Buying a MIG Welder

The main difference between cheap and expensive MIG welders is ease of use. For anyone new to welding that can equate to possibility of use.


It's really difficult to put the differences into words. On the forum we have a section that helps people learn to MIG weld where people can post photos of their welds and ask for advice. It's easy to tell from the photos which price range people have bought in.

Those who have bought a decent welder tend to post photos of good welds first time, and we can help them improve. Those who have bought welders from eBay or from their local supermarket tend to post photos of bird poo and spatter. It's difficult to give them sensible advice and sadly those guys normally give up both their welding and their project.

Go through that section yourself and you'll see what I mean. Notice both the forum and this buyers guide are independant, but we also have a welding shop on here which might be worth a look around.


Don't buy a machine just because it's cheap! Ask on the forum before you buy and post the specifications if you can. We'll point you to feedback from owners of similar welders and give you feedback on whether the specs will suit your application.

For the specs to watch out for read on. But mind - the cheapo rubbish manufacturers have read this page and are altering their specs to suit.

How many amps - Maximum?

The first thing to decide on is what you are going to weld, and how often. Here's my own estimate of what each hobby sized welder can do. Manufacturer's claims vary, but they'll generally claim to be able to weld unreasonably high thickness. Ignore what they say and use this chart instead:

Maximum Amps:

90 amp

110 amp

130 amp

150 amp

180 amp

*¹ Maximum steel thickness (butt weld)

2.0mm

2.5mm

3mm

4mm

5mm

*² Maximum steel thickness (with V and root gap)

3.0mm

3.8mm

4.5mm

6mm

7.5mm

*¹ Find out what your welder will do using the MIG Calculator.
*² An example of V and root gap and an edge to edge butt weld are shown in the 90 amp thickness challenge.

For welding on a modern car with thin chassis panels a small welder might suffice. For an older car with separate chassis a 130 amp welder would be the minimum, and a Land Rover would require 150 amps or more.

Read the spec sheets to determine maximum amps and don't go by the model name. Welders used to have the max amps in their name, but marketing departments have started to become creative. for example the Lincoln SP-135T still offers a maximum current of 135 amps, but the Clarke 135TE only goes up to 130 amps.


How many amps - Minimum?

Don't forget the minimum amps. Most smaller MIG welders have a minimum of 30 amps which is OK for 1.0mm sheet, and passable on 0.8mm steel with a bit of care and technique (see welding thin metal). Some welders have 20 or 25 amp minimum which would be more usable on 0.8mm steel.

Any welder with a minimum of more than 30 amps (normally only very cheap or very powerful welders) would be unusable on car bodywork. One really cheap 100 amp welder has a minimum setting of 85 amps. That'll give a range of 1.5mm to 2mm steel which is all but useless for most jobs. Many big welders designed to run all day at 300 amps will not go below 40 amp minimum.


Workshop power supply

It should be possible to run a welder up to around 150 amps on a UK 13 amp plug. Larger welders would need a 32 amp round blue plug and suitable dedicated wiring, although they can be operated on a 13 amp plug on the lower settings. A 13 amp plug should be changed about once a year as they aren't really up to supplying high currents for long durations.

Some of the cheaper welders (and I won't mention country of origin) seem to be blowing fuses at surprisingly low outputs. I don't know the science behind how they manage it. but if you are on a cost mission respect their advice on power supplies and fuses.


Avoid permanently live torches!

This is where the manufacturer saves a few pennies by leaving the contactor out of the welder. The contactor is the part that switches the electricity supply to the torch when the trigger is depressed. Without the contactor the torch is constantly live, so if you happen to touch anything while positioning the torch you'll get arc eye. Great.

I didn't think anyone made anything this rubbish any more, but it seems that Wolf Welders do. A discussion on the forum is a good read: Why avoid live wire feed. If anyone finds any other makes with a permanently live wire feed then do post on the forum and I'll update this page to warn potential buyers.

Manufacturers will not mention the permanently live torch in their literature so ask before buying.


Quality

The quality of MIG welders (together with the prices) continues to fall as more of them are manufactured in Eastern Europe and China. Expensive MIGs are more forgiving to use than low end welders because they have better electronics inside and better wire feed units. The cost-down performed on cheaper welders does compromise the functionality.

One benefit of a slightly more expensive welders is the wire feed control automatically varies to suit the power. The wire speed knob on these is just a fine control which doesn't need fiddling with when you change power settings. If you can afford one with that feature you won't regret it. Another feature of better stuff is a good sized wire feed motor and a quality wire feed mechanism. A decent wire feed is important for easy welding, much more so than the other bits and pieces inside the machine.

Generally speaking, welders get nicer as they get more expensive, and there is a great deal of choice in the £200 to £500 hobby to semi-professional market.


Duty cycle

This is the percentage of a 5 or 10 minute period (depending on manufacturer) that you can weld before the welder overheats. For example if a welder has a 60% duty cycle at 100 amps over 10 minutes, then the welder can be operated continuously at 100 amps for 6 minutes before it will need a 4 minute break.

Generally duty cycle isn't important for automotive repair work, as the amps tend to be low (higher duty cycle at lower amps), and 9 minutes out of 10 is normally spent setting up, so any welder with fan cooling should have a good enough duty cycle. It would be a big consideration for a fab shop welding steel I beams together all day.

Smaller welders without fans (non-turbo welders) running at full power will tend to have a very low duty cycle and owners report that the thermal cut outs can be annoying even for car restorations.


Which Manufacturer?

Surely all hobby welders are made by Telwin in Italy and are all the same?

Not at all. Welders are made in many countries. The brand can still provide a clue. A decent brand may chose to have their welder manufactured in Eastern Europe, Mexico, or even China. If the brand has specified the design, determijned all of the component specs, and they have decent quality control then these brands might offer you an equivalent product with a cost saving. If they haven't then their brand will start to fall into disrepute. Ask on the forum before you buy.


The Welder Chassis

The chassis is the case and wheels that contain the MIG welder. The main things to consider are whether it has wheels - make anything bigger than the smallest hobby welder much easier to move around, and whether is has a shelf on the back for a decent gas bottle. Most sub-150 amp welders don't have a gas bottle shelf these days, although a DIY shelf can normally be made and bolted on to the welder.

The chassis isn't a major consideration as making a welder trolly can be a great first welding project.


Gas vs Gas less

MIG needs some sort of shielding gas to keep oxygen away from the weld. The choices are gas shielded (oxygen is displaced by an inert or semi-inert (active) gas mix contained in a bottle), and flux cored wire (where a protective covering is produced by a compound included in the wire itself). There are advantages and disadvantages for each type of welding, but gas shielded is by far the nicer method to use, so unless you know you'll only want to weld with flux cored wire it makes sense to go for a welder that can do both, or a gas shielded only welder.

There's a page about gasless welding, but in summary you can't see what you are doing, it spatters a lot, and needs the slag brushing off before painting. On the positive side it can be used outdoors in the wind just as effectively as indoors, and the weld quality and strength is OK once you get the hang of it.

Things become easier with gas shielding. You can see the weld pool, the welds are neater, there is less spatter. The disadvantages are the cost of gas for occasional users, and the need for wind shielding if welding outside.

Gas comes in different sizes and tends to be consumed at around 10 liters per minute. So the tiny disposable bottles costing £10 will last for 6 minutes of continuous welding (about 1m of weld). The BOC size X bottles hold 2,300 liters and cost £50 per year bottle rental plus £30 per bottle full of gas. For a car restoration that would take a year they work out at 1/5 of the price of the disposable bottles. Another alternative is to use CO2 from a friendly pub, or local welding suppliers might be able to provide a lower cost alternative to BOC or Air Products.

Differences between different gases are covered in the welding gas comparison.


What else will you need with the welder?

Torch

The torch almost always comes with the welder, but there are differences to consider. Torches can wear and depending on how much use the welder gets they may need to be replaced during the life of the welder. If you get the option go for a eurotorch - these have a universal quick release connection to the front of the welder, are readily available and cheap. If the welder has a built in torch a replacement will have to come from the manufacturer and will probably be poorer quality and will probably cost twice as much as a nice eurotorch.

Gas Regulator

The main choice in gas regulator for a full sized bottle is whether to go for the cheaper single gauge one (that measures the pressure remaining in the bottle) or the twin gauge (which also measures flow rate). The twin gauge ones are only £10 more expensive and you'll probably save that in gas if you overestimate the flow rate.

Safety Equipment

Molten metal is hot, and the UV light produced by welding is a lot stronger and nastier than sunlight. Cotton overalls and welding gauntlets (thick heat resistant gloves) are a must.

Welding Mask

Most hobby welders come with a hand held mask which is useless as the spare hand can be put to far better use in steadying the welding torch. A full face mask that fits on your head and can be flipped down for welding will only cost £10. People learning MIG welding report that an auto-darkening helmet makes life much easier. These remain transparent until the welder starts arcing which makes positioning of the torch easier.

A few members have reported that the auto helmets bought cheap from eBay have an excessively dark shade, despite being described as shade number 10. Better quality masks will start at about £50.


Features that can be found on more expensive welders

A hobby welder will normally have two controls - one for the power and one for the wire speed. Top end hobby welders or semi-pro welders might have an additional control for burnback. This controls the amount the wire burns back towards the tip after welding, and is useful on thick metal where a machine without burnback will leave a long piece of wire that would need to be trimmed with wire cutters.

Another common control is a spot timer. This is simply a timer that cuts off the power after a certain time and is used for "spot welding" by building up weld on one side of a panel until it penetrates through to the other. A stronger and more fail safe alternative for DIY welders is the plug weld.

Moving higher through the price range (£1000 and more) and synergic or pulsed MIG welders start appearing on the market. These introduce an alternating or pulsing current into the power supply which provides improved arc stability and hence increase control and result in a neater weld. Anyone considering this sort of welder will probably know more than I do about them.


Synergic and Inverter MIGs

Inverters are finding their way into MIG welders, and they can offer a lot of features at a lower cost to the traditional transformer based welders. The inverter technology started off in high end sets aimed at increasing the deposition rate (and speed of welding) in high amp spray transfer, and avoiding the transitional globular transfer phase.

These days inverter technology has also started to find it's way into hobby welders. Inverter welders use electronic wizardry (rather than traditional transformers) to create the welding arc. The advantage is the arc can be controlled by the electronics and manipulated to make welding a whole lot easier. The disadvantage is inverters are complicated and sensitive to knocks and wil not last so long as a traditional transformer welder.

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