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Old 15-10-2011, 16:05   #1
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Two Shunts or One ?

OK,
I will rely on greater minds than mine on this one!
I have a Blue Seas panel with a digital volt meter that also measures current being consumed at the given moment, not amp-hours. I recently bought a Xantrex Link Pro battery monitor so I can keep track of the amp-hours consumed vs generated. The question is this: Can I use my existing shunt that came from the Blue Seas panel or will I get contradicting interference? Do I, can I, should I install two shunts one after the other to avoid having the meters interfering with each other?
Also, is it worth shelling out the extra $$ for the temperature sensor on the Xantrex?

Thanks in advance!
Tom
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Old 15-10-2011, 16:15   #2
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Re: Two Shunts or One?

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Originally Posted by Tortuga's Lie View Post
OK,
I will rely on greater minds than mine on this one!
I have a Blue Seas panel with a digital volt meter that also measures current being consumed at the given moment, not amp-hours. I recently bought a Xantrex Link Pro battery monitor so I can keep track of the amp-hours consumed vs generated. The question is this: Can I use my existing shunt that came from the Blue Seas panel or will I get contradicting interference? Do I, can I, should I install two shunts one after the other to avoid having the meters interfering with each other?
Also, is it worth shelling out the extra $$ for the temperature sensor on the Xantrex?

Thanks in advance!
Tom
I use the Blue Seas ammeter for monitoring the current being used by the DC panel only. Our Link Pro monitors the net charge or discharge into or out of the bank. At a quick glance between the two ammeters I can easily see what my solar panel is contributing. For example I can see that my DC loads are -3A yet my bank is seeing +1.2A charge so my solar panel is contributing approx +4.2A..

You can easily set the shunts up to monitor two different points in the system. I choose to let the Link shunt monitor the bank, record the state of charge etc. and the Blue Sea shunt monitor and display DC current draw for the DC panel only.

The shunt for the Blue Sea panel is installed in the neg return for the DC loads..
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Old 15-10-2011, 16:33   #3
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Re: Two Shunts or One?

If the shunts have the same resistance (or millivolts per ampere), and as is usually the case are supposed to be wired between ground and the battery negative terminal, you will be able to use one shunt for both monitoring devices. If the two shunts have different values you will need to wire them in series between battery (-) and ground.

As Maine Sail points out, there can be good reason to have a separate shunts for monitoring different things, but this is an option.

Re the temperature sensor, is the Xantrex unit a monitor only, or is it also a charge controller? If just a monitor I personally wouldn't bother with a temp sensor. For a charge controller, especially if you are using AGM batteries, the sensor is probably a good idea.
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Old 15-10-2011, 19:40   #4
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Re: Two Shunts or One?

Maine Sail, that panel is beautiful. I'm tempted to print that photo and have it framed.

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I use the Blue Seas ammeter for monitoring the current being used by the DC panel only. Our Link Pro monitors the net charge or discharge into or out of the bank. At a quick glance between the two ammeters I can easily see what my solar panel is contributing. For example I can see that my DC loads are -3A yet my bank is seeing +1.2A charge so my solar panel is contributing approx +4.2A..

You can easily set the shunts up to monitor two different points in the system. I choose to let the Link shunt monitor the bank, record the state of charge etc. and the Blue Sea shunt monitor and display DC current draw for the DC panel only.

The shunt for the Blue Sea panel is installed in the neg return for the DC loads..
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Old 16-10-2011, 16:08   #5
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Re: Two Shunts or One ?

Thanks Mainsail and Paul for your help,
Main: do you have the shunts in line with each other with the LinkPro before the panel shunt or the other way around? Your photo is killer, I wish I had the space for a nice panel arrangement like that! I only see the one shunt in your photo though.

Paul,
The temperature monitor is just that on the Link Pro. I do have a temp monitor on my battery charger already, but that only is in service when I am plugged into shore power and the charger is turned on.

Thanks,
Tom
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Old 17-10-2011, 14:15   #6
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Re: Two Shunts or One ?

I suggest KISS. We, too, have an analog ammeter for our distribution power draw and a separate Link 2000. I do the math in my head when charging sources are present. It's a lot easier to keep them separate.
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Old 17-10-2011, 15:28   #7
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Re: Two Shunts or One ?

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Originally Posted by Tortuga's Lie View Post
Thanks Mainsail and Paul for your help,
Main: do you have the shunts in line with each other with the LinkPro before the panel shunt or the other way around? Your photo is killer, I wish I had the space for a nice panel arrangement like that! I only see the one shunt in your photo though.
The Link Pro shunt is right off the house bank and the DC panel shunt is behind the DC panel on the back plane inserted into the neg return for the DC panel..

The DC Panel shunt is on the load side of the Link Pro shunt and all the DC loads are on the load side of the panel shunt. All loads get read by the Link Pro but only DC panel loads are read by the DC panel shunt.
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Old 17-10-2011, 16:23   #8
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Re: Two Shunts or One ?

Thanks MainSail,

Makes sense. I'll just switch out my Blue Seas shunt with the Link Pro shunt because it is right down stream of the battery bank then I will break the feed to the DC panel and then re-install the Blue Seas shunt for the panel.

It is amazing how much they charge for the 8-conductor wire for the connections on the Link Pro. I can't imagine why it costs over $100 from Defender.....
I will check the guage of wire needed and make my own! Probably 20 Ga.?
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Old 17-10-2011, 17:04   #9
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Re: Two Shunts or One ?

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Thanks MainSail,

Makes sense. I'll just switch out my Blue Seas shunt with the Link Pro shunt because it is right down stream of the battery bank then I will break the feed to the DC panel and then re-install the Blue Seas shunt for the panel.

It is amazing how much they charge for the 8-conductor wire for the connections on the Link Pro. I can't imagine why it costs over $100 from Defender.....
I will check the guage of wire needed and make my own! Probably 20 Ga.?
Don't forget to twist it. These monitors are prone to noise issues. A drill works well for twisting the pairs. The Xantrex price is ridiculous. Years ago it used to be shielded, tinned twisted pair and now it's just twisted pair bare copper... The Victron monitors are a much better deal as they come with everything.
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Old 17-10-2011, 19:59   #10
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Re: Two Shunts or One ?

One shunt rated to the correct amperage.
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Old 17-10-2011, 20:33   #11
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Re: Two Shunts or One ?

Using only one shunt and two measuring devices should work however this is dependent on the input impedence of the measuring devices. All you are doing is measuring a voltage. Sometimes if you have one meter with too low of an input impedence you will provide a secondary path for the current creating a metering error. Best to test by having one hooked up and while monitoring the results attach the second one. Watch for a change.
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Old 18-10-2011, 00:37   #12
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Re: Two Shunts or One ?

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Using only one shunt and two measuring devices should work however this is dependent on the input impedence of the measuring devices. All you are doing is measuring a voltage. Sometimes if you have one meter with too low of an input impedence you will provide a secondary path for the current creating a metering error. Best to test by having one hooked up and while monitoring the results attach the second one. Watch for a change.
In theory this is true, but in practice??? The shunt is milliohms (or less, often 0.0001 Ohm) in resistance, and any voltmeter circuit I can imagine would have millions or billions of times higher input impedance. If you are using a shunt to extend the range of a normal ammeter then this could well be an issue, but for the modern digital measurement systems I don't anticipate a problem.

I could be wrong, and would welcome anyone with real experience with such a problem. Testing the hookup as you suggest is a good idea though.
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Old 18-10-2011, 12:12   #13
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Re: Two Shunts or One ?

Tortuga-
Wire prices are often "what we can get away with". Go to Best Buy or someplace else that will sell you a $800 flat screen TV for ten bucks over their cost. Ask for an HDMI cable. They may ask you $45, when you can buy the same thing on Amazon for $9.95. Because, you're there, it's there, people don't know so they buy it.

You can probably use any "ethernet" cable of any category, just read the label to make sure they are twisted pairs. Sadly, also overpriced at most local stores, look online.<G>

Yes there are differences in copper quality, in consistency of the lengths of the pairs, and so on. Avoid the cheapest possible vendor. And yes in theory, the wiring should be twisted strands not solid on a boat, but in this application? I doubt it will matter. A spare ethernet cable should do for you, probably $10 and easily replaced.
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Old 18-10-2011, 13:12   #14
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Re: Two Shunts or One ?

While I don't disagree with hellosailor about being ripped off, all onboard wiring should be soft annealed stranded tinned copper, even the twisted pair. One can purchase high quality bulk LAN cable from FRY's or similar for the job at a reasonable price.
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Old 18-10-2011, 13:20   #15
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Re: Two Shunts or One ?

Quote:
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In theory this is true, but in practice??? The shunt is milliohms (or less, often 0.0001 Ohm) in resistance, and any voltmeter circuit I can imagine would have millions or billions of times higher input impedance. If you are using a shunt to extend the range of a normal ammeter then this could well be an issue, but for the modern digital measurement systems I don't anticipate a problem.

I could be wrong, and would welcome anyone with real experience with such a problem. Testing the hookup as you suggest is a good idea though.
I have tried this and did have issues which caused amp readings (like 0.1A) which did not exist... That's why I use two shunts and don't have any issues with noise or amps showing up that simply don't exist... Both his Blue Sea meter and the Link came with shunts so he will not need to buy an extra..

The Blue Sea and Link shunts are both 50mV and the Link is 500A as is my Blue Sea shunt. However Blue Sea sells 50mV shunts in varying amp ratings so no way to say for sure what the OP's Blue Sea shunt is rated at for amperage.....
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