Shielding against ac cable noise

Pincoya

Pincoya

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I have a Link 10 battery monitor and at one point the Link cable runs close to other electrical wiring that may be inducing noise into the sense leads for the shunt.

I do not want to re-route the cable and would like to try to shield the twisted pair shunt wires. Does anyone have a suggestion about what I might use to do this?

Paul
 
You say "may be inducing noise", I wonder whether you have any evidence that it is? Have you tried turning off all DC loads and seeing whether AC loads create a false reading on the Link 10?
 
Yes, I have worked with Link and gone, step by step, through their troubleshooting steps; excellent support by the way.

The meter is working correctly but accumulating a 1amp hour defecit per 24 hours when on float. Nothing to worry about but the perfectionist in me doesn't like that and all we are left with is ac current intefering with the twisted pair shunt wires.

Paul
 
Perfectionism is a real pain and, in the absence of anything else to tinker with, perhaps I'll just have to polish windvane.

Paul
 
Like others I can't imagine this a problem but anyway to provide shielding.....
Buy or get some large sized RG8U coaxial cable as long as the wires you need to shield. If you are lucky and get a high quality cable it will have tinned copper braid. Strip the outer plastic insulation cover off then bunch up the braid and pull off. Feed the braid over the wires of concern then cover again with a heat shrink plastic tube.

One end of the braid must be connected to earth. It is not good practice to earth at both ends in case you provide a path for earth current through the braid for other services. If you really wanted to you could connect the other end via a small capacitor ie .1microfarrad 50volt or more.
With an earthed braid so close to the sensing wires to the shunt it is most imperative that you provide fusing for the sense wires between the shunt and the entry to the screen braid.

You might try small capacitors from the sense wires to one another and also to earth. Try .001microfarrad 50 volt rating or higher. This circuit should be essentially DC with very slow changes so I don't imagine capacitors would have any effect on performance. Good luck olewilll
 
Thanks William,

Having read your excellent analysis I have broken out the Bright Boy and will mostly be polishing the Monitor WindVane.

Still can't help wondering where that 1Ah is going though!

Paul
 
The classic way of dealing with this would be to buy some ferrite beads / toroids from maplins and wrap the sense wires at the meter end round them. This raises the impedance of the wires to AC signals.

personally I doubt that the AC is the problem. But how do you know that you are 1 AH out? What are you comparing with what to get that figure?

does it matter anyway ? you will nop doubt be comparing AH used with AH put in to say to yourself something like " I've used 75% of the capacity - better charge the batteries" . And that calc will be accurate whether or not your system misreads by 1AH.

A cautionary tale. I was crossing Biscay and bored to death. Being inclined in the same way as you, I was irritated by the inaccuracies in the old Echopilot log compared with GPS - so I took the display to bits. And in the going I bu**ered up the adjustment potentiometer. So there I am, sat in the cockpit, wind starting to rise with a lap full of electronic components and a hole in the binacle. Took me 2 hours to get any sort oif signal out of it and even then it was more inaccurate. You can just imagine SWMBOs comments when I had to buy a new log.

Leave well alone. /forums/images/graemlins/grin.gif
 
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