Roadtrek E-Trek Battery Replacement

[booster]

I hear, and understand for the most part, what GerryM is saying, but am having a very hard time relating it to what I have seen in our system when I have tested it. Certainly not as long a voltage string, same number of parallel, in ours, compared to an etrek. On top of that is that I have seen more and more recommendations of adding the "balancing" connection between the center connections of parallel strings, so I do wonder why.

I think, and if I am incorrect I would really like to know it, that the ideal system, no matter how cabled, would have the same current and voltage at each and every battery in the grid. If I take that as the basic premise, I come up with some other offshoots, which may or may not be totally accurate, but make sense.

If two batteries are in series, they will split the charge voltage based on subtle variations between them. Current is forced to be the same. I have not seen this to change over time as they are used by very much, although our wet cells in the old system did slowly move closer together by a bit.

Two batteries in parallel are forced to see the same voltage across them, but current can vary depending on the same type of variations.

The current in a series string should be controlled by the weakest acceptance/discharge of the string.

The current in the parallel string will be an average of the two batteries capability.

The voltage in the series string varies by battery, but overall is constant. In the parallel string, the voltage is constant for both.

What keeps coming back into my, non electrical, engineer's mind is that whichever system does the best job of averaging the inherent variations in the batteries should work the best, as the batteries are closer to equaling sharing the work.

In a series string all the batteries see the same current by physics, so no averaging can occur. The voltage is split up by the inherent variations of the individual batteries, so it appears that this would also mean no averaging could occur.

In a parallel setup the batteries see the same voltage so no averaging there. The output from them is the average of the two batteries output, but the individual batteries still are putting out different outputs. This is where it gets a bit questionable. From what I have seen, if you have two batteries in parallel, and do a good job of complete charging (hugely important), one will be slightly overcharged and one will be slightly undercharged at full charge if you stop at the midpoint. We all know that both are bad and can affect capacity and life of batteries. We also know that undercharge can "walk down" capacity even if it is a small undercharge. Most say the a small over charge is not very damaging, and might actually help some batteries. If the above is true, the higher capacity battery will walk down to the lower one and then stay there, it think.

I would think, if you add the balancing jumpers in a series/parallel string, your voltage variation across any give place in the series string should drop by about 50% based on random battery variation averaging. To me that seems like a good thing. As more strings were added the averaging would be even more, so variation should be around 25% for a 4 string setup with the jumpers.

Of course, this blows any chance of accurate monitoring out the water as there is really no practical way of measuring voltage and current on individual batteries, but how many of the RV's in the world have anywhere near that kind of monitoring.

One thing I can say for sure, as opposed to all the theories above, is that when I had series strings, then paralleled, when I isolated the batteries I had batteries at 4 different voltages which stayed that way after sitting for days. When I had parallel first, then series, I had two pairs of batteries at the same voltage which were different from the other pair, but under 1/2 the variation I saw in the series/parallel setup. The parallel first setup also showed about 1/2 the variation in amps to each battery when charging on the individual batteries.

Of course, I realize this is a sample size of one, so it is statistically insignificant, and that at least some of the results could have been influenced by the random locations of the different batteries, as I did not do a full 16 placement variation grid. I would say, however, that the results do seem to line up % wise fairly well with the idea of what might be expected.

My big question at this point would be, what would be the downside of adding the balancing jumpers in a series/parallel grid, aside from complexity and monitoring? The ones I have seen used full sized cables, but they will be carrying tiny currents in real life, so they could be much smaller. I just seems like it might be a good idea.

[Boxster1971]

GerryM in reply to your comments I've entered responses below:

24 -I did not follow the evolution of your battery system. Are you using the chassis as the negative connection to your batteries or a cable-run? Perhaps both the negative and positive runs are on the same side of the coach?
No I'm not using the chassis as negative connection.

25 - I am sure you chose your layout for sound reasons to suit your particular coach and needs. I am addressing others eying your setup with the intent of creating something similar for their coach.
Yes I have two 6V AGM batteries on each side of the van mounted on racks under the van just behind the rear wheels on each side. I mounted them under the van to preserve interior storage space. I also added a 2000 watt inverter/charger which had to be mounted inside.

26 - I am glad you chose the parallel string setup. You do not show a fuse in the negative end of each string, as a short to chassis at the positive end of the bottom battery or above would be dangerous. It would also involve both strings. An internal failure of one string should not affect the other string, which should survive and continue to serve.
I have a fuse on each positive terminal of the 12V series pairs. There is a 4/0 cable from each end of the 12V series pair going up through the van floor next the battery racks. The cables meet in the middle of the van. The positives cables are attached to a three lug terminal bar to feed the Class T fuse for inverter and distribution to solar, chassis battery isolator relay and the 12V house fuse panel. The negative cables are attached to a shunt on a common stud, no need for terminal bar on negative side. The positive and negative cable terminations are in middle of van with offset to make total cable loop, of about 60 inches, from each series pair on curb and road side of equal length.

27 - If the chassis is used for the negative run to the battery-bank and depending whether the distribution panel for 12 volts is on the street or curbside, the layout could be configured a bit differently to take advantage of the battery terminals as 12 volt take-off points. Furthermore the bottom battery of each string would be on one side of the aisle and the upper battery for each string on the other side of the aisle.
As mentioned earlier I'm not using chassis for negative from batteries. Distribution panel is in center of van just where Airstream placed it under the rear lounge seat/bed.

28 - Fuses for one half the total current demand on the battery bank, mounted directly on the negative terminal of the lower battery of each string, are in turn connected to chassis/ground.
Your suggestions to mount fuses on the negative terminals is not standard in RV and boating industry. My fuses are on the positive terminals.

29 - In place of the negative and positive buss-bar/stand-off, the two cables across the aisle could be one piece, joining the positive of the battery forming the lower part of each string on one side of the aisle to the negative on the battery making the upper part of each string on the other side of the aisle. Power in and out is taken from the tied together positive posts of the upper batteries of the two strings.
Only using short bus bar on positive side. My batteries are widely separated, thus the need to bring the parallel connecting point into middle of van near the distribution area.

30 - If additional battery capacity becomes necessary, and there is space for one additional battery on each side of the aisle, the system can be expanded to three parallel strings each carrying one-third the total current. Weight continues to be evenly distributed left to right.
There is no space in my van for more batteries without giving up cargo storage capacity. I also don't plan to need more capacity in this van. If I need more it will be a new van with lighter LiFePO4 batteries. I'll post a wiring diagram of my 12V system when I'm able to get to my desktop PC. Hope this helps understand my layout.

[gsm]

Booster # 101, Boxster # 102 & All


Booster

I am philosophical about lead-acid batteries. Sure you can be kind to them, you can do dumb things. They tend to be stubborn in death. When they work they are sloppy performers.

We are dealing with a relatively robust 150 year old technology that has over the years seen improvements but still retains most of the imperfections inherent in its very nature. Lack of complete control and uncertainty irks modern man and he tends to agonize endlessly over it. All this is reflected by the multitude of often very contradictory studies out there.

In your new system you are dealing with just four batteries and already unknowns and uncertainties have multiplied, and there is tentativeness about everything other than the battery-weight and dimensions. Your adventure in return current is indicative of the overall haziness of the situation. Just because the measurement of one parameter is more intellectually satisfying does not mean overall performance is better. Feel-Good battery connections are just that. You effectively said so in the bottom line of Post 101.

Every electrical parameter of a battery is subject to temperature, and has a spread of values with a probability attached. The spread and probability is seldom if ever touched on in data sheets, and nothing more specific comes with individual batteries.

When building high capacity battery banks for higher operating voltages should some of the levels be paralleled by jumpers, other levels not jumpered and operated as pure strings, because some batteries perform marginally better on one parameter or other? How and on what basis do you choose? And how can this even be physically realized?

What should one do to characterize batteries sufficiently to place them in the best combination of positions in a particular configuration? For how long would that characterization apply after the configuration is put into service? Must one be willing to repeat the characterization on a monthly or biannual basis, and shift batteries according to new data? Is the work worthwhile? Do the test themselves change the battery, do the results reflect the in-situe behavior? If one did all that, would one gain significantly longer service live, significantly more Amp-Hrs, or would the very activities be detrimental to achieving best results for minimum investment? How ever one chooses to quantify benefits, would one be able to project with enough certainty that one will realize them?

I think optimization is largely a pipe dream. There is many decades of experience with lead-acid batteries, any unknowns and uncertainties should have been long ago resolved. But they have not. Is it because batteries are much like balloons? Confine them in one direction and they come out in another? They are beasts that can be herded in the same direction, but not the same pattern. They can never be completely predicted and harnessed.

After philosophizing about the tip of the iceberg, and knowing there is 90 percent of it hidden, what choices/goals does it all lead to when building a battery-bank.

Ignoring original design goals/parameters, cost, physical size, weight, etc. and focusing on satisfactory operational service of the battery-bank we have such as the following;

- Maintain capacity, and service life
- Provide the most supportive installation environment
- Obtain early warning of deterioration and impending failure
- Ensure easy fault location and problem isolation
- Ensure survival of partial service such as 1/2 of capacity
- Design for easy full service restoration such as battery replacement
- Protect from devastation should Murphy's Law come into play
- Etc.

Boxster

Experience has taught me and many before me that Murphy is always ready to pounce. Doing the conventional with respect to fusing does not offer protection from all eventualities. It takes only the contact of one errant wrench-handle that welds in place under the battery current available, to take out not only batteries, but all related wiring, and can set the coach on fire. You cannot claim your losses from the insurance company by quoting a convention. Have a good look at what could happen in a road-accident or if some service technician, not familiar with your battery installation, works in the vicinity of the battery system/wiring. A 100 Ampere fuse in the negative-leg of each battery string offers another layer of protection.

It is fundamental to all fusing considerations to deal separately with protecting circuits fed by the battery, and protecting the battery system itself.

This is not some smart-ass comment, it is just the best advice I can give.

Best Regards All
GerryM

[booster]

GerryM, I think you are missing my point, which really doesn't contradict what you are saying.

The change in return current was an "indicator" if you will, of something changing with the different wiring setup. I readily admit that I have no idea why it changed or if it means anything in reliability.

What was of more significance to me was that with parallel first setup I had 1/2 as much voltage variation across the 4 individual batteries (6 volts nominal). Everything I have ever seen says the closer the batteries see to the same voltage the better, and this was a 50% improvement in voltage variation. The voltage drop improvement also carried over to the amps to the individual batteries.

I also never said to sort or try to optimize by other battery specific methods. What I did say was that if you add the jumper between the middle batteries of the strings, you effectively average those batteries variations, which statistically should be more likely to make the series of part of the strings less variable for voltage split.

Could my setup have been random chance? Of course, but the only way to prove it would be to do the full grid of combination mixes of the batteries and wiring style, and it is too late for that. I had done a couple of different combinations early on with the series first setup to see if it would get more even by rearranging the battery positions (it didn't help enough to make any real difference), but didn't do anything like a full grid.

Of course, I also don't see any harm in adding the jumpers, either along with the fact I think they would help. The only thing I have heard that would say not to use them was that it made it harder to troubleshoot big banks, but that was also for a UPS system.

I do also think that information from UPS systems doesn't really apply to the cycling that we see with the RV batteries very well, as UPS batteries are on float 99+% of the time, which tends to equalize everything a lot more, with near zero current, than when the charging currents are high and impedance is a larger factor in creating error.

Of course I could be totally wrong, but I see more positives to the jumpers than any potential negatives in the information I have seen and tested.

[booster]

I finally tripped across a source of information on the question of using the "balancing" cables between the batteries in parallel strings. I was looking for something else and found this in the Fullriver battery installation manual. I wish they had some explanation of why with it, but they do both plus and minus.

[markopolo]

That's very interesting Booster. I downloaded the manual & read through it. It looks to be a great source of how-to-wire info.

The cross ties do make for the same voltage but overall setup can still be far from balanced as demonstrated by photolimo's posted info:

Quote for background info:

Series:
A + B + C + D
6.33v + 6.43v + 6.94v + 6.88v = 26.58V

Series:
F + E + G + H
6.34v + 6.43v + 6.94v + 6.88v = 26.59V

If balanced, you'd expect to see:
6.65V + 6.65V + 6.65V + 6.65V = 26.6V

Info Source: http://www.classbforum.com/forums/f5...html#post35767

With the cross ties he ended up with:

parallel 6V point: B & E = same voltage (6.43V): low - should be 6.65V
parallel 12V point: A & F = same voltage (6.34V: low - should be 6.65V
parallel 18V point: C & G = same voltage (6.94V): high - should be 6.65V
parallel 24V point: D & H = same voltage (6.88V): high - should be 6.65V

Group BE: 6.43V
Group BE/AF: 12.77V
Group BE/AF/CG: 19.71V
Group BE/AF/CG/DH: 26.59V

[booster]

Yep, it certainly won't/can't totally balance all 8 batteries. At best it can take the issue of having 8 mismatched voltages and turn it into have 4 mismatched voltages. It probably would simplify the use of a balancer or balancers, though, as it is more like 4 bigger batteries than 8 singles.

I don't understand the tieing of the neg and pos, though, as they are the same point electrically. All they would be balancing would be any resistance variation in the cables or connections.

[booster]

It is winter, van is done, I have too much time on my hands, maybe. Stuff that doesn't make sense to me, commonly called the "giggle test" most places I worked, bug me nearly forever until I can find out enough to put them away. The parallel jumper thing is doing just that to me.

In the last post that showed the Fullriver pic, I had mentioned that maybe the balancer jumpers would also simplify balancer use, so I decided to look at some balancer manuals to see what they recommend. Victron is always near the top of the heap on stuff like battery life issues, so I started there.

In there manual for their standard battery balancer, they show a couple of recommended installation illustrations. I found them pretty interesting.






It appears that in both of these series/parallel setups the batteries are wired with the "balancer" jumpers between the intermediate batteries on the different parallel banks. The connections are shown as a size matching the basic wiring not the balancer install wiring is why it looks that way to me.

They also use the same 3 balancers when they go to a single string of 4 series batteries, or 3 parallel strings of 4 series batteries, so they are counting on the jumpers to balance the same voltage, jumpered, batteries and the balancer sees the averaged voltage of them.

As with all the things we seem to see, no real explanation of why, or how well it really works, but Victron does really know their stuff. It would also indicate that Roadtrek did need the jumpers on the etreks, at least once they put a balancer in them.

I think this would also apply to a lesser degree to systems without balancers, but without any input from experts, that is just a guess.

[gregmchugh]

It was never clear to me if the Viltron Battery Balancer is only designed for balancing 12v batteries or if it would work on 6 volt batteries. It will only trigger with charge voltages for a 24 volt input so it seems to not work for 6 volt batteries.

[booster]

Originally Posted by gregmchugh

It was never clear to me if the Viltron Battery Balancer is only designed for balancing 12v batteries or if it would work on 6 volt batteries. It will only trigger with charge voltages for a 24 volt input so it seems to not work for 6 volt batteries.

They are kind of squishy in how they list the specs, but I do think you are correct that the individuals would have to be 12v, or I suppose you could do 6v pairs also, but then you would lose some balancing benefit They probably are targeting the big 4C and bigger 12v applications.

The illustrations were mainly to show how they wired them and balanced, not necessarily that the Victron would work on a Roadtrek. IIRC, the one they put on the Roadtreks did just balance the 12v series pairs, not the individual batteries.

[gregmchugh]

Yes, the Cooper battery equalizer is a different beast with the capability to provide high currents at the 12v output and it also is active all the time, not just when charging.

[Boxster1971]

Do any of the sources say what size wire should be used to cross tie parallel string? Looking at the diagrams I get the impression that the typical cross tie currents would be fairly low, just enough to balance the batteries in the string.

[booster]

Originally Posted by Boxster1971

Do any of the sources say what size wire should be used to cross tie parallel string? Looking at the diagrams I get the impression that the typical cross tie currents would be fairly low, just enough to balance the batteries in the string.

Not that I have found, but there are so few sources that even show using the jumpers I guess that is not surprising. They look to be smaller on the Victron illustrations, and logic would say they could be very small as they would carry very low current, as you say. I think the only exception would be if there was some kind of battery failure that might alter the current flow.

[photolimo]

Originally Posted by booster

I just looked at the "etrek supplement" owners manual for 2014 on the Roadtrek site and it says the batteries are covered for 6 years. If you don't have a copy with your literature, I would print one out so you have it if you need it.

Could you send that my way? Cannot seem to get the PM's to work properly.

[gregmchugh]

Originally Posted by photolimo

Could you send that my way? Cannot seem to get the PM's to work properly.

You can get it here...

Support & Contact | Roadtrek

[photolimo]

Originally Posted by gregmchugh

You can get it here...

Support & Contact | Roadtrek

Our's is a 2013 which is not available for download there.

[booster]

The one we were talking about is under the 2014 owners manuals at Roadtrek. IIRC, at the time, the conclusion was that it was for the earlier ones also.

[booster]

Here is a link to earlier in this thread where Marko said he found the 6 year warranty on an older etrek order sheet, so it had to be on when yours was sold.

http://www.classbforum.com/forums/f5...html#post35330

On edit---found the post with order sheet and it does specifically say 6 years on the battery.

http://www.classbforum.com/forums/f5...html#post12678

edit again--looking closer, it has a price on the 6 year warranty, and listed as on option, so you would need to check the original window sticker to see what it says.

[photolimo]

Originally Posted by booster

Here is a link to earlier in this thread where Marko said he found the 6 year warranty on an older etrek order sheet, so it had to be on when yours was sold.

edit again--looking closer, it has a price on the 6 year warranty, and listed as on option, so you would need to check the original window sticker to see what it says.

We did not have an order sheet as it seems to have been a remanufactured unit that had some updates after the factory did some testing and upgrading.

Our MSRP bulletin lists the E-Trek Features right next to a 6 year warranty.

Then lower down the batteries are under the "Standard Motorhome Features" which have a 4 year warranty.

We are within both and they seem to not want to help us with replacing the dead battery banks.

That is why I would like to see the 2013 E-Trek Supplement. Maybe it is more clear about the warranty?

[booster]

Originally Posted by photolimo

We did not have an order sheet as it seems to have been a remanufactured unit that had some updates after the factory did some testing and upgrading.

Our MSRP bulletin lists the E-Trek Features right next to a 6 year warranty.

Then lower down the batteries are under the "Standard Motorhome Features" which have a 4 year warranty.

We are within both and they seem to not want to help us with replacing the dead battery banks.

That is why I would like to see the 2013 E-Trek Supplement. Maybe it is more clear about the warranty?

As far as I know the supplement showed up for 2014 units, and that is why Marco went looking to find information on the earlier units and found the order sheet information for the earlier ones. The posts about the supplement all referenced the 2014, and there don't appear to be any etrek specific warranty literature before that.

That said, irregardless of the horrible wording, your MSRP bulletin (window sticker basically) would indicate that the etrek features are as litsted and override the standard features listed afterward, so the 6 year warranty is valid. Combine that with the order sheet that was from earlier that said the 6 year warranty included the batteries and you have a really good case of proof. Put on top of all that the fact that Roadtrek later rescinded the 6 year warranty on batteries, which proved it existed, and I don't see how they could not be responsible for the batteries for 6 years.

All that said, what isn't addressed anywhere is the criteria for calling a battery or bank bad enough to replace, and that could be manipulated to do inadequate repairs, I fear. The replacing of two batteries out of 4 battery voltage set, in an 8 battery voltage set is against all the rules of battery banks and that is what we have seen, especially if the batteries are different as they were in the example. If that is done just to get you marginally out of the warranty period, you would still be on the hook for a full set of replacements.