Need help understanding 12V DC system

[Notso727]

Happy Sunday!

New here. We got our 2021 27’ GT a few months ago and I think I wrote on another post I have learnt more about how much I DIDN’T KNOW before purchasing in the last three months but I think that’s part of the journey. We did the lithium upgrade with the dealer which I am happy with but comes with it’s own issues. I have the WFCO 9855-AD and pretty sure that’s not charging fully plus I have no way to monitor the batteries in its current state so I’m trying to install a smart shunt.

With that said I have started pulling panels off and getting smarter. I found the WFCO sitting, unmounted and loose, on top of and in between the furnace ducting under the fridge. Probably replacing that and mounting a PD9160ALV.

Part 2, and the part I really need help with, our battery box and 12V system doesn’t make sense to me. I have 2x POS and 2xNEG coming from the batteries. This doesn’t make immediate sense to me but when I searched for other lithium upgrade pics on here I found similar looking configs. I traced the wires inside into the rat’s nest and it *appears* that one NEG and POS go into the inverter and the other POS and NEG look like they’re going into a (very nice) 12V DC Distribution box/panel. So I unscrewed and opened up the box and it has a great diagram from the factory though a little too small for my aging eyes to see.
Here’s my question after a long story longer. With two negatives coming off the batteries how and where do I install a smart shunt on this? And please feel free to point out anything I have missed in my thought process on the 12V distribution.

Bonus question- is installing the PD9160 as easy as unscrewing the wires from the WFCO and wiring them into the PD?

Thanks,

Dave

[jeffb831]

For the shunt, you need to have them both on the output side of the shunt. There should only be one negative connection to the batteries besides the jumper from battery A to B.

[TitusNW]

The drawing on the inside lid of the distribution box is a bit small. A while ago I asked the factory for a drawing for the 12v Distribution box. See attached.


Steve

[jeffmc306]

Notso727, when I installed my shunt I used a negative busbar to consolidate all the negative cables. One cable from the busbar goes to the shunt load side. The other side of the shunt goes to the negative of the battery.

I installed my shunt in a waterproof box on the side of the battery box until this spring when I installed a Victron MultiPlus and Battle Born GC3 inside the front compartment.

[uncle_bob]

Hi

Water and shunts are not a great combination. Keeping them "indoors" is a better longterm solution. Running one big wire from the batteries to the shunt and then a similar wire to a buss bar connecting the two existing grounds is one of several ways to get that done.

Bob

[jccoder]

We have a 2019 Bambi 21’ Bambi sport. While tracing some wires, the owner’s manual is not very good. I opened a case with airstream asking if they had a better drawing and they sent me the whole package (pdf) of the a/c and all d/c power and wiring. Just some fyi for you and others as I have found AS support to be a big help in matters like these on both the our basecamp and now Bambi. Good luck

[Notso727]

So has anyone seen a pos and neg line direct to the inverter before?

Bob- good point. This is the "new" IP65 water resistant shunt so in the battery box should be fine.

jccoder- that's good info on the case!

Here's a follow on question. Can I break the negative lines (to the inverter and distro box) add terminals and put two lines on each shunt post? Essentially I would have both neg lines from the battery to one post and one neg to the inverter and one to the distro box from the load side. I don't think I have seen that mentioned anywhere. Not as elegant but if it works and is safe might be viable option.

[BGClassic]

Notso727,

If your converter is actually bad, that seems to be a common failure on this forum. If you buy the PD9160, as I did, make sure you let Airstream know, and provide a receipt. It is easy to replace, I did not even disconnect my solar. You will find JC uses more cable than necesary. I also found that they did a poor job of stripping the + and - cables that go to the converter. Good luck.

[1StreamDream]

Originally Posted by Notso727

So has anyone seen a pos and neg line direct to the inverter before?

Here's a follow on question. Can I break the negative lines (to the inverter and distro box) add terminals and put two lines on each shunt post? Essentially I would have both neg lines from the battery to one post and one neg to the inverter and one to the distro box from the load side. I don't think I have seen that mentioned anywhere. Not as elegant but if it works and is safe might be viable option.

I had same as you describe (multiple + and - at the battery box) before I reconfigured to incorporate a smart shunt, lithium batteries, and batteries moved to internal area. You *could* have multiple leads on each side of the smart shunt, but in my experience the depth of that screw terminal on the smart shunt is not such that you can have more than 2 lugs. In any case, you need to be very careful about how you do any consolidation of the wires, + or - are equally critical. If you are combining 2 or more wires into a single wire, the gauge of the new single wire must be substantially larger than anything currently in your trailer, it must be large enough to carry the absolute max DC current that all your devices could pull from the battery, and if you are not familiar with this topic, you should get an electrician involved. For reference, where I combined wires, I used 2/0 AWG wire (welding cable), and at very short distances like 10' or less, its probably good for 400A (more than my current battery bank can provide). If you undersize the wiring, you have a risk of overheating, melting of insulation, short circuiting, and fire. Be very sure you have the correct size wire at every segment in your path. That wire size and max current carrying issue is precisely why it is so common to have a direct + and - cable pair direct from the battery to the inverter, the inverter can pull a significant amount of current when fully loaded, and the dedicated wire path ensures it is adequately sized for that load.

[uncle_bob]

Originally Posted by Notso727

So has anyone seen a pos and neg line direct to the inverter before?

Bob- good point. This is the "new" IP65 water resistant shunt so in the battery box should be fine.

.

Hi

IP65 is not a very stringent spec compared to what likely happens in that battery box. I would still get the shunt (and all those connections to it) indoors.

Bob

[Notso727]

Uncle Bob, Fair point and makes sense. Current plan is to bring it inside just for more room alone.

1StreamDream - I'm kind thinking I might just cut the line into the inverter and the line into the distro box add terminal ends then see if I can fit both wires on each side of the shunt (not combining into one wire)

As you can probably guess I'm rapidly approaching the limits of my capability. Might have to go to a pro.

[1StreamDream]

Originally Posted by Notso727

Uncle Bob, Fair point and makes sense. Current plan is to bring it inside just for more room alone.

1StreamDream - I'm kind thinking I might just cut the line into the inverter and the line into the distro box add terminal ends then see if I can fit both wires on each side of the shunt (not combining into one wire)

As you can probably guess I'm rapidly approaching the limits of my capability. Might have to go to a pro.

I started with an arrangement just like you describe before I upgraded my battery bank to Lion. It is possible, just be sure you use the same wires (same wire sizes) you have in place now. You will likely need a special tool to properly crimp the lugs on the end of the wire (you will need lugs on each end of the cable, loose copper strands will not work). When attaching at the shunt, those bolts securing the lugs need to be very tight, so the electrical connection is very tight (that, and crimping the lugs, is probably your biggest challenge). Loose connections at either junction is bad ... they can develop arcing, and that produces heat, and those are bad outcomes in your electrical path.

[richard5933]

Originally Posted by 1StreamDream

I started with an arrangement just like you describe before I upgraded my battery bank to Lion. It is possible, just be sure you use the same wires (same wire sizes) you have in place now. You will likely need a special tool to properly crimp the lugs on the end of the wire (you will need lugs on each end of the cable, loose copper strands will not work). When attaching at the shunt, those bolts securing the lugs need to be very tight, so the electrical connection is very tight (that, and crimping the lugs, is probably your biggest challenge). Loose connections at either junction is bad ... they can develop arcing, and that produces heat, and those are bad outcomes in your electrical path.

Hydraulic crimping tools are available on Amazon for about $50 and make the job of installing the cable ends simple. The result is a professionally made cable with great conductivity through to the battery.

[Andy Hall]

This is a picture of where our shunt is, inside under the sofa with the DC system, our solar, Cerbo GX and Multiplex. Still working to make sure my setup is correct. Shunt, solar and dongle all talk by Bluetooth. Shunt, solar and multiplex are all connected to Cerbo GX.

The shunt is to the left of the nest of wires, it has has the two large connections you see just up and left of where it says caution. We are using all Victron products and the other attached picture is what you can see on the iPhone when in the trailer.

[uncle_bob]

Originally Posted by richard5933

Hydraulic crimping tools are available on Amazon for about $50 and make the job of installing the cable ends simple. The result is a professionally made cable with great conductivity through to the battery.

Hi

The $50 tools on Amazon do work and they are a giant step up from the "bang it with a hammer" approach to crimping. The gotcha is that the dies they include are *metric*. The lugs you will be using with AWG wire (unfortunately) are not metric lugs.

What does this mean in practice?

To get a "proper" crimp (not over, not under ... just right), you need a die that matches the lug. Then you just cycle the tool and you are done. With a die that has to big an opening, the full crimp is not done, no matter how many times you cycle the tool. With one that has to small an opening, you over crimp.

An over crimp crushes the wire inside the lug to the point that it is likely to be damaged. This damage is not obvious (unless you have X-Ray vision .... ). It may not be enough to impact things significantly.

Further confusing things, some metric dies line up with some US lugs *way* better than others. For example: This brand of 2AWG might be awful and the same brand of 4AWG might work just fine.

Some folks try "short cycling" the tool to get around this. That can create other issues with the crimp.

Is this a massive issue? No, you still are *way* better off with a hydraulic crimp. All the stuff mentioned is pretty much inevitable with the "bash with a hammer" approach.

Still, if you are going to do a lot of this, spend the money on a tool with a good range of "US Sized" dies.

Bob

[richard5933]

Originally Posted by uncle_bob

Hi

The $50 tools on Amazon do work and they are a giant step up from the "bang it with a hammer" approach to crimping. The gotcha is that the dies they include are *metric*. The lugs you will be using with AWG wire (unfortunately) are not metric lugs.

What does this mean in practice?

To get a "proper" crimp (not over, not under ... just right), you need a die that matches the lug. Then you just cycle the tool and you are done. With a die that has to big an opening, the full crimp is not done, no matter how many times you cycle the tool. With one that has to small an opening, you over crimp.

An over crimp crushes the wire inside the lug to the point that it is likely to be damaged. This damage is not obvious (unless you have X-Ray vision .... ). It may not be enough to impact things significantly.

Further confusing things, some metric dies line up with some US lugs *way* better than others. For example: This brand of 2AWG might be awful and the same brand of 4AWG might work just fine.

Some folks try "short cycling" the tool to get around this. That can create other issues with the crimp.

Is this a massive issue? No, you still are *way* better off with a hydraulic crimp. All the stuff mentioned is pretty much inevitable with the "bash with a hammer" approach.

Still, if you are going to do a lot of this, spend the money on a tool with a good range of "US Sized" dies.

Bob

I've found quite the variance with the diameter of lugs sold by different vendors.

My approach has been to under crimp a tad with a slightly smaller set of dies, rotate part way and repeat.

Would be nice to have the proper sized dies. But with the variance in lug sizes not sure that it would be all that helpful.

[1590Denny]

I used two knife-switch disconnects, one on each battery, in the battery box. on the negative side. Pretty simple.

https://www.amazon.com/battery-knife...h=n%3A15684181

[jeffmc306]

I started my upgrade thinking I could use Battery Cables USA for all new cables, carefully measuring lengths and lug sizes before ordering. They came exactly as ordered and were perfect - until I found I needed to move some components.

Not wanting to continue down that rabbit hole I bit the bullet and purchased a TEMCo die-less TM0020 crimp tool that works from 10 AWG to 400 MCM. It had no problem crimping 4-0 lugs. You don’t need such a tool to do what you’re looking to do; follow richard5933’s advice.

I ended up with a Victron Distributor to consolidate all the negative and positive cables. This also allowed me connect positive leads with the correct size fuse in a compact space. One negative lead from the Distributor went to my shunt.

Don’t be afraid to go ahead with your project!

[uncle_bob]

Originally Posted by richard5933

I've found quite the variance with the diameter of lugs sold by different vendors.

My approach has been to under crimp a tad with a slightly smaller set of dies, rotate part way and repeat.

Would be nice to have the proper sized dies. But with the variance in lug sizes not sure that it would be all that helpful.

Hi

This gets you to the "next" stage in the tool world.

You buy a tool that uses "standard" dies ( = the outer body meets some set of specs) and then find a vendor specific die set that uses that standard. In a lot of cases, this is a "good luck with that" adventure.

You buy the vendor's very own tool with their very own dies. Guess what? That's not a low cost tool. Then you only use lugs from that vendor. Hope you checked their prices / availability before you bought that insanely priced tool.

No this is not unique to lugs on battery cables. Pretty much the entire connector industry works this way. Standardization is not good for their bottom line. Locking you in to their system, that's great (as far as they are concerned .....).

Bob

[Notso727]

Jeffmc306- that looks good! All your electrical layout looks great. I’m pretty jealous.

Bob- I spent 30 years in aviation. I’m so used to it I don’t even blink anymore.