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What is this? Some kind of diode?

Have a automotive battery charger/car starter which doesn't work quite right. Won't charge the battery up more than half-way, and I find 5.5VAC rather than the expected DC of 1.5V (+/-) applied to the gate of the SCR that seems to drive the whole thing (NTE5539). My suspicions point to what appears to be a pair of diodes mounted on the massive heat-sink inside (see jpegs posted to a.b.s.e. Sorry for the poor focus in the up-close, but that's the best my camera will do). The two clips are connected. My DMM, using the diode checker, registers .879v one way (neg probe on DUT and pos probe on heat sink), and .397v the other way. I am thinking this is some sort of bridge rectifier? And maybe the previous owner of the machine hooked it up to their car backwards at some point? I am going to disassembel the device in question just to make sure it is not something else, but wanted to ask if anyone else had any ideas on what it is... Any help, or suggestions, are more than welcome and eagerly sought.

Thanks,

Dave

Reply to
Dave
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Nevermind. I can't make a post for a.b.s.e. that stays on the server longer than a couple seconds. Sorry for the waste of bandwidth.

Dave

Reply to
Dave

What gives? I couldn't post the pics to abse and get them to stay, and my "nevermind" post here disappeared! Anyway, I pulled the things off of the heatsink, and they appear to be (each) metallic posts with a ferrite ring around them, housed in opposite ends of a plastic envelope... Tests like diodes. Could that be what they are? Some kind of high current diode? :p

If the pics really are out there, would appreciate comment.

Thanks,

Dave

Reply to
Dave

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Reply to
Michael A. Terrell

Nope. Show all msgs. Are the pics really out there? Don't know what to think, other than that I believe these are diodes of a type I have only read about before (oxidized metal only conducting in one direction, can't remember exactly how it works though...) They are not exactly ideal as diodes though, obviously. Am going to replace them with real diodes. Probably stud-type, whatever that is actually called. The kind that bolt to a heatsink.

Thanks,

Dave

Reply to
Dave

Okay, I'm an idiot. You were right, Michael. Don't know when I did that though... My apologies.

Dave

Reply to
Dave

SdnSrFtuvgjcHVnZ2dnUVZ snipped-for-privacy@earthlink.com...

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Some time back (10 years) they used to make automotive battery chargers of the 4 to 20 amp range with a "pill" type of diode, about a quarter inch in diameter and about the same in length which just got pressed between heat sink surfaces which doubled as the electrical contact as well. Reversed battery leads would take em out every time and just once was all that was needed.

I used to be able to find them for sale in Digi-Key but no longer - I'm thinking everybody finally agreed that the basic design is just not adequate for job they were being placed in.

I also have a Sears 4 amp charger with the metal oxide rectifiers, absolutely bullet proof. The main reason I don't have a collection of all manner of auto battery chargers is that this is still going strong after 40 years, I've re-corded it at least twice now. Best 10 dollars ever spent.

Reply to
melee5

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