SC2 mini lathe pops RCD when turned on?

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SC2 mini lathe pops RCD when turned on?

This topic has 52 replies, 10 voices, and was last updated 10 October 2024 at 21:17 by Robert Atkinson 2.

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9 October 2024 at 11:52 #758173
andy198712
Participant
@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
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9 October 2024 at 12:40 #758189
andy198712
Participant
@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.
9 October 2024 at 16:14 #758206
peter1972
Participant
@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.
9 October 2024 at 16:51 #758210
andy198712
Participant
@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?
9 October 2024 at 17:23 #758212
Macolm
Participant
@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.
9 October 2024 at 17:27 #758216
SillyOldDuffer
Moderator
@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
9 October 2024 at 17:59 #758220
noel shelley
Participant
@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.
9 October 2024 at 18:04 #758224
Ian P
Participant
@ianp
On 9 October 2024 at 17:27 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!
9 October 2024 at 18:08 #758227
peter1972
Participant
@peter1972
Is the “breaker” in the garage an RCD?
9 October 2024 at 18:08 #758230
noel shelley
Participant
@noelshelley55608
The thread titled ” chinese mini lathes and mills earlier today may help. Noel.
9 October 2024 at 18:36 #758237
SillyOldDuffer
Moderator
@sillyoldduffer
On 9 October 2024 at 18:04 Ian P Said:

On 9 October 2024 at 17:27 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
9 October 2024 at 18:54 #758242
andy198712
Participant
@andy198712
Thank you Malcom that gives me a good way forward to try, appreciate that !
9 October 2024 at 18:59 #758245
Robert Atkinson 2
Participant
@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.
9 October 2024 at 19:07 #758251
andy198712
Participant
@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.
9 October 2024 at 19:10 #758254
andy198712
Participant
@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.
9 October 2024 at 19:11 #758257
andy198712
Participant
@andy198712
Hi Peter

this is what keeps tripping
9 October 2024 at 19:13 #758260
andy198712
Participant
@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?)
9 October 2024 at 19:15 #758263
andy198712
Participant
@andy198712
On 9 October 2024 at 18:59 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
9 October 2024 at 19:15 #758266
andy198712
Participant
@andy198712
9 October 2024 at 19:36 #758272
Grindstone Cowboy
Participant
@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
9 October 2024 at 19:37 #758276
Robert Atkinson 2
Participant
@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.
9 October 2024 at 19:50 #758282
andy198712
Participant
@andy198712
On 9 October 2024 at 19:36 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
9 October 2024 at 19:54 #758285
andy198712
Participant
@andy198712
On 9 October 2024 at 19:37 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!
9 October 2024 at 19:59 #758288
Robert Atkinson 2
Participant
@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.
9 October 2024 at 20:58 #758296
andy198712
Participant
@andy198712
On 9 October 2024 at 19:37 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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