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Old 11-24-2021, 01:38 PM   #1
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Where to put the smart shunt?

I recently replaced the house batteries in my Bay Star Sport. With my options, we have a total of 6 house batteries -- four in the main battery bay and two in the engine compartment up front.

At the same time, I was planning on putting in a smart shunt so that I could have a real battery monitoring system. However, in replacing the batteries I noticed that, while the four batteries in the main bay are connected to the two batteries in the engine compartment to make one bank, it appears that the 12V system is connected to the posts on the batteries in the engine compartment, while the inverter is connected to the posts on the batteries in the main battery bay. As a result, I don't know where to put the smart shunt.

I expect that the answer is that I can't -- I need to route either the 12V system ground to be connected, with the inverter (through the shunt), to the batteries in the main bay, or the inverter ground to be connected, with the 12V system (through the shunt), to the batteries in the engine compartment. But I'm hoping that someone with more experience might have a nifty trick that I could use not to have to run another wire.

If I do need to run another wire, is there a reason why I should care whether I use it to connect the inverter ground or the 12V ground? It would make that connection longer, and thus a slightly larger voltage drop. If I do need to re-wire, I'm hoping that I'll be able to just move the inverter wire to the engine bay batteries -- the distance seems similar. Of course, it does seem *slightly* shorter to the battery bay than to the engine bay, so I'm sure Murphy will have a say.

Thanks for your advice.
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Old 11-24-2021, 02:13 PM   #2
D20
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I have the same situation on my Bay Star.

I have briefly looked at where to put a shunt. I didn't get too deep into it but from my initial assesment, the chassis ground connections in the engine compartment would need to be disconnected from the chassis points and put onto a bus bar. Then a new cable would need to be run from this bus bar to the battery compartment where the connection would be made to the shunt along with the other chassis grounds made in the battery compartment.

As far as I understand it, the inverter ground cable would be removed from the battery and then connected to the chassis side of the shunt in order for the shunt to capture the inverter consumption.
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Old 11-24-2021, 03:40 PM   #3
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Are we talking inverter ground or inverter negative cable. May seem the same but are not.

The inverter negative cable, solar negetive cable and any 12 volt house negative cables need to terminate at one point on the shunt.

On the other side of the shunt is where the house 4 bank and house 2 bank negetives need to go.

If your added batteries, in the front, have a cable to a chassis point, remove it and run a cable to the other battery bank.
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Old 11-27-2021, 09:07 AM   #4
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Most owners Iíve talked to about adding the shunt say they just connect the house batteries since itís really that storage capacity is what is what needs to be monitored.

While the chassis batteries do power some of the 12 VDC systems, itís the house 12 VDC circuits that are the critical ones to monitor since chassis battery storage capacity or use isnít used in running the ďhouseĒ for Boondocking.
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Old 11-27-2021, 12:39 PM   #5
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Yes, negative, not ground

Quote:
Originally Posted by twinboat View Post
Are we talking inverter ground or inverter negative cable. May seem the same but are not.

The inverter negative cable, solar negetive cable and any 12 volt house negative cables need to terminate at one point on the shunt.

On the other side of the shunt is where the house 4 bank and house 2 bank negetives need to go.

If your added batteries, in the front, have a cable to a chassis point, remove it and run a cable to the other battery bank.
Correct -- it's the negative, not ground. I've done plenty of AC work and am used to the ground/neutral distinction, but 12V's a bit new to me, so I often make that mistake.

Sounds like what I expected -- there is no magic solution, I just need to run the wire.
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Old 11-27-2021, 12:53 PM   #6
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These are house batteries, not chassis batteries

Quote:
Originally Posted by Steele View Post
Most owners Iíve talked to about adding the shunt say they just connect the house batteries since itís really that storage capacity is what is what needs to be monitored.

While the chassis batteries do power some of the 12 VDC systems, itís the house 12 VDC circuits that are the critical ones to monitor since chassis battery storage capacity or use isnít used in running the ďhouseĒ for Boondocking.
These are house batteries, not chassis batteries. There's a third battery in the engine compartment. Electrically, that's on the other side of the B.I.R.D. (physically, it's the same side of the engine compartment), and I'm sure it does power some systems (especially the chassis-related ones ). But that's not what I'm talking about.

Basically, on the Bay Star Sport model, when you get some combination of options (inverter for bedroom, larger fridge w/ icemaker, 50-amp connection and larger generator), and mine has all of them, Newmar gives you a 2K inverter (instead of 2 1,200W inverters) and increases the number of house batteries from 4 to 6 and places the extra two in the engine compartment. The extra 2 batteries are definitely house batteries, not chassis batteries, and are connected to the standard four batteries in parallel to make them part of the same bank.

So, related question, if I do run a wire to move the 12V negative to the inverter to connect to a shunt that I place in the engine compartment, should I also run a second wire to move the 12V positive to the inverter to connect to the 12V positive of the batteries in the engine compartment? I've seen some information that said you'd get better balancing on the batteries in the banks if the negative and positive were at the opposite ends of the battery bank (as opposed to being connected to the same battery, or the same set of two 6V batteries wired in series to make a single 12V unit). However, that was in reference to lithium batteries, so I'm not sure if it is a factor on lead batteries.
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Old 11-27-2021, 01:46 PM   #7
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Quote:
Originally Posted by southardrv View Post
These are house batteries, not chassis batteries. There's a third battery in the engine compartment. Electrically, that's on the other side of the B.I.R.D. (physically, it's the same side of the engine compartment), and I'm sure it does power some systems (especially the chassis-related ones ). But that's not what I'm talking about.



Basically, on the Bay Star Sport model, when you get some combination of options (inverter for bedroom, larger fridge w/ icemaker, 50-amp connection and larger generator), and mine has all of them, Newmar gives you a 2K inverter (instead of 2 1,200W inverters) and increases the number of house batteries from 4 to 6 and places the extra two in the engine compartment. The extra 2 batteries are definitely house batteries, not chassis batteries, and are connected to the standard four batteries in parallel to make them part of the same bank.



So, related question, if I do run a wire to move the 12V negative to the inverter to connect to a shunt that I place in the engine compartment, should I also run a second wire to move the 12V positive to the inverter to connect to the 12V positive of the batteries in the engine compartment? I've seen some information that said you'd get better balancing on the batteries in the banks if the negative and positive were at the opposite ends of the battery bank (as opposed to being connected to the same battery, or the same set of two 6V batteries wired in series to make a single 12V unit). However, that was in reference to lithium batteries, so I'm not sure if it is a factor on lead batteries.
You may get better balancing with equal length and placed cables but with proper size cables , the benefit may be slight.

Voltage drop on large battery cables is pretty small. Besides over a short time, they will equalize, thats paralled batteries do.
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Old 11-27-2021, 02:31 PM   #8
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My shunt is in the battery compartment, close to the batteries. The batteries are AGM's. There is also an inline circuit breaker reset fuse with a cutoff switch. The next and separate compartment has the solar controller, a catastrophic fuse and the inverter/converter.







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