Replacing Selenium rectifiers

Very probable. I converted an OLD tombstone to DC. Comes on handy now and again. What do you get for a set? Might come in handy to have a back-up.

I get $100 and up for them, depending on size and the best offer.

I sold about four already.

These are from old Linde welders that I scrapped for copper transformers. People are very happy with those rectifier bridges.

You can supply one or three phases to them.

i

O.K. That is for three phase in (via the aluminum straps which appear to have been bent), and it is three each of forward polarity diodes (on one plate) and of reverse polarity diodes (on the other plate).

For the battery charger, you would only need one plate (which is a function of the polarity of the original selenium rectifiers) and only two of the three rectifiers on it. So -- just grab one of those, select which plate has the right set of rectifiers for your needs, and either pull out the third diode -- or leave it in there for a quick swap-in if one fails (and trips the breaker before it cooks the other diode. :-)

Enjoy, DoN.

Putting a full wave bridge in place of a half wave selenium will cause overcharging - the voltage will be increased by virtue of full wave rectification, AND lower voltage drop of Si over Selenium

You can only put one phase in. No problem.

Actually, for one phase, you can hook it up as follows:

Your in-terminals X, Y, Z, connected to single phase A and B like this:

A, B, A

In other words, one side of single phase is in the middle, and another side of single phase is on both ends). That allows for somewhat better cooling.

ROTFLMAO!

I wonder how close cal is on those.

What do you think of these? I've seen them rebadged and priced anywhere from $54 to $80, delivered. Several youtube lektronikers like 'em.

I have a very similar looking opwer supply, that I use almost daily for almost everything.

i

That's good to hear.

snipped-for-privacy@snyder.on.ca fired this volley in news: snipped-for-privacy@4ax.com:

Clare, you apparently know something about electronics, but also obviously have never peeked inside a commercial battery charger. Pretty much everything on the market has (and has _always_ had) a full-wave center-tapped arrangement.

So, no... it won't cause overcharging. The lower voltage drop across the diodes MIGHT, but most chargers with selenium rectifiers didn't have any particular voltage control, anyway. They were designed to charge until you removed them. The charge tapered off with time, of course, but never stopped... those units hardly ever were made to go into 'float' after charging, and even then, only high-priced professional chargers did that.

And THEN, they did it with a current relay, not with electronics.

Lloyd

I don't see your original ROTFLMAO! post, only Iggy's reply and this one.

I posted a favorable opinion of the power supply a while ago and haven't changed my mind.

Mastech warns that similar models are unsuitable for charging batteries and recommends their Volteq line instead. My PS-305DM doesn't quite match any of their photos. I put a 10A Schottky diode in series when I charge a battery to keep the 12V from backfeeding the supply if the AC power fails.

I think my linear PS-305DM is more stable than my switcher when feeding an inductive load, like forcing 1A through a transformer winding to measure its resistance to the milliOhm.

jsw

The megger I bought reads high-precision lab standard resistors in the

300-800 Meg range accurately within nearly the width of the needle. I can't recheck them now because they are frozen into the shed out back in the woods. They are all unusual values like 301.6 Meg, which is why I got them cheap, and they don't align with the scale marks.

The needle aligns perfectly with the 10 MegOhms graduation when connected to the voltage input of my Fluke 8022A DVM and cranked below about 200V. Above ~200VDC the input impedance drops a little, maybe due to the DVM's protection circuit. It revealed that the function switch is bad on the intermittent Fluke 8060A I just bought for $10, so thanks for prompting me check.

Cranking speed doesn't affect the resistance reading since the megger's meter senses and displays the ratio of applied voltage to resulting current, R = E / I. jsw

ly/cat_6.html

Hello Jim, I don't know about the mastech switching supplies. But the lin ear supplies have a "feature" that disables the output if the load is too s mall... It won't source current into a dead short. However if you send an email to Mastech they'll tell you which diode to 'snip' to disable this "fe ature". And then it's a pretty nice supply for the money. (we resell a one of the Mastech.)

George H.

If they work, you can measure it. It won't be a very large number, though.

If you can read the rectifier device number, you can probably find a datasheet, and read the series resistance.

Another way is to calculate what the circuit needs to protect all affected components.

The number isn't tremendously critical, but there needs to be some series resistance. It's not uncommon to see surge limiting resistors in modern power silicon-rectifier supplies.

Joe Gwinn

Ahh, the sweet and alzheimish nuances of USENET!

I remember that conversation with the solar chargers and immediately bought spare diodes for that purpose. $4.70 + $2.99 s/h for 10pcs 10A

50V Schottky Diode on eBay. That's just $0.77 each!

OK, thanks for the info.

Frozen into the shed, eh? Talking with some of you guys reminds me of why I enjoy, so very much, living here in a more temperate climate.

Oh, that'll be cheap and easy to source and repair, huh? =:0

Oh, so that's what those cranks do. It's a little generator to create its own E for the I.

Hello Jim, I don't know about the mastech switching supplies. But the linear supplies have a "feature" that disables the output if the load is too small... It won't source current into a dead short. However if you send an email to Mastech they'll tell you which diode to 'snip' to disable this "feature". And then it's a pretty nice supply for the money. (we resell a one of the Mastech.)

George H.

===================== This PS-305DM which I bought locally is branded "Option Tools". It just forced 0 to 5A into a dead-short dual banana jumper with the output voltage at 24mV (jumper removed).

What does Mastech say about switching ranges with the 1A/5A pushbutton while under load?

jsw

If you have the meters, I'd put the charger on a fairly new fully charged battery while monitoring voltage and current to see if and how much adjustment is needed to keep the voltage at or below 14.8V.

They give 2.45V per cell max, which is 14.7V.

2.5V per cell is 15V. Sometimes I need over 16V to make a sick battery accept current. You could switch out your limiting resistors to try salvaging a sulfated battery, but don't leave it unattended too long since the current can rise considerably as it heals.

jsw

Hmm is the PS-305dm a switcher or linear? (I went to a few web pages but couln't tell.)

I only really know about the mastech linear supplies. this one (30 V at 5A) has no switch,

We use their 50V 3A linear supply. It would 'crap out' with a load of 5 ohms or less.

George H.

OK just say this on the mastech site.

It appears that the hi/lo switch is an evolving "feature". George H.