Welding

[Little John]

Adam.

You appear to be the main man around here when it comes to electricity, so I was wondering if you might be able to help me with a bit of understanding. My electrical knowledge is very limited and extends only so far as what I have picked up in the last few weeks really. It is:

As volts rise, amps fall on a liner basis...and vice versa

Therefore doubling the volts will give half the amps

Power is measured in watts and is the product of volts and amps

Therefore to work out what the equivalent amps are for given voltages, you would divide the watts by a given voltage.

For example:

Starting with 40 volts 60 amps

40 * 60 = 2400

2400/240 = 10

So, 40 volts at 60 amps is equivalent to 240 volts at 10 amps.

Assuming all of the above is correct (please put me right here if it's not);

What I want to know is the following.

If I produce a welding arc of, say, 40 volts at 100 amps, will this produce an arc of identical or different characteristics to a welding arc of, say, 80 volts 50 amps? In both cases, the watts are the same, but I am assuming it is the amount of amps that affects the arc and not the watts. Then again, watts are a measure of the actual power coming down the wire, so they must affect the strength of the arc...right? I'm a bit confused here.

Secondly, if I have a welding setting of, say, 40 volts at 100 amps as compared to a welding setting of, say, 80 volts at 100 amps, will the arc be the same or different (e.g. stronger or weaker) for these two settings? The amps are the same, but the power (as measured in watts) is different due to the different voltages being employed. Again, I'm confused here.

[clv101]

The relationship between voltage, currant and power is described by Ohm's Law, the Wikipedia page is pretty good.
http://en.wikipedia.org/wiki/Ohm%27s_law

As far as welding goes, the first few pages of this pdf provides some clues about the impact of voltage and current:
http://shodhganga.inflibnet.ac.in/bitst ... er%205.pdf

[Little John]

The relationship between voltage, currant and power is described by Ohm's Law, the Wikipedia page is pretty good.
http://en.wikipedia.org/wiki/Ohm%27s_law

As far as welding goes, the first few pages of this pdf provides some clues about the impact of voltage and current:
http://shodhganga.inflibnet.ac.in/bitst ... er%205.pdf

Cheers CLV.

However, that second pdf talks about how voltage is affected by arc length, not about how manually adjusting the voltage affects the characteristics of the arc.

There two questions I guess I am getting at are;

How does changing the voltage (whilst keeping the amperage constant) affect arc strength and arc characteristics?

How does changing the amperage (whilst keeping the voltage constant) affect arc strength and arc characteristics?

I get the answer to the second of the above question as it's pretty obvious from direct experience. All other things being equal, more amperage gives a stronger/smoother arc/

It's an answer to the first question I need. Then, I can work out how these two answers intereact with each other when actually using the welder on a given voltage/amperage.

[adam2]

Volts and amps are not allways directly related.
Leaving welding aside for a moment, an electrical load subjected to a reduced voltage may use more or less amps, it depends on the type of load.
Consider a 240 volt 2.4KW electric heater, subject to manufacturing tolerances, it will use 10 amps at 240 volts.
If connected to a reduced voltage of 216 volts it will use about 9 amps
If connected to 264 volts it will use about 11 amps.
That is, the current increases at higher voltages, as does the heat produced.

Now consider 2.4 KW worth of 240 volt tungsten lamps connected to a 240 volt supply, the current drawn will be 10 amps.
If the same lamps are now connected to a 216 volt supply, the current will drop but not not by as much as with the heater. It will be about 9.5 amps.
Now connect the same lamps to a 264 volt supply, they will draw more current, but not as much as the heater, they will use about 10.5 amps.

Now consider 2.4KW worth of switched mode power supplies.
At 240 volts they will use 10 amps
At a reduced voltage of 216 volts they will use more current, about 11 amps.
At an increased voltage of 264 volts, they will use less current, about 9 amps.

It may therefore be seen that there is simple real world relationship between voltage and current, it depends on the type of load.

Now returning to welding, which is more complex.
Setting a welding set to 100 amps* does not mean that the output will be 100 amps, it means that the equipment is set up so as to be capable of about 100 amps* When striking the arc the current will probably be greater than 100 amps, with an average welding current of about 100 under average conditions. If the arc is pulled out to the greatest possible length, then the current will be less than 100 amps*

Selecting a higher voltage on the welding set will allow a longer arc, which may be desireable for some types of work.
Depending on the design of welder, a higher voltage setting may restrict the available current.
The voltage setting is normally the open circuit voltage, as may be measured by a voltmeter with no arc struck.

100 amps at 80 volts is clearly 8KW which is well in excess of that available from a 13 amp socket.
In practice though the running voltage might be only about 40 volts, and the load about 4KW output from the welding set.
With losses, the input might be about 4.5KW, which you might get away with for short term use on a 13 amp socket, though it is poor practice.

4.5 chinese KW should be fine on a 13 amp socket.

*UK amps !

[biffvernon]

Hang on, hang on, I know Part Pee is bonkers but that's part of Buildings Regulations, nothing to do with notifying electricity companies.

[Catweazle]

Power is also equal to the current squared x resistance. You can see from this formula that increasing the current makes a big difference to the power into the weld, it's also the reason why power distribution is done at high voltage and low current - so as not to waste power heating up power lines.

[adam2]

Hang on, hang on, I know Part Pee is bonkers but that's part of Buildings Regulations, nothing to do with notifying electricity companies.

Yes, that is why I said that a like for like electric shower replacement is NOT notifiable to the power company because it represents no increase in load.
But it IS notifiable to the part pee police as it is in a special location.

A new electric shower IS meant to be notified to the supply company as it is a new load of more than 3KW, it would also be notifiable to the part pee police.

And soon we will have new smart meters that will assuredly rat on us and tell TPTB if anyone has installed a new elecltric shower without informing both the power company AND the building control.

[biffvernon]

Ok, you've almost convinced me, Adam. Can you point to where the 3kW inform the electricity company legislation is please?

[Catweazle]

And soon we will have new smart meters that will assuredly rat on us and tell TPTB if anyone has installed a new elecltric shower without informing both the power company AND the building control.

That's it, stop the country I want to get off.

What is the matter with these people ? We'll have to have our appliances plugged into the socket by a "competent person" soon.

I despair.

[adam2]

Ok, you've almost convinced me, Adam. Can you point to where the 3kW inform the electricity company legislation is please?

AFAIK it is not a law passed by parliament.
I believe that it is in the fine print of the form that must be submited to the supplier when requesting a new or upgraded power supply.
One must notify them of the maximum demand of the installation, and undertake to NOTIFY THEM OF ANY INCREASED LOAD beyond 3KW/1HP.

Failure to so do is not AFAIK a criminal offence, but would be a breach of contract and in theory at least one could be liable for any damage caused to the suppliers network.
They would probably be entitled to bring a civil prosecution for breach of contract.

[JavaScriptDonkey]

Power is also equal to the current squared x resistance. You can see from this formula that increasing the current makes a big difference to the power into the weld, it's also the reason why power distribution is done at high voltage and low current - so as not to waste power heating up power lines.

I remember those now! The electric power equations.

P = V^2/R etc

Happy days indeed.

[biffvernon]

Ok, you've almost convinced me, Adam. Can you point to where the 3kW inform the electricity company legislation is please?

AFAIK it is not a law passed by parliament.
I believe that it is in the fine print of the form that must be submited to the supplier when requesting a new or upgraded power supply.
One must notify them of the maximum demand of the installation, and undertake to NOTIFY THEM OF ANY INCREASED LOAD beyond 3KW/1HP.

Failure to so do is not AFAIK a criminal offence, but would be a breach of contract and in theory at least one could be liable for any damage caused to the suppliers network.
They would probably be entitled to bring a civil prosecution for breach of contract.

Ah, so one needs to know what was the original 'maximum demand of the installation' agreed for the house. That may include scope for normal cooker, heating and shower circuits. The notification is only required for installations that go beyond this.

[adam2]

[quote="biffvernonAh, so one needs to know what was the original 'maximum demand of the installation' agreed for the house. That may include scope for normal cooker, heating and shower circuits. The notification is only required for installations that go beyond this.[/quote]

I would not count on this.
Many older supplies were only sized for lighting, ONE portable heater OR ONE other large loading appliance such as a washing machine, and normal use of any normal number of low loading appliances.
When a supply is requested, I dont think that one can put "normal cooker, heating, shower, circuits"
Each large load must be listed, together with size and number of general purpose subcircuits.

The maximum demand is then calculated by a formula*, not by simple addition, and approval given or not.

If the original application, and any subsequent requests for upgrades, did NOT include an 8KW shower, but one has been installed, then in theory the customer is guilty of breach of contract.
Likwise if cooking was originaly by solid fuel with no mention of electric cooker, but one has been added, then again the customer is in breach of contract.

Most of the time this is not enforced, but they can and do enforce it if problems result.

* cant remember the formula in detail, and it has changed over the years anyway, but it is something like

1) lighting=66% of the installed load
2) general purpose small power circuits, 100% of the largest circuit plus 40% of the remainder.
3) storage water heating, 100% of the instaled load.
4)Instantaneous water heaters (inludes showers) 100% of the largest 2 units, plus 25% of the remaing units.
5) electric cookers, 100% of the first 10 amps of the appliance rating, plus 30% of the remainder of the appliance loading, plus another 5 amps if the cooker switch has a socket outlet.
6) thermal storage heating, 100% of the connected load.

This is from my imperfect memory and may well be wrong in points of detail, but gives the general idea.

[biffvernon]

I've checked my contract and there's no mention of this sort of stuff.
http://www.ecotricity.co.uk/customer-se ... conditions
Unless perhaps it's buried in this clause:

By entering into an Energy Supply Agreement with us you are also entering into a Standard Connection Agreement with your electricity operator (the people who run the local grid) or gas transporter (the people who run the gas supply network). Please let us know if you would like a copy of this.

I wonder if anyone has ever asked.

[biffvernon]

Without asking, I've looked it up in this 85 page pdf:

http://www.energynetworks.info/storage/ ... 3Nov11.pdf

The nearest I've got is

13.3 The Customer shall ensure that the import of electricity from, and/or the export of electricity to, the Distribution System through the Connection Point does not exceed the Maximum Import Capacity and/or the Maximum Export Capacity (respectively).
Where the Customer is unsure of the Maximum Import Capacity and/or the Maximum Export Capacity, it shall contact the Company (and the Company will inform the Customer of the applicable capacities).

I'm not a lawyer but that says to me that if you are 'unsure of the Maximum Import Capacity' you 'shall contact the Company'. Which probably puts 20 million householders in breach of contract right now!

Hands up, who is sure of their Maximum Import Capacity? Anyway, I can't find any mention of a >3kW change being notifiable.