reverse polarity

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roger

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Fl
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Re: reverse polarity

Jim, your grasping for straws now, and you still haven't explained your earlier posts.

Roger

[ February 14, 2004, 05:58 PM: Message edited by: roger ]
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: reverse polarity

Roger swap the hot with neutral.
Now you have 120 on that MOV that was intended to be only a volt or 2.
That ground from the plug goes to the same point as the ground symbol on the MOV
If that MOV overheats it will burn other components on that circuit board.
 

iwire

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Location
Massachusetts
Re: reverse polarity

Jim are you even reading the posts?

There is no ground here, it is a two wire cord.

You might want to go back to Derecks post. :)
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: reverse polarity

In this case no there is no ground .But very similar circuits are used in other electronics that do have grounds.So add a ground and tell me what happens.That washer had a ground.
 

dereckbc

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Plano, TX
Re: reverse polarity

Roger & Bob, give Sam some time to respond. If it is 3-wire (not shown) or if the unit were connected to ground say via coax, there would be a problem with the MOV's asumming they are something less than 140 volt units and with R2.

This is a problem with many electronic circuit designs. Designers add filters between L-G and N-G rather than L-L and L-N. This causes common mode noise problems in the EGC, harmonic problems, and in some cases a polarity issue. IMO it is poor design. Filters should never be installed from L-G or N-G including TVSS. If they must, the values should only be choosen to respond at the target frequency.
 

iwire

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Location
Massachusetts
Re: reverse polarity

Jim I admitted I do not know much about electronics but I do have faith in Wayne's knowledge and what he says here seems to make sense.

Originally posted by hurk27:
And while some designers might install a MOV device to try to block any transient spike between the neutral and ground. It wouldn't be below the 130 volt threshold of a MOV that would be used on a line to neutral as this would be a very poor design. Most transient spikes that damage equipment are line to neutral and this is because this is where the load should always be connected. so why would you install a MOV between neutral and ground when any surg's between these would not have a load to damage. Also if a MOV with a 2 volt threshold was installed between the ground and neutral it wouldn't last any way as any voltage drop in the neutral would cause current in the MOV as the most circuits will have more than a 2 volt drop. the EGC wont have the voltage drop as it will be at the main neutral bar potential. because there is no current on it to cause a drop.
The question I picked up on was Sam's about running a PC on reversed grounding conductors, as I have experience feeding these line to line with a grounding conductor and the units working fine I felt I could jump in.

If this washer truly was designed in a way that reverse polarity could take it out that is a very poor design as a lot of old buildings have polarity issues.

To me it sounds like service guy BS to get money from the consumer.

[ February 14, 2004, 07:30 PM: Message edited by: iwire ]
 

iwire

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Re: reverse polarity

Dereck no problem I was busy putting together my last post while you put up yours.

I was responding to Jim.

Turns out I am thinking like you, poor design if this washer can be taken down by reversing grounded and ungrounded conductors.
 

dereckbc

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Plano, TX
Re: reverse polarity

Originally posted by iwire:
[QB] Dereck no problem I was busy putting together my last post while you put up yours./QB]
Bob, I just wanted to point out jimwalker, and Sam made a point. There is poor design in consumer grade electronics. It revolves around competition, cost cutting measures, FCC, and foreign electrical architectural differences. If you look here http://www.arrl.org/notes/1816/templates/13v40aps.pdf , you will see a similar design. I have built 4 of these 13.8 VDC@ 40-amp power supplies for HAM radio, and it is similar to all commercial switch mode power supplies with a 3-wire ACEG (EGC) input. You will notice it can accommodate either 120 or 240 volt input with a flick of a switch. Look at the AC portion before the diode rectifier bridge; you should notice there is no reference to AC ground other than a RFI filter. Input polarity makes no difference.

I have designed a few large scale UPS/balanced power systems (120/60) for data centers, and have run into this type of polarity/voltage problem before in a small percentage of consumer grade electronic products. The problem/solution was always the same. Some polarity or voltage sensitive surge or filter component(s) on the AC input stage was the culprit. The biggest offenders are MOV?s and low voltage capacitors installed on the PCB between N-G. These types of components are better served installed L-L and L-N.

There is no good reason to install a filter device in electronic equipment between N-G and L-G in small grounded services like residential. EGC impedances (with respect too earth) are too high for them to be effective. They belong between L-N (diffential mode). Reason being is how much better does it gets than the MBJ at the service entrance. Components installed between L-G and N-G only produce common mode noise on AC system ground circuits. There are circumstances in large installation where these types of devices are useful, but IMO, not small residential installations. The DC power supply is the key to low noise/harmonics by using SPG on the rectifier output which has nothing to do with the ACEG (EGC).

Ok enough soap box preaching for now. Good night. :D
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: reverse polarity

"To me it sounds like service guy BS to get money from the consumer."
Why would you feel he needs to do this ? This is a new washer and under warranty.He gets paid by the mfg.to repair it if the washer was defective.Now if the problem was caused by defective house wiring then warranty is void.
 

hurk27

Senior Member
Re: reverse polarity

Jim warranty's are done at a reduce rate when you agree to do warranty work from a certin manufacture they will have a reduce rate because it is one of the agreements to do there work. you might has a set rate to repair this washer which allow you to charge only so much.
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: reverse polarity

Wayne ,yes that part is true, but i would think customer satisfaction would be more important.When i was working for an RCA dealer we would far rather collect the reduced pay and keep our customer happy.If this customer feels they been ripped off they will tell friends.Yes there are some repair people that only care about how much they make and careless about customers.
 

iwire

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Staff member
Location
Massachusetts
Re: reverse polarity

Originally posted by jimwalker:
Why would you feel he needs to do this ? This is a new washer and under warranty.He gets paid by the mfg.to repair it if the washer was defective.
You are right Jim the service person does not have to do that and an honest one will not.

But you surprise me, you have little trust in the inspection process but much trust in service people.

The news is full of unscrupulous people that take advantage of the unsuspecting.

In this case the service guy could collect money from the consumer and get reimbursed by the manufacturer.

No it is not right, but have you never watched 20 20 and all the AC service guys that charge for things that are not needed.

I wish I had more faith in people but when I have service guys in my house (oil burner techs) I make them leave any parts that have been replaced if I pay for the new part.
 

hurk27

Senior Member
Re: reverse polarity

Iwire
Years ago when I had my mother living with me. I was out of town working on a large job and my furnace went out. I already knew what it was as I needed a new main gas control valve. it would once in a while stick and you had to tap it to get it to open. but it hadn't acted up in a while and we hadn't needed the furnace as it had been to warm. But while I was out of town she tried to get to come on and it wouln't bring the main burner on. even with the taping of the main gas valve so I called a trailer furnace repair shop that was close by and told them what the problem was. when I got back to town I about fell over when I got the bill. $4300.00 I think they thought they were just dealing with just my mom and didn't know that I would check it. they even said they had to replace a cast iron fire box door because it showed signs of rust. and they said they replaced the blower motor when in fact they didn't as it still had the date stamped on it when I replaced it. I called the sheriff department right away and filed a complaint. they were charged with theft and a few other charges against the elderly. The stand pipe they supposedly changed still had the same rust on it. about the only thing that I could see that was changed was the main gas valve and that cast iron door.
The funny thing was when the investigator went through there records he found out that they only charged $1400 for a whole new furnace INSTALLED!
we recovered all the monies paid and they had to pay the court cost plus they received a heavy fine. the service man received probation I think 5 years.
 

wanderer20001us

Senior Member
Re: reverse polarity

iwire, dereckbc -

Just wanted to make sure you guys know that the web sites I sent you to are not mine. Just a coincidence that I share the same name.

That said, there are many designs that are not polarity sensitive. There are, however, designs out there that are polarity sensitive. Bad designs happen frequently (Imagine that)

The newer data center equipment with input voltage ranges from 80Vac to 250Vac (self switching or manual switching)are not going to be affected (by design). They rely on UPS power and up stream surge protection to limit input power quality problems.

A washing machine is not data center quality and designers may assume a polarity correct system. Right, wrong, or indifferent, this exists and can be a problem.

The only way to determine what impact the reverse polarity had on the failure would be to review the schematic for that device. Otherwise, the speculation will continue.

On another note, when you find a reversed outlet, earn some extra money and check the rest of them in the house.

Sam A.
 

dereckbc

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Location
Plano, TX
Re: reverse polarity

Sam, I agree with you. If designers are installing MOV's, SAD's, resistors, etc between N-G on their devices, there is going to be a possible polarity or voltage issue. All these type of devices are likely to impose load current on the EGC circuit to some degree. IMO, that is a bad design. There is no need to have any circuitry between N-G or L-G for that matter. THX Dereck
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: reverse polarity

Hurk , they shoulda been sent to prison and never allowed to own another company.I quit a job over something like that many years ago.I watched as the owner of the shop recharged a picture tube on a used tv ,right in front of the customer and told him the set was in great shape,and sold it to him.I will not be a party to such dishonesty.
Repairmen like this are what gives the rest a bad name and mistrust.
I have more respect for Jesse James than guys like this,at least use a gun

[ February 16, 2004, 06:11 PM: Message edited by: jimwalker ]
 
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