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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 1:59 pm 

Joined: Tue Sep 22, 2015 12:36 pm
Posts: 178
Quote:
Why reinvent the wheel? Diesel locomotives have been using 32V headlight bulbs with dropping resistors since the 40's.


I understand your point but I know the application our friend Robert is using this on and we really do not have the spare power to waste heating the electrical cabinet due to the poor condition of the aux generators in that unit. They barely have enough current to charge the batteries and excite the mains.

But this is an argument for another time and place.

To be honest the locomotive in question needs a wiring overhaul by a qualified shop, but financially this is not in the cards and knowledgeable volunteers are not available in our neck of the woods. So zip ties and electrical tape have to hold together the other 4 layers of bailing wire and duct tape dating back to the 40's.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 2:05 pm 

Joined: Tue Sep 22, 2015 12:36 pm
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And from a safety standpoint I don't want a 500 degree resistor sitting right behind a 16ga steel panel door with no ventilation or cooling air in a small cab that is often standing room only. Where one hard brake application will cause 2nd degree burns on an unsuspecting crew member or guest because they were were standing in the right spot.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 8:19 pm 

Joined: Mon Apr 30, 2007 12:45 am
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Location: Illinois
sousakerry wrote:
And from a safety standpoint I don't want a 500 degree resistor sitting right behind a 16ga steel panel door with no ventilation or cooling air in a small cab that is often standing room only. Where one hard brake application will cause 2nd degree burns on an unsuspecting crew member or guest because they were were standing in the right spot.


From a safety standpoint, having a cab that is crowded to the point of being "standing room only" is already a serious safety issue, with or without a hot spot on the electrical cabinet.

Jeff

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 8:22 pm 

Joined: Tue Dec 11, 2012 1:40 am
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Probably none of my business? But, what diesel are we talking about?

Robert


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 8:33 pm 

Joined: Mon Apr 30, 2007 12:45 am
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Location: Illinois
sousakerry wrote:
And from a safety standpoint I don't want a 500 degree resistor sitting right behind a 16ga steel panel door with no ventilation or cooling air in a small cab that is often standing room only. Where one hard brake application will cause 2nd degree burns on an unsuspecting crew member or guest because they were were standing in the right spot.

Alternative suggestion(s)
a) mount the resistor(s) under the hood(s), up near the headlight(s), away from the "occupied" cab area. Should be more airflow in that area as well

b) Mount it to a fireproof, insulating material, like Transite (or the modern equivalent), and mount that to the support structure of your choice

Jeff

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Wed Nov 25, 2015 8:48 pm 

Joined: Fri Mar 26, 2010 11:43 am
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Location: Floyd, AR
If you wanted something more efficent, a PWM dimmer/reducer wouldn't be hard to make. But if your aux gen is 7 amps away from death you might have bigger fish to fry.

Which, what, and where is this unit? Maybe I can help you out some time next year.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Thu Nov 26, 2015 12:16 pm 

Joined: Tue Sep 22, 2015 12:36 pm
Posts: 178
The unit is a ge 44 tonner located in southern Michigan, it is of 1944 vintage.

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Nov 27, 2015 7:23 pm 

Joined: Fri Mar 14, 2014 11:44 pm
Posts: 23
Quote:
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.


That's a bit too hot. It is a dropper, not a cab heater. I would say not more than 300F surface
temperature, since this is a continuous load.

You are only using part of the resistor body, so the wattage is de-rated.

Does it have to be this particular resistor? Why not order what you need out of the Digikey or
Allied or Newark etc. catalog and you'll have a modern, reliable resistor with a known rating.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Tue Dec 01, 2015 6:47 pm 

Joined: Thu Nov 22, 2007 5:46 am
Posts: 2447
Location: S.F. Bay Area
Western Maryland 75.

The resistors are 3"x12" (11" bolt centers). The two OEM resistor positions are vertically mounted deep inside the high voltage electrical cabinet. Two additional resistors were added (I suspect based on a factory bulletin) bolted to the underside of the top of the electrical cabinet. I am not happy with that position because there's no convection.

We use one headlight (the other aims back into the train). Its resistors are in the OE site, so to work around it, I used the other (top) site for my test rig. Its job was to provide valuable measurements. Now that I know the resistor values I need, I am redesigning it to fit the OE form factor so it can go in the OE site.

The GE resistors I tested above, I suspect they are intended for headlights very similar to this one, and similar to the Ohmite resistors described in the link several posts above, intended to run at 675F at rated power. I agree with several others, I'm not comfortable with that. Maybe I'm a wuss.

I’d actually prefer a buck converter, preferably in CC mode. Doing X doesn’t mean I’m against Y, it means I’m worried about project momentum. Projects at SMRS tend to stall out. Case in point the auxiliary generators.

The auxiliary generators have issues, and the full skinny can be found here.
http://www.wolfharper.com/rail/smrsdocs ... port15.pdf
The upshot is that the previous owner retrofitted modern regulators, tore out too much stuff, and left out a circuit which prevents a generator overloading when the other engine is started. That needs to be restored, and then we need to rewind and/or service at least one generator. (preferably both, since the ability/craft of electrical firms to do this work is slowly being lost, and we will want to enter that long dark with equipment tip top.) The project is stalled because the Board is reluctant to spend the $400-500 for proper contactors, which certainly precludes the $3000+ to have an auxiliary generator rebuilt.

Our "high" resistor is 5 ohms and flows 7.5A based on testing, for 281 watts.
Here is a picture of the test rig, which I plan to dismantle and repackage into the smaller OE form factor. Each resistor is 1 ohm, 100 watt and 6.5" long.
Attachment:
File comment: resistor unit at Techshop
IMG_6698.jpg
IMG_6698.jpg [ 48.65 KiB | Viewed 1223 times ]


Jeff, I don't know your basis for specifying 300 degrees F surface temp, but that's a tall order. Assuming 80F ambient and 220F temperature increase, and looking at the Ohmite data sheet linked on page 2, that requires derating the resistors to 18-20% of rating. Which requires a 1500 watt resistor. And then another 750w, 6 ohm resistor for the "dim" mode. Resistors of that size would be physically difficult to fit in the present locations, even using the undesired top position.

Up until now, my plan was to use five 1-ohm 100W resistors, for $35, which works out to 53% of rating, 400F rise (480F surface temp). Plus three 2-ohm 100W resistors for the "dim" circuit, also running at 53% of rating when used. This package would fit in a single OE location and the top positions would not need to be used.

I could, instead, use ten 100W resistors at 27% of rating for about a 280F rise (360F surface temp). Added to the six 1 ohm resistors to make up the "dim" side, that would mean mounting 16 resistors, but it would fit if we really stacked them.

The last option would be use resistors designed for heatsinks and use "PC CPU cooling" technologies like heat pipes or water cooling (I would be reluctant to add them to the nearby #1 engine's cooling loop since it may not be running.) But at this point, we've exceeded the difficulty level of a buck converter by a stretch. Like I say, 300F is a tall order!


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Dec 04, 2015 1:02 am 

Joined: Fri Mar 14, 2014 11:44 pm
Posts: 23
It depends on what else is around. I'm not familiar with your equipment but I can see
a number of factors that would de-rate the "nameplate" capacity of a wirewound vitreous
enamel power resistor in that application, including elevated ambient temperature, enclosed
space, and several resistors grouped together.

The figure of 300F is a very conservative one used in electronics work such as circuit board
mounted. If there is less "sensitive" stuff around then you can go higher. But if the resistor
is running at over 600F then you'll need to use high-temperatue insulator on the wires leading
to the terminals. This is a continuous load so it will actually reach that temperature, no 'cheating'
by saying it is an on/off load.

No matter what you have to dissipate a fixed amount. So it is a matter of spreading it out to
the most surface area that you can get away with subject to your mounting limitations. If you can
do the 10x100W job that sounds reasonably conservative. If not, the 5x100W will be OK as long
as it has enough clearance from heat-sensitive equipment.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri Dec 04, 2015 6:12 pm 

Joined: Thu Jan 12, 2006 10:10 pm
Posts: 670
Location: Iron City
Use a CM57 contactor. The CM15 is long obsolete.

DPK

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sun Dec 06, 2015 6:06 pm 

Joined: Thu Nov 22, 2007 5:46 am
Posts: 2447
Location: S.F. Bay Area
The mounting point is inside an electrical cabinet not wildly different from that in this photo, fairly typical of this family of engines (photo being a GE 25-ton). That giant array of resistors is not present on our unit, similar sized resistors are mounted individually on 3x12 blocks as you see the other blocks mounted.
http://www.locomotives.net/images/elect-cabinet-X.jpg

I threw three prices at the Board and they went for the middle one, which lets me do the lower-temp 280 degree rise resistor array (16 resistors)... or do the higher-temp 400 degree rise array and hold back some cash for an electronic solution. Although really I expect the cost of that to be low. (time being another factor).

In this later generation of GE 44, GE had rearranged things so all the traction current is in the front cabinet (along with some battery voltage stuff, e.g. the headlight resistors) and the smaller rear cabinet is exclusively battery voltage stuff. It's obvious they put some thought into it, and intended to make it reasonably safe to work in the rear cabinet while underway (e.g. changing fuses, adjusting voltage regulators).

I'd love to learn more about the CM57 contactor. Google has not yielded much.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Sun Dec 06, 2015 7:45 pm 

Joined: Thu Jan 12, 2006 10:10 pm
Posts: 670
Location: Iron City
Off the top of my head...certainly not all inclusive:

CM 57 were applied as the Fuel Pump and Generator Field contactors in both Alco Century and GE U Series (74 volt coil) and in several applications in NY MTA M-series commuter cars (32 volt coil).

CM57 features the encapsulated (blue) coil that is characteristic of later model GE equipment.

A number of different control interlocks could be applied to the CM57 such as AF41, etc.

FWIW, Logan Corporation of Nitro, West Virginia used to be GE's distributor for material applied to the various permutations of the GE twin-engined switcher line.

DPK

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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Mon Dec 07, 2015 9:56 am 

Joined: Tue Aug 24, 2004 3:07 pm
Posts: 641
For what it's worth, the GE drawing for the resistors in the original inquiry does not show any wattage rating for any of the variations listed.


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 Post subject: Re: Watt's the wattage capacity of this resistor?
PostPosted: Fri May 06, 2016 4:13 am 

Joined: Thu Nov 22, 2007 5:46 am
Posts: 2447
Location: S.F. Bay Area
JeffH wrote:
The figure of 300F is a very conservative one used in electronics work such as circuit board
mounted. If there is less "sensitive" stuff around then you can go higher. But if the resistor
is running at over 600F then you'll need to use high-temperatue insulator on the wires leading
to the terminals. This is a continuous load so it will actually reach that temperature, no 'cheating'
by saying it is an on/off load.

No matter what you have to dissipate a fixed amount. So it is a matter of spreading it out to
the most surface area that you can get away with subject to your mounting limitations. If you can
do the 10x100W job that sounds reasonably conservative. If not, the 5x100W will be OK as long
as it has enough clearance from heat-sensitive equipment.


And that's pretty much what I wound up doing: upsizing the resistors even more, aiming for 300F operation. . I was able to obtain the enormous 1000W resistor at a workable price. It is precisely the resistance needed for "bright". Six of the smaller resistors mentioned earlier are still involved, they add to it for "dim". TechShop's IR thermometer failed (and their power supply can't kick 250W anyway) but bench testing at lower power levels gave temperatures as expected.

As with all things electrical, it's 90% physical, and the mounting frame went through four iterations. Here's the last, without the adapter plate that lines it up to the holes on the bracket.

Attachment:
hl-resistor-on-bench.jpg
hl-resistor-on-bench.jpg [ 56.37 KiB | Viewed 752 times ]


Here are the resistors on the unit. The mounting locations are the same as the original headlight resistors; as-built there was one resistor per headlight. As-we-received-it, those locations held two resistors connected in series to regulate one headlight; and the now-disused "ceiling" site held two more for the other headlight.

Attachment:
hl-resistor-in-engine.jpg
hl-resistor-in-engine.jpg [ 108.25 KiB | Viewed 752 times ]


The top connection is not made on the left resistor, which means the front headlight is stuck in "dim". That is because the front headlight has not yet been converted to the new 250W 34V type.

There had been two major alterations to the wiring. The original wire connections had been extended to reach the ceiling site; that work was done poorly and is gone. Most wires are now the original wire and lugs, except for a few extensions done with new-stock wire courtesy Western Railway Museum.

The other alteration was a second set of headlight dim switches mounted on the cab sidewall. The wires to those are bundled up. Dimmer switches work by shunting part of the resistor bank. As found, these shunted a different section of the resistor, giving 4 levels of brightness. I don't know why. Perhaps the side switches were changed for bulb type. I think more likely they were meant to be found in a hurry by touch, unlike the row of 10 identical switches at the engineer's feet, devilishly easy to hit the wrong one even in the daylight.


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