roughnecks ( sarcastic ) which makes testing often necessary.  You wouldn't believe how many different ways they can make a light illuminate with 480v.   :o
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Offline birdhouse

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Re: inverter doesn't like my coffee maker
« Reply #39 on: May 03, 2012, 11:07:08 pm »
thanks watt!

Quote
The use of GFCI devices is obviously not a substitute for using good common sense. If you have your hairdryer, toaster or other electrical apparatus powered through GFCI receptacles or GFCI-protected extension cord, this doesn’t mean you can do dangerous things. It is possible to have an AC-operated tool or other device powered through a GFCI and still get electrocuted. GFCI’s only operate when they sense a ground fault (short through to ground). If the operator puts himself between the hot wire and neutral without any current flowing to the earth, the GFCI will not open the circuit. As a rule, DO NOT use any AC-powered tool while you are standing in water. NEVER use any electrical tool if you or the tools are wet.

this is what they tell you, but like chris has sated, GFCI's will trip from a multitude of reasons.  sometimes they will even trip if you plug in a two pronged device a little crooked where the hot hits before the neutral...  even a 20A rated GFCI will trip long before the same circuit 20A breaker trips.  being a contractor in the states, all of my power usage outdoors is supposed to be GFCI protected.  i tried that for a minute, but the CONSTANT tripping of the GFCI with big draw equipment was a no go.  just try running a 3 horse 4 gallon twin stack air compressor on a GFCI, it's not going to happen!   i tell my guys that if they get shocked (usually using a circular (double insulated) saw in a downpour) that they should call it a day, or work indoor if its an option.  if i had to halt my crew every time a GFCI blew, or repeatedly blew, i wouldn't make any money! 

then there's AFCI's, but lets not get started on that! 

adam

Offline birdhouse

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Re: inverter doesn't like my coffee maker
« Reply #40 on: May 03, 2012, 11:14:03 pm »
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Neutral and ground bonded at the switchboard, and separately distributed thereafter. A 2 pin appliance sitting on a plastic tray cannot trip any remotely decent leakage detector... and no current can leak out of the circuit.

forget the ground for now.  lets say two pronged stuff:

if the neutral arcs to the hot for a millisecond, doesn't that create an imbalance?  to me that makes sense, but you, OZ know WAY more electrickery than i do!!!

adam

Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #41 on: May 03, 2012, 11:17:16 pm »
thanks watt!

Quote
The use of GFCI devices is obviously not a substitute for using good common sense. If you have your hairdryer, toaster or other electrical apparatus powered through GFCI receptacles or GFCI-protected extension cord, this doesn’t mean you can do dangerous things. It is possible to have an AC-operated tool or other device powered through a GFCI and still get electrocuted. GFCI’s only operate when they sense a ground fault (short through to ground). If the operator puts himself between the hot wire and neutral without any current flowing to the earth, the GFCI will not open the circuit. As a rule, DO NOT use any AC-powered tool while you are standing in water. NEVER use any electrical tool if you or the tools are wet.

this is what they tell you, but like chris has sated, GFCI's will trip from a multitude of reasons.  sometimes they will even trip if you plug in a two pronged device a little crooked where the hot hits before the neutral...  even a 20A rated GFCI will trip long before the same circuit 20A breaker trips.  being a contractor in the states, all of my power usage outdoors is supposed to be GFCI protected.  i tried that for a minute, but the CONSTANT tripping of the GFCI with big draw equipment was a no go.  just try running a 3 horse 4 gallon twin stack air compressor on a GFCI, it's not going to happen!   i tell my guys that if they get shocked (usually using a circular (double insulated) saw in a downpour) that they should call it a day, or work indoor if its an option.  if i had to halt my crew every time a GFCI blew, or repeatedly blew, i wouldn't make any money! 

then there's AFCI's, but lets not get started on that! 

adam

Adam, don't confuse the two different devices.  A gfci is not a circuit breaker and is not meant to current limit the circuit.  Dual function incorporated devices are available however, in a gfci/breaker package.   
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Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #42 on: May 03, 2012, 11:21:47 pm »
Quote
Neutral and ground bonded at the switchboard, and separately distributed thereafter. A 2 pin appliance sitting on a plastic tray cannot trip any remotely decent leakage detector... and no current can leak out of the circuit.

forget the ground for now.  lets say two pronged stuff:

if the neutral arcs to the hot for a millisecond, doesn't that create an imbalance?  to me that makes sense, but you, OZ know WAY more electrickery than i do!!!

adam

I'm not oz but, I'd like to answer this.  An air gap arc is a circuit and you will have current returning in the same amount as supplied.  No, that does not mean that circuit is unbalanced.  That is also why your welder doesn't trip your gfci.  The example you gave regarding plugging in the two prong plug to the ' hot ' before the neutral was contacted, that's not a circuit until both prongs made contact and there was a load. 
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Offline birdhouse

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Re: inverter doesn't like my coffee maker
« Reply #43 on: May 03, 2012, 11:22:42 pm »
i wasn't confusing them.  all i'm saying is if your pushing the limits of a 20a breaker and have a GFCI in line with that breaker, in totally dry three pronged situations, with zero ground potential, the 20A GFCI will ALWAYS!!! trip before the breaker does. 

GFCI's are finicky!  no question...  ask any contractor!  it's proven! 

adam

Offline Watt

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Re: inverter doesn't like my coffee maker
« Reply #44 on: May 03, 2012, 11:25:28 pm »
i wasn't confusing them.  all i'm saying is if your pushing the limits of a 20a breaker and have a GFCI in line with that breaker, in totally dry three pronged situations, with zero ground potential, the 20A GFCI will ALWAYS!!! trip before the breaker does. 

GFCI's are finicky!  no question...  ask any contractor!  it's proven! 

adam

I agree gfci's are finicky, but 6mA is very small and so is m/s in time.  I've searched for days to find faults in the past.  One was a 16awg extension cord laying on the ground ( dry ground ) that had gotten wet weeks prior and had a pin hole in the insulation and one ' neutral ' conductor.  I tore the pvc jacket off and found the paper like reinforcement damp.  I dried the cord where the tiny pin prick was and heat shrink-ed a sealing jacket over it.  Then reset the gfci and no more problems.  Yes, I know how finicky they can be.
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