Sparkies ?? sizing mcb for compressor

[normspanners]

Hi guys looking for ideas I plumbed in n wired a broom wade ac41 compressor at week end,the original compressor circuit had c20 mcb. and ran perfect BUT was DOL but a MUCH smaller unit.
The new set up has started every time for me with NO issues but...
It now is blowing the breaker on start up---- only in the morning, I have shortened the timer on the S/D to try and help but now thinking tonight,I realise that maybe the issue is, it actually has an unloader system, that requires air in the tank for the unloader solenoid to actually unload, whilst in transition from S-to-D, it is using the SD timer to open a solenoid valve to the unloader valves , so it maybe needs a much shorter S/D, time but the timer seems to be all or nothing ie loads of time or turn 1 deg of turn and there is then no time delay !!
I have bought another C20 today but it wouldnt fit (no name on the board and working by phone to the guys in the workshop!!) so swapped out one of the other c20 they where running a single off, so its not likely to have been stressed. I have now got the old mcb for comparison, to return to factors tommorow
Question is would I be better going c25 or D20
ps correctly set motor OL doesnt trip just mcb.
It is just to get it through the initial start first thing, BTW oil is good and ambient temp obviously not cold -----YET!

 

[123hotchef]

the mcb is there to protect the cable what size cable has been used from the CU

 

[WorkshopChris]

What size are the supply cables?

 

[normspanners]

thanks I realise 8M 2.5mm x 4 swa clipped direct

 

[WorkshopChris]

Does it have a solenoid vent between pump and tank?
If so might need a longer Delay before change.
Our big old clarke had the above set up.

 

[123hotchef]

keep the 20amp then I am no spark though

 

[normspanners]

Does it have a solenoid vent between pump and tank?
If so might need a longer Delay before change.
Our big old clarke had the above set up.

No it has solenoid valve to fed the unloader valves, so cant actually unload till air in the tank !! so in fact requires less time so it get online asap coz its working straight away and in star it struggles.
my other thought was to rig up a system to keep the power on whilst in transition ie resistors setup to stop the delta surge. but might be a little ott for just first starts

 

[WorkshopChris]

Your going to be right at the limit of the cable on a 25A.
How much of a job to run a 4 or 6mm.

 

[normspanners]

Cheers for the help guys
yep I know we are sailing close, its a time factor issue they start it at 6 in the morning !! and it works all day it is just to get them through, for a few days as mcb are peanuts, I might have to run a 5core in coz I am fitting a 1ph water drain timer too and a cyclone water trap, I have to make for it at some point, but I am really busy with all kinds of things at mo. so just want to keep it going for them. in the short term.

 

[WorkshopChris]

Can they vent the tank on start up or does that not help with the set up fitted.

 

[normspanners]

The other way is just to let it run 24/7 I suppose. they have no major leaks BUT there is always the poss of a line blow off etc !

 

[normspanners]

Can they vent the tank on start up or does that not help with the set up fitted.

Not really its the check valve that is causing the back pressure initially IMO
----- but a tee on the feed pipe with a 1" quarter turn valve would help I suppose but then you have the heat to contend with. and all this... for the first 5secs !!

 

[WorkshopChris]

Does it have a solenoid vent between pump and tank?

This worked fine but occasionally when we had a real cold night it would ice shut and trip on start up.

 

[normspanners]

This worked fine but occasionally when we had a real cold night it would ice shut and trip on start up.

Yep I had two of these ac41's at the metal yd, years ago they wanted one for the lads ( labourers) to be super reliable and have no starting issues etc --------so I fitted 20hp DOL----- HEHE so no messing "JUST GET ON WITH IT " if in doubt get a bigger horse ---no------ get three

 

[normspanners]

what do you think about D20 or 25 after all the motor has its O/L ??

 

[brightspark]

clock it starting and running with a clamp meter with inrush current and work your breaker type and amperage from there

 

[normspanners]

clock it starting and running with a clamp meter with inrush current and work your breaker type and amperage from there

Cheers BS but thats VERY early my eyes dont open to see clamp on's till about 7 ish and would need long arms to reach from my sack---- HEHE PLUS I need to be on here till at least 12/1
what about d rate coz the loop imp shouldnt be too high on 8 -10 M IMO ? just in the sort term--- till I can get a 4mm 5core in .

 

[normspanners]

It must be right on the ragged edge coz I have started it several times from cold and had no issues, so its on the knife edge. it starts fine when its got pressure up .

 

[WorkshopChris]

Personally i would rather short term go up a mcb size than fit a D, but only you know the site and conditions.

 

[normspanners]

OK I respect that just gone and got the mcb its a GE unit nearest dealer is 70m !!