| Author | Message | ||
| ChuckMC9 (Chucks) (69.3.75.22)
Rating: N/A |
Man, after that last foray into electrical theory I'm almost afraid to get started with this, but while ya'll are all riled up I might as well help you get it out of your system. ;)  The circled item costs $120 from the source, and I'm loathe to spend that for such a little thing. I cannot find any more info about the specs for the piece other than the mfgr. part #. I found something from RadioShak with the same resistance, but have a strong feeling that it would not be "robust" enough for this application.  So the answer is "X" watts, and the question is: How does one know?  | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
Can you look at the old one and is it the same physical size? I can't tell from the schematic what what the power requirements would be. But if the one in your unit is the size of a coffee cup, it will be a high-power unit and will be more expensive. You cannot get any markings off the old unit? Gary | ||
| ChuckMC9 (Chucks) (69.3.75.22)
Rating: N/A |
That's the problem. Ain't no old one there. The only thing on the coach that was missing. (besides the spare wheel/tire! ;) I've located a nearby non-running MC9 that *should* be a parts bus, but owner won't do it. Maybe I can pay him afew bucks for a look-see. It's easy to get to. This is the pot/knob in the middle of the driver's switch panel if anyone happens to have theirs torn apart. It's been too long since I've done anything with schematics - I don't *think* this pot is controlling the blower directly, or that would be major amps probably. Oh well, it's not my biggest project. I'll just keep freezing my buns off! Thanks Gary | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
Problem with that schematic is there are no values listed, with the exception of resistances. Is there more to the schematic than what is shown here? If you knew the other values you could figure it out, or just get a big 5Kohm Rheostat and go with it. Is this 12, or 24V system? I have a local surplus place here where I can get stuff like that for way less then a penny on the dollar. Gary | ||
| Darryl (68.184.119.198) Rating: N/A |
Chuck, I can't tell you what the power requirements are, but I can tell you what it controls. I belive you are talking about the rheostat that controls the heater valve. It would appear from your diagram that it acuates a relay which probably opens or closes the hot water heater valve. | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: N/A |
Chuck, To echo the comments above, there is not really enough information on the schematic to answer definitively. However, it appears to be a low-voltage, low-current control circuit and parts with fairly low power ratings should work. With a good meter, you should be able to put a part in, and then check to make sure the power going through it is OK. The bigger problem I see with the part you found is that it is what is known as an "Audio Taper" potentiometer. I would bet money that the application you have calls for a linear potentiometer. The difference being that the resitance level changes logarithmically (or exponentially, depending on your point of view) as you turn the handle of an audio taper, while with a linear, of course, it changes linearly. Radio Shack may not carry the value you need in a linear unit. Try Allied or Newark electronics or a similar catalog house. Once you have your part, install it and adjust it until the unit comes on. Then take your voltmeter and measure the voltage drop across the part. Immediately remove the part and measure the resistance setting that you had just set with an ohmeter. Take the voltage you measured and square it, then divide by the resistance that you measured -- this will be the power dissipated in the part, in Watts. Compare that against the listed rating of the part you bought. I would bet it will be well within, however, if you only have the part in place for the few seconds it takes to get these measurements, you probably will not melt it even if it is way over the rating (in which case, throw it away and get a part rated for the power you just measured). Hope this helps. -Sean | ||
| Greg Corbett (Kootking) (24.70.251.188)
Rating: N/A |
Sean is right on, this is a logorithmic potentiometer, you need a LINEAR POT. Your current draw is the mercury sensor, should be very little I would think, look for the resistors, match that wattage (about a 5 W max I would think). | ||
| Lyle Jensen (48gmc) (216.16.4.200)
Rating: N/A |
Call Caylor salvage in Kansas City at 785-878-3405 . They are one of the largest MCI salvage yards in the country . They will have the right pot in used condition for a good price | ||
| Stan (24.67.45.35) Rating: N/A |
I have several of these lying at my shop but the snow is too deep to get to it (maybe July). If I remember correctly, the original was a 2 watt wire wound. | ||
| Richard Bowyer (Drivingmisslazy) (24.196.191.70)
Rating: N/A |
As a last resort, go to NAPA and get a heater/defroster potiometer. They are cheap and rated at 25 watts I believe, and around 5K. Hook it up and see if it gets warm. I suspect it will not. Then do the measurements others suggested to find the correct value. Too big will never hurt. Too small and you will let all the smoke out of it. Also, the pot on your windshield fan could be used as a temporary fix to find the correct watt rating. Richard | ||
| ChuckMC9 (Chucks) (69.3.75.22)
Rating: N/A |
You guys are excellent. You can't imagine the gratitude I have for your participation and for this board. Thank you again for the forum, I@N. This issue is a low-priority one, but something that's been bugging me. Greg & Lyle, you win the prize. Look at the other resistors for their values, (duh) and/or call Caylor!!! Here's the full schematic, if you still want to look. You will have to enlarge to get the area of interest. | ||
| Jayjay (152.163.252.163) Rating: N/A |
Chuck...stop by your local electrical supply house and tell the counterman you need a 5k (5,000)ohm wire-wound, resistor, rated at least 250 watts, although a 100 watt unit will probably be sturdy enough. It should cost about $12 to $15 dollars, and I can't conceive of it being more than $25.00. An alternative is a McMaster/Carr or Graybar catalog. This is a dinosaur piece of equipment, and is a faily common item. One off of a 5,000 watt, 120V AC space heater should work well too, since the value of 5K is a nominal one and anything from 4.2 to 6.5K Ohms will probably do just fine. Don't worry about whether it's linear or logarithmic...all heavy duty wire-wounds are linear. Good Luck...JJ | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: N/A |
Chuck, Definitely do not need the 250-watt unit that Jayjay suggests. Now that you've posted the PDF I can read the whole print -- worst case (when the pot is at a dead short) you'll have less than half a watt through this at 24 volts (24^2/(920+600)=~.38watt). That's what I suspected earlier when I saw it was only a 16ga wire. Just make sure you get a linear unit, and anything off-the-shelf should work as long as it's rated at a watt or so. -Sean | ||
| Bus Jock (4.41.168.36)
Rating: N/A |
Chuck, The unit in my MCI is a 2W 5K Linear taper Pot. Available from ANY electronics store.. Sometimes from Radio Shack. The Log taper will put all the range at one end.. It will work but not well. I buy most of my electronics parts form: WWW.alliedelec.com WWW.newarkinone.com www.digikey.com www.goldmine-elrc.com Any of these will probably have the pot, unfortunatly I think they all have a $25.00 minimum. The pot you want is similar to the Newark 01F6272 ($18.60) or the Allied 753-5059-C3 ($10.59) Perhaps you need some swithches or something else to make up the $25.00 minimum. Radio shack commercial division (see web site) did not have a minimum last time I used them. email me if you have more questions. of course you need to remove the NOSPAM. I see that Radio shack shows a linear taper in the catalog. Its #271-1714. It says mounts in 5/16 hole, that says to me that it is not the standard 3/8 X 1/4 type pot.. However Its only $1.49 in my old catalog. Jock | ||
| Jayjay (205.188.209.8) Rating: N/A |
Sean, I suggested 100/250 watt ratings because wire-wounds seldom are seen smaller than that, and I felt that he may need the sturdy construction they provide, A similar unit on a GMC or Flxible is of that type. Yes, definitely overkill, but you will only have to install it once, (as opposed to install, test, remove,re-install, re-test etc.) and will never have to worry about letting the smoke out. ...JJ See 'ya at the Rallye! | ||
| Richard Bowyer (Drivingmisslazy) (24.196.191.70)
Rating: N/A |
JJ. Although I do not remember ever seeing a 200 watt WW resistor, I would suspect it would be about 12 inches in diameter, six inches thick and weigh in the neighborhood of 50 pounds. That would be one big resistor. LOL Richard | ||
| Jayjay (205.188.209.8) Rating: N/A |
Richard, the one on my 4905 (part of the graddustat system) is about 2 inches in diameter, and has # 6 screws for wire lug attachment, rather than solder holes. ...JJ | ||
| Richard Bowyer (Drivingmisslazy) (24.196.191.70)
Rating: N/A |
OK JJ, just curious. I have a 25 watt wire wound pot that is used to control my windshield fans and it is about 1-1/2 inch in diameter and about 1 inch tall. Just have never run into a 200 watt one. Richard |