Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

I'm now looking at getting another compressor as I want to do some
sandblasting and don't think my single unit is going to have enough
oomph.(it's rated at 10 cfm FAD)

I'm guessing that I won't be able to run both compressors from the same
circuit as if they both kick in at the same time then the draw is going to
be too much for the circuit and something is going to give.

So the ideas I came up with to run the both at once would be

1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

3. Try and set the compressors to kick in at slightly different pressures.
Presumably it's just at start up that causes problems once going they should
both run together OK ?

Any views or suggestions most welcome

Thanks

Jim

Jim presented the following explanation :
Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

Maximum running load of each will be around 2.5Kw, or roughly 10amps -
though the initial start up surge could be much higher than this.
Some/many have a soft start, where the motor is allowed to get up to
speed before the compressor comes on load.


So the ideas I came up with to run the both at once would be

1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

Correct!


2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

You need to determine which circuit the garage is actually fed from,
then you could run the 2nd unit from a different circuit.


3. Try and set the compressors to kick in at slightly different pressures.
Presumably it's just at start up that causes problems once going they should
both run together OK ?

With no pressure, both would attempt to start at the same time. Up to
pressure with air being consumed, it would be very difficult to
synchronise both to start at exactly the same point - so basically
start one, then the other after which there would probably not be a
problem providing they are not both on the 16amp MCB.

Method 4 would be to add a larger air receiver, if you could work in
shorter bursts of activity.

Are you sure 20cfm is adequate for sand blasting?

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Fri, 27 Jan 2006 23:15:32 GMT, "Jim" wrote:

Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

I'm now looking at getting another compressor as I want to do some
sandblasting and don't think my single unit is going to have enough
oomph.(it's rated at 10 cfm FAD)


Probably not. Do you know what you do need?

It may be that use of a larger receiver as an add on would achieve
what you need unless it is for very long bursts of operation.

I'm not sure that combining two compressors together is a very good
idea. You would probably be better off selling the one you have -
which is more than ample for a lot of applications like nail gun use
etc. - and getting a single larger one with bigger receiver.


I had the same issue, although with spraying, and went for a larger
single product.


I'm guessing that I won't be able to run both compressors from the same
circuit as if they both kick in at the same time then the draw is going to
be too much for the circuit and something is going to give.

So the ideas I came up with to run the both at once would be

1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

You could find that out. Measure the diameter of the cable and look
up the type - probably 4,6 or 10 sqmm.

You can then refer to the tables for the cable type; the two factors
being rating and volt drop.

http://www.tlc-direct.co.uk/Book/1.1.htm

is quite helpful.

You may find that you can upgrade the circuit.




2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

This suggests that it's a smaller one?



3. Try and set the compressors to kick in at slightly different pressures.
Presumably it's just at start up that causes problems once going they should
both run together OK ?

There is also a rise in current as the pressure approaches cut off
because the motor is working harder.

Also, pressure switches on typical compressors are not adjustable.





Any views or suggestions most welcome


I would look at the single larger compressor and extra receiver
options first.

Have a look at this site

www.thorite.co.uk and ask them for a catalogue.


--

..andy

In article ,
"Harry Bloomfield" writes:


2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

You need to determine which circuit the garage is actually fed from,
then you could run the 2nd unit from a different circuit.

You will also need a thick extension cord. For a 13A extension cord,
1.25mm² conductors OK up to 12m long,
1.5mm² conductors OK up to 15m
2.5mm² conductors OK up to 25m (but 2.5mm² won't fit in a 13A plug).

--
Andrew Gabriel

On Sat, 28 Jan 2006 10:08:58 +0000, Owain
wrote:

Jim wrote:
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..
1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

Also AIUI 16A sockets have to be protected on a 20A circuit, so you
would need to install a mini consumer unit with 2 x 20A MBCs one for
each socket.

Can you use a generator for the second compressor, especially if it's
only going to be for occasional use. (Usual warnings about mixing
generator and mains electricity apply.)

Owain


The trouble is that


£ { compressor 2 + generator } £ { new compressor - sale of existing
on Ebay }

Most likely.


--

..andy

Jim wrote:
Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

I'm now looking at getting another compressor as I want to do some
sandblasting and don't think my single unit is going to have enough
oomph.(it's rated at 10 cfm FAD)

I'm guessing that I won't be able to run both compressors from the same
circuit as if they both kick in at the same time then the draw is going to
be too much for the circuit and something is going to give.

So the ideas I came up with to run the both at once would be

1. Swap the 20A MCB for a 32A - guessing this isn't really acceptable as
don't know what the wiring is rated at.

you need to find out. Another possible may be swapping the B type mcb
for a C or D type. If you do run 20A of compressors on a 20A rated
supply, it might be worth using a battery backed-up worklight.


2. Run an extension lead from the house ring main to the garage. The new
compressor runs off a standard 13 amp socket. Is this likely to cause any
problems ?

probably not, but beware that long thin leads can cause v drop that can
cause induction compressors problems. This can be got round with either
heavy cable or a step up transformer. A transformer providing say 5v at
10A is not large.


3. Try and set the compressors to kick in at slightly different pressures.
Presumably it's just at start up that causes problems once going they should
both run together OK ?

Any views or suggestions most welcome

Thanks

Jim

If youre stuck with low supply rating, you might also be able to make
some use of the fact that the compressor loads are intermittent.


NT

Jim wrote:
Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.

First, what is the actual current draw?
Is that 3 'real' hp, or a much smaller figure?
As a first cut, I'd stick in a 5A fuse, and see if it blows.

On Fri, 27 Jan 2006 23:15:32 GMT, Jim wrote:

Hi guys, got a poser for the electrical guru's on the group.

I've currently got a 3hp compressor that is run off the garage electrics.
From what i can tell the garage is supplied by a radial circuit, via a 20amp
MCB along fairly hefty armoured cable. I've wired in a 16amp socket in the
garage and this is what the compressor runs off..

I'm now looking at getting another compressor

snip

Any views or suggestions most welcome

Hmm, how soon before, quite co-incidentally, we have someone who lives
close by complaining that he can see this odd sort of flickering and
dimming that happens at all sorts of odd times on his lights.....

:-)

--
the dot wanderer at tesco dot net

Ah the "Wanderer" having ceased to post in other UK groups, after
making wrongful accusations of child abuse, has moved on to pastures
new!........................notice he/she is just as unhelpful on here
as other groups that have in the past been blighted by his/her
prescence!

You would be able to run a small blast cabinet without any problems
using a 10CFM (FAD) compressor, but the compressor would run
continously, and you would have to give it time to recover, so would
need to blast in small bursts.

If you need to run a larger cabinet, or need to work continously then
the way to go would be to get hold of a twin 3hp motor 240v compressor,
with a start box which phased motor starts so they didnt start same
time. One of these would provide about double the CFM you have at the
moment, and would run a small cabinet just fine.

If you have a larger size industrial cabinet, then you need to be
looking at 3 phase compressors, or cheaper option if you have the space
and noise is no problem, would be diesel towable compressor, of the
type used for road breaker drills and the like.

k

On 29 Jan 2006 00:31:31 -0800, Ken wrote:

Ah the "Wanderer" having ceased to post in other UK groups, after
making wrongful accusations of child abuse,

Post the message ID Ken. But you can't, can you, because I have never made
such a post. Once again you resort to out and out lies to try and prolong
your totally inept trolling attempts.

My apologies to the regular readers of this NG now this creep has found his
way here.

--
the dot wanderer at tesco dot net

"Wanderer" is one of several posting IDs used by this prat! His/her
most recent posts have been threats against someone, who has had the
audacity to point out the fact that "Wandrerer" appears to be a liar
and a coward!

k

Ken wrote:
"Wanderer" is one of several posting IDs used by this prat! His/her
most recent posts have been threats against someone, who has had the
audacity to point out the fact that "Wandrerer" appears to be a liar
and a coward!

k

take it somewhere else.

NT

I have posted a helpful reply to the OPs orginal question, perhaps you
and "Wanderer" should attempt to do the same?

k

Thanks for all the input guys. After reading all the comments I think the
sensible option is to see how I get on with just the one compressor.

Thanks again

Jim

You should be OK with just one 3hp compresser. I use a 1.5 hp
compresser with mine. Works fine with small parts. I tend to blast for
10sec wait ten seconds and so on. If you do decide to upgrade your
compresser then the size of receiver do'st realy matter, it's the CFM
that matters.

Mike Cole

Jim wrote:

Thanks for all the input guys. After reading all the comments I think the
sensible option is to see how I get on with just the one compressor.

Thanks again

Jim

Its really down to the type of blasting you want to do. If you have a
small blast cabinet, and dont want to use it continously then a 3hp
compressor will work fine. On the other hand if you need to do anything
much more than that, you really do need more air.

k

In article .com, Ken
wrote:

I have posted a helpful reply to the OPs orginal question, perhaps you
and "Wanderer" should attempt to do the same?

Perhaps if you were to offer some context, we might have a clue what you
were going on about?

--
AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems
http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk