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Author Topic: SDA /SDT Generator Manual copy available and question on de-magnetised generator  (Read 788 times)

Alexdick

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Hi Alex, 240 Volt AC is a sine wave it swings from +380 volt to -380 volt. Get a Bridge rectifier that is good for 1000 volt. I personally prefer ones with screw terminals, something like this would be ideal https://www.ebay.co.uk/itm/1600V-Single-Phase-Diode-Bridge-Rectifier-Power-Module-60-100-150-200-300-400A-G/142636237023?hash=item2135c840df:m:mHdv3EQvIAK-AnA4EtBmkeQ:rk:10:pf:0

You will also need a heat sink, a piece of 6 mm x 50 mm x 150 mm aluminium would be ideal.

The Selenium diode in the top box can be replaced with a modern silicon diode, something like this should be fine https://www.ebay.co.uk/itm/1N5408-Diode-Silicon-Rectifier-Bridge-Diode-3A-1000V/201950776806?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20160706105120%26meid%3D2e29568a7e32460eb9b9b0afffde8b2c%26pid%3D100508

You will need to be very careful to mark the wires connected to the old bridge rectifier to ensure polarity is right when fitting the replacement. Take lots of photos as you go. You may find that the lugs on the old wiring are the wrong size to fit the screws on the new rectifier. You will probably need to solder on some new lugs. Yes I use solder, I do not trust crimp connectors on any wiring supposed to handle 240 Volt at 30 Amps

When you mount your new bridge rectifier it should look something like the photo

Bob

Thanks Bob, I really appreciate this. I will order the parts tomorrow. You mention ensuring polarity is right which I understand but what I don't know is which wires are positive and which are negative on the existing  rectifier? also, which is the selenium diode in the top box? there are so many things there i don't know what's what.....
the journey continues!
thanks
alex

Bob,

I guess the 60 Amp option is the one I want on the Bridge Rectifier available on the ebay link you sent me?

Alex

ajaffa1

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Hey Alex, yes the 60 Amp unit will be more than adequate for what you need, it`s also the cheapest.  ;D

Bob

Alexdick

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ok thats ordered....and 3 amps is ok for the modern silicon diode as shown in the ebay link you sent me? i assumed it would need to be bigger (30 amp?) ! thanks
alex

ajaffa1

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Hi Alex. the link I sent you was for a pair of 3 Amp diodes. The battery should only be charged at about 1 to 2 amps otherwise it will over charge and get hot. If you are concerned we will use both diodes in parallel which would give you six amps on the charging circuit.

Bob

Alexdick

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Hi Bob
Good news, the parts are here (photos below) ! i need to find some 6mm wire today but, in the meantime, I guess i can get to work although I haven't got a clue what goes where!
Alex

ajaffa1

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Hi Alex, sorry I didn`t get back to you sooner but I had to go away for another round of medical tests and assessments. Total waste of time as the experts I visited didn`t have the results from any of the recent tests I had done. The Doctor I was seeing is the top Government assessor, I think he is really pissed that he didn`t have the most recent information in front of him and said he would be contacting the regional Judge to complain. Some one is going to get a reaming, bloody sure it`s not going to be me.  :laugh:

Bob

ajaffa1

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Hi Alex, sorry about the confusion about when you wanted to make a start on this revamp, thought you were still waiting on parts.

Your fist job is to remove the selenium bridge rectifier and old rheostat from the plastic cover. Clean up the cover and fabricate a couple of L brackets to mount your heat sink. Then fit your new rectifier onto the heat sink. I found self taping screws worked very well into the aluminium heat sink. (see photo)

Second job is to disconnect the rheostat from the old selenium rectifier, give it a bit of a clean. If you are as obsessive as me you can give it a coat of high temperature spray paint (these get hot, exhaust pipe paint is ideal). Next is to refit it to the plastic cover and reconnect the wiring. You will need to fit new lugs to accommodate the larger screws in the new rectifier, use solder or quality crimp fittings (not the cheap sh1t they sell in auto centers), heat shrink is optional but I think it makes for a safer/more professional finish. The two wires connect to the side of the rectifier marked with a squiggle/sine wave symbol, the polarity does not matter for the rheostat. (see photo)

Third job is to remove the front plastic cover and clean up the larger rheostat found within, when you are done it should look like the photo.

Bob


jonnymcc

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Hi,

I read with interest about the selenium rectifiers. I have a SL SOM 4.5kva. The control box (on the wall) smells a bit like Garlic and the unit is 1960's - so I assume its about had its day! Is the SOM job similar to the one described in this thread? Also is the rectifier in the SOM in the wall box or the one on top of the head?

Cheers,

Jonny

Hi Alex, there is a very good reason I mentioned modifications, the thing in my original photo, that looks like an old fashioned school radiator, is an old selenium bridge rectifier. They have a life expectancy of around fifty years, yours is due to fail. It will smell of garlic when it does start to fail, please don`t breath this in as it can cause cancer.

It s a very easy fix to replace the selenium rectifier with a more modern silicon rectifier and heat sink, all the parts are available on fleabay for about ten quid. No, I am not trying to sell you something and no, I can`t come and do the work for you. I live in Northern New South Wales , Australia. I live in the middle of nowhere and rely on a old 1970`s Lister/Brush generator for back-up power. If you rely on your generator for primary power you should replace the selenium rectifier before it fails.

Where in Berkshire do you live? I was unlucky enough to go to school in Pangbourne, Berkshire.

I completely understand your concerns regarding starting handles. Many full grown men have been injured by these, children do not belong anywhere near them. If you are hand starting your generator please regularly grease the shaft and ratchet pin so you don`t get hurt.

Bob

dax021

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Hi Jonny, could you please post some photo's of your control box internals.  Want to see if it is similar to mine.  I am also having battery charging issues on my SR2 SOM

jonnymcc

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Sure will, I'll try and get a few tonight.

It seems a common problem, many people plug in a battery charger; but I don't like to let it beat me!

Cheers,

Jonny

jonnymccni

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Hi,

See Pictures below of my unit internals.

One thing that worries me is that there appears to be a high voltage connection to the Fuel Control Solenoid, which i would expect to be 24v......

Any advice from anyone on how to improve safety of the unit appreciated.

Jonny

dax021

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Bummer, totally different from my setup, but thanks for the shots.