Wiring my new LiFePo4 Batteries

[Griswald One]

I am getting closer to installing my new LiFePo4 batteries and trudged up through snow today to go have a look at my current wiring configuration and start to plan the new set up. I will be installing 2 new 200ah Renogy LiFePo4 batteries replacing the existing 4 FLA's.

The current set up has two racks with two batteries per rack. I labelled them for myself starting in the top left corner as battery A and proceeding clockwise to D. The batteries are currently wired in Series/Parallel with A/C and B/D connected via the +/-. A/B have the positive connection and C/D have the Negative.

Looking at the house connections. A is connected via the positive terminal to the inverter/converter via a fuse bar and D is connected via the negative.

C is the negative to ground via the frame. B is also connected via the positive terminal to a fuse bar and then into the house... this is the one I don't quite understand? Where would that be going??? I freely admit I don't fully understand the energy flow and how the various parts cross paths.

The new set up will be the two batteries in parallel with each battery connected via the positive and negative posts. Luckily they fit in the existing racks... just! The space is not currently conducive to utilizing Bus Bars to connect everything, but I could fabricate the changes if truly needed. But my thoughts were to connect the Inverter/Converter via the Positive on Battery 1 and the negative on battery 2. Then put the ground on Battery 1 and the 2nd positive wire on battery 2??? Would this be the appropriate set up?

2nd question... If i want to add a battery disconnect, will this mean I actually need two, one for the negative going to the inverter/converter and one for the cable going to ground?

[Visionquest2]

All previous posts on the topic of 2 lifepo batteries in parallel recommend taking the ONLY positive connection from say "A" and the ONLY negative connection from say "B". keep the +to+ and -to- connection cables short and equal in length. That is the recommended way to maintain EQUAL loading and draw down of the two batteries.

[workingonit]

What you describe in your new configuration is a series circuit. This will give you 24 volts DC not 12. I assume you want 12 volts. Based on the previous 4 batteries in sets of 2 I would think you will need to use one battery in one circuit and the other in the other circuit. So basically replace 2 batteries with one in each circuit. Without knowing what you have exactly it's hard to make a recommendation.

[Mudfrog]

I think I understand what Griswald is saying but I'd still want to be absolutely positive before trying to answer. Sure wouldn't want to cause a bunch of sparks. Clark, posting a picture of your present battery connections would certainly help to get the right answers.

[PS89]

Just consider that each pair of 6 volt batteries currently in a series circuit arrangement is the equivalent of a single 12 volt battery. Once you master that concept, the connections for the replacement 12 volts batteries is easy.

[SafariBen]

Need to know, and better yet, see, the cables hooked up.



Call the new batteries X and Y, positive cable to X and negative cable to Y, with a jumper between positives, and a jumper between negatives. That will give you as equal current/voltage as bus bars will.

[Griswald One]

Here are quick sketches of the current wiring and the proposed wiring.

My understanding of properly balancing two batteries with a standard single positive and single negative feed out is to use the positive post off of one battery and the negative off the second while connecting the two batteries in parallel. So in the case of the inverter, the positive post on battery X and the negative on battery y. That part of my plan is as per Renogy's instruction for second best set up... they prefer the use of Bus Bars.

The lines between +/+ and -/- are meant to indicate jumpers... andthen the outfeeds from there.

It is the second positive feed and the ground in the current set up that are causing me consternation. My thought was that by using the second set of connections, so the y positive and X negative to ground I was continuing to balance the load?!? Part of this thought process stems from the fact they were separated on the original setup.

[SafariBen]

I agree with your first pic as being balanced. Only issue would be if one of the jumpers acts up it may be more confusing to diagnose than bus bars.



The second drawing has three leads labeled house, so not sure what's up.

[Griswald One]

Originally Posted by SafariBen

I agree with your first pic as being balanced. Only issue would be if one of the jumpers acts up it may be more confusing to diagnose than bus bars.



The second drawing has three leads labeled house, so not sure what's up.

I probably should have relabeled my original scratch drawing... The three marked house are A+ and D- to the Inverter and then B+ to the unknown...

Would the unknown be to the starter on my Genny? If yes would that be why the original set up seperated its connection from the inverter?

[SafariBen]

The unknown would be to the house 12V loads, and the generator if it's on the house battery.

[oldenavy]

A few points.

1) if you install disconnect switches, do that on the positive side, not the ground/negative side. Li batteries have very low internal resistance, so disconnect switches are a very good idea.

2). The way you have drawn it is fine. Or, you can place both positive leads on one battery and both negative leads on the opposite battery. Be sure your jumpers are rated for full inverter + house current. The important thing to remember is that you must put the negative lead on the opposite battery from the positive lead. That keeps the impedances equal and will keep both batteries drawing down equally.

3). With Li batteries, your voltage doesn’t vary much until they are almost drained, so think about installing a shunt. Otherwise, you really have no clue what your state of charge is. If you do, then your drawing doesn’t work any longer. For the shunt to correct measure the amps in/out, it needs to be placed between the battery negative and ALL loads. In that case, you want both positive leads on one battery and a new jumper from the second battery to the shunt. Both negative leads then go to the other side of the shunt. Here’s my favorite:
https://www.amazon.com/Victron-Smart...LX2SYG6DY&th=1

[oldenavy]

Just re-read your switch question. You can have just one disconnect switch if you add a jumper between battery positive and the switch. Then attach both inverter and house positive leads to the other side of the switch.

[Griswald One]

Originally Posted by oldenavy

Just re-read your switch question. You can have just one disconnect switch if you add a jumper between battery positive and the switch. Then attach both inverter and house positive leads to the other side of the switch.

Had not thought of that option. I assume if I were to do that then the negative to the inverter and the ground should both be moved to the same negative post on the opposite battery from the positive jumper?

You also mentioned the shunt, the batteries actually came with one it was part of Renogy's current promotion. I do wonder though how redundant it is. I say that because the onboard systems do give me limited information including current SOC and amp draws. In addition the batteries have onboard Bluetooth which seems to give all of the same information a shunt would. Further to that, I have 4 slideouts which make finding a natural location to bring the wiring for the monitor into the coach a logistical nightmare.

[Punkinhead]

Life is easier when you use bus bars.