Half-wave rectifier capacitor - Page 1
Forum section: electronics / projects

author: rodrigopires
author_rank: Regular Contributor
timestamp: December 18, 2023, 02:00:05 pm
content: Hello everyone, I have a 90a AC flux core welder, and I am rectifying it to DC. I came for help in choosing the right capacitance value.The welder max output is 90A 53VDC @50hz. Let's go for a 5 V ripple.Using the formula C=(I*t)/V -> C=(90*0.01)/5 = 0.18FThis capacitance seems to be very high for the space I have left in the welder. Even for a 10V ripple, 90 000uF is a lot. From what I could find, the best capacitor was a 22 000 uF 80V or 63V.How high can I bring the ripple without changing the welding experience?Also in series with the positive side, I have a inductor that I salvaged from a damaged inverter welder (don't know its inductance). Doesn't this inductor play a role in snoothing the DC output (when in load), requiring a smaller capacitor?Thanks!

author: Vovk_Z
author_rank: Super Contributor
timestamp: December 18, 2023, 05:34:26 pm
content: You'll have lower rectifiex DC voltage with inductor than with a capacitor. If ghat's ok then it may be easier to go with an inductor rather than with a capacitor.You'll have higher rectified voltage with a capacitor. It doesn't likes high ripple current so it wan't work long if you don't have enough capacitance. 'Enough capacitance' is when ripple is no more then 5-10%. And you have to check rated ripple current too.

author: TimFox
author_rank: Super Contributor
timestamp: December 18, 2023, 05:45:34 pm
content: Your title states a "half-wave" rectifier.In that case, the time in the ripple equation is 1/f= 0.02 sec, not 1/2f= 0.01 sec (assuming 50 Hz).Afull-waverectifier gives you two pulses into the capacitor in one cycle.

author: johansen
author_rank: Super Contributor
timestamp: December 18, 2023, 06:51:47 pm
content: You don't need a big capacitor, just big enough to keep the current flowing through the arc. more might be better, but just use what you have.wire feed welders only need 30 volts at the wire, your 53v open circuit will drop to 30 during use.and why would you rectify it half wave? your transformer may burn up.

author: TimFox
author_rank: Super Contributor
timestamp: December 18, 2023, 07:53:44 pm
content: Yes: a half-wave rectifier results in direct current through the transformer secondary, while a proper full-wave rectifier (bridge or center-tap) results in negligible DC there.

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2023, 07:58:05 pm
content: Don't use a capacitor. It will result in an unstable arc. Use an inductor, as it's the current which needs to be stabilised, not the voltage.

author: johansen
author_rank: Super Contributor
timestamp: December 18, 2023, 10:35:35 pm
content: Quote from: Zero999 on December 18, 2023, 07:58:05 pmIts a wire feed welder. They need CV

author: Benta
author_rank: Super Contributor
timestamp: December 18, 2023, 10:39:07 pm
content: Quote from: johansen on December 18, 2023, 10:35:35 pmHow did you conclude that from the OP? Just curious.

author: Ian.M
author_rank: Super Contributor
timestamp: December 18, 2023, 10:51:13 pm
content: "...flux corewelder ..."

author: Benta
author_rank: Super Contributor
timestamp: December 18, 2023, 10:59:27 pm
content: Quote from: Ian.M on December 18, 2023, 10:51:13 pmAh. Not a welding guy myself, so the terminology evaded me. Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2023, 11:08:02 pm
content: Quote from: Benta on December 18, 2023, 10:59:27 pmNor am I. I thought all arc welding required a constant current, but I've just Googled it and found that's not the case.If it's a constant voltage, then a capacitor would be better.

author: Ian.M
author_rank: Super Contributor
timestamp: December 19, 2023, 12:11:03 am
content: Technically, one can get flux core TIG filler rod, for some specialist applications but the only type of welding that specifically requires flux core wire is gasless MIG.https://www.mig-welding.co.uk/gasless-mig.htm

author: Gyro
author_rank: Super Contributor
timestamp: December 19, 2023, 01:49:03 pm
content: Looking at the datasheet ripple current ratings of 22 000uF 80V capacitors at 50/100Hz is going to be a depressing experience. I suspect that you are going to be looking at a very parallel capacitor implementation.