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Old 07-05-2019, 07:13 PM   #1
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6V wiring for 12V

Hey all - I am returning to this topic seeking a bit more help. It seems the deeper I get into this project, the more questions that come up!

I have acquired six 6V new Trojan T-105ís which will be wired into series / parallel to make a large 12V battery pack. I have found a few diagrams of the wiring of the 6 batteries, but if anyone has a photo or diagram that they think may help, please share - wiring diagrams for 6 batteries are not as prevalent as they are for 4 or 8 batteries.

The question I now am faced with concerns hooking to the coach.

For purpose of this message, the existing four 12V batteries can be labeled L1, L2, R1 and R2, with 1 being innermost to coach. I have identified five connections from the batteries:

1. Positive from L2 to what looks like a shunt, then up into the coach
2. Negative from L2 up into coach
3. Positive from R2 up into coach
4. Negative from R2 to ground (bolt on frame of vehicle)
5. Negative from R1 to a black plastic gizmo with Winnebago name, and what looks to be a telephone wire out of it

So, I could use advice, input, etc., on which batteries I should connect these five wires to. Does it matter if it all checks out to be 12V?

For responses, letís use a similar numbering: L1, L2, L3, R1, R2 and R3.

Thanks in advance for any and all input. John
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Old 07-05-2019, 07:56 PM   #2
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Photos would really help.

Your six 6V batteries should be wired like this image: http://www.marxrv.com/12volt/wiring1.gif
Yes, this only show 4 batteries. You will add an additional pair in the center and then all positive and negative wires would attach to a single point on the center pair of 6V batteries.

Simply put: All negative wires should to to a single attachment point and the same for all positive wires.

Are you sure you have a positive lead going to a shunt? It would be very unusual for a shunt to go to the positive side of the battery. Normally a shunt goes to the negative lead. The make and model of the battery monitor attached to the shunt would be very helpful.

Assuming you have a shunt that has a small cable going to a monitor, there should be a single large wire (cable) going from the battery pack to the shunt and then the other side has all the wires from the RV attached.

I assume you (or someone) will be building a number of heavy cables make out of 1/0 or 2/0 to interconnect the batteries.
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Old 07-05-2019, 08:38 PM   #3
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In the photo on the right side those connections are perfect. One thing you can do is set the batteries out lined up just as they go in the RV tray. Then measure the cables you need to connect as in that photo. Then you can order the right gauge from Amazon - two days and done. Lot easier than making them especially if you don't have the right equipment. It is usually easier to get a size larger than the original. If the arrangement in the tray means some posts are too near it is still important to connect as shown in the diagram with exact length cables. Stuff the extra but make each cable the same length. This prevents one battery set from becoming weak or not charged as much or overloaded - imbalanced.


In the middle of this page of connects is a 6 battery series/parallel diagram which is what you are doing - it is the yellow connect diagram:
https://www.survivalmonkey.com/threa...arallel.37039/



Shunt? Perhaps that is really the fuse for the inverter protect? Without complicating things this would be a great time to put in a real physical battery disconnect.


As Al noticed the shunt would be on the most negative ground side - the one where the chassis ground wire is attached.


https://www.amazon.com/battery-lengt...ateway&sr=8-31


https://www.batterycablesusa.com/00-...yAAEgJxE_D_BwE
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Old 07-06-2019, 04:43 AM   #4
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I tried to upload a diagram I made for wiring up the six batteries - hope it is attached to this....
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Old 07-06-2019, 07:30 AM   #5
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Quote:
Originally Posted by John Vista View Post
I tried to upload a diagram I made for wiring up the six batteries - hope it is attached to this....
The diagram looks good. The one thing I would change is to attach the plus and minus cables from the RV to the center battery pair. This way the cable length to the 2 outside battery pairs is equal.

It is not clear if you have a battery monitor which show the total AH used and the percentage of the battery charge. Also it should show at a glance the amps going in or out and the battery voltage as well.

Without a good battery monitor you are flying blind as to the true state of charge of your batteries. Especially to know if your batteries are fully charged to 100%. Also so the AH's don't fall below 50% of capacity.
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Old 07-06-2019, 05:59 PM   #6
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More info

Upon further inspection, the existing leads from my four 12V batteries (see numbering convention in earlier post) are as follows:

1. Positive from L2 to voltage protection (which I thought was a shunt), then up into coach
2. Negative from L2 up into coach
3. Positive from R2 to fuse, then to coach
4. Negative from R2 to ground bolt on frame
5. Negative from R1 to battery temperature sensor.

Wiring between batteries is either 4/0 or 3/0 - I plan to rewire using all 4/0, unless someone sees an issue with that.

One response I received suggested that I connect all positive cables from batteries to one post in middle of pack, and all negative cables to one post also in middle. I donít know if I can get these all stacked on one post as it wouldnít be tall enough. Any further suggestions?

John
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Old 07-06-2019, 07:03 PM   #7
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Quote:
Originally Posted by John Vista View Post
Upon further inspection, the existing leads from my four 12V batteries (see numbering convention in earlier post) are as follows:

1. Positive from L2 to voltage protection (which I thought was a shunt), then up into coach
2. Negative from L2 up into coach
3. Positive from R2 to fuse, then to coach
4. Negative from R2 to ground bolt on frame
5. Negative from R1 to battery temperature sensor.

Wiring between batteries is either 4/0 or 3/0 - I plan to rewire using all 4/0, unless someone sees an issue with that.

One response I received suggested that I connect all positive cables from batteries to one post in middle of pack, and all negative cables to one post also in middle. I donít know if I can get these all stacked on one post as it wouldnít be tall enough. Any further suggestions?

John
Yes, that is a problem, you can't stack all those lead on a battery post. Here is a link to a post that you can attach several leads to and then one cable to the battery. https://www.bluesea.com/products/cat...tors/PowerPost
For the positive lead, the main heavy cables which would be coming from your charging sources, inverter/charger or converter and solar, that is best going to the center set of batteries. The smaller loads can be distributed to the other batteries. That is not a "perfect" installation, but will not be a problem.
For the negative lead, you really want a shunt to go to a battery monitor. for the battery monitor, you must have a single cable from the shunt to the battery and all other leads going to the RV side of the shunt.

Victon and Trimetric make very good monitors.
https://www.victronenergy.com/batter.../bmv-712-smart
- Bogart Engineering

That is assuming you will be doing a lot of dry camping or boondocking. If you are only going to dry camp for a night or two and then back to elect hookups you really don't need the monitor. Then again, if that is the case, you probably don't need the 6 batteries either.
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Old 07-08-2019, 04:25 PM   #8
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For the short jumpers between the + and - posts of the 6V batteries, IMHO 4/0 is total over-kill and will create many issues with dealing with the large wire and lug size around your batteries and fuse / terminal blocks. I suggest 1/0 for short runs of under 18" or so. 1/0 can handle up to 300 amps and is a lot more flexible. You'll see that all the current jumpers and short runs to the fuse blocks are 1/0.

Personally, when I upgraded my Vista to 4 6 volt batteries I used a Victron BMV-700 battery monitor and mounted the shunt very near the batteries, and ran a 1/0 cable direct from each pair of 6V batteries negative post directly to the shunt battery post then connected all the negative leads that used to be on the batteries to the shunt load post. I thought the negative bus bar that Winnebago welds to the chassis was not good as it had the negative lead of the inverter tied there instead of directly to the negative on the battery so I moved that lead to the shunt, too.

On the postive side I installed a insulated junction post and ran 1/0 from the positive side of each battery pair to it. That post has the heavy OEM lead running to the Battery Isolation Manager Power Relay, and two short 1/0 jumpers from there to the Winnebago in-line fuses.

I wanted there to be exactly the same wiring path to/from each set of batteries so that load current and charging current would split as equally as possible.

If you do the way where you use the center post of the middle battery pairs the right and left battery pairs will have two extra jumpers each compared to the middle battery pair. The middle battery pair will discharge and charge slightly faster due to the lower resistance.

I bought 1/0 copper cable, 1/0 copper terminals, a inexpensive large terminal crimping tool, and heat shrink tubing to make my own custom length cables. I got the kind of tool that you hit with a small sledge hammer to make a gas tight connection.

I made my own custom 1/0 jumpers rather than re-use the jumpers from the old batteries. I used very flexible fine strand 1/0 copper cable rather than the cheaper stiffer larger strand OEM copper cable that Winnebago used.
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Old 07-09-2019, 06:02 AM   #9
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I used 1/0 in my little View when installing new batteries. The thing is normally those interconnects are very short so more important to measure the same exact lengths so current flow in theory is evenly distributed among the batteries. That never can be completely achieved but it is a lofty goal. Never you say? Yes, because no two batteries will be exactly identical. Is it a worry? Nope but about once a year at least do a tedious specific gravity check of every cell in the bank to tell you if you have a "wildcard" in the coral.


In my rig I will seldom put very large draw on the bank anyway, just a continuous low amp draw with occasional larger but barely over 25 amps any time.


Here is a chart ripped on the net which is handy but remember you don't really want 2% or less you want as low as possible for battery interconnects. Just easy reference for not using the calculator every time.
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Old 07-09-2019, 08:48 AM   #10
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http://www.winnieowners.com/forums/a...1&d=1562673704

For anyone using wire size charts and applications: BE SURE the chart specifies if the length of wire you are using is for "one way" or "round trip".

All wiring size determinations MUST be for round trip. So if the distance from say the battery to the inverter/charger is 2 feet the length of the wire must be for 4 feet unless the calculator specifies it uses the round trip distance in its calculations.

The chart above does not specify one way or round trip so I would double the wire length when deciding wire size.

This is the calculator I like to use: http://nooutage.com/vdrop.htm This calculator automatically calculates for the round trip distance.
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Old 07-09-2019, 09:27 AM   #11
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Al,


I have NEVER heard that rule before. I normally use the voltage drop calculator here:


https://www.calculator.net/voltage-drop-calculator.html


There are many available. Do NOT double the wire length in the calculation, that is definitely expressed in most calculators, note the one link I gave states that in a footnote.



The table was meant as an easy guideline, not as a calculator as it helps to see the effect of gauge and distance with varying loads.


I think my table is easier to read - higher resolution and not fuzzy.


Now, why on heaven's earth would I double the length in my calculation? DC current and voltage.


"Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. V = I R {\displaystyle V=IR} . Also, Kirchhoff's circuit laws state that in any DC circuit, the sum of the voltage drops across each component of the circuit is equal to the supply voltage."


You are referring to the fact that there are two paths, positive and negative in the complete circuit. Voltage calculators assume you know that so you never, ever double the length. It is really difficult to get all the involved lengths equal in an RV, the interconnects yes, but after that more of a challenge. It depends on the complete path so interconnects the same length and the POS main feed and NEG ground from batteries same gauge and as near the same length as possible.


I have several times had issues with varying grounds in RVs. Many times you can find chassis ground in several places, of course the battery chassis ground is in only one. That really causes strange things in a larger RV when grounds get flaky or inferior terminal posts are used to join ground wires. Every thing in the circuit has some resistance.
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Old 07-09-2019, 09:39 AM   #12
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Quote:
Originally Posted by Kayak73 View Post
Al,


I have NEVER heard that rule before. I normally use the voltage drop calculator here:


https://www.calculator.net/voltage-drop-calculator.html


There are many available. Do NOT double the wire length in the calculation, that is definitely expressed in most calculators, note the one link I gave states that in a footnote.



The table was meant as an easy guideline, not as a calculator as it helps to see the effect of gauge and distance with varying loads.


I think my table is easier to read - higher resolution and not fuzzy.


Now, why on heaven's earth would I double the length in my calculation? DC current and voltage.
The link you does specify to only use the one way distance, which is exactly what I wrote about.

If you use a calculator that only calculates the loss on a single wire, or in other words the one way trip distance, you will wind up with twice as much loss as you planed for. You must calculate for the length of both the positive and negative wire distance.
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Old 07-09-2019, 09:53 AM   #13
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Quote:
Originally Posted by Kayak73 View Post
Al,


I have NEVER heard that rule before. I normally use the voltage drop calculator here:


https://www.calculator.net/voltage-drop-calculator.html


There are many available. Do NOT double the wire length in the calculation, that is definitely expressed in most calculators, note the one link I gave states that in a footnote.



The table was meant as an easy guideline, not as a calculator as it helps to see the effect of gauge and distance with varying loads.


I think my table is easier to read - higher resolution and not fuzzy.


Now, why on heaven's earth would I double the length in my calculation? DC current and voltage.


"Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. V = I R {\displaystyle V=IR} . Also, Kirchhoff's circuit laws state that in any DC circuit, the sum of the voltage drops across each component of the circuit is equal to the supply voltage."


You are referring to the fact that there are two paths, positive and negative in the complete circuit. Voltage calculators assume you know that so you never, ever double the length. It is really difficult to get all the involved lengths equal in an RV, the interconnects yes, but after that more of a challenge.
By the way, I used the chart you provided, selected for an example the 6AWG wire for 6 feet at 100 amps. Then entered those figures into the calculator you provided (which states to only enter the one way distance). The calculator says the loss is 3.95%. NOT the 2% loss the chart states. So the chart is only showing the loss for one way distance not the round trip distance.

For anyone only using the chart, you MUST double the wire length. If you use the calculator then just enter the one way distance.
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Old 07-09-2019, 10:02 PM   #14
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No, please do NOT double the distance, just put in the total circuit distance. Again, the chart is not for calculations of anything, not meant to be and no one would or should use it for a calculation of exact requirements.


Do not double the distance. The chart is used to show the approximate loss for given values over a given distance which is a basic guideline in selecting wire size. Just put in the circuit distance. If you have to run a circuit 25 ft then in DC you know that means 25 ft to the load and 25 ft back -normally. So you are looking at 50 feet and not 25 feet. I don't get the double thing at all but it's OK with me if you think about it that way. The accurate thing to do is measure the run for POS and NEG.



I'm really sorry to have posted the chart, apparently it really bothers for some reason. It is just kinda silly to discuss it anyway, it is obvious to all but the most casual observer - who really would not care anyway.


It is a common mistake folks make to say "double" the distance because many times in a DC circuit the distance is NOT double the positive lead or negative lead, in an RV you frequently find a short drop to a ground, just like an auto. In that case the old DOUBLE it dumps on you and is totally out of whack. In other cases the leads will be the same length but not often. The good news is that the double approach works most of the time with a calculator but they all make that assumption - nothing you need to input.



Indeed, if you knew the circuit was 12 feet why look at the 6 ft value? I just don't get it.


So if we are to be really nitpick about words, the only true way to know the voltage loss is to measure the entire circuit accurately and use the formula I gave. In reality that gets hard to do so most folks just use a calculator which assumes double distance - doesn't mean it is correct at all, just another guess - estimate.


A lot like a battery monitor - an estimate of what your batteries are doing and their state of charge.
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