Any Experience With "victron Batteryprotect" Low Voltage Disconnect?

Subsequent to recent posts by Dustin Auto Battery Load Disconnect about an automatic trailer battery low voltage disconnect, and before I pull the trigger, I thought I'd canvas any other of the electrically astute out there to see if they had ever bought, installed, considered, or dismissed this: https://www.victronenergy.com/uploa...1.2076984279.1669013872-1468887778.1617717896

For the uninitiated, it's primary purpose is to protect the trailer battery from unintended deep cycling or complete discharge, which could occur through appliance use (or excessive use), prolonged natural discharge without interim charging, or other such inattentiveness and misadventure... regrettable activities which we all seem to toy with now and again.

(This device is different from the battery isolator which prevents the trailer from draining the tow vehicle battery, and from the CTEK which enhances the tow vehicle's charging of the trailer battery under some circumstances, and from the TriMetric which is an enhanced volt-amp meter and trailer battery condition monitor. But none of these is a low-battery disconnect device.)

The Victron seems to solve Dustin's minor issue with his particular device, which is that his has its own parasitic drain of 0.125A, after it has protected the battery. The Victron 's drain, after it has disconnected the battery, is only 0.0015A. Or, essentially nothing.

It is programmable to the fairly useful cut-out/cut-in pairings of 11.8V /12.8V, and 12.0V / 13.0V. These are the best among 8 other pre-established Voltage pairings that wouldn't really serve us well for our trailer battery setup. The Victron is programmable for Lithium batteries as well, which have a discharge profile completely different to lead acid, and which could do with some protection too, especially given their price.

Despite it's diminutive size (about 2"x 4" x 1") for the 65A version, I can't seem to find a location within the battery compartment for it. As such it would have to go in the bottom of the bin along with the Marinco charger. And given the exposed terminals, I would have to create some sort of shield for it, lest a frying pan short out it, the battery, or the trailer wiring. But the install and programming seem simple enough with only two terminals, an LED window and a button. There is a more expensive version that is programmable through a Smartphone app. Neither are what I would consider cheap. But what they could be protecting, and extending the life of (an AGM or a Lithium) is neither. For a $129 Walmart flooded lead acid that is quickly and cheaply replaced with the same thing, this is most likely over-overkill.

Some other brands of these cut-off devices may have a greater variety of settings, but they scare me a little as they have completely exposed circuitry, and may not have the quality and/or reputation of a company like Victron. The last thing I want to do is create new unjustifiable complexity and an impediment to diagnosing electrical issues, or insert a weak link into the chain.

If nobody has yet tested these waters, I probably will. (Dustin: I trust you'll have some sage input on this experiment.)

Steve

 

It certainly looks like a more robust, with more functions, and some nice features that my inexpensive one has. I really like the fact that it delays the disconnect for 90 seconds after the voltage drops below the cutoff threshold, like in the case of the current drop from the Dometic first starting up, with the voltage coming back up once it's running during that 90 seconds,and also the ultralow current draw after cutoff. Take a look and see if there isn't room to mount it near the top of the back side of your battery/ storage compartment cover/divider. Mine is similar in size and I was able to get it mounted there, so it is protected from things in the storage compartment.
Otherwise, the only thing that concerned me was that it can only be used with one of the preset programs, which makes it most suitable for batteries that don't mind being discharged below a 50% SOC. If it were custom programmable, I think it would be close to perfect. As it is, I think it still may be that for you. Keep us updated!

 

Thanks for looking at it so thoroughly. My impressions as well.

That was about the only place I thought it could go, if I could origami my body into position to mount it . Solves any other issues about inadvertent contact with it. Or taking up bin space.

I’d be happy with the 11.8/12.8 setting, with or without the Dometic plugged in. But yes… custom programmable would make it perfect.

I thought the cut-ins were a little high. But then remembered that if the cut-out process is initiated, then it’s going to need a re-charge before the battery can do anything. And if it recharges from shore, or even solar, then the charging voltage (14.3 ‘ish) will far surpass any arbitrary factory cut-in that is already set, and allow the battery to be used. Though I venture to guess that simultaneously drawing upon and charging a deeply depleted battery should probably be avoided until it somewhat regains its feet again.

 

Yes, user configuration to make it adaptable to whatever battery/charger combination you have would make it much more versatile.
Just enjoying the beautiful weather here in site 126 at CICO today! Hope it continues for the rest of the weekend like is forecast.

 

Had a look at the CICO map 2 minutes ago and was secretly wishing I could have somehow turned my PA bicycle trek this coming week into an Around-the-Great-Lakes-tour. Next year. Enjoy

 

Dustin: One more question about your (or any) L-V disconnect device: Is it/they smart enough to discern between the resting State of Charge voltage, and the temporary drop in voltage when under load, and act accordingly? I notice that when our Dometic is running that the voltage displayed drops anywhere from 0.3V-o.4V. when using the old factory battery that is still installed. (This may be an extreme or exaggerated drop, if the battery is damaged, and/or old. I don't know). Any drop under load, however, I now understand, is natural and expected, and is due to the battery's internal resistance.

+ or -0.4V, when you are setting the cut-off limit, is a significant range to have to deal with, if the device isn't "smart". If it trips based upon the voltage it is reading while the battery is under load, this would require setting the cut-off artificially low, in order to get the most use out of your appliance, and the battery. However, this risks damaging the battery under a different or very low drain scenario. The corollary would be setting the limit artificially high i.e. the device will trip long before the battery has actually reached its critical SOC voltage. Safe for the battery, but you have now drastically limited the range and utility of the battery.

And this is the voltage drop of just one particular appliance. Other separate or combined drains on the battery could create their own voltage drop that is lesser or greater than the Dometic's and confound any calculations and setting compensation that one might make to the device.

My question/concern was phrased similarly here:
AGM voltage drop under load with high SOC - Multiplus 2 - Victron Community The question poser is describing an admittedly more complicated electrical setup, but it's essentially the same issue.

Am I missing something?

 

You raise a good question, which I hadn't taken into consideration. I knew there was more of a drop with the current required for startup, and then it would rise up again somewhat while running,then back to resting voltage when it stopped. I probably won't take the time to try to analyze it that deeply anymore this season, which for us will be this weekend at CICO.
Maybe next year, or maybe I'll wait for your ongoing analysis.

 

Fair enough. I have some other resources (marine buddies) that I may be able to tap before I pull the trigger.

To me, it would be inconceivable that these devices would be made by reputable companies, in quantity, and marketed for this specific purpose, if the voltages that they are required to detect, and guard against, are always a moving target.

Perhaps my substantial voltage drop under load with the Dometic is an extreme anomaly reflective of the battery's poor health, and that the new Fullriver AGM will behave far differently.

All I know is that having alarms go off erroneously, or having to constantly recharge the battery in order to reset the device is asking for more problems than it is preventing.

 

I fooled with the Dometic powered by a 72ah sogen (about same profile as the CI lithium battery) which was in turn charged by a 100w solar panel, and had similar tricky situations.

The bottomline for me is the panel needs to be be a bit bigger/more efficient,

And the Dometic in freezer mode just draws too much power to be replenished.

In cooler mode, depending on ambient temps, settings, etc it lasts longer but the Dometic shutoff settings dont include the ability to reliably turn back on, once battery recharged. Sometimes I had to disconnect the power to restart the Dometic. (Which I cant explain...but will dig into more next trip or when have time to, before...

My takeaway on the Dometic-gotta fool with it some, to understand your realistic useage.

Btw; I did NOT have an SOC display on this older sogen, that the new CI lithium option does have in the TriMetric or others might in Victron. So that would help understand what to expect, with less trial and error on the Dometic, amiright?

 

Thanks Kevin. My battery is truly dead. It powered the Dometic for 4 hours, hit 11.8Vand the Dometic cut-out kicked in. So this experience I described above was confounded by its poor health, and would not be typical. When I get the new battery I’ll play with various load voltage drops (Dometic, Pump, lights) and get a better concept of how the Victron cut-off could be affected by each, or all of the loads cumulatively. If it is affected at all.

My current (no pun intended) suspicions are that if the Dometic will be my most robust power draw, and the only one that could occur while I’m not in attendance with the trailer, and the Dometic cut-out works properly at the set voltage, then the Victron could very well be a redundant protection and more trouble than its worth to install.

 

Well... with a full, new AGM battery and the Dometic drawing 5A (I measured it at 5.0A even though the spec sheet says 7.0A), the voltmeters (I used two, for corroboration) dropped from 12.8 to 12.4 while the Dometic was running. They then shot back up again to 12.8 when the Dometic was unplugged. So... a 5.0A draw results in a 0.4V drop. Which I would say is significant.

I'd also say it's a safe bet that with any Low Voltage Disconnect device installed (like the Victron, or Dustin's version), or when programming the Dometic's internal Low Voltage cut-offs, one now would have to take this voltage drop into account when setting the lower limits of either device. And govern your usage and reliance upon the battery accordingly, lest you drain your battery below your intended target of 12.0 or 11.8. Or your device (Dometic, or other) cuts out long before you anticipated that it would.

Going by the resting State Of Charge only, as an indication of your battery's remaining capacity, it seems, could provide you some erroneous real world results.

If there are any electrical gurus out there who have experienced something different, I'm all ears; I would love to be told that I'm wrong as I'm finding these numbers to be somewhat disconcerting, and if they are valid, an impediment to getting the most use out of the battery's capacity without risking it's health.

 

Thanks for posting your observations! That is interesting. So it sounds like the voltage dropped 0.4 and stayed there until the fridge stopped. I was guessing there would have been an initial significant drop on startup, with a partial recovery during running, followed by near complete recovery on shut down.
Thanks

 

Actually… the drop was gradual: 0.2, 0.3, and it stayed at 0.4 until the compressor shut off. I only ran the fridge for 10 minutes, so I wouldn’t expect that I could have depleted the battery by any measurable amount in that time. So yes… afterward, back up to 12.8. This certainly wasn’t a temporary “surge” issue upon start-up, which the Victron, I believe, could have sensed, timed out and ultimately ignored.

This could throw all our careful calculations about battery protection and maximizing its capacity into the trash. I haven’t uncovered any information about how to deal with this discrepancy between open circuit voltage, and the displayed voltage while under draw, and how (seemingly) half of one’s battery’s capacity effectively disappears the moment you start using it.

That gripe aside… and to the matter of battery protection: which voltage should you pay attention to and consider to be line you don’t ever cross, if you don’t want to damage it ?

Confusing.

 

I don't have any data to back me up, but my gut says the resting, not the working voltage is the line you don't want to cross, and in that case the Dometic's 11.8 cutout may be essentially equal to a 12.2 resting voltage considering your observations, and makes more sense that what it initially appeared to make.
I guess they probably don't want their manual to get too wordy, but it would be nice if Dometic gave some sort of explanation behind the theory of the cutoff point options they chose to offer, and considerations that the user may want to employ in making their choice of which one to use.

 

I might have found some answers: Under-Load Battery Voltage vs. SoC - Marine How To

… in which (if I am reading this correctly) cautions against using the standard SOC resting voltage charts as an indicator of remaining capacity, or how close you are to “the line” and damaging the battery. “Under load voltage” is what you want to pay attention to. And stay on the correct side of.

There’s lots of variables (surface energy, how long since a load, where the voltage is taken within the system in relation to the battery, and the quality of the voltage measurement device) that go into giving you an accurate benchmark(s) upon which you can act. There may be more subtleties that can be gleaned from this. But a simple bottom line to safe care and feeding (that the author suggests) is to begin recharging when the under-load voltage reaches 12.2V, or 12.15V, at the absolute minimum.

This puts the Dometic’s 11.8 cut-off (High setting) far outside the bounds of safe usage. And would make a Low Voltage Cutoff Device with highly programable cut-outs and cut-ins (i.e. not one with only a couple pre-programmed pairings), almost a necessity, if you are to install one.

Some light reading for you on a Saturday night. I’ll be looking for another authoritative source to corroborate this advice.

 

Good find!
It sounds like I may have given Dometic credit a little prematurely, and I can leave my add-on cutout set at the custom setting it's at (12.2/12.6 cut-out/cut-in) . So much for trusting my gut.
Thanks for digging that out!

 

It seemed authoritative enough. And made sense. Glad you're already in compliance, and on the safe side of things.

Unfortunately, for me, it seems to be one of those things: the more you are informed of something, it becomes disconcertingly apparent the less you actually know. Which direction this one takes me, as far as the low voltage cut-off device is concerned, I don't know. I'll mull it over this winter.

Now I'm onto another electrical bugbear on the other end of the battery spectrum: I'm second-guessing not getting the CTEK in the build, and wondering if there are ways that I can compensate for my smart alternator not completely topping off the battery during non-electric stays, without actually installing a CTEK. I do have a 100W panel and separate charger.

This trip with the new battery will require extra vigilance, if only to keep a record of what does, and doesn't happen, and when. And assess the necessity and risk of doing anything (or nothing) about either under-charging, or over-discharging.