Needs Pictures: 0
Results 46 to 60 of 70
Thread: Same MIG new problem
-
29th Mar 2020, 04:03 AM #46
Hi Stuart,
Do not under any circumstances use a variac !
Use a transformer, say a 6 volt ideally or a 12 battery charger transformer. Measure the voltage output from it first and then when connected measure the primary voltage from the welder transformer. You shouldn't have to limit the current at all but it is worth checking the loaded to unloaded voltage drop.
Since the capacitors in the welder are rated at 40 volts and I would expect them to be over rated by, say 25%. So the output voltage from the welder transformer would be around 30 volts. Since the mains voltage into the transformer would be 240 volts.
Divide 240 by 30 gives a transformer ratio of about 8. So 6 volts AC in to the welder transformer secondary should produce 6 X 8 = 48 volts on the primary side, with 12 volts you can expect double that.
Please take care !Best Regards:
Baron J.
-
29th Mar 2020, 08:59 AM #47Most Valued Member
- Join Date
- Jul 2010
- Location
- Melbourne
- Posts
- 9,088
Hi Baron,
Well that is disappointing, I know where that it is.
I'm bound to have an 6 or 12V transformer around some place, I'll find one, but could you please explain why I cant use variac?
All makes sense. About the transformer ratio, that would apply to the turns of the windings wouldn't it? So for example 50 secondary turns would be 400 primary.(now the secondary is 2 parallel windings so that would mean 200 turns) I'm sure its not that simple but I'm just trying to work out a ball park. If its a smallish number trying to unwind the secondary in place maybe worth it. If its a large number I might have to try cutting the core* which would at least make unwinding the secondary easy.
Certainly will
Thank you.
*I don't mean cutting through the laminations. The core is welded together, so to separate I would have to cut the welds out. Cutting it open brings issues with assembly of which I am sure I am only aware of a few, like air gapes and excitation currents. Don't confuse being aware of with knowing a great deal about them lol
-
29th Mar 2020, 12:17 PM #48Most Valued Member
- Join Date
- Mar 2011
- Location
- Southern Flinders Ranges
- Posts
- 1,536
You will need to put a current limiting resistor in line with the supply from the test transformer. The secondary of a welding transformer will present to the test supply as something akin to a dead short. Failure to do so will result in the smoke being released from your test supply.
Personally, I’m not convinced the issue is the transformer at this point.
-
29th Mar 2020, 03:06 PM #49Most Valued Member
- Join Date
- Jul 2010
- Location
- Melbourne
- Posts
- 9,088
-
29th Mar 2020, 05:28 PM #50Most Valued Member
- Join Date
- Mar 2011
- Location
- Southern Flinders Ranges
- Posts
- 1,536
Anything bigger than 9ohms. 9V/9ohm=1A
47ohm will supply around 180mA that should be plenty for what you are doing.
Best not to lick the primary contacts either, assuming around 8:1 step you’ll be looking at around 70V give or take across the full side of the primary, that will be a rather unpleasant sensation. 47ohms will limit to 180 on the secondary side and you’ll see it at around 25mA ish on the primary.. not lethal but still painful
-
29th Mar 2020, 07:22 PM #51
Hi Stuart, Russ,
I'm bound to have an 6 or 12V transformer around some place, I'll find one, but could you please explain why I cant use variac?
They are also not guaranteed to provide a smooth voltage rise, usually just little steps as the wiper crosses over the windings. The windings can also move and you can sometimes get spots where the wiper doesn't make contact at all, sometimes arcing, particularly if the variac is old and well used. Some variacs used a carbon brush wiper, which wears leaving conductive dust between the windings causing partial shorts and overheating, particularly at low voltages, other types use a folded brass or copper brush which smears the copper windings. Again causing some problems.
In their day they were the bees knees for theatre and cinema lighting !
The "Ohms Wheel" can be used to work out what resistance and current values are given any two values. As far as a current limiting resistor is concerned, just use a 12 volt side or headlight bulb.
EDITED to add:
the secondary is 2 parallel windingBest Regards:
Baron J.
-
29th Mar 2020, 10:56 PM #52Most Valued Member
- Join Date
- Jul 2010
- Location
- Melbourne
- Posts
- 9,088
Evening guys,
I will try my very best to avoid the temptation.
thank you.
My maths doesn't like that. But I've already dug out my resistance box.
Yes. The thing I was trying to get at is, guessing from looking at the picture there are 50 turns on the secondary. As its two parallel windings that's really 25 turns. So if my ball park number of 50 is about right and your ratio of 8 is about right that would mean 200 primary turns would be about right. Thats all.
-
30th Mar 2020, 01:48 AM #53Golden Member
- Join Date
- Dec 2007
- Location
- Adelaide
- Posts
- 574
In testing the transformer have you thought about disconnecting everything from the secondary side of the transformer, then connect the primary directly to the mains through a 240v incandescent globe ie the globe is in series with one of the mains leads, before you power it up make sure everything is insulated and securely connected with terminal blocks etc, not crocodile clips or wires twisted together. About 75W or 100W globe should do it, it may come on dimly even if the transformer is good, check each of the taps this way, if the globe lights up full brightness then I'd say the transformer is toast, if the transformer is good you should be able to measure the welding voltage on the secondary side.
-
30th Mar 2020, 02:58 AM #54
-
30th Mar 2020, 03:03 AM #55
-
30th Mar 2020, 09:36 AM #56Most Valued Member
- Join Date
- Jul 2010
- Location
- Melbourne
- Posts
- 9,088
Morning
It was considered, and I can see it working on smaller transformers but wasn't so sure it would show anything on a transformer of this power. Having said that I'm happy enough to try it if you think it will show something, providing 1. I can find a bayonet fitting. 2. I can find a 75W/100W bulb.....haven't seen one of them for some time. I do have some 25W ones.
First let me say, I love using headlight bulbs as loads as they have built in spade connectors.
But a 55W headlight bulb is showing about 0.3ohm, now that is not going to increase much until its well after a 9V 1amp supply is maxed out surely? Even a 6W bulb is only showing 1.3ohm. Now if it was a 9V bulb that wouldn't matter as when it heated up it would draw about .666Amp(well in a DC circuit). But its a 12V bulb so its not going to heat up nearly as much....I'm missing something
I wont get to try another until late this afternoon at best.
Thank you guys
-
30th Mar 2020, 10:20 AM #57Golden Member
- Join Date
- Dec 2007
- Location
- Adelaide
- Posts
- 574
If you are using mains AC voltage to power up the primary then you need to use a mains rated light globe ie 240v, I think 25W may be too small assuming the transformer is ok there will be a small amount of magnetising current that will light up a 25w globe a bit more than dim, any incandescent globe is ok even a halogen type. For testing amplifiers I generally use a 60W globe it does not light up even dimly when connected to a 300w transformer that has no load ie everything disconnected from the secondary. If the transformer seems ok then perhaps start connecting things on the secondary side one at a time the capacitors will cause the globe to light momentarily due to inrush charge current but it the globe should dim back down one the capacitors are charged, the bleed resistor needs to be disconnected.
-
30th Mar 2020, 10:43 AM #58Most Valued Member
- Join Date
- Mar 2011
- Location
- Southern Flinders Ranges
- Posts
- 1,536
55w bulb is going to draw 6.1A at 9v
6W bulb will draw 660mA at 9V
Keep in mind:
There is no need to run the the little plug pack at full noise, you just need enough to overcome losses and produce meaningful numbers, a couple of hundred mA will be adequate in that regard
You can use a variac to test a transformer from the primary side if necessary
-
30th Mar 2020, 01:45 PM #59Most Valued Member
- Join Date
- Jul 2010
- Location
- Melbourne
- Posts
- 9,088
Yes but I'm not even sure I have one of those. Mostly down lights here.
Are you sure about those numbers?
Sure a 9V 55W bulb is going to draw 6.1A, but we are talking about 12V rated bulb. Its not not going to get as hot as it should so (as I understand it) the current will go up. But 6W is 6W lol I dont know. Going to have to test it and see.
About connecting low V to the secondary. Do I need to connect the parallel secondary windings? (I can't see why I would, but thought I would ask)
-
30th Mar 2020, 05:03 PM #60Most Valued Member
- Join Date
- Mar 2011
- Location
- Southern Flinders Ranges
- Posts
- 1,536
Without having gone back to check the circuit diagram again, I can’t see a need to power both secondary windings, all you are after is a comparative reading across the primary windings to find out if anything is astray there, you should be able to see that just applying AC to one winding.
Similar Threads
-
mt3 problem
By TKO in forum METALWORK GENERALReplies: 27Last Post: 3rd Apr 2013, 09:59 PM -
Problem with PMs
By jerryc in forum FORUMS INFO, HELP, DISCUSSION & FEEDBACKReplies: 5Last Post: 27th Nov 2007, 01:19 PM