This thread started as my description of the failure of my Astron RS-20A power supply, caused by a bad electrolytic capacitor on the regulator circuit board. Several hams posted advice that a 20Amp supply was really too small for a K3/100, especially if running full power. This led me to order an Astron RS-35 supply.
Chris Hoover, AI6KG, posted the below advice, warning about possible under- engineered rectifier diode arrangement in the RS-35A. Today the big brown truck delivered my RS-35M-AP (the M and AP signify it has meters and Anderson Power Poles on the front panel). Chris speculated that Astron may have made changes more recently. So the first thing I did was to open the case to check out the rectifier arrangement. Here's what I found: My unit bears Serial Number 2019110051. I am speculating that the leading digits 2019 signifies 2019 manufacture. Interestingly, the schematic that shipped with the unit says Rev.1, April 2020. The schematic shows two bridge rectifiers, DB3501. Two diodes are used from each bridge, and sure enough the diodes are paralleled. The DB3501 is spec'd at 35A, so that seems to be an improvement from the 25A diodes Chris mentioned. That's what's in the schematic. Inside the power supply, there are indeed two rectifier packages bolted to the floor, with heavy (maybe 14ga) solid wires connecting terminals in parallel. I'm unable to confirm what the rating of these diode packages is. They are not labeled DB3501. Instead, they say "Astron 5001," and one of them also bears some Chinese characters. So custom made for Astron? Well, I have ordered a 50Amp rated diode package, but am undecided if I will replace the diodes in the supply. 35 Amp rated diode bridges is an upgrade from the 25 diode bridges that Chris mentioned finding. It does puzzle me why, with 50A (and better) diodes being so cheap, would Astron do it this way? I can only think of two reasons: 1) We think having two packages bolted to the case will make for better heat dissipation of the total heat generated at max current and 2), the ever present, "because we've always done it this way!" Finally, I'll mention that, like my old RS-20A, I found the negative terminal bonded to the case. I consider this bad practice so I removed that bond. 73 to all Ray K2HYD On Sun, Apr 19, 2020 at 6:07 PM Christopher Hoover <[email protected]> wrote: > You might want to replace the bridge rectifier in that new 35A power > supply. > > Yep, right out of the box. > > At some point, Astron started shipping RS-35A's with a 25A bridge > rectifier. They paralleled two out of four of the 25A diodes twice over > to make, supposedly, a pair of 50A diodes for center-tapped full-wave > rectification. That's not good engineering practice as the diodes in each > pair will not share current equally because of differences in Vf and > tempco. Once one blow, the other will blow shortly after. > > After I fixed my own RS-35A with this problem, I've helped several other > hams fix this same problem in theirs. Not a random sample, as this is just > folks on my local machine and in local clubs. > > You can get a 50A bridge in the same package for under $3. > > Perhaps Astron has fixed the problem since .... > > 73 de AI6KG -ch > > > > > On Thu, Apr 16, 2020 at 10:28 AM Ray Albers <[email protected]> wrote: > >> Many to all who posted/responded to my recent post about an electrolytic >> capacitor failure in my power supply. Lots of very interesting reading >> about peoples' industry experiences - thank you! >> >> Several have pointed out that using a 20A supply with my K3/100 is pushing >> close to (or over!) the limit. Even though I am measuring just 16A at the >> power level I'm running (and not running anything but the K3 on this >> supply) I agree that I'm skirting the edges. So even though I've been >> getting away with it for a long time, this morning I ordered a 35A supply. >> I'll probably sleep better. >> >> 73 >> Ray K2HYD >> >> < >> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon >> > >> Virus-free. >> www.avast.com >> < >> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link >> > >> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] >> > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> Virus-free. www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
