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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 3:32 pm 

Joined: Sat Aug 21, 2004 10:52 pm
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Hi,

You could record the voltage and current on the resistor and when it fails, the whattage is just a little less.

Destructive testing.

Doug vV


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 4:16 pm 

Joined: Sun Aug 22, 2004 7:19 am
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Location: southeastern USA
Actually, by my reading he's asking for the wattage capacity of the ceramic tube, not the wire in the first post. Are we providing the wrong information?

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 7:35 pm 

Joined: Mon Sep 06, 2010 10:51 pm
Posts: 80
robertmacdowell wrote:
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.


Generally, for common, vitreous enamel, power resistor tubes such as those made by Ohmite, Milwaukee, etc. the Wattage is determined by length of the core (tube).
A 10" tube would be good for about 200 Watts, a 10.5" would be good for 225 Watts and so on. One of the most common lengths used on trolleys / streetcars and interurbans is 8.5" which is rated at 175 Watts. Note that the max. Wattage is based on the full length of the winding. Use of taps between the two end terminals will reduce the Wattage capacity accordingly. If not properly rated, these tubes can and will glow red hot.

Gord McOuat


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 7:43 pm 
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http://www.ohmite.com/techdata/res_select.pdf

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sat Nov 21, 2015 10:38 pm 

Joined: Wed Oct 22, 2008 8:18 pm
Posts: 2072
Jdelhaye wrote:
dinwitty wrote:
The Electroliner uses its resistors as a cooking element in the diner.


Totally incorrect.


I dig dugged, I need to see a full circuit of this what the transformer is functioning for, if for just the cooking utensils or controlling other apparatus on the Liner.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sun Nov 22, 2015 12:22 am 

Joined: Sun Aug 22, 2004 7:19 am
Posts: 5250
Location: southeastern USA
Gord M wrote:
Generally, for common, vitreous enamel, power resistor tubes such as those made by Ohmite, Milwaukee, etc. the Wattage is determined by length of the core (tube).
A 10" tube would be good for about 200 Watts, a 10.5" would be good for 225 Watts and so on. One of the most common lengths used on trolleys / streetcars and interurbans is 8.5" which is rated at 175 Watts. Note that the max. Wattage is based on the full length of the winding. Use of taps between the two end terminals will reduce the Wattage capacity accordingly. If not properly rated, these tubes can and will glow red hot.

Gord McOuat


Gord is an encyclopedia of valuable information who has saved my butt a few times in the past couple months. Thanks.......

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sun Nov 22, 2015 1:33 pm 

Joined: Sun Oct 19, 2008 12:58 pm
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Location: Chicago USA
dinwitty wrote:

I dig dugged, I need to see a full circuit of this what the transformer is functioning for, if for just the cooking utensils or controlling other apparatus on the Liner.


Transformer? AC? Isn't the cooking done with trolley DC or was that too dangerous? That would be a lot of wattage to run off an MG and even if they did, why bother to turn it into AC and run it through a transformer if you can just generate the voltage you need? I am intrigued.

Assuming resistance heating, your original statement "The Electroliner uses its resistors as a cooking element in the diner." is technically correct. Presumably not part of the propulsion circuits but they are resistors and they do belong to the Electroliner so that's all true.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sun Nov 22, 2015 8:47 pm 

Joined: Mon Apr 30, 2007 12:45 am
Posts: 442
Location: Illinois
filmteknik wrote:
dinwitty wrote:

I dig dugged, I need to see a full circuit of this what the transformer is functioning for, if for just the cooking utensils or controlling other apparatus on the Liner.


Transformer? AC? Isn't the cooking done with trolley DC or was that too dangerous? That would be a lot of wattage to run off an MG and even if they did, why bother to turn it into AC and run it through a transformer if you can just generate the voltage you need? I am intrigued.

Assuming resistance heating, your original statement "The Electroliner uses its resistors as a cooking element in the diner." is technically correct. Presumably not part of the propulsion circuits but they are resistors and they do belong to the Electroliner so that's all true.


The "Liners" had a unique way of "heating" the stove. A motor-generator provided AC current to the stove, and there was an induction coil under each "burner". The pots and pans were heated by induction from these coils. The top of the stove would remain at a much lower temperature, minimizing the amount of hot metal a crew member could accidentally come into contact with.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Mon Nov 23, 2015 11:56 am 

Joined: Thu Feb 03, 2005 9:32 pm
Posts: 241
So it looked like what you wanted to run is a 32 Volt, 125 Watt lamp on a 72 Volt source. Just using Ohms Law to work that out the lamp needs a current of 3.9Amp.
Use the voltage drop across the resistor of 40V to get about 10 Ohms, it will need to dissipate 160 W.

Assuming the dim wattage at 75 and going through the same exercise you get about 18V, 2.3A at the lamp that works out to a total resistance of 23 Ohm, total wattage of 122.

So in theory I get a 10 Ohm in series with a 13 Ohm that is switched to short for bright.

Tungsten filaments are lower in resistance when cold as well as open circuit voltage on generators high so using “dim” when turning it on will extend the life of the lamp.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Mon Nov 23, 2015 12:00 pm 

Joined: Mon Aug 23, 2004 3:01 pm
Posts: 1436
Location: SouthEast Pennsylvania
The Electroliners' cooking pots and pans were the other coil
of a very inefficient transformer, it made heat instead of changing
much voltage.
Induction stoves can still be purchased for expensive kitchens, but
they require heavy and inelegant metal pots and pans that must be
kept right on top of the stove coil to get hot.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Mon Nov 23, 2015 7:53 pm 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
No doubt using eddy currents induced into the pots/pans to create the heat. You can induct into any metal that way. This also means you could charge your phone on the North Shore's cooktops if you had one of those inductive phone cases from Ikea.

Normally you make armatures and sometimes fields out of laminates to minimize those eddy currents, that is why you don't want to run a DC motor on AC - the field pieces are not laminated. A laminated field piece doesn't bother DC, which is why we can run the GG1 on DC.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Mon Nov 23, 2015 10:42 pm 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
Here is the resistor on the bench. Turns out I botched my previous measurements, resistance is actualy half my numbers above, which means I need one of these, not two. But can it handle all the current?

Here I put 6.00A at 25.90 volts into the high current section. This 155.4 watts of power stabilizes at 550 degrees F, and running for a half hour, the resistor is not glowing or showing any sign of distress.

Unfortunately this bulb calls for driving 7.5A through it, which would be 243 watts. I can't test that, I am at currentmax for this power supply.

And of course its value of 4.3 ohms falls shy of the ~5.0 ohms that field testing shows is needed.

Attachment:
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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Tue Nov 24, 2015 4:11 pm 

Joined: Tue Sep 22, 2015 12:36 pm
Posts: 177
I still say center tap the batteries. I really do not want to burn our lone operating locomotive down due to a glorified cab heater in a cabinet without ventilation.

Someone somewhere must make a solid state voltage controller that will fit our needs.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Tue Nov 24, 2015 5:55 pm 

Joined: Mon Apr 30, 2007 12:45 am
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Location: Illinois
sousakerry wrote:
I still say center tap the batteries. I really do not want to burn our lone operating locomotive down due to a glorified cab heater in a cabinet without ventilation.

Someone somewhere must make a solid state voltage controller that will fit our needs.

Why reinvent the wheel? Diesel locomotives have been using 32V headlight bulbs with dropping resistors since the 40's.

Jeff

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 1:46 pm 

Joined: Thu Nov 22, 2007 5:46 am
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And trolleys for a lot longer than that. With much higher voltage differentials. How did you power a 32v headlight when the only electricity on the car is 600v?

Yup. And that's installed on a wooden car.

Consider Westinghouse HL controls (Hand selected points, Line power as opposed to battery). How do you get 50-ish volt control voltage for an MU interurban when the car has no battery system, given that it needs to energize a varying load of 0 to 12 magnet valves depending on notch position and cars in train? Yup, resistor ladder! A stack of resistors constantly flowing between 600v and chassis, tapped near the bottom. Flowing current all the time - enough that the varying load won't vary the voltage beyond the magnet valves' rating. And it does work. Really. The Sacramento Northern cars ran that way for many decades, and we restored that system faithfully. It works as Westinghouse intended.

Yes, it rankled my eye when I first saw the design... but then again, I'm not at a museum to reinvent things. So I shut up, learned, and eventually got it.

The ancients didn't have buck converters, but they did have M-G sets and in the SN's case, dynamotors owing to their dual voltage 600/1500v. They could have put a 50v tap on the dynamotor, a reliable voltage divider at near 100% efficiency, using a machine that's already present and spinning. Several ways to skin that cat, and still, they chose resistors.


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