Interference

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dougg

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With my raymarine instruments turned on I can see all the Data ie heading, speed, cog etc etc.
When I fire up the engine I get a message that says "heading unavailable" several items disappear including heading, set and drift, true ground wind angle.
If I turn off the engine they come back.
If I just turn on the ignition only,the data is still all there.
So this morning I took of the alternator drive belt, ran the engine and hey presto the data was all still available.
Question, is there something in the alternator that can break down to now cause this interference or do I need to look further a field.
Boat and systems all 7 years old, have worked ok up until recently.
No new equipment added.
Fluxgate has been calibrated etc.:confused:

,
 
I find that sometimes when I transmit on SSB, especially the lower frequencies, that my GPS drops out, the light in the compass lights up and the depth sounder skips sometimes.

On the other hand, the gps data bursts and the depth sounder emit noise that can be heard on ssb.
 
Assuming this is a new phenomenon, the rectifier pack may have lost a diode. This would result in a strange waveform to the nominally DC output and might be the source of the problem. That's the trouble with trouble-shooting interactions between all the kit, lots of maybe's and ifs! There are ways to reduce interference by winding the leads on bobbins, they are supplied with new Raymarine instruments (happily I haven't found need of them - yet).

I'd suggest you find out where the local motor trade take their alternators and starter motors for repair, usually a one-man, garden shed business. This is by far the cheapest way to get the alternator checked out and he may recommend a refurbish whilst it's out of the boat; well worth while to take the opportunity. Having checked/repaired the alternator he will most likely also be the ideal person to advise on other effective measure to prevent interference. Oh, and check whether the alternator cables are running parallel to the instrument wiring, this often induces a current which can easily obliterate the signals.

Rob.
 
Most modern alternators use an integral pack, though older models had a seperate pack. Do you have the engine type and, ideally, the alternator model?

Rob.
 
We used to fit a capacior to alternators on small aircraft. The capacitor is about .2 micrrofarrad in capacity. It is called a feed through type capcitor. it has a terminal at each end for the alternator output to go into and out of. In fact it is just a solid conductor throught the middle. The outer body is clamped to the case for negative connection.
You could try running the electronics off an isolated battery just confirm interference is coming in via the battery charging. A series inductance and bypass capcitors in battery supply to instruments may help.
But my guess is as said a bad diode in alternator. If you have an amp meter if you cna induce the alternator to supply near its rated current then it is obviously OK. A bad diode will limit max current to about 1/3 of current rating. (which you may not notice under normal use) good luck olewill
 
Rob.
Our engine is Yanmar 4JH4E
Alternator deteils. LR180-03C 119573 77201 12V 80A C REG Built in Hitachi.

William H
Thats interesting re the out put. I've suspected it to be down on out put for a while even when the 4 house batts are down to say 75% the alternator will put in only about 25A. When I put on a large load like the toaster, via the inverter with the engine running there is still a large discharge, with the alternator rated at 80A, this, I would have thought would easily cover the 50a that the toaster would use.

Thanks for the replies guys.
 
I have to say that if the alternator gives actual 25 amps then it is probably OK. I may be wrong but I was thinking in terms of only a handful of amps if one phase is dead (diodes or coil). The alternator may be rated at 80 amps but this would be at full alternator speed into a load like an inverter or lights. As a battery charger much depends on what the batteries will accept rather than what the alternator will give. Anyway as said an alternator check on the bench may be beneficial. good luck olewill

dougg said:
Rob.
Our engine is Yanmar 4JH4E
Alternator deteils. LR180-03C 119573 77201 12V 80A C REG Built in Hitachi.

William H
Thats interesting re the out put. I've suspected it to be down on out put for a while even when the 4 house batts are down to say 75% the alternator will put in only about 25A. When I put on a large load like the toaster, via the inverter with the engine running there is still a large discharge, with the alternator rated at 80A, this, I would have thought would easily cover the 50a that the toaster would use.

Thanks for the replies guys.
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