# DIY Signal Shielding?



## rwaudio (May 22, 2008)

PeterH said:


> I built a slick little system for monitoring and controlling the temperatures in my 5 battery boxes with an Arduino contoller. It is working perfectly so far, as long as I'm not operating my EV. Which is ok because I only heat them when the EV is parked in my garage.
> 
> However, it would be great if I could monitor the temps while driving. The only thing preventing me from doing so is the interference caused by my Soliton Jr. controller.
> 
> ...


Shielded CAT6 cable is great for things like that (only 8 conductors though) and dirt cheap. You could try shield for ground though. You can also get copper tape and braided copper sleeve that you can use for existing wires. Do these wires run near the controller or main battery cables?


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## PeterH (Mar 20, 2009)

Thanks for your reply!

At this point it is too late to employ shielded Cat6 cable or even a pair of them without major re-work. In a car this size, ( a 1991 Geo Tracker) everything is fairly close. In this case, those data cables come within 12 to 18 inches of the controller and the probably closer to the main DC power lines. 

Fortunately, I did use shielded wires from the junction box to each of the battery boxes so I think it might still be practical to try shielding the wires between the junction box and the Arduino to see if that helps.

Now I need to put my hands on some form of copper foil or mesh to wrap around the data wire bundle. Of couse, that shielding will also be grounded to the frame some how.

Given my current budget, I wonder if simple aluminum foil might be worth a try. Certainly would cost nothing to try.

Thanks,
Peter H.


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## TEV (Nov 25, 2011)

Hi, did you got a charger yet ?


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## PeterH (Mar 20, 2009)

I'm using a borrowed Elcon that is taking FOREVER to charge my EV! 

Haven't decided what I'm going to do with my dead TCCharger yet. Holding on to it for the moment.


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## dougingraham (Jul 26, 2011)

It sounds like you are sending a digital data stream over multiple wires, are you using the chassis ground to carry the ground reference? Often just twisting the ground with the signal lead and twisting the power cables between the battery and controller will resolve these issues. You should probably look at the CPU end of your signals, if you are seeing a couple of volts of noise riding on top of your signal then your CPU is at risk because the transients are being clampped to the supply rails and this will cause localized heating on all these signal input pins. You should also make certain the traction pack is isolated from the 12 volt car power.

In severe noise situations you run differential signals over twisted pair. This technique is highly noise resistant.

It would be helpful if you describe the kinds of signals and what the sensors are and how they are wired up. By this I mean that you can sense temperature by measureing the reverse voltage drop on a diode or you can buy temperature sensor chips which send a digital data stream. The way noise affects these systems is very different.

Best Wishes!


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## Tesseract (Sep 27, 2008)

PeterH said:


> I built a slick little system for monitoring and controlling the temperatures in my 5 battery boxes with an Arduino contoller.
> ...
> The only thing preventing me from doing so is the interference caused by my Soliton Jr. controller.


I've posted about this at least a half dozen times over the years so forgive me if I don't go into great detail. 

Yes, motor controllers can emit a lot of electrical noise - this is the inevitable byproduct of switching hundreds of volts and hundreds of amps in hundreds of nanoseconds.

The first/best thing you can do to attenuate noise is to run the traction battery cables as close to each other as possible (side by side or even twisted together) over their whole run. That includes the cell-to-cell connections.

The motor side cables benefit more from electrostatic shielding than running them close together, but that is rarely needed.

A good test to see if you have a lot of interference in your particular installation is to tune an AM radio across its entire band while blipping the throttle (with the transmission in neutral). Some minor buzzing or whistling is acceptable and normal - AM has *zero* noise immunity, after all - but if every single station is obliterated every time you apply throttle then you have a bit more interference than average. Make sure all connections are tight, including all to chassis ground in the car. People tend to not realize that the sheet metal unibody chassis acts as a shield, but as with any shield, the interference induces currents that circulate in it, causing voltage drops between any two points that more-sensitive devices like radios will treat as a valid signal.

That said, the Arduino really has no business being used in an EV. The circuit design and board layout are not robust enough for the expected noise level. You've already figured that out, though. I would try adding a snap-on ferrite core to both power supply leads first, followed by a largish electrolytic capacitor at the power supply input on the board (say in the range of 220uF to 1000uF). Next install a snap-on ferrite across all of the signal wires (including ground(s)) at the same time. Finally, I would try installing individual snap-on ferrites across the positive power lead and then each signal wire.

NB - The ferrites installed across both positive and negative conductors at the same time (power or signal) act as common mode chokes, while those across the individual positive leads act as differential mode chokes.


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## swoozle (Nov 13, 2011)

Tesseract said:


> ...I would try adding a snap-on ferrite core to ...


Tesseract, 

I've got a couple of interference issues also and this info has helped, thanks very much.

It would be nice to reduce my problems even further. I'll try more experimentation, but I'm interested in the theory as well so some follow-up questions if you don't mind:

Snap-on ferrites on the battery voltage leads near my Celllog 8's helped reduce voltage signal jitter during charging. To reduce further, do more ferrites at the same location help? Or would putting some at the other end of the car where the leads come off of the batteries be better?

I've got my temp chips (similar to the OP's setup) signal wire in shielded cable with the shield grounded at both ends but still have unreadable signal during charging say 20% of the time. I assssume that snap-on ferrites won't help if installed over a shielded cable; is that true? Would it help to install some on the wires that ground the shield to the chassis?

Thanks


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## Tesseract (Sep 27, 2008)

swoozle said:


> ...It would be nice to reduce my problems even further. I'll try more experimentation, but I'm interested in the theory as well so some follow-up questions if you don't mind:


I have several 400+ page books on this subject, so... don't expect me to be able to summarize them in a forum post.



swoozle said:


> Snap-on ferrites on the battery voltage leads near my Celllog 8's helped reduce voltage signal jitter during charging. To reduce further, do more ferrites at the same location help? Or would putting some at the other end of the car where the leads come off of the batteries be better?


Snap-on ferrites can go anywhere, and the more you use the greater the attenuation of common mode noise. The only requirement is that they must enclose both the forward and return conductors.



swoozle said:


> I've got my temp chips (similar to the OP's setup) signal wire in shielded cable with the shield grounded at both ends but still have unreadable signal during charging say 20% of the time. I assssume that snap-on ferrites won't help if installed over a shielded cable; is that true? Would it help to install some on the wires that ground the shield to the chassis?


Snap-on ferrites will, indeed, help on a shielded cable. In fact, that is a very popular use for them.

Generally speaking, you want your connection to "ground" (whatever that is) to have as low an inductance as possible, so you don't want to put a snap-on ferrite around a ground connection (and anyway, you always want snap-on ferrites to go around all forward and return conductors at the same time, so that "normal" currents will cancel out).


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## PeterH (Mar 20, 2009)

Obviously I need to watch this forum a bit closer. I missed all this discussion that was posted since I lasted checked and this thread seems to have proven very helpful. 

I haven't tested for interference yet using an AM radio but I will. I get zero interference during a charge. The Arduinio and the sensors all work perfectly whenever the Soliton is not driving the motor. So soon as I take my foot off of the throttle, the display shows valid data.

I'm not complaining about the Soliton at all. It is doing exactly what it should be doing and any problems I'm having with interference are strictly myfault. For example, when I ran the main power lines from the battery boxes to the controller they never even get close to each other until they are in the engine compartment... had I ran them close together and twisted them as suggested I might have a lot less noise.

I am using a DC/DC converter in the power supply to ensure the power for the arduinio and my JLD404 is isolated from the pack and any noise on the 12VDC system so I think my power is clean.


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## Tesseract (Sep 27, 2008)

PeterH said:


> ...
> I am using a DC/DC converter in the power supply to ensure the power for the arduinio and my JLD404 is isolated from the pack and any noise on the 12VDC system so I think my power is clean.


The problem is unlikely to be the DC power supply; rather, it is the "signal level" inputs that are picking up the noise.

Like I said before, the Arduino isn't made for this environment. Perhaps the "Machina" version made by RechargeCar is better suited? Dunno, I'm not much of a hacker, so to speak, so I don't normally mess around with that kind of stuff.


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