SC2 mini lathe pops RCD when turned on?

[andy198712Participant @andy198712]

Hi all.

 

bit lost and after some advice.

 

bit of back ground:

new to mini lathes

made a couple car ECU’s and can use a multi meter at a hobby level, happy to swap components and solder.

 

been using my new to me 12 year old sieg SC2 lathe for a while and enjoying it.

i was making a new handle wheel, cutting a bit of a heavy cut at a taper if I’m honest (my fault)

 

made a pop and the power went off in the garage.

glass fuse had popped and the breaker for the garage. Which was odd.

replaced glass fuse with a 5amp breaker

now when ever I plug it in, all is fine, UNTILL I hit the power switch and it pops the garage breaker (not the lathe fuse)

 

I tried disconnecting the motor and still the same happens.

couldn’t see or smell any dead components

couldn’t find any breaks to ground but I may have missed one?

 

any thoughts or ideas to test?

 

Thanks

Andy

[andy198712Participant @andy198712]

Just to add some more meat to the bones

 

What I have tried

 

disconnect motor = still blows main garage fuse

disconnect output wires from the kill switch  = does not blow, green power light lights up while I hold the power button but won’t latch on (as expected)

 

reconnect wires from kill switch to the board. Motor and speed dial disconnected so literally just the board connected = blows.

 

must be something on the board but nothing seems obvious.

[Peter WebbParticipant @peter1972]

I wonder whether an interference suppression capacitor connected to earth has been ‘blown up’ by an inductive voltage spike caused by the 5A fuse blowing.

[andy198712Participant @andy198712]

Hi Peter,

Thank you,

not something I’d heard of, had a quick google but are they just normal caps?

seems hard to test them while on the board other then visually which is a pain isn’t it?

[MacolmParticipant @macolm]

If your multimeter lowest resistance range shows in tenths of an ohm (eg 0.3 etc), it is often possible to chase down the location of a short by probing to find where the lowest value is. A better but more complicated method is to connect a current through the shorted path, say using a 5 ohm resister from 5 volts to define and limit the current. Then use the multimeter on millvolt range to find the minimum voltage drop which will exist across the faulty component. Draw out the layout and values measured if necessary.

[SillyOldDufferModerator @sillyoldduffer]

Wot Peter said, plus several other components.

An RCD detects a current imbalance caused by something in the system connecting to earth.

The capacitors mentioned by Peter keep the mains clean by deliberately earthing noise.  If they fail, the RCD will pop.   The capacitors are specially rated for this so don’t substitute them.  No need to because they are widely available and inexpensive.   Look for X and Y rated suppression capacitors.

Although burning and melting may be obvious, components often fail without visible damage, in which case  electronic diagnosis is needed.

When a controller board fails whilst taking a heavy cut, it’s usually one or more of the power mosfets that’s failed, and replacing them isn’t too difficult.  Unfortunately, the initial overload and extra stress caused by the FET(s) burning out may have damaged other components, which also have to be identified and fixed.

Though I have the gear, diagnosing faulty boards gets up my nose. Unless it’s obvious, I’d replace the board with a new one.   Someone on a tight budget who enjoys debugging and learning new skills can have go!  Can you provide some photos?  The forum can probably help more than I have!

Dave

 

[noel shelleyParticipant @noelshelley55608]

An RCD detects an imbalance in the in and out. This can be caused by numerous faults. You mention a 5A fuse, is this the original value ?

I’m with Dave on the power mosfets. take them out and test, it’s worth a punt for what they cost to change them. Noel.

[SillyOldDuffer]

On SillyOldDuffer Said:

Wot Peter said, plus several other components.

 

An RCD detects a current imbalance caused by something in the system connecting to earth.

 

The capacitors mentioned by Peter keep the mains clean by deliberately earthing noise.  If they fail, the RCD will pop.   The capacitors are specially rated for this so don’t substitute them.  No need to because they are widely available and inexpensive.   Look for X and Y rated suppression capacitors.

Although burning and melting may be obvious, components often fail without visible damage, in which case  electronic diagnosis is needed.

When a controller board fails whilst taking a heavy cut, it’s usually one or more of the power mosfets that’s failed, and replacing them isn’t too difficult.  Unfortunately, the initial overload and extra stress caused by the FET(s) burning out may have damaged other components, which also have to be identified and fixed.

Though I have the gear, diagnosing faulty boards gets up my nose. Unless it’s obvious, I’d replace the board with a new one.   Someone on a tight budget who enjoys debugging and learning new skills can have go!  Can you provide some photos?  The forum can probably help more than I have!

Dave

 

Don’t RCDs’s work by detecting an imbalance between the L and N and don’t reverence themselves to ground?

Ian P

 

Edit Well it sounds like reference if you say it quick!

[Peter WebbParticipant @peter1972]

Is the “breaker” in the garage an RCD?

[noel shelleyParticipant @noelshelley55608]

The thread titled ” chinese mini lathes and mills earlier today may help. Noel.

[Ian P]

On Ian P Said:

On SillyOldDuffer Said:

Wot Peter said, plus several other components.

 

An RCD detects a current imbalance caused by something in the system connecting to earth.

 

…

Don’t RCDs’s work by detecting an imbalance between the L and N and don’t reverence themselves to ground?

Ian P

 

Edit Well it sounds like reference if you say it quick!

Normally the current in the Live wire is exactly balanced by the current flowing in the Neutral wire.

What then could cause an imbalance between the two?  It can only be due to current flowing from live to a sink other than neutral.  As 50Hz electricity can’t escape into mid-air, it must be flowing to earth.  Either through the official safety earth wire, or direct to ground through a damp floor or some other scary path. such as a human being electrocuted!

The RCD doesn’t need to reference earth.  It only has to detect that L and N don’t balance.

Dave

[andy198712Participant @andy198712]

Thank you Malcom that gives me a good way forward to try, appreciate that !

[Robert Atkinson 2Participant @robertatkinson2]

SOD said:

“The RCD doesn’t need to reference earth. It only has to detect that L and N don’t balance.” That is totally correct.

“It can only be due to current flowing from live to a sink other than neutral. As 50Hz electricity can’t escape into mid-air, it must be flowing to earth.”

That is not correct. A connection from live on that RCD to a neutral on another (or no) RCD will cause a trip. A connection from Neutral on that RCD to a neutral on another (or no) RCD is likely to cause a trip as will a connection between two lives. This is because a the two lines will not be at exactly the same differential so differential current will flow.

Practically for the OP have you measured the resistance to ground from the live and from the neutral to earth with the e-stop held down?

Robert.

[andy198712Participant @andy198712]

Hi Dave,

 

thanks for taking the time!

yea both scenarios make sense, I found a test for the mosfets and need to complete it but the ones I tried on the large heat sinks seemed okay (need to complete the tests)

 

just a pain these boards are fairly expensive, I believe I ruled out the board that takes the power from the mains (guessing it’s a step down from 240v to 12v? ) by having the control board unplugged and getting the green power light to come on and nothing tripping.

[andy198712Participant @andy198712]

yes I belive the one that blew (literally smashed the glass) is a 5amp and listed as a spare part on arc euro as 5a. I did think it was low… but there we go.

 

your right they are a nice cheap item thankfully, will complete my tests on them but worth a punt.

[andy198712Participant @andy198712]

Hi Peter

 

this is what keeps tripping

 

[andy198712Participant @andy198712]

Thank you I’ll have a look.

 

at the cost of a new board if it comes to it I’d probably buy a new bigger motor and board for less or same money (seems silly not to?)

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

SOD said:

“The RCD doesn’t need to reference earth. It only has to detect that L and N don’t balance.” That is totally correct.

“It can only be due to current flowing from live to a sink other than neutral. As 50Hz electricity can’t escape into mid-air, it must be flowing to earth.”

That is not correct. A connection from live on that RCD to a neutral on another (or no) RCD will cause a trip. A connection from Neutral on that RCD to a neutral on another (or no) RCD is likely to cause a trip as will a connection between two lives. This is because a the two lines will not be at exactly the same differential so differential current will flow.

Practically for the OP have you measured the resistance to ground from the live and from the neutral to earth with the e-stop held down?

Robert.

Ah no Robert not yet. Good idea.

i did check for continuity between the poles of the plug and had none as I thought that might be an easy fine if there’s a chaffed wire ect

[andy198712Participant @andy198712]

[Grindstone CowboyParticipant @grindstonecowboy]

Technically, that’s not an RCD, that’s an RCBO. Not an electrician, but I understand an RCBO to have the same current imbalance detection as an RCD PLUS an over-current protection.

So it may be being tripped by either of those conditions. Whether that helps or not, unsure, but if it blew a 5A fuse to pieces, I’d suspect over-current.

Rob

[Robert Atkinson 2Participant @robertatkinson2]

Hmm,

Andy said: “yes I belive the one that blew (literally smashed the glass) is a 5amp”.

That is a indication that (typically) the fuse fitted is not suitable for the application. I suggest replacing it with a 5A HRC (high rupture current) type. These have a ceramic body and sand filling..

The device that tripped is an RCBO. This will trip on either overload or leakage current, you can’t tell which caused the trip. It may not be a short to ground.

Robert.

[Grindstone Cowboy]

On Grindstone Cowboy Said:

Technically, that’s not an RCD, that’s an RCBO. Not an electrician, but I understand an RCBO to have the same current imbalance detection as an RCD PLUS an over-current protection.

So it may be being tripped by either of those conditions. Whether that helps or not, unsure, but if it blew a 5A fuse to pieces, I’d suspect over-current.

Rob

Cheers Rob,

yeah was a “pop” and I was suprised it was smashed when I looked

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Hmm,

Andy said: “yes I belive the one that blew (literally smashed the glass) is a 5amp”.

That is a indication that (typically) the fuse fitted is not suitable for the application. I suggest replacing it with a 5A HRC (high rupture current) type. These have a ceramic body and sand filling..

The device that tripped is an RCBO. This will trip on either overload or leakage current, you can’t tell which caused the trip. It may not be a short to ground.

Robert.

Thanks,

I brought some fuses like you put in your plugs but there 6mm and the glass ones are 5mm this don’t fit in the holder sadly, so I saw a video about these style of breaker and fitted this

HUWREW 5 Amp Push Button Circuit… https://www.amazon.co.uk/dp/B0D2VGVWHR?ref=ppx_pop_mob_ap_share

 

Thinking it would work but sadly it wasn’t my fix!

[Robert Atkinson 2Participant @robertatkinson2]

Yes the fuse is 5 x 20 mm. The British plug fuse is deliberately different from standard “equipment” fuses to stop the wrong type being fitted.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Hmm,

Andy said: “yes I belive the one that blew (literally smashed the glass) is a 5amp”.

That is a indication that (typically) the fuse fitted is not suitable for the application. I suggest replacing it with a 5A HRC (high rupture current) type. These have a ceramic body and sand filling..

The device that tripped is an RCBO. This will trip on either overload or leakage current, you can’t tell which caused the trip. It may not be a short to ground.

Robert.

But would the fact it trips without running now mean leakage or no? Every time I hit the power button with the board plugged in.

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