Re: [CAD_CAM_EDM_DRO] Re: Mariss' power supply circuit

I think you should change your name to More Watts.

John H. Berg
Berg Engineering, LLC
1133 Kensington
Grosse Pointe Park, Michigan 48230

Phone: (313) 999-1227
Fax: (313) 881-6421
E-Mail: berg1133@...

----- Original Message -----
From: "Les Watts" <leswatts@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, June 18, 2002 9:14 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Mariss' power supply circuit


> I think I see. C1 charges up through R2 linearly thus forming the sawtooth
> wave portion of the modulator.
>
> I am building a new servo supply for my machine. The current one is not
> stiff enough and causes following error estops with the high acceleration
> high speed moves I want to do. I will incorporate this circuit in the
supply
> I think.
>
> I need about 30 amps cont at 85v and the 50 or so pounds of transformer
> iron laying on the floor says I will get it. I am using stepdown isolation
> transformers at half voltage so that iron won't be at the full flux
density
> but there is still plenty of room. I will nominally go from 120v to 60
> so I should get 60*1.414= 84.8vdc. My amps turn off at 92v and have
> 100 wv caps in them.
> Since my line voltage is notoriously high I may put a few bucking turns
> on the transformers. I read why power companies like higher voltage-
> revenue goes up as the square of that voltage! Too bad they can't control
> it.
>
> As for sizing R7 in your circuit- well lets see.... my 25 joule of max
> regeneration
> energy could attempt to pump up the 20,000uf supply cap from its normal
> 72 joule @ 85v to 72+25=97 joule. That would be 98.5v. It would be some
less
> from losses but that is a maximum. With your circuit at 100% duty cycle
> dumping
> 25 joule in say .05 sec would require 500 watts as a linear approximation.
> So the value would be about 20 ohms. I use Dale 10 ohm 25w wirewounds
> to short the servos in my estop circuit and they don't even get warm
> so 25w should be fine. I could use a lower value.. if I chose the resistor
> current
> to be the ps rated current it would be about 4 ohms but if I go too low
> I think I will estop on every power flicker.
>
> As a check for power failure 3*R7*C= 1.2 seconds ; long enough. My estop
> will short the servos in a sustained failure anyway.
>
> Les
>
>
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA
> http://www.rabun.net/~leswatts/wattsfurniturewp.html
> engineering page:
> http://www.rabun.net/~leswatts/shop.html
> ----- Original Message -----
> From: "mariss92705" <mariss92705@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Monday, June 17, 2002 8:09 PM
> Subject: [CAD_CAM_EDM_DRO] Re: Mariss' power supply circuit
>
>
> > Les,
> >
> > I appreciate you taking the time to understand the circuit. The PWM
> > modulation is actually a linear function of the over-voltage seen by
> > the supply. The amplitude of the 120 Hz sawtooth (R2,C1) is set to
> > about 2V peak-to-peak, this being the "regulation" range of the
> > circuit. The "trough" of the full-wave rectified reference clamps the
> > negative excursion of the sawtooth to the difference voltage.
> >
> > The IRF540 has an Rds of about .07 ohms. It always operates as a
> > switch, the current being limited by the 10 to 20W shunt resistor.
> > The resistor must be wire-wound because wire-wound resistors have a
> > superb overload capability, typically 10 times their rated wattage
> > for 5 seconds, 50 times rated for 200mS.
> >
> > In an undervoltage situation the circuit would attempt to adjust
> > itself to the new, lower voltage. It would be abley assisted by the
> > load in this endevor.
> >
> > Like all silicon, MOSFETs invariably fail shorted if abused. The
> > consequence would be the shunt resistor would rapidly overheat and
> > fuse open, clearing the circuit. Everything else would fail
> > harmlessly and would leave the basic supply uneffected.
> >
> > Another thing about the circuit is the component value choice for the
> > +12VDC supply. The size of C3 is chosen so that the circuit remains
> > functional for .5 second after AC power removal to fully discharge
> > the supply.
> >
> > Thanks again for your comments; my pleasure is designing minimalist
> > circuits the way others might enjoy working crossword puzzles.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Les Watts" <leswatts@r...> wrote:
> > > I finally found the .pdf file and had a look.
> > > As I understand it the circuit will perform shunt regulation
> > > using PWM at 120 hz. Duty cycle will vary from 0-100% over a
> > > couple volts diff between the filter cap and transformer secondary
> > > peak. I think it will modulate with a raised cosine law. Right?
> > >
> > > Question: what is the on resistance of the Fet you selected? Just
> > > want to calculate heat sink thermal resistance. Also, what happens
> > > in a line power undervoltage scenario?
> > >
> > > And as a little FMEA thing, what would be the most likely part to
> > fail?
> > > Would it be the fet if say the primary mains went very high? Would
> > it
> > > fail open or shorted? (I currently have a floating neutral argument
> > with
> > > my Georgia Power supplier and their electrical feed)
> > >
> > > I want to publicly thank you for publishing this as open source.
> > > I appreciate your weekend efforts.
> > > These things cost about $300 from other suppliers.
> > >
> > > Les
> > >
> > > Leslie Watts
> > > L M Watts Furniture
> > > Tiger, Georgia USA
> > > http://www.rabun.net/~leswatts/wattsfurniturewp.html
> > > engineering page:
> > > http://www.rabun.net/~leswatts/shop.html
> > > ----- Original Message -----
> > > From: "mariss92705" <mariss92705@y...>
> > > To: <CAD_CAM_EDM_DRO@y...>
> > > Sent: Sunday, June 16, 2002 3:54 PM
> > > Subject: [CAD_CAM_EDM_DRO] Re: Power Supply Circuit
> > >
> > >
> > > > Hi,
> > > >
> > > > OK, here's my Saturday's project. I posted a "Power supply
> > > > circuit.pdf" in the files section of this list.
> > > >
> > > > It wound up being different than what I started with. Sensing
> > current
> > > > was too crude. Instead this circuit compares the power supply
> > voltage
> > > > against the xformer secondary voltage. It pulse width modulates
> > the
> > > > dump resistor and has a very nice proportional response. The PWM
> > goes
> > > > from 0% to 100% as the power supply voltage climbs to 2V above
> > the
> > > > nominal voltage. It has been tested and works very well.
> > > >
> > > > Mariss
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
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if
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> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this as a
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> >
> >
> >
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> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this as a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
>
>
> Post messages: CAD_CAM_EDM_DRO@yahoogroups.com
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