What is the right way to connect battery cables?

[imnprsd]

I took a look at my 2004 Itasca Horizon Battery Boost and Battery Disconnect Solenoid diagram and noticed they way Winnebago diagramed the battery connections is slightly different than my setup.

So, now I wonder what is the right way to connect my battery and inverter cables to the house battery?

Notice in the Winnebago diagram "A" below... the inverter-charger battery-positive cable is not connected to the same positive battery terminal as the battery-positive cable that is feeding the Boost Solenoid.

Likewise the ground cables are configured to be diagonal from their respective positive cable, which is the rule I have always followed.

Consequently, the Winnebago diagram "A" implies the Inverter-Charger battery cable is connected to Battery #3; and battery cable to the Boost Solenoid is connected to the positive post of Battery #1. This connection forms an "X" pattern as drawn below.

...I know both methods will work, but I would like to know if one method will result in longer battery life? ...Or will result in a more "balanced" or "equalized" battery configuration?

A) The "X" Pattern as shown below?

or

B) Connecting all the positive battery cables to one end of the battery bank and then connecting all the negative battery cables to the other end of the battery bank... "diagonal" from one another?

Please do not attempt to answer this question unless you know can state your reasons why? I.e., this is not an "opinion" type question. I am looking for the right answer based on battery technology.

Alternatively, if you have used both configurations and have field tested both methods, please share your conclusions... even it you say "It does not matter."

DOES IT MATTER IS THE QUESTION?

[Morich]

My opinion? This is assuming you don't really mean connecting the negative post to the positive post of another??? I think you got the drawing wrong but do know that we want only the negative sides connected to ground, right?
But assuming we are meaning to connect all 12 volt batteries in parallel, not series as we might if they were six volt, I see no difference worth mention as the cable length is so short and the resistance in the short heavy cable is so small that where we choose to place the input or output is not worth worry.
Part of the story is that any point along the positive connections should be very near the same if we keep the cables clean and tight.
When connected together, there will always be a "weak sister" in the bunch and it may fail somewhat sooner but there really isn't any way to wire around that in a small group like we use.

[imnprsd]

For clarification: I believe most 38-40' RVs from Winnebago, and maybe some 36' RVs, come from the factory with 3-12V house batteries connected in parallel.

The parallel battery bank is made more obvious by connecting all positive connection points together, as are the negative terminals connected together.

The colored arrows in the diagram I edited merely denote the diagonal (or relative) position of the positive vs. negative posts.

...And yes, all interconnect cables should be the same length and type.

You mentioned the "weak sister" in the bunch... and by that I'm guessing you mean a battery cell that shorts out before the others. ...And is gets to the heart of my questions.

In the Winnebago Diagram "A" you can see how the Inverter-charging positive connection is not the same as the discharging-positive post that goes to the Boost Solenoid.

This is different method than Diagram "B," which I edited... based on the rule you connect the positive cables diagonal from the negative cables.

So now that I have diagramed two different ways to connect the battery cables (+ & -)... to prevent a "weak sister cell" from causing premature battery bank failure, which configuration method is best? ...A or B?

Note: I'm only discussing 3-12V batteries connected in parallel at this time.

[Morich]

No different in the real world as the positive post on battery one is electrically the same as the positive post on battery three at the voltages and cable size and length we use. That leaves both options very much the same or one could use the positive post of battery 2 and still be the same as long as they are all tied together with no real resistance.

Part of what we get into and create a problem in our thinking is the way we often speak of the current flowing in one direction or another.

A better way to think of current flow is that the current will flow from the higher potential that we measure as voltage to the lower potential and this set of solenoid and relay shows how that works. as it changes the direction of current flow depending on the situation.

If we are plugged into power and the charger portion of the inverter charger is charging the coach batterie, we might say current ins flowing from the charger to the batteries but if we change the situation and unplug and the inverter portion is then using DC battery form the coach batteries to make AC, the current would then be flowing in the opposite direction!

In a different setup when we are driving and the start battery and engine alternator is higher potential than the coach batteries, the current will flow from the solenoid to the coach batteries to get them charged a bit more. But eh flow is opposite if the boost switch is used to let the coach battery current flow from those batteries to the solenoid and to the start battery to help it!

That leaves the line with the 300 amp fuse as being input or output, depending only on which is higher potential! Very much like water flow, it is hardly ever going from low to higher!

By "weak sister" I just meant that one battery will be weaker than the others in the string and it is more prone to fail as it charges and discharges more, making all the things that weaken a battery happen to it sooner. With lead acid batteries we can spot the weak one by the amount of water we need to add to it versus the others.

In our small operations on RV, there is no meaningful difference in any arrangement of where we connect each input or output as they are all the same point electrically, assuming we do keep them paralleled. If we were speaking of a big operation like a field of solar connecting 50-100 cells stretching over hundreds of feet and many, many connections, we might want to look at what might help but it just doesn't matter on our RV.

[Elkman]

The confusing aspect is that there are two overlapping circuits, one for the inverter and one for the 12-volt circuits in the RV.

The inverter negative lead connects to the negative terminal of one battery and the positive lead connects to the positive terminal of the other battery. There should be a separate negative terminal to negative terminal and a positive to positive terminal to connect the two batteries for the inverter connections.

Additional 12v connections into the battery compartment are from the alternator and the solar charge controller to the batteries. If would be nice if Winnebago labled the wires but they don't bother.

[Morich]

Originally Posted by Elkman

The confusing aspect is that there are two overlapping circuits, one for the inverter and one for the 12-volt circuits in the RV.

The inverter negative lead connects to the negative terminal of one battery and the positive lead connects to the positive terminal of the other battery. There should be a separate negative terminal to negative terminal and a positive to positive terminal to connect the two batteries for the inverter connections.

Additional 12v connections into the battery compartment are from the alternator and the solar charge controller to the batteries. If would be nice if Winnebago labled the wires but they don't bother.

This part is true to a certain extent as it does take both a negative and a positive connection for the inverter to work and that is true of almost all 12 VDC items. But whether that connection is made at one negative battery post or another is of no real value as once there is a solid connection between ALL the negative posts they can be considered the same for electrical purposes, so it just gets down to what fits best mechanically.

As I understand the newer regs for vehicles, using an actual lead back to the battery is required now but before, the inverter negative lead might have simply been grounded to the frame at whatever point was handy.

Whether this is a "fault" by Winnebago to not label the wires depends on outlook since most vehicle wires are not labeled at all while many of the Winnebago wires ARE labeled and they do give us a way to decode the wires.

While we can always look for better service, we should also recognize that Winnebago does go far beyond what Ford or General Motors does to help us repair our own!

Try looking for the wiring diagram for your car to see what a difference there is in available info.

[imnprsd]

I whole heartedly agree: "Winnebago does go far beyond what Ford or General Motors does to help us repair our own!" ...But there is room for improvement.

Moreover, ALMOST every time I try to improve on what Winnebago designed, I end up leaving it alone. This includes color schemes much to my surprise.

After all, I'm driving a 15+ year old RV that still looks and runs great so that counts for a lot!

Anyway, this post is not just about "battery nodes" all behaving alike. It's also about battery cells "equalizing" and what Morich described as trying to prevent a "weak sister" in the group.

I was hoping the way I connect the battery cables would account for these conditions, but it sounds like that is not a factor.

Note: My house batteries are only lasting 2 to 2.5 years; and I never let them fall below the 40% SOC level between charge intervals.

However, I think this relatively short battery life has to do with the fact I drive 6,000-9,000 miles during the summer months; and I have a residential refrigerator.

This means my inverter is always working to drain the batteries; while my alternator and 400W of solar panels on the roof are working to charge the batteries. ...Then I spend 2 months in Montana with shore power.

So let's say I was hoping to "align" my current paths... especially "on the road."

So looking at this problem another way... when the inverter is drawing power out of the battery bank (when I'm driving or boondocking), is there any advantage to a "serial" battery bank vs. a "parallel" battery bank? I'm asking in the event I replace my FLA with LiFe04.

The shorter battery life I am reporting may also have to do with storing my RV without disconnecting the battery cables. ...And on several occasions, after 5-7 months of storage, I have returned to find my batteries really dead due to parasitic drain.

This storage season I moved to a parking stall with 120Vac power and I installed a 17A Victron Battery Charger/Maintainer. So I hope by using this charger will result in longer house battery life. (TBD)

[Morich]

First and foremost of all things to shorten a battery life is letting them go totally down and the longer they are down, the more damage created. That makes anything we can do to avoid running them way down is going to be the first thing to take care of for me. Since we know that there are those parasitic drains on both the coach and the start, even a short term fix of a cheap battery disconnect, just to open when we store can pay for itself in the first storage. Taking the negative lead off the battery will do the same but more effort and grime involved.

But driving should not be a problem for the batteries as the inverter is not really going to be using the battery when the alternator is running. Since current always flows from the higher potential point and the alternator is designed to always put out higher voltage than the battery so it charges them, we can assume the higher voltage is the alternator.

If we have an alternator putting out something like 65 amps available and we are running all the things we can run off the inverter, even the biggest inverter load will be far less then the 65 amp available from the alternator, so that current will go to the inverter as needed and the excess will still be charging the batteries!

The question of serial or parallel connections depends on what we are trying to do. The only time I see going series is if we are using a group of six volt batteries and we need to joint them in series so that two six volt are added together to make the 12 Volt we need. Most of the time we use 12 volt and run them parallel.

But we need to be sure we are speaking the same language as there are lots of small details if we go far enough.
Series--If we use 6 volt, connected negative to ground and the positive of the first battery connected to the negative of the next until we get to the end of string and the output voltage we want. If we use two 6 volt in series we get 12 but if we want 24 volt we can add another pair of six volt inline. Mostly for RV we want just two in series to get 12 volt.

Parallel-- If we use 12 volt batteries and want more storage capacity (more amp hours available) we wire them with all the negative posts connected together and ground while all the positive posts are connected together and run to the load.

But if we want to use 6 volt batteries and also get far more amp hours output, we can go for more complex wiring with series parallel.

Series parallel--If we wire two six volt in series to add up to 12 and do it multiple times on different groups of batteries, we can wind up going as many times as we want and still maintain 12 volts if we wire each set set of two as if it was a single 12 volt battery and wire those sets in parallel.

When is series parallel used? Only when goofy and desperate, perhaps.
Like if the 911 system is down and your battery rack is crushed and there is no AC for way too long, you can build a high amp hour 48 volt system using 6 and 12 volt batteries from all the local auto parts stores!!

[imnprsd]

Thanks for thinking about my 12V system. I appreciate your thoughts

Question: Let's say you want to build a 12V battery system for use in an RV.

Both configurations produce ~410AH to 420AH and cost about the same. This being the case, would you prefer:

A) 3-12V batteries in parallel?

B) 4-6V-GC2 batteries in series & parallel?

[Morich]

Due to cost, ease of replacement, etc. I go with the simple 12 volt and not worry the issue of how long they last as it will be cheaper and easier to replace them if I do keep the coach that long.
Some plan big and others plan smaller and defer the cost. I like to keep my money invested and let it grow to cover any other future expenses as the RV may be just a temporary thing which is gone tomorrow.

Money invested is far more flexible than having a super great battery bank!

But that is just a personal view and I do not have any argument with how others view the same question.

[Bobn1957]

The Winnebago diagram is only drawn that way to allow for the text. Both ways described are correct.