Suppresor

[MacDavid]

A while ago someone was on about depth sounders ( NASA target ) .I seem to have trub reading when the engine is running as the sounder just runs up and down the scale, I recall that someone said that it would help to fit a suppresor, well I'v got one now but I cannot find anyone who knows where to connect to , not even the guy who sold me the thing. So help !! I'm sure someone out there will know the answer to my problem, Incidently I went agroud the other week becauce of the thing not working right, by the way the engine is a Volvo MD2B

 

[philip_stevens]

Have you checked that the voltage output from you alternater is clean with no A.C. component. By this, I mean, check, with a digital multimeter, on D.C. first to see what voltage you are getting from the alternator, and then change scale to A.C. to see if there is any a.c. from it. There should be no a.c. reading. If there is, you could have a duff diode in the alternater. That could possibly give the sounder the problem.

As to where to fit the suppressors, they go between the alternater positive ouput terminal and the engine block. The tag should be on the terminal, and the wide flange around the suppressor goes to any bolt on the engine or the alternater mounting. Ensure you have a diesel type suppressor, as there are also petrol engine types. I don't know what the difference is, only that there are two types in Halfords. I suspect it is the microFarad capacity that is different.

Perhaps someone else, well up in electronics, would be able to answer why there is a difference.

For some reason, and I cannot now remember why, I fitted two on our last boat. But that was 8 years ago, and the reason is now lost to my memory.



regards,
Philip

 

[VMALLOWS]

A 'diesel' suppresor compared to a 'petrol' suppresor is ridiculous. We are talking here of the output from the alternator. Usauly a 0.5 microfarad capacitor is connected between the alternator positive output and the alternator casing, since this is the nearest ground.

In DECCA days I found that sometimes a 20 microfarad (elecrolytic) helped DECA reception due to the very low frequencies that DECCA used. This is irrelevant now with GPS.

If you have a petrol engine, you may need to look at the spark-plug suppresion ,
though I think this unlikely.

Personally, I would guess that the trouble is with your oil-bath for the sounder (if you have one). The engine vibration stirs the oil up and the air bubbles make it go crazy. Might need refilling.

Do let us know.

 

[VMALLOWS]

MacDavid,
I posted a reply to Phillip-Stevens which I should have directed to you. Please check the forum. Specifically, it sounds like youve bought a standard automotive suppressor...should be fine. The positive wire 'tag' on the suppressor goes to the '+' terminal on the alternator. This will almost certainly be the 'biggest' and have the thickest wire connected to it. The other (negative) connection may be a wire or may be a clamp...either way connect it to the alternator body.

Wherever you connect it, it should not do any harm as long as you do not create any short-circuiits.

 

[jfkal]

I tackled the same problem differently, placing ferrites around the alternator + output and the sounders supply input. Ferrites are of the snap on type used for computer cables. Works fine.

 

[philip_stevens]

With reference to your Decca days, I also had trouble with my Decca losing signal strength when the engine was running. To combat that, I fitted the advertised (at the time) Decca Mate suppressor. It worked, where the ordinary car-type didn't.

As an electrician myself, I could not understand why there were different suppressors on sale for petrol or diesel engined vehicles. I'll have another look when I am next near a Halfords and see if the ?uF is any different.

Since the demise of Decca, I have left the Decca Mate connected - for no other reason in that it is doing no harm by still being there.

I wonder if it has any advantageous effect with Navtex transmissions??

regards,
Philip