Alternator Wiring

[Guest]

I have just rebuilt my alternator but lost my wiring diagram. SEV Marchal fitted to a Volvo MD5. The system works fine on a single battery, without the split charge assembly, following the workshop manual diagram but this does not cover the split charge circuit. The split charge assembly consists of 3 diodes on an aluminium plate all facing the same way. Two diodes have large terminals labelled B+ which are obviously the two battery connections the other terminal is smaller and labelled 61/D-. I am sure this was wired to something but can not work out what. As far as I can tell the system would work without. Can anyone help?

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[colvic]

I am not familiar with the alternator you are refering to, but if it works OK when charging a single battery then things are OK with the alternator.

The split charge diode works by splitting the charge between two batteries, or battery banks, so that each receive a charge but are isolated from each other so that if one battery/battery bank goes flat then the other is OK.

Sounds as though the D terminal is the input from the alternator and the B+ connections go to the seperate batteries/banks. Any split charge diode will do the job as long as it is rated at a little above the alternator output.

HOWEVER, there is a voltage drop of about 1v across split charge diodes so you will not be charging your batteries as well unless you are also using something like an ADVERC battery charging controller. If you can usually remember to do things perhaps a manual 3 position switch would be a better bet so that you can select which battery/bank to charge, or both.


Phil

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[Guest]

Thanks for the info. The third terminal is another output from the splitter diode pack. The alternator is currently wired to sense one battery voltage (The domestic battery) I am wondering if the third diode is intended to allow the system to sense alternator output (The third diode will certainly not sense the voltage of either battery) so that one battery does not dominate charging. The system has worked ok for 18 years. I rebuilt the unit because some of the windings had almost corroded through and there were some bad connections on the rectifier diodes. The system is giving plenty of Amps but the third diode was definately attached to something before. (I can not see any spare wires in the boat loom) It must have been providing some control function but if I wire the regulator into this I can not see how I will get any field current on start up. Any ideas?

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[VicS]

The small diode connection marked 61/D- provides compensation for the volt drop mentioned below by colvic (normally said to be 0.7 volt). I'm surprised by the D- as I would have expected it to be D .
There is presumably a common terminal to which the alternator output is taken, the two marked B then go, as you deduce, to the two battery positves
The third then feeds the D connection on the regulator which in the absence of the split charging diodes would be feed from "61" on the alternator.

You do not say if the regulator is separate from the alternator, in which case the alteration to include the split charging diodes is simple, or whether the regulator is inside the alternator, in whch case you have to identify the 61 to D connection inside, break it and connect D to 61 on the split charge diode pack.

The negative connections on alternator and regulator should be marked E and D- and if colour coded the wire between them will be black. The field connections should be marked F and DF and the wire between them either white or green. The wire between 61 and D will be red or brown.

The connection fom the warning lamp will go to D on the regulator

My source of information is the workshop manual for my elderly Volvo car which was originally fitted with a SEV Marchal alternator and a separare Bosch regulator. Some models were fitted with Bosch alternators. Marchal regulators were also used.

It is difficult to describe things without a diagram but I hope this makes sense and helps.

Just read your reply to colvic . You mention a battery sensing connection thats what goes to the third diode'


<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by VicS on 05/04/2003 14:37 (server time).</FONT></P>

 

[HaraldS]

by car standards, 61 is for the charge control light. D- would be alternator minus which on non-isolated systems would be the same as ground. If you have a grounded standard installation with non-isolated minus, then I think you don't need that terminal. My guess is that it is connected to a small diode, the other way round than the big battery diodes and that way it provides ground level (minus level) when the alternator is not working. I assume there is a fourth terminal for the alternator + to connect to, that you have not mentioned.

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[Guest]

Yes it was D+. Thanks for the excellent advice. The alternator is now wired up and pushing out plenty of amps and should be good for another 20 years.

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