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Delco and other Low Voltage DC Light Plants Antique Generators, Light Plants, Typically 24, 32 or 48 volt although some are 110 volt. DC Lamps, Motors and appliances.

Delco and other Low Voltage DC Light Plants

Calculate the correct resistor to use?


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  #1  
Old 10-14-2018, 03:21:47 PM
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Default Calculate the correct resistor to use?

My brain hurts....

This is the wirewound resistor off of Western Electric light plant #2 that I have. It is still intact, where the one on #1 light plant is a mess of broken magnet wire ( cannot save it period).

The purpose of it is in the charging circuit, when in battery charge mode, the current is limited through this to the battery. When in overcharge mode, the small portion of the resistor is used via a knife switch to go from one to the other. I get it changes the resistance to either charge at a reasonable rate or overcharge to equalize the battery set.

I need to figure out what wirewound power resistor to use. So far I have tried to meter it from lead to lead on both sections. Perhaps 175 milliohm for the large side and 50 milliamps for the small one. That does not make sense to me..

Ok, then tried to figure out amps. Hooked a 12 volt battery on one lead and a meter lead on the other and one on the battery. Large section dropped from 12 volts to just under one. Small section dropped to 1.5.

Then I put a 12 volt bulb in series with it and measured at battery. About half an amp for both. I am going to use 3 12v garden tractor batteries.

The specs for the plant are 1500 watts at 40 amps at 40 volts. It uses a charging relay in series with this resistor. The literature suggests to adjust it so the relay opens when the current drops to about 14 amps, stopping the charge. The literature says the batteries are fully charged. It supposedly takes 7 hours to charge the 180 amp batteries.


I've been on those sites with the calculators for watts and power resistors The literature does not specify the ohm or watt rating for this resistor. I am not coming up with a plausible replacement.


Could someone hurt their brain too and let me know what you think??


Thank you
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Old 10-14-2018, 03:49:38 PM
Zephyr7 Zephyr7 is offline
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Default Re: Calculate the correct resistor to use.....

Hmm. You need to measure the resistor you have correctly to be able to get a replacement. To get the value, measure resistance across the two ends (the tap in between doesn’t matter for this test). You should see some number of ohms, although there are fractional ohm resistors out there. You mention seeing milliohms and also milliamps so I’m not sure what you were measuring before.

If you can’t measure the resistance directly, try connecting the resistors ends (ignore the tap again) in series with a lightbulb and an ammeter. Connect 12v dc or whatever the supply voltage is. The ammeter will tell you the current the lamp is drawing through the resistor. Measure the voltage across the ends of the resistor with a volt meter. From this info, you can calculate the value of the resistor using ohm’s law like this:

Volts you measured = current you measured * R
Solving for R gives:

Volts you measured / current you measured = resistance

This method will work reliably for even very small resistance values.

You’re going to have to guess at the power rating. I’d get a resistor that is close in physical size to the one you have and try that. You need a variable tapped wire wound resistor which will have a similar sliding tap to what you have now.

I hope this helps you with your restoration work.

Bill
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Old 10-14-2018, 03:59:29 PM
Vanman Vanman is offline
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Default Re: Calculate the correct resistor to use.....

Does that resistor actually go in series with the battery and generator armature? Or in series with the generator shunt field?
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Old 10-14-2018, 07:35:52 PM
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Default Re: Calculate the correct resistor to use.....

Thank you Bill. I did connect one end of it to the 12v battery, and had a 12v light in series with a meter. I had measured half an amp. That would give me a 24ohm resistor. I think the half an amp will be the same though 36v?


I believe the resistor is in series with the battery and series field (reality check welcomed...) Here is the diagram for it.
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Old 10-14-2018, 10:35:36 PM
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Default Re: Calculate the correct resistor to use.....

Zephyr7 looks like from the diagram there are two separate resistances. I would try measuring each resistance using sharp tipped probes. May have to measure from each end of each resistance in several places if resistance wire is broken in several places. Should get an approximate resistance for each resistor. I think I even confused myself... Allie
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Old 10-15-2018, 10:13:21 AM
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Default Re: Calculate the correct resistor to use.....

There are 2 separate windings of wire on the tube. You can see it in the picture. The wire is wrapped around a piece of conductor at each "end" of the resistance tube wiring for a total of 4 wires coming from it.

I have been able to pass current through it at .5 amp so far at 12 volts.

I am going to get a different meter to check what I had seen earlier. Milliohms just does not seem right at all....
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Old 10-15-2018, 11:03:49 AM
Zephyr7 Zephyr7 is offline
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Default Re: Calculate the correct resistor to use.....

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Originally Posted by Mike Schweikert View Post
Thank you Bill. I did connect one end of it to the 12v battery, and had a 12v light in series with a meter. I had measured half an amp. That would give me a 24ohm resistor. I think the half an amp will be the same though 36v?
It’s unlikely the current would be the same at a higher voltage. Assuming the lamp and resistor don’t change, 36v would give a higher current. If you are connecting the resistor directly across a 12v supply to see that 1/2 amps current, then the same resistor connected across a 36v supply will give 1.5 amps.

Quote:
Originally Posted by Mike Schweikert View Post
I believe the resistor is in series with the battery and series field (reality check welcomed...) Here is the diagram for it.
It looks like that resistor is actually two seperate resistors in a single package not connected in any way. That’s probably a custom resistor, you you’ll have to replace it with two seperate units. If you use the hollow cermic resistors, you can put a mica washer or two (these are insulating washers that can take some heat) between them, you can mount both with one long screw and maybe install it the same way the original resitor is mounted.

The sharp-pointed probes for the meter are a good idea. The points will poke through the oxide layer on the terminals to get a more reliable measurement. Poke them with some pressure, wiggle them around a little while keeping the point in the same spot, then hold them tight and take a reading.

If the resistance wire is broken you’ll need to measure the length of the wire and the resistance of the longest piece. Then you can calculate what the total resistance should be for the resistor so that you can order a new part.

Bill
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Old 10-15-2018, 01:31:08 PM
radiodoc radiodoc is offline
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Default Re: Calculate the correct resistor to use?

I've reread the original post. You have two power plants. Are the #1 and #2 referring to the model numbers or #1 refers to one of your plants and #2 refers to the other. If both plants are the same model, I would try measuring the resistance of the undamaged resistor and procure a couple standard value power resistors closest to the measured resistance. Allie
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Old 10-15-2018, 05:51:08 PM
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Default Re: Calculate the correct resistor to use?

Yes, I have two of these plants. The resistance tube pictured is what I thought was a good one.

After trying to get a continuity on what I think is the "good" one, I find that once you hit the magnet wire, I lose it. It is probably so corroded under the paint that its hopeless. I took it off the switchboard and I had it in my hand and cleaned the wire connections and where it comes off the roll. No dice. Tried measuring ohms and got nothing.

Soooo, I measured the remains of the other tubes wire, which is mostly torn off. It is .010 or 30 awg. It appears to be wrapped in one layer across the tube. I ordered a spool of enameled 30awg magnet wire, and am going to rewind the tore up one and see what I get. It will be tedious, but not impossible.

I'll report back when I get it done to see what it actually measures. I could probably count the turns on the intact one too if I have to.


I guess I should expect this from 100 year old tiny wiring that is exposed to the elements.....
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Old 10-15-2018, 08:42:22 PM
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Default Re: Calculate the correct resistor to use?

Mike if these are resistors, I am pretty sure they would be wound with Nichrome resistance wire instead of magnet wire. I would try using sharp probes and a VOM and pierce the "cotton" covering on the wire and try to get a value of the resistance. I have done this to resistors that had the value burned off of them. Allie
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Old 10-15-2018, 09:20:42 PM
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Default Re: Calculate the correct resistor to use?

Thank you for the correction to my thinking. I ordered that resistor wire as I hadn't known about that. I can use the magnet wire for coils on my other projects.....

I'll try to probe the other one harder. I can see they wrapped the resistance wire around larger gauge wire loops at each end of the run, Which are soldered to the wires top the switchboard, then wrapped it on the tube as you see in the pic. I could not get a intact reading at all probing at the actual resistance wire on either end of run. They were cleaned off with a Dremel and a brass brush. I could try scraping with a razor blade too.


The specs on the wire are 6.5 ohms per foot. It will be interesting to see how many turns it will be per foot on this tube. I'll measure out a foot, and then see how many turns it really is. It would be nice to replicate this and actually have it work, even though buying a new one is easier....
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Old 10-15-2018, 09:35:56 PM
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Default Re: Calculate the correct resistor to use?

Mike using sharp probes to go thru the "cotton" covering on the wire, you may have to try the probes in several places along the resistance. Even if you measure only half of the total resistance you would then double your reading. Allie
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Old 10-16-2018, 04:43:50 PM
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Default Re: Calculate the correct resistor to use?

Resistors can’t be wound with copper wire, the wire expands too much when it heats up so it gets loose. I’ve tried this you can only do it for low enough power levels that the wire stays cool.

Nichrome wire is not usually insulated so be careful when you wind it. You could use the enameled wire as an insulating spacer, wind both wires together side by side so that the enameled wire is always between adjacent turns of the nichrome wire. This should help you to keep the winding even, and then leave it in place to preserve the spacing and provide insulation. You can secure turns with glass cloth or kapton tape.

I commend you for your adventures in resistor building one has not truly entered the realm of electronic tinkering until one has built one’s own component-level parts.

I’m surprised your original resistor seems to be open everywhere. Usually there is only a break in the wire somewhere so measurements can still be made on the intact sections. Be careful when you poke your probes that you don’t break the wire.

Bill
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Old 10-16-2018, 06:19:52 PM
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Default Re: Calculate the correct resistor to use?

Many thanks!!

I fool with tube radios so have a little experience with coils, but not a wirewound resistor. I'll try probing it again. It does look intact, and usually the break will occur right at the beginning or end of it. I post this as I am sure there are others out there who may run into this on various plants. The wire on the original appears to have been varnished or potted by something. The turns appear to be close to each other, so not sure how they wound it without touching each other. The new nichrome wire I shopped around for was not insulated, so I will use the magnet wire to try to insulate it from itself as it is enameled.

The tube on the ruined one has ridges in it from the original wire. When I wrap it, will see if it will be just far enough away from each other not to short..dunno till I get it here....
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Old 10-16-2018, 06:52:51 PM
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Default Re: Calculate the correct resistor to use?

Quote:
Originally Posted by Mike Schweikert View Post
Many thanks!!

I fool with tube radios so have a little experience with coils, but not a wirewound resistor. I'll try probing it again. It does look intact, and usually the break will occur right at the beginning or end of it. I post this as I am sure there are others out there who may run into this on various plants. The wire on the original appears to have been varnished or potted by something. The turns appear to be close to each other, so not sure how they wound it without touching each other. The new nichrome wire I shopped around for was not insulated, so I will use the magnet wire to try to insulate it from itself as it is enameled.

The tube on the ruined one has ridges in it from the original wire. When I wrap it, will see if it will be just far enough away from each other not to short..dunno till I get it here....
It might have been coated with something like glyptal. It wouldn’t be a bad idea to do that on your rebuild once you have it working.

The ridges in the form may be part of the form. It was common in the old radios to have ceramic coil formers like that. The grooves may well be enough to hold the coils in place without needing any additional insulation. You need very little spacing between coils since the voltage across a single turn is only a small fraction of the total voltage across the entire resistor.

Bill
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Old 10-17-2018, 07:48:39 PM
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Default Re: Calculate the correct resistor to use?

While I am waiting for stuff to get here, I looked at the "good" original resistance tube. I carefully scraped off insulating stuff with a razor blade and attempted to get readings. I found that just digging a bit out, it fractured easily and was corroded. There just is no way to do it, its toast.. The "bad" resistance tube that had some stray wire still wrapped on it was looked at. I found that one turn around the tube end to end of one wire is 3 3/4" long. I then scraped either end of the wire and found it measured 3.4 Ohms. On the "good" resistance tube I could count the turns and came up with 92 give or take one or two. The short section was 12-13 turns.

New wire is 6.5ohms per foot. This old stuff would net about 10 ohms per foot, however I'll bet its higher due to corrosion, I could pay out a foot and remeasure too.....I think it would come out to 28.75 feet just for the big side, 4 feet for the small. If that is close, I get 26 ohms for the small, and 186 ohms for the bigger one.

Thoughts??
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Old 10-17-2018, 09:41:20 PM
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Default Re: Calculate the correct resistor to use?

Maybe you can get smaller diameter resistance wire that will allow you to rewind the resistor and get closer to the original value?

Another option is to get some high temperature insulating film. I’d recommend kapton. It would probably be easiest to use adhesive kapton tape. I’ve actually built custom resistors with kapton film, aluminum rod and bar stock, and magnet wire before. If you can’t find kapton tape for cheap, PM me and I can mail you some. I have several rolls of the stuff and can run off a little for you. Wind the resistor form with one flat layer, wind on the kapton tape, then wind another layer until you get to the resistance value you need.

Bill
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Old 10-18-2018, 08:34:52 AM
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Default Re: Calculate the correct resistor to use?

Appreciate the offer!. I do have glass tape coming so will see how that goes.

I was fooling with this calculator. https://www.rapidtables.com/calc/ele...alculator.html

Varying ohm and seeing what the amps were, it seems at 38 volts I'm looking at less than an amp of current. That seems low relative to the plant charging relay kicking off when it sees 12-13 amps. Perhaps its function is to slow down the rate of charge. The explanation of it is not very clear. This resistor could be 200 or even 250. The small could be as high as 50. There are commercial ones available that would work at a higher specified watt than the calculator is showing. I'm just not sure what is plausible.

Its a shame it wasn't specified in the original literature. It would have made this a lot easier.
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Old 10-18-2018, 01:01:26 PM
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Default Re: Calculate the correct resistor to use?

Glass cloth tape is probably going to be too fat to make a clean job of winding a second layer coil on that resistance tube. The kapton stuff is super thin.

I tried reading your schematic here on my phone, which was not all that easy to do! It looks like the smaller resistance on the resistance tube is a current limiting resistor for the shunt winding on the generator. The larger resistance appears to either bypass or adjust the “regulating relay” to charge the battery at a higher rate (note that the larger resistor is only in the circuit when that switch is in the “overcharge” position). The regulating relay is difficult to figure out from the schematic, especially using my phone to view it.

My guess is you won’t care too much about an overcharge feature for your battery (which might be for equilizing a string or real wet cells now that I think about it). The smaller value looks to be the more important one for the operation of the set.

Bill
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