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Old 12-16-2018, 02:08 AM   #1
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Default Shunt installation

I would like to install a battery monitor which requires (unless I'm mistaken) the installation of a shunt. However, on my Roadtrek Simplicity, the battery and it electric connection to the chassis are outside under the chassis. Considering this, how could I install/protect a shunt?

The only solution I could think of would be to install the shunt inside after routing the negative cable inside and them outside.

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Old 12-16-2018, 02:23 AM   #2
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I would like to install a battery monitor which requires (unless I'm mistaken) the installation of a shunt. However, on my Roadtrek Simplicity, the battery and it electric connection to the chassis are outside under the chassis. Considering this, how could I install/protect a shunt?

The only solution I could think of would be to install the shunt inside after routing the negative cable inside and them outside.

We had the same issue with ours, so when I redid our power system I did bring all the negatives, including chassis, to the shunt inside the van. There have been some installs underneath but you need to keep the shunt clean, particularly of conductive stuff like salt, and cool if you charge a fairly high rate. I think the methods used were to put it in a large surface area aluminum box for cooling, as long as it is a cool area under the van and not by the exhaust or other hot area.


You might also check with the manufacturer of your monitor to see if an Inpower (or other brand) inductive pickup will work with their monitor. Inpower claims that the inductive can replace shunts for most meter types, so that may be a possibility. The inductive is weatherproof and can even mount on the positive cable or negative cable with no cutting needed.
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Old 12-16-2018, 02:39 AM   #3
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Another option is a DC current Hall sensor which can be placed under the van, not as accurate as shunt but could be better than inductive. I used this one, it was OK.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It is just current meter but I have seen battery monitor. The key issues are that it requires occasional resetting and is not as accurate shunt.
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Old 12-16-2018, 02:49 AM   #4
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Another option is a DC current Hall sensor which can be placed under the van, not as accurate as shunt but could be better than inductive. I used this one, it was OK.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It is just current meter but I have seen battery monitor. The key issues are that it requires occasional resetting and is not as accurate shunt.

Very similar to the Inpower, but less expensive for sure. Inpower's claim is that they are much more accurate than the other inductive or Hall effect sensors are. We have two of them in our Roadtrek that I use for real time amp readings from the alternators and to the batteries, with Inpower ammeter. Readings less than 2-3 amps are of no concern to us, so I can't speak for the accuracy that low, but they are very good at even 2 amps, when compared to the shunt based monitor we have. The Inpower are configured with a 0-50mv output to directly replace shunts, so easy to install.
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Old 12-16-2018, 05:00 AM   #5
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Very similar to the Inpower, but less expensive for sure. Inpower's claim is that they are much more accurate than the other inductive or Hall effect sensors are. We have two of them in our Roadtrek that I use for real time amp readings from the alternators and to the batteries, with Inpower ammeter. Readings less than 2-3 amps are of no concern to us, so I can't speak for the accuracy that low, but they are very good at even 2 amps, when compared to the shunt based monitor we have. The Inpower are configured with a 0-50mv output to directly replace shunts, so easy to install.
I wasn’t aware off this type of sensor mimicking shunt with +/-0-50mV, so any battery monitor using this voltage range shunt could be used. Learning every day.
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Old 12-16-2018, 06:36 AM   #6
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I wasn’t aware off this type of sensor mimicking shunt with +/-0-50mV, so any battery monitor using this voltage range shunt could be used. Learning every day.
Yep, the 0-50mv is very unique, I don't know if there are any others doing the same thing, or not.


It likely would be compatible with the battery meter, but I think the biggest question would be the accuracy at very low amperages. Shunts are so good at low readings that is hard to compete with them and the hoops have normally been not very good there. When I got ours, I talked to them and got their accuracy data which was typical meter speak terminology with all the percents of reading, plus or minus so much, and plus or minus X significant digits.....so very hard to figure out what it would really be. Even the tech on the phone couldn't give hard numbers, but said at the 2-3 amps I would fine within a couple of tenths, and ours are that close.


Data on the pickup is here:


InPower Direct - Solutions you can count on
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Old 12-17-2018, 12:07 AM   #7
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I really wanted a Victron battery monitor (with Bluetooth) but it won't possible for me to redo the battery wiring before we leave at the end of January. I'm now wondering if I could use the Victron monitor with the sensor you suggested.

If I understand correctly, it outputs 2.5V +/- 50 mV?

Here's Victron settings regarding the shunt.

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Old 12-17-2018, 12:16 AM   #8
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I really wanted a Victron battery monitor (with Bluetooth) but it won't possible for me to redo the battery wiring before we leave at the end of January. I'm now wondering if I could use the Victron monitor with the sensor you suggested.

If I understand correctly, it outputs 2.5V +/- 50 mV?

Unless I misunderstand the spec, you would want the +/- 50mv version, which should be the same output as the shunt would be. They say the meter has to have a least 20 ohms of internal resistance, which seems to be the only added requirement. A call to Victron may be a good thing for you to do to see if they would even think it would work.


I think this would be the series of pickup you would use.


http://www.inpowerdirect.com/docs/OM-23D.pdf
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Old 12-17-2018, 12:22 AM   #9
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Yes, I will call them tomorrow.

Thanks again!
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Old 12-17-2018, 12:53 AM   #10
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I'm wondering if I could install the shunt inside a waterproof electrical junction box under the chassis... From the first picture, would it be easy to disconnect the battery cable from the chassis, enter the electrical box and install a new cable to the chassis?

Is heat dissipation a consideration when installing a shunt?
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Old 12-17-2018, 01:21 AM   #11
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I'm wondering if I could install the shunt inside a waterproof electrical junction box under the chassis... From the first picture, would it be easy to disconnect the battery cable from the chassis, enter the electrical box and install a new cable to the chassis?

Is heat dissipation a consideration when installing a shunt?

Yes, heat is an issue as a shunt is just a very low resistance resistor. There have been several discussions that I have seen over the years that had different opinions on how hot the shunt would get in a sealed box anywhere, including under the van. The specs usually say something like not to run a shunt continuously at more than something like 70% rated amps because of heat buildup.



In the big picture of what you need right now, you will not have any big currents for long periods, I think. The battery is small, so it won't accept much current for very long, and microwave runs would probably be done with the engine running so no current through the shunt. With low currents, there is less heat, and especially if you use a 500 amp 50mv shunt, it will be cooler than a 100 amp shunt. You lose a bit of resolution and accuracy with the bigger shunt with some meters, but that is normally not a problem in the real world.


An aluminum box will transmit heat better than steel, and plastic would probably be the worst.


The risk is really quite low as not much bad could happen if it did get too warm, as I doubt you could ever put enough through it with the single battery to heat it up much.


You may just want to try it and see what happens. You could easily put a wireless outdoor thermometer on it, or even a wired one so just a probe and you are running wires to the meter anyway, to a display by the meter in the van. It is very possible it would work well most, if not all the times, with hot weather or long drives that put a lot of hot air under the van being possible exceptions.
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Old 12-17-2018, 01:44 AM   #12
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Thanks again booster!

In your opinion, it should not be too hard to connect the cable to a shunt inside a box? Those cables look very stiff.
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Old 12-17-2018, 01:49 AM   #13
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Thanks again booster!

In your opinion, it should not be too hard to connect the cable to a shunt inside a box? Those cables look very stiff.

They certainly will be stiff. With an engine generator they are probably 4/0 cables. The larger the box the easier it would be, I would think. If you have the cables positioned outside the box to go straight in to the shunt at the right height and position, you can probably not have much bending to do in the box.
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Old 12-17-2018, 06:10 PM   #14
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I installed the Link 10 shunt on my trailer 20 years ago aft of battery banks on the tong. The unit was hidden under the floor, with holes drilled on top of the project box covered with window screen to prevent infestation but allow warm air to escape.

The box was made from an aluminum extrusion with fins, anodized black to improve radiation heat transfer, and it worked great. Similar to this box https://www.amazon.com/Eightwood-Enc.../dp/B0107WU67M

At 500A current the shunt will need to dissipated 25W if my math is right but how often will you run at 500A draw.

Make sure to use a twisted pair cable to connect your battery meter with the shunt.
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Old 12-17-2018, 11:50 PM   #15
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This a nice box. Thanks for sharing your experience!
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Old 12-18-2018, 06:11 AM   #16
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At 500A current the shunt will need to dissipated 25W if my math is right but how often will you run at 500A draw.
If I remember correctly, even a few watts power resistor become hot to the touch in free air so I can't imagine so much power in a sealed box.

However, I am now wondering if much of the heat will not just flows in the cables. A 500A / 50mV shunt has the same resistance (and thus heat dissipation) as 2 feet of 4/0 cable.
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Old 12-18-2018, 12:01 PM   #17
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If I remember correctly, even a few watts power resistor become hot to the touch in free air so I can't imagine so much power in a sealed box.

However, I am now wondering if much of the heat will not just flows in the cables. A 500A / 50mV shunt has the same resistance (and thus heat dissipation) as 2 feet of 4/0 cable.

A good place to see the affects of heat and ventilation is with the Blue Sea Circuit Wizard which allows you to see the amperage rating of wiring. You can put in if it is in conduit or free air and see how different the amp ratings for the same wiring is. It is quite a bit different and much more than most of us would guess. The ratings are the same for short bursts of time at higher amps, though.



Circuit Wizard - Blue Sea Systems


With a single 100ah battery, you will rarely see even 50-75 amps in the shunt, and then not for very long, so you will not have as much issue as one would with a big system, but heat is still needed to be allowed for.
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Old 12-18-2018, 12:14 PM   #18
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At 500A current the shunt will need to dissipated 25W if my math is right but how often will you run at 500A draw.
George, wouldn't that be 2.5 watt?
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Old 12-18-2018, 06:09 PM   #19
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George, wouldn't that be 2.5 watt?
A 500A/0.050V shunt with resistance of 0.0001 Ohm should generate 25W at full current range, I think.
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Old 12-19-2018, 04:55 PM   #20
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I now considering installing the shunt inside but I have no idea how I should pass the cable though the floor. Considering that the floor is composed of many layers of different material, I suppose you can't simply use a grommet.
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