Yoda's Victron MultiPlus and Solar Install - just hope I don't mess up.

[Yoda]

New question while we are pondering the above.
How important is is to have all battery cables the same length? I have seen this discussed numerous sever times across several sites and all say keep cable length the same. I was looking at my battery box and trying to decide how to turn/rotate the 6V battery's to best align with the back of the box to tie in the the Lynx power in bar. As I have switches in line, do I just measure through them? The battery box will be sitting in front of the shunt and switches on the Right in my photos and vented top and bottom.
Thoughts?

I am wiring my 6V battery in 2-series pares to get 12V and then parallel to the Lynx power in through disconnect switches on the positive leads. This allow me to separate the two banks.

The real fun is going to be getting the loaded battery box in the front bay as I don't have room to tilt the batteries into place over the lip of the box if it is put in first without spilling. I am looking forward to Battle Born down the road. Everything I have can be reprogrammed to work with Lithyum

I just had a brain F&*. I have one of these (well similar) https://www.amazon.com/dp/B0855CH72P...g=roucb_a_3-20

I wonder if I can fab up a tray out of wood to hold the battery box steady to get it over the lip of the front bay and not damage or break anything? Help around here is scarce and my back cant take the lift if someone helps.
Thoughts?

Thanks
Keith

[Jlawles2]

Yoda Keith, Can you lay a couple of 2x or 4x just inside the doorway to keep the battery box off the lip? Then stick the box in as far as possible leaving room outside the compartment for setting 1 battery in the box. This should let you get most of it loaded. As a last resort for the last one, you can most likely tilt the battery for a short time and not loose any acid, just don't keep it tilted any longer than needed. This is only required if you cannot get the last battery in the box and it slid in to the compartment without damage to the box.

[Yoda]

Yoda Keith, Can you lay a couple of 2x or 4x just inside the doorway to keep the battery box off the lip? Then stick the box in as far as possible leaving room outside the compartment for setting 1 battery in the box. This should let you get most of it loaded. As a last resort for the last one, you can most likely tilt the battery for a short time and not loose any acid, just don't keep it tilted any longer than needed. This is only required if you cannot get the last battery in the box and it slid in to the compartment without damage to the box.

Joseph
I did a test on the battery to see how far I can tilt to get it in the box without lousing acid - no go. They need to be in the box when moving it through the doorway. I even thought of hinging the box side to do it. Let me sleep on it - ill probably come up with another hair brain idea - only problem is my lack of hair

[howson]

I just assumed it needed to be as large as the largest negative wire.

The term ground is misleading when the subject is a DC circuit. A better term IMO is return. Even more relevant is to use the term return when using conventional current flow, CCF, (+ to -) to describe a circuit.

To understand the rest of this, it must be understood that a return line's size needs to match the positive line's size along the path that current will flow.

Imagine a flashlight's circuit in your head. Power flows out of the + side of the battery, through the bulb, and then back to the battery on the return side. (Remember, we're using Conventional Current Flow). No where is this circuit "grounded".

Now look at the DC circuit side of the Multiplus. Power flows out of the batteries to a single point (wire size from batteries to bus bar are 2/0). From the junction of the four batteries 4/0 is used to allow power to and from the Victron and to/from the junction for the negative side of the battery bank.

So why is there a ground wire on the trailer for the DC circuits? To save wire. Instead of running the return for every 12vDC device (or circuit) back to the battery bank, the frame is utilized as a "wire". The ground lug is where the frame is tapped to attach a wire to connect to the battery.

Here's the key point: the wire from ground to the battery bank must be large enough to carry the loads of the connected devices that utilize the frame as the DC return path. Since GD uses a 6ga wire (in most trailers) on the positive side to go from the battery to the Power Distribution Center (PDC), the largest wire needed from the ground lug back to the battery bank is 6ga. Remember--the only power that will flow through this 6ga return line are the circuits supplied power through the PDC and utilize the frame as a "wire".

Your Multiplus' DC circuit does not use the frame as a return path. The DC power flows to and from the inverter and battery bank through the 4/0 (and 2/0) wires.

[howson]

How important is is to have all battery cables the same length?

I can only address what I did with my Battle Born batteries. Garret Towne (AMSolar) sent me this note in response to a very similar question about wire length and where to attach the 4/0 wire (Mar 2019):

Balancing will happen as soon as the batteries are connected. The performance differences between diagrams are so insignificant that consequences may never be noticed, but what I have attached is the best for the equipment you have.

The diagram he sent:



Howard

[Yoda]

The term ground is misleading when the subject is a DC circuit. A better term IMO is return. Even more relevant is to use the term return when using conventional current flow, CCF, (+ to -) to describe a circuit.

To understand the rest of this, it must be understood that a return line's size needs to match the positive line's size along the path that current will flow.

Your Multiplus' DC circuit does not use the frame as a return path. The DC power flows to and from the inverter and battery bank through the 4/0 (and 2/0) wires.

Thanks Howard
This all makes sense now. Ill actually just use the OEM ground cable.

Now for what may appear to be a stupid question. The true ground wires for the equipment. These are the green grounding screws that are supposed to be wired to a frame or natural ground per instructions . Can I wire them into the negative buss bar below the MultiPlus? Or should I wire them to the grounding lug? I was wondering if they are wired to the buss bar if it would upset the 712 .They are probably already grounded as I mounted them to the aluminum plate that is screwed to the trailer frame. But I was going to run a separate wire anyway per the instructions - but maybe I don't need to?

Thanks again for the help
Keith

[howson]

The true ground wires for the equipment. These are the green grounding screws that are supposed to be wired to a frame or natural ground per instructions . Can I wire them into the negative buss bar below the MultiPlus? Or should I wire them to the grounding lug?

Now we're getting into an area where I think I know how it works, but hope the real electricians will correct the information if it's wrong.

In an AC circuit, the neutral wire can be thought of as the return line. (AC works so differently this is a little misleading.) Just like the electrons from a battery will do everything they can to get back to their source (the battery), so will 120vAC try to get back to it's source. Since typically this is from a distant power generation site, the ground wire provides a safety path for the power to "get home" (literally through the ground) if there's an issue with the 120vAC wiring (or a device).

Again--I could be wrong about this--but in a 100% operational 120vAC circuit I don't think the ground is used. Power flows back and forth across the hot and neutral wires. (A 50A circuit with two hots is more complicated, so let's stick with one hot and one neutral!)

I don't have my Multiplus' frame connected to the trailer's ground or any ground. I don't have the MPPT grounded, either. This could be a safety issue that I'll need to address at some point, but it certainly hasn't affected the performance of either component to this point.

So to your question: with what I currently know and understand, I suggest connecting the case of the Victron components to the trailer's frame ground.

Again, if someone reading this disagrees by all means correct what I've written or clarify. (Please!) I'm a shadetree electrician (at best).

Howard

[openrangeowners]

To answer your question about grounding the MultiPlus and the Victron Solar Charge Controller ....


Answering as an electrical engineer .... in a catastrophic failure in the Multiplus where lets say your positive DC connection bolt breaks and leaves your 4/0 positive cable dangling where it can touch the casing - this would cause it to probably arc-weld itself to the casing and the 400amp T-Fuse would blow. Lets take a different scenario where the 120V AC line hits the casing (ie: slips out of its connection) - this would cause the Multiplus chassis to become live. If it was not grounded, one would receive a bad shock if touching the casing. Grounding the casing would cause the circuit breaker to trip. In this case the AC ground can handle the problem.

For the Victron Solar Charge Controller, lets say you have 80 volts or 140 volts or something larger than 48 volts coming from your solar panels. Now lets say you have a transient voltage condition - lets say lightning or buildup of static electricity. The charge controller will shunt (divert) the transient to the ground (ie: chassis ground in this case) to protect it (think of a surge protector). Without that ground, there is no where for that transient to travel so it can destroy the electronic components of the solar controller.

In either case you are both protecting humans and hopefully electrical components with connecting the chassis ground.

My example - I was using a 4" hole saw on my cordless drill to make a hole for a vent in an outside wall of my house. I hit a 120 V wire in the wall with the saw. It hit the 'hot' wire - I did not know until I touched the metal part of the drill. It gave me a nasty shock, causing me to jerk the saw, shorting the two wires and popping the breaker. The hole saw was welded to the wire. Had I been using a grounded drill plugged in, as soon as it hit the hot wire, it would have popped the breaker, preventing me from getting shocked.

Definitely connect the chassis grounds on your Victron items to the trailer's frame ground with sufficiently large enough wiring to handle the full fusable/breaker rating of whatever circuits are connected to it. In the case of the Multiplus, I used 4/0 AWG because that is what I used for the DC wiring and I have a 400 amp fuse protecting the Multiplus. If I used an AWG 10 wire as a chassis ground, that wire would act as a fuse and possibly melt before the 400 amp fuse would blow ....

In the case of the Charge controller, I used 2 AWG wiring as my chassis ground since I used that on my DC 12V side of the controller (for 85 amps). I am fused at 100 amps.

The chassis grounds I used are overkill (you can usually downsize 2 AWG sizes for a chassis ground, but since I did not want to buy extra wire of a different size, I used what I had.

I did run my MPPT ungrounded when I first hooked up things - it was on my ToDo list and I eventually got around to it. It normally won't affect performance unless you have a catastrophic failure, then it is there for your safety like a fuse, circuit breaker or surge suppressor.

[howson]

Definitely connect the chassis grounds on your Victron items to the trailer's frame ground with sufficiently large enough wiring to handle the full fusable/breaker rating of whatever circuits are connected to it. In the case of the Multiplus, I used 4/0 AWG because that is what I used for the DC wiring and I have a 400 amp fuse protecting the Multiplus. If I used an AWG 10 wire as a chassis ground, that wire would act as a fuse and possibly melt before the 400 amp fuse would blow ....

Trying to learn and understand your post, so don't take this as argumentative.

If a 4/0 is attached from the Multiplus frame to trailer ground, what wire is transmitting the energy from the Multiplus' frame-to-ground connection back to the battery? Isn't the battery where the DC energy will work to get back to in the failure mode described? The only wire from the trailer ground lug back to the battery in most setups is the OEM 6 ga...unless you're also advising an upgrade of that wire to 4/0, too?

I can certainly see the feasibility of a ground wire on the MPPT and Multiplus for the surge transients and the 120vAC "hot case" scenario presented, but if the trailer is hit by lightning it's probably going to fry a whole bunch of stuff (thus the reason for insurance). I'll probably need a new pair of undershorts, too, if I'm in the trailer when it's struck.

[howson]

Yoda (Keith),

openrangeowners ' post gives me pause that I'm probably wrong about what I've written in the posts above. I'd advise calling the vendor you purchased the items from and getting their professional advice on the installation. As I've stated repeatedly, "I'm just a guy on the internet". I'd hate to lead you astray.

[Yoda]

Yoda (Keith),

openrangeowners ' post gives me pause that I'm probably wrong about what I've written in the posts above. I'd advise calling the vendor you purchased the items from and getting their professional advice on the installation. As I've stated repeatedly, "I'm just a guy on the internet". I'd hate to lead you astray.

Beat you to it Howard - they are working on it.
openrangeowners
So I understand - use 4/0 to ground the Multiplus. Can this be run to the negative bus bar (mounted below the multiplus) and then 4/0 to ground. I need to take a ground from the negative bus bar to the frame anyway to maintain the OEM wiring. They had the negative battery wire going to the frame directly.

Thanks
Keith

[Yoda]

I made some wiring progress today. I decided to start withe the 4/0 runs that I could get to. Below are the results.

I really like my lug crimper - easy to use and does a good job.


Before


In the crimper


The completed first crimp.


After second crimp.

Next up heat shrink tubing.

[Yoda]

Heat shrink tubing. I got the adhesive 4:1 shrink tubing and used my new heat gun.



With the multiple heat setting it was easy to dial it in. I did most of the work at 380 degrees F.



Now a couple of tools I am using.
To cut the cable I found my Pex pipe cutter does an excellent job. Ill need to replace the blade at some point.

This is a slick insulation cutter. Once you get the depth set (red knob at bottom) it does a fantastic job and does not cut any wires. I can thank Howard for the tip. Its one of Will Prose (sp) favorite tools.

Well more wiring and component install tomorrow - my copper bar stock should be here too.

Questions or if you spotted a goof ( I never make them ) please let me know.

Keith

[howson]

Yoda and openrangeowners ,

I took advantage of my customer-relationship with AMSolar and sent them the question. Garret responded quickly (to my delight and surprise). Below is the complete unedited text of my question and his response.

Keith--if this post sends your thread off on a long tangent I'll copy them to a new thread (and leave a note here in your thread).

Let me further state that my motive with sharing this exchange between myself and Garret is to clarify why there seems to be differences between various sources online regarding this subject, not to try and convince anyone of anything. Each individual installing their system should heed their supplier's advice, system design, and their own knowledge based on experience with electricity.

For the record, at some point I'll be adding a standard copper 6ga ground wire (I have lots left over from the 6/3 wire I originally purchased) and will be attaching it from the Multiplus' external chassis ground lug to the trailer's frame. It won't hurt anything to do so and adds another layer of safety, even if an incident is very unlikely to occur.

---------Howard's Text to AMSolar via their website-----------------

As a Senior Moderator on Grand Design's Technical Forum (https://gdrvowners.com) I have often pointed individuals to your drawings and services. One discussion that never seems to get resolved is the grounding of the case of a Multiplus to the trailer's frame, aka "ground". None of the AMSolar drawings show this, but the Victron manual seems to imply it is required? There is also discussion on the forum of grounding a SmartSolar MPPT's case to the trailer frame. In most references on these topics I find the individual advocating for this grounding states the largest wire used in the system must be used for this extra safety feature, thus in my case I'd need 4/0 from the Multiplus' case to the trailer's frame. My system works great as it is so I can't wrap my head around this...hoping you'll provide a succinct rationale (either way) that I can post in response on the forum. (If I need to go back and ground the case that's fine--just need to know.)

-------Garret's Response------------------------

Howard,
Thanks for reaching out. Good questions too. Victron recommends connecting the inverter chassis to the rig chassis with a cable half as thick as the DC cables suppling power to the inverter. So, for a Multiplus 3000, with 4/0 cable, you would use 2/0 cable to make that connection. But, I think a lot of these “rules” are written by attorneys, rather than people who know how electricity works. I don’t claim to know everything, but do know some things, and I have a hard time seeing the importance of this. A connection like this would only protect you from a perfect storm of very strange things happening all at the same time (pretty much never). It won’t improve performance (nor hurt it). That being said, I still don’t see why a 10ga wire wouldn’t do the trick, because the fault would be related to alternating current, not DC. So, our stance is that we don’t specifically recommend it, but if someone wants to, they can go for it.

As for grounding the chassis of an MPPT charge controller to the chassis of your rig, when you are on rubber tires, I can’t imagine a scenario where that would make any sense. Maybe it gives you some protection from lightning that is close, but not too close? I don’t know what someone would gain from that.

For background, I have worked in solar since 2009. I have been at AM Solar since 2015. I got my Electrical Engineering degree in 2003.

I hope this helps. Let me know if you need anything else.

Garret Towne,Electrical Engineer

---------END----------------

[ThePowells]

I don't have a dog in this fight (yet) and mostly am sitting back going , but this caught my eye,

"As for grounding the chassis of an MPPT charge controller to the chassis of your rig, when you are on rubber tires, I can’t imagine a scenario where that would make any sense. Maybe it gives you some protection from lightning that is close, but not too close? I don’t know what someone would gain from that."

Would the circumstances of being parked at almost anytime change that equation as you will have jacks / levelers (or at least the nose jack) in contact with the ground rather than than being insulated by the tires?