With a full wave bridge, you would get about 16.8 VDC out of it. 1.414*12

The DC current is less than the AC current rating of the transformer.

See: http://hammondmfg.com/pdf/5c007.pdf

 

So iv just stumbled upon a 28vac transformer but the only problem is that it doesn't show how many amps only voltage, its a 220v primary and 10v / 28v / 32v secondary its has a model number of E6640# but Google is not showing anything on the transformer

 

To find the power and current rating of a transformer, lookup a Hammond 28V at 120VA and its datasheet will show its weight and size. then compare your transformer.
You will definitely need to use the improved opamps with the higher voltage. Also many resistors must be larger.

 

Audioguru

Sorry to be a pain is there any chance there is a picture of the board with the mods carried out, just so I can see it for myself thanks

 

Sorry to be a pain is there any chance there is a picture of the board with the mods carried out, just so I can see it for myself thanks

You bought the cheap Chinese kit that has had many complaints. Some people made it and smoked many parts, then since larger and cooler parts do not fit on the pcb then they used it with only 15VAC or 18VAC and only 1.5A for it to survive.

 

I don't see any flaws in the circuit, but then I have not done a power analysis of it, only looked at the functionals. Is there any problem that using adequately rated parts and enough bypassing capacitors would not solve? It could be built up on a Vector board with as much room as needed. Not that I really need another supply .I got one of those 0-50 volts and 0-50 amps units because nobody could make it work. You had to read the manual to make it work. AND, for the full 2500 watts power it does need to run on 220 volts.20 amp service.

 

You had to read the manual to make it work.

Ye Gods! Surely not! What is the world coming to?

 

Ye Gods! Surely not! What is the world coming to?

SOME manuals are very useful, other manuals consist primarily of warnings and safety precautions, all in ten different languages.

 

manuals

What's a manual?

 

What's a manual?

I remember them. They had a gear stick.

 

New at this...just have a question related to microwave transformers used to build a spot welder. Having removed the high-voltage winding and replacing it with an eight gauge cable wrapped around the plates of the transformer (that will become the contacts for the welder), Do I need to insulate the transformer plates from touching the aluminum box I am installing it in? Also can I use polyurethane to touch up the scratched surfaces on the transformer from cutting the high-voltage windings from it?
Thanks CAB55

 

Welcome to AAC.

First, if the insulation of the primary coil has been damaged, you may want to start over.
Second, 8 gauge wire is going to get hot when you spot weld.
Third, this is an older thread. If you want to post a question you can do so. To take someone else's thread and ask an embedded question is considered "Hijacking" someone else's thread. It's preferred that threads not be hijacked.

As far as insulating the MOT (Microwave Oven Transformer), no. Actually, in your cabling, your hot and neutral should go to the primary winding - as I'm sure you already know. However, the MOT and the aluminum case should, nay, I say, MUST be grounded for safety concerns. The MOT should be grounded to the aluminum case and the case should be grounded to earth ground. That's purely for safety reasons. Since you nicked the insulation of the primary, there's a risk of shorting to the case. If you're rig is not grounded you could become a ground path. But only for a short period of time as you will either be shocked away, knocked away or fall away dead.

Messing with line voltage should always be done with safety as the first three concerns. Safety - safety - safety. Beyond that, caution when dealing with lethal voltages is highly recommended.

I started to build a MOT spot welder, but never finished mine. I have an "Ot" gauge wire as my secondary and it has two turns around the iron core. And I haven't gone any further with it since then. The heavy wire was very difficult to wind through but was done with great care to not nick any of the wires at all. In fact, the first MOT I converted I, too, nicked the primary windings which DID result in shorting to the core. No, I didn't get a shock because I checked for that before powering it.

Again, Safety (x3), then caution. Then testing before you apply power. Be safe. We'd love to have you around here on AAC for many years.

 

Welcome to AAC.

First, if the insulation of the primary coil has been damaged, you may want to start over.
Second, 8 gauge wire is going to get hot when you spot weld.
Third, this is an older thread. If you want to post a question you can do so. To take someone else's thread and ask an embedded question is considered "Hijacking" someone else's thread. It's preferred that threads not be hijacked.

As far as insulating the MOT (Microwave Oven Transformer), no. Actually, in your cabling, your hot and neutral should go to the primary winding - as I'm sure you already know. However, the MOT and the aluminum case should, nay, I say, MUST be grounded for safety concerns. The MOT should be grounded to the aluminum case and the case should be grounded to earth ground. That's purely for safety reasons. Since you nicked the insulation of the primary, there's a risk of shorting to the case. If you're rig is not grounded you could become a ground path. But only for a short period of time as you will either be shocked away, knocked away or fall away dead.

Messing with line voltage should always be done with safety as the first three concerns. Safety - safety - safety. Beyond that, caution when dealing with lethal voltages is highly recommended.

I started to build a MOT spot welder, but never finished mine. I have an "Ot" gauge wire as my secondary and it has two turns around the iron core. And I haven't gone any further with it since then. The heavy wire was very difficult to wind through but was done with great care to not nick any of the wires at all. In fact, the first MOT I converted I, too, nicked the primary windings which DID result in shorting to the core. No, I didn't get a shock because I checked for that before powering it.

Again, Safety (x3), then caution. Then testing before you apply power. Be safe. We'd love to have you around here on AAC for many years.

Thanks for steering me straight Tony! This is my first attempt at asking a question and wasn’t sure where to post it. Still not sure...Fortunately I did not nick the primary winding only the metal plates of the transformer itself so I think I’m OK there. I already tested it placing a screw between the two cables. I appreciate the info regarding the cable thickness. I have viewed many YouTube videos and one of them showed this smaller cable example by winding it one more time through the transformer. I’m not planning on using this a great deal so maybe the smaller cable will work for light duty work?? What do you think?

 

Time will tell if the smaller wire will be sufficient. Depends on what size welding you intend to do with it as well.

 

Thanks for steering me straight Tony! This is my first attempt at asking a question and wasn’t sure where to post it. Still not sure...Fortunately I did not nick the primary winding only the metal plates of the transformer itself so I think I’m OK there. I already tested it placing a screw between the two cables. I appreciate the info regarding the cable thickness. I have viewed many YouTube videos and one of them showed this smaller cable example by winding it one more time through the transformer. I’m not planning on using this a great deal so maybe the smaller cable will work for light duty work?? What do you think?

Really, for the duration of a single spot weld, the heat input of #8 wire should not result in much temperature rise. Of course that depends a whole lot on what you are welding and how many seconds the weld power is on. Temperature rise is driven by the watt-seconds passing through the wire, and is inversely proportional to the mass of the wire being heated by those watt seconds.

 

The ones I was trying to copy showed the system melting a 1/2 inch nut and a bunch of other stuff. As to the final application of the TS's spot welder, wire gauge may be sufficient, might be too small.

 

I've seen them with heavy gauge wire and with smaller wires. It all depends on how much heat you're going to be pushing. What I've seen was spot welding wires across each other, like a shopping cart where there's a grid. That's going to take some heat. Not sure if the smaller gauge wire will handle the load.

 

I do not consider an MW oven transformer to be a constant duty device anyway. The old formula of 100 watts per square inch of center core area puts many of them in the under 500 watt realm. Some are larger some are not.

 

Like @ThePanMan, I, too messed with a few of those MOT's. Those cores, the ones I messed with, have the core welded along the two outside seams. Having cut those welds with a friction wheel, one side comes off. Then you just slide the coils out. Put whatever you want back in them then weld the seams back. I have yet to do something with the few I have. More useful has been the control boards. I did a project where I use a control panel to power an electrical outlet, then plug my soldering iron into it. When I want to solder I just set the timer for 30 or 60 minutes, then solder. As so often I forget to turn my iron off and end up letting it sit hot and idle for long periods, the MO control board solves that issue. Plus, it beeps to remind me it has been shut off.

 

Using the control board for any other application is an interesting concept indeed. Probably some of them with fewer functions would be more useful, though. Some of the much older mechanical timers with the rotary knob setting would make an easier to work with package.
My thinking has been to use one of the transformers with a diode voltage multiplier setup to provide an anti-carjacking system for personal protection. My thinking is that an attacker with a gun in their hand is an OK target for a more extreme response. However no discussion of such hardware is allowed on this website. Not even a rat zapper can be discussed.