Chip extractors & 16A supply question

[moosepig]

Hi all,

I'm in the process of trying to work out what chip extractor will be best for my "shop" (pronounced "shed"). I've read the excellent sticky on dust extraction, so have been looking at some of the more powerful units as well as hobby-rated 1HP extractors. While looking around I notice that some of the 2HP units (e.g. Charnwood) specify a fixed 16A supply, whereas others (e.g. Fox) do not. There is even a SIP unit with a 3HP motor that claims to run off a 13A supply.

What's going on here then? Is this just down to the specific motors that each manufacturer has chosen to use?

Given that space is very tight I expect I'll end up with a 1HP unit just because they are smaller, but I'd be grateful for any insight nevertheless.

Thanks,
Moosepig

 

[Ttrees]

From what I've read on other forums, you can run (Start) quite a large motor in a DC unit if you close the blast gates off first .
I was told that a three phase motor with VFD will be no different than a single phase motor for this application...
I'm not so convinced ....

I'm probably mistaken with the next comment, as all manufacturers might have figured out/adopted the most efficient impeller shape by now ?
but if this isn't the case allready, there is a whole load of variables in impeller shape to consider when comparing DC units.
Matthias Wandel has done a video on the efficiency of these various shapes.
This might be a clue along with duct diameter.

Another thing to consider is the supply to your workshop ..
What size MCB breaker your using (can be changed to a type C 30A fairly easily although I've never done it) , but more importantly what gauge of wire is it, and how long is the run ?

Tom

 

[Paddy Roxburgh]

From what I've read on other forums, you can run (Start) quite a large motor in a DC unit if you close the blast gates off first .
Tom

Hmmm, I'm not convinced of this. The problem with motors tripping out/blowing fuses is the amount of power needed for start up, typically double the running power draw. This can be further compounded by the resistance offered by the machine, in this case the power needed to turn the impeller. I would have thought that there is less resistance when the blast gates are open than when closed. The least resistance would be with the pipe disconnected, although it may be impractical to disconnect the pipe for stat up.

 

[kevinlightfoot]

For what it's worth my experience of the Charnwood 2hp extractor is that I have to run mine off a dedicated 16 amp supply and I have a C20 mcb fitted a B20 mcb keeps tripping out on start up and my electrician sorted it for me .My advice would be to contact an electrician,there is a lot of advice from non electricians that can cost you in the long run and may not be totally safe.Also check the cable that supplies your shop,sorry shed,it may not be up to the job if it's a long run.I have recently put a feed to my new workshop and my electrician insisted on it being at least 10 MM cable.Be safe at all costs!

 

[Ttrees]

Sorry I should have said, shut off all blast gates apart from the one you intend to use on startup.
[edit] I checked this since
There is less current drawn with all blast gates shut off on startup until it gets to around 50%
This would be do-able with some sort of soft start or a programmed ramp up with a VFD etc.

I may have got the wrong impression, but I think there is danger of overworking the motor also when all blast
gates are open...
This is for 3 or 4hp units I'm talking about, I'm not sure so many problems occur with smaller units.
I can paste a bit from that thread if it's of interest when I find it

Tom

 

[HappyHacker]

The startup current can be in excess of 5 times the running current. This temporary surge can trip B type MCBs as they are relatively sensitive and quick. They do not trip once the current exceeds their rated value there is a curve on a graph involved so they can take small overloads for a long time. The time before they trip decreases as the overload current increases.

I have a 3HP compressor which the manufacturer states needs a 32A supply. It started and ran without problems temporarily on a 15A MCB until I sorted a 20A supply for it.

A C type MCB has a different graph of trip current vs time which allows for an increased current for longer before it trips (less sensitive). In many, but not all, circumstances it is safe to replace a B type with a C type but you need to do tests on the supply to determine if it is safe. If you can't do the tests and calculations you need to get an electrician in.

As has been said you need to get the supply to your shepd sorted and again getting advice from an electrician is a good idea to reduce future problems.

 

[moosepig]

Thanks all - plenty of food for thought 8)