Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

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Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

January 07, 2018, 02:43:51 pm

I would appreciate help with the following installation. We are heading south from the San Francisco area to Anza-Borrego State Park in southern CA around February 10th, and the rv shop I trust in this area has a full schedule and cannot take me in time.

I can obtain the extra cables (2/0?) and connectors and follow your advice for the setup below, but I would also be willing to pay someone who lives near our route south to assist me on our way to Anza Borrego (via I5 to I210 to CA57 to CA71 to CA91 to I15 to CA79).

I have a diagram showing the proper basic way to cable 4 6v AGM batteries for a 12v system. My understanding is that it is conceptually a hybrid parallel/serial setup.

However, in the current setup of 2 6v batteries in a 12v system, I have the following connected: main converter, solar converter, whole-house inverter, and battery monitor with shunt and low-voltage twisted pair to led digital readout panel.

I also have a Progressive hardwired surge/electrical wiring protection unit, but not sure if that is connected directly to the house batteries. Same for a compressor that pressurizes an aftermarket rear suspension air bag system.

If I were replacing 2 batteries with 2 batteries, I could just tag the connections and replicate the current terminal connections. But with 4 batteries in the new setup, which connectors from the 2-battery setup should be attached to which terminals in the 4-battery setup? Is there a general conceptual theory/rule-of-them to follow for migrating the connections of all these devices from a 2-battery to 4-battery array, or is it more complicated?

The old batteries are stored under the rear-facing dinette bench, and the 4 new batteries will be stored in the same compartment.

Thanks--Ted (2004 RB)

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #1 – January 07, 2018, 03:23:12 pm

Ted-

This link shows (mid-page) a 4 x 6V cable layout.

If you have a lot of devices attached to the positive post of the current batteries, and/or the non-battery side of the shunt, you might want to consider adding a positive and/or negative bus bar. A selection can be found here. This would allow you to neaten any cable clutter.

Mark

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #2 – January 07, 2018, 03:32:30 pm

Thank you very much, Mark. Can you shed any light on how to map the connections on a 2 x 6v system to a 4 x 6v system? For example, do I follow the diagram you mentioned for the basic setup and then map the device connections to the two "outer" batteries in the array, the two "inner" batteries in the array, or some other connection mapping protocol from the terminals in a 2-battery system to the terminals in a 4-battery system? Thanks.

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #3 – January 07, 2018, 03:43:51 pm

Since the old batteries are located under the bench seat, the battery wiring has been changed from the stock wiring configuration.
Makes it tough to tell you how to wire it, without looking at it.

The batteries need to be wired into three sets of 2 batteries each and them the three sets are wired in parallel, as you mentioned.
It might not be too difficult, considering you are just adding another two pairs of batteries, with them connected to the existing battery pack.
You might not need to change any of the other wiring, as long as the new batteries fit under the bench without moving the existing batteries.
The surge protector is not wired into the 12-volt system, only the 120-VAC power.

Are you planning mixing old AGMS with new ones? How old are the 'old' batteries?.
Normally it isn't a good thing to mix old and new batteries, getting worse as the age difference, between the old and new, increases.
It prevents getting a full equalization and usually ages the new batteries faster than normal.
I would recommend removing the two old batteries and installing six new batteries.

Larry

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #4 – January 07, 2018, 04:27:42 pm

Thank you, Larry. I have followed your advice for years and value it highly.

Obviously, I was not clear. A bit of history. I replaced the original Trojans with 2 AGMs. The original wet battery tray is also located under the rear-facing dinette bench, so the 2 AGMs reside right next to the original tray under the same bench.

The 2 AGMs are now dying and are being removed and replaced. The new system will have 4 brand new 6-volt batteries (4 x 250A/6v batteries equals 500AH capacity for a 12v system).

I have the diagram to wire a simple 4-battery array. I can follow that. What I need to know is, for the accessory connections (e.g. converter, solar converter, inverter, battery monitor/shunt), to what terminals on the 4 battery array do I move the connections from the 2-battery array?

In other words, if I were simply replacing two batteries with two batteries, I would wire the new ones exactly as the old. But I will be moving connections from a system with 2 positive terminals and 2 negative terminals to one with 4 positive and 4 negative terminals. In addition to the cables needed to connect the batteries to each other (I have the diagram for that) I need to migrate the connections from converters and monitors from the posts on a 2 battery system to the posts on a 4 battery system. That's where I need help.

Am I not understanding the problem correctly with my minimal knowledge of electrical systems, making it difficult for you to provide guidance? I fear that I may be in so far over my head that I cannot communicate what I do not truly understand. If that is the case, I apologize for making this request difficult. Just about all I know I learned on this site. I learn as I go, but have no systematic/theoretical training.

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #5 – January 07, 2018, 05:50:49 pm

Oh, much simpler than I was imagining.
Mount the two new batteries next to the originals.
You will need three new 2-gauge cables (or whatever gauge the existing cabling is).
Install the new batteries first before ordering cables, to allow measuring for correct length, add a little slack.
Leave the existing wiring for the solar, inverter, and other accessories where they presently are, if possible .

Use the 6-volt schematic from the link below, the one on the right side of the screen.
Battery Wire Diagram
Make sure all the negative load passes through the shunt and that the battery terminals are all securely covered, to prevent shorts.

Be very careful not to get the cables mixed up, there is explosive power sitting the the batteries, waiting to be released.
I have a lot of respect for primary battery systems, there are many ways to hurt yourself or the RV if you are not paying attention.

Larry

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #6 – January 07, 2018, 06:40:51 pm

Thanks. At the risk of trying your patience further, could you clarify one point? You say:

"Mount the two new batteries next to the originals. You will need three new 2-gauge cables (or whatever gauge the existing cabling is). Install the new batteries first before ordering cables, to allow measuring for correct length, add a little slack.
Leave the existing wiring for the solar, inverter, and other accessories where they presently are, if possible ."

"the two new batteries"? I am mounting 4 new batteries, not 2. If I place two new ones next to the two old ones, when do the other two new ones get installed and the two old ones discarded?

"Leave the existing wiring...where they presently are...." That would be wiring to the two old batteries. I have the impression you are telling me to leave, for now, the two old ones where they are with all cabling attached. Then place two of the four new ones next to the two old ones. Here is where I get lost. I still need to disconnect the cabling from the old batteries, remove them from the compartment, and install the second pair of new batteries in their place, achieving a 4-brand new battery array with the two old batteries discarded.

Sorry I am so dense about this. Perhaps, if you are willing, we could discuss privately and not bore the group further. If you are willing, please let me know how we can follow up offline. Thanks again for your patience. Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #7 – January 07, 2018, 07:26:53 pm

Ted-

When you are done, you'll have two pairs of 6V batteries (in series, to make 12V) connected in parallel. That is what the diagrams show. All positive leads to your existing equipment can be connected to either of the two 12V positive posts; in the diagram, I'd pick the "top" one.

The negative leads should not be attached directly to the batteries. If you look at your existing negative battery connection, you will see that it is connected by a cable to one side of the shunt. On the other side of the shunt are all -12V connections, including the ground to the chassis. It's wired this way so that all the current in-and-out of the battery passes through the shunt, and thus the battery monitor displays the correct state-of-charge for the battery.

In the new set of four, you can attach the shunt connection to either of the 12V negative posts; in the diagram, I'd pick the "bottom" one.

By picking one end of the battery set for the positive, and the other for the negative, you ensure that both 12V pairs charge and discharge about the same.

As I suggested previously, if you find the positive terminal on the 4-battery set getting crowded, or the non-battery side of the shunt, you can install bus bars to spread out the connections. You can also use the bus bars instead of cables to connect the 12V battery pairs together. This does not reduce the number of cables, but it could help neaten things up.

Mark

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #8 – January 07, 2018, 08:40:28 pm

Terrific, Mark. Exactly what I needed to know.

I take it a bus bar is a heavy piece of metal connected to the positive terminal with "extension" terminal post connectors on the bus bar, so that all the connections do not need to be piled on the positive terminal post on the battery itself. Is that correct? Is there anything special to look for in purchasing the right/best bus bar?

Also, the total capacity of the array is 500 AH at 12v. Are the existing 2/0 cables (from the old 2 battery, 300AH at 12v system) sufficient capacity or are heavier gauge cables advised (3/0, 4/0)?

Final question (I promise). I read somewhere that although the general rule is to use the shortest cables possible, one should use cables of the same length throughout to achieve equal resistance across the 4 batteries and, thus, ensure equal discharge and charge among the batteries. Does that make sense to you or should I just use the shortest possible cable, with a little slack, for each connection?

Thanks a million. I think I can do the job now with your instructions.

Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #9 – January 08, 2018, 12:22:06 am

While it's possible to add an extension to a battery post, a busbar typically is a separate item. See for example, the four-place Blue Sea #2104. You'd run a short, fat jumper to the one terminal of the busbar, then connect your loads to its other terminals.

You will also want to make certain you have adequate fuse protection. Those four big batteries pack a helluva wallop. And if you have a whole-house inverter, you're probably doing things like running the microwave oven, which draws 100 to 150 amps at 12 V. In that kind of setup, you'll probably want a 200 A class T fuse and matching fuseholder.

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Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #10 – January 08, 2018, 03:45:17 am

Quote from: LD-TED - January 07, 2018, 08:40:28 pm

Also, the total capacity of the array is 500 AH at 12v. Are the existing 2/0 cables (from the old 2 battery, 300AH at 12v system) sufficient capacity or are heavier gauge cables advised (3/0, 4/0)?

Final question (I promise). I read somewhere that although the general rule is to use the shortest cables possible, one should use cables of the same length throughout to achieve equal resistance across the 4 batteries and, thus, ensure equal discharge and charge among the batteries. Does that make sense to you or should I just use the shortest possible cable, with a little slack, for each connection?

Are you running any high amperage devices, such as a large inverter? If not, the 2-gauge cable will be adequate.
You really don't want to get involved with 3/0 or 4/0 cabling.
Since the batteries are to be located close to each other, a few inches difference in battery cable length isn't a concern, it's more of a problem when the batteries are well separated.

Larry

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #11 – January 08, 2018, 03:44:10 pm

Thanks for your response, Larry. I am running a Xantrex 1800w modified sine wave inverter mounted on the inside side wall separating the original battery tray and the remaining cavity under the rear-facing dinette bench where the batteries also reside.

The microwave is hooked into it so we can do short bursts of the microwave without starting the generator.

The fridge is also wired into the inverter. Its purpose is to allow us to shut off the propane tank while the coach is rolling down the highway, and power the fridge electrically through the inverter. Of course, the fridge is never powered through the inverter when the coach is stationary, which would discharge the batteries in a matter of minutes (had a close call once).

Current cabling is 2/0 for this configuration.

Does that give you the info you need to advise further on cable gauge?

Thanks again for taking the time to respond. Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #12 – January 08, 2018, 03:50:26 pm

Andy, thanks for your response. I had a big T fuse and fuse holder installed (about $40-50, as I recall) when I had the Xantrex 1800w MSW inverter installed. But I'm glad you mentioned it, so I can check to be sure it will be adequate with the 4 new batteries.

I am getting the impression that it is the power draw that matters for the fuse and for the cabling, not the capacity increase of the batteries themselves. This project involves only replacing 2 batteries with 4 batteries and increasing system capacity from 300AH to 500AH. No change in power draw and the four batteries will reside where the two batteries are now, so no appreciable differences in cable lengths.

Does my response make sense in addressing your comments?

Thanks for your help.
Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #13 – January 08, 2018, 04:18:12 pm

New 2/0 cables will fine be fine.
Now, all you need are these tools.
Specialty tools needed for inverter installation | Top- adju… | Flickr

West Marine used to crimp lugs on cable bought there. Some truck part and repair centers crimp lugs too.

Larry

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #14 – January 08, 2018, 05:04:01 pm

I may never do this again. Does it make sense (cost) to buy the tools and to fabricate my own cables if I am unlikely to do it again? I thought I would just measure and order premade ones. Bad idea?

I couldn't find convenient local sources for premade cables, so I had planned to order them online. I didn't think to check truck repair places. Also, are you saying west marine doesn't do it anymore?

thanks--Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #15 – January 08, 2018, 10:10:18 pm

Mark, Larry, and Andy--

A fellow Lazy Daze owner in my area will help me with this installation. He found out that a NAPA store near where I store my LD will assemble 2/0 cables for me.

I am indebted to all of you for patiently closing my wide knowledge gaps. Thank you for your time and expertise, once again.

Happy New Year to all--

Ted
2004 RB

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #16 – January 09, 2018, 11:39:52 am

"I am getting the impression that it is the power draw that matters for the fuse and for the cabling, not the capacity increase of the batteries themselves."

Right. If your power usage isn't going to change and your electrical system is already set up to handle it, adding batteries won't require a different fuse.

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #17 – January 09, 2018, 07:31:12 pm

Hi Ted.
That was fun helping install your 4 new 6 volt batteries.
The guy at the local NAPA Auto parts did a great job on the cables. They fit perfectly.

Hope you can do a write-up with pictures.

Total time 3 hours.

Happy trails,
Rod M.
redbirddog - a hungarian pointer (vizsla) blog

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #18 – January 11, 2018, 11:43:44 am

Rod was a life-saver. Did a great job. Will post pics as soon as I figure out how to do so.

Thanks, Rod and all for the help

Ted

Re: Proper cabling: replacing 2 6v AGMs with 4 6v AGMs

Reply #19 – January 11, 2018, 12:15:19 pm

Photo with text now up. Trying for first time to do this. Hope it works. See:

http://www.lazydazeowners.com/index.php?action=media;sa=album;in=551

Ted

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