rdi@cci632.UUCP (Rick Inzero) (04/11/89)
I was just given a car "battery charger" (at least that's what I was told). Anyway, I can't figure out if/how it works, since it's pretty old, and the technology pre-dates me. When I plug it in (with both output leads unconnected- just floating with no load), I get only AC out, *no* DC, so I don't think it's in working order, but I can't be sure... opening up the 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 metal, insulated from the box by insulating paper, in the center is a 2" disc of brass, with a brass hole thru the middle, 1" brown insulating disks on top and bottom, and a bolt passing thru the hole to hold the metal device in place plus connect the center brass hole to the metal case. Sprayed on the surface between the metal square and the brass disc seems to be a granular grey substance, and it is NOT in electrical contact with the metal square. The granular surface IS electrically connected to the 2" brass disc. Is this metal/brass component some archaic diode (rectifier) that is no longer 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. 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! Here's all the info printed on the case: Battery Booster Model 421B 115v 60 cycles Output 2-4 Amps Appx. Automatic Reset Fuse Electric Service Systems, Inc. Minneapolis, Minnesota Unfortunatly, no output VOLTAGE is specified, so I don't even know if it's meant to be used with 12V or 6V car batteries. The metal "mystery component" has an inspection type stamp on it that says "Syntron Aug 3 1959" and the characters "L8" and "SD 1081". I'd sure like to see this working, hopefully without gutting it and starting over with new modern components. Hopefully, one of you can tell me that it's working properly already, and just needs a load... So is (was?) it truly a battery charger or merely a booster or what? Thanks for any advice you may offer... Rick --- Rick Inzero rochester!cci632!rdi Computer Consoles Inc. (CCI) uunet!ccicpg!cci632!rdi Rochester, NY uunet!rlgvax!cci632!rdi "Your grandmother never, ever called me stupid. She always called me 'pinhead'." -Jimmy Stewart in 1988 Campbells Soup
garnett@batcomputer.tn.cornell.edu (Roger Garnett) (04/12/89)
In article <27792@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: >I was just given a car "battery charger" (at least that's what I >was told). Anyway, I can't figure out if/how it works, since it's pretty old, >and the technology pre-dates me. When I plug it in (with both output leads >unconnected- just floating with no load), I get only AC out, *no* DC, You probably get rectified AC (ie. pos only, 1/2 wave), but as the charger doesn't have (or need) a filter Cap, it may be hard to get a DC reading. >opening up the >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 >metal, insulated from the box by insulating paper, in the center is a 2" disc >of brass, with a brass hole thru the middle, 1" brown insulating disks on top >and bottom, and a bolt passing thru the hole to hold the metal device in place >plus connect the center brass hole to the metal case. [etc...] Probably a selenium or similar rectifier. It could be replaced with a large, modern diode, IF it isn't working. Hook it up and find out. >Unfortunatly, no output VOLTAGE is specified, so I don't even know if >it's meant to be used with 12V or 6V car batteries. Most car battery chargers are just crude, unregulated power supplies. Current is determined by a combination of the transformer windings, and the battery voltage/state/resistance. Therefore, a 6 Volt battery will charge at about twice the rate of a 12 V. Too small of a transformer won't be able to produce enough current to charge a 12 V battery, and too large will overcharge whatever. (6 V first) Most chargers with multiple charging rates just have a multiple-tap transformer to select a charging rate. ___________________________________________________________ Roger Garnett (garnett@tcgould.TN.CORNELL.EDU) Cornell Phonetics Lab (plab!roger@cornell.uucp) Ithaca N.Y. (sggy@cornellC) (607) 255-0704 (sggy@vax5.ccs.cornell.edu)
ISW@cup.portal.com (Isaac S Wingfield) (04/13/89)
Your mysterious "brass disk" is a single junction Selenium rectifier (if it's still any good). The reason you see AC under no load is because those things had, by today's standards, terrible reverse leakage. Check out the waveform under load; if it rectifies, it's OK. IF IT SMELLS LIKE ROTTEN EGGS, LOOK OUT. Selenium sulfide (I think) is toxic. Regards, Isaac isw@cup.portal.com
parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S) (04/13/89)
In article <7724@batcomputer.tn.cornell.edu>, garnett@batcomputer.tn.cornell.edu (Roger Garnett) writes about a battery charger: > Probably a selenium or similar rectifier. It could be replaced with > a large, modern diode, IF it isn't working. Replacing a selenium rectifier with silicon diodes will change the charging characteristics of the battery charger. The relatively high voltage drop of the selenium stack plays a role in limiting the charging current. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Bob Parnass AJ9S, AT&T Bell Laboratories - att!ihuxz!parnass - (312)979-5414
jim@trsvax.UUCP (04/14/89)
>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.
irwin@m.cs.uiuc.edu (04/15/89)
Re: The battery charger, Rick has pointed out that the "thing" is a selenium rectifier. This is probably true. Since it was built when that technology was in use, it is probably a 6 volt unit, but MAY be a 12 volt. You can tell by going to Radio Shack and pick up a capacitor, something like 20 to 25 microfarrads with a rating at least 20 volts. Put it across the output of the charger, observing polarity. You can then measure the voltage built up in the cap. If around 8 or so DC, then it is a 6 volt charger, if around 16 DC, then it is a 12 volt charger. Since there is no filtering in the standard charger, you must smooth the output a bit to tell what you have.