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Threadless control box

Jimmy Mack

Jimmy Mack

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As mentioned on a previous topic (I'm fixing up an old SCM si150).

The two button control box has a bit of an issue.... the existing face plate is hanging off! The housing/ back box is metal and the integrated threads are completely gone on the right h/s ...

I've a couple of options:

Tap out the threads up a size (I don't have a tap set)...
Buy a new box
Find a fix trick... perhaps glue in a nut?

The twist release has gone on the emergency stop also, I'll have to see what that's doing when we get power, as it may not even work/ be an issue.

Jim

(pics in next post)
 
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You could try gluing in a nut but it is an awful bodge solution. Grease the screw you use to hold the nut in place to save gluing it in place too!

or drill right through the box and out the back and fit longer screws with nut and washers on the back.

lots of ebay vendors selling individual or small packs of nuts and bolts.

Bob
 
Thanks Bob.

Yes, I agree, gluing the nut in would be a bodge, too much torque and they could fail and I'd be locked out!

Not sure if you can make it out, but the two black tips on the bottom of the box are screws which go right through the box holding it in place, these block off screwing right through, as they are in line[emoji46] ...nice idea though.

However I don't see why these can't be shortened...I guess this was done to make installation easier.

Jim


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You could always discard the box and use the same mounts to fix a piece of angle iron/aluminium and onto that, fix a new push button station. There are several ebay suppliers doing ready built units with a variety of switches fitted.

Bob
 
Tusses":2h5djusi said:
Long time since I looked at them, but can you get "riv nuts" that size ?
Click to expand...


I wondered about that but there would be very little meat if any to mount it and likely to crack the box.
Helicoils would do too but the OP does not even have stand taps let alone oversize helicoil taps.

Bob
 
ok then .... :lol:

"(I'm fixing up an old SCM si150)."

anyone that is fixing up things has the perfect excuse to buy a new toy, like a tap and die set !
They're not expensive (one of your options was a new box ! ) , and will prove useful over an over :)
 
I'd forget the existing holes and drill one new one half way between them then fit a self tapper screw. job done.
 
Robert":21dn5nzz said:
I'd forget the existing holes and drill one new one half way between them then fit a self tapper screw. job done.
Click to expand...
I think the box has thin sides with the corners filled in to give enough metal to be drilled and tapped.
Buy a set of taps and the fill the striped holes with car body filer, then redrill and tap them, would be my solution.
 
DaveL":244jafe7 said:
Robert":244jafe7 said:
I'd forget the existing holes and drill one new one half way between them then fit a self tapper screw. job done.
Click to expand...
I think the box has thin sides with the corners filled in to give enough metal to be drilled and tapped.
Buy a set of taps and the fill the striped holes with car body filer, then redrill and tap them, would be my solution.
Click to expand...

Yes, Dave's right there with the box description, I should of opened it up for a picture.

I think I'll wait till my sparks pops over next week and see how she's running. Managed to get my head in on the back of the motor to snap the spec plate (the dealer I bought it off thought it was the standard 3.3KW ,4hp model...

:o :o mother?! :shock:
 
...actually thinking about it.. a 19A Start up seems too low...I'd expect something in the mid 30's

:eusa-think:

I'll fish about in the schematic book
 
9fingers":2v0c2k3f said:
No those all fla running currents. Quite a bit more for starting inrush. Make sure you fit type c mcbs in your fuse board to avoid nuisance trips on start up. There are soft start solutions if you get desperate but cost!!!

Bob
Click to expand...


Ah ...Thanks Bob, I have some c Curve 16A MCB's

I'm still a bit in shock, (no pun intended)...RIPPING will be an absolute breeze :eusa-dance: not sure about my electric bill tho :shock:

Still, SWIMBO's got some pretty mean hairdryers :D
 
Kinda like motorway driving... Bigger engine and bigger the wheels ( blade ) the more energy it can store and less likely under load therefore less consumption ?

Pushing a few amps on start up to meet the inital resistance?

That's my logic...probably talking rubbish though [emoji23]

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9fingers":fkrnwy5g said:
Not really a good analogy

Just keep a blade spinning takes very little power. Feeding lumps of wood through absorbs lots of power and it is power that you pay for.

Bob
Click to expand...
My understanding is a little sketchy. [emoji43]

More current drawn under load to maintain rpm(?) makes sense, but what makes the initial current pull higher?...is it the initial resistance of the motor mass, the amount of coil or both?

Is the KW rating the max potential under (heavy) load Work and start up, with a lower KW in idle/ low load as the potential different between amps and voltage is lower in this state?

Probably talking gobble de goop and confusing myself [emoji23] ...could do with some further reading [emoji3]. I guess what I'm trying to understand are the pros and cons of a bigger motor

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Bit too much of a complex subject to deal with in a thread but I hope this might help.

When running, a motor also acts as a generator and will always generate a voltage in opposition to the applied voltage. This is often called back emf. This reduces the current when it is rotating compared to the stationary current when it first starts up.

The power you pay for (in a domestic leccy meter) = voltage * current * power factor (0>pf>1)

When the load on the motor in minimal, the pf is low. What power is consumed is used to drive the fan, overcome friction in bearing and belts and heat up the motor windings due to their resistance.

Under high load the current goes up a bit but it is the power factor that approaches unity and so the power you pay for goes up but only when the machine is working hard.

When the motor is overloaded, it can no longer maintain its speed. So the generator effect is less, the back emf starts dropping and the current rises above the full load current, generates lots more heat, fan cooling drops off and soon the magic smoke appears and the motor insulation breaks down etc etc.

What might be difficult to understand is that the current drawn under light load is still relatively high maybe half that of full load but it is the power factor which varies more with load.

Pros and cons of a larger motor? mainly pros is terms of capability, deep ripping etc and in normal use, staying well away from the overload point. Cons? slightly higher idle power consumption but that is about it.

Hope this helps

Bob
 
Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?
 
If all else fails could you glue a piece of wood behind the holes in the box and then use screws to hold the front on?
 
RogerS":3ihpqasn said:
Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?
Click to expand...

Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob
 
Nice post Bob .. :)
reminds me of years ago, when factories would turn the florescent lights on in groups, rather than all at once to keep the leccy bill down .. is that the same thing ?

I didn't know Domestic meters worked like that ..
 
Industrial users are encouraged to balance the current on each of the three phases.
No problem with a proper 3 phase load but lighting is usually single phase to bays of lighting would normally be wired to different phases in the same way as houses down the street are wired to each phase in turn.
When you next have a power cut, sometime you will see 1 house in three along a road with no lights due to 1 phase having failed.

Industrial users are also encouraged to correct their power factor to near unity by having leccy meters that measure the product of voltage and current - so called VA meters. Domestic meter measure Watts which it he useful power your extract from the mains.
The leccy generators have to generate the volts and the peak amps so they generate VA and householder pay for Watts. The cost of so called Wattless power - the difference - is lost to them which is why they want the industrial users to correct their PF to near 1.

I have done some measurements on my belt sander. About the only machine I can load up to maximum with one hand and take meter photos with the other - safely (ish!)

OK firstly off load readings

Voltage


Current


VA the power they have to generate and your wiring/switches etc must withstand


Power that you are paying for


Power factor


Applying a near maximum load to the sander with a block of wood

We get no change in the voltage

but the current is


The VA is


The power you pay for


and the power factor


Hope this gives some idea of what to expect

The idle running cost is less than a third of the full load running cost. I'd expect nearer 4:1

Now this a bit of a bodge experiment as my belt sander is a 3 phase and I only have a single phase power meter so the sander was jury rigged to a static phase converter (not 100% efficient!) so I could measure single phase power parameters to show you.

Hope this helps a bit more

Bob

PS I've left this on the end of the original thread as fixing the control box comments had possibly been made now and it gives some context with the machine.
 
I have one of those plug in dooferies ..

I mainly use it to keep an eye on voltage drop when I have a few machines running ...
I inherited the wiring to the workshop, which is about 50m of arrnoured cable from the house fuse box.

I was never interested in more than the basic "electrics" . Just enough t get by. I prefer(d) analogue amplifiers and logic circuits .. yes I know they are completely different ! .. but I love audio .. and like programming and logic stuff.

I never get time to play any more though :(
 
Bob,

:text-bravo:

That's a great demonstration! Very kind of you to spend the time putting it together. I've learnt a lot today...I hadn't considered that the motor (when running) acts as a generator, makes total sense.

I'm going to have another read in the morning with my coffee and a repaired daddy-day-care head to digest the power factor (pf) element of the discussion.

Thanks again,

Jim
 
Andyp":2nyqeohi said:
If all else fails could you glue a piece of wood behind the holes in the box and then use screws to hold the front on?
Click to expand...

Andy - I like this idea, though the screw would be very close to the end of any piece of wood (split potential) as the holes are right in the corner (unless I've misinterpreted). You've got me thinking sideways though...I'm wondering it I could pop a 'red' rawl plug in the holes and wood screw in - not ideal, but a work around while I get up and running :D

Many thanks,

Jim
 
9fingers":3tah4lw9 said:
RogerS":3tah4lw9 said:
Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?
Click to expand...

Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob
Click to expand...

Any links to something a bit more in-depth ?
 
RogerS":l9dglfpl said:
9fingers":l9dglfpl said:
RogerS":l9dglfpl said:
Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?
Click to expand...

Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob
Click to expand...

Any links to something a bit more in-depth ?
Click to expand...

Not really to be honest. Things that I've found get very theoretical and after a while you lose the wood for the trees. Discussions of power factor seem to end up in power factor correction.
Maybe your google foo is better than mine.

Bob

EDIT: try https://en.wikipedia.org/wiki/Induction_motor
and http://www.engineeringtoolbox.com/power ... d_654.html
 
Swapped the box round to the correct side, and closed the end (with damaged threads) with the humble zip tie.

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I suspect it was swapped to the inside as it was getting knocked, which is why the box is damaged. ...but it's hard to get to on the inside. The contactor is working, but the lock on the stop button is broken. Any tips for online shops for this kind of component?

Jim

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