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Old 11-18-2018, 08:26 AM   #1
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Victron BMV-712 Install Question

Howdy,

This seems like a good "easy" upgrade. Being new to RV's and Airstreams I want to make sure I do it right the first time.

I have a 2019 Sport 22FB and I just took a look under the bed platform and saw the rats nest of wires of which I understand very little.

I have the factory solar option installed.

[Side note: I was a contractor and worked with lots of home electrical systems. Minor old time auto electric... but I'm good at this sort of thing]

I am assuming I leave ALL the wiring in tact for now and simply splice the shunt in the negative cable.

I have also see mention of a power lead to the "buss bar" but I see a number of bus bars throughout the Sport.....

Anyone done an install on late model Sport 22FB that has photos to share?

I'm about tapped out with what I want to invest this time around so along with new converter and adding a second 12v battery that will be my upgrade.

Remember easy is relative. "Whiskey Before Breakfast" is "easy" to play on guitar AFTER you learn it!

Thanks,

Rounder44
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Old 11-18-2018, 08:38 AM   #2
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Welcome Aboard!! 👍

snip..."I am assuming I leave ALL the wiring in tact for now and simply splice the shunt in the negative cable."

Exactly what I did...In our Classic the two batt's are in separate compartments. I brought both negative Cables together and connected them to the battery side of the shunt.
The out side of the shunt going to the Neg buss bar.
Once I got everything wired and working I did replace some of the cables with the new six gauge.

Bob
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Old 11-18-2018, 10:02 AM   #3
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[QUOTE=ROBERT CROSS;2181251]snip..."I am assuming I leave ALL the wiring in tact for now and simply splice the shunt in the negative cable."

Exactly what I did...In our Classic the two batt's are in separate compartments. I brought both negative Cables together and connected them to the battery side of the shunt.
The out side of the shunt going to the Neg buss bar.
Once I got everything wired and working I did replace some of the cables with the new six gauge.

Bob
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Hmmm..

You didn't wire the batteries together negative to negative, positive to positive and then positive off of one battery and negative off the other like in my diagram.....????

That's how I gathered I'm supposed to do it....

Confused...

R44
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Old 11-18-2018, 04:14 PM   #4
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[QUOTE=Rounder44;2181293]
Quote:
Originally Posted by ROBERT CROSS View Post
snip..."I am assuming I leave ALL the wiring in tact for now and simply splice the shunt in the negative cable."

Exactly what I did...In our Classic the two batt's are in separate compartments. I brought both negative Cables together and connected them to the battery side of the shunt.
The out side of the shunt going to the Neg buss bar.
Once I got everything wired and working I did replace some of the cables with the new six gauge.

Bob
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Hmmm..

You didn't wire the batteries together negative to negative, positive to positive and then positive off of one battery and negative off the other like in my diagram.....????

That's how I gathered I'm supposed to do it....

Confused...

R44
Your diagram is correct.

Our wiring is different only because of the separate battery compartments, the wiring joins at the pos&neg buss bars.

Bob
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Old 11-19-2018, 06:47 PM   #5
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Hi,

Having trouble determining which is negative direct from battery... and if that is in fact which I splice into. (Batteries are out of the AS, no shore power!)

BUT I think my photo is what I need...???

The photo is almost straight down, wood is the floor, so the main harness is coming up from the bottom.Possible bus bar labeled top left.

Do I just cut that black wire and splice the shunt in? Should be enough length...

Thanks,


R44
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Old 11-19-2018, 06:59 PM   #6
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That is one neg cable from one battery?

Yes...that is correct.

Bob
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Old 11-19-2018, 07:48 PM   #7
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Hi

You are slightly better off if you run a cable from each negative post directly to the shunt.

Bob
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Old 11-19-2018, 08:59 PM   #8
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Am I rong?

The 22' Sport has but one battery with one negative cable. 😂

Bob
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Old 11-19-2018, 09:40 PM   #9
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Hi

You are slightly better off if you run a cable from each negative post directly to the shunt.

Bob
How you you fish a second cable through?

Seems to go into a space between exterior and the floor so the holes are offset.... and sealed.....

R44
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Old 11-19-2018, 10:26 PM   #10
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So the new 22's have 2 batts? with just one cable running to the negative buss bar?

The single negative wire & single neg buss bar is all that is in your system?

As Bob 1 noted...."slightly" may not be noticed.
But I did follow his advise.

Our Classic had a two into one wire set-up before I changed it when I upgraded the OEM converter in 2007.
For the Victron shunt I was able to lengthen them and connect both directly.
PITA to get to them but most of stuff was apart and out of the way.

Do you plan on a converter upgrade down the road?
It may be an easier job if you do.

Bob
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Old 11-19-2018, 10:59 PM   #11
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Quote:
Originally Posted by ROBERT CROSS View Post
So the new 22's have 2 batts? with just one cable running to the negative buss bar?

The single negative wire & single neg buss bar is all that is in your system?

As Bob 1 noted...."slightly" may not be noticed.
But I did follow his advise.

Our Classic had a two into one wire set-up before I changed it when I upgraded the OEM converter in 2007.
For the Victron shunt I was able to lengthen them and connect both directly.
PITA to get to them but most of stuff was apart and out of the way.

Do you plan on a converter upgrade down the road?
It may be an easier job if you do.

Bob
����
I am adding a second battery.

Right now single wire and bus bar. I don’t think I’ll have to add a bus bar......

Upgrading to Wildkat converter at same time batteries go back in. How would new converter make it easier?

I could grease up a couple wires and tie onto existing negative and see if that pulls them through but I’d hate to loose it in the “space” between. I’ll look closer.

I could also punch a new hole in the bottom as I don’t think there’s much there but need to be 100% before I considered that seriously.

Haha! All the threads I read said it’d be easy!��

Thanks!

R44
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Old 11-20-2018, 06:44 AM   #12
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If it is that difficult and requires a 'hole'... I would just splice into the one wire and go with it.
When I contacted Victron and explained my situation they advised I could do exactly that. But I had everything apart and decided to just lengthen the second wire and attach directly to the neg bar.

In my case having the converter out just opened up the space making it much easier to get to the wire that was to short.

Good on 'ya...the second battery and converter is a excellent first upgrade.
Make sure they match, even consider two new, are they Interstate?
You may be able to have the dealer pro-rate the one you have so you end up with two that match.

We learned the hard way on our first boon docking adventure, batteries crapped out and we spent 14 daze on the Honda. 😂👎


Stream HAPPY...

Bob
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Old 11-20-2018, 08:05 AM   #13
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Hi

If you are going from one battery to two batteries, both of the pair need to be same / same. Put another way, you need to dump your old battery and get a pair of new ones. That way they will work properly together. You don't want one supplying all the power while the other just sits there.

The same thing applies to battery cables. If you are going to see heavy loads (like an inverter) you want to pull current equally from both batteries. That works best if you have the same cables to each battery. If the cabling is un-equal between the batteries, one will supply more of the load than the other.

In either case, you wear out one battery a lot and the other loafs along. Sometimes the hard working battery takes out the loafer and you get a real mess. Of the two, having the two new batteries is by far the most important. Do the cabling as best you can and accept that things are not quite ideal ...

Make sure that any added cables are at least as big as the combined cross section of whatever they are attaching to. AS runs separate cables to the inverter and this can fake you out ....

Bob
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Old 11-20-2018, 08:05 AM   #14
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Quote:
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If it is that difficult and requires a 'hole'... I would just splice into the one wire and go with it.
When I contacted Victron and explained my situation they advised I could do exactly that. But I had everything apart and decided to just lengthen the second wire and attach directly to the neg bar.

In my case having the converter out just opened up the space making it much easier to get to the wire that was to short.

Good on 'ya...the second battery and converter is a excellent first upgrade.
Make sure they match, even consider two new, are they Interstate?
You may be able to have the dealer pro-rate the one you have so you end up with two that match.

We learned the hard way on our first boon docking adventure, batteries crapped out and we spent 14 daze on the Honda. 😂👎


Stream HAPPY...

Bob
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Thanks!

I guess models vary enough that installs could be quite different.

I surmise I have to be spliced into the lead directly from the battery.... I can't splice at the converter even if there is a solid negative lead at it. (I have just done a quick peek so far just to determine ease of replacement)

My original is August 2018 and new one factory fresh and I was told close enough. They are Lifeline AGM GPL-24T

I bought the second battery and Wildkat from best converter and trust they are a good match.

Reading up on the Victron elsewhere I read of some issues with a parasitic load that drained batteries in short order. I quote: "...however it does not measure the power which the gauge consumes on its own and it will consume every last amp left in your battery until it is completely dead and unusable." He went on to state and include photos of Victron indicating 100% battery but a gauge at the battery at 30%. The 30% was accurate as he could not turn over his vehicle. Went on to say it was left in "idle mode" which sounds like ON to me as opposed to OFF! Is there an option to turn it OFF so no battery drain?

Thanks!

Rounder44

Aka

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Old 11-20-2018, 09:04 AM   #15
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For two or more batteries, the best practice is to ties the +ve and -Ve to two bus bars close to the batteries. Then run cables from the bus bar to each battery.

THE KEY is to ensure all the cables from the bus bar to the batteries are the same length. As the current draw grows, this becomes far more important.

if not, the different lengths will cause different voltage drops and the battery will not charge or discharge at the same rate
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Old 11-20-2018, 09:56 AM   #16
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Originally Posted by Rounder44 View Post
Thanks!

.......

Reading up on the Victron elsewhere I read of some issues with a parasitic load that drained batteries in short order. I quote: "...however it does not measure the power which the gauge consumes on its own and it will consume every last amp left in your battery until it is completely dead and unusable." He went on to state and include photos of Victron indicating 100% battery but a gauge at the battery at 30%. The 30% was accurate as he could not turn over his vehicle. Went on to say it was left in "idle mode" which sounds like ON to me as opposed to OFF! Is there an option to turn it OFF so no battery drain?

Thanks!

Rounder44

Aka

Warren
Hi

Ok, the BMV 712 pulls a bit under 0.001A. Running for a month, it will pull a bit less than 0.72AH. Your batteries self discharge while sitting completely disconnected. That will be in the 5% to 15% per month range. 5% of 200AH would be 10AH. Simply put, the BMV will drain a 10X less than the best case for self discharge on the batteries.

Assuming the batteries have zero self discharge rate, the BMV will "drain them dead flat" in 23 years or to the "stop using" point in 11 years. That's a very long time.....

Things like the propane detector pull *way* more than the BMV. The typical parasitic loads in most trailers will run the batteries down in a couple of weeks. That's with or without a BMV involved and regardless of the setting of the use /store switch.

Indeed if you drain the batteries with a really low current load for a really long time, the BMV will not keep up with that. There's only just so much it can do. Since it also knows nothing about battery self discharge, it's not going to log that either. For normal camping use it does a really good job.

If you want to "improve" the low current monitoring capabilities of the 712, there are settings you can fiddle with. There is a setting for "ignore anything past this". You can drop it down from the default of 0.1A. Just how low it goes and stays accurate ... who knows. I very much doubt it will do a good job on a 0.01 A parasitic load, no matter what the setting.

Bob
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Old 11-20-2018, 11:33 AM   #17
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Quote:
Originally Posted by waninae39 View Post
For two or more batteries, the best practice is to ties the +ve and -Ve to two bus bars close to the batteries. Then run cables from the bus bar to each battery.

THE KEY is to ensure all the cables from the bus bar to the batteries are the same length. As the current draw grows, this becomes far more important.

if not, the different lengths will cause different voltage drops and the battery will not charge or discharge at the same rate
POI...Two battery compartments 4' apart.

Cable length really...Our longest 6ga is 8ft,(starboard) and shortest is 4ft(port), please tell how much efficiency I've lost with our 200ah bank?

I can see it being a concern on a 40' boat with 800ah.
But on a 8' run, not really.

Bob
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Old 11-21-2018, 08:33 AM   #18
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POI...Two battery compartments 4' apart.

Cable length really...Our longest 6ga is 8ft,(starboard) and shortest is 4ft(port), please tell how much efficiency I've lost with our 200ah bank?

I can see it being a concern on a 40' boat with 800ah.
But on a 8' run, not really.

Bob
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Hi

..... well since you asked

The cabling difference is 4 feet. The cable is 6AWG. That's 0.4 miliohms per foot or 1.6 miliohms difference.

If you have an inverter that pulls 100A, ideally that should be 50A through each wire. At 50A, you would have 50 x 0.0016 = 0.08V more on one battery than on the other. That would result in unequal current flow. How much is highly dependent on your exact batteries. ( = you have lithiums with low internal resistance / he has lead acids with high internal resistance ... different results)

If one *assumes* zero resistance batteries (sure ... those are real common ... ) then the currents are simply the ratio of the conductivities. One cable is 2X the other so it has twice the resistance / half the conductivity. One third of the current comes from that battery and two thirds comes from the other one.

Obviously the real world is going to be somewhere between the two thirds / one third case and equal loads. We only looked at the ground side cables and *assumed* the B+ cables were identical. Lots of variables ....

Again ... only because you asked

Since you didn't ask, I will not mention that not all my battery cables are identical . The pair on the tongue and the pair under the sofa are wired slightly differently.

Bob
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Old 11-21-2018, 09:22 AM   #19
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Hi

..... well since you asked

The cabling difference is 4 feet. The cable is 6AWG.

Bob
Hi!

I see my wiring is 6ga but can only find 4ga for connecting the batteries to each other.

Does that cause any issue?

I suppose I want to make sure I don't use a thinner gauge but not sure if thicker causes any issues!

Thanks,

R44
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Old 11-21-2018, 10:13 AM   #20
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Hi!

I see my wiring is 6ga but can only find 4ga for connecting the batteries to each other.

Does that cause any issue?

I suppose I want to make sure I don't use a thinner gauge but not sure if thicker causes any issues!

Thanks,

R44
Hi

Bigger is always better

A lot of this depends on just how you are running the wires and exactly what is in your trailer. If you have a 1000W inverter and run it at full load, you can get up above 100A in some cases. If you have a single wire from the battery(s) and want to stay inside NEC guidelines and have low temperature insulation (yes that's a lot of qualifiers) a piece of 1/0 would be what you would need. With high temperature insulation (and surroundings) a piece of number 4 might be fine. Double up the wires (one from each battery) and number 4 is likely ok no matter what (yes the unequal length stuff gets into it on two cables ...).

So, exactly what is in your trailer?

Bob
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