Wire feed PSU mod - wire speed won't increment

[skotl]

Just realised this, which I'm sure is obvious to most but may be of interest to others who do one of the wire-feed motor power supply mods;

The manual says that motor speed increases when you up the amperage. But if you have a separate power supply feeding the wire motor, this is no longer the case.
Post wirefeed supply change, the amperage setting has no impact on the wirefeed speed so the good news is that you just need to figure out wirespeed once for your welder. You just need to know that...

 

[Wedg1e]

Don't they call that 'synergic' when the motor speed increases in proportion to the welding voltage? My Oxford 120s does it, yet my Oxford 300 (that dates from the same era) doesn't. The 300 has a massive speed range: from so slow you can scarcely see it move, to so fast Robson Green could use it for casting a line

 

[skotl]

"synergic" - yep - I can see that.

The only reason I mentioned it is that I decided, finally, to scribble up a table of power settings / wire speed setting / actual wire speed and was confused that changing the power setting did not affect the wire speed. Until I realised that I had replaced the entire wire speed circuitry

So, yep, I presume that many welders have a synergistic relationship between power settings and wire speed, until you change it

 

[mike 109444]

As you now have a separate supply that is always on rather than one that is on on when trigger pressed you can do as I did (not a SIP!) and add a digital volt meter to the front of your machine. This will give you a very accurate read out compared to a dial with a pointer even a good dial!. I initally replaced the feed knob on mine for a clearer one from Maplins but then the cost of a digital panel meter < £5 ! and free post from far east (takes a week or two to come through). You get a 3 digit + decimal point. Cheep as chips. Works best with a always on supply but could be used on a triggering on feed to motor but that would be a pain.
Does allow for fine tuning and looks good

 

[skotl]

Nice idea, Mike - I may do that!

 

[skotl]

As you now have a separate supply that is always on rather than one that is on on when trigger pressed you can do as I did (not a SIP!) and add a digital volt meter to the front of your machine. This will give you a very accurate read out compared to a dial with a pointer even a good dial!. I initally replaced the feed knob on mine for a clearer one from Maplins but then the cost of a digital panel meter < £5 ! and free post from far east (takes a week or two to come through). You get a 3 digit + decimal point. Cheep as chips. Works best with a always on supply but could be used on a triggering on feed to motor but that would be a pain.
Does allow for fine tuning and looks good

Thanks Mike - just ordered one of these (£4.30 with free postage from Notts)

I had the side off to verify the voltage range and it seems quite strange. The PSU is 20VDC out and when I measure the output at the relay when the trigger is not pressed, it always shows 20V. It's only when I press the trigger that the voltage is reduced, based on the speed knob, to ~1V up to 20V. I would have thought that the output from the PCB would always be the regulated voltage, but apparently not.

No biggie - just means that after I fit the meter, I'll need to remove tension on the wire feed, press the trigger and get the voltage reading.

 

[mike 109444]

Rather than mess with roller tensioner you could fit a switch in one of the feed wires to (near motor) maybe mount it by the feed roller or on the front next to the digital meter. Flick switch to off, pull trigger, note reading, adjust even with trigger pulled then try welding. If good note reading + power setting and thus you can create a chart. I have noted that as little as 1/2 to 1 volt can make quite a difference. Reason you might be seeing the voltage could be due to a capacitor holding the voltage.

 

[skotl]

Bl**dy hell - that's a great idea! I'll definitely do that - good one, Mike

 

[Richard.]

Shoot me down here if I've miss understood but is this not how a mig works. Most basic migs have volts and wire speed. (Wire speed generates the current amps) if the machine has an amperage setting this is just wire feed speed. It's not synergic or anything fancy it's how they operate. A proper synergic set is where you adjust one parameter or give the machine a bit of info like plate thickness and it will work out the conditions for you to fine tune.

 

[mike 109444]

Ill put me gun away But what the ideal behind the digital read out is that unlike a pot with a series of poor lines marked out the digital gives a clearer and more accurate reading of where the pot is set. As some members have said in the past they move the pot then try and find the same position "that works" ! again can be difficult. With digital read out you should be back at the same position for wire speed.
Voltage (power) sets the voltage at the wire tip and the wire feed rate can be used to fine tune the welding power. There is a more detailed (correct!) write up somewhere on the forum.
Note some more expensive machine have a digital readout for wire speed (maybe in volts but academic what it is) and they may also have current digital readout but that is a bit more difficult to ad to get a constant reading as the current only flows when trigger pressed.
Hope that makes sense

 

[skotl]

Shoot me down here if I've miss understood but is this not how a mig works. Most basic migs have volts and wire speed. (Wire speed generates the current amps) if the machine has an amperage setting this is just wire feed speed. It's not synergic or anything fancy it's how they operate. A proper synergic set is where you adjust one parameter or give the machine a bit of info like plate thickness and it will work out the conditions for you to fine tune.

I might get shot down, but my understanding is that the opposite applies; welding power is driven by current, which is set by the windings on the transformer.
On my SIP TopMig 150, there are six power settings and these select a different takeoff from the welding transformer.
The volts at the welding tip (feed wire for MIG) are constant, at around 30VDC but the current is dependent on where the feed is taken from the transformer.
In other words, the wire feed speed is a consequence of the welding power, not a cause of it.

Wire speed is variable (based on voltage). More volts = higher motor speed = higher wire feed speed.
On most MIGs I understand that the wire speed increases as you increase the power which, from a thickness / power / feed-per-second perspective, makes sense.
My point was that when we feed a new power supply through to the motor in a SIP, we bypass that power = speed configuration on the control circuitry. So now wire feed speed is completely independent of power setting.
Which is fine by me. Or it will be, once I've fitted Mike's voltage meter

 

[Richard.]

I'm not that clued up on the electric side of things but I don't think out put voltage has a relation with wire speed.
Voltage is set to give you the heat to burn the consumable.
Wire feed is set to give the voltage something to burn
Amperage is generated from the welding process and goes up and down with the wire feed.
In cc you would set the amperage you wish to achieve and the wire feed will adjust it's self to maintain that current. (Basic migs don't usually have this)

 

[Richard.]

Unless your machine is cc (constant current) this would mean you set your current and the wire feed speed would be adjusted by the machine to maintain the current you set.
But this is amperage related
Voltage should have no relation on wire speed
You should be able to set the voltage at where ever you like and the wire speed should not alter.

 

[skotl]

Richard; bear in mind here that what I'm talking about is voltage to the wire feed motor, not voltage to the arc. AFAIK, voltage to the arc is constant (?30VDC?) on these machines.

 

[Richard.]

Ah I was talking arc voltage.

 

[Richard.]

Voltage to the arc must have some adjustment to enable the weld at different wire speeds.

 

[Richard.]

It sounds to me like yours is a CV (constant voltage) machine so yes when you are welding the voltage will remain pretty constant but you set that ocv (open circuit voltage) on the machine. The range is usually around 10-50 volts.

 

[skotl]

Finally got round to adding the digital volt meter as suggested by Mike

Works great, although Mike's other suggestion of adding a switch to cut power to the motor, so that you don't waste wire, seems to be a non-starter on the SIP (may work on other machines). The reason is that under no-load, the board seems to output the full voltage.
Not a massive issue, though, as it just means I flip the pressure plate off the wire feed and set the voltage without wasting wire.

Here's the new switch and the volt meter in all their glory;

A video of the meter in action;

And the (rather untidy) wiring of the meter, the wirefeed transformer (a laptop docking-stating supply, bottom right of the unit) and the relay for the wirefeed switching;

Many thanks to @mike 109444 for the ideas!

 

[BChild]

I think I might have to try this........ I went a different way in order to find repeatable settings but I still get some variation as the machine warms up (or I did last time I used it) if I was getting changes in wire feed voltage the numbers would go up or down and I could trim accordingly.....

 

[mike 109444]

I think I might have to try this........ I went a different way in order to find repeatable settings but I still get some variation as the machine warms up (or I did last time I used it) if I was getting changes in wire feed voltage the numbers would go up or down and I could trim accordingly.....

If you already have a digital meter for general testing then to check if you are getting drift you can hook the meter onto the motor terminals this will give a reading much as Skotl. It will also show how much or little a small movement of the wire feed knob does or does not make. Try for example your normal setting is say WF5 then with meter attached turn WF control down to zero then back up to where you THINK 5 is. Run welder and note meter reading. Then turn WF up to max then back to where you THINK 5 is and see if same. May or may not be as you only have a dial and pointer. It may not make a lot of difference but it's nice ti see an exact figure that is repeatable.