A small transformerless welding machine circuit can be built using a few high voltage, high value capacitors and a rectifier diode, the following article explains more on it. The idea was requested by Mr. Tun.
In one of my earlier posts we came across a full fledged 100 amp SMPS welding inverter circuit for working with reasonably bigger joints and metals.
The Design Concept
Being an SMPS based design and involving high power specs, the above circuit is complex and may be out of the reach of the new hobbyists.
As requested by Mr.Tun a homemade small scale welding machine circuit is what most of the new hobbyists and mechanical engineers would be looking at for solving their occasional work bench metal welding jobs.
A mini welding machine without using complex circuitry could probably be built using a capacitive power supply as shown in the following diagram:
The idea shown above is an ordinary capacitive power supply circuit incorporating extreme capacitors in terms of their values.
At the input side we can see a formidable 500uF/400V capacitor, while on the output side also a similar rated capacitor can be seen positioned for reinforcing current.
The most basic parameter essential in a welding system is a high current, so that an extremely high temperature can be formed at the short-circuit junction, over the metal joint in question.
This high current generation can be achieved either by using a high watt transformer or an SMPS version of the same which we discussed in the first paragraph.
A transformer could be too bulky and heavy, while the SMPS circuit too complex for the newcomers, the only alternative way to achieve the high current welding through a relatively simpler design is perhaps by employing the high current capacitive power supply as shown above.
The 500uF/400V capacitor can be expected to generate bursts of current upto as high as 36 amps @ 220V, and reinforced with the complementing output filter capacitor this current can be expected to do some serious welding actions.
You can verify the above mentioned specs by using the following two calculator software:
The shown push button enables the user to achieve the welding job through shorts bursts, and not through a continuous arcing, which can be dangerous, and anyway is not recommended in welding operations.
The input 500uF/400V capacitor looks massive and it might not be readily available in the market, therefore this can be built by using 500 numbers of 1uF/400V PPC capacitors wired in parallel, this could occupy some space, but still the method is easily achievable.
Use Non-Polar Capacitors
This capacitor needs to preferably a non-polar capacitor, however since a diode is positioned in series means an electrolyte capacitor could also serve the purpose without issues.
The second capacitor at the output side can be an electrolytic type for sure.
For more current, the values of the caps could be increased to higher limits, that's the only parameter that needs to be focused on.
Advantage and Disadvantage
The advantage of this circuit is that it is small, cheap, and can be quickly built and used. The disadvantage is that it is very dangerous since there may be AC voltage at the output, therefore you will have to handle the whole system wearing rubber hand gloves.
CAUTION: The mini welding machine circuit explained above is not isolated from mains and has the potentials to kill a person within seconds, therefore extreme caution is advised while handling this equipment in the powered condition.