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Old 09-05-2013, 05:19   #1
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Multiple Shunts

Hello,

I picked up a box of clever dual display Amp and Volt meters at an auction of a electrical supplier that was going out of business.

Since I have these, I thought I could place them in several locations (Flybridge and engine room) for easy reference.

I have the Victron Blue Power Panel at the pilot house, and I do not want to do anything to disrupt its accuracy.

I am wondering if I have several shunts inline, is it OK ? I have emailed Victron but have not received a reply yet.

Have a look at the diagram and tell me your thoughts...

Alan
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Old 09-05-2013, 05:32   #2
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Re: Multiple Shunts

As installed in your drawing you will only display current. The shunts' voltage drop will vary due to current and you will drive the instruments' ampere readings with that small voltage. If the instrument is sensitive enough it will display the millivolt drop across the shunt but not the house bank voltage which you desire. In order to sense the house bank voltage you must wire the displays to the positive (red) side of the house bank (note the red wire to the Victron shunt which allows it to monitor the voltage as well as power the instrument.

Several shunts in line are fine but why not use the same shunt that the Victron uses? The Victron should never know the other instruments are there as long as they are small electronic loads.
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Old 09-05-2013, 05:46   #3
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Re: Multiple Shunts

Hello,

I do have the meters being fed from the positive post of the battery to read the voltage of the bank.

The meter does not require any additional feed to power the LED's. I am not sure how it is done... but I have one installed on each engine bank, and it works nice.

I talked to the Victron dealer I bought the 24/5000 Multiplus from here. He said that I cannot connect any other meter to the Victron Shunt. It will effect accuracy. They did not know how to answer the question (100%) about the multiple shunts inline, so passed me to Victron directly.

Alan
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Old 09-05-2013, 05:52   #4
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Re: Multiple Shunts

Those additional shunts will have ZERO effect on the VICTRON.

They are added complexity in your system and the connections have to kept tight to avoid high resistance and its associated heating but they are no different electrically than any other load put on your system - a fan or a laptop or other - except they are such a small load they should be imperceptible to your VICTRON.
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Old 09-05-2013, 06:14   #5
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Re: Multiple Shunts

Quote:
Originally Posted by Hkalan View Post
Hello,

I picked up a box of clever dual display Amp and Volt meters at an auction of a electrical supplier that was going out of business.

Since I have these, I thought I could place them in several locations (Flybridge and engine room) for easy reference.

I have the Victron Blue Power Panel at the pilot house, and I do not want to do anything to disrupt its accuracy.

I am wondering if I have several shunts inline, is it OK ? I have emailed Victron but have not received a reply yet.

Have a look at the diagram and tell me your thoughts...

Alan
Both of those meters can be fed from a single shunt. You don't need both there. You can't use the Victron shunt because it is a 50mV shunt and the other shunts you show are 75mV...

Make sure your new meters are calibrated for a 75mV shunt and not a 50mV shunt. A lot of the stuff showing up from China eBay re-sellers these days is 75mV..

If the displays are set for a 50mV shunt then you could just tap into the batt and load sides of the Victron shunt and get your amperage readings with a single shunt.
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Old 09-05-2013, 06:38   #6
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Hello,

The shunt and meter are together in the package and matching 75mV.

On the back of the package it says "engineered in Japan, Manufactured in China". Same as my Sony TV HaHaHa...

I am going to try with individual shunts, then with 2 in parallel off 1 shunt.

Thanks for your feedback !!

Alan
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Old 09-05-2013, 06:45   #7
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Re: Multiple Shunts

That's also my idea. Maybe one shunt is enough?

b.
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Old 09-05-2013, 06:47   #8
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Re: Multiple Shunts

The current is the same anywhere in a series circuit (basic law). It's the voltage which changes with loads/resistances.

Shunts measure voltage-drops across the shunt. In this case, each shunt individually.

Ergo....you can put them in series without affecting their accuracy.

Bill
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Old 09-05-2013, 07:48   #9
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Re: Multiple Shunts

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Originally Posted by btrayfors View Post
The current is the same anywhere in a series circuit (basic law). It's the voltage which changes with loads/resistances.

Shunts measure voltage-drops across the shunt. In this case, each shunt individually.

Ergo....you can put them in series without affecting their accuracy.

Bill
Yes exactly! But, why add all the unnecessary connections if you don't have to. A 0-75mV drop is the same anywhere in the system so one shunt with both panels measuring the VD on the same shunt will work fine. It will also avoid any more connections than necessary in the large gauge wiring.... All that is needed is to stack the load and batt wires for the meters on the load and batt side of one shunt.

Of course in order to get accurate measurements the Victron and Japan meter shunts need to be "equal" and no loads can bypass either shunt or they will be inaccurate.

As drawn the ship ground (assuming going off to engine) and the Japan meter neg leads all need to be run to the 500A buss bar...

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Old 09-05-2013, 08:12   #10
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Re: Multiple Shunts

I don't think the Victron works this way, but there is a situation where you can't share shunts. Stewart Warner has (had?) an ammeter that uses a shunt where the gage is an ammeter, not a volt meter. Both paths are low resistance, with the gage getting 1/6th of the total current. Adding another gage to this shunt, gages in series or parallel, will change the resistance ratios and mess you up.
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Old 09-05-2013, 08:51   #11
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Re: Multiple Shunts

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I don't think the Victron works this way, but there is a situation where you can't share shunts. Stewart Warner has (had?) an ammeter that uses a shunt where the gage is an ammeter, not a volt meter. Both paths are low resistance, with the gage getting 1/6th of the total current. Adding another gage to this shunt, gages in series or parallel, will change the resistance ratios and mess you up.
All these displays are doing is looking at the mV drop across the shunt. I have done this many times with Blue Sea and other simple ammeters so long as they are both the same mV range display & shunt it will not be an issue. The two wires measuring the mV drop across the shunt really carry no meaningful current they are just sensing voltage. The meters are fed by a separate power wire and the load and batt side wires are simply mV sensing wires.

It's really no different than putting my Fluke across a shunt set to the mV scale. It would read the same on both shunts thus one shunt will avoid more terminations than are necessary and be easier to install....

Course the OP can wire it however he decides is best, I am just trying to make his life a little easier....
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Old 09-05-2013, 18:23   #12
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Re: Multiple Shunts

Hello,

Great feedback ! Thank you so very much !

I was not thinking about the voltage negative coming from the 500A buss bar. Had my eyes on the shunts all the time worrying about the current reading ! Thanks !!!

I will try this...

Alan
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Old 02-06-2013, 05:44   #13
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Re: Multiple Shunts

you need the ship ground on the bus as well. if they were battery monitors I would use all 3 shunts. the 2 gauges in parallel would probably effect the readings a bit. although if it's just an amp gauge, and not a battery monitor calculating AH I probably wouldn't worry about the minor error you're probably end up with. and go with 2.
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Old 10-06-2013, 07:55   #14
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Re: Multiple Shunts

Why is a wire from the pos battery to the neg shunt?
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Old 10-06-2013, 08:32   #15
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Re: Multiple Shunts

Just be aware that some of these DPMs cannot be powered from the device under test , check your documentation, `ie they cannot measure relative to their supply GND.

Usually a negative rail generator is needed, some DPMS have then , real cheapies dont.

dave
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