Shop Vac and RPM

1115 Views 8 Replies 8 Participants Last post by  Stick486
Hi there,
I'm trying to get my new lock miter bits figured out. When I turn on my shop vac, it seems to me like it sounds like the router loses a bit of power. Should I factor that drop in power as a drop in RPM?
many thanks
stuart
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What's the power draw on each? Do you have extension cords in place? Are the router and shop vac plugged into the same outlet, same circuit?

Yes, in answer to your question. If you're setting it at 18k rpm, for instance, and it slows to 16k rpm then you may need to set it at 20k rpm to compensate. But I would be more interested in figuring out why it's slowing down first.

David
4
What David said! In spades.
what David said...
and the drop in voltage generates more heat in both units.. not a good plan...
scientific method:
Use a voltmeter , measure voltage on line when nothing runs,
measure with router on, measure with both on.
If it goes down more than about 10 percent, you got a too long,
or too thin power line.
say 100% voltage is 100 % power on router
then 90 % voltage will give 81 % power at router.

You can see it changes fast.

Approximative explanation:

P (power)= U x U ( U= voltage) So it is U at power of 2 divided by resistor value.
--------
R

It is right for pure resistors like a calorific heater, but It' s an aproximation, because with an universal motor, the power reduction is worse than that.

so if U= 1 (100%) then U to a power of 2 is U x U = 1 x 1 = 1 (100 %)
If U= 0.9 ( 90%) then U to a power of 2 is U x U = 0.9 x 0.9 = 0.81 ( 81%)

That shows how fast a 10 % voltage drop gives a 20 % power loss.
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One other question. Where is the vac sucking from? Near the bit or out of the bottom of a box?
Hi there,
I'm trying to get my new lock miter bits figured out. When I turn on my shop vac, it seems to me like it sounds like the router loses a bit of power. Should I factor that drop in power as a drop in RPM?
many thanks
stuart

Stuart, I had a similar problem and added two more circuits. I started blowing breakers. I knew from the start at this house I was going to have to add circuits and kept putting it off until a couple of months ago. You might as well fix your problem now.
1
Plug them into different outlets, aee if there is any change.
Herb
Plug them into different outlets, aee if there is any change.
Herb
but on different circuts
2
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