How build safely a welder points «Soloelectronicos

spot welding takes us some 40 years, but despite his age still enjoys good reputation in modern times using it intensively also in electronics applications where conventional with Tin solder is not effective, as for example at the time to connect batteries between if with sheets of nickel among its thousands of applications more.»

obviously thanks to the evolution of technology the current points welders has better capabilities to control different aspects of the process especially with the introduction of power sources with DC inverter and control of closed-circuit, change of the polarity of the power sources of discharge to power balance weld nuggets In addition to the addition of measurement instrumentation, as well as the possibility of adjustment of the displacement of the strength of the electrodes, which gives users more tools to ensure the quality of the welding.

in essence spot welding technology isn’t anything complex because the typical configuration of a welder of points has not changed over the years, basically consisting of a very low voltage source (2 or 3V) high-intensity attached to a header soldering

Unfortunately a though that does not include too much technology , a welder of points is one of the few teams where home construction this is much cheaper to buy it mounted, even if you decide to buy it in any of the famous Chinese portals, since even buying them there, their prices range between € 200 onwards.


posts to make them for us in youtube you can see a lot of soldering points (search by its English translation: “spot welder”), manufactured home-made always using old microwave (provided that are easily obtainable) transformers. These transformers deletes them AT secondary by mechanical means and is just surrounded in the interior of the entre-hierro in that space that has been emptied of two more turns of cable large (at least 8mm section). Obviously be careful if you decide to go out there as t rabajar even with parts of a microwave oven is extremely dangerous because should know that anyone has survived a chance of high voltage contact, because the available power more than 1000W is enough to kill instantly (unfortunately for mankind in the horrible electric chairs used 1500V) since high voltage inside an oven microwave is 3400Vrms. As we know that the power is proportional to the square of the voltage, this 5 times more dangerous this voltage as an airline of 1500V for a train clearly in contrast with circuits HV of many low-power electronic products, which are not lethal,

low my opinion all these arguments are more than enough to not take into account that method mainly because e ork other methods much more insurance of building a home point soldering iron so do not recommend to build a welder of points based on a transformer microwave not only for the voluminous space it occupies, but above all by the danger involved removing the transformer as this very close the capacitor of high voltage, whose load can be present long time when the microwave oven is unplugged (and a shock of this kind is extremely dangerous). Do not rely on internal condenser drain resistance, because it can fail and is very dangerous (if you are going to do, at least to connect two alligator clip test leads to the land of the metal chassis of the microwave, making sure that the cables are not broken, hold a 10 K resistor… 1 m on the other side of a cable test and download the two terminals of the capacitor one by one through a resistance of 1MΩ using insulated pliers).

Please note that power some high microwave ovens u tilizan electronic power HV inverter instead of a transformer to save weight (de hecho esa es la tendencia actual), obviously, in that case not would like utility that component…

in a nutshell there are two forms of solder with a soldering iron points:

  • spot welding series configuration: electrodes are on the same side. It is very important that the strength of both electrodes is almost identical because otherwise a side will be soldier badly.
  • opposite configuration spot welding: this technique is the most widely used consisting of the parts to be welded are fastened between the electrodes.

professional lightweight portable spot welders offer a welding current at least 4000 A, which allows the welding of 2 sheets of 1 mm steel. A homemade spot welder can normally offer 1100A, which is fine soldering small electronic parts ( for example to connect batteries between if with sheets of nickel ) Although it is known that there are people who have welded 2 0.75 mm blades with this type of point welders.

a continuation see several very different options alternative and very secure that move away from the use of the typical recycled transformer to perform a home point soldering iron


is the form more usual of and easy to build a welder at a quite affordable price points.

these settings work for a long time and at my discretion this configuration is much more optimal and efficient that welders based on modified microwave transformers.

the high temperature destroys lithium batteries, so the traditional thermal welding is not an option, so this configuration is perfect (so there are people who call her “cold welding”)

as seen in the following circuit, is principle is quite simple using 8 Mosfet transistors of the parallel IRF1401 in configuration type to control the discharge of a novel of 1 Farad of 15V  which stores enough energy to produce the spark that permit the welding points.

resistances of 1 k and 10K only serve to ensure to pass transistors reason why a button is used to driving to driving only during a short space and time


another option instead of transistors is to use a power of at least 100Amp thyristor to control the discharge of the novel , but this means that you need a small battery attached to a a normally open to Prime to the thyristor switch and that this may lead to allowing the discharge of capacitor on the electrodes (more information at

on the latter circuit also there are interesting variations especially controlling the exposure time of thyristor gate as for example with an astable circuit to provide adequate pulse.

if ele are interested in the first design (perhaps the most simple) in the following video we can see the process of building the first Assembly:

this setting is very typical for welding the typical panasonic lithium batteries ncr18650b (the same batteries used by vehicles and solar panels of Tesla) as we can see in the video below :

this welder offers one unique pulse enough for most welding wing, but it is possible to construct other more advanced also based on capacitive discharge which is capable of producing double pulse emitting up to 400 amps in 60 micro seconds using additional electronics such as for example an Arduino…

welder points PORTABLE

now we will see how to build a small arc welder to operate with battery 3.7V single na. Other capacitor or a larger one can be replaced and the voltage set low to increase the total potential of the joules but apparently with a capacitor of 1000uf / 35v is sufficient for welding wires of silver, nickel, the nichrome and in the kanthal’s 28 – 34g together.

really any old power supply can be replaced by battery, provided it is within the limits of the voltage input to the plate used (LM2577)

the cost of the components is about $25.

this is just a reference of parts (with pair(you from digikey #’s), feel free to substitute their own equivalents:

  • support of the mixture: BH-18650-W-ND
  • project box: 377-1165-ND
  • toggle switch: 507PB-ND
  • resistance: 3.6W-10-ND
  • fuse: 507-1032-ND
  • module LM2577;
  • diode: 1N914B-ND capacitor
  • : 399-6556-ND (CAP ALUM 1000UF 20% 50V RADIAL)

  • clips mandibular smooth crocodile: 314-1018-ND

as we see apart 1000UF capacitor from the soul of the circuit is the LM2577, a corrugator dc-dc with 3 digit LED display. These are their main carastericticas

  • input voltage: DC 3 – 34V
  • output voltage: DC 4 – 35V (adjustable)
  • input current: 3A (max.)
  • output current: 2.5A (max)
  • size (L w x): approx. 2.56 x 1.4 x 0.5 inch / 6.5 x 3.5 x 1.2 cm

adjustment method: first connect the power input (3-34V), then use a multimeter to monitor the output voltage and adjust the potentiometer.

in the following see operating scheme done left over the comments because only the circuit load capacitor and through the p

plate has solder pads on the top, for all connections, lead wires from the back of the plate and solder to the pad. Some boards have IN / OUT and +/-marked on the back of the plate, others do not.

with all wiring complete, can test and verify that everything is working as it should be and adjust the plate voltage using the potentiometer. Attach to your meter crocodile clips and the momentary button, you should see the voltage go up a little and remain constant around 12-14v, which is where the plates are set when you buy them.

using a small screwdriver start rotating the knob while holding the switch down. If the voltage does not rise, it is doing so incorrectly. Press and hold the button and turning the screw until you reach 35v, the cal allows approximately stores 0.6 joules of energy in the capacitor. Touch the wire cables together and cause a spark (proposed action) which means that you can already begin to weld (more info at

welder double point

based on the principle of a point welders improvement of the circuit in the first place is to make a smaller download to clean the surface of the material of impurities such as oil and create a weak weld. The second pulse with more energy makes final link. In order to have a pulse stable during the download of a large capacitor was employed

new design adds an Arduino UNO and a Driver of MOSFET MIC4451 to send control signals to IGBTS that must check the circuit, delivering pulse drivers used to deliver up to 700 pulse high current amps must be not smaller than the high filament wire gauge 4. a momentary pedal with audio jack ¼ “is used to send the control signal microcontroller.

for more information look at

welder based on the use of a battery 12V /45ah

there are people who choose instead of using supercondensadores to instead use 12V vehicle batteries to generate the spark. In order to have more control a car relay can be used to control the discharge but others opt for electronics more sophisticated, such as using an Arduino Nano

this welder points can be used to weld 18650 batteries. You need a 12V charger and used a car battery 12V as welding current source. Typically a battery 45Ah provides enough current to obtain good welds with strips of nickel of 0.15 mm. If using thicker nickel strips may need a battery but large or two in parallel.

the machine generates a double pulse, where the first is 1/8 the second time. The pulse of the second pulse time is adjustable by the potentiometer and appears on the screen in mS so you can accurately adjust the time. Adjustable 1… 20 mS.

see the video for detailed instructions on how to build it.

project files:

General aspects for the construction of soldering points

arms: : the insulation between the joints of the arm should be good and the friction between the arms must be very low; Tighten the bolt so that the friction is small but the gap is not too high. Electrode

: electrode holders can become a land of rectangular brass radiator clamp of 20 mm width. Drill a 4 mm hole in the Center mounting screw. Enlarge the hole for cord welding to 7 mm.

welding cable: use a flexible welding 3AWG cord / 25mm 2 with a length of 140cm, this allows 3 windings. A thicker cable does not give a higher welding current. As the electrode force is critical, the arms of welding must be able to move freely, not hampered by the rigidity of the cables. Therefore, the wires have a large curve. Do not use solid cable, welding cable is flexible and will cost just $15 / m.

welding electrodes: it is important to use a bar of pure copper. No brass or electrical wire, which is soft annealed. Use a bar with the same size as the slot of the holder or place the bar in the right size. A proper tip diameter is 1.5 mm. To keep it simple can archive the tip of the electrode instead of round.
Welder electrode holder by point s: periodically clean the tips of electrode welding with sandpaper.

Spring clamps: the electrode force is an equally important parameter as the other welding parameters such as the welding current and pulse time.  Set the electrode force moving the position of the spring clamp and measure the force with a kitchen scale

operating lever: I used a plate of plastic materials but can produce a beep in aluminium.

current measurement of welding

can determine the welding current by measuring the voltage across a certain distance from the welding cable.
To calculate the welding current can be used the following formula:
I = U * diameter [mm2] / (0,0175 * length [m])
for measurement of welding current, two cables are attached to a cable of 44.5 cm distance welding. Short circuit voltage is 0. 34V; So the maximum welding current = 0.34 V * 25 mm2 / (0,0175 * 0,445 m) = 1100A.


  • make sure have a good connection clamps, newspaper with 400-grit sanding may be necessary.
  • make sure that the ends of the cable as close to the clips as possible.
  • If your cable has a coating on it, lightly sand tips to weld.
  • instead of trying to push the ends of the wire together, try to overlap the ends of 1 mm for a strong joint.

If you have any questions or need help troubleshooting your welder, the best place to get answers is here: – welder.html


the galvanized metal combustion can release toxic fumes of zinc oxide. This project is extremely dangerous and should not be attempted without the supervision of an adult and the proper training. Misuse or careless use of tools or projects can result in severe electrical shock, heart failure, serious injury, permanent damage to the equipment and properties and / or death. The use of this video content is at your own risk.

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