SIP Compressor blowing breaker long before pressure is reached.

[Anglefire]

Starting current is around 7x running current and a c type mccb (as already said should be used ). 

2.5mm cable is rated at something like 20a in ideal conditions. 

If it was me, I’d use 4mm cable - if it was a long run it could be moved about a bit, I’d use welding cable as it’s very flexible 

[SpitFire6]

Hi Mark,

 If you used hi-flex welding cable you would have to install it in a flexible/fixed conduit?

Cheers,

Iain.

[Anglefire]

Iain, you could clip direct - depends if you want mechanical protection or not. I’m not up with the latest (18th) regs. But get where you are coming from.

A flex from a spur or a 3pin socket would have no more protection- less actually as welding cable is designed to be dragged about the place to a degree. 

[Colin Lindsay]

On 22/01/2019 at 19:14, Spitfire6 said:

Replace that excuse for a breaker with something better though. Nice compressor. If I could weld I would make & connect a desiccant dryer so my dew-point was -30c. Alas, I also have no garage.

Firstly thanks Markus for that excellent post on compressors; I'll forgive them for being American and try to translate most of the jargon into English.

Secondly: Iain - that breaker is a direct replacement for the original that was fitted to the unit by SIP, I put in the unit code a few years back and bought an identical one when the original did exactly the same thing. It's rated 20A and to be honest I'd be wary of upgrading to, say, 25A unless I had someone else to blame..

I was sandblasting today and on initial startup the pressure went right up to about 120 on the gauge, maybe 130, then the breaker cut off again. When the pressure dropped too far for further blasting I reset the breaker and this time it went to about 70 or 80 and stopped there. Further resets went no higher. I'm now running it with the cover off so there's absolutely no discernable heat rising from the motor.

I'm intending to replace the breaker with a (hopefully) better unit if I can identify a 'good' 2 terminal push-button replacement, this one is listed as a thermal magnetic circuit breaker on many sites, including the one I almost bought a replacement from - except that the cost was £11.50, VAT brought it up to £13.80, 'handling charge' was £3.99, postage was £5.99. Ripoff city!

https://uk.rs-online.com/web/c/fuses-sockets-circuit-breakers/circuit-breakers/thermal-magnetic-circuit-breakers/

[SpitFire6]

Hi Colin,

The main purpose of the panel breaker is to protect the cable when subjected to thermal and short-circuit/v.high current events. Do not touch this one unless you have made some calculations. Moot point as you have already excluded this. But do ensure you compressor breaker is less thermal and mag.

It sounds like your breaker is tripping on the thermal setting. Is the motor getting too hot to touch? If not, the breaker is suspect. (Amongst other possible mechanical defects)

Thermal protection for a motor is not the same as a cable. A proper motor thermal with magnetic protection and disconnect is not cheap.
 

Do ensure that the single pole consumer breaker you are intending to buy is fitted to the live feed. Some are not from the supplier.

Cheers,

Iain.

 

 

 

[SpitFire6]

27 minutes ago, Anglefire said:

Iain, you could clip direct - depends if you want mechanical protection or not. I’m not up with the latest (18th) regs. But get where you are coming from.

A flex from a spur or a 3pin socket would have no more protection- less actually as welding cable is designed to be dragged about the place to a degree. 

Hi Mark,

 I thought that welding cable suitable clipped together would be good for rough service. Cable is rated for 400V +. The welding cable I looked at was good for 150ish if not suitably protected.

We are talking about a stationary compressor, so your choice of cable is valid/good of course. A flexible cable is normally a better choice over a more rigid one. Apart from cost.

Cheers,

Iain.

 

[Colin Lindsay]

On 22/01/2019 at 19:14, Spitfire6 said:

Replace that excuse for a breaker with something better though. 

Hi all - just to resurrect this old thread - it's happening again. The thermal cutout is getting hot, the motor switches off way before operating pressure, and the two spade terminals on the thermal cutout are going black and literally melting. I had replaced that thermal circuit breaker - the one in the photo, like for like, as it's what was originally fitted - and got about six months out of it before we've started again - blowing before I get enough pressure to sandblast.

Two things arising from earlier posts: if I wanted to replace this with a more heavy duty item, what should I go for? This one's a 20amp:

https://uk.farnell.com/eta/2-5700-ig1-p10-dd-000040-20a/circuit-breaker-20a/dp/8567450

However I managed to find a SIP help page and they reckoned that if an extension lead is used, this increases the resistance and may lead to overload; I'm wondering if by extending the power lead from the original five feet to almost ten - to avoid an extension lead plug and socket - I've inadvertently caused the problem? The cable came from a local electrical supplies shop, very long-established and very knowledgeable, and, based on the original cable, they got me the longer length of replacement. I'm wondering now if I should go back to the original length and just move it closer to a socket? Does a thicker cable mean higher or lower resistance?

Going to spend today stripping it down and servicing, then off tomorrow to the Electrical spares guy and buy - possibly - a thinner cable.

[JohnD]

Colin,

Re: your advice from the SIP site.  Any conductor (unless a super-conductor, but that needs a very low temperature)  has some resistance, so yes, an extension lead will have more resistance than a short lead.      A thicker cable will have less, and be able to carry more current without overheating (think ordinary wiring and a starter cable).  But the resistance is distributed along the lead and so will be the heat.     It cannot make a component inside the equipment any more resistant, or hotter.     I can't see how that advice can be true.

In your picture, the heat is confined to the spade connector, and the wire immediately behind it.    I suspect that many of the fine wire strands in the cable inside the insulation have broken, so that only a few carry current.     This is like having a much smaller wire, too small for the current, so it overheats.     Cut off the spade, cut back the cable a short way and attach a new spade, using a crimper for preference.  I hope that will sort it!

John

[Colin Lindsay]

I hope so, John - I'll try that today. I'm going to carry out a full strip-down and service later this morning, test all joints and connections, clean all electrical components and try a lighter oil than before. The SIP oil was SAE 40, I tried an engine oil which was 10 - 40 and still blows so I have dug out a container of 5 - 30 to see if that makes any difference.

The bit about the motor overload tripping due to excessive resistance was on the SIP help page https://www.sipuk.co.uk/troubleshooting-guide and states:

"Extension lead will cause a voltage drop, increasing the amperage – resulting in the motor overload tripping. Use from mains plug."

I'm assuming that the thermal cutout is the overload mentioned? I'm also going to shorten the long power cable - necessary in my last garage due to the position of the sockets - to about four feet.

[Clive]

I have never understood that sip, and heard elsewhere, advice.

Yes, you get a voltage drop. But that means a lower voltage across the compressor.

The only thing with a motor is that it produces "back end" (acts as a generator as it is running, so reduces the current flowing through the motor) if the voltage supply is reduced, the motor may run slower, and then draw more current? But I don't see it a issue with an extension lead. My garage ran off a 20m 13a extension lead for 2 years. Including building my spitfire and spraying it with a 3hp sip compressor (plus heaters, welding etc etc etc, never blew a fuse but did get warm!

But indeed, some new terminals with good connections and we'll terminated will help. The heat may have caused internal damage? Melted plastic or suchlike?

[JohnD]

The resistance of common wire gaiges is given here (from the Hyperphysics webpage)

As you can see it's measured in ohms per THOUSAND feet (or meters).  So adding say six feet will increase the resistance by less than 0.04 Ohms.   Trivial, insignificant.

Perhaps SIP were concerned about their products being used on industrial sites on very long extensions. 

 

I think I understand Clive's point.   My compressor has a lead about four feet long, but it kept blowing the 13Amp fuse in the 3-pin plug on the end of the lead.   Always, but not every time, it would fail on start-up.    So I changed the connection to a wired-in one, as for an electric oven, and relied on the circuit breaker on the ring main.   No probs since, and the cable stays cool to the hand.     A motor does draw more current when it starts, until the back EMF builds up.   But I still don't think that any extension of a reasonable length will be a problem.

JOhn

[SpitFire6]

Hi,

 as mentioned above that crimp/connection is kak.

IMHO the crimp connect failed & kaked the OL. Cut the cable/wire back until you have good copper & PVC. Re-crimp with aircraft spec crimp.

New crimp(s) & breaker & you are good to go. 

Cheers,

Iain.

 

[Colin Lindsay]

Have done that - trimmed and recrimped the wire (using one of those huge recrimping tools from the 1960s...) and shortened both ends of the power lead to about half the original length. As I have three of those thermal cutout switches I reused one (no trace of any damage to body or terminals) changed the plug for a new one and refilled the oil with a lighter grade.

All good so far, but I remember that was the case six months ago before it all started again...

[SpitFire6]

Let's hope the connection stays fresh & good. Periodic finger touch to unpowered connections might warn of impending doom.

Contact grease will delay any potential corrosion.

Cheers,

Iain.

[Colin Lindsay]

Just took ten years of my life whilst testing the compressor to see what pressure it now reaches... it's running way past the old cut-off point but the pressure-switch hadn't started to cut out, so I was watching it intently when there was a huge bang behind me... the elderly tyre-inflating airline that I had been using with a blow-gun wasn't up to that sort of pressure and had burst. In a closed garage it was deafening. 

Thankfully the blast-cabinet line is reinforced heavy line... but at least now we're getting to a proper pressure.

[JohnD]

WooHoo!    Diagnosis, Correct! 

[PeteH]

HI

Not to Jump Start the original thread, which appears to have been solved. But Most if not all have, or should have, a Non Return valve in the outlet from the compressor. It is not unknown for those to leak back, back pressure then places an extra load on the compressor at start up, especially if any air is in the vessel already. The "Venting valves" don`t always compensate quickly enough. Worth bearing in mind if anyone else is experiencing similar issues.

[SpitFire6]

3 minutes ago, PeteH said:

HI

Not to Jump Start the original thread, which appears to have been solved. But Most if not all have, or should have, a Non Return valve in the outlet from the compressor. It is not unknown for those to leak back, back pressure then places an extra load on the compressor at start up, especially if any air is in the vessel already. The "Venting valves" don`t always compensate quickly enough. Worth bearing in mind if anyone else is experiencing similar issues.

Hi PeteH,

 I do not understand what you have just said. To me the two points are contradictory? 

Where do you want an NRV to be situated?

Thanks,

Iain.

[PeteH]

6 minutes ago, Spitfire6 said:

Hi PeteH,

 I do not understand what you have just said. To me the two points are contradictory? 

Where do you want an NRV to be situated?

Thanks,

Iain.

Ah!!. Right?. The venting or "blow-down valves" (usually on the Stop/Start pressure controller), vent the Compressor when it shuts off (reaches designated pressure). The intention being that the compressor does not then start up against compression, there is a slight delay before they shut on startup to allow the compressor to get to speed. The NRV should be in the outlet pipework to the tank, if it where leaking back, again, the compressor would be trying to start against any remaining pressure in the vessel.

[SpitFire6]

Hi,

Fitting an NRV valve between the Tank & pump.

The compressor will cycle when the pressure drops during normal operation. Fix ALL air leaks and close the outlet of the tank with a TSO valve after use. It would be ideal if you did start against pressure?

Do not know why one would fit an NRV to aid a reduction in pressure.

Confused,

Iain.

[PeteH]

I spent my formative years, Working on and with Air compressors in a Marine Environment, which where multistage and went up to (and well beyond) 600psi. Whilst they had inlet and outlet (usually spring loaded poppet type) valves at each stage they ALL had a non return valve in the outlet pipework which was there to stop back pressure from the Storage vessel. When the compressor was in the "un loaded" state the Pipework between the Compressor and storage vessel was at Atmospheric pressure, As the compressor started it`s initial few stokes where against ONLY atmospheric pressure, which reduced the loading during the "Startup phase" when the electrical load was greatest.When working condition was established, the venting valves where closed and the compressor could work as designed. It is similar in principal, (those old enough to remember) to the "Decompression valve" on old single cylinder motorcycles. to "assist" with Kick Starting.

[Colin Lindsay]

Morning team, must add my bit to the thread, just to update or clarify a few things since Pete has resurrected it again!

The compressor has been working well since I shortened the wiring and cleaned up the contacts; there's no longer any heat given off in the thermal cutoff box so that appears to have sorted that problem out. Grateful thanks to John and Iain.

The fuse-blowing on startup was cured by a thinner oil; not SIP compressor oil any more, which regularly blew the 13amp fuse on cold startup, but now I'm using standard 30w engine oil. How this affects the piston and block remains to be seen but it's running away nicely and I have not had to replace the fuse in an age.

The most recent problem was the lack of restart when pressure dropped; this was cured within the last few days by the fitting of a new pressure switch - the old one being of poor manufacture meant that it cutoff alright, but when the pressure dropped the copper contacts were sticking in the open position and not returning to closed. Initially it could be cured by teaching it manners in the shape of a rubber hammer but then it progressed to manual resetting with a screwdriver very time, and finally total failure. I bought a replacement for £12 on Monday, of far superior quality even from visual inspection, and it's been working well ever since. I had another mammoth two-hour sandblasting session yesterday - bellhousings, suspension wishbones and heater boxes, and it's been running perfectly.

Reference starting against pressure: I drain it after use every time, the amount of water that comes out is amazing and many times on startup I let the air drain out of the drain tap before closing it, but even by itself, with the drain tap closed, it will hiss for some time before pressure snaps the automatic pressure release closed and it builds up pressure as normal. This is perfectly normal and shows it's now working as it should - for which I'm grateful as between the sandblaster and impact wrench it gets a lot of use.

 

 

[Clive]

Dont worry about the 30W oil. If a decent one...

Friend does about 12-15K a year in his herald (plus 5 or 6 in his spit) Both have been run on straight 30W oil. As he says, it comes out the tap at work.... (used on all Nissan Forklifts)

So that is a combined mileage of 300K plus in his ownership. With a minor refresh on the herald about 5 years ago,and teh spit was done when he built it. When he had the herald apart, he reckons the sump was not at all sludged up, and the bores just got a light hone, one replacement piston plus all new rings and bearings. So it really is decent oil for the cars, and will no doubt be fine in a compressor. 

Out of interest, what sandblaster do you use? I had a try years ago, but it was hopeless. Seems you are getting on well with yours, maybe I should have another try?

[Colin Lindsay]

3 hours ago, clive said:

Out of interest, what sandblaster do you use? I had a try years ago, but it was hopeless. Seems you are getting on well with yours, maybe I should have another try?

I'm on my second cabinet; the first I built back in the late 1990s but had a chance to buy a professional cabinet a few years ago and switched to that. It was being replaced as part of a tax dodge by a local firm so sold off very cheaply.

 

I find the gun is the most important part; mine cost me about £80 but is a professional blast gun - there's no trigger, it's meant to be run from a footpedal - which I do have but never use. It's pointless under 100psi but get to about 120 or 130 and the paint just flies off - hence the problem with the compressor not reaching proper pressure. It's a large compressor so it keeps running and in fact fills faster than the gun can empty it.

As you can see it makes short work of metal bits - l all I need is some good music on headphones to drown out the compressor and the time flies by.

[Clive]

Thanks Colin. 

How big (power) is teh compressor? I have a 3HP jobbie, as big as I can use on a 13A plug. I had a cheap and cheerful gun when I tried, it was woeful.