How does it work?

J. Forster jfor at QUIK.COM
Mon Jul 19 12:22:40 EDT 2004

If you think about a tuned circuit, driven by a sinusoidal steady state sine
wave, the phase of the tuned circuit depends on the relationship between the
driving frequency and the resonant frequency. Thus, the relative phase can be
adjusted in the design phase by making the reed resonant above or below the line
frequency. IMO, they likely used a 'cut and try' approach. It was likely tuned
so that the transformer was only conected to the battery during the peak of the
sine wave.

BTW, this 'pulse charging' was likely good for the lead acid batteries of the
day, to prevent sulphation. The thing is rated at 6 A, so the pulse current was
likely several times that.

A down side of the design is that the thing would be line frequency dependent, a
issue in the early days but not now.  OTOH, it probably worked well enough.

Apparently, these devices were used in small telephone exchanges to charge the
batteries, (jackiv)  although I don't think that was this one's intended
purpose. Telephones tend to use 48 VDC, not 6 VDC.


Ian wrote:

> I'd suspect there is a way to MECHANICALLY change the configuration - maybe
> the positioning of the contacts somehow so that you introduce enough lag
> that you can synchronize them.  However I'm not sure how you mechanically
> change reeds.
> I guess some inductance might be useful.
> What in the unit looks like it would serve that purpose to adjust "phase"?
> I wonder if it's old enough that they wouldn't have scopes (oscillographs?)
> to view the waveform.  I would think you could put a DC meter on the output
> and adjust for maximum and know that it is unlikely that you had much of the
> negative going part of the wave.
> How far we've come with sold state devices.  Just thinking back about all
> the automobile radio vibrators that I've replaced and attempted to repair by
> cleaning contacts and making adjustments makes me glad I didn't have to work
> with something like what you have!  Better than those stinky selenium
> rectifiers but I would have though that metal oxide rectifiers might be
> available during that era.
> Ian
> -----Original Message-----
> From: J. Forster [mailto:jfor at]
> Sent: Monday, July 19, 2004 8:03 AM
> To: Ian
> Subject: Re: How does it work?
> Agreed. Now, how did they get the contact phase with respect to the AC input
> right?
> (Trial and error is my guess)
> -J
> Ian wrote:
> > Huh???...  I think we are both saying the same thing.
> >
> > I said the reed vibrates at the frequency of the input and I agree
> > with you about how it works and the output is pulsating unidirectional AC
> as I said.
> >
> > The waveform without a cap across it should look like the output of a
> > full wave rectifier without filtering on the output.
> >
> > I think we are both saying the same thing.
> >
> > As somebody said it'd make a good battery charger because pulsating DC
> > is the usual output of the "DC" battery chargers.
> >
> > Ian, K6SDE
> >

This list is a public service of the City of Tempe, Arizona

Subscription control -
Archives -

More information about the Boatanchors mailing list