Help rebuilding a rectifier bridge.

[kazlx]

I'm looking at rebuilding a rectifier used to power a magnetic chuck that goes on a surface grinder that I recently bought. I just re-wired the machine wiring and now I need to tackle the rectifier for the mag chuck. I thought I would ask for some help. This looks like a relatively simple circuit. I popped the cover open to look at everything and just want to build a new one from scratch. I would also consider buying something if they are available. I can solder decently enough, but I'm not sure what the actual pieces are? I plan on making a trip to a local electronics place, but can't get down there for at least two weeks. I'm wondering if I can order everything from Mouser or somewhere similar.

This looks like it was built a while ago and I'm wondering if maybe there is something commercially available that would just replace the whole thing?

The small black ones look to be diodes. Are the orange ones capacitors? The larger yellow one looks to be a capacitor as well. I was hoping someone that knows electronics can tell me what is going on in here.

 

[rlitman]

The four diodes are the bridge rectifier. If you know the specs, it is usually cheaper to buy a bridge rectifier, than it is to buy four (or perhaps even one) diode(s).
What is the maximum voltage and current it needs to deal with?

 

[kazlx]

It's 110 coming off the wall. I will have to look at the chuck again and maybe clean the plate off a little better, but I believe it said 2A max. It's basically powering a big electromagnet.

So are pre-made rectifier bridges available to buy?

 

[someone else]

the orange ones are capacitors, likely in the .0XXX microfarad range - they are most likely polypropylene film capacitors, and the yellow one is an electrolytic capacitor, >40 microfarads, most likely. The black things are the diodes.

The orange capacitors will be ~$1 (or less) each, the electrolytic, depending on capacitance and voltage, will be <$5, and then the diodes won't be very expensive either.

Wipe off everything and see what you can read. Then we can point you in the right direction on parts. I usually get my stuff from digikey (or antique electronic supply, but i mostly restore old radios, so thats a moot point), but moser is just as good.

 

[kazlx]

Awesome. I'll try to get as much info as I can tonight. If I can buy one piece that does what this whole circuit does, that would be ideal. Otherwise, it doesn't look too hard to build.

 

[theoldwizard1]

You always buy diodes/bridge with a large safety margin. Look for 200-300V rating at 5A.

Radio Shack might have them in the store (at least in the old days).

Online I guarantee Digikey or Jameco will have them. Check eBay for "full wave bridge rectifier".

 

[cnc-me]

You always buy diodes/bridge with a large safety margin. Look for 200-300V rating at 5A.

Radio Shack might have them in the store (at least in the old days).

Online I guarantee Digikey or Jameco will have them. Check eBay for "full wave bridge rectifier".

I second that idea, get a 1000 volt 35 amp bridge, they are not that
much more money. Spikes from inductive devices like this can take out
a lower voltage rated unit.

 

[Jrican]

I buy almost all of my electronic components from digikey:
http://www.digikey.com/
You have to have a good idea what your looking for. there site is not always easy to navigate. But prices are good, and they have everything!

Given the simplicity of that circuit you should build it for yourself just for the experiance, even if it's cheeper to buy ready made.

 

[sr71]

For added consideration...you might be able to use a terminal block to minimize your soldering / clean up the setup.

 

[Jrican]

here is where to look for the first 4 caps
http://www.digikey.com/scripts/dkse...tock=0&pbfree=0&rohs=0&quantity=0&ptm=0&fid=0
you will have to filter for capacitence then pick a reasonably high voltage.

This diode may work for you (~$0.50 each)
http://www.digikey.com/product-detail/en/1N5388BG/1N5388BGOS-ND/1474201

the other capacitor should be found here:
http://www.digikey.com/product-sear...tric-double-layer-capacitors-supercaps/131084

some one should probably second these though, before you buy. but it shouldn't be to costly.

 

[BillK]

Kaz,
I just rebuilt a high voltage supply for a ham radio amplifier and I got everything from Mouser. It was very similar to what you have there. You might be real surprised if you call the equipment manufacturer. They might have the parts available too.

 

[dipper]

Yup that's what it looks like to me. See if you can read any of the markings off at least one of the diodes and the capacitors. They will have markings which indicate the size of the capacitors. Post the info back up and I can help decode it if needed.

The diode bridge can now be bought as a single unit, they are about 1/2" square and 3/16" thick with 4 leads that come out of it. The diode bridge will be a cleaner way to rebuild this circuit instead of using the individual diodes.

Digikey, Mouser, Jameco and Newark are all going to have that stuff.

the orange ones are capacitors, likely in the .0XXX microfarad range - they are most likely polypropylene film capacitors, and the yellow one is an electrolytic capacitor, >40 microfarads, most likely. The black things are the diodes.

The orange capacitors will be ~$1 (or less) each, the electrolytic, depending on capacitance and voltage, will be <$5, and then the diodes won't be very expensive either.

Wipe off everything and see what you can read. Then we can point you in the right direction on parts. I usually get my stuff from digikey (or antique electronic supply, but i mostly restore old radios, so thats a moot point), but moser is just as good.

 

[kazlx]

The diodes aren't marked. Is there a way to test them to see what they are? I got pictures of everything else. I have a DMM and know enough to be dangerous

 

[dipper]

400V, 3A diode bridge
cost: $.90

http://www.digikey.com/product-detail/en/3KBP04M-E4%2F51/3KBP04M-E4%2F51GI-ND/2139746

 

[rlitman]

Digikey, Mouser, Jameco and Newark are all going to have that stuff.

Actually, bridge rectifiers are a stock item at Radio Shack too. Not that I'm a fan of the place (I feel dumb-erer every time I walk in there), but this is a really run of the mill item. They'll have about half a dozen options in the drawers, for different current ratings.

True RS story from about 2 weeks ago:
First, the guy there says to me "sir, I don't even know what either an Integrated Circuit or CMOS is".
Then, an elderly lady walks in as I'm about to leave. She's carrying a box from a new cordless phone, with an old Panasonic cordless phone (with the rubber ducky antenna) on top of the box. She enters the store really distraught, and starts arguing with the guy there that this isn't going to work, and she wants her old phone number back.

 

[kazlx]

400V, 3A diode bridge
cost: $.90

http://www.digikey.com/product-detail/en/3KBP04M-E4%2F51/3KBP04M-E4%2F51GI-ND/2139746

So would that replace all that stuff, or would I need to add to it? Questions may seem basic, but I would like to understand what I'm doing.

 

[dipper]

okay, the yellow cap is 200 microfarad (that's what 200MFD is) and 150V, since this is on an ac line you want 150V or greater.

Orange caps are 0.1 microfarad 400V.

The diodes should be marked, unless it was rubbed off. I'd be willing to bet that they are 1N400X (where X = 1,2,3,4,5,6 or 7 which indicates they voltage.)

 

[dipper]

no, that would replace just the diodes from your original setup. You'd still need the caps to filter the noise and ripple. You do realize that this is just a very crude DC power supply?

So would that replace all that stuff, or would I need to add to it?

 

[kazlx]

no, that would replace just the diodes from your original setup. You'd still need the caps to filter the noise and ripple. You do realize that this is just a very crude DC power supply?

Yea, all this was housed in a rectifier box, which I knew is to convert AC to DC to run the magnetic chuck. I'm guessing at some point, the guy built his own to replace the original one, because the guts look home made and not produced. Well, at least I don't think anything would leave a factory on crudely cracked plexi with randomly drilled holes and sloppy soldering. I'm guessing he just stuck it back in the same housing. I'm not sure how 'clean' the power needs to be to run the chuck. It's basically just an on/off electromagnet.

On a side note, would there be any way to wire in a variable strength control or am I getting over my head for that?

 

[dipper]

i have this in my hands right now:

6Amp, 400V diode bridge, follow link for data sheet.

http://www.newark.com/vishay-formerly-i-r/vs-kbpc604pbf/bridge-rectifier-1ph-6a-400v-thd/dp/19M4415

 

[dipper]

On a side note, would there be any way to wire in a variable strength control or am I getting over my head for that?

anythings possible, maybe you could try a dimmer switch to limit the voltage going into the bridge.

 

[gatchel]

anythings possible, maybe you could try a dimmer switch to limit the voltage going into the bridge.

How about a Variac?

http://www.variac.com/

 

[Max Headroom]

Can you post additional pictures of the magnetic chuck? That does look like a homemade circuit that probably replaced the original. The diodes are probably either 1n4003 ( 1 amp ) or 1n5402 ( 3amp). Earliest info I could find on either of those diodes was from 1966. Was hoping to be able to possibly identify what they are via their size, but that doesn't look like that will work. My assumption about that circuit not being original to the device is based on the information that I could locate on the picture you included with the “D & W Fuse Co” logo. It looks they became defunct in the 1920s and may have not been making the product after that. So from the limited information I could find, magnetic chuck is at least 40 years older than when those diodes first started manufacturing.

The original controls may have also included, in addition to the normal on/off switch, a demagnetize switch might have also been part of the original circuit. I did a bit of searching and didn't come up with any matches for the model number shown, although I probably have it wrong - STD5XI3

If you post more pictures of the magnetic chuck, we might be able to see a schematic on it someplace, or get some additional information about it.

It would probably be the easiest way to proceed if it has a diagram someplace. If it does not, you might have to broaden out and ask over at the practical machinist forums to see if anyone is has one that they could get you a picuture of. Or if they have a recommendation on a drop in replacement controller.

If that doesn't work, we can figure out what sort of magnet it should be ( probably based on the windings ) figure out what max voltage on it should be, and the possibly do a replacement circuit that would additionally have a fuse for protcetion and a demag setting ( either direct AC (which probably would work ) or slow down dc polarity reverse )

I'm not saying that you can't fix it as . You just probably only need to go with like replacement parts and it will be working as well as it was last time fixed, which might mean you aren't getting as much of a field as you should be, or too much of a field wihch ends up generating too much heat and shortens the life of the unit, and you could be missing out on the demag settings.


So if you post more on the chuck, me might be able to better replace what it has at the moment.

It certainly seems like a great find to me. You have a couple different directions you could pursue to get it going again. Maybe you could do the qucik fix part replacement and then come back later and make changes. You just need to ask yourself when do you start needing to use this by and how many hours could I spend working on it between now and then and is it going to be something I enjoy doing and will I learn anything from it. And if you still aren't sure, the folks here at GJ are usually more than willing to add in their own personal advice.

 

[Charles (in GA)]

www.surpluscenter.com

25 amp

35 amp version

Each under $5.

Charles

 

[kazlx]

Can you post additional pictures of the magnetic chuck? That does look like a homemade circuit that probably replaced the original. The diodes are probably either 1n4003 ( 1 amp ) or 1n5402 ( 3amp). Earliest info I could find on either of those diodes was from 1966. Was hoping to be able to possibly identify what they are via their size, but that doesn't look like that will work. My assumption about that circuit not being original to the device is based on the information that I could locate on the picture you included with the “D & W Fuse Co” logo. It looks they became defunct in the 1920s and may have not been making the product after that. So from the limited information I could find, magnetic chuck is at least 40 years older than when those diodes first started manufacturing.

The original controls may have also included, in addition to the normal on/off switch, a demagnetize switch might have also been part of the original circuit. I did a bit of searching and didn't come up with any matches for the model number shown, although I probably have it wrong - STD5XI3

If you post more pictures of the magnetic chuck, we might be able to see a schematic on it someplace, or get some additional information about it.

It would probably be the easiest way to proceed if it has a diagram someplace. If it does not, you might have to broaden out and ask over at the practical machinist forums to see if anyone is has one that they could get you a picuture of. Or if they have a recommendation on a drop in replacement controller.

If that doesn't work, we can figure out what sort of magnet it should be ( probably based on the windings ) figure out what max voltage on it should be, and the possibly do a replacement circuit that would additionally have a fuse for protcetion and a demag setting ( either direct AC (which probably would work ) or slow down dc polarity reverse )

I'm not saying that you can't fix it as . You just probably only need to go with like replacement parts and it will be working as well as it was last time fixed, which might mean you aren't getting as much of a field as you should be, or too much of a field wihch ends up generating too much heat and shortens the life of the unit, and you could be missing out on the demag settings.


So if you post more on the chuck, me might be able to better replace what it has at the moment.

It certainly seems like a great find to me. You have a couple different directions you could pursue to get it going again. Maybe you could do the qucik fix part replacement and then come back later and make changes. You just need to ask yourself when do you start needing to use this by and how many hours could I spend working on it between now and then and is it going to be something I enjoy doing and will I learn anything from it. And if you still aren't sure, the folks here at GJ are usually more than willing to add in their own personal advice.

I can post more pics of the chuck, but the only info that I saw was on that plate. I searched prior to posting this thread and wasn't able to find much information on it either.

There is an on/off/demagnatize switch on the machine, to which this rectifier is wired.

The model number, for the chuck I just believe refers to Standard 5 x 13. Mag chucks usually referred to by their size.

Obviously, it would be ideal if it worked the way it should work, but I'm guessing it also worked good enough the way it is. That would be good enough for me to use. I know it worked as is (was) because I plugged it in and turned it on. It was also still hard wired at the place I got it from. You could flip the switch and the magnet would turn on and easily hold down a piece of steel. He also had a light wired to the circuit that turned on when the magnet was on.

I'm hoping to get some more done on this next week. I'm leaving for San Fran this weekend and won't be back until Christmas.

I appreciate the help so far guys.

 

[RonM3]

Two notes. One: I don't think the orange capacitors are needed. They honestly don't do anything in this circuit. The second note is to warn you that the large capacitor is an electrolytic capacitor. That means you must be careful of the polarity. If you hook it up backwards it could explode like a firecracker.

 

[dipper]

ya you don't normally see the orange caps in a bridge circuit like that. I was originally thinking that the rectifer circuit was original to the piece of equipment and that maybe they were put there for some specific reason but now it appears that it was somebody's homebrew project. Those could probably be omitted from the design.

Two notes. One: I don't think the orange capacitors are needed. They honestly don't do anything in this circuit. The second note is to warn you that the large capacitor is an electrolytic capacitor. That means you must be careful of the polarity. If you hook it up backwards it could explode like a firecracker.

 

[kazlx]

Hmm. Well I went to a local electronics place yesterday after work and they got me a bridge rectifier. Would that alone be sufficient for the chuck? They didn't have a replacement for the larger yellow capacitor. I'm assuming I could find one online. Does that just help to smooth out the DC?

 

[RonM3]

The large capacitor is required. You don't have to get the exact value any Electrolytic close to this value should work. Didn't this electronics store have any large capacitors? I miss the day of the old Radio shack when they mostly only sold electronic kits and components! Now Radio Shack is just a toy store. Online I have always had good luck with Mouser.

www.mouser.com

 

[zuk123]

You probably have a junk power supply or old printer or pc that has a suitable capacitor in it...

zuk

 

[foolishpride]

www.mcmelectronics.com

 

[racingtadpole]

First up... SOME OF THE STUFF MENTIONED PREVIOUSLY MAY GET YOU KILLED!!!
The circuit you are playing with is potentially lethal.

DONOT use a capacitor from a printer or PC. Printers and PC's run on 20V or less, again, you are rectifying mains supply voltage. BIG!!!!! Difference. Nor will the light dimmer assist you in any way, the dimmer wont like having to drive a full wave rectifier.

PUT A FUSE IN THE AC INPUT SIDE OF THE BRIDGE rated a little higher than the circuit requires to operate, ie if you need 3A to run it, install a 5A fuse.

The .1uf caps (the orange ones) are for noise supression. Removing them as someone suggested may cause issues with motor operation when the DC is applied to the electro magnet. They MUST be high voltage rated as they are providing a path for HV transients to go to ground.

The 200uF Electrolytic (yellow one) is as you assert a smoothing cap. If you buy a replacement the general rule of thumb is rate the Cap for AT LEAST 1.5 times the DC output voltage.

For future reference, to test the diodes, power it down and render it safe, release one end of the diode from the solder joint and put your DMM on diode test function. Place the leads across the diode. With the leads one way you will get a reading of zero. With the leads the other way, you will get a reading of either .2 to .3 (roughly) or 0.6 to 0.7 (roughly). 0.2 indicates a Germanium diode, 0.6 indicates a silicon diode. A short or open reading in both directions indicates its rooted. Its rare to see a shorted diode, normally they go open because the junction vaporises.

If you want to make it variable the only reliable way is to provide variable DC to the magnet. Two ways to do this, first is use a variac (variable transformer) on the AC input. The second is to insert a variable regulator in the DC output path. For the sake of this conversation the Variac in the AC is the easiest option, given the limited background in electronics.

I'll draw the schematic of the circuit for you later tonight when Im done painting the kitchen.

Above all else, please, please, please BE CAREFUL.

 

[racingtadpole]

I just drew the circuit out. In the first picture there looks like posts through the board to the other side of the board. Are there any componets on the other side of the board?
Is the positive side of the yellow cap facing down in the top picture?

 

[kazlx]

I'll have to take another look. I just got back from vacation this weekend and plan on tackling this pretty soon. I went to a local electronics house before I left. The guy went off the pics that I had and set me up with a bridge rectifier and the large capacitor that was close to what I have. He said they don't have the exact specs and if I didn't want to use the one I bought, I can just bring it back (it was only $4). He also said I can easily use the orange capacitors as they almost never go bad and also said they are for smoothing out the DC.

The circuit does not go anywhere behind what you see. The circuit is mounted to a piece of plexi that was drilled and tapped and mounted on standoffs to the housing. Like I said before, it looks (to me) as the original guts are long gone and the guy had rebuild the circuit (kind of a crappy job, but it worked) and just stuffed it in the same housing.

Like I said, I can solder and follow directions. Plus, I'd like to learn how to do this so I understand what's going on. I got some more of the grinder taken apart before I left for vacation and was able to replace all the wiring from the wall to the motor and power up the motor. Seems to spin nice and smooth. So, at least now I know I'm not wasting my time with improving the chuck or cleaning up the machine. The ways all look pretty good as well.

 

[racingtadpole]

Got a honey do job to finish up then I'll scan the circuit drawing and post it up for you with some notes that might help explain what happens to the AC to become DC.

Edit: Sounds like your electronics supplier is staffed by people that actually know what they are talking about, that is a very rare thing, at least here in Australia it is