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Now! Before I try

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Ian Rogers

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… I have the need to make a welding turntable... I have a 12Vdc wiper motor.. I have and old ATX PSU with a 12Vdc 17A capability... Looking good!

I normally buy a motor driver on these odd occasions, like the Pololu stuff, However!!! The green wire on the ATX PSU switches the whole thing off and on..

Apart from the fan ( which probably wont like this ), If I stick a simple PWM on the switch? Wadaya think... Not the way it should be done granted!
 

AnalogKid

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I think No.

The green wire (On / Standby) is a logic input to the switcher control chip or maybe the power factor corrector. The circuit often has a capacitor on it for soft start. It has a response time measured in large fractions of a second. This will not take a PWM signal.

Also, as with most low cost multi-output switchers, the "main" output probably has a minimum load requirement, needed to stabilize the magnetics. In your case, it is the +5 V output. If it has zero or a very low load, the +12 V output might not be well regulated. Of course your results may vary, but I've ridden the ATX wave from the beginning, and despite there being many instructional videos about turning one into a bench supply, lab supply, etc., they do not make good general-purpose supplies. They are designed and tweaked from the ground up to do one thing only, power a motherboard (seen as a capacitive and/or resistive load) for the absolute lowest possible installed cost. Outside of that, all bets are off.

ak
 
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Ian Rogers

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Fair dues.... I'll just put a break in the power to the motor... Just extra cost I didn't need...

As for the pill... As you know AK at our age we take too many anyway... One more won't hurt.
 

JonSea

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Xbox power supply bricks put out 12V at 14 - 16 amps depending on the model, controlled by an input line to +5, which is low current, always on.

I wonder if switching a single voltage supply would be more successful. These can often be found in thrift stores for a couple bucks - a little more if they realize what they have.

If and when I get around to it, I'm going to make a 12v bus in the bedroom to power CPAPs and a few LED lights with failover to a 12v lead-acid battery in the garage. Much easier to deal with power failures in the middle of the night if the CPAPs have a beefy battery backup.
 

Ian Rogers

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Xbox power supply bricks put out 12V at 14 - 16 amps depending on the model, controlled by an input line to +5, which is low current, always on.

I wonder if switching a single voltage supply would be more successful. These can often be found in thrift stores for a couple bucks - a little more if they realize what they have.

If and when I get around to it, I'm going to make a 12v bus in the bedroom to power CPAPs and a few LED lights with failover to a 12v lead-acid battery in the garage. Much easier to deal with power failures in the middle of the night if the CPAPs have a beefy battery backup.
I'll build a simple pwm switcher today and see how it goes... The ATX PSU was free to a good home, I picked up several of them as I want to make a decent bench supply as well..

But the welding turntable is extremely urgent... Powerful motors these wiper ones..
 

alec_t

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To keep the ATX supply happy I'm guessing you might need a minimum fixed load in parallel with the PWM'ed one?
 

dr pepper

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Yes the power supply wont like pwm on the grren wire if thats what you meant, maybe if you went real slow it'd work, but then the turntable would pulse.
You need a return ground for the turntable, if you allow weld current through the motor it wont last long.
They had turntables where I used to work, if the brushes failed the motor didnt last long.
 

Mickster

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What is a welding turntable?

Mike.
The work piece sits on a platform which is able to be rotated, allowing a continuous weld to be made on a cylinder, for instance.

Example:
 

Ian Rogers

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To keep the ATX supply happy I'm guessing you might need a minimum fixed load in parallel with the PWM'ed one?
Fans running!!
What is a welding turntable?

Mike.
What Nigel said..

One of our main products is an "Anti two blocking" switch... If anyone has ever used a block and tackle if you keep the tackle going up, the two sheave blocks hit each other.. Usually this is the time to stop pulling.. On a crane it will snap the cable and the hook block comes back down to earth.. Thus killing any one it hits.. Anywho! This is tubular with a hanging bracket welded to the end.. We can't weld in circles so we have a machine to rotate the tube while we stay still.. I'll try and do a photo when I'm done.
 

Ian Rogers

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Actually! my biggest issue ( not with the ATX PSU ) is isolation... The welder puts out quite a bit of current, so I have make sure the two supplies are separated.. I have some nylon to make a kind of universal joint so the drive will not touch the electronics..
 

shortbus=

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Actually! my biggest issue ( not with the ATX PSU ) is isolation... The welder puts out quite a bit of current, so I have make sure the two supplies are separated.. I have some nylon to make a kind of universal joint so the drive will not touch the electronics..
Two things as a welder that has used one of these turntables.

1. you definitely need isolation from the motor to the turntable. Either by using a rubber belt btween the motor and the turn table, or if using direct drive a Lovejoy coupling with a rubber insert.

2. You don't say what kind of welding, but a wiper motor may be too fast. Most of them even on low speed are ~45RPM. So reduction with a belt drive would make the first option above a good one. Decide on a RPM and then build the drive ratio so when the motor is at full speed the table turns at that RPM, then you only need to use PWM when a lower speed is needed.
 

Ian Rogers

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You don't say what kind of welding, but a wiper motor may be too fast. Most of them even on low speed are ~45RPM.
Mig welder... The one we used to use was on a small table. A small AC motor with the top of an old pillar drill.. We could drop the speed via the pulleys and get the speed we needed... We used to just clamp the welder earth to the round bar that housed the job at hand...

That table is gone so I need a quick fix. The wiper motor turns well using the PSU.. I have pre-loaded the 5v rail so the 12v will be constant.. I have a few 3055 transistors on the way ( I know they are 10A, but the wiper only pulls 5A so it will be a smite less when using though PWM) I may need to put two in parallel if they get warm..

1. you definitely need isolation from the motor to the turntable. Either by using a rubber belt between the motor and the turn table, or if using direct drive a Lovejoy coupling with a rubber insert.
I have made a nylon UJ to isolate the motor from the welder.. Very strong... I just need to make a frame to put it all on..
 

shortbus=

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If this is in a production situation, you also need to watch for overheating the DC motor when running it at a lower RPM.
 

Ian Rogers

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Each tube is 40mm diameter and he get's about 40 done each time.. But I'll take that onboard and keep an eye on the motor temperature.

I make searchlight electronics and I don't get a lot of motor overheating even when the light is barely moving..
 

dr pepper

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Commercial turntables I've had experience with do not isolate the ground from the weld set.
Which means if the weld set's earth goes open the mains cable earth wire turns to charcoal.
I guess they do that as weld voltages can be 90v or so, and higher than 50v in the Uk is considered 'dangerous'.
 
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