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 Post subject: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 2:36 pm 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
This is a General Electric resistor tube/body, about 10" long and ceramic. I'm wondering what the wattage capacity of this ceramic tube is.

Obviously the wattage of the resistor is going to vary depending on how it's wound (i.e. which wires are used). The ceramic tube is used for a variety of resistors with different values.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 3:50 pm 

Joined: Mon Aug 23, 2004 11:38 am
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Robert,

Is there a manufacturer's nameplate? Yeah, I know, it's a silly question, but possibly their catalog (I'm not suggesting they might still be in business) would then tell you in what power series this resistor might be.

Dave Crow


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 4:21 pm 

Joined: Fri Aug 20, 2010 8:25 pm
Posts: 245
Well, it depends somewhat on the environment you plan on using it in.

Will there be forced air cooling ? If so, the allowed wattage will be higher.

If not, then it will have to be derated to a lower allowed wattage.

I have seen 500 watt resistors smaller than this.

I would guess it is between 500 and 5000 watts, perhaps higher.

The ultimate limit is the melting temperature of the wires and terminals, any wattage below that will work (for a while). Hard to tell from the photo, but if that is a wooden base the limit maybe determined by a safe temperature that does not ignite the base.

And of course if it is near other components you need to be concerned about heating those.

Cheers, Kevin.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 7:40 pm 

Joined: Fri Mar 26, 2010 11:43 am
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I can't see 5000 watts. At that level, you are talking about enough heat to keep a large room warm in the middle of winter. It would be glowing red hot in less then a minute. Any enclosure would be a literal oven. Lacking any kind of heat sink, the way it is, i'm guessing in the 200-400 watt range. If you know any two of the volts, amps, or ohms, you can quickly find out what they were asking it to do.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 8:33 pm 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
Nameplate says it's a CE-247-A resistor panel/tube. General Electric. The base is too heavy to be wood.

The left 1/3 of it (the heavier wire) needs to dissipate 125 watts. When the headlight is in "dim", heat will be spread across most of the unit, and will need to dissipate about the same amount of power.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 8:58 pm 

Joined: Thu Jan 12, 2006 10:10 pm
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My parts book calls out 8 different catalog numbers for a CE-247 resistor panel, each with a different resistance. There is no call out for wattage. Base is probably asbestos.

Common application was headlight dimming and GF suicide circuit on an Alco/GE roadswitcher.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 9:44 pm 

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Couldn't you use Ohm's Law to determine wattage?

T7


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 9:59 pm 

Joined: Fri Mar 26, 2010 11:43 am
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Location: Floyd, AR
You can determine what the wattage in the circuit was, if you know what the voltage drop or amp draw on the unit was in service. But the actual rating was only on an engineer's drawing somewhere.

What kind of lamp/voltage are you trying to use this on? 125 watts is a significant deviation from your original plan to run a 32 volt 250 watt bulb on a 72 volt system.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 10:29 pm 

Joined: Thu Feb 03, 2005 9:32 pm
Posts: 241
My guess also below 500 watts without active cooling such as a fan. Without a fan something this big needs to have a lot of airflow. Put it in a closed box and you have an easy bake oven.
If it still functions (you can measure resistance) run some current through it and monitor the temperature. Start low, a couple amps, and work up slowly. When you get to around 300 deg. F. that’s would be a maximum for me. Below 150 deg. is more nominal. Once you have that wattage and resistance you can use Ohm's law to work the details.
If it needs replacing and you can't find wattage by testing or part number match the resistance but to be safe go bigger on size. New ceramic resistors of the same approximate size should handle the same wattage or better.
With all the taps I see it looks like three or four smaller resistors in series would work, again if you can still measure the resistance of each section. The wattage of each section can be figured again with Ohm's law if you have a good answer on the total.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 11:25 pm 

Joined: Wed Dec 15, 2010 8:17 pm
Posts: 139
The Alcos use a little different CE-247 panel with 4 resisters.

If you can determine the part number of the resister, I maybe able to call someone that might know.

Along with the CE-247-A should be a GE Cat. number on the tag attached to the base.
Or engraved in the end of the resister, near were the wire ends, should be some numbers. There should be 7 numbers followed by a "G" and then another number.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 20, 2015 11:50 pm 

Joined: Fri Aug 20, 2010 8:25 pm
Posts: 245
Well, the original post asked about the wattage capacity of the pictured resistor. Not the Watts dissipated in a typical application of this resistor. The manufacturer may have had a standard series of resistors that could handle "up to" 5000 Watts. Many circuit designs may have incorporated that standard resistor because the next smallest resistor (500 W ?) would be "borderline" for a specific application.

Resistors come in "wattages/sizes" much like pipe. Your calculations may show that you only need 1-2/3 inch pipe to meet your design requirements, but those danged pipe manufacturers only decided to make 1-1/2 and 2 inch pipe. This might be the 2 inch pipe applied where only a 1-2/3 pipe would suffice.

Resistors have many usages; ballast to dim a light bulb, voltage divider for motor excitation circuits, shunt resistors to sense current flow, and dynamic braking resistors.

Without more information it is hard to tell what this was used for.

In many of my listed applications the power dissipated by this resistor may be tens or hundreds of Watts.

But judging by the construction details that can be gathered from one photograph this resistor may be quite capable of dissipating several kilowatts of power if properly cooled.

It does look like it may have one "tap" that is adjustable by moving a clamping band (on the right hand side of the photo) along the length of the wire coil. Could be a means to adjust an excitation voltage to a motor ?, or a light bulb brightness adjustment ?

Cheers, Kevin


Last edited by NYCRRson on Sat Nov 21, 2015 12:22 am, edited 1 time in total.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 12:20 am 

Joined: Wed Oct 22, 2008 8:18 pm
Posts: 2076
it does look like it has an adjustable tap, with other tapped locations. My first thought..it was NOT going to be for heavy power motor control. You'll fry that in a hurry. Sounds like your safe with blower motors/headlight dimming. Traction resistors would be far more heavy duty that this. The Electroliner uses its resistors as a cooking element in the diner. Now thats heat...why they were ..."Electroburgers".


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 2:50 am 

Joined: Thu Nov 22, 2007 5:46 am
Posts: 2447
Location: S.F. Bay Area
Pegasuspinto wrote:
You can determine what the wattage in the circuit was, if you know what the voltage drop or amp draw on the unit was in service. But the actual rating was only on an engineer's drawing somewhere.

The OE situation used 1 resistor per headlight, worst case it dissipated about 100w.

The current situation uses 2 resistors per headlight, of different values than OE. One headlight uses 2 resistors in OE locations, the other uses 2 resistors mounted in a new location. I suspect this resistor type/tube was chosen because they physically fit in the location of the original resistors.

As-found, the two resistors tested (at the picture, per segment, left to right) 4.5 ohm, 4.1 ohm, and 11.3 ohm to the slider. To the right of the slider resistance varied, 15 and 12 ohms.
There were two of them, in series connected at the left. Power was fed to one slider and the lamp connected to the other slider, so 40 ohms "dim". (huh???) The locomotive has two "bright" switches (huh??), one bypassed the 11.3 ohm and the other the 4.5+4.1 group. Resistances were 40, 28.5, 20 or 31 depending on how the two "bright/dim" switches were set. Those values make no sense for any bulb I could find, and indeed the headlight was very dim.

Quote:
What kind of lamp/voltage are you trying to use this on? 125 watts is a significant deviation from your original plan to run a 32 volt 250 watt bulb on a 72 volt system.

For that bulb (based on testing) I need 5.5 ohms to limit current to 7.5A, and 11 ohms dim (at 4.8A). Note what you get if you parallel 2 of the above resistors :)

I'll still need to add a 1 ohm resistor somewhere, but those I got.

This has the advantage of keeping the locomotive reasonably OEM.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 3:50 am 

Joined: Fri Mar 14, 2014 11:44 pm
Posts: 23
GE was fond of winding multi-tap resistors with different sizes of resistance wire.

It isn't really meaningful to speak of the wattage of the overall unit. Each section
has a rating based on current. That information may be in the catalog but since these
were purpose-built resistors, the rating is based on the application and may not have been
published as a spec. For generic power resistors such as grid resistors, GE catalogs (and
WH catalogs) had current ratings based on duty cycle.

The porcelain frames were standard sizes. At first I thought that was a KM motor control
resistor for an all-electric GE PCC!

Power resistor ratings in general are based on surface area. I would say 5-7 W/sq. in.
Figure the circumference multiplied by the length of each section and compare against
the wattage being dissipated in that section I^2 * R.

Or, do as the other poster suggests, and test it on the bench with a power supply or a variac.
Spit on it. If your spit sizzles rapidly, it's too hot. If it just evaporates slowly that's about OK.
More than that is hard to say. Old resistors like that sometimes fail from a little nick or defect
in the resistance wire that corrodes it from the inside out.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 9:46 am 

Joined: Mon Apr 30, 2007 12:45 am
Posts: 442
Location: Illinois
dinwitty wrote:
The Electroliner uses its resistors as a cooking element in the diner.


Totally incorrect.

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