grounding shunt ?

Posted by jcmontana

Oct 26, 2018 at 7:39pm

lifeline 8dl 255ah battery, 3-100w renolgy eclipse panels, 40amp commander controller.

I also have between batterys a blue sea charging relay ML-ACR. A 40amp fuse between controller and battery.

 House battery is the "main battery" in my setup and the starter battery is the aux.

 Have the MT50 digital solar gauge, and a Xantrex "linklite" gauge that will let me monitor the starter battery.

 The xantrex has three ground wires hooked to separate terminals of the negative shunt.

1:Should one of the terminals on the negative shunt be grounded to the frame, which seems redundant to me since the whole system is already grounded to the frame through the starter battery and wondering if introducing the shunt to a frame ground would increase resistance so the xantrex wouldnt read correctly.

2: should the commander be grounded to the frame?

thanks for your thoughts.

Posted by v10

Oct 28, 2018 at 4:31am

Jim, I'm not familiar with a set up like that and based on 17 views and no replies, I would say no one else is either.

This does have somewhat of a guide for terminal connections; not sure if it helps but take a look

Posted by playersz28

Oct 28, 2018 at 5:07am

All 3 wires on the shunt are high capacity? Are there small terminals on it that are connected?

A shunt would be installed on either the low side or high side of the battery depending on design of the monitor that uses it. If yours is on the negative leads then it may also be hooked up to serve as a binding post. I'm guessing this is in a motorhome. If it's being used by aa monitor then just look it as part of the negative battery cable and there shouldn't be anything else connected to the neg terminals of the battery.

Posted by jcmontana

Oct 28, 2018 at 9:28am

playersz28, yes there are 3 small wires hooked to the shunt for the xantrex meter but in three specific spots, 2 large cable terminals and 2 #10 terminals,

V10, I wired my shunt off of the xantrex diagram, the same one you sent me,,the only thing in the diagram which is different then what I have going is the diagram shows the AUX battery which in my case is the "starter battery"(just like in the diagram) "grounding to the shunt then grounding to the frame".
In my case the starter batt(aux) is grounded to the frame under the hood, then a 2/0 (neg)cable is ran back to the shunt(for the xantrex) then from the shunt the house(main) batt hooks to the other side of the shunt.
So I was wondering if I should add a negative ground to the house battery OR is it enough to just be hooked into the starter batt negative through the shunt.

I am a newbie to all this solar/charging relay stuff, so If you think I am doing something wrong let me know, thanks.

Posted by bupkis

Oct 28, 2018 at 12:45pm

you starter battery is connect to frame so that any circuit can return via the vehicle metal.

All you appliances have a return and so attaching to chassis would not help.
the two batteries are connected with + & - big wires so attaching to chassis would not help.

There is no need to connect the commander to the chassis.

vehicle and RV use the chassis as a common return to the batt negative. only the current that flow through the shunt is measured so depending on what you want measured you generally wire for only one return path!

I understood the relay was for the alternator to charge the house battery when 'running'.
Do you have it wired for solar to charge the starter battery?

Posted by jcmontana

Oct 28, 2018 at 1:39pm

bupkis, the blue sea charging relay "automatically" lets the solar and alternator charge "both" battery's as needed.
And if I did NOT have 150amp fuses at both battery positives the house battery would be able to start the engine.
So I have a feeling that if the starter battery ever dies and I try to start the vehicle not knowing the starter battery is dead and the house battery sends full cranking amps to the engine starter, I will probably blow both fuses, I am guessing that will happen.

Posted by jcmontana

Oct 28, 2018 at 2:06pm

Any idea how to have fused type protection on both batterys and still allow my charging relay to allow the house battery to start the vehicle?

Posted by swampmonster

Nov 4, 2018 at 5:41pm

Question 1;....Best to install a large terminal ground bus bar on the output side of the shunt....With Nothing except the battery bank neg on the input side of the shunt....nothing.

From there connect ALL chassis grounds to the ground buss bar, and connect the ground bus to vehicle frame/chassis INCLUDING charge controller grounds.

Small wires of battery monitor(black/white) go to designated posts on shunt, with small positive(red) of monitor going to battery pos.

Question 2; Yes, see above.

If you desire that your vehicle alternator also charge your house bank, then install a CONSTANT duty solenoid with proper capacity, but include a dash mounted switch one the low amp relay side so you can isolate/activate it as required.....Yeah, yeah, folks install them every day where the solenoid only operates to charge the house battery when vehicle is running, but trust me there will be times you don't want that.

Posted by jcmontana

Nov 6, 2018 at 7:53am

swampmonster, as I am a newbie to this, which is the output side of my shunt?
The starter batt neg connects to the shunt and so does the xantrex meter, which connects to the same side of the shunt as the neg from starter battery, also the xantrex connects to the two small connections on the shunt, the house battery connects to the other side of the shunt.

Posted by swampmonster

Nov 6, 2018 at 9:07am

If installing shunt, pick one...doesn't matter.

Once selected, it then matters how the small sensing wires are connected in relation to the large ground lugs.

If shunt is already installed, it will be the side that goes to chassis ground.

OK, let's sort this out....You have two separate batteries connected to a single shunt, right?...OK, then here is how they must be connected:

-Select one battery as the primary battery you want to monitor where the ONLY thing connected to that battery neg post is the input of the shunt.

-On the output of the shunt, you must then connect the auxiliary(second) battery neg....On that same lug of the shunt you must then connect to vehicle chassis ground.

All of the wires above must be very large gauge and able to carry full battery amps with very low resistance.

Now for the meter sensing wires!...Wheee!.....On the back of the meter you will see many connections...Look for the ones labeled 1+, and 1-....Those wires go directly to the shunt small screws....The wires you will connect to the shunt will be arranged as a twisted pair..... the 1+ wire must go to the side of the shunt that the secondary(aux) batt and chassis ground is connected to.....The 1- wire goes to the side of the shunt your primary battery is connected to.

Almost should have 4 small wires left where three contain inline fuses....Connect one of the fused wires to the VA meter connection, then to the pos terminal of the secondary(aux) batt.

Connect the second fused wire to the meter VM connection, then to the primary batt pos.

All that is left is to connect the meter main power, and meter main ground....Those terminals are labeled + and - on the meter.....Main meter pos connects to the primary batt pos post, and the main meter - connects to the shunt output on the secondary batt side of the shunt side.

OK, Cowboy...your shunt, meter and batteries are now properly connected, yup .....BUT the meter only glows to show it is powered and the numbers it displays are meaningless until you follow ALL programming instructions properly AND begin with two FULLY charged batts and have reset the meter to read 100%

First go get a cold beer, relax and pet the dog.

Posted by swampmonster

Nov 6, 2018 at 11:23am

So lets talk about shunts when used to monitor battery charge state....Shunts of every size are used for many things, but for us here all we are concerned with is battery charge state, and pat yourself on the back for the effort, and your batts will reward you with much longer life.

The shunts we here require are rather large and usually rated at 500amps/50 milivolts...What that means is the shunt will develop a 50MV resistance when at 500 Amps current...Guaranteed, and guaranteed forever....So if you have a shunt with a KNOWN resistance at a certain current, then you can determine the resistance at different levels of current, huh?...Yup

The shunts we here are concerned with were actually developed way back in 1892 by an English born American guy named Edward Weston...Ed was in the process of inventing a wet cell battery, and he needed a way to very accurately measure those then magical mystery characteristics of electricity so he could better understand electricity....Ed was actually a chemist by trade.

So being a chemist, he experimented with metals and invented the alloy Manganin..Yup, the very metal currently used in your solar shunt was invented way back in 1892, and is STILL used unchanged today...Those thin fins in your shunt are made of Manganin alloy courtesy of old Edward Weston.

Yaknow, old Ed eventually invented many new things still used today in greatly refined versions...The first amp meter, voltage meter, and Ohm meter.

He also invented the Weston Cell...The Weston Cell was a battery that was so reliable and stable that until about 1990 was used in labs to calibrate electrical meters...Yup, old Weston is perhaps the top unsung hero of his age.

I thought it might be interesting to you guys here to know a little background history of all the really neat tech we are applying today.

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