How many amps Can I pull safely???

[jsmith]

Hi All,

I'm in the process of building a piece of equipment which uses 2 or 3 1400w motors, the motors will draw 6a max each - obviously making a total of 18 amps....

Can I safely pull 18 amps from a standard wall socket, or will I need to beef something up....?

Is it just a case of putting a bigger fuse in the plug or am I asking for trouble...

Thanks in advance..

John

 

[kendor]

firstly to answer your question, No, Secondly when using motors it's not just a case of reading the rating off the plate as you have to take into consideration the starting current which can be many amps higher than your calculation.

 

[jsmith]

they are standard dyson vacuum motors.... rated at 1400W

 

[BR]

A standard wall socket is rated at 13A and this is the absolute max. The next up is a 16A industrial socket (blue) and then a 32A industrial socket. If it was just 3 motors (18A) you would probably just about get away with the 16A socket, but it's pushing it.

Anything more and you'll have to go for the 32A which is red in colour and quite large. Another option would be to supply the equipment by means of a connection unit. BUT this means that the unit is in a fixed place and therefore not portable (which may be totally unacceptable for the design)

A motor can draw up to 6 times it's rated load in 'starting current' and this may need to be taken into consideration when designing the device.

Some more info would be very useful.

 

[Big_Spark]

they are standard dyson vacuum motors.... rated at 1400W

That is their NORMAL RUN LOAD, as the other have been trying to tell you, on startup they will pull considerably more.

When these motor start will they be under load or not..this may seem trivial to you, but it is critical to designing the circuit to run this kit.

You need to tell us what the motors will be doing and whether they will be under any kind of load at startup or not.

Telling us they are standard Dyson Vac motors is only partially helpful, in that they will be Squirrel Cage Induction Motors..means bugger all to you..

 

[plugwash]

industrial connectors are colored by the highest voltage present

in single phase conenctors this is the voltage between the live and nutral so britsh mains single phase wired between a phase and nutral is blue

3 phase conenctors for british mains are red as are single phase conenctors for intended to be wired phase-phase (never seen theese used in practive but they are made)

single phase connectors are refered to as 2P+E
3 phase with no nutral is refered to as 3P+E
3 phase with nutral is refered to as 3P+N+E

all are availible in current ratings up to 125A

probablly the best connector for your perposes is a 32A blue 2P+E the supply to this should be wired on a dedicated cuircuit with a rating to match the socket (as you would a cooker or shower cuircuit)

another alternative is the 20A powercon but you would have to put this on a wallplate yourself and you aren't supposed to use them in domestic installs because you can dismantle the plugs without tools

as for the flex to the device if it's on a 32A plug you should probablly use 4mm flex if you go for the powercon you want 2.5mm flex these are availible here

a 20A powercon would only need 2.5mm flex

within the device the motors should definately be fused seperately i dunno whether you want the motors switching seperately or not if you do you could use a 6 way grid plus box with 3 switches 3 fuses (and the switches after the fuses and mathed to the fuses that is 20A switches with 13A fuses)

if you want them all controled from one switch a small din rail cu is probablly your best bet

what exactly is this device supposed to do?!

 

[masona]

what exactly is this device supposed to do?!

I think it going to be a indoor one seated 3 wheel hoover car

 

[AdamW]

what exactly is this device supposed to do?!

I am pretty sure we have all had the same suspicions about this!

This isn't intended to be a "central vacuum cleaner" is it? If so you can already buy ready-built equipment that you can plumb in to have outlets in each room.

 

[Big_Spark]

OK, I did a little experiment with my Dyson Vacuum.

Momentary startup current under no load was 15.27A for about 1.2 seconds, then it dropped back down to 5.99A normal running current.

Therefore, with no load on the motors, your machine will draw up to 46A from the supply momentarilly, but will draw, as you stated, 18A continuous.

Any other loading this machine has must be factored into the equation, however even without anything else the machine should be on it's own circuit, a radial supplied with 4mm twin and earth and protected by 20A Type C or D MCB, Type C will possibly be sufficient, but if this machine is intended to start under load conditions then you should consider type D breakers.

 

[jsmith]

That's the kind of info I need FWL.

I am building a flow bench. It is used for measuring the flow in CFM through car cylinder heads, carburrettors, exhaust manifolds etc.

Basically the motors suck through the cylinder head and you measure the pressure differential across them.

There are many different size flow benches which can test at different pressures, normally 10"H2O, 15"H2O, 25"H2O or 28"H2O.

The flow bench does not need to be portable, it will sit in a garage or workshop.

I guess the question is, how can I run a supply to the garage capable of coping with these high amperages?

Also, the motor speed is regulated so perhaps I could switch the motors on 1 at a time or at a slow speed? Would this work?

 

[jsmith]

Momentary startup current under no load was 15.27A for about 1.2 seconds, then it dropped back down to 5.99A normal running current.

Therefore, with no load on the motors, your machine will draw up to 46A from the supply momentarilly, but will draw, as you stated, 18A continuous.

If the dyson pulls 15.27A on start up, how come it doesn't blow the fuse every time?

 

[Big_Spark]

If the dyson pulls 15.27A on start up, how come it doesn't blow the fuse every time?

The 13A BS1363 fuses in plugs are slow blow to a certain degree. They will stand up to about 8 times their maximum rating for very short periods, just like any type of fuse for MCB


If you want to put this in your garage, then you should use an armoured cable to supply a consumer unit in your, being fed from a MCB in your main consumer unit, or splitting the supply, via an RCD, and supplying a larger load. Personally I would do the latter as I think you may well be adding more machinery in you garage..would I be correct?

 

[jsmith]

Indeed.

Strange thing is, I am basing my design on a commercially available unit which is advertised as 240v 10amp.. However, I am not sure what motors they use and I am sure they only use 2.

Do you think if I was to only use 2 motors I would get away with it? This would be 12 amp max, but as you say it may be higher on start up....

 

[pipme]

Jsmith
Oh dear, your slip is showing .. if you take my drift.

As one 'amateur' to another, you need to do more research and be aware of your current limitations.

As a start go to http://www.tlc-direct.co.uk/Book/3.6.1.htm Better to be here than elsewhere

Then talk to the experts again.

Sorry, other info posted while I typed the above ... so you probably on track now.
Good luck P.

 

[jsmith]

I apologise,

I thought this was a diy forum not 'expert'.

However thanks for the link, it does look useful.