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 1000CCA (cold cranking amps) battery is a good choice. It should be able to provide more than 1300 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. Another draw back is that at full charge, a lead acid battery has a surface charge which is quickly dissipated after a few spot welds in quick succession. This feature could mess with your weld consistency since your test welds and calibration can not account for the voltage drop.

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.

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 a good option. 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.

A very nice set up is to use a 12v lead acid battery to feed the kSupply and kCap module(s) in turn  I have a small solar panel recharge the lead acid battery which can be placed on the floor or at a convenient distance.  This set up avoids the problematic surface charge and allows for the heavy car battery to sit on the floor or a nearby shelf as opposed to on my workbench.

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 

1 comment

  • Beau

    Good information. thankyou. Can you feed the Kcap with 2s (8v) or a cheap 10 amp dc power supply with out the need of a K supply?

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