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Bill McLeod
06-02-2012, 12:58 PM
I bought a Roto-phase for 3 phase in the shop and it has about 12 big [to me] capacitors. I know they need to be discharged before I start wiring but I have never done this and prefer to not get killed. Any help from someone who knows what they are doing would be appreciated

lakeside53
06-02-2012, 01:37 PM
Clip leads and a 2 watt resistor - say 1K-39k. Mine had 39K bleeders installed on the caps already.

For the savage and careful (wear safety glasses), a screw driver on the teminal works.

Check the caps with a voltmeter. They may already be discharged - all depends on exactly when the power was removed WRT the mains cycle.

BTW.. take more care IF it has start caps. They will be big electrolytics. The Rotophase I have seen did not have start caps - starting was by motor design.

metalmagpie
06-02-2012, 02:28 PM
If the capacitors are connected directly (both sides) to motor leads then they should be discharged already through the motor's windings.

Lakeside53's method is the best way to discharge though, if you need to.

Abaker
06-02-2012, 03:53 PM
If the capacitors are connected directly (both sides) to motor leads then they should be discharged already through the motor's windings.


This explains something I noticed recently when I built my new RPC. While I was tuning it I always checked the caps after I turned it off, but they never had any charge.

Is the fact that they discharge through the motor considered sufficiently safe, so you don't need to add a draining resistor?

hsm'er
06-02-2012, 04:01 PM
Yes, the motor will drain them faster than any resistor will.

macona
06-02-2012, 04:01 PM
With AC there is rarely a charge on the caps. Just use a multimeter to check them (Set to DC mode)

Fasttrack
06-02-2012, 04:58 PM
For the savage and careful (wear safety glasses), a screw driver on the teminal works.




This method can damage electrolytic capacitors and even some oil filled capacitors. Unless it is an energy storage/discharge capacitor, shorting the terminals while charged can cause microscopic damage to the surface, leading to premature cap failure.

lakeside53
06-02-2012, 05:03 PM
As I said... "for for savage". Rarely does it cause a problem though.


I doubt there any charge in the run caps of the Roto-phase designs - they are always across the motor windings which is bascially a direct short to DC (what the caps has after the ac is removed). Never have seen a Roto-phase with start caps.

Fasttrack
06-02-2012, 05:05 PM
As I said... "for for savage". Rarely does it cause a problem though.




Agreed :) Didn't mean to sound argumentative, just pointing out something that some folks may not be aware of.

Bill McLeod
06-02-2012, 08:04 PM
thanks guys I appreciate the conversation I certainly know more now than I did before, I will check with a voltmeter to start with that sounds safe and easy. feel free to make any other comments. it's rated for a total 45 Hp with the max being 15hp for one motor. The trick for me will be getting everything working and still have anything left for the rest of the house. I thinking the heat in the house will be shut off when the shop is running stuff. I have 100 amp service so it's a stretch no matter how I do it.

lakeside53
06-02-2012, 09:48 PM
The 45 hp is a bit of a marketing spin.

If it starts a 15 hp (probably optimistic and only a "light start" motor) think of it as a 25hp rpc motor. You might sneak in on a 100 amp breaker, but... it all depends on the startup surge. I like pony starts on big motors for this reason. Warn the wife to expect some "light dimming" ;)

As a point of reference, a 15hp rpc (maybe start an 8-10hp) requires a 50-60 amp breaker.

J Tiers
06-03-2012, 12:17 AM
That would probably be an Arco model "C" Roto-phase converter. Possibly the light-duty ST-15.

http://www.arco-electric.com/Product.aspx?ProductID=1

Light duty

http://www.arco-electric.com/Product.aspx?ProductID=3

The Arco units carry a dual rating, with one being the largest single motor it will start, and the other being the total HP connected it will deal with, the others all being smaller.

Not marketing Hype at all, but a straight-up description of what it will do. They also make a heavy-duty version with more "oomph", and a lighter duty as well.

I have a Model MF (1HP/3HP) that works fine. The Arco units use a single start/run capacitor (may be made up of several units), and use a dual surface and buried conductor type rotor for best starting and running.

You should not need to do any discharging, the caps are always connected in-circuit, and will discharge thru the motor as noted.

They have wiring and applications data on their site.

The Arco folks seem to be pretty down-to-earth, and not given to "hype".