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Old 01-12-2012, 06:32 PM   #43
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Brookfield , Wisconsin
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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, 07:01 PM   #44
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Brookfield , Wisconsin
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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, 08:55 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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