Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!haven!rutgers!bellcore!texbell!merch!cpe!hal6000!trsvax!jim
From: jim@trsvax.UUCP
Newsgroups: sci.electronics
Subject: Re: Whatizzit?  ("Battery Booster")
Message-ID: <190700038@trsvax>
Date: 13 Apr 89 23:53:00 GMT
References: <27792@cci632.UUCP>
Lines: 40
Nf-ID: #R:cci632.UUCP:27792:trsvax:190700038:000:2341
Nf-From: trsvax.UUCP!jim    Apr 13 18:53:00 1989


>metal case, I see only 3 components:  a transformer, a current-sensing 
>shutoff device rated at 10 Amps (to protect against the output leads 
>shorting), and one really mystifying component... it's a flat 3" square of 
Congradulations, you have stumbled onto a Selenium Rectifier. It is often
used in the old battery chargers as it was a good high current device
before the silicon diodes got cheap and robust enough to replace them.

>working up to par?  To my continuity tester, it acts like a diode.  Testing 
>w/between 1 ohm and 4K ohm resistive loads on the output terminals caused 
>a maximum of about 3-4V *DC* to be produced.  Pretty useless for charging
>a car battery.
Yes, these things work just like a diode, but have a different forward
voltage drop. (Anyone know the value for 5 points? 8{)
This battery booster is a low-current battery charger used for people who
need to charge a barrery but don't care about time. It is NOT a 12VDC power
supply. It produces pulsed DC at 60Hz. You can not measure the output with
a simple analog or digital voltmeter - you will be measuring the average
voltage - not the peak. These charge the battery near the peak of each
pulse and loaf for the rest of the line cycle.

To measure the output of it, either use an oscilloscope or peak-reading
voltmeter. If, like myself, you can't afford these, attach the output to
an electrolytic capacitor of about 100uF/16WVDC or better and measure the
output with a DC voltmeter. The capacitor will charge to near the peak
voltage output and allow you to measure with cheaper equipment.

These can be used as a low output DC supply if you hook them to an old
motorcycle battery and don't pull out more than the charge rate. This is
a passable way to operate CB/ham radios, chgarrette lighters, etc...
>Could it be that this "battery booster" box will start to function (produce DC) 
>only in circuit, i.e. when connected across a 12V lead/acid car battery?  
>I sure don't want to just connect it to a battery and find out!  
Yes, it will - try it and find out. Hope this helps!

James T. Wyatt  UUCP:{vaxnix,trsvax}!{jim,rwsys!jim,mycube!jim}  KA5VJL

>"Your grandmother never, ever called me stupid.  
>	She always called me 'pinhead'." -Jimmy Stewart in 1988 Campbells Soup
The difference between a brown-nose and a sh*thead is depth perception.