# How much power does a welder use

• posted on September 18, 2005, 11:54 am
I have a Kemppi Master 1400 Stick welder that I'd like to be able to use aboard my boat I have a 2400w inverter fitted that I think is a square wave, might be modified square wave.
or... I do have access to a 3.5kv generator. would either of these run it. The Kemppi has a maximum output of 140amp, but at what is the voltage, how many watts do I need to strike the ark etc
thanks
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2005, 3:00 pm
The Generator would run your welder, but the Inverter would only be able to handle it if you were charging your battery bank at the same time. I have a 2000watt inverter and 800 AH battery bank and I know it would be pushing my capacity.
Just an Idea! The off-roaders, have little welders that they run off their alternators for back woods welding repairs. Maybe these are specially modified alternators. All I know is that my son has one on his off-road Toyota.
Steve s/v Good Intentions

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2005, 3:10 pm
Welder typically runs around 25 volts while welding (open circuit voltage is a different story) with reasonable efficency. That would put your max power at around 4kw. But you can do nice stick welding of 1/8" 6013 at around 110 amps, 3/32" at 80 amps. Depends on what you are welding. Big problem is when you stick the rod, it pulls the full amperage setting.
I did a quick search, it's not clear if the Kemppi is an inverter unit or a transformer unit. (If it's heavy, it's a transformer!) I would NOT want to feed an inverter welder off of a square wave inverter, too much chance the circuits will start fighting each other. A transformer welder MIGHT work on an inverter, depends on how well the inverter takes to the heavily reactive power factor as well as the inductive surges you will see. Net: I don't think I'd chance it on your inverter, even at low power.
I run both a 120 volt MIG welder and a 225 amp (dialed down of course!) AIRCO stick welder off of a 5kw generator. Works ok, either one will load the generator quite heavily.
Nigel wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2005, 3:17 pm
You can get a welder that operates directly off of lead-acid batteries and (reportedly) works well. I'm too lazy this morning to google it for you. Paul Mathews
RoyJ wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2005, 4:20 pm
Paul Mathews wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2005, 12:08 pm
Thanks all, for your advice I found Kemppis address and emailed them, I got a reply back in a few hours, I'm impressed with their aftersales service (even if it wasn't what I wanted to hear)
------------------------------------------ From the rating plate on this machine, the mains supply is norminal value is 1phase 230v ( 198v - 254v) the rated fuse is 16amp slow blow The input current is proportional to the output value set on the current dial.
At max output the power is 6200 VA (6.2Kva) power factor 0.75 therefore output power in watts is 8267 watts At 75 amps output the power is 2900 VA so an estimate of power in watts (pf approx 0.6) is 4833 watts
Therefore we would NOT recommend using your battery/inverter supply to power this equipment because of the in-rush and surge currents even at the low output and using 1.6mm electrodes.
The generator supply is probably also not large enough, unless it has a very well regulated output, again due to the in-rush and surge currents even at the low output and using 1.6mm electrodes.
We recommend a minimum generator of 6.2Kva.
Best Regards Martin Forster Service Technician
Kemppi UK Ltd _________________________________________________
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2005, 9:16 pm
Nigel wrote:
<Of welders>

You have that backwards! 6.2KVA @ 0.75PF is 4.65KW, but is still 27A@230V. 2.9KVA @ 0.6PF is 1.74KW, but is still 12.6A@230V.
Use the VA number to calculate the load current, and multiply VA by power factor to get real power.
Note that the PF will probably be lagging in this case and you will need to be careful about the inverter ratings....
Note also, that the VA rating determines the minimum current that the supply must be able to source, but the real power determines engine size. It is quite possible to have a very large alternator driven by a small engine which will give a spuriously high current rating for most loads.
You could always just hook the electrodes up to some of that battery bank (reconfigure it to give 24V or so), and weld that way (BTDT), it does work to get you out of a tight spot!
Regards, Dan.