Battery Cables, Fuses, and shunts, oh my!!

[mlydon]

I've been planning my electrical system upgrade for some time now, absorbing every tidbit from all the sharpies on the site, etc, and have some niggling conundrums I thought to air here.

First off, Battery cables, as in the cables connected DIRECTLY to the batteries:
On the load side of my system, an inverter and big honking windlass are the big draws. In fact, Victron calls for 2x 2/0 cables to power a multiplus 3000

Assuming I have 3 batteries in parallel, most 'standard' installations have one POS terminal jumpered to the next battery, etc, until the last battery, where the POS wire goes to a bus, etc. Same for Neg. Now if I pull 300amps with my inverter, the final battery cable is carrying 300 amps, the jumper between batterys 2 and 3 is carrying 200 amps, and the jumper between 1 and 2 is carrying 100 amps (assuming all the batteries carry the same share of the load)

How do I wire this? 2x 2/0 on every cable? (crazy mess and expensive)
Taper? 2x 2/0 to the bank, single 2/0 first jumper, single 1/0 second jumper? (so what happens when a battery fails, or disconnects if Lifepo4?)

My thought was to have each battery connected with a moderate cable (say 2/0) to a bus bar. I would think you would want all the cables to be the exact same length so as to prevent one from being 'favored', or does that matter (self-balance due to parallelism)

How would/did YOU do it?

Next - Shunts & fuses (really terminations)

The system I'm building (still in my head, mind you), will likely have:

A multiplus 3000 charger/inverter
Wakespeed regulator
Smart Blue solar (limited, I only have a couple hundred watts of panels)
a BVM 702 (already have that)
Lifepo4 batteries (hopefully DIY).

Putting all that together, there are shunts along the negative line for the regulator, BVM, and presumably the BMS.

On the positive line, say the load side, you have a main fuse, contactor, battery switch, and who knows what.
Add in battery, bus, load panel or combi terminals, and there are a hell of a lot of breaks in the path, each with a voltage drop along the way.

Now, most of these connections can't be avoided, but do we really need 3 shunts doing the same job? can a single one be shared?

Again what would/did YOU do?

thanks for thinking about it,

Matt

[Wotname]

Originally Posted by mlydon

I've been planning my electrical system upgrade for some time now, absorbing every tidbit from all the sharpies on the site, etc, and have some niggling conundrums I thought to air here.

First off, Battery cables, as in the cables connected DIRECTLY to the batteries:
On the load side of my system, an inverter and big honking windlass are the big draws. In fact, Victron calls for 2x 2/0 cables to power a multiplus 3000

Assuming I have 3 batteries in parallel, most 'standard' installations have one POS terminal jumpered to the next battery, etc, until the last battery, where the POS wire goes to a bus, etc. Same for Neg. Now if I pull 300amps with my inverter, the final battery cable is carrying 300 amps, the jumper between batterys 2 and 3 is carrying 200 amps, and the jumper between 1 and 2 is carrying 100 amps (assuming all the batteries carry the same share of the load)

How do I wire this? .........

My thought was to have each battery connected with a moderate cable (say 2/0) to a bus bar. I would think you would want all the cables to be the exact same length so as to prevent one from being 'favored', .........
How would/did YOU do it?

................

I would do it the way you have suggested.

I'll leave it to others to comment on the other questions you raised.

[Pete7]

By chance I have just watched this on You Tube and thought his work and ideas well thought out, see what you think.

https://www.youtube.com/watch?v=Ipe2nDfAGO4

[Frankly]

Don't know about sharing shunts, but on the parallel battery connections I would use single cables between the batteries (connect to lead post vice screw terminal) connected to bus bars (pos and neg). You can then fuse the individual loads and wiring as appropriate. If the shunts are serving individual devices they might not need to sense total current as with more typical arrangement.


Frankly

[Tillsbury]

Calling to a bus bar seems a workmanlike way to do things. I doubt you need to be millimetre-perfect in your lengths, but having them approximately the same would be good.

But rather than a bus bar, why not cable all three to one end of the main fuse, then the other side of the fuse to the victron in 2x2/0. On the negative side, the same thing but to one end of your shunt. With a fuse and a shunt, you effectively already have positive and negative bus bars.

[mlydon]

2/0 is pretty massive cable, and the lugs are large as well. wrestling 3 or 4 of them onto a single stud means leading one in at 9 o’clock, the next near 6 o’clock, etc...before you know it the wiring looks like a freeway map with cables in every direction.

In my particular case, the free space in my battery compartment is roughly 2 cubic feet, with only about a 12x18” bulkhead to mount everything. There’s already 2 bus bars, a shunt, a fuse block, a duo charge, and the backs of 4 battery switches in there, plus lots of jumpers and cabling. Keeping things fairly neat is already a major challenge. Upgrading all that to double 2/0 would be a bear....

I’m thinking individual 1/0 cables from the batteries to a dedicated battery terminal or bus, single 4/0 from there to fuse, same into and out of switch, then to distribution bus bar, where I can do dual 2/0 to inverter and whatever else.

Thinking about that raises another point - ‘good practice’ says have separate load and charge buses, so you can disconnect only the appropriate bus in a hvc/lvc situation......but the multiplus is both a charge source AND load....where does one tie the cables in? If on load, and you get an lvc, it’s not connected to charge the batts, same if it’s on the charge bus and sucking down your batts, lvc cutoff won’t stop it....

Matt

[skipgundlach]

I have just one thought after reading thus far.

2-0 is a bit skinny, I think, if you're going to use 300A, particularly for any length of time.

Residential copper runs out at ~200A for 4-0. Marine is a bit better, but not notably. Here's Blue Sea's chart: https://www.go2marine.com/docs/mfr/bluesea/115209F.pdf

You may have seen my battery upgrade story here:
http://www.cruisersforum.com/forums/...ba-199204.html but the link name was changed; here's the right one for the pictorial: Pictures: Flying Pig 2015-2018 Shake-and-Break-Down/Electrical Upgrade

We used 2-0 throughout, on a system which rarely would see 100A, and those only briefly. It's not a big deal to work with, if you stick with that, and, other than the in/out +/- terminals, there won't need to be more than one connector on any of the other terminals as you make up your series/parallel setup.

But if it were my boat, and I realistically expected those loads, I'd want to make sure that whatever it was using it also had that or larger cabling.

We have several charge sources; they all go to a buss terminal, and a single 2-0 goes up to the battery; the negative goes directly to another terminal mounted on a bulkhead and thence to the distribution buss and the negative terminal on the battery.

Hope that's helpful - marine, fine strand, tinned cable will bend relatively easily in case you have to do something other than straight line chunks. My gallery link shows all of my prep and makeup if you like.

[ramblinrod]

Originally Posted by mlydon

I've been planning my electrical system upgrade for some time now, absorbing every tidbit from all the sharpies on the site, etc, and have some niggling conundrums I thought to air here.

First off, Battery cables, as in the cables connected DIRECTLY to the batteries:
On the load side of my system, an inverter and big honking windlass are the big draws. In fact, Victron calls for 2x 2/0 cables to power a multiplus 3000

Assuming I have 3 batteries in parallel, most 'standard' installations have one POS terminal jumpered to the next battery, etc, until the last battery, where the POS wire goes to a bus, etc. Same for Neg. Now if I pull 300amps with my inverter, the final battery cable is carrying 300 amps, the jumper between batterys 2 and 3 is carrying 200 amps, and the jumper between 1 and 2 is carrying 100 amps (assuming all the batteries carry the same share of the load)

How do I wire this? 2x 2/0 on every cable? (crazy mess and expensive)
Taper? 2x 2/0 to the bank, single 2/0 first jumper, single 1/0 second jumper? (so what happens when a battery fails, or disconnects if Lifepo4?)

My thought was to have each battery connected with a moderate cable (say 2/0) to a bus bar. I would think you would want all the cables to be the exact same length so as to prevent one from being 'favored', or does that matter (self-balance due to parallelism)

How would/did YOU do it?

Next - Shunts & fuses (really terminations)

The system I'm building (still in my head, mind you), will likely have:

A multiplus 3000 charger/inverter
Wakespeed regulator
Smart Blue solar (limited, I only have a couple hundred watts of panels)
a BVM 702 (already have that)
Lifepo4 batteries (hopefully DIY).

Putting all that together, there are shunts along the negative line for the regulator, BVM, and presumably the BMS.

On the positive line, say the load side, you have a main fuse, contactor, battery switch, and who knows what.
Add in battery, bus, load panel or combi terminals, and there are a hell of a lot of breaks in the path, each with a voltage drop along the way.

Now, most of these connections can't be avoided, but do we really need 3 shunts doing the same job? can a single one be shared?

Again what would/did YOU do?

thanks for thinking about it,

Matt

When dealing with high current systems, wiring becomes more critical.

I recommend including an isolation switch, fuse, and cable, suited for the normal max load, for each battery connected in parallel. This allows one to isolate on more parallel batteries from the bank, and still be able to support all loads.

This may be important for testing, trouble-shooting, servicing, or isolating defective batteries.

The more high current connections on any one terminal stud or screw, the greater the risk of a loose, high impedance connection, heat, and fire. So I prefer each battery connected individually to a bus bar single terminal.

To ensure all batteries are treated equally with respect to charging and loading, the cables need to be the same gauge and length (well, same total resistance actually).

Regarding shunts, basically one measures voltage across a fixed resistance. Because a voltage measuring device has relatively high input impedance, a number can be connected across the same shunt with no detrimental effect IF the shunt is the correct resistance for the device.

Because shunts are relatively low resistance devices, 2 or 3 shunts in series is not a problem.

[Mad Multi]

The lengths of cable matters very little. First because it is DC voltage (it would matter a lot more on AC) and second because you are talking about large over rated cables on short runs ( we really only worry about length even on AC systems when were dealing in miles of cable or near capacity runs unless we are dealing with information multiplex systems)

[sailah]

I won't comment on actual cable sizes just a general thought as I recabled my entire boat this spring.

Think everything out, draw it out in a schematic and then post that. Gives people more to comment on. It also really helps with planning.

I also mapped everything out on a piece of plywood sitting in my office on a large table. That way I could play with everything and figure out the ideal way to route thick cable.

Then I decided to just use that plywood, painted and transfer to boat. In my situation it was much easier than doing in place as it was very tight.

Buy good quality crimpers and especially lugs. Same with heat shrink.

[ramblinrod]

Originally Posted by Mad Multi

The lengths of cable matters very little. First because it is DC voltage (it would matter a lot more on AC) and second because you are talking about large over rated cables on short runs ( we really only worry about length even on AC systems when were dealing in miles of cable or near capacity runs unless we are dealing with information multiplex systems)

Per ABYC, the max loop length voltage drop of battery cables to the supplied distribution panel is 3%.

Since for a given max current and cable size, resistance and voltage drop are directly proportional to length, length IS a critical factor.

The longer the distance, the larger the cable required, to keep the resistance and hence voltage drop below 3%.

I believe what you may be referring to is skin effect in high voltage transmission lines, which does not have anything to do with marine electrical systems.

[wingless]

Start w/ obtaining, reading, understanding and planning a rewire / repair according to ABYC standards.

My boat has been maintained to meet / exceed all ABYC standards.

Assuming a partial or complete rewiring is planned, then implemented, one of the most important issues, that is frequently insufficient is usage of appropriate / quality crimp tools, quality terminals and marine wiring.

It is very possible / likely that much of the existing would be reused during the rewire. Ensure that the result meets or exceeds ABYC standards. IMO, the ABYC standards exist to prevent problems, including safety problems.

This reply shows my thick wire crimp tool.

This reply shows my medium sized wire and my Faston flag crimp tool.

This reply shows the tool I like to use for the red / blue / yellow crimp connectors.

This reply shows my Brady ID Xpert labels applied to marine wires and surfaces.

One option for the battery cables are these really nice NAPA compression battery terminals? Those don't need a crimp tool. They are available on-line and from any NAPA store.

For 2/0 here is a battery terminal. They also have a 2/0 right-angle flag terminal. They also have a 2/0 lug. It doesn't list the size, but it looks like 3/8" to me.

If there are only a couple of battery terminals and there is not access to an appropriate crimp tool, then these compression lugs provide a foolproof solution.





My suggestion would be to avoid the "all eggs in one basket" and instead of a single large bank, plan for at least two battery banks. One bank could be for one engine and the helm electronics. The other bank could be for the house and another engine, if applicable. The two bank approach provides redundancy in case of problems, such as running the battery down too low to start the engine.

The factory built my boat w/ these contactors. They permit easy on/off control at multiple locations, including an illuminated rocker switch status indicator.

ABYC permits four wires, maximum, connected to any one terminal. I like to instead limit that maximum to two wires.

On the battery layout question, I would suggest usage of 2/0 or 4/0 for the main battery wiring, positive and negative. One in / out attached to each lug, before moving away from the batteries.

Don't forget / neglect proper wire sheathing and securing, per the ABYC standards.

[ramblinrod]

Originally Posted by wingless

Start w/ obtaining, reading, understanding and planning a rewire / repair according to ABYC standards.

My boat has been maintained to meet / exceed all ABYC standards.

Assuming a partial or complete rewiring is planned, then implemented, one of the most important issues, that is frequently insufficient is usage of appropriate / quality crimp tools, quality terminals and marine wiring.

It is very possible / likely that much of the existing would be reused during the rewire. Ensure that the result meets or exceeds ABYC standards. IMO, the ABYC standards exist to prevent problems, including safety problems.

This reply shows my thick wire crimp tool.

This reply shows my medium sized wire and my Faston flag crimp tool.

This reply shows the tool I like to use for the red / blue / yellow crimp connectors.

This reply shows my Brady ID Xpert labels applied to marine wires and surfaces.

One option for the battery cables are these really nice NAPA compression battery terminals? Those don't need a crimp tool. They are available on-line and from any NAPA store.

For 2/0 here is a battery terminal. They also have a 2/0 right-angle flag terminal. They also have a 2/0 lug. It doesn't list the size, but it looks like 3/8" to me.

If there are only a couple of battery terminals and there is not access to an appropriate crimp tool, then these compression lugs provide a foolproof solution.





My suggestion would be to avoid the "all eggs in one basket" and instead of a single large bank, plan for at least two battery banks. One bank could be for one engine and the helm electronics. The other bank could be for the house and another engine, if applicable. The two bank approach provides redundancy in case of problems, such as running the battery down too low to start the engine.

The factory built my boat w/ these contactors. They permit easy on/off control at multiple locations, including an illuminated rocker switch status indicator.

ABYC permits four wires, maximum, connected to any one terminal. I like to instead limit that maximum to two wires.

On the battery layout question, I would suggest usage of 2/0 or 4/0 for the main battery wiring, positive and negative. One in / out attached to each lug, before moving away from the batteries.

Don't forget / neglect proper wire sheathing and securing, per the ABYC standards.

Again, one cannot know the appropriate min battery cable size without knowing max load current and cable loop length.

[wingless]

Originally Posted by wingless

Start w/ obtaining, reading, understanding and planning a rewire / repair according to ABYC standards.

On the battery layout question, I would suggest usage of 2/0 or 4/0 for the main battery wiring, positive and negative. One in / out attached to each lug, before moving away from the batteries.

Originally Posted by ramblinrod

Again, one cannot know the appropriate min battery cable size without knowing max load current and cable loop length.

Assuming my suggested wiring compliance to ABYC, the short length between the adjacent batteries and the ABYC-specified short length to the fuse / disconnect will be fine w/ either my suggested 2/0 or 4/0 wiring for a 3% maximum voltage drop.

[ramblinrod]

Originally Posted by wingless

Assuming my suggested wiring compliance to ABYC, the short length between the adjacent batteries and the ABYC-specified short length to the fuse / disconnect will be fine w/ either my suggested 2/0 or 4/0 wiring for a 3% maximum voltage drop.

The minimum battery cable size is not dictated by the distance between the battery and the fuse. One can use an MRBF and the distance is zero. The minimum cable size is dependant on the total loop length from the batteries to the main load distribution point and back to the bank. Theoretically, this could be any distance.

Nobody, not even I, could recommend a reasonable and compliant cable size, without reviewing the system. It could easily be anywhere between 8 AWG and 4/0 or beyond. Huge difference kids, huge difference.