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Old 01-12-2012, 10:26 AM   #41
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Originally Posted by TG Twinkie View Post
One might ask. With the notching characteristic of a PWM. Is it possible or does anyone know if this would cause static on a radio or possibly interfere with television reception.
I was in error I believe in the previous post. If the power consumed by the motor is 12 watts it would run at 1/4 speed not 1/2 speed. Since at full speed it consumes 48 watts.
I get no interference with the PWM motor controller. I do, however get interference in the stereo only with a PWM LED controller. Gotta work on that sometime. It's minor, but bugs me.

Again, I believe that is a function of the frequency.
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Old 01-12-2012, 10:34 AM   #42
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One other note about motors running on variable speed electronic drives, ie PWM's for DC and variable frequency inverters for AC motors. These drives can be hard on motors that are not specifically designed to run on these devices.
The variable frequency inverter is a different animal from the inverters used in RV 's. This type converts AC to DC then back to a modified sign wave AC. Much more complexed device than what is used in an RV.
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Old 01-12-2012, 05:32 PM   #43
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Resistor vs PWM

Typed in a response and all of a sudden it disappeared! Hmmm, must have been operator error. Thus will do individual responses.

Relative to resistor versus PWM, pwm turns on and off constantly, thus does not generate heat to reduce power. The on time versus off time determines the motor speed. I geneally use FETs in the four milliohm (0.004 ohm) range thus little power is dissipated. In fairness, I always have a cpu (say 20 milliamps at 5V) and switching regulator (kind of pwm for voltage supply) and thus do burn a little power and usually run that cpu fast enough to support CAN communications interface with same crystal. So the pwm approach uses far less power, but it costs "a bit more" than a series resistor.

Relative to motor turning on and off at high frequencies, the motor brushes on DC motors do this to spin the motor. Ya, doing it at higher frequencies can generate some electronic noise, but that is a design issue. Most of this can be eliminated via design, some by adding some noise filtering parts, but again, cost a bit. When power is low, would prefer the technology. When power is abundant and assuming resistor large enough to not overheat resistor will do the job.
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Old 01-12-2012, 06:01 PM   #44
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Market research

Thanks for the comments on furnace motor controls. We will have to "ponder" that a bit. Seems like a programmable device that could be used for "lots of applications" is probably the best approach. Again, not quite ready to provide that, but we have done this kind of stuff and, in fact, the programmable features are currently disabled in our first product.

Our first product in this market does have a motor pwm in it, but it is a "very small" motor and thus noise is not an issue. We are looking at some other areas with "pretty big" motors that are as big as anything on the trailer, but the initial discussions wanted a forwarding/reversing controller to "sell" for what the "parts cost". Hmmm, not a good product. Howver, a "system approach" can reduce the costs to probably acceptable levels.

So how do you service these "very cost senstive markets"? Well, one approach is the just stated systems approach. Our first product contains a color display / keypad that talks over CAN network to another module. Now this same display module could talk over CAN to the PWM module for configuration / tuning, diagnostics and so on, and thus "more features" are provided where perhaps you could set your desired speeds and so on and "not" buy a separate user interface module. Thus "system cost versus features" is superior to a stand alone product and possible at a slightly higher cost.

This kind of stuff isn't for everyone, but hey your car or tow vehicle is full of computers on these networks. So putting some of this stuff in trailers, if it adds benefits and if it "contains sufficient diagnostics" to enable the owner to identify the problem and usually fix it, then I think its acceptable. The issue is, if these communicating products are poorly designed and"fail", they will get a bad name, and never be used. So if vendors use sufficiently derated parts as is common in industry and vehicles, as well as eliminate all the "proprietary garbage" in both these industries and allow any trailer vendor to connect, you have a solution.

All that garbage said; "What applications in a trailer/RV would use a forward/reverse motor PWM module?" The greater the number of target applications the greater the likelhood of a generic product.


It appears this market has plenty of individuals with "courage" and many whom will constantly ask for "low cost" and thus an environment to keep small business guys like me honest. The older I get the more I am willing to "pay a little more" for something I know will work, and for a long time, then rolling the dice on cheap stuff. Heck, all those "apple user" comments I get on this sight some time ago indicates many seem to spend more on some stuff!

Looks like the mix here will be a lot of fun.
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Old 01-12-2012, 07:55 PM   #45
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Many DC motors today are permanent magnet type and have no brushes. I'm not sure about the furnace blower motor. Motors with brushes require maintenance. Permanent magnet motors are virtually maintenance free.
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Old 01-06-2018, 12:08 PM   #46
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I'm pretty good with electrical, but a little weak in electronics.

What I am trying to accomplish: I want to be able to control my furnace blower speed to be able to recirculate air to the holding tanks in winter while utilizing electric heat (shore power) AND with intermittent furnace operation. So... fan running half speed, thermostat commands furnace on....speed automatically goes to full speed, and upon thermostat command "off", fan speed returns to half speed.

What I have done: Got a PWM motor controller (see pic #3). It, unfortunately controls the ground circuit. Problem is: In order to control motor variably, I must disconnect motor ground. (See pic #1) This prevents the fan from going to high speed when thermostat commands furnace on. Then I get no fan sail switch input and controller throws the sail switch code and, of course, no gas ignition.

I need to be able to give the fan motor an uninterrupted ground when the thermostat commands on.

Pic #2 shows a proposed fix, but I have questions before I start letting the smoke out of the electronics.

1)Can I use a relay with the primary circuit from the blue thermo wire (is that blue wire 12 volts and enough amperage?) to ground with the secondary from motor ground wire to ground?

2)Does this need to be a transistor instead of a diode protected relay? (this is where I am particularly weak) What do I walk into Radio Shack and ask for?

Hope this makes sense and I apologize for the pic quality!

Thanks!
Whatever happened to the idea of keeping things simple ?
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Old 01-06-2018, 02:16 PM   #47
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Whatever happened to the idea of keeping things simple ?
It still lives within simpletons, apparently.
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Old 01-06-2018, 03:16 PM   #48
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May have to use an Arduino or the like to control the speed relays and accept thermostat input. Then after a short delay, initiate full speed to blower and activate ‘real’ thermostat input to the furnace to get heat running.

Could be also done with just relays but gets ugly in a hurry
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Old 01-07-2018, 09:10 AM   #49
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It still lives within simpletons, apparently.

I am a certified simpleton, one completely dedicated to living life by the KISS method. And my wife thinks I am not good looking but at this stage in our lives she sure appreciates the fact that I am very handy.
I am 6' 3'' and can get her stuff down from high places.
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