PHOTOS of my 17.5 HP phase converter

http://igor.chudov.com/projects/17.5-Phase-Converter/
I need to do a few extra things, like adding a pushbutton (which I do
not have yet, I bought it on ebay yesterday), some crimpable butt splices and ring terminals, and preferably adding a second motor starter instead of a definite purpose contactor. The starter would add overload protection, which the 10 HP motor has but 7.5 HP motor does not yet.
i
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wrote:

The leads torqued onto the capacitor terminals backwards is nice. The ground stud having a plastic cable clamp mixed in with leads is good too. A large capacitor bank should have bleed resistors as well, it's for your safety.
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On Wed, 14 Dec 2005 07:13:08 +0000 (UTC), Cydrome Leader

What do you mean by backwards?

Good point, although the screw still conducts.

Well, remember that the capacitors are connected across the windings of the motors. I did think about it, I think that they discharge very quickly through the windings. I will double check that though.
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On Wed, 14 Dec 2005 12:01:49 GMT, Ignoramus19198

Unless you have some wiring removed for maintenance. Then you stick your paw across the isolated capacitor and zap!
Capacitors should not only have bleed resistors, they should have individual bleed resistors mounted directly on their terminals, through their own solder tags, placed below the main terminal. If the studs are long enough, they should even be nutted down separately so they never have to be removed.
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Hm, if I have wiring removed, then they do not get charged.
I just verified it. I ran the RPC and turned it off and immediately (in perhaps 5 seconds) measured DC voltage across the caps. There was nothing.

I do not really mind it, but I do not see the big need in this application. As always, I am open minded.
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On Wed, 14 Dec 2005 12:43:47 GMT, Ignoramus19198
There's also a problem known as "dielectric absorption", where a charged capacitor that's discharged then left disconnected will generate a charge of its own accord. This has delivered enough of a shock to make a nun swear (if not more).
You're running your capacitors on AC at a fairly low voltage, so they're pretty safe, whatever you do. My experience is more with HT DC laser PSUs at a few kV, where they're real killers if you're not careful.
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But they are never disconnected from motor windings. I made sure of that.
They are basically directly connected to motor windings, they are wired into at the contactor/starter outputs along with the motor leads.
When the motors are running, there is induced voltage between 1-3 and 2-3, so the caps help with keeping it more stable across the range of 3 phase power demand (and possibly prevent phase shift).
When the motors are not running, the caps quickly discharge through the windings. Any resistor that I would install would have resistance orders of magnitude less than the windings.

Well, 240V AC could charge them at peak voltage of what, about 380 volts? In other words, if the cap is disconnected (which would not happen in my system), when the charge is at the max, it could be charged up to 380 volts or there about. That's quite serious at 92 uF and 184 uF in two paralleled ones.
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wrote:

Sure you are, so why not cut off the ground prongs on all your equipment. Ater all, it will never fail, so there's no need for ground anways.

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Or if the wire is bolted on counter clockwise so wants to fall off by itself.

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wrote:

It doesn't matter if the screw conducts if there's a fault current and the plastic melts off and you lose solid connection to that bolt.

This is the wrong mentality to be working on nonsense electrical projects like this.

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On Fri, 16 Dec 2005 02:23:32 +0000 (UTC), Cydrome Leader

Okay, I buy it. What value (ohms and watts) would you suggest?
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wrote:

Tell me the size of the caps in uF and the voltage you measure across them and I'll come up with some values for you.
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On Mon, 19 Dec 2005 05:56:40 +0000 (UTC), Cydrome Leader

240 VAC, each cap is 94 uF.
i
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wrote:

1/2 watt 150KOhm will drop the residual voltage to about 15% of 240 in 30 seconds. That's two RC time constants of 150kOhm x 94uF. That gives us a peak of about 240*1.4 * 0.15 (50 volts) after 28 or so seconds, assuming the caps were charged just before the peak of the 240 volt cycle.
since power is (I^2)/R, we get 240 * 240 or 57600/150000 which is 0.384 watts.
You may need to adjust these for variations in line voltage and capacitor tolerance. The 30 seconds to a "safe" voltage I made is arbitrary. 30 seconds seems like a safe amount of time to shut of a project, unplug it and start playing with the insides.
Just for fun, utility company power factor caps are designed to discharge to 50 volts or less after 5 minutes of disconnect.
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On Tue, 27 Dec 2005 01:53:33 +0000 (UTC), Cydrome Leader

Thank you CL. I will follow your advice, maybe will use 100 k instead of 200, but I will do it.
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wrote:

Although I didn't mention it, this is the value of resistor per capacitor. While it's true about 400uF at a few hundred volts probably won't kill you, it is on par with the voltage and energy of a medium sized on-camera camera flash. It's quite unpleasant to touch. The main concern is you jump/jerk/fall into something more dangerous.
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On Thu, 29 Dec 2005 08:52:54 +0000 (UTC), Cydrome Leader

Yes, that's how I understood it. One resistor per capacitor, very close to terminals.
In my case, it is more of a feel good, neatness issue, but worth doing "just in case".

I tried shorting one of those caps with a screwdriver. The sound was like a crack of a .22.
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wrote:

You don't conduct electricity?

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| > The leads torqued onto the capacitor terminals backwards is nice. | | What do you mean by backwards?
Normally wires are wrapped around the terminal or fastener shank clockwise. What happens is that the tightening action pulls the wire into the joint, whereas to wrap it the other way will cause the wire to "squirt out." In your case you probably didn't see it because you have washers on both sides of the wire. BTW, with devices that have any kind of vibration, crimped lugs with proper insulation grip are the best way to do. The only time you'll see wire wrapped around a terminal in "legal" applications is for residential wiring, which is not likely to vibrate. Tying the wires together will also decrease the stress on the connections, which in your case will get really ugly when a wire breaks off. I have a terminal crimper from a seller in Seattle that has really good crimper sets to suit your need for a good price, considering what you get for your money. http://stores.ebay.com/EE-INDUSTRIES NFI, just a satisfied user (They were bought for me for providing automotive services.)
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Thanks. I have a cheapo crimper that actually does a decent job crimping (meaning that I cannot pull put the wire out). I will redo those leads in crimped ring terminal form. I also need to crimp on a few 6 gauge ring terminals, as well. When I do that, I will post new photos.
i
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