Author Topic: 60 hz cycle  (Read 13130 times)

rcavictim

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Re: 60 hz cycle
« Reply #15 on: January 04, 2007, 08:20:59 PM »
Or you can pick one up from Fair Radio Sales for US$2.25. Take the savings and buy yourself a nice, big, old fashioned, Bakolite (sp?) knob to suit!!

See link below:
http://www.fairradio.com/catalog.php?mode=view&categoryid=4233

Best regards,
Andy "The Cheap Swede" Hall

Ahhhh, that`s more like it!  They call these rheostats but the Ohmite ones I was referring to actually have three terminals making them potentiometers.  The Fair Radio parts may be pots as well since `rheostat` is a slang used to infer a higher power type of potentiometer by some.
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rcavictim

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A WORD OF CAUTION SIZING RHEOSTATS
« Reply #16 on: January 04, 2007, 08:28:08 PM »


If the specs call for say a 50 ohm resistor with a dissipation rating of 100 watts for example, if you buy a 100 ohm rheostat rated at 100 watts and plan to use it set in the neighborhood of half way your 100 watt rheostat is only rated at 50 watts in this position and you would overheat it, possibly letting the smoke out.  Potentiometers and rheostatas are rated at the wattage they can handle when the entire resistive element is in use.  You have to de-rate them according to where the setting is expected to be or buy oversize wattage ratings accordingly.  This is not a concern with fixed resistors where the entire resistive element is always used and the wattage rating can be a fixed value.
-DIY 1.5L NA VW diesel genset - 9 kW 3-phase. Co-gen, dual  fuel
- 1966, Petter PJ-1, 5 kW air cooled diesel standby lighting plant
-DIY JD175A, minimum fuel research genset.
-Changfa 1115
-6 HP Launtop air cooled diesel
-Want Lister 6/1
-Large DIY VAWT nearing completion

adhall

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Re: 60 hz cycle
« Reply #17 on: January 04, 2007, 08:57:23 PM »
It appears to me that the intent is to insert an adjustable resistance in series with the field rather than to power the field from a voltage divider. That being the case, either a rheostat or a potentiometer could be connected to do this.

As far as power rating goes, the Utterpower website says that the field current is 2.1 Amps without the added resistance. With the resistance installed, the current would be reduced--although I can't say how much.

To figure current carrying capacity in rheostat mode you should really look up the manufacturer's specs. However, a rough approximation is to figure what the current would be at full rated power through the full winding. This tells you how much current the winding can stand but does not take into account what the wiper can take. So, in this case a 5 Ohm device rated at 50 Watts comes out to about 3.2 Amps. Lacking more complete information, I would say a 50 W device would be OK (although it is a bit more stressed than I like).

For a real world comparison, an Ohmite RJ series rheostat is rated at 50 W and the the manufacturer gives the 6 Ohm version a 2.88 A current rating.

For what it's worth, when I use a potentiometer as a rheostat I like to connect the wiper to one end of the winding. The advantage is that you don't end up with an open circuit if the winding burns out.

Best regards,
Andy Hall
« Last Edit: January 04, 2007, 11:09:39 PM by adhall »
JKSon 6/1, 5 kW ST Head, 1992 Dodge RAM Cummins 5.9L Turbodiesel, 2001 VW TDI 1.9L Turbodiesel, 2006 Jeep CRD Turbodiesel, Yanmar FX22D Diesel Tractor

adhall

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Re: 60 hz cycle
« Reply #18 on: January 04, 2007, 11:07:51 PM »
Wow, I think my evil twin has been posting for me today--after my earlier mistake, I fouled up again at the end of my last post.

When I said "I like to connect the two ends of the winding together", I should have said "I like to connect the wiper to one end of the winding".

The only benefit to be gained from this is it saves you from getting an open circuit when the winding burns out.

My further comments about messing up the linearity and improved power dissipation do not apply in this case.

My apologies to the forum for the mistakes. I have gone back and corrected the original post.

Best regards,
Andy Hall
JKSon 6/1, 5 kW ST Head, 1992 Dodge RAM Cummins 5.9L Turbodiesel, 2001 VW TDI 1.9L Turbodiesel, 2006 Jeep CRD Turbodiesel, Yanmar FX22D Diesel Tractor

rcavictim

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Re: 60 hz cycle
« Reply #19 on: January 05, 2007, 01:03:59 AM »
Andy,

I followed your description of tying the two outside ends of the pot together and figured that this would be a super way to rewire the volume control of an annoying boom car.  The inconsiderate, hard of hearing (insert favourite expletive noun here) behind the wheel could turn up the control to 11 and all around could enjoy their golden silence.   :-*
-DIY 1.5L NA VW diesel genset - 9 kW 3-phase. Co-gen, dual  fuel
- 1966, Petter PJ-1, 5 kW air cooled diesel standby lighting plant
-DIY JD175A, minimum fuel research genset.
-Changfa 1115
-6 HP Launtop air cooled diesel
-Want Lister 6/1
-Large DIY VAWT nearing completion

adhall

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Re: 60 hz cycle
« Reply #20 on: January 06, 2007, 01:05:07 AM »
Rcavictim,

Yeah, I guess it would work just like you say.

Darn, I was hoping nobody had read that post before I fixed it...

Foot in mouth, MMM tastes good...

Best regards,
Andy Hall
JKSon 6/1, 5 kW ST Head, 1992 Dodge RAM Cummins 5.9L Turbodiesel, 2001 VW TDI 1.9L Turbodiesel, 2006 Jeep CRD Turbodiesel, Yanmar FX22D Diesel Tractor