most of the recifiers I can find have a max rating of 35 ampsI might be tempted buying a crappy HF battery charger and ganking the bridge in it to copy what MikeW did.just wondering if these bridge rectifiers I am finding are rated at 35A or max 35AthanksRyan
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k to make the little bridge work, can I use it on the input side, since Im not drawing more than 35 amps? will a transformer step-up DC? or do you have to stepup AC then convert to dc.sorry if this is basic stuff I wish I knew more about electronics Ryan
Reply:Sberry should be able to answer this correctly, He is the resident electrical guy!!StangnetShop Full Of Stuff. Joey
Reply:I had a guy here the other day that could have filled you right in. My knowledge of electricity is minimal. I do know something about wiring basic circuits for hooking up equipment, thats about it. Maybe I will look at a drawing later but I am sure you need heavy rectifiers, the output is usually done. Sorry, I havnt been following all the threads to see what you are working on.www.urkafarms.com
Reply:well I got a cheapy ac stick and regret not spending the money for ac/dc thought I could bargin buy a bridge rectifier or atleast a few(4) heavy duty diodes and a cap to make dc out of my current machine. Local electronics places only have a 35a bridge but its not going to be big enough. I asked earlier if I can convert to dc before the transformer, this is where my knowledge is zip, but after a little research it looks like ac is needed for the transforer to step up on the secondaryso now I have to find some 150a diodes or a 150a bridge rectifier to make this work, but am not having much luck. I wanted to know if a bridge from a Harbor Freight battery charger would be up to the task for my welder.also the problem is cost, if its going to cost me more than 50 or so bucks, Id rather skip it and start paying out on credit a Precision Tig 185Ryan
Reply:Ryan,You can get just about anything you need from digikey.com. They have rectifiers up to 10KA. The higher current diodes get very pricey though. You might want to try the usual surplus stores like mpja.com, allelectronics.com, bgmicro.com, hosfelt.com, meci.com, electronic goldmine, etc..Remember you can also use multple 35A rectifiers in parrallel. You may want to add more than you need so that if one fails, you dont blow them all, or you could use a fuse arrangement.A transformer relies on changing magnetic flux, so applying DC to a transformer will not do anything (except mabey destroy the transformer). It seems you want to use a cap to smooth the rectified DC. Please be aware of ripple current ratings of the caps. 150A is asking a lot of a cap. Consider dumping the cap idea and going with inductors. Surplus Center has an actual welder reactor listed on their website. Hope this helps some.Regards,Art
Reply:Here is where I would likely op to sell the thing for what I could and get one that you want due to the fact all the parts come tuned to work with each other. If one was an electrical engineer and had a barrel full of stuff it would be one thing, but for the avg guy it is pissing into the wind especially if you have to buy parts.www.urkafarms.com
Reply:Originally posted by art887 Ryan,Remember you can also use multple 35A rectifiers in parrallel. You may want to add more than you need so that if one fails, you dont blow them all, or you could use a fuse arrangement.Art
Reply:anyone knows if this is correct way?
Reply:Ummm... sort of right. A few caveats, tho.Diodes don't like to be run in parallel becuse the diode that is warmer carries MORE current (the opposite of conventional resistive materials) and therefore gets warmer yet. Fairly quickly, one diode of each parallel pair carries most of the current.The key is to mmake sure the diodes in parallel are tied to the same heatsink so they will stay at the same temperature, and to note that you don't get double current capacity with paralleling, but maybe only 1.5 times, and then only if you can keep the pairs at the same temperature.Good sources for high current bridges, which are also fairly tough: junkyard altermators, particularly boat alternators. Look for the big 100A Leece-Neville 32 or 64V units (they have the three AC lugs on the back as well as the field and rectified outputs). There are three pairs (a 3-phase bridge) in each, and they are tied to the same heatsink. Two of these lets you make a bridge with 3-parallel sets, properly heat-sinked, etc. Note that the voltage rating on these is typically about 1.5 times the rated output of the alternator, so a 12V alternator may not have sufficient diodes for a welder.
Reply:eBay is also a good source for diodes and rectifiers but you kind of have to know what you are looking for. I picked up a dozen 150 amp 100 volt Russian military surplus diodes for a couple of bucks a piece. I also found a spare rectifier bridge for my Miller 300A/BP for 30 bucks. It cost more to ship than I paid for it. The only thing about eBay is you usually can't be in a big hurry. If you are accumulationg parts for a project, it's great. If you have a machine down, don't count on eBay for help.
