Balmar voltage sense wiring

[gregmchugh]

This was posted by a fellow named Rod Collins on the Roadtrek eTrek & Ecotrek Facebook group. May be old news but it may be useful...

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I just joined this group because we had eTrek owner contact us back in the spring for some LiFePO4 consultation. We don't really work on RV's (marine electrical/energy management systems only) but they guy was persistent. He's now apparently sent us another eTrek owner...

I have been involved in LiFePO4 marine systems since about 2008. The cells on my own vessel were manufactured in 2009 and still, to this day, exceed the factory Ah rating after about 1300 cycles (most to 80% DoD). The problems with LFP are most often related to installation, use and charging/discharging not the cells themselves.

After a quick perusal this morning one thing that stuck out to me, after seeing a charging graph, is that the voltage sensing on the Balmar regulators is likely wired incorrectly on most of these eTreks. It was incorrect on the customer whom we met with in the spring.

Even Balmar's own manual has voltage sensing shown incorrectly. The article below should help put some perspective about what I am referring to. Accurate voltage sensing with LFP systems is quite critical to charging performance. Hope this can help out and thanks for the info I may gain here for the next eTrek owner..

https://marinehowto.com/alternators-voltage-sensing/

[avanti]

Well, before you get too excited about this issue, please note that this is a MARINE website, not an RV one. Unlike boats, most RVs use the chassis as the return, NOT a negative wire as assumed in the article. A proper chassis ground has HUGE ampacity and a correspondingly tiny voltage drop. It is simply not true that "only half" the voltage drop is accounted for. In a properly wired RV, it is much less than this. The advice given in this article is very unlikely to make much of a difference when applied to an RV.

Lots of DIYrs think that using the chassis as a return rather than running a long piece of 4/0 is "cheaping out" and somehow inferior. Just the opposite is true. People seem to have some kind of vague discomfort with running high-current circuits through the chassis, but this concern is misplaced. In addition to the ampacity issue mentioned above, there is also the matter of ground loops. Most alternators have their negatives internally bonded to the chassis mount, so it is very difficult to isolate it. In such a setup, adding a separate return will create a second, redundant path. (Indeed, depending on details, even the proposed "sense return" wire may do this). This is called a "ground loop" and best practice says to avoid these, since tiny differences is impedance tend to produce small unintended current flows that can cause various problems--especially hum on audio systems. A proper ground system is a "tree" that branches out from the battery negative terminal, with no cross-connections.

In summary: This guy isn't wrong, but his advice is mis-applied in the RV world.

[booster]

I think Rod Collins is the same guy that wrote the glowing praise of the Smartgauge and also articles about the evils of having a battery monitor because of inaccuracies.


Those articles have been talked to death, so no need to rehash them, but I certainly wasn't impressed with a lot of his tech arguments.


The link seems to be referring to AGM batteries as they are talking about having long enough absorption time to get full charge. If you have inaccurate voltage sense that gives low voltage, it takes longer to get fully charged, which is certainly true. The fact that the voltage drop that is seen in an AGM system goes away as the charge current drops just really extends the time a bit, but if you are sensing the current to end charging, the quality of the charge will not be affected as those amps are tiny. Ours is 2 amps in a 3/0 cable.



The issue on Lithium, I think, would be more critical as most systems end charging based on voltage, and the lithium acceptance of charge holds the amps pretty high right up until you are nearly full. Many want to stop before the current has dropped very low as it is now said that going totally full is not all that great for lithium batteries. In the low voltage at the batteries because of sensing up upstream with voltage drop, the system would stop early because of the drop. You would lose capacity, but not do damage as it would be an undercharge which is fine for lithium.


I think a worse issue with the Balmar is that it does not cut off the charging, just goes to float, which another discussion completely.


The better system, I think, would put the Balmar on a longer than necessary absorption time, and control the field on/off with a battery + and - connected sense from the BMS or other source that triggered on desired ending voltage.

[gregmchugh]

I don’t really have a dog in this hunt, just posting this to see if it is useful. There has been some follow up discussion with inputs from Ecotrek owners that might be useful to other owners...

If this info is bogus then so be it...

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Dan Winterburn Good article. Most of us have read this and some have made the changes necessary to mitigate charging errors at the start of the charge curve for depleted lithium modules. The error is negligible though at very low charge rates. Roadtrek and Hymer group ecotrek modules are more reliable than they once were but incorrect settings and wiring (besides the sense wire) were the predominant factors for battery failures.
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Tom Schwartz
Tom Schwartz Rod Collins . . . we have been using this article and more from your referenced site. Last March I moved my positive sensing wire back to the Ecotrek. However, it was discussed here and determined the negative didn't need to be moved back. I wish I had moved it . . . maybe I will eventually.
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Dan Winterburn
Dan Winterburn Tom Schwartz With the quality of wiring used and the lengths involved on our vans, I am not convinced it makes a significant difference in battery longevity. At lower charge rates the error is virtually zero. I would love to see a chart by chart comparison of an individual system with sense on alternator vs sense on battery. Never mind the math involved...a real world test is what is needed. I always carry these issues to extremes and if you look at no current flow then the error is zero, regardless of where the sense wire is located. Is there an error under high current demand...yes, but that doesn't last long as the batteries ramp up their SoC. My opinion anyway.
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Tom Schwartz
Tom Schwartz Dan Winterburn When I asked my RT Service Dealer to move the sensing wire according to my schematic they stated they had measured a significant voltage drop from the alternator to the Ecotreks in back. If I remember well . . . something like 0.5V. They thought it was good to move the sensing wire when I requested it.
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Tom Schwartz
Tom Schwartz Dan Winterburn In defense of your position . . . we also have dialed back the Balmar charging parameters quite a bit so not to kill the Ecotreks. My Balmar comes out of bulk in about 20 minutes most times . . .
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Dan Winterburn
Dan Winterburn Tom Schwartz I may dial mine back a tad as well. I have the switch on the Balmar but it would be nice to have the system more 'automatic'. Can I ask what values you are using? I'm contemplating 13.8, 13.7 and 13.6
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Tom Schwartz
Tom Schwartz Dan Winterburn . . . here is a snip of my cheat sheet . . .
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Dan Winterburn
Dan Winterburn Tom Schwartz That's basically what I have in place at the moment. Thanks.
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Tom Schwartz
Tom Schwartz I have L1's and I can run the solar and/or the inverter/charger for days and the Ecotreks never shut off. The only charger that shuts them off is the Balmar/GU . . . but it is rare. The last time was when we were plugged in for 4 days at our campsite…See More
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Dan Winterburn
Dan Winterburn Tom Schwartz I've never had mine (L1) shut down. Charge disconnect yes, but they've always supplied power. I'm assuming that's the same for your setup. It sounds like you and I have very functional systems. Besides the beer that is...😁
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Tom Schwartz
Tom Schwartz Dan Winterburn Thanks, corrected above . . . charge disconnect opened . . .
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Rod Collins
Rod Collins Tom Schwartz On your cheat sheet the CL is set to 14.6V which is fine, however these systems should not be using a battery temp sensor, just and alternator temp sensor. Battery temp compensation should only be used on lead acid batteries.
The one I w…See More
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Dan Winterburn
Dan Winterburn Rod Collins None of the Zions have battery temp sensor...but yes, I agree, my Balmar had the alternator temp sensor connected to the battery sensor terminals from the factory. That mistake will affect regulation.
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Rod Collins
Rod Collins Dan Winterburn on a cold day, with batteries already at high SoC, it could actually serve to destroy the batteries.... I wonder how many others had alt temp connected to battery temp? I thought that one owner was probably just a fluke but if you had that too..... Oops....
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Dan Winterburn
Dan Winterburn Rod Collins My original H batteries failed in less than 60 days. November Ontario weather that was below zero so probably that didn't help. Yeah... the factory quality control was less than stellar to put it mildly. I'm hopeful that Rapido/Roadtrek will sort things out in future builds.
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Greg McHugh
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Rod Collins
Rod Collins The eTrek I did a consult on had the MC-614 Reg B- and terminal #9 v-sense measuring voltage at the alternator B- & B+. Voltage drop on B+ was 0.91V and voltage drop on B- was 0.76V and this was with the regulator already limiting charge current and no…See More
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Lam-May Wong
Lam-May Wong Was it the graph from me?
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Rod Collins
Rod Collins Yes, I believe it was...
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Lam-May Wong
Lam-May Wong Rod Collins I did the +ve but not the -ve battery voltage sense already.
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Greg McHugh
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Bonnie Hildebrandt
Bonnie Hildebrandt So, if we take our rig to one of the few shops that can do this rewire or Dan or Steve, what numbers are they using or should they be using?
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Rod Collins
Rod Collins It is not a big rewire. Simply run a negative wire (black wire in Ford plug), 10GA, and a positive wire (terminal #9), 12GA is fine here, to the battery bank or the positive & negative bus as close to the bank as possible. The + v-sense needs a fuse at the battery end. Terminal #9 and the regulator B- wire make up the volt sense circuit of the MC-614.. Only running the + v-sense only corrects for half the voltage drop.
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[avanti]

Just to be clear: Moving the "sense" wire makes perfect sense. That is not controversial. But the referenced article was primarily talking about the "ground" (neutral) wire. THAT is what the Balmar documentation allegedly got wrong. But, the statement in the Balmar booklet in fact makes perfect sense in an RV. Many of the comments cited above seem to be addressing the "sense", not the "neutral" line.

[booster]

Originally Posted by avanti

Just to be clear: Moving the "sense" wire makes perfect sense. That is not controversial. But the referenced article was primarily talking about the "ground" (neutral) wire. THAT is what the Balmar documentation allegedly got wrong. But, the statement in the Balmar booklet in fact makes perfect sense in an RV. Many of the comments cited above seem to be addressing the "sense", not the "neutral" line.

Exactly, there is only really one exception to the sense being on batteries being the best choice or at very least just as good.


That exception would be if you have an big voltage drop and are using the stock alternator or a parallel second alternator with the remote sense.


In that situation, you can have the voltage regulator increase the voltage enough to cook the starting battery, or even burn out bulbs and electronics faster. This apparently happened quite a lot when folks moved the sense wire to on their alternator to the batteries if they had an isolator with the .7v drop.

[avanti]

Originally Posted by booster

Exactly, there is only really one exception to the sense being on batteries being the best choice or at very least just as good.


That exception would be if you have an big voltage drop and are using the stock alternator or a parallel second alternator with the remote sense.


In that situation, you can have the voltage regulator increase the voltage enough to cook the starting battery, or even burn out bulbs and electronics faster. This apparently happened quite a lot when folks moved the sense wire to on their alternator to the batteries if they had an isolator with the .7v drop.

Yeah, good point.
This is becoming a moot point with modern vehicles, though, since with modern smart charging systems and LIN-controlled alternators, the "sense" wire is becoming a thing of the past.