fitch williams 10 hp converter

levi88 · Oct 18, 2005

hey all,
i mostly am a lurker here , but i need a little help. getting ready to construct a converter per fitch williams 10 hp design, but i been studying this schematic for days, and i do not understand how the start caps are switched out using the switches that are called out in the parts list. it would make sense (to me anyway) if S2 was a momentary contact switch. what am i missing here ? oh by the way, you guys have already been a big help to me, even if you didn't know !
thanks kindly
levi

toolnut · Oct 19, 2005

I have the Fitch Williams 10 hp converter schematic and parts list. I believe there is a mistake in the parts list. The description for S1 and S2 are interchanged. S1 should be the maintened pull on / push off mushroom head switch and S2 should be a momentary switch. I have been building converters for more than 15 years but I use a potential relay to drop the start capacitors from the circuit. I think Fitch's circuit will work fine and I do use his balancing technique. In fact, the last converter I worked on would start without the starting circuit once the phases were balanced. I managed to get the phases to within 3% when operating a motor of the same horsepower as the idler.

levi88 · Oct 20, 2005

toolnut, thank you kindly

Now i can see it, that makes a world of difference. boy do i feel dumb now, that is so simple and right there, talk about not being able to see the forest for the trees ! anyhow I certainly appreciate that. got the motor, contacters,switches and all just got to pickup an enclosure and i'll be set. have a smaller converter (3hp)now , but it has no balancing caps, and i need a bigger converter anyhow.

thanks levi

T. Overeynder · Nov 24, 2005

Where can I get Fitch Williams design and parts list? I have a need to build a 10 hp RPC. Or, dose anyone have a good proven design for a 10 hp converter?

Thanks,

Tom

levi88 · Nov 24, 2005

hey dude,

here is where i found it http://www.practicalmachinist.com/FitchWConverter.pdf

later levi

ebas7565 · Dec 2, 2005

Can anyone tell me how many amps the converter draws under no load?

jhg · Dec 2, 2005

Under no load it only has to overcome its own windage and friction. Fitch told me once but I forget- it was about as much as a 100 watt light bulb. Not very much at all.
jhg

fsmyth · Dec 2, 2005

A generic idle current for a 10 HP motor is about
7 amps. Motor construction will determine the true
idle current, as will the phase relationships
between poles, and the terminal voltage. And unless
properly balanced, you need to add/subtract the cap
currents.
But it's a bit more than a 100W bulb. <g>
<als>

T. Overeynder · Dec 2, 2005

Anybody have pictures of their up and running Fitch Williams 10 HP converter? I.E., how the componets are breadboarded. Please post or e-mail me direct. Thanks for any input.

Tom

Adrian Williams · Nov 25, 2019

T. Overeynder did anyone ever get you pictures? I know this its an old thread but I'm. looking for a "Fitch Williams for dummies" diagram somewhere. I'm not educated on ladder diagrams and the connecting points are confusing when not familiar. I'm an electrician for retail commercial and not used to anything in controls. any photos or simple diagrams would be appreciated. I've read a million posts and watched videos but now I'm looking for a simple photo and/ or diagram to get my head around it. Not looking to veer from Fitch's design as a friend of mine used to have one made from his design and it worked flawlessly for years till he sold off for retirement. I've used VFDs and they're fine but with a new shop layout id like a one piece solution the 3 phase issue. I have all the parts I believe and even dug up an old 96 Grainger Catalog to cross reference to ensure I wasn't getting something re numbered. I added an overload and a few more indicators as well as digital displays to see the balance as I had a few kicking around. just looking to wire exactly to Fitch's intent. Thanks

jim rozen · Nov 25, 2019

fsmyth said:
A generic idle current for a 10 HP motor is about
7 amps.

That's the amp-clamp number. Most of that current is reactive and will not spin
a residential watt-hour meter. A 5 hp converter draws about 140 watts of real power
at idle. One could expect a 10 hp one to draw about twice that.

thermite · Nov 26, 2019

Adrian Williams said:
T. Overeynder did anyone ever get you pictures? I know this its an old thread but I'm. looking for a "Fitch Williams for dummies" diagram somewhere. I'm not educated on ladder diagrams and the connecting points are confusing when not familiar. I'm an electrician for retail commercial and not used to anything in controls. any photos or simple diagrams would be appreciated. I've read a million posts and watched videos but now I'm looking for a simple photo and/ or diagram to get my head around it. Not looking to veer from Fitch's design as a friend of mine used to have one made from his design and it worked flawlessly for years till he sold off for retirement. I've used VFDs and they're fine but with a new shop layout id like a one piece solution the 3 phase issue. I have all the parts I believe and even dug up an old 96 Grainger Catalog to cross reference to ensure I wasn't getting something re numbered. I added an overload and a few more indicators as well as digital displays to see the balance as I had a few kicking around. just looking to wire exactly to Fitch's intent. Thanks

Sounds like you are making a problem out of a solution.

Fitch furnished a simple schematic, parts list, theory of operation and instructions as a .pdf. It is referenced from within PM's "stickies", top of this forum:

https://www.practicalmachinist.com/FitchWConverter.pdf

10 HP. Because it is a good size. And because it scales easily to any other idler size.

The only "ladder" fu a body might need is to mount the bugger in his attic for lack of shop floorspace?

PS: Useful numbers, Jim. Thanks for that.

jim rozen · Nov 26, 2019

Those numbers were from my stone age converter, no capacitors were harmed in its construction.
At the same that I borrowed a digital scope from work to check the waveform balance, I used a non-inductive
ten ohm resistor to plot the current and voltage being supplied from the utility phase on this system.

I think the number basically came from the amp clamp reading, adusted for the apparent phase angle
between voltage and current waveforms. Phase angle difference between current (green) and voltage (red)

Setup photos. Very scary. Don't do this. The fused knife switch is on the wall above the oak toolbox,
current and voltage leads tagged into this and lead to the measurement setup:

Yeah, definitely do not do this. At least not this way. The gold item under the mallet is the non-inductive
resistor, the smaller resistors are 10 megs that go in series with the one meg scope probes to give a 100X probe.

I seem to recall I measured 120 watts in one way, and 140 in another. The 140 was the amp clamp reading times
the phase angle, the 120 was by multiplying the waveforms in the scope. Both the current and voltage waveforms
are pretty non-sinusoidal.

The takeaway here is the power factor for the unloaded coverter is really very very low. So even the though the
amp clamp reader gives a number, that is not how fast the watthour meter is spinning, by a long shot. IF, and only IF
it is a residential meter. Those ignore reactive power, at least the Con Ed ones here do.

thermite · Nov 27, 2019

jim rozen said:
Yeah, definitely do not do this. At least not this way.

LOL! "used to do...much the same".. Then the local Goodwill had a Herman Miller computer desk donated. NICE!.

I waited for the price drop. It became the power lab bench. Mind - just for the worng and controls. Motors, Variacs, transformers, etc. are not ON it. Mostly they are on reinforced furniture dollys, wheeled to and away.

But.. there are two layers of bare 3/4" plywood cut to fit atop the original Herman Miller laminated top. Boxes of screws and clamps are kept handy.

Each setup since I implemented that rig, I just screw-down everything from transformers to terminal strips, to perf-boards, to brackets for potentiomers, switches, breadboards, pin-jacks, to ... scrap Lucite or Lexan covers, to... whatever suits.

I ain't dealing with 5V Vcc any longer whilst messing with machine-tool power.
Lethal stuff, right next to low-voltage controls, nearly all of it, rather.

Besides.. all the meters and the 'scopes are my own, I DO have proper HV leads, so with any given experiment literally "screwed down" it also serves as "non-volatile memory" as I take breaks t do other stuff. Or not do - and don't come back to it for long periods.

Too many holes, flip the plywood. Haven't reached the point of swapping to the second sheet of it yet.

Plywood has gone dear, but it is still way to Hell and gone cheaper than funerals.

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