REFLECTOR: PWM Controller

[Scott Derrick]

This is the controller I'm considering

http://www.criticalvelocity.com/item.php?itemid=spdc01

There spec sheet does mention RF interference with the standard methods 
on reducing it.

Scott

Joel Smith wrote:

> I was a little surprised to that you might be using an SCR controller 
> to vary the speed of a DC motor. In my opinion, you have to do some 
> unreliable things in electronics (none of which are RF quiet) to 
> de-gate an SCR under a DC load. I would have thought that with today's 
> technology, a MOSFET would have been utilized. They do not have some 
> of the bad characteristics of an SCR. They are more reliable and lower 
> on resistance which results in lower power dissipation.
>
> So I went to the web site suggested and the controller I found did 
> indeed use MOSFET. If you have a choice, I would recommend the MOSFET 
> design. It is likely to be noisy since they are using pulse width 
> modulation via square wave to control the power. While this reduces 
> the load on the controller, it will produce a lot of high frequency 
> harmonics in the square wave. It could be that their design is doing a 
> slow switch on the MOSFET to reduce RF noise. This might be reflected 
> in the specs by observing a higher dissipation in the controller. If 
> so, you would want to mount it in a location where it gets reasonable 
> cooling.
>
> The lighting circuit is probably not a problem. If it is, shielding 
> the controller and a low inductance capacitor across the controller 
> would probably solve the problem. Higher motor currents may take more 
> work.
>
> You should be able to get an idea via ground testing by turning on 
> your av radio, antenna connected, unused frequency, and open squelch. 
> Listen for noise as you vary the controller across the full range.
>
> I am surprised that they would say their controller emit no noise 
> unless they are linear. The say they are PW controlled.
>
> Joel
>
> Hiroo Umeno wrote:
>
>> I have built a MCU based annunciator panel that incorporates PWM 
>> based panel light dimming mechanism.  It also incorporates a slaved 
>> cabin light dimming solution based on its own logic.  (Each PAX has 
>> control over the brightness of their map lights but the PIC can set 
>> the maximum brightness up front).
>>
>>  
>>
>> I have not flown it and it has so far seen a fairly limited ground 
>> testing but so far, I have not seen any RF or audible interferences.  
>> The circuit only average a couple mA with 20mA peak current.
>>
>>  
>>
>> I will also be carrying PWM based camera servo control eventually.  I 
>> am more worried about that one since there is a motor connected to it.
>>
>>  
>>
>> Hiroo
>>
>>  
>>
>> ------------------------------------------------------------------------
>>
>> *From:* reflector-bounces at tvbf.org 
>> [mailto:reflector-bounces at tvbf.org] *On Behalf Of *NMFlyer1 at aol.com
>> *Sent:* Thursday, June 09, 2005 6:36 AM
>> *To:* reflector at tvbf.org
>> *Subject:* Re: REFLECTOR: PWM Controller
>>
>>  
>>
>> Scott,
>>
>>  
>>
>>  I am using a transistorized DC Motor controller for my fan speed. It 
>> is the SCR type.
>>
>>  
>>
>> I talked to the manufacturer of mine, and they said that there is no 
>> RF interference from the controller. There might be some from the fan 
>> motor itself they warned.
>>
>>  
>>
>> Just to be safe(er), I wired the switch/pot to the unit using 
>> shielded wire.
>>
>>  
>>
>> Since I still have my panel out for final wiring, I haven't been able 
>> to test the RF on my installation. I'll let you know when it is done.
>>
>>  
>>
>> I bought my controller from www.winland.com <http://www.winland.com>  
>>
>>  
>>
>> They were very helpful. They removed the board mounted pot for me and 
>> provided tabs for my own remote mounted one.
>>
>>  
>>
>> Hope this helps.   Kurt
>>
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