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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 6th Feb 2020, 4:02 pm   #1
cdm1christopher
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Default Sprague atom capacitor +ve or -ve correct way round

Hi all
just got this electrolytic and as you can see on pic the positive is situated to the Ali can and negative seems to be at rubber grommet end.
Have I got this the right way round or have they put the casing round wrong way.
Just usually rubber end is positive.
Cheers Chris
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Old 6th Feb 2020, 4:20 pm   #2
Nuvistor
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Default Re: Sprague atom capacitor +ve or -ve correct way round

I would say that they are marked incorrectly see this photo but you may have specials. Does the capacitor perform correctly or does it get warm?
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Old 6th Feb 2020, 4:23 pm   #3
cdm1christopher
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Default Re: Sprague atom capacitor +ve or -ve correct way round

That's what I would have expected but code is different on mine. Pic attached.
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Old 6th Feb 2020, 4:30 pm   #4
turretslug
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Default Re: Sprague atom capacitor +ve or -ve correct way round

It would certainly go against expectation- I've been racking my head as to when I've ever seen a "can positive" electrolytic. Rather than connecting it straight into circuit, I'd try connecting it to HT via a 100k resistor and a 5mA (or thereabouts) meter- rubber bung to +ve to start with- and see what the leakage is once charged, then try it the other way round and see what it settles at. I'm pretty darn confident that rubber bung to +ve will turn out to be right, but don't leave it too long connected at what turns out to be the high leakage direction as that will be eroding the thin insulating layer on the aluminium foil.

I'd also contact the supplier, as they may have a lot of disgruntled customers otherwise if this is a batch problem.
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Old 6th Feb 2020, 4:31 pm   #5
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Default Re: Sprague atom capacitor +ve or -ve correct way round

The TVA 1709 uses a case code HJ for a 20uf 450v capacitor, I cannot find any further info. If you are in doubt replace it.
https://hfc-fs.s3-eu-west-1.amazonaw..._tva_range.pdf
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Old 6th Feb 2020, 4:34 pm   #6
cdm1christopher
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Yeah I did contact them RS but apparently they don't have a technical department i.e Just sell the part.
But I'm convinced the lable is put on the wrong way round every sprague you see +ve always towards rubber bung well all caps that I've ever used are never to ali can end.
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Old 6th Feb 2020, 4:38 pm   #7
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Default Re: Sprague atom capacitor +ve or -ve correct way round

There is an email contact for Vishay on the link I posted. Send them a photo.
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Old 6th Feb 2020, 4:42 pm   #8
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Yep its definitely labled the wrong way round everyone ive looked at is positive to rubber grommet end.
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Old 6th Feb 2020, 5:00 pm   #9
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Components are sometimes mis-labelled, and I suspect that's what has happened here: I was hit by this a while back with some small diodes that had reverse-polarity to what was marked, leading to much head-scratching, a week's delay shipping the first run of the product, and acrimonious letters between our lawyers, the board-assembler and his supplier.
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Old 6th Feb 2020, 5:01 pm   #10
cdm1christopher
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Well that's bad if your a novice you'll put it in and bang.
Let RS know and associated dangers.
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Old 6th Feb 2020, 6:46 pm   #11
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Default Re: Sprague atom capacitor +ve or -ve correct way round

The Vishay datasheet and the product photo both on RS clearly show label fitted to show bung end positive. Someone's had an off day somewhere!
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Old 6th Feb 2020, 7:01 pm   #12
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Well I got in touch with RS again apparently they do have Technicians not what I was told by first person.
Anyhow all in hand there checking all stock and were very apologetic plus compensation. As I made it clear that a novice would automatically think that was correct way round and the inherent dangers of it exploding, damaging the unit and if testing in circuit ie you have your head over it not nice.
Must admit though first time for me hence post just threw me that one.
Thanks for the input guys.
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Old 7th Feb 2020, 2:35 am   #13
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Default Re: Making an RF probe for VTVM

Biggest problem when an electrolytic cap goes bang ( especially when its new) is that it chucks its guts everywhere. AND its conductive so cleaning up the slop from the electrolyte is difficult, ESPECIALLY with a high impedance circuit such as a VTVM is there.
Thats not to mention bits of aluminium foil goes EVERYWHERE and is a true PITA to remove. It wraps around component legs so cleverly days of looking wont find it, BUT the moment you put the back of the unit on, it will fall off the component leg and short something out. This is a bit of a lesson for you I guess, electrolytic caps can be dangerous, thats why BIG ones have "blow holes", usually a soft rivet that will blow out to relieve pressure inside the can. ALSO !!! do not forget a good quality electrolytic can hold a charge for years if not fitted with a bleeder. Probably wont kill you, but makes you jerk about like a disco dancer causing you to drop things, like metal screwdrivers, pliers, sidecutters etc, into a running piece of electronics making lotsa sparks, or chucking the whole chassis on the floor, which will ALWAYS fall on the most expensive valves first!!! followed by expensive transformers and multi wafer rotary switches.

You get my point

Joe
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Old 7th Feb 2020, 11:47 am   #14
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Dodged a bullet there - good show.
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Old 7th Feb 2020, 12:28 pm   #15
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Hi Joe. Sounds like you might have more than one tee shirt!
The only time I recall was the mess to clear up and damage caused to a couple of new transmitters when the main chassis mount 33000 uf 63v smoothing cap was fitted with polarity reversed. This was in the hot room where gear was left at up to 55c, powered on and routinely keyed into dummy load. Psu was a 16A toroid.
The large yellow stain was still visible on the floor several years later.
Rob
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Old 8th Feb 2020, 7:37 pm   #16
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Yeah think its lucky I have a year and half of refurb under my belt but must admit did scratch my head on that one there was no chance I was going to fire her up. I did not even bother to switch it round and try it. Be interesting what RS have to say as I'm waiting on them getting back to me on rest of the stock. I BET IT'S THE ONLY ONE!!!!!
Still like you say Joe my thoughts where for someone new to refurb see the plus signs put it in then head over it to test in circuit not good. So morale to this story is fully check polarity not just see plus or minus and whack it in without thought!
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Old 10th Feb 2020, 11:28 am   #17
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Quote:
Originally Posted by cdm1christopher View Post

So morale to this story is fully check polarity not just see plus or minus and whack it in without thought!

No.... morale (yours) is what is good now after this positive outcome. The story has a moral.

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Old 10th Feb 2020, 1:06 pm   #18
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Default Re: Sprague atom capacitor +ve or -ve correct way round

I have another example of an incorrectly marked capacitor.
Many years ago we purchased a batch of STC 68uF @ 450Vdc capacitors from a major UK suppler.
One of our engineers was working on an equipment and was about to install one of these when he decided to test one for leakage. This shouldn't have been necessary as they had been supplied with a Certificate of Conformance (C of C). Starting from zero volts he found that very quickly there was significant leakage. A further test showed the capacitance was far greater than marked.
The capacitor was determined to be 6800uF @ 10Vdc.
If he capacitor had been put into the circuit the results could have been dramatic.

The picture shows on of the incorrectly marked capacitors on the left and what it actually was on the right.

https://www.vintage-radio.net/forum/...1&d=1581336297
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Old 10th Feb 2020, 4:30 pm   #19
cdm1christopher
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Default Re: Sprague atom capacitor +ve or -ve correct way round

Oh dear just goes to show you. That's why I brought it up as beginners would buy ask about polarity and everybody bound to say make sure the +ve -ve is right way round just look at the original installed or it might be marked on board.
Anyhow they're pulling the stock. I felt the supplier needed to be told.
Cheers Chris
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Old 14th Feb 2020, 3:22 am   #20
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Default Re: Sprague atom capacitor +ve or -ve correct way round

It used to be that the +ve of an electrolytic that was marked, then at some point the convention changed, and we have the -ve side with a prominent band.
What was the reasoning behind the change?
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