[ARC5] Vibrator Power Supplies

[Kenneth G. Gordon]

On 8 Dec 2012 at 9:59, brianclarke01 at optusnet.com.au wrote:

> Dynamotors typically have a conversion efficiency of no more than 50%.

Well, actually, that is OVERALL efficiency, and includes the starting power 
required. 

When running steadily, a dynamotor's efficiency is very much higher than 
that, but I have forgotten the exact figure. I know it approaches that of a good 
vibrator pack.

> A vibrator supply can reach 70% easily, and often more, if designed
> properly.

Correct. However, vibrators packs are not particularly reliable when high 
power and/or high voltage is required. For instance, I doubt if one could build 
a reliable vibrator supply that would provide all the necessary voltages and 
currents for an ART-13, for instance. 

> The modern day development of the vibrator is the
> switched-mode power supply, which often reaches in excess of 95%
> efficiency.

True, indeed. I have a Motorola power circuits handbook that details all that 
and the various designs.

> I suppose when fuel was plentiful and cheap, what did it matter if you
> consumed a gallon to do a job that a quart could do?

That is not the point. Dynamotors were chosen because at that time they 
provided the reliability and service required whereas the vibrator packs of the 
time did not.

I have (or had) a 300 watt vibrator pack from that period: it was absolutely 
IMMENSE for the power output. It would easily make 4 dynamotors of the 
same voltage and power output. And keeping vibrators working for it was a 
never-ending task.

> Then you need to consider the downstream effects - the filtering
> components for a dynamotor are much smaller and lighter than for a
> vibrator, because of the frequency.

Huh? I don't understand what you mean here. The dynamotors output DC, or 
0Hz. The filters in the ARC-5 receivers are not there to filter the AC 
component out of the DC output, but to filter the RF noise produced by the 
brushes. The filter choke is 3 H and the caps are .22 MFD. I don't consider 
those to be very large.

> But with SMPSUs, operating at 1
> MHz or so, the filtering components are very much smaller

...than for a 60 Hz AC or a vibrator supply at 115 Hz...

> than for a
> dynamotor.

Please explain: I don't understand what you mean by this last.

Ken Gordon W7EKB