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Old 06-05-2021, 07:22 AM   #1
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Max current

I am trying to install a Victron SmartShunt on a new RV and there is no room in the battery box that will work *, so it looks like I have to run a wire from the negative battery terminal to a location in the RV and then run a second line back to the load line. The problem is that I don't know what gauge wire to use.

The current line from the negative terminal is a 2 gauge wire, and perhaps that is what I need, but when I looked at the voltage drop tables they all asked for distance and max current. I know the distance, about 12-15 feet round trip, but I have no idea what the max current would be for 2 100 AH Lithium batteries in a small B+ 30 amp RV. Can anyone tell me?

Alternately I could just temporarily hook this up to sit in the step area until I could have a professional do the job but I do want to have some idea what is going on with the system on our next trip and I can't get anything done by a professional for another couple of weeks. Too many RVs around here needing work.

* And since the battery box is not weather proof I assume it is not a good place in any case.
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Old 06-05-2021, 07:33 AM   #2
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The shunt is not very big. Have you considered cutting the neg wires back far enough to accommodate the shunt? You’ll need to crimp on new terminals, but it could be easier.
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Old 06-05-2021, 07:35 AM   #3
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New RV, Mike? Did I miss something?

You want the wiring to be short and stout (like a teapot). The Smart Shunt can be placed in the battery box and use 2ga or thicker. Just find a little room in there. It doesn’t have to be pretty.

A 200 amp bank obviously has a max current of 200 amps.
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Old 06-05-2021, 07:44 AM   #4
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High current loads on most coaches are the generator starting circuit which is usually protected by a 100A breaker, the circuit that powers the converter power center which is usually protected by a 50A breaker and the circuit that goes to whatever battery isolator you have which is not usually breaker protected and is often #2 gauge.

So I think you will rarely see more than the 100A that the generator starter draws (and it will actually draw less than the breaker rating. The other high draw situation is when you hit the aux start switch and use the coach batteries to help the chassis engine to start. Don't know what current that will be but it is short term and almost certainly less than the 210A rating of #2 wire.

So that is a long way of saying, go with #2 wire.

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Old 06-05-2021, 08:03 AM   #5
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Originally Posted by Marine359 View Post
The shunt is not very big. Have you considered cutting the neg wires back far enough to accommodate the shunt? You’ll need to crimp on new terminals, but it could be easier.
There is very little extra room in the battery box. There is perhaps 2 inches available in the width, but the batteries themselves are not tied down so they can move as the vehicle moves. There is no depth available and only about 1-2 inches in height. I just don't know where I could put the shunt in the battery box.

In addition the box itself is not weather proof and I would think that rain and/or wet roads would be a serious issue.
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Old 06-05-2021, 08:07 AM   #6
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New RV, Mike? Did I miss something?

You want the wiring to be short and stout (like a teapot). The Smart Shunt can be placed in the battery box and use 2ga or thicker. Just find a little room in there. It doesn’t have to be pretty.

A 200 amp bank obviously has a max current of 200 amps.
As I mentioned to @Marine359 the box is not weather proof and I worry about water getting into it from wet roads. And there is very little space. Even if I could find a location in the battery box, and I don't think I can, the batteries would be moving around and impacting the shunt.

I will take another look but I don't see how that would work.
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Old 06-05-2021, 08:29 AM   #7
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Thanks for this information.

I am going to see if there is any way that I can find some room in the battery box, even if only for the short term. I don't think there is, but if I can find the room I assume that the wiring to the shunt would be a very short distance - perhaps 3 feet max for both sides combined, and then based on the tables I assume I could use 4 gauge as the recommended gauge for 100 amps for that short distance is 6 gauge.

Is there anything in that assumption that I need to rethink?
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Old 06-05-2021, 09:04 AM   #8
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It's my opinion and it may be incorrect, but I think you need to equalize the wiring -- same gauge on positive and negative sides. Going smaller would be the last thing I would do. But, I'm no expert on this stuff. This is just my opinion.

My Smart Shunt is mounted in my battery compartment which is not weather sealed either. It's mounted high enough that not much road spray is seen on the side wall it's mounted to. But it's not in a sealed compartment.
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Old 06-05-2021, 11:52 AM   #9
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Is there anything in that assumption that I need to rethink?
One more suggestion, then I’ll shut up.
You may be able to affix a small waterproof junction box somewhere on the periphery of the battery box. Using the junction box punch outs, run your neg cables thru to the shunt.
I would stay with 4awg and try to match cable length as close as possible. Unless you have hd crimping gear, it’s probably cheaper and less hassle to buy two short cables with terminals already installed.
I installed 1/0 which was very expensive, but I think 4awg is a lot cheaper.
Try here: https://www.batterycablesusa.com/4-g...y-cables-4-awg
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Old 06-05-2021, 12:10 PM   #10
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It's my opinion and it may be incorrect, but I think you need to equalize the wiring -- same gauge on positive and negative sides. Going smaller would be the last thing I would do. But, I'm no expert on this stuff. This is just my opinion.

My Smart Shunt is mounted in my battery compartment which is not weather sealed either. It's mounted high enough that not much road spray is seen on the side wall it's mounted to. But it's not in a sealed compartment.
Your post prompted me to go back to the RV (which is in storage) to take some photos to show just how little spare room there is in the battery box as there is no space on either side of the battery for the SmartShunt.

So I took the photos, planning to upload them, when I looked above the battery and thought that perhaps there really was enough room for the SmartShunt. There is precious little room, but the shunt is not that big and when I stuck it on the ceiling of the battery box (which is the floor of the RV) I realized that, yes, there was room. Not only that, but it was going to simplify the entire process because I no longer needed to run cables to and from the electric compartment and I could actually use the existing load cable. It is too short to run to the side of the battery box, which is where I originally thought it might fit, but it is long enough to reach the ceiling in between the two batteries.

This being the Phoenix area it is already too hot to do the work, but I plan to do it tomorrow morning and it looks like it ought to be quick. If it works I will post some photos tomorrow.

Thanks for the idea. I was sure there was no space available, but I am reminded of the old adage - sometimes the things you know just ain't so.
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Old 06-05-2021, 12:19 PM   #11
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One more suggestion, then I’ll shut up.
I find your suggestions quite helpful, so please don't.

Quote:
Originally Posted by Marine359 View Post
You may be able to affix a small waterproof junction box somewhere on the periphery of the battery box. Using the junction box punch outs, run your neg cables thru to the shunt.
If the SmartShunt fits well onto the ceiling, as I now suspect it will, I will look for some plastic box to fit around it so as to protect it as much as possible. I don't like the idea of it sitting in an enclosure that is not weatherproof and would be much more comfortable if I could find something to protect it from any rain or wet roads.

Quote:
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I would stay with 4awg and try to match cable length as close as possible. Unless you have hd crimping gear, it’s probably cheaper and less hassle to buy two short cables with terminals already installed.
I installed 1/0 which was very expensive, but I think 4awg is a lot cheaper.
Try here: https://www.batterycablesusa.com/4-g...y-cables-4-awg
It looks like all I need is perhaps 1 or 2 feet of new wire to connect the negative battery post to the minus battery connection on the SmartShunt, so the cost will be negligible either way. I already have more than enough 4 gauge wire and ring connectors as well as a decent crimping tool so I will do that. If the install works properly I will probably go down to HomeDepot or Lowes and get some 2 gauge wire as that is what the load cable is. I will also have to get some ring connectors for 2 gauge as the ones I have now are sized for 6 gauge. They fit onto the 4 gauge wire, even if only barely, but would never fit onto 2 gauge.
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Old 06-06-2021, 08:56 AM   #12
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That turned out to be a lot easier than I thought it would be once I saw that there was some room in the battery box after all. Not on the sides, but at the top. Not much, but enough, so I have now installed the SmartShunt and it is working. Photo below.

I knew that I was lacking a lot of information without it and was hoping that the shunt would tell me what was going on in the system once it was installed. I have been having power problems - running a propane fridge and nothing else than a small LED light and the system overhead we went from what the solar controller told me was 80% SOC to completely dead batteries in about 6 1/2 hours during the night.

The system overhead seems to be a bit high - about 2 amps with nothing that I can see running except the background stuff - but the real problem seems to be that I can see no power from the solar input. The dealer installed the BB batteries and the DC-DC Charger and perhaps they just forgot to attach the solar leads? I don't know but will have to find out. But if there is no solar input, then that does sort of explain why we went through our batteries so quickly.

Anyway, thanks to everyone for their input. The job is really not quite done as I will replace the 4 gauge wire to the SmartShunt negative battery side with 2 gauge wire as soon as I can get it from the local auto supply store. I just wanted to see what the shunt would tell me and used what I had on hand at the moment.
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Old 06-06-2021, 09:02 AM   #13
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Nice job Mike. Hope you get the solar sorted out. Did you try testing amperage using a clamp meter on cc output side?
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Old 06-06-2021, 10:09 AM   #14
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Nice job Mike. Hope you get the solar sorted out. Did you try testing amperage using a clamp meter on cc output side?
Thanks.

If by "cc" you mean the charge controller used to convert AC from shore power and the generator to DC to charge the batteries, then no. I hooked the RV up to shore power at my home and saw that the charge current shown in the Victron SmartShunt app was adding about 40 amps to the batteries (well, 37-38 amps after the 2 amp overhead load), but I did not try to use a clamp meter. In fact I don't have one.

If by "cc" you mean the solar charge controller, then that power would be DC and I don't think that a clamp meter would work since I always assumed it was an AC only device. But then my expertise in actual electric and electronic work could fit into a thimble, although my theoretical knowledge is somewhat greater.

One of the things I found out in school is that I can learn the theoretical stuff pretty easily, but if you put a wrench or screwdriver in my hand you probably need to stand back so as to not get hurt.

There is something else that puzzles me. The solar charge controller shows a significant solar out, but the SmartShunt shows only the overhead drain of 2 amps. That made me think that the solar controller was not actually wired to the batteries, but the solar controller also shows the battery voltage, which means that it is wired to the batteries, so why am I not seeing any of that solar output go to the batteries? I am clearly missing something.
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Old 06-06-2021, 10:18 AM   #15
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There definitely are DC clamp on ammeters. In fact I recommend that any serious dry camper get one so he can track down missing power or power hogs.

Two good but relatively inexpensive brands on Amazon are Extech and Klein for about $75. You can pay much more for ones by Fluke but that is over the top even for me.

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Old 06-06-2021, 10:30 AM   #16
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Most clamp style multimeters these days are switchable. If you read over 14 amps on cc output you should be getting some kind of charge. If the cc output is much below that, you won’t be getting much of a charge. Probably because the cc is not sensing enough voltage difference between battery and pv input voltage. Some cc need 5v or more delta. Also check to make sure your shunt is wired properly to enable the shunt to “see” the cc. CC neg to shunt load is the correct wiring. The only thing that should be connected to shunt batt is the battery negative.
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Old 06-06-2021, 10:43 AM   #17
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Mike, make sure you have ALL negative leads running through that shunt on the load side. You should have one for the chassis ground, one for the inverter, one for the solar charge controller and one for the DC/DC charger. I assume you don't have one from the alternator because of the DC/DC charger.

If you see any other wires connected to the batteries they too will need to be relocated to the smartshunt.

I see only one negative cable on the load side and one on the battery side of the shunt in your photo. The system will not work accurately without every single negative battery connection attached to your load side of the shunt.

I had trouble getting all the leads onto the short bolt on the shunt and bought a cheap negative bus bar on Amazon. Then you have tons of room for your load wiring and one single lead from the bus bar to the load side of your shunt.
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Old 06-06-2021, 10:47 AM   #18
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Most clamp style multimeters these days are switchable. If you read over 14 amps on cc output you should be getting some kind of charge. If the cc output is much below that, you won’t be getting much of a charge. Probably because the cc is not sensing enough voltage difference between battery and pv input voltage. Some cc need 5v or more delta. Also check to make sure your shunt is wired properly to enable the shunt to “see” the cc. CC neg to shunt load is the correct wiring. The only thing that should be connected to shunt batt is the battery negative.
Well, I learned something new today, and that is always a good thing. There are DC clamp meters, and I will have to get one.

But I still don't understand what "cc" you mean - the charge converter for shore and generator power? Or the solar charge controller for solar?

The solar charge controller on my previous RV was from Zamp and I could see even small amounts of input charge show up on my Victron 712 Smart display, but the solar controller on the new RV is some unknown Chinese model and I have no idea how it works or how well it works. It looks identical to this one and I have seen it displaying 5-6 amps solar input with nothing showing up on the Victron display.

Perhaps the SmartShunt is hooked up incorrectly because nothing in the Victron documentation says anything about what to do about solar input and I don't have any real idea what wires are solar. I followed the instructions about installing the SmartShunt and it is wired directly off of the negative of the battery and the load is wired directly to the other side of the shunt, but I don't know if the solar wire is in the wrong place. I guess I will have to look some more.

What I do know is that the shunt app is properly displaying the shore power input and I will test the generator as well, but so far nothing for the solar. I do have a Renogy PWM solar controller that I bought just in case and I suppose I could use it to replace the existing solar controller, but I want to be sure of what I am doing.
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Old 06-06-2021, 10:50 AM   #19
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I use a neg bus bar too, making it easy to connect to shunt load. Make sure it’s 250amp rated though.

Here’s a clamp multimeter on Amazon for $40. Looks like mine, but Chinese stuff can be the same but change names constantly.
https://www.amazon.com/dp/B0721MKXBC...ERZ7KEXJDN8NF8

By cc I mean solar charge controller, not charger/converter, which is not a controller.
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Old 06-06-2021, 10:56 AM   #20
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The solar charge controller on my previous RV was from Zamp and I could see even small amounts of input charge show up on my Victron 712 Smart display, but the solar controller on the new RV is....
Mike, what new RV do you have???? You traded the Fuse or sold it?

Details Mike, we need them.
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