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.
Circuit Operation
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.
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.
thanks a lot
what is the used of the capacitor the one in series with the mains? if its only function is to provide small constant current then why don’t we use a fuse instead?
Abba, fuses are not designed to suppress current they are designed to blow off as soon as the rated current is exceeded through them. A Capacitor cannot be compared to a fuse
thanks a lot for the reply
sometimes I hear electronics student say their capacitor exploded, though I never encountered such a situation but I really want to know the cause and how to prevent that from happening. am referring to the capacitor used in transformerless power usually connected in parallel with resistor in AC lines.
Capacitor will blow when the the supply voltage across its terminals exceeds the printed breakdown voltage value. In transformerless power this may happen due to sudden current surge when the capacitor is unable to stop the rise in voltage and bursts, a resistor and zener network will normally prevent this situation.
HI SWAG how to make this as adjustable current
Hi dennis, you can put different ranges of capacitor from 100uF to 500uF and add a selector switch to chose from them….
Pls sir,is there any chances of electrocution as this circuit is not isolated with transformer.
yes definitely there is…even in transformer based welding machines you will have this danger
Hi sir please show how to make a 0-40v 0-3a smps
you can try the following concept
https://homemade-circuits.com/2017/06/12v-2-amp-smps-circuit.html
the Rfbb can be changed for getting different voltages at the output
Hi tun, I do not have asn SMPS version at the moment, however you can build an iron core based auto-transformer for the achieving the results
Hi sir,i need to show me how to step down 230VAC/2A to 150VAC/2A
You should put the 230v line wire on top of the step, and depending the number of taps each one will have a specific voltage drop (230v/no.of tapping). The last one is at the lowest level and should be connected to ground. The output you take it from the desired step and the ground.
Hey there,, I have a 470uF 250v cap,, can I use it?
Also what is the component no for 50A diode.? I have 5A diodes, can I put 10 in parallel to achieve 50A??
470uF/250 can be tried and will work as long as the input voltage does not exceed the 250V mark.
please search online regarding "50amp diode" you will be able to find a suitable one.
5A diodes in parallel will not help, and is not recommended
Hi dear,
thanks for your best site,
Inpute voltage is 220 v? How can i use it ?like a welding machine to connect output?
Can melt Iron?
Thank you
Thanks Ali!
This circuit won't melt iron but join iron with the help of welding rod.
just connect the iron which needs to be joined with one of the output terminals, and the other output terminals with a welding rod, now touch the welding rod end at the point on the iron which needs to be fused…
Thanks Swagatam,
input is 230 V AC?
560uf 450v can i use?
what is the model 50amp diode?
50 amp push is a fuse?
thank you
yes will do.
50 amp diode is required for rectification.
the 50amp push is a push button which is required to be pushed and released while operating the power supply