Puzzled by my coach batteries

Oldchinahand · 11-26-2018, 03:15 PM

Thought I had a shade tree's understanding of electricity but my coach batteries puzzle me.

I am running four 6v deep cycle. Due to the geography of the battery drawer, I use a battery minder system to top off the two batteries in the back. We keep the rig connected to 50amp when she is snug in her berth alongside the house. I generally check the batteries weekly. Boil off, etc

The two "front" batteries seldom need topping off. The "back" two always do.

Your thoughts appreciated.

Fair Winds and Following Seas

**creativepart** · 11-26-2018, 05:25 PM

The only thing I can guess is that the minder's clips are attached at the post where the cable running to the forward batteries is on top of the post. So, the power is going to those front batteries and in essence skipping the rear batteries.

I'd put one minder clip on a positive post on the "first" front battery and the negative clip on the "last" negative post of a rear battery.

I say that... because that's what I've done on 4 batteries wired in parallel and it worked. I'm kind of befuddled how that would work when the 4 batteries are wired in series.

I still don't know if I've worded that correctly.

Oldchinahand · 11-26-2018, 07:07 PM

Creativepart you worded it perfectly. I confused the issue by referring to our Flow-Rite battery filler system as the battery minder.

Your thoughts generated Eureka moment. I just crawled under and laid a multimeter on the genset starter lugs. Getting 6v. Should be 12v.

Tomorrow I will go through all of the various cables that are attached to the coach batteries.

How does all that tie in? We recently had warranty replacement of one of the four 6v batteries. Then we left for our fall trip. The genset would only start if we fired up the Cummins first. Been back a few days and had getting after that issue on the front burner. In addition to the minder wring, bet I find a series vs parallel situation.

Fair Winds and Following Seas

BobC · 11-26-2018, 07:28 PM

If I understand your setup, you have two sets of 6v batteries. The two batteries in each set are connected in series (pos to neg) so as to act as a single 12v battery. These two "12v batteries" are then connected in parallel (pos to pos, neg to neg) to create the equivalent of one very large 12v battery.

Let's look at it this way:

12V Pos>+BattA- Connected to +BattB-<12V Neg

12V Pos>+BattC- Connected to +BattD-<12V Neg

These two sets are connected in parallel, BattA Pos to BattC Pos and BattB Neg to BattD Neg

Electrically, as long as you connect the Battery Minder to any pair of the posts labeled "12V Pos" and "12V Neg", you should be fine. Any difference in water boiling off would be related to something else, such as the condition of the batteries.

I'd have to think about what would happen if you connected to any other combination but, in any case, it would be incorrect.

Morich · 11-26-2018, 08:54 PM

Truth is that batteries are sometimes weird little things that have "personalities" that we can't always see. I have to assume part of it is simply tiny differences in the materials and how they are put together when new as well as where they fall in the string.
I'm thinking of the big strings of battery cells where 24 cells were connected to make a 48 volt battery supply. They were built, installed and connected in a long row where one was an near alike as possible to the others but they did behave differently. Some just seemed to take more water than others and some would take far longer to fully recover after a loss of power where they were run down.
Looking at the connections and cleaning is always a good thing but you may never find why some act so different.

BobC · 11-27-2018, 05:11 PM

This is probably what creativepart was saying and may be helpful as you fine-tune your cabling. It turns out that I was wrong in my earlier statement about the choice of pos and neg pairs was electrically equivalent.

https://www.impactbattery.com/blog/t...s-in-parallel/

In your case, however, Battery A is actually two 6v batteries in series and Battery B is two 6v batteries in series.

Also, if any of your four batteries are weak or bad, they should be replaced. All four need to be identical or similar in condition.

**creativepart** · 11-27-2018, 05:15 PM

^This is what I was initially getting at.

Though this article is for parallel wiring I was suggesting the same thing would count for 6v batteries wired in series to create 2-12v battery groupings.

Oldchinahand · 11-30-2018, 09:33 PM

Thought I'd circle around with the fix, rather than leave an indeterminate thread.

As usual, a series of operator errors. Would like to blame someone, but it's my rig.

As you all deduced, we run four 6V deep cycle batteries wired series parallel giving us in effect two 12V batteries in series. As they sit in the battery drawer, two are "outside" and easy to service, two are "inside" and require a Flow rite filler to service.

Then one "inside" 6V battery developed a pronounced bulge and would not take a charge. We had it replaced. All four had to be taken out for access. I should have "trusted but verified" and didn't. The battery bank was wired in parallel when they were put back in. Giving us in effect one 6V battery. One of the four new, three past expected mid-life.

Not knowing, I did not adjust the charge rate. So it was charging "hot". Added to that, our niece was in town for about six weeks for a class out at the U. We used the rig as a guesthouse. The coach sat plugged into our 50AMP outlet so she could have AC. She left. We left on our fall trip. Fought with the generator starting.

So, we took on board all your good thoughts and bit the bullet. Replaced all four batteries. Our battery source was decent. Replaced the newer battery, now bad too, as warranty, replaced the other three for price of two. We all went over the wiring setup together. Checked for 12V to the genset.

As to the excessive boil-off, the dealer advises it is common for the two batteries in parallel/series set ups that all the + & - cables and minder are attached to, to use more fill water. The "hot" charging rate and extended time plugged into 50AMP exacerbated that.

Thanks for all your advice. One issue down. Without a doubt more to arise.

Fair Winds and Following Seas

Morich · 12-01-2018, 08:49 AM

Quote:

Originally Posted by Oldchinahand

Thought I'd circle around with the fix, rather than leave an indeterminate thread.

As usual, a series of operator errors. Would like to blame someone, but it's my rig.

As you all deduced, we run four 6V deep cycle batteries wired series parallel giving us in effect two 12V batteries in series. As they sit in the battery drawer, two are "outside" and easy to service, two are "inside" and require a Flow rite filler to service.

Then one "inside" 6V battery developed a pronounced bulge and would not take a charge. We had it replaced. All four had to be taken out for access. I should have "trusted but verified" and didn't. The battery bank was wired in parallel when they were put back in. Giving us in effect one 6V battery. One of the four new, three past expected mid-life.

Not knowing, I did not adjust the charge rate. So it was charging "hot". Added to that, our niece was in town for about six weeks for a class out at the U. We used the rig as a guesthouse. The coach sat plugged into our 50AMP outlet so she could have AC. She left. We left on our fall trip. Fought with the generator starting.

So, we took on board all your good thoughts and bit the bullet. Replaced all four batteries. Our battery source was decent. Replaced the newer battery, now bad too, as warranty, replaced the other three for price of two. We all went over the wiring setup together. Checked for 12V to the genset.

As to the excessive boil-off, the dealer advises it is common for the two batteries in parallel/series set ups that all the + & - cables and minder are attached to, to use more fill water. The "hot" charging rate and extended time plugged into 50AMP exacerbated that.

Thanks for all your advice. One issue down. Without a doubt more to arise.

Fair Winds and Following Seas

Nice to have the update and I have to say it matches what I often find on batteries. We think they are so simple, we sometimes screw up! And it does help to keep the charging even as possible on all cells in a string. But in our small strings of batteries like under 6 cells, it often is not practical to do the extra needed to make all cells get exactly the same charge/discharge, so we have to kind of live with less than optimum operation as watering and or replacing the batteries can be better than the extra needed to do it a bit better.

BobC · 12-01-2018, 10:54 AM

When I've screwed up on batteries it seems to result in sparks and smoke!

Ray,IN · 12-02-2018, 09:11 PM

"One battery was replaced" out of a bank of four, of which you state are 3 are mid-stage. It's never good practice to replace only one of a bank of batteries unless all battery cells test the same and are of approx the same ages..
I had one fail a few years ago, entire bank still under warranty. I strongly requested Exide replace all the bank due to different stages of wear N tear; they reluctantly complied .