Welding

[Little John]

Woo hoo....

The inverter went for £295. So, all costs of transition over to the Bantam AC welder plus the cost of all the kit relating to the carbon arc torch are covered.

In fact, I'm about a 100 quid up.

[JavaScriptDonkey]

Adam will probably be along shortly with the de facto answer but in short it's down to Watts.

Under DC, Watts = Volts x Amps and is often expressed as VA although under AC that is slightly misleading as, obviously, the AC voltage is alternating.

The output power is always going to be less than the input power and I guess you're running this welder of a 13A 240 mains supply?

[Little John]

Adam will probably be along shortly with the de facto answer but in short it's down to Watts.

Under DC, Watts = Volts x Amps and is often expressed as VA although under AC that is slightly misleading as, obviously, the AC voltage is alternating.

The output power is always going to be less than the input power and I guess you're running this welder of a 13A 240 mains supply?

I would have thought the output power will be identical (putting aside the obvious heat losses in the transformation of voltage) to the input power (expressed as watts). It's just that the ratio of volts to amps in the output will have changed. So, for example, the watts on both the input and output will be just the same for, say, 40 volts/160 amps on the output side as compared to 80 volts/80 amps on the output side. Now, of course, on the output side of a welder, neither of these settings will blow a fuse because there is no fuse to blow on the output side. There will also be no difference between their propensity to blow the fuse on the input side either since their demands are the same in power terms. However, on the input side, amperage demand will vary (and so will the propensity to blow a fuse) if you change the the voltage output setting whilst keeping the amperage output setting the same

For example, if you choose a 30 volts/100 amps output, this will demand 240 volts/12 and a 1/2 amps on the input side. If, on the other hand, you choose a 60 volts/100 amps output, this will require 240 volts/25 amps on the input side. Clearly, if you are using a 13 amp fuse on the input side, the 25 amp input demand will blow the fuse.

I'm guessing that these old welders use two voltage setting (I think they are 40 and 80 volts respectively) in order that you can get a high amperage, but only need to use a low voltage to get it. On the other hand, in order to get a low amperage, you need to use a higher voltage, but still one that is within safe parameters. Modern inverter welders also use different voltages for the same purpose, but do so automatically by adjusting voltage on the fly as you adjust the amperage output setting.

By only raising or lowering voltage by the minimum amount necessary, such inverters are able to always find the perfect balance between amperage requirements on the output side whilst keeping amperage demands on the input side to a minimum. Consequently, my inverter was able to weld at 160 amps without ever blowing a 13 amp 240 volt input supply.

My old Bantam welder has an overlap on the amperage settings for the two output voltages I mentioned earlier. These are 100 though to 120 amps. I can choose these amp settings on either voltage. However, on the higher voltage/same amperage setting, the arc burns hotter and is more prone to blow the 13 amp input fuse. As you suggest, watts are watts and the extra energy for that hotter arc has to come from somewhere. That somewhere must be a greater amperage demand on the 240 volt input side required to provide 100 amps at 80 volts as opposed to 100 amps at 40 volts on the output side. Hence the greater propensity to blow a 240 volt/13 amp input fuse on A voltage/X amperage output as opposed to B voltage/X amperage output.

Having, said all of the above, I should reiterate is it only speculation and deduction on my part since I know next to bugger-all about electricity.

[JavaScriptDonkey]

All sounds good.

I think that calculating Watts in an AC circuit is subtly different from doing it in a DC circuit on account of how the voltage varies either side of zero. This needs you to apply a power factor which is just a reduction to allow for the times of low voltage and is commonly noted to 0.8.

That gives you 13 x 240 x 0.8 = ~2500W which looks about right.

So an AC welder outputting 100Amps from a domestic supply only has a peak of 25Volts before it all starts to go very wrong.

Or I'm barking up the wrong tree and will shortly be corrected.

[Catweazle]

Don't assume that a 240v welder can only take 13 amps, mine was ( and will be again ) connected to a 32 amp circuit.

From memory, power factor is used to compensate for the fact that voltage and current can be out of phase in a capacitive or more commonly inductive load. A welding transformer is definitely an inductive load.

For most calculations you can simply use volts x amps = watts.

[JavaScriptDonkey]

32Amp sockets aren't commonplace and I'd assume SC would mention if he had one. Even 16Amp circuits aren't usual in a non-industrial setting.

I was on a site a few weeks back where the sparky, having been instructed to lay in a 16A socket with trailing cable decided that the safest thing to do was plug it all in and terminate it with a connector block and insulation tape.

[Little John]

32Amp sockets aren't commonplace and I'd assume SC would mention if he had one. Even 16Amp circuits aren't usual in a non-industrial setting.

I was on a site a few weeks back where the sparky, having been instructed to lay in a 16A socket with trailing cable decided that the safest thing to do was plug it all in and terminate it with a connector block and insulation tape.

I've had a sparky mate fit a 30 amp socket this evening. Running like a goodun now on all amps and voltages. It definitely runs a stronger arc/carbon-arc-flame on a given amperage than my inverter. Which is weird on two fronts. Firstly, amps are amps and should be the same (unless my inverter ran high amps on a very low voltage compared to my oil cooled welder?). Secondly, I think I read somewhere that AC loses a bit of power because of the alternating current. Maybe I read that on here posted by one of you guys.

Anyway, I don't know what I'm talking about now in a fairly major way. The main thing is it's definitely more powerful than my invertyer, is as powerful as I'm ever going to need and the carbon arc torch works perfectly. Finally, it would seem that it basically doesn't have a duty cycle in the sense that the oil-cooling is so efficient that it never gets hot. I've read on the welding forums that you can weld all day long with these welders.

So, it's all good....

Edit to add:

I've since read on the welding forums that these particular welders do indeed need to run on 30 amps on a 240 volt single phase supply if you want to avoid having to change popped fuses on a regular basis

[adam2]

It should be the same though. 100 amps is 100 amps...right?

Unless they're Chinese amps.

Indeed, the old welder is from the days when 100 amps was 100 UK amps, not only were suppliers more honest in those days, but the purported 100 amp output at mains frequency could be measured by anyone who doubted it.

The new welder is probably chinese amps.
"estimated equivalent effective welding amps"
"plus or minus 15% tolerance"
"initial striking amps, running amps automaticly optimised"

[adam2]

I presume that you or your electrician have notified the electricity supplier of the extra load

Anything over 3KW or 1HP is meant to be notified

[biffvernon]

Anything over 3KW or 1HP is meant to be notified

Eh? Do I have to tell the electricity company if I have a shower?

[mobbsey]

32Amp sockets aren't commonplace and I'd assume SC would mention if he had one. Even 16Amp circuits aren't usual in a non-industrial setting.

I use the 30A main coming off the domestic distribution board that was setup for an electric cooker (which we don't use). I've terminated it with an IEC309 socket and use a heavy-duty cable to connect up any juicy power tools I want to use. Also fitted some suppressors to the socket to stop returning power spikes frying other appliances in the house.

...luckily I rigged that a few years before Part P came in

[woodburner]

Part P has made as many dangerous situations as it has removed IMO. Instead of having a shed wired with all the wires in trunking and sockets bolted to the wall, I now have extension leads strewn about.

[mobbsey]

Part P has made as many dangerous situations as it has removed IMO.

+1

Also makes people cover-up dodgy/unapproved installations because they don't want to go through the hassle of certification/potential legal penalties.

[adam2]

Anything over 3KW or 1HP is meant to be notified

Eh? Do I have to tell the electricity company if I have a shower?

You do not have to tell them each time you use an existing shower, but you are meant to tell them about the installation of a new electric shower, if over 3KW as they virtually all are.
A like for like replacement electric shower is not notifiable to the electricity supplier, but the part pee police should be notified.

I doubt that many people do notify extra load, but you are meant to, if over 3KW or 1HP in the case of motors.

[adam2]

Part P has made as many dangerous situations as it has removed IMO.

+1

Also makes people cover-up dodgy/unapproved installations because they don't want to go through the hassle of certification/potential legal penalties.

Yes