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Old 07-24-2018, 08:36 AM   #1
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Wiring for battery monitor with inverter

I am doing some planning for installing a battery monitor (Victron BM-712 most likely). We recently purchased a 2015 27fb Flying Cloud and I believe the electrical is stock as it came from the factory with the 1000W inverter option.

For reference, as part of this project, I also plan on upgrading the charger/converter to a multi-stage charger (55A). Future project will be upgrading batteries (probably stick with 2 group 27 AGMs) and solar (probably 200W utilizing prewire - discussion for another day).

I have read through lots of threads trying to figure out how to wire it up, and I have seen folks do this several different ways. If this has been answered before, I apologize - I did do a fair amount of digging.

The factory wiring has 6 ga wire from batteries to house 12v and 4 ga wire from batteries to inverter in two separate runs. The monitor requires all negatives to flow through one path through the shunt. Some folks seem to keep both wires between battery and shunt, some seem to keep only the 4 gauge, and I have seen some upgrade wire gauge from battery to shunt. Of course, it is easier to not have to run new wire - thus my questions. I have provided a diagram below to describe.

My questions:
1. Is it OK to keep the two wires running in parallel (6 ga and 4 ga) shown in 2nd diagram below? I am not an electrician, but this does not seem correct?
2. Is it better to use one wire from the battery to the shunt shown in the last diagram below? Or, is either configuration OK?
3. If one wire is utilized, do I need to increase the wire gauge? If I check different sources for wire size, I get different results? Th run is short - less than 10 feet since all electrical connections are near the battery box under bed. I assume it should be sized for 55 amp from converter plus 100 amp from inverter. I cannot ever imagine pulling 155 amps from the battery though? I assume greater losses are OK for the 155 amp figure then - just needs to be safe.

Thoughts? Thanks in advance!

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Old 07-24-2018, 10:50 AM   #2
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Best wiring for shunt and inverter.

Quote:
Originally Posted by SabaRocks View Post
I am doing some planning for installing a battery monitor (Victron BM-712 most likely). We recently purchased a 2015 27fb Flying Cloud and I believe the electrical is stock as it came from the factory with the 1000W inverter option.

For reference, as part of this project, I also plan on upgrading the charger/converter to a multi-stage charger (55A). Future project will be upgrading batteries (probably stick with 2 group 27 AGMs) and solar (probably 200W utilizing prewire - discussion for another day).

I have read through lots of threads trying to figure out how to wire it up, and I have seen folks do this several different ways. If this has been answered before, I apologize - I did do a fair amount of digging.

The factory wiring has 6 ga wire from batteries to house 12v and 4 ga wire from batteries to inverter in two separate runs. The monitor requires all negatives to flow through one path through the shunt. Some folks seem to keep both wires between battery and shunt, some seem to keep only the 4 gauge, and I have seen some upgrade wire gauge from battery to shunt. Of course, it is easier to not have to run new wire - thus my questions. I have provided a diagram below to describe.

My questions:
1. Is it OK to keep the two wires running in parallel (6 ga and 4 ga) shown in 2nd diagram below? I am not an electrician, but this does not seem correct?
2. Is it better to use one wire from the battery to the shunt shown in the last diagram below? Or, is either configuration OK?
3. If one wire is utilized, do I need to increase the wire gauge? If I check different sources for wire size, I get different results? Th run is short - less than 10 feet since all electrical connections are near the battery box under bed. I assume it should be sized for 55 amp from converter plus 100 amp from inverter. I cannot ever imagine pulling 155 amps from the battery though? I assume greater losses are OK for the 155 amp figure then - just needs to be safe.

Thoughts? Thanks in advance!

SabaRocks,
Nice description and diagrams.
Of the 3 diagrams, the middle option would be best. It provides the least resistance and thus least voltage drop under heavier current loads due to the combined paralleled connections.
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Old 07-24-2018, 11:24 AM   #3
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Hi

It turns out that the "easy" way to do this usually involves adding a wire.

Move the two existing wires to the shunt. This probably involves crimping a lug on the end of one or both. You are stuck with all of that no matter what you do. You have to keep the shunt out of the wet / dirty ( = likely inside the trailer) so the cables may or may not make it to the shunt. (you can get inline splice adapters at Lowes if they don't ...).

Coming up with a cable from the battery to the shunt is generally pretty easy. Either a local shop or Amazon can supply one. It should be a pretty short run, 4AWG will work. If you want to go bigger 2AWG is more than adequate. Also consider that this is a great time to think about a battery disconnect switch.

Ultimately the issue of "how do I put on lugs" will come up. The cheap ($40 or so) hydraulic crimp tools on Amazon are the most cost effective way to get a reasonable job done.

Bob
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Old 07-24-2018, 11:28 AM   #4
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I did the third option because that's what I'd seen other places. Simplifies the wire run too.
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Old 07-24-2018, 12:15 PM   #5
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Thanks, y'all. So, is the second option (i.e. running both the 4 ga and the 6 ga wires together in parallel) an acceptable way of doing this? That would mean that any load would presumably be split between the two wires at any time. I wasn't sure if that was some sort of electrical no-no?

Good points about more connections versus running a new wire as well... Great idea on going ahead and adding the battery disconnect. That would pull the phantom loads off of everything, including anything the inverter may pull in standby. I typically see these switches and fused on the positive wire - any reason I couldn't just do it on the negative since I am already messing with the negative wires?

As part of this, I am also considering rewiring at least the subwoofer to be on the other side of the disconnect relay. I wonder why the heck the subwoofer would be on the "always live" circuit anyway...
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Old 07-24-2018, 01:04 PM   #6
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Quote:
Originally Posted by SabaRocks View Post
Thanks, y'all. So, is the second option (i.e. running both the 4 ga and the 6 ga wires together in parallel) an acceptable way of doing this? That would mean that any load would presumably be split between the two wires at any time. I wasn't sure if that was some sort of electrical no-no?

Good points about more connections versus running a new wire as well... Great idea on going ahead and adding the battery disconnect. That would pull the phantom loads off of everything, including anything the inverter may pull in standby. I typically see these switches and fused on the positive wire - any reason I couldn't just do it on the negative since I am already messing with the negative wires?

As part of this, I am also considering rewiring at least the subwoofer to be on the other side of the disconnect relay. I wonder why the heck the subwoofer would be on the "always live" circuit anyway...
Electrically it is fine, but you are better off having the wires of equal size and length connecting to the batteries.

I just disconnected the subwoofer altogether. I don't need it or miss it.

There are safety reasons for not switching the negative. If you really want to be safe then disconnect both. Just install a 2 pole disconnect (http://www.littelfuse.com/products/s...uble-pole.aspx or https://www.amazon.com/SD-Automotive.../dp/B004XCGDMK). But it does complicate the wiring since your trailer isn't setup for it.

My big phantom load is the stereo. Especially if I don't manually power off the stereo. There seems to be 2 modes of power off, one if you just press the power off button once and the second where you need to hold the power off button for a few seconds. Forgetting to do the second one will leave it in standby mode drawing quite a bit of current.
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Old 07-24-2018, 01:08 PM   #7
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Old 07-24-2018, 03:04 PM   #8
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Quote:
Originally Posted by SabaRocks View Post
Thanks, y'all. So, is the second option (i.e. running both the 4 ga and the 6 ga wires together in parallel) an acceptable way of doing this? That would mean that any load would presumably be split between the two wires at any time. I wasn't sure if that was some sort of electrical no-no?

A: Combining 4 and 6ga (parallel) is same as combining 2 wires creating effect of one larger diameter wire. In this use, would not pose an issue.

Good points about more connections versus running a new wire as well... Great idea on going ahead and adding the battery disconnect. That would pull the phantom loads off of everything, including anything the inverter may pull in standby. I typically see these switches and fused on the positive wire - any reason I couldn't just do it on the negative since I am already messing with the negative wires?

A: some may advocate one or other. If you disconnect directly at the battery terminals many manufacturers suggest negative as less chance of it shorting to frame (already ground ) when installing moving it or tightening with tools.

As part of this, I am also considering rewiring at least the subwoofer to be on the other side of the disconnect relay. I wonder why the heck the subwoofer would be on the "always live" circuit anyway...
A: Agree. Always fun bettering the standard (at times almost ignorant) methods.
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Old 07-24-2018, 04:05 PM   #9
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[QUOTE=gator.bigfoot;2133274]

There are safety reasons for not switching the negative./QUOTE]


Can you expand on this?
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Old 07-24-2018, 04:43 PM   #10
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i added the victron MUTIPLUS converter/inverter to integrate with my other victron items

here is my schematic

http://www.airforums.com/forums/f317...fb-184499.html

i used #8/3 wire to run the AC in and AC1 out and AC2 between the multiplus and the breaker area
i used #6 flexible or #10 flexible for all the DC runs
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Old 07-24-2018, 05:14 PM   #11
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Hi

Ok, if we are going to go safety nuts, then yes, hooking the two wires in parallel without proper fusing on each wire is unsafe. Also remember to check that your shoes are tied every time you take a step, not doing so is also unsafe .....

Why is is unsafe? If the "fat wire" comes loose ( like a lug isn't crimped right) then all the current goes through the "skinny wire". You can then exceed the current rating on the smaller wire.

Roughly 99.999999% of all RV setups would ignore this issue. The same way they would simply switch one side of the battery for a disconnect.

Bob
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Old 07-24-2018, 05:43 PM   #12
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i bought a hydraulic compression tool

i now use it all the time, i was a good investment vs renting.

i crimp all #12 and larger cables
for #14 and higher i use from amazon
"Crimper Plier Set, Preciva 0.25-10mm˛ Self-adjustable Ratchet Wire Crimping Tools with 1200 Wire Terminal "
it ensures there are no loose wires or frayed cables

IMHO, both are a must if you are doing any DC electrical work on your trailer
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Old 07-24-2018, 06:16 PM   #13
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Thanks, y'all. Vantair - you answered my question about how this would work with the wires - they essentially provide more area for more current carrying capacity. And uncle_bob explained why I was worried (I tend to err on the side of worrying too much sometimes). I don't see the lug or loose nut scenario happening.

I'll definitely check the crimping tools out. I have one for small wire but definitely need something else for the big ones.
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Old 07-24-2018, 08:44 PM   #14
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TMS 16 Ton Hydraulic Wire Battery Cable Lug Terminal Crimper Crimping Tool 11 Dies

from amazon
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Old 07-24-2018, 09:01 PM   #15
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Hi

The Amazon hydraulic crimpers are far from perfect. There are a number of them and I don't think any are better than the rest. The gotcha is that all are targeted at metric wire and lugs. That makes using them with US lugs and wire a bit of a challenge. You have to watch what you are doing and possibly stop the swage process a bit early to get it done right.

Bob
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Old 07-25-2018, 11:45 AM   #16
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Quote:
Originally Posted by uncle_bob View Post
Hi

The Amazon hydraulic crimpers are far from perfect. There are a number of them and I don't think any are better than the rest. The gotcha is that all are targeted at metric wire and lugs. That makes using them with US lugs and wire a bit of a challenge. You have to watch what you are doing and possibly stop the swage process a bit early to get it done right.

Bob
They may not be perfect, but what is perfect? You can use the Metric to AWG conversion chart. It certainly is light years ahead of the crimper that you use with a hammer. I certainly wouldn't worry about it for anything under 1 AWG. These crimpers work just fine, especially with the lighter crimp lugs that are available.

https://www.victronenergy.com/upload...on%20Chart.pdf
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Old 07-25-2018, 11:52 AM   #17
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My local battery outfitters store sells battery cable by the foot up to 4/0 as well as lugs and will cut cable to length and crimp it for you.--Frank
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Old 07-25-2018, 02:04 PM   #18
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Doing it correctly

Quote:
Originally Posted by SabaRocks View Post
1. Is it OK to keep the two wires running in parallel (6 ga and 4 ga) shown in 2nd diagram below? I am not an electrician, but this does not seem correct?
References used in the discussion below:
[1] ANSI/RVIA Standard for Low Voltage Systems in Conversion and Recreational Vehicles, 2018 edition
[2] ABYC E-11, AC AND DC ELECTRICAL SYSTEMS ON BOATS, 2015 edition

Recommend reading the manual for your inverter and using the specific installation instructions. Just because your trailer has 4 AWG does not mean it is correct.

My Xantrex ProWatt SW 1000W inverter manual specifies "Recommended DC fuse 150 A". My previous Magnum MMS1012 recommended even larger. Suspect yours has similar requirements.

For 150A circuit protection, from [1], Table 2, the minimum size conductor is 2 AWG 105C. This is consistent with [2], TABLE VI - B. Some manufacturers allow 4 AWG per [2], TABLE VI - B, but this is only allowed at 150A for 105C stranded that is "not bundled, sheathed, or in conduit". Recommend using the more stringent [1].

Your diagram does not show an over current protection device (OCPD - fuse or circuit breaker) in the inverter or house circuits. For my inverter, I used 2/0 AWG Ancor cable with a Blue Sea 187 Series, Surface Mount 150A breaker. Be sure to include insulating caps for the various terminals, such as Blue Sea 4010 CableCap Stud Insulators.

Per [1] 3-5, as shown in your diagrams, your inverter circuit breaker should be no more than 18" from battery.

There should be a 50A circuit breaker in your house circuit, which is adequate for 6 AWG house wiring.

Don't forget to check that a 6 AWG green AC grounding conductor is connected from the inverter case ground terminal to the trailer chassis.

Recommend using UL 1426 listed Ancor 105C battery cable.

Quote:
Originally Posted by SabaRocks View Post
2. Is it better to use one wire from the battery to the shunt shown in the last diagram below? Or, is either configuration OK?"
You should use one properly sized cable. If either one shown failed, became loose, etc. you have a remaining conductor of insufficient capacity with improperly sized over circuit protection. This is an unsafe condition, and violates [1] 3-2.

Quote:
Originally Posted by SabaRocks View Post
3. If one wire is utilized, do I need to increase the wire gauge? If I check different sources for wire size, I get different results? Th run is short - less than 10 feet since all electrical connections are near the battery box under bed. I assume it should be sized for 55 amp from converter plus 100 amp from inverter. I cannot ever imagine pulling 155 amps from the battery though? I assume greater losses are OK for the 155 amp figure then - just needs to be safe.
Again, start with your inverter's manual for the required circuit ampacity. Add to that the ampacity for your house, which should be 50A.

In my Xantrex case, that would be 200A. For AWG 2/0 105C, [1] allows 195A and [2] allows 231A. So 2/0 AWG 105C is a reasonable choice for the shunt to battery cable in my inverter example.

Overall, now is the time to incorporate all the safety knowledge gained by the RV industry, via [1], and the boating industry, via [2].

Design, install, and maintain for years of safety.

73/gus
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Old 07-26-2018, 07:09 AM   #19
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Here is a nifty calculator from BlueSea that will get you the information without having to lookup a bunch of tables and through piles of other stuff.

http://circuitwizard.bluesea.com/#

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Some other factors to consider. This one is on interconnecting batteries. But there are many other great pieces of info on this website.
http://smartgauge.co.uk/batt_con.html
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Old 07-26-2018, 08:52 AM   #20
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Quote:
Originally Posted by gator.bigfoot View Post
They may not be perfect, but what is perfect? You can use the Metric to AWG conversion chart. It certainly is light years ahead of the crimper that you use with a hammer. I certainly wouldn't worry about it for anything under 1 AWG. These crimpers work just fine, especially with the lighter crimp lugs that are available.

https://www.victronenergy.com/upload...on%20Chart.pdf
Hi

What is far closer to perfect are the crimpers made by people who sell lugs. Buy their ($$$$$) crimper and their ($$$$$) lugs, use them together. If you do this sort of stuff for a living, spending $250 or a good tool is not a big deal. The cost of the lugs gets passed on to the customer.

Indeed you can detect a gross under crimp pretty easily. Tug it and it comes apart. An over crimp is a bit harder to spot. In both cases, what you can "inspect in" is not the whole story. Without x-ray vision you can only spot just so much.

Bob
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