Introduction: DIY Arduino Battery Spot Welder
Due to many requests for the PCBs
I do currently have some PCB Sets and prebuilt kits in stock. Take a look here:
You can also take a look in the comments below this instructable. Some people who ordered boards at PCB manufactures are willing to sell some of them.
New V2.2 available with some pcb improvements and the new "AutoPulse" feature. Read More
The Spot Welder has a new PCB layout ! Improvements in the V2:
- only one mosfet driver instead of four
- changed electrolytic capacitor to film capacitor
- capacitors closer to the mosfet driver
- wider pcb traces for high current paths
- added gate resistors for the mosfets
- aluminum u-shaped part for the mosfet board (much easier to assemble)
- general pcb layout improvements
- pcb is now designed in KiCad (more open source than Eagle)
An Arduino Nano based Spot Welder for battery welding
This Spot Welder can be used to weld 18650 batteries. It needs a 7-12V power source (12V recommended) and uses a 12V car battery as welding current supply. Typically one 45Ah battery delivers enough current to get good welds with 0.15mm nickel strips. For thicker nickel strips maybe you will need bigger battery or two in paralell.
The Welder generates a double pulse, where the first one is 1/8 of the time of the second one. Pulse time of second pulse is adjustable by the potentiometer and displayed on the screen in mS so you can exactly adjust the time. Its adjustable from 1 ... 20 mS.
Watch the Video to get detailed instructions on how to build it.
Project Files: (BOM, pcb files, aluminum template, arduino code...)
Step 1: Making the PCB (V2)
You can find the Eagle / KiCad files for the PCBs on my Github.
Easyest way is to order the boards at an PCB manufacturer. For example at pcbway.com .There you get 10 boards for about 25 €. The necessary gerber files for ordering at pcbway.com can be found in my Github.
You can support me by registering through this link http://www.pcbway.com/setinvite.aspx?inviteid=128...
This way you get a 5$ coupon for your order and i get some percent discount on orders for upcoming projects.
But if you like diy you can also build it on a prototype pcb board with hand wiring. This is how i did the first prototype of the spot welder. In the pictures you see a manufactured board looks much cleaner.
The trace that connects the two boards in the combined gerber is only a ground connection not needed for the spot welder to work. It is only there to make clear to the pcb manufacturer that this is meant as one board and they dont need to make v-cuts or something else. With this modification it is possible to order at pcbway without problems.
Step 2: Optional: Ordering PCBs at a PCB Manufacturer
So many people asked how to order the pcbs. So here is a little instruction.
Ordering the new V2.2:
For Version 2.2 you need to order the Mosfet and the Arduino board individually because the Mosfet board needs a 2oz copper layer. The Arduino board can be ordered with standard 1oz copper. Dimensions for the 2 boards the same (50mm x 60mm).
Ordering Tutorial (V2 or 2.1): (pcbway.com)
Just go to http://www.pcbway.com/orderonline.aspx . (This is the "PCB Instant Quote" Tab on their Website)Type in Board Dimension (100mmx60mm) and quantity (cheapest is 10). Rest of the options don't need to be changed. You can of course change the colour of the Solder Mask (board colour) or the Silkscreen (text on the boards) to what you like. This does not affect the price. You can see how it shoud look like in the picture.
Then click quote now, choose your favorite shipping option and click "add to basket".
(ONLY FOR THE OLD VERSION: You can also order each board on its own with the Arduino_Board_Gerber.zip and the Mosfet_Board_Gerber.zip from my github.)
After clicking "submit order now" the guys at pcbway check if everything is ok with the gerber file. This can take only a few hours but can also take some days, depending on how busy they are.
In the Spot_Welder_V2_Gerber.zip Gerber file the "Mosfet" pcb and the "Arduino" pcb are on one
PCB. So ordering 10 pieces means you get 10 full sets. You have to cut the boards in half at the middle line when you receive them.
Step 3: Populating the Arduino PCB (V2.1)
Most parts used for this spot welder are throug hole components. Only some 1206 SMD parts are used. So its very easy to solder. If you buy the parts i recommend ordering some more of the smd parts because these little things like to disappear on the floor if your not carefull.
In the new V2 version i used 1206 SMD parts for the resistors and the led because there was not enough space for through hole parts.
To solder this SMD parts i figured it is the easiest way to put some solder on all of the pads. Then hold the SMD part in its position with a tweezer and solder one side. Now the part stays in place and you can solder the other side. Now heat both sides alternating and the part will automatically be pulled in its correct position by the solder.
Take care of the SMD leds polarity (see the picture). If it is put in the wrong way arround it wont work.
Populating the rest of the through hole parts is very straight forward. Start with the small flat parts and work your way up to the bigger ones. You can see this in the pictures.
Step 4: Populating the Mosfet PCB (V2.1)
The new mosfet pcb can use a aluminum part instead of the u-bend 16mm2 wire. This makes it much easier to build because you dont need a high power soldering iron and tons of solder. You can of course still use a u-shaped wire instead of the alumium part.
The template for the alumium parts is on my Github. Alumium Parts Template
First screw the u-shaped alumium part to the pcb with m2x8 or m2x10 screws and m2 nuts. Make sure the screw heads are on the pcb side. This is necessary if your srews are a bit to long (m2x10). If you put them in the other way arround they may touch the mosfets later and cause a short circuit. Alternatively solder a 16mm2 wire bend to an u-shape to the pcb.
Now you need to install the mosfets and the straight alumium part. In order to do this bend the mosfets leg in a 90 degree angle with some pliers. Use m3x10 screws and m3 nuts to srew the mosfets with the aluminum part to the pcb. After this solder the mosfets legs to the pcb. Put plenty of solder on the pcb traces that run from the mosfets to the u-shaped aluminum part to make these traces more rigid.
Since you already installed pin headers to the arduino pcb, it is now easy to install the pin headers to the mosfet pcb. Just put the female headers for the mosfet pcb on the ones on the arduino pcb. Lay the Arduino pcb on the table, put the mosfet pcb on top of it and solder the pin headers.
Step 5: Adding Protection Diodes (optional)
Schottky: VS-100BGQ015 Mouser.com Part: 844-100BGQ015
TVS: 5KP13A-E3/54 Mouser.com Part: 625-5KP13A-E3
Why add diodes ?
The diodes can be used to make the spot welder more reliable when using very high welding currents or long welding cables. They reduce the peak voltage which appears because of the inductance of the welding wires. This is necessary because high voltage spikes could damage or kill your mosfets. A very detailed explanation whats going on can be found here
Adding the diodes:
You can either build some nice wires with cable lugs for the diodes to make it look pretty or solder them directly to the spot welder. The function will be the same. Just make sure to solder on the schottky only with a high power soldering iron so the diode does not become to hot while soldering. The cable for the diodes should be 10mm² ( 7 or 8 awg). For the tvs diode you can also use thinner cable if it is just a very short piece.
Short conclusion of whats going on:
I did some measurements with my 20$ oscilloscope, which is not very accurate, but you can see the effect of the diodes.
The first measurement was done with the normal spot welder with no extra diodes installed.
As you see at the end of the first pulse there is a voltage spike, which reaches up to about 34V. This is no problem as the mosfets are rated for 55V maximum. But if you use longer welding cables or a very strong car battery that can deliver very high current this voltage could probably exceed the 55V. This could then damage or destroy the mosfets.
To get rid of the voltage spikes you can install diodes to the spot welder. You need a TVS and a Schottky diode.
I first did a measurement with only the shottky installed. This lead to a strange oscillating behavior, which can even effect the arduino so the programm crashes. You can see this in the picture with the oscillating voltage.
Last i did a measurement with both diodes (TVS and Schottky) installed. Now the voltage spike at the end of the pulse only reaches about 20V. Even with higher currents or longer welding cables the voltage can not go much hgher because the diodes will prevent this.
Step 6: The Foot Switch
To control the welder you need a foot switch, because both hands are used to hold the welding tips in place.
For the first welder I built it with a simple wood box and a little switch. But meanwhile i bought a dedicated foot switch from china.They are available for example at aliexpress.com for arround 3-4 $.
You can use any switch that is NO (normally open) as a foot switch. It does not carry any current.
Step 7: Using the Spot Welder
Now that your finished builing the spot welder here is how to use it.
- recommended welding battery: car battery 12V 40Ah 440A
Arduino board power: 12V 2A power supply / 3s Lipo/Liion battery
Welding cable: 16mm², each about 50cm long
recommended welding material: 0.15mm nickel strip
Only use the spot welder if you have some basic understanding of electricity. We are dealing with very high currents here which can be dangerous.You can not kill yourself by high voltage (its only 12V) but you can for example burn your fingers on the welding tips.
The spot welder is capable of up to 650A welding current for safe operation. Do not use a car battery that can deliver more Amps. For example a 40Ah 440A Car battery works fine to weld 0.15mm Nickel strips to batteries.
If you want to use higher currents or longer welding cables you can do this at your own risk. Absolute maximum rating is about 1000A welding current. In that case or if the device is used very much I recommend upgrading the spot welder with some protection diodes, like the ones described in the diode step.
Do not connect it wrong way around to the car battery. The U-shaped aluminum part which is screwed to the welder goes to the batteries minus (black) pole.
On the first use set the welding time to 1 or 2ms and see how it welds. Then increase the time until you get good welds. If time is set to high, e.g. 20ms for very thin nickel your nickel material will “explode”
Optional: For maximum safety measure the voltage on the two welding tips before every use, to make sure it is around 0V. If it shows 12V (your car batteries voltage) something is shorted out or you got a defective mosfet.
- Connect the welding cables and the spot welder according to the connection sketch.
- Optional: connect the diodes according to the diagram
- Connect your foot switch to the spot welder
- Set the welding time with the potentiometer (Display shows 1-20 in milli seconds)
- Now you can start welding
Step 8: Adding the "AutoPulse" Feature to Your Existing Spot Welder
In the new V2.2 PCBs the “AutoPulse” feature is integrated, but you
can also upgrade your “old” Spot Welder with the new feature pretty easy.
You only need a few parts: (SMD 1206 or wired parts, depending on what you prefer)
- 1x 470 Ohm resistor
- 1x 620 Ohm resistor
- 1x 20 kOhm resistor
- 1x Z-Diode (4,3V 0,5w)
- a piece of thin wire (optional with a connector)
Connect them according to the schematic. (Probe is the mosfets middle Pin) Then upload the new V2.2 Arduino Code to your Arduino Nano.
While the AutoPulse feature is activated you can not use the normal foot switch to activate a pulse. So it is recommended to make the cable that connects to Pin D3 of the arduino removable with a connector. If you do this you need to install the 20k resistor from Pin D3 to GND to make sure the Arduino reads a solid GND signal if the connector is removed.
Alternatively you could flash the Arduino with V2.1 of the Spot Welder software again to disable the AutoPulse feature. Using this method there is no need for the 20k resisor or to make the cable removable with a connector.
Instructions Video: (20k resitor from Pin D3 to GND is missing in the Video, sorry)
Step 9: Populating the PCBs and Adding Wires (old Version)
All the parts used for this sopt welder are throug hole components. So its very easy to solder. Start with the small parts and work your way up to the bigger ones.
Welding tips are made of 10 square mm thick solid copper wire. The cables are 16 square mm flexible copper wire. Do not make the welding cables to long (max. 50-60cm each). very long cables can cause high inductive voltage spikes which could damage the spot welder.
- In the new Version you have to connect JP1 on the Arduino Board with JP1 on the Mosfet Board and JP2 on the Arduino Board with JP2 on the Mosfet Board. Use pin headers and sockets. These jumpers connect the ground of the two boards. You can see how it is done in the new pictures with the green pcb pretty good.
- added a new picture series of populating the pcb, which should make it more easy to understand.
Step 10: Frequently Asked Questions - FAQ
What car battery can i use for the Spot welder ?
Recommended is a 12V 40Ah 440A car battery but everything that can deliver 400A to 600A should be fine. I do not recommend to use a so called “deep cycle” battery.They look like a car battery but these are not made to deliver very high currents for a short time. They are meant to deliver little current like 20A to 50A for some hours. They are maybe capable of delivering the high welding current, but could be damaged after some welds.
What nickel strip can i weld ?
You should use 0.1mm or 0.15mm nickel strips.
I have not tested 0.3mm nickel strips. Some people report it works, other say it does not work.
What foot switch can i use ?
You can use any switch that is NO (normally open). The foot switch does not carry any current, so even very tiny switches will work. (Example foot switch)
How long should the welding cables be ?
Make the cables as short as possible. I recommend 16mm2 (5awg) 0.5m for each cable. If you make the cables longer the welding pulse will become weaker unless you use thicker cable.
What power supply do i need for the Arduino board ?
12V 2A or 1A power supply works good. Alternatively a 3s Lipo / Liion battery also works perfectly.
Can i use the car battery to power the arduino board ?
No, you need a seperate power supply or battery.
The voltage drop of the car battery is not the problem. That should be compensated by the capacitors next to the mosfet driver. But at the end of the pulse there is a voltage spike that reaches about the voltage rating of the mosfets. So arround 50V for the IRF1405 mosfets. It is only few micro seconds short but could damage the components on the Arduino board.
Can i get more than the 20mS welding time ?
Yes you can change the welding time in the first line of the Arduino Code by just entering the maximum value you want. (but not higher than 99mS). To learn how top update the Arduino code watch the Youtube Video
Is it possible to use a PC power supply instead of the car battery ?
No, you need a car battery. A pc power supply can not give you enough Amps to weld. You need about 400A. Typicall power supplys can deliver maximum 50A. Also power supplys usually dont like to be shorted, which is what the welder does.
My computer does not find the Arduino when I plug it in with USB !
If your System does not automatically install the necessary driver you need to install it manually. Check out this page: https://arduino-info.wikispaces.com/Nano-USB-Driv...