stivvy Posted April 26, 2014 Share Posted April 26, 2014 hi all, im sorting out the electrics for my Rover 8 FFR restoration, and the last bit of the puzzle is the Rectifier (Toast Rack) Nearly all the fins are corroded and peeling but i dont think they are coated with just paint, it looks like a Lead like material. can it be repaired or should i look for a new one? i havent tested it yet to see of it works but will not be installing in such a state Chris Quote Link to comment Share on other sites More sharing options...
g0ozs Posted April 26, 2014 Share Posted April 26, 2014 I seem to remember when I started in electronics in the 1970s you could still buy "Selenium Rectifier Substitutes" comprising a large silicon diode and a series resistor - so you could probably make a replacement that way with a modern bridge rectifier and wire wound resistor of a few ohms - the challenge will be calculating the resistor to give the same voltage drop on full load as the Selenium rectifier did, without a working selenium rectifier to measure. See http://w3hwj.com/index_files/RBSelenium2.pdf for a write up on doing it for low current radio applications. Hope this helps Iain Quote Link to comment Share on other sites More sharing options...
fv1609 Posted April 26, 2014 Share Posted April 26, 2014 Chris the CAV type RUS-3 is quoted as having a forward resistance of 10 ohms. Of the 9 elements, 3 are for a common negative, 3 vehicle +ve, 3 radio +ve It is not made clear whether that 10 ohms is per element (or pair in series) or per trio in parallel (or per trio in parallel in series with its trio pair) Quote Link to comment Share on other sites More sharing options...
stivvy Posted April 26, 2014 Author Share Posted April 26, 2014 thanks to both for your help so you think im better off replacing the elements with diodes and resistors and not find a NOS unit? i have 2 of them but both have corroded elements Quote Link to comment Share on other sites More sharing options...
g0ozs Posted April 26, 2014 Share Posted April 26, 2014 (edited) Chris My understanding of selenium rectifiers is that they do not age well, so even a cosmetically good NOS one may be out of spec. I would go the silicon diode and resistor route, starting with 33 ohms per section (gives just over 10 if three sections are in parallel) and reducing to 10 ohms if the voltage drop is too much, given the ambiguity noted by Clive Iain Edited April 26, 2014 by g0ozs correct resistance Quote Link to comment Share on other sites More sharing options...
fv1609 Posted April 26, 2014 Share Posted April 26, 2014 Chris if I had a Toastie or earlier (bearing in mind the 40A system was originally retro fitted to Rovers Mk 3 & Mk 5) I would be tempted to test the electrical properties of the rectifier & see how it performed. There are a few vehicles around that function perfectly satisfactorily with the original installation. It is always a particular delight to see them. Selenium rectifiers in radios set invariably would be for the HT supply typically 250v not 24v. In such circumstances an electrical breakdown could have unpleasant consequences, particularly a design that just uses a dropper resistor in series with the mains! The situation is rather different in the 40A system. The negative output of the rectifier is not 'earthed' it is fed to the control board through a current regulator & the radio supply output is fused. Unlike a domestic radio that would be used indoors, in the event of a failure where noxious fumes would be most unwelcome they are somewhat more removed by being in the engine bay & may be limited by the action of the current regulator. A little while ago someone posted pics of his 40A system on EMLRA. The rectifier had few & thicker fins. This seemed very odd but on scrutiny you could see silicon diodes pressed into the holes accommodated into the fins. This looked to have been done quite some time ago. I don't know if this was a sympathetic restoration or an official update. Although I have never found any EMERs relating to such a change. Quote Link to comment Share on other sites More sharing options...
fv1609 Posted April 26, 2014 Share Posted April 26, 2014 Quote Link to comment Share on other sites More sharing options...
stivvy Posted April 27, 2014 Author Share Posted April 27, 2014 thanks for your input everyone i will speak to a colleague of mine who has a lot of electronics knowledge, but for the time being i will focus on something else since its probably better to have all the wiring in place to test the charging system Chris Quote Link to comment Share on other sites More sharing options...
Rover8FFR Posted April 27, 2014 Share Posted April 27, 2014 Hi Chris I hope you find a genuine rectifier. I bought one some years back as NOS and haven't seen one since. It took years to spot them but perhaps in hindsight I was just very very lucky. Im interested what solutions you decide upon. It may be well worth checking the performance of them as is though even though cosmetically they have suffered. If you do have major problems then one option I mused over if I didn't have a solution was to change to the 90amp set up. Albeit I never researched the what's and where fors???? Good hunting Best wishes Quote Link to comment Share on other sites More sharing options...
stivvy Posted April 28, 2014 Author Share Posted April 28, 2014 definitely will not be installing a 90a system... i will decide when its next to go on Chris Quote Link to comment Share on other sites More sharing options...
Rover8FFR Posted April 28, 2014 Share Posted April 28, 2014 definitely will not be installing a 90a system... i will decide when its next to go on Chris I like this comment Quote Link to comment Share on other sites More sharing options...
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