kCap, kSupply, Lead Acid battery, LIPO battery, power sources for kWeld -

How to select a power source for kWeld spot welder

kWeld is a very capable battery spot welder. It can handle up to 2000 amperes of current at up to 30 volts. You are best to aim for 1500 to 1800 amps at 12volts or less to achieve a good level of performance. A very common question we get is how to select a good power source.

I would suggest there are three common options that do this well.

Option 1:

The least expensive option is to use a larger lead acid car or truck battery. Lead acid batteries are actually very well suited for this application. They are built to provide a lot of power for a short time such as is used by the starter motor on an internal combustion engine. We would suggest that a healthy, but not necessarily new, 800-900CCA (cold cranking amps) battery is a good choice. It should be able to provide more than 1500 amps for the milliseconds that are required by the kWeld spot welder. The main drawback with this set up is that the spot welder must sit between the terminals in order to keep the length of the wires short, and inductance as low as possible.  Keeping a battery minder or solar charge controller connected to your battery will ensure it is always ready to go.

Option 2:

If portability is required, it may be a better choice to select an appropriate LIPO (lithium polymer) battery. These are used in the RC world and can provide the needed jolt of energy despite their small and light form factor. The downsides to this option are that, unlike lead acid batteries, providing maximum power is harder on the battery and LIPO batteries tend not to last as long. Once they swell up, they should be discarded responsibly and replaced. LIPO batteries can be quite expensive and require specialized chargers. They are also known to catch fire and special precautions must be taken to avoid burning down the house.  Keeping your batteries in a fireproof bag and not charging them when unattended are examples good practices.

Option 3:

keenlab, the manufacturer of the kWeld does provide a good solution. The kCap ultra-capacitor module will provide 1300+ amps at 8.2v. This module can recharge very quickly and provide consistent, repeatable power surges needed for quick work. The kCap module can be charged at 70amps by the kSupply board. Alternatively, a suitable bench top power supply that can be voltage regulated may be an option, albeit slower. For those looking for maximum performance, two kCap modules can be connected in parallel and charged to about 7.8 volts to provide about 1850 Amps of current at the electrode tips. A single kSupply can be used to charge the doubled up powerhouse.

Perhaps the best feature of the keenlab line-up is that, given the multiple setup options, it is possible to first start with the simplest option 1, and upgrade your system at a later time.

We'd love to see a picture of your setup!  Share your thoughts and pictures on the kWeld World Facebook group.

Get in touch with your comments or questions by writing to info@gridrewired.com 


  • kevin kozijn

    i want to supply power to the k caps with a DROK buck converter. do i need to add a diode to stop back flow or is that incorporated into the module?

  • Jeff S

    I just purchased the KCap and the Mean Well power supply that was listed and recommended. I adjusted the output voltage of the PS to 8.2v as recommended. When I first plugged in the KCap it started clicking for a few seconds and then stopped. Only the left charge LED is on indicating insufficient voltage or current from charger. The KWeld also displays low voltage.

    Is this normal? It appears it’s not charging the capacitors. What should I do now? I need a fix ASAP!!!


    I do have a server PS that outputs 12v at 54a. I’m not sure if it has voltage and current regulation, thou. Could this PS work without damage?


  • Vincent

    I am reading through the Ksupply manual and it references FCCM operation and “two quadrant operation” for which there is no further explanation. Do either of the mentioned power supplies (DPS-800GB or HSTNS-PR01) support the FCCM? Or is this some future type feature?

  • Anonymous

    The use of two LiPo batteries in parallel is a good solution if the current obtained from one is too low. The best method to implement this is to connect a single LiPo battery and run the kWeld’s calibration sequence. Take note of the current (I = ) value. If this approaches the 1500A target, one is enough. You can then add the second or even a third (if needed) to hit your target current. It is very important to correctly change the “CableLen” setting to accurately represent the wire length used. Tip: keep those as short as possible. If you are not accurate or deliberately enter a length shorter than really used, you will be circumventing the built in safety which is meant to protect the welder from damage.

  • Anonymous

    Good question Beau. A battery directly connected to the kCap will damage the kCap. The reason is that the capacitors can take the full influx of power BUT the other components of the board can not. The kSupply will limit the charge current to 70A protecting the kCap’s circuits. The 10A dc power supply will work but will be seven times slower than the kSupply meaning you will have to wait for the charge light to turn on (not blinking) on the kCap before you can perform the next weld. Keep in mind that you can always upgrade in the future if this performance is not sufficient for your workflow.

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