Why the "resistor with Thermal Link" in Fan-Tastic Fan? - Page 2 - Fiberglass RV


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Old 11-05-2017, 09:41 PM   #21
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Name: Richard
Trailer: 2009 Scamp 13'
Alberta
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So here is a chart of the results I got from following Gordon's instructions for finding the weak link in this system. I've taken voltage readings with a multimeter at the various points (A through F) and recorded the voltage under 12 different situations. First, I've taken readings with the reverse switch set at OUT. These readings include the voltage as I've changed the 3-way switch from OFF, to #1, to #2, and to #3. Then I've turned the reverse switch to the neutral/off position and taken readings with the 3-way switch at different settings. Finally, I've turned the reverse switch to draw air IN and then taken readings at different 3-way switch settings. After I took all these readings at A, I moved on to B (See Gordon's wiring chart for the letters). I think the really small numbers that showed up on the meter (.01 and .03) are irrelevant, but I recorded them anyway. They seemed kind of unstable, but they did register something differently than what I've recorded as "0". The 12.55 voltage perhaps wavered a wee bit, but only perhaps down to 12.47 at the lowest. I don't think that's relevant. Anyway, if these numbers show the source of my problem to anyone who knows about electrical circuits, I would be delighted to be enlightened!! The problem has me stumped, but it's not the first time.
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Old 11-06-2017, 06:37 AM   #22
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Name: Gordon
Trailer: 2015 Scamp (16 Std Layout 4) with '15 Toyota Sienna LE Tug
North Carolina
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Consider your readings that are well under one volt to be zero. Consider anything within a volt or so of your current battery voltage (or converter output) to be “full voltage.”

Working from the input side, you should always have “full voltage” at points A, B, and C. You should also have “full voltage” at D with the 3-way switch in any position OTHER THAN off. That is because the resisters for switch position low and med speed are very low value will not drop the voltage very much at low and med setting, and there is no resister involved at the full speed fan setting. If the fan is running, that load will drop the voltage a little but again, not much. You can eliminate that variable by putting the reversing switch in the off position.

With your reversing switch in the off position, your readings are what they should be. But with the switch in the in or out position, when the fan should be running, the voltage drops to “zero.” As I mentioned, I would expect to see a slight voltage drop with the load of the fan on the circuit, but not much and certainly not a drop to “zero.”

So the $64,000 question is why is the voltage dropping to zero when the fan should be running? Since the voltage is zero at the first connection in the fan assembly, the fuse “hot side,” I now suspect a problem with the wiring in the camper. Perhaps a bad connection so that you have full voltage with no load, but not with a load. This would be a less likely problem but off-hand I can’t see how anything in the fan assembly would drop the voltage to zero at point A (fuse hot side) since this is before anything in the fan assembly. (A dead short would, but it would also blow fuses so it can't be that.)

Perhaps I am missing something - I feel like I might be. In that case hopefully someone else will have an idea. But at this point I think I would disconnect the fan from the camper's power, get some zip cord (wiring) and connect the Fantastic Fan directly to a battery (or minimum six amp 12 VDC power supply) using points A and Z. If the fan then works as it should, that would indicate that the camper’s wiring is the problem.

I might also call the company and get a conversation going with a tech support person, and kindly ask him or her to review this thread. Most companies would not go to that much trouble but I think they might.
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Old 11-06-2017, 12:29 PM   #23
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Name: Richard
Trailer: 2009 Scamp 13'
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Many thanks, Gordon, for your guidance. I'll follow up with your suggestion re: using points A and Z. A part of me is pleased to see these results suggest I'm not a total electrical dolt! But another, greater part of me would like to get this fan running! If anyone else can see the problem hidden in this table of figures, please chime in. I will say that Fantastic Fan folks have been excellent about mailing out replacement switches, but I haven't actually engaged a tech support person for this particular electrical gremlin.
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Old 11-17-2017, 12:29 PM   #24
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Name: Richard
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OK, weather and life finally permitted me to follow your suggestion, Gordon, regarding connecting the Fantastic Fan directly to the battery using points A and Z. First, I double-checked the voltage figures I had posted, and confirmed their accuracy. Then I made the connection directly from the battery with two 16 gauge wires. The fan operated like a charm, EXACTLY as it is supposed to, including all three speeds (plus OFF) and intake/exhaust/OFF!!! So does this show that my long-standing problem is with the camper's wiring, not with the Fantastic Fan wiring and switches? But if the problem is with the camper's wiring, I don't understand why I was getting ANY voltage readings.
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Old 11-17-2017, 03:20 PM   #25
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Do you have the fan cover (black twist knob) elevated enough to allow the fan to come on? There is an interlock of sorts that will keep the fan from coming on if the vent cover isn't open far enough. It may have already been posted, but I just haven't seen anything that discussed this in the thread.
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Old 11-17-2017, 04:13 PM   #26
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Yes, that's been looked after long ago, but you'd have to read this Tolstoy-length novel to find it on this post! Thanks for the suggestion, but I think I'm much farther up the proverbial tributary by now.
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Old 11-17-2017, 05:01 PM   #27
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Originally Posted by Richard Davis View Post
OK, weather and life finally permitted me to follow your suggestion, Gordon, regarding connecting the Fantastic Fan directly to the battery using points A and Z. First, I double-checked the voltage figures I had posted, and confirmed their accuracy. Then I made the connection directly from the battery with two 16 gauge wires. The fan operated like a charm, EXACTLY as it is supposed to, including all three speeds (plus OFF) and intake/exhaust/OFF!!! So does this show that my long-standing problem is with the camper's wiring, not with the Fantastic Fan wiring and switches? But if the problem is with the camper's wiring, I don't understand why I was getting ANY voltage readings.
Well if it works 100% correctly when connected direct to a battery, but not when connected to the battery via the camper's wiring, then there is no other possibility other than a problem with the camper.

Why do you get voltage at a point that will not run the fan? Because something is restricting the current. If, for example, one of your wires supplying power to the fan was damaged so that only one thin strand of wire (out of maybe 25) was still intact, then you would still see the full voltage but the little wire would not be able to pass enough current to run the fan. That is one possibility but there are others included corroded connections. None are likely going to be easy to find.

Voltage is like water pressure.. current is like the quantity or amount of water. You can have very high water pressure but if you pipe the water through a nurses syringe with a small needle, you wont get much water at all.

I'm not even sure how Scamp wires the power to the fan. In mine the wire seems to run under the rat fur toward the port side rear upper cabinet but off hand I dont know where it ties into the rest of the system. I think I would go over every connection from the middle of the camper to the rear that I could reach. Remove wire nuts and make sure wires are making good contact when you put them back on. Check connections in the fuse block, clean anything that needs it. Visually check the length of any wires you can see (but most is hidden).

If none of that works, run a new line to the fan and tape off the old one. If you have a fuse block (power distribution box) like I do, then you can add a fuse to create a new circuit and run wire from there to the fan (actually the fan's built in fuse holder). Making it neat however, under the rat fur, is not easy.. others have used stiff piano wire to fish the line under the rat fur.

Anyone else have an idea?
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Old 11-17-2017, 05:54 PM   #28
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Name: Richard
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Well, as ever, thank you SO much for this good explanation as to why I'd be getting voltage but not adequate current to run the fan. And thank you SO much for getting me this far with a diagnosis of "why the wheels don't roll." Having been able to trace things down this far, I think the next obvious step is to take out the butt splice connectors that join the 2 wires from the Scamp to the 2 wires to the Fantastic Fan unit. I can only hope that is the point where things go South. Thanks again, Gordon, and all the other helpful posters.
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Old 11-17-2017, 06:31 PM   #29
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Originally Posted by gordon2 View Post
Well if it works 100% correctly when connected direct to a battery, but not when connected to the battery via the camper's wiring, then there is no other possibility other than a problem with the camper.

Why do you get voltage at a point that will not run the fan? Because something is restricting the current. If, for example, one of your wires supplying power to the fan was damaged so that only one thin strand of wire (out of maybe 25) was still intact, then you would still see the full voltage but the little wire would not be able to pass enough current to run the fan. That is one possibility but there are others included corroded connections. None are likely going to be easy to find.

Voltage is like water pressure.. current is like the quantity or amount of water. You can have very high water pressure but if you pipe the water through a nurses syringe with a small needle, you wont get much water at all.
I think this is an excellent description to apply in troubleshooting the basic circuits in our trailers!

We think of 12 volt DC wiring for simple devices such as lights and fans as being either "on" or "off", but this is an excellent description of how it can fall somewhere in between and perplex us... I've been caught out by this sort of thing before.

There is always some loss whenever current is run through a conductor, but we get used to simply working with "did the device turn on or not?".

Unless we see a dim light bulb, or something similar, it's easy to forget there is a range between "on" and "off", and to not consider this type of scenario.
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Old 11-17-2017, 08:31 PM   #30
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Name: Richard
Trailer: 2009 Scamp 13'
Alberta
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So I cut out the butt splice connectors to see if one of them was the point at which I was losing current, but no such luck. Now that I know the problem is not with the Fantastic Fan unit, I was thinking it was time to describe the problem to Scamp and see if they could suggest where at the fuse box I might start looking, given that the fuse for all the interior/exterior 12V lights seems to be the same as the fuse for the Fantastic Fan. (I was hoping I might be wrong in thinking this). As a last check, I turned on all the 12V lights, BUT the 12V light over the main table/bed area did not come on! I checked the bulb and it is fine. This light was working a month ago when I had the Scamp on the road for a month. So this seems a very strong suggestion that I have a (growing!) wiring or wiring connection problem in the ceiling, and given that it has been raining a lot this past month, I'm guessing my electrical problem is water-related! Not what I wanted to hear! But it sure makes sense given what Gordon has said about corrosion, etc. I have had small leakage around the Fantastic Fan, but that was (I thought) fixed two years ago by having it professionally fixed with Dicor Lap Sealant at a good RV agency. The fan was working well at the time the Lap Sealant was applied; I know it worked 6-8 months after, as well. So I'm now wondering if -- in addition to the electrical issue -- I'm getting water in at the Fantastic Fan or perhaps even back at the main ceiling vent above the table. And that possible water might be creating the electrical issue. Oi veh.....
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Old 11-17-2017, 08:58 PM   #31
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Yes Scamp could help you figure out where to look. In my 16 footer, the fuse block (PDC) has one 20A fuse for everything in the back, and another for everything in the front. (Also one for the charge line to battery, one for fridge and one for furnace). So everything in the back is wired off one fuse / circuit, but exactly how is hard to know. It appears that a two conductor wire comes to the port side reading light (above the dinette seat), and it is connected to another two conductor wire that I assume goes to the reading light on the starboard side rear. The connection for the fan to this circuit could well have been made under the ratfur and therefore be inaccessible.

It does seem likely that the light problem is related. Is the fixture getting power? It does not seem as likely to me that the prior leak is the problem, but it might be.
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Old 12-02-2017, 05:28 PM   #32
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Name: Richard
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Sorry once again for the long silence, but we only had two days in November that it didn't rain!! I have been able to determine two things, however. 1) According to the multimeter, there is normal voltage coming to the light over the bed/dining table whenever the light is switched on. I'm not sure if this is a problem like the fan: that is, the voltage is normal, but there's not enough current to light the bulb (or run the fan). 2) There IS water leaking in at the forward/driver's side corner of the Fantastic Fan unit!!! I have the fan unit covered on the outside now, so no more water is seeping in (that also tells me the leak is coming from around the fan unit itself and not coming in elsewhere but draining at the fan unit. That's a relief). The forecast for next week is for much better weather, so I might be able to pull the fan unit apart again and track down the faulty connection and also to try to find the source of the leak.
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Old 12-02-2017, 07:20 PM   #33
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Originally Posted by Richard Davis View Post
...1) According to the multimeter, there is normal voltage coming to the light over the bed/dining table whenever the light is switched on. I'm not sure if this is a problem like the fan: that is, the voltage is normal, but there's not enough current to light the bulb (or run the fan). ...
Yes you are on to something here....
I had a similar situation with the front outside light, and while I should have been able to figure it out, for a time it had be stumped so I asked for help in this forum.

What I found was that the voltage at the light socket was normal when the switch was on (~12-13 VDC) but with the bulb in the socket, the light would not come on. I replaced the incandescent bulb with a LED bulb and suddenly it worked. In hindsight, that was the clue I needed. It was not an intermittent connection that worked sometimes but not at other times. It was the lack of current getting to the bulb. The incandescent requires a good deal more power than the LED, so it did not light, but the LED would shine with only a slight amount of current.

It turned out that the bottleneck in my wiring was in the switch at the light fixture. Once the switch was cleaned up (or it could have been replaced), the light works fine.
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Old 12-03-2017, 01:34 PM   #34
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current == voltage / resistance. thats the Law. Ohm's Law

so, if you have voltage with an open circuit, and you put a load (resistance) across that voltage and now you don't have voltage, there must be resistance upstream.
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