E-Trek Battery Monitor Install

[markopolo]

Originally Posted by booster

I made a quick sketch of how I think the markup would look in schematic form. Should be a bit more easily followed compared to all the lines crossed off, etc.

That's a lot easier for me to follow.

I don't see any smoke rising but will defer to Greg and Avanti. Still waiting for the smoke from earlier to clear here!

How would you handle the neg wire to the inverter?

[booster]

Originally Posted by markopolo

That's a lot easier for me to follow.

I don't see any smoke rising but will defer to Greg and Avanti. Still waiting for the smoke from earlier to clear here!

How would you handle the neg wire to the inverter?

I actually forgot to put the inverter on the schematic, too.

Offhand, I can't think of any reason that the inverter couldn't just be grounded to the chassis, and then back to shunt if you put in the monitor. Without the monitor the batteries would ground to chassis to complete the inverter circuit. I think as long as it isn't a battery, you can do the device/chassis/shunt/battery thing and keep your monitor accuracy.

[BobB]

Originally Posted by markopolo

......1/2 the amps needed at 24v....

Did not catch that. Need to read up more.

So a 400Ah bank at 24v = a 800Ah at 12v. Is that right?

Thank you.

[markopolo]

That's right.

[gregmchugh]

If you want to compare two systems that operate at different voltages convert everything to watts and watt hours.

Battery banks, 400 amp hours X 24 volts = 800 amp hours X 12 volts = 9600 watt hours

Alternators, 100 amp X 24 volts = 200 amp X 12 volts = 2400 watts

Loads, 10 amps X 24 volts = 20 amps X 12 volts = 2 amps X 120 volts = 240 watts

[BobB]

Originally Posted by markopolo

That's right.

Thank you. Have you (or gregmchugh- thank you) or someone else ever calculated the cost of a 24v vs 12v system assuming the same Ah load requirements? Also assuming the loads are at 12v. I would find that interesting to see.

[gsm]

Clarification Of My Comments On The Battery Configuration Of The AGM Battery E-Trek


Hi All – Markopolo

Yes you captured the essence of what Booster and I are saying.

However, from the photo I have of the six batteries in the rear compartment (photo attached), I see that RT has already strapped the battery-pairs C and G and D and F together in the desired manner. These two six-volt blocks form the step from 12 volts to 18 volts and then to 24 volts. There is no need to rewire these two blocks. Use them as is unless there is some mechanical reason not to.

NOTE: - I will use your battery naming and connection convention. Two battery names directly adjacent to each other means a parallel connection between these two batteries.

It is less work to strap batteries E and F in parallel, making a six-volt 440 amp-Hr block. The two now paralleled wires together with their fuses/breakers from under-hood connect the positive terminal of the AB block to the negative of the EF block. The positive terminal of the EF block goes to the already strapped negative of the CG block. That finishes the job. It is not that complicated to make the changes, but it requires care to avoid wiring errors such as somehow bypassing the fuses in the circuit. The fuses are the first line of protection.

Now there is a single battery ground under the hood, a tightly coupled, charge/discharge path through the four battery-pairs. The vagaries and virtually all the problems of the original battery chain have been eliminated.

I do not think a battery-balancer is need, but if one is used there are now only three tightly couple intermediary points in the battery chain to connect to.

Some have suggested that the eight batteries might be operated as two chains only interconnected at the chassis ground and the 24 volt points. In my opinion this would not get the best from the batteries and make balancer use more complicated and expensive.

More

I do not wish to belabor the various aspects of this subject, but I am concerned with assembling maximum help for those suffering through AGM E-Trek Woes by being as complete as possible on the fundamental electrical issues.

I have no idea how many variants of the AGM battery configurations have been shipped by RT. I have photos of two variants of the rear battery compartment wiring. They probably date from at least three years ago. It would be helpful to have pictures guaranteed as a group to reflect the systems of a particular more recent variant.

One of the two photos I collected of the rear battery compartment shows a confusing mess of wiring that is best entirely ignored. RT probably does not want to unscramble this either.

The other photo shows a cleaner layout that appears to be the more recent of the two. It gives a reasonably complete picture of the battery-wiring on this variant. Sorry, I lost track of the sources of the photos I suspect I got at least one of them from a dealers web-site.

I find it appallingly arrogant that RT uses masking tape labels to permanently identify wiring runs. They appear to unwilling to help themselves down the road. To me it is a clue to the view taken of these coaches.

Some good photos of the battery compartment and ancillary equipment of recent AGM E-Trek builds would be very helpful to determine where the design is now heading.

It appears to me that the second photo likely more closely reflects the rear compartment layout being discussed in this thread. I will attempt to attach these photos for reference.

In conjunction with the photos of the under-hood and the clearer rear compartment wiring, I am using markopolo's modified schematic from earlier in this thread, in which letter-names are assigned to each of the eight six-volt batteries. I will stick to his naming-convention.

On the photo of the two under- hood batteries A and B, are clearly connected in series to form a 12 volt string. The ground strap is shown as is the cable attached to the six-volt point and that attached to the 12-volt point.




The photo of the open battery compartment at the rear, shows six batteries. In the bottom row of four batteries, battery E is the very left with battery F right next to it, followed by G and H. The two batteries shown in the back/top row are C and D going left to right.


The wiring that connects the six volt and 12 volt points between the A & B and E & F strings can be clearly seen in the photo of the battery compartment.

Batteries E and F form the 12 volt string paralleled to the 12 volt string formed by batteries A and B under the hood. The negative terminal of battery E appears to be connected to chassis, as shown on the schematic, perhaps via RT's “proprietary” under-floor junction-box. (See photo below. The box seems to contain two stand-offs for interconnecting multiple cables and two circuit-breakers) I cannot tell whether the wires run through this junction-box, or determine the real function of the junction-box. Some one with access to an AGM E-Trek of this variant could provide some help here.



The overall difference between the installation-photo and the schematic is that in the photo the junction between batteries C and D is connected to the junction of batteries G and H. The photo shows these two stacked 440 Amp-Hr six-volt blocks, that in turn are stacked on the 12 volt block previous dealt with bring the four step battery system to 24 volt at 440 Amp-Hrs.

RT's designers attempted to create two more six-volt blocks by essentially putting battery A in parallel with battery E, and battery B in parallel with battery F., via the long cables and the two widely separated chassis grounds for the third connection.

Since the suggested re-configuration each of the series connected paralleled-battery-pairs, AB, EF, CG and DF are closely coupled both members of each pair is forced to experiences a common terminal voltage and internally almost identical state of charge, and charge and discharge currents. This ensures as much as electrical coupling as possible, so that all eight batteries equally share charging and load current. If all batteries are sound and close in capacity, there is no weak link in the battery chain.

I should mention at this point that the lower terminal-voltage of the normally hotter AB block under the hood, represents for the overall 24 volt battery system, only one quarter of what would be exhibited if the whole battery system was at that hotter temperature. (Whereas A & B represented half in the Original configuration.) Therefore the overall effect is considerably buffered. Charging is mainly controlled by the needs of the other three sections/blocks of the battery-system. If a battery temperature sensor is used it is probably preferable to locate it in the warmest spot, attach to a terminal centered in the battery-nest in the rear. This probably comes at the price of not precisely responding to the needs of the two batteries under the hood. However it ensures that the other six batteries in the rear are not penalized by being consistently somewhat undercharged. I believe it is worse for batteries to be consistently undercharged by five or 10 percent than being overcharged by the same amount. Booster may have the answer on this issue.

I will now once more return to the original arrangement of batteries A and B in combination with batteries E and F, as understanding the full repercussions of the existing RT E-Trek configurations is the aspect central to existing performance issues, followed closely by the impacts of the 12 volt tap on the battery chain. The tap's impacts will vary widely depending on the amount 12 volt current used by the owner. For reliable performance and lasting satisfaction the 12 volt tap has to be replaced with a 24 volt to 12 converter of ample capacity. This the best and cheapest solution. End of story.

Avoiding direct solution of both these issues and going onto other matters means dabbling with the design without solving root-problems. (RT has already done enough of that.) At best it ends up partially masking the problems under some conditions (RT seem to do enough of that also) pushing problems further down road in a never ending saga of revisits, frustration and inability to fully enjoy the coach.

We must accepted that each of the four series connected six-volt blocks may exhibits a slightly different terminal voltage in spite of the blocks being charged to identical capacity. Using a battery-balancer to force all four pairs of battery-terminal-voltages to the same theoretically number can forcibly reduce the capacity of a block leading to a detrimental reduction of the available capacity for the whole 24 volt system.

Beside the natural variations in battery-production-runs themselves, we have a case in point in the most glaring example of the normally much warmer parallel AB battery-block under the hood. Besides the potential that this battery-pair will age much more more quickly then the other pairs, are we going to use a balancer to force this battery block to have a higher terminal-voltage or should we force the terminal voltages of the other three blocks down in line with the AB block? What about when the AB block is cold (engine off), such as charging from shore power, it has a higher terminal-voltage then?

In my previous post I stated my appraisal of using a battery-balancer between the 12 volt sections of the existing RT battery configuration. My opinion has not changed. Adding more components is not necessarily a sign of better performance, but a clear sign of greater investment. For RT a few bucks spent to show how much the company cares, and it gets rid of the disgruntled owner.

Besides a balancer between the 12 volt battery halves cannot possibly equal the performance benefit and minor cost of a few battery-cable changes, obtained without complicating maintenance. Changes that in effect simplify the battery configuration. A balancer is certainly a most inefficient way to get a 12 volt tap on a 24 volt battery unless its an active converter type device. In which case it becomes in effect a 24 volt to 12 volt converter. And the reasoning has gone full circle.

There are other anti-balancer arguments that can be formulated pertaining to AGM batteries. As discussed above our case argues strongly against using a battery-balancer on the four battery blocks, for its normally intended purpose. Let the above suffice.

If you still have the battery-balancer on your mind try to leave it for another day, a time after the basic battery configuration is rectified. After reading what I explained above you should see why I doubt you will it will ever entertain the need for a balancer.. If used, it certainly will complicate maintenance of the electrical system. Even turning battery power off will not be as simple. Just having a direct 12 volt tap on the 24 volt battery-bank complicates turn-off. I think that is why there is the extra relay shown in the schematic.

In summary

In the proposed configuration each of the four series connected six-volt blocks unquestionably sees the same charging and discharging current.

There is only a single balanced current path through the 24 volt battery bank. There are no alternate loop-paths that come into play on charge or discharge as there is in the original RT designed configuration..

This condition is optimized for individual batteries by choosing equal gauge and length jumper-cables, as short as can be easily worked with, between battery-pairs. To series connect the four battery-pairs/blocks use the diagonally equal-distanced terminals to ensuring each battery of the pair has a jumper in series. This connection pattern starts at the chassis-ground under the hood. It ensures that each battery of a parallel pair sees the same amount of cable resistance and therefore current. Uniform and sufficient battery-terminal toques are of great importance. This information is not news to you, but it it may help a newcomer.

As can be seen in the photo of the battery compartment, there are two lighter gauge red wires and two lighter gauge black wires connected to the battery stack in the rear compartment. Some exploration of these is needed. Are they charging, discharging, battery-balancer wires. etc.?

There are two heavy gauge cables connected at the 24 volt battery terminals. I assume that one cable probably goes to charger/inverter perhaps via RT's under-floor junction-box. The other cable probably ends up at the high-current alternator up front. Where is the battery-voltage sensed for the alternator/charging regulator system?

There is still a lot to explore by AGM E-Trek owners, maybe with assistance from some knowledgeable helpers.

Hopefully the technical content of the thread gives owners a single source for
AGM battery based E-Trek power system information, until such time as RT has a change of heart or is embarrassed enough. Our findings also offer E-Trek owners a sound technical basis if a legal route becomes necessary for them.

Well that is about it from this end.

I am looking forward to hearing of an E-Trek owner with the gumption to implement the battery reconfiguration, with verified good batteries. From what I see everything else can remain as is, at least as a first step in the upgrade/correction.

I am really looking forward to have a Lithium E-Trek owner come forward for help with the battery system. This would be very interesting.


Best Regards All

GerryM

[markopolo]

I've attached a drawing to help me visualize GerryM's design. Please point out what I missed or incorrectly added and also if I've created any sparks.

E-Trek Battery balanced layout.jpg

I left the Cooper device in place functioning as an equalizer and relabeled it. It will supply 12v to loads and also AB/EF which is now 12v. I figured it is better to have a battery as buffer on the house side for the 12v separator.

I wasn't sure where to put the ABEF / CDGH serial connection to make 24V so please check that. (I used C- F+)

[gregmchugh]

GerryM, great analysis. I am not seeing any photos, are they in an album?

[markopolo]

Might be the same two photos in one post here: http://www.classbforum.com/forums/f5...html#post15272

and Hal Devera's photo here: http://devera.org/family/2015_Roadtrek.html#18 (with equalizer DIY install I think)

[gregmchugh]

Very good markopolo, I thought there might be some other ones besides those but those seem to be good examples of the rear batteries and I now recall that I had seen them before...

[booster]

I think Marko has an extra ground at battery E. Rehooking the way Gerry M will work, as however you get to a parallel setup on A/B is good. I think looking at the system and figuring out how to get the cable length balance between whatever setup you use is important, but if all the pairs are bridged, it is much less so.

All of the above go the Gerry M statements of some of the batteries getting over or under charged. His concern on the heat is very valid, and if you pile on some cable length issues, it gets even worse. As far as which is worse, there seem to be a lot of mixed messages on that. On the undercharge side, it is pretty much agreed that you will semi-slowly walk down the capacity of the battery, with some of it recoverable by "conditioning-used to equalizing). On the over charge side, some manufacturers are no desiring a short overcharge at the end of the the cycle (Fullriver for one), many others still don't want the higher voltages. They do agree that you don't want elevated voltages for a long time on full batteries, which by most accounts will shorten battery life. The rule I have heard the most often is that undercharge gives a slow death, and lots of overcharge gives a fast death, but have no actual data on that.

If it were my system, I would get rewired in some sort of parallel system, and use the often described converter instead of a balancer. Perhaps the balancers that are big enough to run all the 12v loads would work also, but the small outputs ones would not be as desirable. I would also very seriously consider closing in the front battery box and having forced road air, or fan pushed, through it for cooling.

There is another possibility, that may be out of the question, but I think would give even better results. IF a reduction in amp hour capacity can be handled, from 400ah at 24v to 320ah, you could simply put in 6 eight volt batteries in the rear compartment. Trojan, for one, makes an 8 volt AGM that has a GC2 case size and is rated at 160ah at 8 volts. Put on a converter and you are done, balanced well if you pay attention to cable lengths, no heat to worry about, no huge front to back connection.

[BobB]

Originally Posted by BobB

Thank you. Have you (or gregmchugh- thank you) or someone else ever calculated the cost of a 24v vs 12v system assuming the same Ah load requirements? Also assuming the loads are at 12v. I would find that interesting to see.

Oops - meant "load" requirements, not "Ah load". As you said, convert to watts, to compare systems.

A lot of this now making sense, especially articles about car/truck manufacturers considering going to 24v systems, given the increasing amount of electronics in vehicles. And just read article about someone using 24v solar panels on their Class A RV to keep wire sizes down and minimize voltage drops.

Looking like the future Class B may have 24v/Lithium systems (if they get the kinks worked out)?

If base vehicles go to 24v chassis systems, do you think Class B RV up fitters will start going to 24v house systems (especially with more use of microwaves, induction cooktops, etc.) to simplify things/make it all more efficient?

[avanti]

The approach of attempting to engineer "hybrid" battery systems that are expected to produce multiple voltages looks to me like a loosing proposition. If I were designing a 24V system, I would build a "pure" 24V battery using well-understood techniques. I would then source 24V appliances wherever possible (which is not hard in most cases--modern DC power supplies typically are capable of accepting a wide range of voltages, and 24volt charger/inverters are common). For whatever is left, I would use a DC-DC converter to produce 12V.

This is an approach that does not lead to a science experiment.

[booster]

Absolutely on the DC to DC converter. I hope that is what others have been thinking, as I just assumed it would be silly to do an AC converter off the inverter to get the 12v.

[avanti]

I am currently in the middle of installing a couple of these:
mac adaptor.jpg
Charging our Mac laptops was the last low-current item that forced us turn on our inverter. We are now 100% DC except for the microwave, Keuirg and A/C (and I am thinking hard about the A/C).

[booster]

Originally Posted by avanti

I am currently in the middle of installing a couple of these:
Attachment 2964
Charging our Mac laptops was the last low-current item that forced us turn on our inverter. We are now 100% DC except for the microwave, Keuirg and A/C (and I am thinking hard about the A/C).

That is what we do, also. DC chargers for the phone, tablet, laptop, Kindle, camera, etc.

We only turn on the inverter for the microwave, maybe a hair dryer once we get more battery finished.

[markopolo]

The etrek owners who did the first DIY Cooper equalizer installations used 80A & 100A models from what I saw.

I think there's an advantage to installing it as an equalizer in an E-trek as it would be involved in the charging process as well helping with supplying power to 12v loads. In converter mode it only supplies power to loads.

[booster]

Originally Posted by markopolo

The etrek owners who did the first DIY Cooper equalizer installations used 80A & 100A models from what I saw.

I think there's an advantage to installing it as an equalizer in an E-trek as it would be involved in the charging process as well helping with supplying power to 12v loads. In converter mode it only supplies power to loads.

I wish I knew more about how the equalizers work, especially the ones that supply power also. I think the big question for me would be which would be easiest on the batteries, a center tapped system with a two point equalizer, or a pure 24v system with a DC converter on it to 12v. I would guess if you had a pure 24v system with full, all battery, balancing system on it that would be very good, but complex and spendy I would imagine.

[gregmchugh]

I don't think there is anything special inside the Cooper unit, I think it just produces a voltage that is 1/2 the 24 volt input side voltage on the 12 volt side with a limit on how much current it can handle. The 12 volt batteries stabilize to 1/2 the 24 volt input side when used is an equalizer and you can power loads off the 12 volt side whether there is a connection to the center of the bank or not. Am I missing anything on that one?

I think the Victrons might do the same but it has a very limited current during the balancing and it is only active when it senses charge level voltages. I may not have it right so feel free to let me know if it is more complex in terms if what it does to balance the batteries.