Startup Current - Belt vs Direct Drive

[richie00boy]

Currently I have a SIP 3hp 50L direct drive compressor. When I run it in the garage the startup current trips the 16A breaker in the house. I have been thinking of upgrading to the Wolf 3hp 90L belt drive compressor and wonder if the startup surge may be even worse with this as being lower speed running the motor torque is lower so pulls more current?

 

[piman]

Hello Richie,

it doesn't follow that the motor speed is lower, all motors in their group run at more or less the same speed.
The critical thing is how quickly the motor starts and runs up to speed. All you can do is try it and if necessary swap the type of circuit breaker, alternatively fit a 13 A plug and plug it into a socket which should have a larger breaker.

Alec

 

[rtbcomp]

Is it OK when you run it in the house? If so are you using the same rating breaker?

It could be the length of cable to the garage is giving you a voltage drop which won't allow the motor to reach full speed before the breaker trips. You could try a slower breaker, but don't be tempted to fit a higher current breaker as that could leave the wiring unprotected.

 

[richie00boy]

At the moment I have to run it from an extension lead from the cooker plug in the kitchen.

 

[rtbcomp]

That could be the problem, get a beefier extension or install a proper mains supply in your garage.

 

[richie00boy]

You have it misunderstood. If I plug the compressor into the proper mains supply in the garage, the trip in the house fuse box goes. So I have to run it from an extension from the kitchen cooker socket.

 

[rtbcomp]

You only mentioned running it on an extension lead - you didn't say the circuit in the garage was a fixed circuit.

In that case I'd try the c-curve MCB in the garage circuit.

 

[piman]

Hello Ricie,

the Kitchen cooker socket will be at least a 30A breaker.

Alec

 

[richie00boy]

Yes, that's why I'm using it, as the garage breaker is 16A and trips.

 

[AndyStobbs]

Would imagine that having to accelerate the extra mass of pullies would only exacerbate the situation.

 

[roofman]

Would imagine that having to accelerate the extra mass of pullies would only exacerbate the situation.

those direct drive comps are a terrible design with regards to starting...a pump getting turned via a massive pully from a much smaller drive pully is always going to be easier than straight off the motor shaft.

 

[Paul G]

Just had a look at my consumer unit to refresh my memory and all three of my three pin plug ring mains
are 32 MCB's, same as the cooker and shower circuits.

The garage ring is 2.5 with 6 double sockets. It's not unheard of for me to be running a couple of major
items at once, i.e. compressor & Harrison lathe.

I've tried using the spot welder, the MIG and the TIG at the same time but I ran out of hands.

Cheers
Paul G

 

[penfold]

those direct drive comps are a terrible design with regards to starting...a pump getting turned via a massive pully from a much smaller drive pully is always going to be easier than straight off the motor shaft.

There's not much practical difference provided the unloader valve is working; compressors just suck loads of current on start-up.

 

[richie00boy]

The socket rings in the house are on 32A breakers (one for upstairs one for downstairs) but the garage is only 16A. Not sure why.

 

[brightspark]

The socket rings in the house are on 32A breakers (one for upstairs one for downstairs) but the garage is only 16A. Not sure why.

because the feed to the garage is probably a radial wired in 2.5mm cable and they have fitted a 16 amp mcb , u could up rate it to a 20 amp either that or run a heavier cable across and up it to a 32

 

[Wallace]

The socket rings in the house are on 32A breakers (one for upstairs one for downstairs) but the garage is only 16A. Not sure why.

That sounds like a dedicated supply to the garage with cabling to suit.

 

[richie00boy]

because the feed to the garage is probably a radial wired in 2.5mm cable and they have fitted a 16 amp mcb , u could up rate it to a 20 amp either that or run a heavier cable across and up it to a 32

Ok thanks. Why would they not have given it a 20A breaker in the first place though?

Heavier cable would be difficult as some of it runs under the patio.

 

[brightspark]

Ok thanks. Why would they not have given it a 20A breaker in the first place though?

Heavier cable would be difficult as some of it runs under the patio.

most electicians would just fit a 16 amp a some places dont keep the 20 in stock . i generaly look at the loading and fit whats apropriate

 

[hareng]

Direct or belt drive you will have same trouble. Mine is fed via 5 yards decent cable from 20A MCB and trips 1 in 3 startups, even less with welder.
As mentioned above, dedicated supply to garage is the way forward with C type MCB. Powered via a C type 32A MCB feed, inverters, welders and other power hungry items never ever trip, just the RCCB split load 80A 30mA feeding the bank of MCB's with 7.5KW inverter.