capacitor welder (for battery tabs) - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: December 14, 2015, 10:46:38 pm
content: Hello all,I would like to build a capacitor welder to use for welding battery tabs. I wonder if you might have a look at this circuit diagram and let me know whether what I plan will work.D1 is a 1N5408R1 - 4 are 10KR5 is 6 Ohm (although I'm not sure this will work to limit the current to 2A)Q1 is anIRLB3034PBFQ2 is anIRF510Switch 1&2 are actually just 1 DPDT momentary switch.The capacitors are 5x 2.7V 5FaradMaxwell BCAP0005capacitors, connected in series.So here are the many questions:1- Will the 5 capacitors in series handle 12V @ 1Farad ?2 -Will the capacitors discharge in this configuration? (As opposed to the positive / negative leads connected to the two electrodes)?3 - Will my switch and layout ensure that when I press the switch, the charging is stopped and the discharge occurs through the welding electrodes?4 - How do I connect an LED (to tell when the caps are charged) and a drain resistor (to discharge the caps) to this circuit?5 - Will a computer PSU be able to charge the caps? Or will the Over-Current protection kick in?Thanks,

author: SuzyC
author_rank: Frequent Contributor
timestamp: December 14, 2015, 11:48:57 pm
content: It won't work. This circuit idea of yours is real smoker. The first time you try this circuit wear protective glasses.Google this topic and find better ways to skin this cat.The idea here is to parallel capacitors not hook then in series. What you want is low voltage at very high currents.Some good designs use a modified microwave transformer.For DC circuits, the current capacity of the capacitors must very high. Shorting small-sized high Farad caps out with welding probes will instantly smoke them.

author: made2hack
author_rank: Frequent Contributor
timestamp: December 15, 2015, 09:07:04 am
content: Ok, what am I looking for on the data sheet of a capacitor? What current handling factor am I looking for?Should I then for example provide a lower voltage, say 2-5V to 16V rated caps that have relatively high capacitance? (Ie 0.1F)? And parallel a few of those?

author: Seekonk
author_rank: Super Contributor
timestamp: December 15, 2015, 09:21:42 am
content: I have a strain gauge welder which is a similar function, welding thin stainless sheet to metal surfaces. That charges a large capacitor and dumps that voltage into a transformer to develop the current.

author: made2hack
author_rank: Frequent Contributor
timestamp: December 15, 2015, 11:31:53 am
content: @Seekonk What kind of voltage is used? And capacitance?

author: mzzj
author_rank: Super Contributor
timestamp: December 15, 2015, 02:20:48 pm
content: Quote from: trs80 on December 15, 2015, 09:07:04 amUmm, you should start by looking at the "Absolute Maximum Current" as it is specified 3.2 Amps for BCAP0005there are few ways to do this (there was a discussion here on eevblog some time ago):1. Chinese ready made unit: Reasonably cheap, reasonably good performance, reasonable safety2. Mains powered transformer with triac control, pretty much like above chinese option, safety depends on your skill level.3. transformer coupled high voltage electrolytic capacitors, IE 450V capacitors. Potential for very high performance, safety depends on your skill level. (potentially most dangerous of the options)4. 16 to 25 volt ~1F electrolytic capacitor bank. Not cheap, safest of all above options.https://www.eevblog.com/forum/testgear/battery-tag-welder-from-china/https://www.eevblog.com/forum/beginners/trivial-capacitor-based-battery-tab-welding-machine/And Nickel strip is nowadays easy to find on ebay.