Beta alternator suppression

[doug748]

Has anyone fitted a capacitor to cut down electrical interference from a Beta 722 20 hp engine (I am sure others in the range are similar). I have a capacitor with ring for earthing to the body of the alternator, but where do I fit the wire? The alternator has a stout wire which terminates in a L shaped rubber boot which looks substantial and pretty immobile. There are two smaller wires; one goes into the body of the device at the top back with little obvious sign of any connector. The other is connected to the body just below the L shaped boot and seems to terminated by some form of patent connector. As can be gathered by the above any purely technical advice will go right over my head.

 

[noswellplease]

Have you tried phoning the Beta people, at least they answer the phone without giving you the run around press this press that and making a fool of you. I found them helpful the odd time I phoned them.

 

[doug748]

Yes, they are very good......but their explanation still sounded like Greek and, to be fair, the very helpful chap was not familar with the particular unit. To be honest there is a limit to the number of times you can ask someone to explain..

 

[ytd]

Normally the wire end of the capacitor goes to the same terminal as the stout wire (under the rubber boot) and the body of the capacitor is bolted to the body of the alternator using a convenient nut. I've not had much success with noise supression capacitors. If the brushes or bearings in the alternator are going bad the capacitor will not be enough. There are lot's of other things on modern boats that make noise and tracking them down is the hard part.

 

[William_H]

if you are sure it is the alternator that is causing the interference you should determine that the alternator can deliver something like its rated output. This especially so if the interference seems to get worse with more load on the alternator. ie low battery or lights on.
You need an ampmeter or volt meter and a way to really load the alternator with electrical current drain.
An inverter with a good load plus a fridge on 12volt electric jug and lots of lights to total a current drain at least 50% of the rating of the alternator. At decent engine reve it should be able to maintain more than 13 volts with a load.
Now this may be beyond you in which case you should remove the alternator and get it checked by an auto electrical overhaul shop.

What can happen is that one diode can die. The alternator has 3 pairs of diodes each pair rectify an AC cycle there being 3 different cycles at 3 phases or times in the alternator rotation. The 3 pairs of diodes contribute to 6 lumps of power to the positive terminal per rotation. If one diode fails due to the automatic regulation of the alternator you may still think it is working OK but the 2 functioning pairs of diodes give power then there is a gap with no power in the rotation. This gap can give interference. When normally a good alternator does not give much trouble. I have seen cases on a light aircraft alternator where it was just an in balance in the diodes that caused interference. So if all else fails have a new diode pack fitted.
(yes these suppressors are made for the job so the they do have a use and may fix your problem.
In answer to your question. A capacitor usually has 2 wires. sometimes one has a positive mark the other being negative. The neg. goes to gound of the alternator while the positive goes to the wire on the large terminal.
However it sounds from your description like you have a purpose built suppressor capacitor. This has a metal body which is bolted to the alternator and is the negative connection. It has a terminal at each end. (possibly a screw terminal) Both terminals are the positive.)
You can use just one terminal and connect it to the fat wire and large alt. terminal. However the intention for better filtering is that the fat wire of the alternator be cut so that alternator current passes through the body of the capacitor. So one terminal to the alternator the other to the wire that went to the alternator. Rather than cut you can remove the wire from the alternaor and provide a new short wire alternaor to suppressor. The 2 ends of the suppressor may be interchangeable or may be identified if there is a preference.I hope this helps olewill

 

[doug748]

Thanks for the replies. Bye the bye, it is a new engine with under 200hrs. I shall remove the unit so as to have a good look first, and then go for it.

 

[alldownwind]

[ QUOTE ]
............ Bye the bye, it is a new engine with under 200hrs.........

[/ QUOTE ]
In that case I would do nothing until I had spoken to Beta.

 

[doug748]

All done, the immobile rubber boot proved easy to lever off, exposing a simple stud, all much easier after taking the alternator off. Extending the wire on the capacitor meant it could be neatly earthed on a mounting bracket stud. Wait till the spring to see if it works now.