Victron BMV702 Install

[chugchug]

I just did this exec mod a couple of months ago. Mine is the queen bed. So removing the bed panel will be different.

1. You have to remove the entire bed panel. The hatch doesn't provide enough access to much.
2. There are actually 4 different connection to the battery. You need to combine them into 1 - the inverter, the jack, the solar charger plug and the rest of the trailer via the distribution bar.
3. The shunt includes some electronic components that are not protected, so you want to install that inside, not in the battery box.

My solution is to use the #4 inverter wire for the shunt. The back side of the shut is where I connected everything else. My mod also includes a solar controller and 4 AGM batteries, but that is really not related to the Vectron. I tried to sort out the rat race of wires, but gave up. It is out of sight anyway.

First pictures: the shunt is installed above the inverter, using the black wire originally connected to the inverter.
Second picture: the remote unit installed in the cabinet above the stove.

[GMFL]

Originally Posted by CoorsLite

I am preparing to install a BMV-700 into our 2018 FC25 FB twin and looking for a little advice.

First the electrics. I am not a pro but I have worked a lot on 12 volt marine systems. Aided by forum posts I am reasonably confident on a successful install. I share the view that everything must run through the shunt/monitor so that will be my approach. I also want to organize the wiring. Based upon what I can see through the small hatch, things look pretty disorganized down there.

My question is - How do I gain access to install the shunt and organize the wiring?

My battery cables enter through the curb-side floor under the head of the curb-side bed. Removing the plywood top of the bed is easy but does not provide necessary access to the inverter etc.. I need to remove the panel that runs the full width of the trailer including the cabinet-drawer in the middle. There are two obvious screws connecting the top panel to the AS body. It seems improbable that these are the only screws. I am hoping I do not have to pull the carpet-liner out of the front storage compartment to find more screws. Thoughts?

Thanks in advance.

Remove the furniture and make it easy on yourself.

[CoorsLite]

Thanks for the advice and great pictures - these are helpful. Both examples illustrate my goal. It's the "remove furniture" part I am struggling with. The FC FB25 twin bed layout with center night stand shows only two visible screws in the entire forward area. My guess (and fear) is that the furniture is held together with pocket screws accessible only after removing the carpet liner from the front locker. I would like to confirm this before ripping-out the carpet-liner from the forward locker.

[GMFL]

Should not be that hard to remove. Mine (on 23D) came out in one piece and was help in place with 4 screws in the floor and 4 screws in the wall.
Remember that Airstream’s are manufactured from the outside in, so all the furniture is removable and will fit out the door.

[Philip Jones]

Originally Posted by chugchug

I just did this exec mod a couple of months ago. Mine is the queen bed. So removing the bed panel will be different.

1. You have to remove the entire bed panel. The hatch doesn't provide enough access to much.
2. There are actually 4 different connection to the battery. You need to combine them into 1 - the inverter, the jack, the solar charger plug and the rest of the trailer via the distribution bar.
3. The shunt includes some electronic components that are not protected, so you want to install that inside, not in the battery box.

My solution is to use the #4 inverter wire for the shunt. The back side of the shut is where I connected everything else. My mod also includes a solar controller and 4 AGM batteries, but that is really not related to the Vectron. I tried to sort out the rat race of wires, but gave up. It is out of sight anyway.

First pictures: the shunt is installed above the inverter, using the black wire originally connected to the inverter.
Second picture: the remote unit installed in the cabinet above the stove.

Sorry. Just a point of clarification. What does “#4 inverter wire” mean? Is that a 4 gauge wire that you diverted from the inverter to hook up to your shunt?

My main source of confusion is that the negative terminal on my battery has many wires attached to it. These of course then all go into the trailer. So, when I open up the bed to see all of the wires under the bed, will all of these wires have separate terminations where I can wire them directly to the shunt?

Many thanks.

[chugchug]

Originally Posted by Philip Jones

Sorry. Just a point of clarification. What does “#4 inverter wire” mean? Is that a 4 gauge wire that you diverted from the inverter to hook up to your shunt?

My main source of confusion is that the negative terminal on my battery has many wires attached to it. These of course then all go into the trailer. So, when I open up the bed to see all of the wires under the bed, will all of these wires have separate terminations where I can wire them directly to the shunt?

Many thanks.

Yes, that is the dedicated 4 gauge negative wire from the battery to the inverter. I connected it to the shunt and another 4 gauge wire from the other side of the shunt to the inverter. There is a 6 gauge wire from the battery that goes into the distribution panel. I removed it from the battery and connected to the shunt.

[Philip Jones]

Ok. Thanks. I think I now understand.

Regarding the other 4 gauge wire (from the shunt to the inverter), do hardware stores sell these pre-terminated with crimped ring connectors or did you crimp one yourself?

[chugchug]

Originally Posted by Philip Jones

Ok. Thanks. I think I now understand.

Regarding the other 4 gauge wire (from the shunt to the inverter), do hardware stores sell these pre-terminated with crimped ring connectors or did you crimp one yourself?

Some auto stores have per-terminated battery wires.

[uncle_bob]

If you are going to go buy a pre-terminated wire, get something like number 2 rather than number 4 gauge. Probably the best approach is to pull *one* of the wires off the battery and feed it back into the trailer. Then measure how long the "excess" is. That will give you a good idea how long the wire needs to be.

[Philip Jones]

Great suggestion. Thank you!

[Paprika]

I prefer to make my own cables, but if you don't want to spend the money for a good crimper and lugs, you can have cables custom-made by a company such as GenuineDealz. (Don't be out off by the sleazy-sounding name; they are a reputable supplier of marine-grade items.) I have used them in the past when I was traveling without my two-foot-long FTZ crimper.

What you'll get is marine cable--very fine strands, making it much more flexible and thus easier to route than the cheap battery cable used by auto-parts stores--with every strand individually tinned to prevent corrosion. On the ends will be heavy-duty power lugs--not the cheap, thin starter lugs used by auto-parts stores. And they'll crimped on with professional equipment rather than a twenty-dollar "hammer crimper," and protected against corrosion by adhesive-lined shrink tubing. It makes a difference, believe me!

[chugchug]

If I remember correctly the inverter 12V input connectors don't take lugs, just bare wire. So 2/0 gauge may be too big for that particular connection.

[Paprika]

My working method: first I use ampacity and voltage drop references to decide what wire size is appropriate. There's no point in using, say, AWG 2 wire if AWG 4 is all you need. It just costs more and is harder to route because of its thickness.

If the device's terminals are too small to accept the wire size I want to use (this is unfortunately all too common), and the difference isn't too great, I strip back the wire as needed and then clip a few strands from the end until I have it down to a size that will just fit in the terminals. As long as I don't have to clip away too many strands, the resulting minor reduction in gauge over the last half-inch or so of wire won't have a significant effect on ampacity or voltage drop.

[uncle_bob]

Hi

If your only concern is not starting a fire, yes you run off to the tables and figure out what size cable is safe in terms of temperature rise. That's how a house is wired. That's where the "ampacity".

We're not wiring a house here ... this is a low voltage circuit. A one volt drop is a *really* big deal if you are only starting from 11 or 12V. Indeed most stuff is not going to operate once you get much below 11V. Understanding the details *can* be important.

What we are doing here is to substitute a single cable for a bunch of cables. The single cable runs over to a shunt. A second cable runs from the shunt to a distribution block. The individual cables connect to the distribution block. If you really want to have fun, you can try connecting them all to the shunt ... yuck ....

Bob

[CoorsLite]

I cannot locate a negative lead for my jack. I assume the jack is simply grounded to the AS frame. Do you see this as a problem? It seems to me that if there is only one cable from the negative battery post(s) to the battery side of the shunt this should not be a problem for Victron accuracy. In other words, with only one negative cable running from the batteries to the battery-side of the shunt, the trailer frame itself logically must be on the "load" side of the shunt. Make sense?
Thanks

[Philip Jones]

See posts #45 and #46

[uncle_bob]

Originally Posted by CoorsLite

I cannot locate a negative lead for my jack. I assume the jack is simply grounded to the AS frame. Do you see this as a problem? It seems to me that if there is only one cable from the negative battery post(s) to the battery side of the shunt this should not be a problem for Victron accuracy. In other words, with only one negative cable running from the batteries to the battery-side of the shunt, the trailer frame itself logically must be on the "load" side of the shunt. Make sense?
Thanks

Hi

As long as the negative of the battery does not hit the frame, you will be ok. Frame grounded stuff will run through the shunt at whatever point the frame and negative are connected together.

Bob

[CoorsLite]

Thanks Uncle Bob for your help and confirmation.

Now, to take this one step further, when I charge my batteries using booster cables from my TV, I considered connecting the negative from my TV to the frame of my AS (a well-grounded bolt), and connect the positive from the booster battery to the positive battery terminal(s) on my AS. I reckon this approach should satisfy the need for the Victron to properly "see" all electrons passing by. However, I noticed the frame is grounded by what looks like 3 - 14G wires. I suspect these wires are not be capable of handling the amps-output from my TV alternator, especially when the AS batteries are low.

Alternatively I am considering fabricating a negative charging post with a lead to the load-side of the shunt via a bus.

[uncle_bob]

Originally Posted by CoorsLite

Thanks Uncle Bob for your help and confirmation.

Now, to take this one step further, when I charge my batteries using booster cables from my TV, I considered connecting the negative from my TV to the frame of my AS (a well-grounded bolt), and connect the positive from the booster battery to the positive battery terminal(s) on my AS. I reckon this approach should satisfy the need for the Victron to properly "see" all electrons passing by. However, I noticed the frame is grounded by what looks like 3 - 14G wires. I suspect these wires are not be capable of handling the amps-output from my TV alternator, especially when the AS batteries are low.

Alternatively I am considering fabricating a negative charging post with a lead to the load-side of the shunt via a bus.

Hi

Well, first off, charging batteries that way is really a pretty awful way to do it. The BVM will probably be ok, but either the battery in the TV or the TT is getting nuked in the process. Regardless of what we say about the converters in the AS, they are much better for the battery than a jumper cable setup.

Now, if indeed your TT batteries are flat dead and you need to pull out of the storage lot (I have data on this) ... errr .... how many choices to you have? In that case the battery monitor will be a bit confused anyway. I'm only suggesting that the jumper cables should be an emergency item, not part of routine use.

You also might look at the power lead on the 7 pin plug and consider it to be like a jumper cable. The difference there is that the 7 pin has a long small piece of wire on both sides of it. You simply can't move enough current to really get into trouble. (Unless the battery is flat ... again .... I have data )

Bob

[CoorsLite]

Once again Uncle Bob you have provided valuable guidance. Thanks very much.

You may have saved me an expensive battery (my Touareg TDI has an AGM battery with an imbedded chip), not to mention my new AS batteries (two Group 27’s).

My spidy sense told me that rapid charging with jumper cables may not be a good thing. You have just confirmed that. So why did I consider booster cables?

My Touareg has a 10AWG wire that leads to the 7Pin charging circuit. My worry was that heavy charging may overwhelm the 7Pin circuit, as I have at least a 150 Amp alternator. Hence the booster-cable approach. I have recently learned that the Touareg manages the 7Pin circuit to ensure correct current and if all else fails it is fused.

All of this points to alternative charging methods described well on the forum - Solar (I plan to install) and a generator (still considering but may be inevitable).

Thanks again.