arnie Posted January 5, 2012 Share Posted January 5, 2012 Dear All Happy New Year!! I am need of some help please. I am trying to find out if my spare Rotax BA 2803 Alternators, for my FV432, are working. I have been asked to find out what the resistances of the stator and field windings in the alternator should be. I have read the information (see below) given by Clive Elliott in 'All Charged Up' Part 2 but I am not sure if this is the correct data I have been asked for. Output winding (each phase) 0.24-0.28 ohms at 20 degrees centigradeField resistance 0.34-0.37 ohms at 20 degrees centigradeField current 4.9-6.1 amps at 1,750 rpmField current 5.0-6.2 amps at 8,000 rpm If anyone can let me know if this is what I need or advise me as to the correct data I would be very grateful. Thanks for your help Arnie Quote Link to comment Share on other sites More sharing options...
fv1609 Posted January 5, 2012 Share Posted January 5, 2012 (edited) Arnie, the resistance of the field winding is quoted by Rotax in their technical manual & repeated in the EMER as 0.34-0.37 ohms at 20 deg C. Bearing in mind that is both the field windings which are in series. Be wary of the earlier EMER (1967) as it quotes 0.18 ohms at 20 deg C but this is per winding, so the figures are in agreement. In the article the output winding (each phase) is quoted as 0.24-0.28 ohms at 20 degs C. Rotax do not state any values but if you look in the 1970 EMER POWER W 104/12 Paragraph 7(b) it states the typical resistance of each phase as 0.026 ohms at 20 degs C. This in disagreement to what is stated in the article, however I was influenced by the 1976 Inspection Standard EMER POWER W 108/12 Part 2 that gives 0.24-0.28 ohms at 20 degs C. Of course you have to remember you cannot conveniently measure the resistance of each stator winding as they are wired in a stellate manner with each winding at one end joined to the other two & each phase comes from the other end of the three windings. So using three output connections, on any two leads you will be measuring the two windings in series, so the resistance reading is doubled. Of course measuring such low resistances without very expensive equipment is a hopeless task. The only reliable way is to pass at least 10 amps through each pair of windings & measure the voltage drop. Then by Ohms Law calculate the resistance. You could rig up a 12v battery & car ballast resistor to deliver this as described in All Charged Up 4 when it was used for testing the Gen No.10. PS The more I think about it I'm wondering if indeed the Inspection Standard figures are wrong, I'll check & see if I can find any amendments that correct this. Edited January 5, 2012 by fv1609 Quote Link to comment Share on other sites More sharing options...
andym Posted January 6, 2012 Share Posted January 6, 2012 Clive - I absolutely agree about measuring sub-ohm resistances but I wonder if as a first stab a simple continuity test isn't the best approach? These beasties are pretty bomb-proof and the most likely failure mode is overheating through lack of oil. Andy Quote Link to comment Share on other sites More sharing options...
fv1609 Posted January 6, 2012 Share Posted January 6, 2012 Andy I think a resistance measurement is an instinctive first step people feel they want to take. But as you say there are others factors involved & I think leakage tests with a Megger type device should be an integral pointer to trouble. As you say overheating might well be a likely cause of failure & insulation breakdown is likely to be the first casualty of that. I didn't allude to that in the original article & plan to update with this sort of content as I have done with the 90A article. Apart from colour pictures I have done a lot of tests & measurement on CVR alternators which I need to share / inflict on others! With a 500v Megger readings should not be less than 2 megohms from case to, field windings, stator & PL1 with all connections paralleled. Arnie, references to field current, is only something that can be measured when fitted in the vehicle or installed in a test bench with proper oil cooling. Quote Link to comment Share on other sites More sharing options...
arnie Posted January 6, 2012 Author Share Posted January 6, 2012 Hi Clive & Andy Firstly, many thanks to you Clive for your prompt and very informative reply. I have digested every detail! and will attempt to use the given information to find out if the alternators are still working and serviceable. Andy, thanks also for your input....helpful as always. I will post to let you know the outcome of my testing. Arnie Quote Link to comment Share on other sites More sharing options...
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