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Old 07-04-2018, 11:12 PM   #1
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Shunt base recommendations?

The other day I went to pop the top and discovered I had no power... all symptoms seem to point to a bad ground: I see full power at the batteries and the solar is generating ~38V etc. Buy Iím only seeing ~3V across the fuse box. And the problems comes and goes.

After cleaning a bunch of connections under the van I get to the shunt. Iím reading almost 9V across it when things are bad and 0V when they are good (what I expect with this voltmeter).

The shunt in mounted on a ďfoamĒ like base. The bolts are embedded in this material and appear to have wiggled/vibrated some space for themselves. The shunt is bolted right to the foam and the extra space lets it make a bad connection I THINK. If I adjust so itís tignt everything works but if I drive around it fails again.

I pulled the foam and tried replacing w a PVC conduit box that I mounted the shunt to. Now everything works but the controller doesnít show accurate amp readings. Itíll show some amps when I first turn on lights or the inverter but then it sorta slowly comes back down to zero. Maybe PVC is too conductive?

So what should I use? Looks like I can find some shunts w a base for sale but there are also plenty w/o a base. What do they expect people to use? What do you use?

Any ideas ó including second guessing my diagnoses appreciated. Thanks
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Old 07-05-2018, 07:55 AM   #2
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What equipment is the shunt tied to? You need to match a new one to the controller that is using it. (sometimes this is a programmable setting). Shunts will come in amp and millivolt rating ( usually 50 or 100 )



I would say that installing a shunt under the van in the elements would not be my first choice, as a shunt is a precision resister adding any corrosion can alter the accuracy of the shunt, and lifespan.

-greg
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Old 07-05-2018, 08:34 AM   #3
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Its hard to read in the image but its a 100a / 75mV rated shunt. There are some available on the market but I was wondering if I could just replace the insulated base which is what failed. Only I don't know what I can use or why some are sold w/o bases.

Under the vehicle mounting is a bit lame but is also where my batteries are. After I get the system working again I can add something to protect this space but I agree it will never be completely ideal. Sadly dictated by the battery location.
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Old 07-05-2018, 08:44 AM   #4
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.....I'm struggling with the idea that the PVC base is causing excessive current leakage at 12VDC....


....as an experiment, mount the PVC base to another piece of plastic or some other insulator to see if that changes anything. The dielectric strength of virtually any plastic should be plenty sufficient for 12VDC potential.


As another easy test....just bypass the shunt and see if your voltage problems resolve.
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Old 07-05-2018, 09:00 AM   #5
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I agree, I totally thought the PVC would be sufficient.

What I'll do at lunch is wire the shunt in just hanging in space -- if the behavior is similar to when its on my PVC base then I'll be able to exclude that as the issue. I'll report back.
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Old 07-05-2018, 09:32 AM   #6
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Most likely, corrosion has increased the resistance of the connections. Try cleaning up all the connections shiny bright. Check the connectors that are staked to the wires too, moisture wicks into the wires eventually corroding them. Heat shrink adhesive filled ones are best. PVC is fine for insulation, its used as insulation on wire, or a piece of wood works too, but will eventually will rot if not saturated in epoxy. Far better would be to move the whole thing inside, or at least into a water tight box, the environment under the van is toxic and what ever they put on the roads in the winter is death to unprotected electrical connections.
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Old 07-05-2018, 10:18 AM   #7
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re Cleaning: I've already taken every connector apart and cleaned with a wire brush. I feel its reasonably clean at the moment. My remaining problem is this bad reading from the amp meter. (I think).

re Moving things inside: I'll probably install a protective box to try and keep this area clean for now. Technically I do have space near the wheel well inside the van but its really hard to get to and I'd have to disassemble and rebuild a lot to make this change. Something for this fall/winter and not for the week before a big trip -- and it wouldn't address a few other components under there anyway. I'll make that call later. For now to fix whats broken. In the meantime I just want to understand/fix whatever is going on in the existing system.
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Old 07-05-2018, 12:23 PM   #8
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Solved. I hope.

With PVC or just hanging in space has the same result. Conclusion: PVC is a perfectly fine tool for the job. I've buttoned it all back together.

I have a theory and it makes me look bad so I'm going with it: The amp meter was reading 0 etc because the sun was out. My test load of all the LED lights and the inverter was less load than the solar was putting into the system. Therefore no current to ground. I tested this by throwing a blanket over the solar and I do see my amp draw go back up into the ranges I kinda expect. Its not like I keep notes on this -- I normally only ever glance at that panel at night when we're actively drawing down the battery. Does that make sense?

I do know I found and fixed two loose ground connections. One at the fuse box (not mentioned earlier as it was just a bolt that must have not been tightened) and the other with my new shunt platform. Unless murphy strikes again I'm gonna assume the pop-top etc will all work for a while. Protecting the connections from the elements is on the list.

Thanks for providing a sounding board.
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Old 07-05-2018, 12:27 PM   #9
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My PVC shelf in case future readers are interested
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Old 07-05-2018, 02:46 PM   #10
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Give all those connections a liberal coating of corrosion protection such as

https://www.walmart.com/ip/Boeshield...&wl13=&veh=sem
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