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Old 02-08-2014, 17:11   #1
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Talking Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

Hi All!

I am pretty confident in the set up that I have going right now. I am just looking for a bit of confirmation by the pro's. I have (8) Trojan L16H-AC batteries. There are two banks that each are comprised of four batteries. Two in series to make 12v and then two strings of two in parallel for a nominal 12v 870Ahr @ a C20 discharge.

After much due diligence, I understand that the wires that are doing the series connections should be the same length and gauge, and that the wires that are paralleling the two strings together are to be the same length and gauge. The Hot and Ground runs that will come from opposite diagonals of the respective bank will also be the same length from the terminal post to the respective Bus Bar ( + or - ).

This said, it is not required that ALL interconnecting cables be the same length and gauge. Albeit, ALL of the series cables should be the same L&G and ALL of the paralleling cables be the same L&G.

In essence, this is to achieve an equal length of cable between the batteries connections and the runs to their respective bus bars.

PIC 1

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Purple Bank is Bank 1
Orange Bank is Bank 2
All Paralleling cables (green) are same length and gauge (16.5" x 1/0 AWG)
All Series cables (yellow) are same length and gauge ( 5" x 1/0 AWG)
The cables that will connect to the (+)Bus and (-)Bus for each bank (blue) will also be of equal length. Said another way, bank 1's "blue" cables (+&-) will be the same length to the common Bus bars, Likewise for Orange, but Oranges will be shorter since the common Bus bars are located at the bottom of the drawing in reference to the two banks.


PIC 2

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Both banks are fuse protected at the (+) terminal with a BSS Terminal fuse block (PN 5191) and a 250A fuse (PN 5189). I have the system fused as such since we do have a 3000w inverter and want the ability to crank the engine from the house Bank/Banks.

I have the two banks wired to the same Bus bar for charging with Blue sea's switches (PN 9006) to isolate which one is charging and which is being used for house loads. There will be a second Hot lead from each bank that will run to a 1/2/BOTH switch. This switch will determine which Bank (or both) will power house loads and crank the battery in the event that the dedicated starter bank fails.

PIC 3

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The hot lead from each battery bank (labeled A&B in this pic) will terminate in a 1/2/BOTH switch that will determine which bank/Banks will supply house/cranking loads. From the House Selector switch, one cable will go to the house distribution panel, the other will go to a second 1/2/BOTH switch that will determine where the cranking load will come from.
( I plan to have it on the cranking battery unless there is a cranking battery failure).

That pretty much all!

Thank you all in advance for your input and constructive criticism!
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Old 02-08-2014, 17:21   #2
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

Oh... also, the Alternator is a high output Delco Remy Freightliner 28si. Puts out 200A rated, so I will likely have a terminal fuse block with a 200A fuse for the alternator. my question is, I know you are supposed to put the fuse closest to the source of power, should I fuse the alternator with a BSS terminal fuse block and a 200A fuse at the at the alternator terminal?? I guess it can be done that way. just wondering if this is the best way, or if there is a better solution. Thanks all!!
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Old 02-08-2014, 17:25   #3
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

hahaha.... One more Also...

In pic 2, each of the ground terminals coming from the two banks will have a shunt inline for a Xantrex LinkPro (one for each bank).

I think that's it for now....
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Old 04-08-2014, 00:14   #4
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

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Old 04-08-2014, 00:59   #5
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

Looks good to me - My only question is where you put the alternator sense wire. With your switch setup it looks like you could theoretically have both banks isolated from all charging sources. (PIC 2 & 3) Or are you planning to have alt sense on House Bank Selector Switch "C" terminal?

I would only fuse the alternator supply at the buss end. The circuit is protected and when the engine is off the source will always be the battery end.
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Old 04-08-2014, 16:25   #6
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

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Originally Posted by Ex-Calif View Post
Looks good to me - My only question is where you put the alternator sense wire. With your switch setup it looks like you could theoretically have both banks isolated from all charging sources. (PIC 2 & 3) Or are you planning to have alt sense on House Bank Selector Switch "C" terminal?

I would only fuse the alternator supply at the buss end. The circuit is protected and when the engine is off the source will always be the battery end.
Haha! great question! I was just going to connect it at the positive bus bar. Yes. I would have the ability to completely isolate the batteries from all charging sources. No Bueno.... But with the lack of young kids and a spare in the case that I do accidentally fry the alternator, I will be covered.

The thing about this bank set up, and the reason for having room for 8- L16's is that the area that the bank will residing in is dead center, just forward of the engine room( huge space!!) . The main distro panel is aft of the engine room. My Engine room is roughly 6 feet from the bulkhead forward of the engine that is shared by the aft most portion of the bank, to the bulkhead aft of the engine that the AC/DC panels are located. This is also where the current 40A charger is located The engine room/workshop span the entire beam of the vessel.

In order to achieve minimal voltage drop, I will be mounting the new charger on the bulkhead forward of the engine. Running an AC line to the charger from the distro panel will be much more efficient with just a short run to the (+) Charging bus. This will ensure that these batteries get the voltages that they require to get to 100%.

The solar will also be run to this bulkhead forward of the engine where the MPPT controler will be mounted as well. We have a very unobstructed area on top of our dinghy davits that will support (5) semiflex 150w panels that will be wired in series to bring higher voltage to the MPPT. All the while, avoiding the heavier cables. I will likely still use 6AWG for the solar.

soooo..... there is the question.... where to attach the alternator sense so that it can read the terminal voltage of the bank it is charging... could I somehow run one lead with a diode from each banks (+) to the same sense terminal on the alternator? in effect, this would keep from series connecting the two banks because of the diodes , and the higher voltage of the two would trump the lower voltage and be what the alternator would be reading..... Hypothetically.....

it sounds good on paper!
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Old 04-08-2014, 17:51   #7
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

With this setup you are going to have the same issues with all the sensing and controlling equipment - i.e. where to attach.

As you know a battery monitor shunt has to be on the neg terminal between the psot and all loads.

With two full house banks are you planning to have dual monitoring systems?

Sense for shore charger, MPPT and alternator seems to me the only compromise place is house switch common post and then make sure you never have both banks "off"

If your runs form the banks to house switch are short and the connecitons are clean I think, while a compromise for accuracy it may not mean much in terms of alternator charging errors.

In regards to all the equipment in the engine room - I presume you have evaluated temps and operating environment and the equipment will have a long happy life and not get too hot?

In my design I am fortunate to have a bulkhead next to where the batts reside. I am going to run the batt cables through the bulkhead and all the equipment will reside on the cool and clean side.
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Old 04-08-2014, 20:00   #8
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

You would be much better off combining your batteries into one house bank. There has been much written about it in this forum and in Nigel Calder's book "Boatowner's Mechanical and Electrical Handbook". As well as giving you more usable power and potentially longer battery life it simplifies your electrical system.

Are you using an external regulator for your alternator? One with battery and alternator temp. sensing would be a good way to go.
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Old 05-08-2014, 00:14   #9
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

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You would be much better off combining your batteries into one house bank. There has been much written about it in this forum and in Nigel Calder's book "Boatowner's Mechanical and Electrical Handbook". As well as giving you more usable power and potentially longer battery life it simplifies your electrical system.

Are you using an external regulator for your alternator? One with battery and alternator temp. sensing would be a good way to go.
Correct.

This was the original plan, based off of Nigel's and several other books along with a bunch of other peoples steadfast knowledge on the subject. However, what is not often mentioned are the challenges that are involved with charging a bank that comes in at over 1500Ahr (our bank is 1740Ahr @ C20). In order to EFFECTIVELY charge a bank that size, to a FULL SOC, it would take either, a generator and Massive HEAVY expensive charger ($$$$), forever for the alternator and solar at absorption voltage to get it there (if ever), Or for efficiency's sake, I can split the bank for charging to get a higher SOC on the two individual banks, while still utilizing them both for house loads. I would effectively be alternating their 30% DOD whilst also alternating their charges. You are correct that it would make it simpler by way of numbers of connections and such, that said, it would not make them last any longer with the lack of proper charging capabilities. {cant charge properly = dead batteries}

Besides Keeps me from having to buy a $3000 200A charger for a proper equalization (12% of ampacity) which is something the L16's need on a regular basis. This way, I can equalize half the bank at a time. It will in, truth, probably add to the batteries cycle count if anything. And keep a lot of money in my wallet. Both of which I am okay with.


We have a Delco Remy Freightliner 28si that is internally regulated with remote sensing at the terminal post.


To ansewr Ex-calif's Question, Yes, we will have 2 Xantrex linkpro's (one for each of the two banks).
Shunts are already installed in both negative leads from bank to Common (-) Bus.

The runs from the main Bus bars to the batteries are less than 5 feet and I am using 1/0. If I have to use a multimeter to calculate voltage drop @ the terminal and adjust voltage from the source (MPPT, Charger) to accomplish the 14.8v absorption charge I am looking for at the terminal post,.... I am okay with that too.
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Old 05-08-2014, 11:37   #10
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

There can also be a potential issue with fusing on really large banks as the amp potential can grow quite large. For instance with a bank of the size discussed it may be better to go with a T class fuse rather than an ANL as the ANL rating if I remember is below 10,000 amps. I think this may mean we see some more divided banks in the future or we will se different approaches to battery fusing.
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Old 10-08-2014, 00:39   #11
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

As to where to place the alternator sensor...

The 28Si has remote sense (one wire to the battery terminal) I can just put it on a 2 way toggle to switch between banks....

Thoughts?
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Old 10-08-2014, 12:04   #12
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

Don't worry about equal or unequal length inter battery connections. On real life it makes no difference of the lengths are variable ( within reason )

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Old 10-08-2014, 12:47   #13
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

With analog ameters the shunt can be on the positive side. With digital meters it has to be on the negative side OR you can get a shunt shifter and put the shunt on the positive side.

DC Shunt Shifter - Blue Sea Systems

I have one for the hot side of each alternator so that I can see the alternators output on a digital ammeter.
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Old 10-08-2014, 14:24   #14
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

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With analog ameters the shunt can be on the positive side. With digital meters it has to be on the negative side OR you can get a shunt shifter and put the shunt on the positive side.

DC Shunt Shifter - Blue Sea Systems

I have one for the hot side of each alternator so that I can see the alternators output on a digital ammeter.

This isn't really the reason, DPMs can and are readily available to read positive shunts. The primary reason is safety. A negative shunt short is far less dangerous then a positive one.

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Old 10-08-2014, 15:48   #15
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Re: Interconnecting/Bus Bar Battery Cable Lengths - Some Closure

Hi,
I'm paranoid about electrical fires, and so nothing connects directly to the batteries. Everything is separately fused and goes through a single switch that turns everything off.

The goal is that if we ever smell smoke, we flip two switches (the battery disconnect and the solar panel input breaker), and absolutely everything is off. The four voltage sense wires are connected to the bus after the switch.

The main problem with our boat is that this master switch is in the lazarette-- the last places I want to crawl into in a smoke filled cabin. So this is our 'temporary' configuration, before we move the batteries and this switch and wiring (the shunt is immediately below the switch):


Also, I agree with everyone else that one big battery bank is better. Maybe just leave your switch on Both most of the time, and keep the 1/2 option for a quick fail over. I also have 750 watts of solar power and a similar sized battery bank, and at anchor we tend to be fully charged by 11am. We tend to consume about ~100-130 amps from sunset to sunrise, which is mostly the single fridge compressor, lights, fans, and inverter. There's plenty of capacity to equalize the batteries just off solar.

Matt.
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