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Problems with inverter

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Taffy Turner

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Can anyone help please?

I upgraded my lathe at Christmas to a Record CL4 with variable speed inverter drive. (My old one was a cheapy with belt speed change).

It ran fine for a couple of months, and then started knocking the RCD which protects my workshop out as soon as it was switched on.

I sent it back to Record and they changed the inverter. Everything worked fine for a couple of weeks, and then the problem came back. I returned the lathe to Record again, but this time they said there was no fault.

The lathe still won't run in the workshop, although it runs fine if I plug it into one of the house sockets. The house is protected by an RCD also, but I think it is a higher rated one.

I have received conflicting advice - some people have told me that I must have a faulty RCD, and others have told me that inverter drives are not compatible with RCDs. Record Power are no help whatsoever!

Anyone else had problems with inverter powered lathes?

Any advice gratefully received!

Gary
 

Alf

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Welcome to the forum, Gary. Can't help with your query I'm afraid :( , but had to say hello to a fellow cricket fan. Good result in the test, eh? :D

Cheers, Alf
 

Adam

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I'd ask Record for a bit more assistance - either by telephoning them again, or alternatively they have a forum like this on their website - which seems to be very actively managed - so you may get a good response there - or someone who knows here, although I have some knowledge - this question is just a bit to electrical for me (electronics more my thing), or you could try the screwfix forums - the electrical one (or maybe the DIY one) there seems to be lots of qualified sparkys very active on there.

HTH

Adam
 
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Anonymous

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Gary

RCD's (Residual Current Devices) are tripped by very small earth leakage currents (30mA typical) between a piece of equipment and the yellow/green earth conductor and are often paired to MCBs (Minature Circuit Breakers) which trip on over current. Safe as you can get as they both trip incredibly fast and are accurate and sensitive, unlike fuses.

Inverter drives usually rectify the incoming mains to produce high voltage DC and then chop this up to produce an approximation of a sinewave using a technique called Pulse Width Modulation (PWM). Whilst this allows the frequency of the AC current applied to the motor to be alltered and thus the motor speed (ac motor speeds are frequency dependant, not amplitude dependant) it is a very eletrically 'noisy' technique and you need to filter the mains supply to the inverter to prevent noise being sent back down the line. Most cheapish inverters do not have very good filtering as it costs money and does not effect the perfomance of the drive when considering the control of the motor.

OK, what does this long preamble mean?

I suspect that the mains noise may well be nuisance tripping your RCD. In industrial machinery, there is usually very good mains filtering as one has loads of drives and the noise will effect performance of other equipment + there are additional power costs with noisy supplies.
I would suggest that you consider either, adding a mains filter to the machine between plug and inverter (RS, Farnell sell these but make sure you get one that will handle the current) eg. Farnell 992240 at £12.19

http://uk.farnell.com/jsp/catalog/viewp ... dId=992240

or bypass the RCD with your supply to the inverter - this will still provide overload protection and will be safe although the RCD is the safest bet.

Of course, it may be tha tyour RCD is a little sensitive and needs replacing. Hard to tell for sure over the internet

A mains power quality analyser is the best way to find out for sure but these are specialist kit and cost a bundle

http://www.fluke.com/products/home.asp? ... 3&PID=5177

It is easy to test if the RCD is OK with an RCD tester but I guess you don't have one of these?
I see that you are an engineer. If you work in a factory, then the maintenance people will most likely have an RCD tester and you may be able to borrow one over the weekend to test the tripping current and time of the RCD


http://uk.farnell.com/jsp/home/homepage.jsp

http://rswww.com


Good luck

Tony
 

Chris Knight

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Tony,

You certainly seem to know a lot about this subject - I shall be sure to give you a shout if I run into electrical problems! Were you in the trade?
 

Philly

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Hey Newbie Neil,
Be careful, the Welsh are everywhere :wink:
Sometimes you can't catch the accent over the internet!
Cheers,
Philly :D
(a.k.a. Taff)
 

Taffy Turner

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Thanks to everyone for the welcome and also the advice.

One thing I should have mentioned is that the RCD trips as soon as I power up the inverter, i.e. before I even have chance to turn the motor on. (The inverter is made by Telemechanique).

I don't know whether this makes a difference or not?

I have tried contacting a few local electricians, but they are more clueless than me!

I used to work in a steel plant where we had inverter drives, but they were much bigger than the one causing me all the problems. Sadly, I am a Mech Eng, and not an Elec. Eng. :(

I guess the cheapest option is to try replacing the RCD (which is I think a 30 milliamp one) for a bigger one (say 100mA) and see what effect that has?
 
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Anonymous

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waterhead37":35lxk1to said:
Tony,

You certainly seem to know a lot about this subject - I shall be sure to give you a shout if I run into electrical problems! Were you in the trade?
Hi Chris

Yep. ONC in electronics and a degree in Mechatronics which is combination of mechanical and electrical/electronic engineering - basically robotics :)
 
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Anonymous

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Taffy

Telemch are one of the best industria lcontrol people around, the inverter is probably adequately filtered.

Not a good idea to replace the RCD with a higher rated one. 30mA is plenty enough to kill you as it is. At low voltages (240V is low), it doesn't take muich current to send you to your maker.

Other problems might be a lose wire in plug or socket or machine. Lose wires cause high resistance paths which reult in nuisance trips. I have experienced nuisance trips in the past due to a badly connected neutral wire.

First stop is to check all wires are secure and screws fully tightened MAINS OFF FIRST

Who wired the workshop? The mains loop within the workshop could be to blame. If the neutral is not connected to the neutral bar near where the feed to the plug emerges from the RDC? MCB, then you may well get a long return path (loop) for curent which causes a high enough in balance between mains and nuetral to trip a sensitive RCD.

With MAINS OFF Check wiring in the RCD box and trace the feed to the socket back to the neutral bar and the MCB output. Try locating the neutral closer (along the neutral bar) to the mains outlet MAINS OFF

Try these and then let me know outcome. I will consider the problem further i nthe meantime

Cheers

Tony
 

Taffy Turner

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Tony,

The workshop is my converted double garage. It is fed by a supply from the house, and the RCD in question is in the house, on the outgoing supply that feeds the garage (workshop), stables, outside lights etc.

All my other tools work fine in there (my router is 1900W, the lathe is only 1000W). It is only the lathe that causes the problems, which is why I suspect the inverter, but the strange thing is that it works OK in the house, which is also protected by an RCD which is much bigger (100mA I think - the plate is difficult to read).

I should perhaps mention that the "outside" RCD trips out at the least provocation - thunderstorms are a favorite cause, so maybe that has a fault on it which is making it overly sensitive?

Hope that this sheds some light on the mystery!

Regards
Gary
 
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Anonymous

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Gary

This does indeed shed some light. You should feed the outbuildings from an MCB and NOT through the RCD in the house. There is likely to be enough imbalance between live and neutral + some small leakage to earth to trip the RCD. An RCD has two coils of wire around a toroidal former and trips when the live current does not equal the neutral current by , say 30mA. Noramlly both are equal and opposite, thus no trip occurs. The imbalance must be a leakage to earth due to conservation of energy principle. Your cable might be leakingto earth slightly in the moist ground and the addition of a noisy load takes it over the edge. Also, long cable runs result in voltage drops in condutors when a load is applied at the far end. These voltage drops can be significant and not the same for live and neutral conductors causing a small imbalance and trip.

Put an RCD in the outbuilding and feed it from and MCB that does not have a feed from the RCD in the house. The MCB in the house should be specified to protect the cable, not the machines. The RCD and MCB in the outbuilding should be specified to protect you.

Cheers
Tony
 

Taffy Turner

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Thanks Tony,

The trouble is that the feed to the outbuildings runs underground, and so it isn't an easy job to run another supply directly off the house MCB.

Because of the layout and location, running a suspended cable isn't an option, and neither is digging up the paths and garden to run one underground.

I suppose the easiest thing to do would be to remove the RCD from where it is and fit one on the MCD board in the outbuilding where the supply is switched and split off to the other buildings, taking the supply for the lathe from the side before the RCD?

Cheers
Gary
 
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Anonymous

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Underground cable is OK. You just need to identify it at the consumer unit end and disconnect from the RCD protected supply. The consumer unit for my house has two sides to it, one is NOT protected by the RCD (about 6 MCBs andd the other IS protected by RCD (6 more MCBS). Simply move the supply to unprotected side of distribution board.

Your idea to remove the RCD from where it is and fit one on the MCD board in the outbuilding where the supply is switched and split off to the other buildings, should be fine.

Cheers

Tony
 
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Anonymous

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waterhead37":1a0ljp87 said:
Tony,

You certainly seem to know a lot about this subject - I shall be sure to give you a shout if I run into electrical problems! Were you in the trade?
I would happily exchange my engineerign/electrical knowledge for your superior woodworking knowledge.

Yes, I saw your website/work again :shock:
 

Chris Knight

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Tony,
Thank you for the compliment - makes me blush :oops:

That's one of the great things about forums like this, the shared knowhow of the participants is huge and usually shared very readily. There are many things about the modern world that drive me nuts but the internet isn't one of them.
 
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Anonymous

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It may be the input filter in the inverter that is causing this. They often have capacitors connected to earth which cause the leakage. Any electrician doing safety checks (a health and safety requirement these days) should be able to check it.
 

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