Victron monitor defaults and programming

[booster]

To continue down the road on the Victron settings, I think a couple of assumptions/opinions that I have about it all.


*By far the most accurate way to tell if batteries are full is by controlling the charging off a shunt and doing the controlling by looking at the voltage and amps going to just the batteries.


*A monitor can tell you when you hit the full battery point based on the volts and amps at the batteries, so will a very accurate reflection of the battery SOC and true full point when set to do that. If it has calibrated/zeroed/synchronized/whatever other term they use, it will be very accurate on that discharge for amp hours used and SOC. Charge efficiency will give slightly inaccurate SOC readings on the recharge cycle, though.



*Almost no shore chargers, solar controllers, and alternator charging system can do that kind of volts/amps controlled charging accurately, so unless you spend the bucks/effort to get those few available charging systems you will be dealing with less than perfect and likely also very variable charging. A monitor is capable of telling you the batteries aren't charging accurately, but it doesn't/can't do anything about it unless you add other systems.


*Before the correct settings for your system can be determined, it is necessary to look at the charging source specifications and also to probably run some tests under various conditions to see how the charging sources are handling the profiles.


*Odds are you will need to make some compromises in the settings to account for the rest of the system, so at that point it would be time to determine what information is the most important to you, and how much if any input you are willing, or want to, put into the running of everything.


This sounds like a lot of work, but I think most will be able to get pretty reasonably what they want without a lot of trouble. The hardest part, at least for me, is that the monitor is going to show you a bunch of shortcomings in the other systems, but they have always been there and you can't do anything about that without replacing some relatively expensive items. For me, "this is as good as it can get without a bunch of changes" doesn't register very well as I like stuff to be a good as it can be.

[booster]

It would be interesting, I think, to see what current monitor users look at and use in their monitors, and what new users would want to see and what they expect to be able to do with the monitor.

My guess would it be something like being able to see the state of charge of the batteries accurately, being able to see how much power they are using at any given time with various stuff on, how much power they use in a day. In reality, now that our system is tweaked out, about all I look at is how many amp hours we used in a day, and the amps going to the battery during charging as that give me an idea of how long it will be before the charging is done.

So I guess the very basic question is "what do you want/expect your monitor to do for you?"

[booster]

As mentioned it is a good idea to actually test your charging stuff so you can make a better guess at the best settings, unless you have really good charging equipment.


Before you have the monitor that will be very hard to do, but once you have it things get a lot easier. The results may be mixed, with charging sources that overcharge and others that undercharge, plus they will vary in how they do it based on depth of discharge and such.


Probably best to see if you find a charge profile or spec for the chargers, but not absolutely essential. It does give you a good idea what to look at if you have some information.


Set the monitor up with the recommended voltages for the charge stages, and set the tail amps to about 1%C to start. This should make so most chargers won't get the batteries to that low of amps, so you can watch how low the charger actually will get it.


Run the batteries down until you get about 12.0v rested voltage, which is a reasonable place for a typical discharge for many users. Let the batteries rest, and if the come back up some discharge them a bit more until you stay with .1v or so with the batteries rested. This gives you a reference point you can go to again and again as needed to take out most of the depth of discharge variations between tests. Use the rated ah of your batteries.



Turn off all the loads in the van except the 12v power so probably only the detectors running. Start the charger you are testing and watch the volts and amps over time. What you likely will see:


*Depending on how big the charger and battery bank are, the voltage should be between the 12.0v and set absorption voltage of the charge source. Amps will be near the max rating of the charger. Log the time, voltage and amps when gets relatively stable or in about 3 minutes.


*You probably know about how long charging takes so let it charge, noting the time/volts/amps maybe every 10 minutes. Volts will climb over time and stabilize. Amps will be quite steady for quite a while. Near near the same time the voltage will level off at the charger absorption setting and the amps will start to drop.



*At some point, probably measured in hours, the voltage will drop to the float voltage and amps will be fairly low. This is the point your charger thinks the batteries are full. Log the time/volts/amps once the amps settle in and aren't changing quickly. It is probable the amps will go negative for a short time as the surface charge from the higher voltage comes off. Don't worry about it until the amps stabilize in the positive direction. Log the amps and volts at the end of the couple of hours you can find that point again if you need to.



*You now have a "typical" recharge of your batteries, but you don't have nay good idea yet how much you actually got charged compared to the capacity of the batteries. You can look at the ah in compared to when you started, but the charge efficiency makes that less than very accurate.


* Let it run in float for a couple of hours and log it all again. The amps will probably drop over that time. The more the amps drop over that time, the less full the batteries were charged to.


*Now all you need to is discharge the batteries back to your 12.0 volts like you did in the beginning, after resetting the amp hour counter to zero or noting the reading. When you get to 12.0v, rested, the amp hour counter will tell you how many usable amp hours you have after a charge from your charger on a typical discharge cycle of around 50% discharged to whatever your charger will charge to. You will also know the what amps it got to at the end of the cycle to set that into the monitor if you want to have that point set as full because it is likely you would never get much more full except on a very shallow discharge.


I would make the setting for the amps at a point a couple of amps higher than you saw in the test to make sure the "full battery and synchronization are done in the battery monitor.


I would use it that way for a while to determine if the full battery is always indicated after a charging cycle, and also try to catch it under various use conditions to see if the amps are getting really low on shallow discharges, which is pretty unlikely with a shore charger and much more likely off the alternator on long driving days. Solar is another story completely, so don't worry about that until you have it set for the other too sources.


If the amps do go very low when driving, the only thing you can do is add a disconnect on the cable from the engine to batteries, which is pretty easy, to prevent overcharging. If you are overcharging that way, it is already happening, but you will know it now.


If you don't have the time or patience to determine your typical recharge this way, the people on here can probably give you a reasonable guess on the settings to try. You would then do the same watching and adjusting in real time use for the full battery light, but you won't know what your actual usable capacity is because you have no real reference to the rated amp hours of the batteries.


I think this last way is what many hired installers do, but slant very much toward lighting the full light early to keep from getting complaints. That doesn't change the actual full point your charger does, but it makes you think you have more capacity then you really do.

[GallenH]

This is a fantastic discussion. Just the instruction I was looking for. At my age/knowledgebase a step-by-step is precisely what I need. RV in storage right now but we'll pull it for camping at the end of the month. I plan to run tests at that time. Great doc. Many thanks.

glenn

[tgregg]

Originally Posted by booster

It would be interesting, I think, to see what current monitor users look at and use in their monitors, and what new users would want to see and what they expect to be able to do with the monitor.

My guess would it be something like being able to see the state of charge of the batteries accurately, being able to see how much power they are using at any given time with various stuff on, how much power they use in a day. In reality, now that our system is tweaked out, about all I look at is how many amp hours we used in a day, and the amps going to the battery during charging as that give me an idea of how long it will be before the charging is done.

So I guess the very basic question is "what do you want/expect your monitor to do for you?"

Because I have 200ah of LiFePo4 batteries, I use the Victron 712S primarily allow charging from the alternator when the SOC is below 90% and stop it when it reaches 95%.

Other than that, my uses are similar to yours. How much did I use, how many amps is the alternator charging and when will the battery be charged enough to allow whatever usage I have planned.

Because of the vagaries of charge efficiency, Peukert effect and usage during charging the displayed SOC drifts from 'nominal' SOC.

Once a month or so I use a LiFePo4 specific 10 amp battery charger that stops charging when the tail current goes to zero to synchronize the Victron's SOC. I shut off all DC loads during this process otherwise the load will prevent the charger from shutting off.

I have set the Victron parameters for charged voltage at 14.6, tail current at 2.0a, Peukert at 1.04 and charge efficiency at 99%.

If the ah replaced is close to the ah used when the charger shuts off then I think the parameters are pretty close. If it takes more amps to reach full then maybe the Peukert value is too low or the charger efficiency is to high.

If the tail current is set too low and there is an intermittent load like a DC refrigerator, the Victron may never synchronize.

Eventually, I may run an actual load test annually like Winston does to measure any loss in battery capacity.

[booster]

Originally Posted by tgregg

Because I have 200ah of LiFePo4 batteries, I use the Victron 712S primarily allow charging from the alternator when the SOC is below 90% and stop it when it reaches 95%.

Other than that, my uses are similar to yours. How much did I use, how many amps is the alternator charging and when will the battery be charged enough to allow whatever usage I have planned.

Because of the vagaries of charge efficiency, Peukert effect and usage during charging the displayed SOC drifts from 'nominal' SOC.

Once a month or so I use a LiFePo4 specific 10 amp battery charger that stops charging when the tail current goes to zero to synchronize the Victron's SOC. I shut off all DC loads during this process otherwise the load will prevent the charger from shutting off.

I have set the Victron parameters for charged voltage at 14.6, tail current at 2.0a, Peukert at 1.04 and charge efficiency at 99%.

If the ah replaced is close to the ah used when the charger shuts off then I think the parameters are pretty close. If it takes more amps to reach full then maybe the Peukert value is too low or the charger efficiency is to high.

If the tail current is set too low and there is an intermittent load like a DC refrigerator, the Victron may never synchronize.

Eventually, I may run an actual load test annually like Winston does to measure any loss in battery capacity.

Thanks for the information, good to see for lithium batteries also.


I think you could probably gain a bit of accuracy by ditching the charge efficiency (set it to 100 or 99.9 if it will go there). IMO, Peukert does really apply to the variable load we use in RVs, and with lithium it is essentially 1.0 anyway, you are close that anyway. I am little surprised the in and out wouldn't be closer at 1.0. Charge efficiency is really an issue with lead acid batteries, but normally not even considered with lithium. Taking those out will add consistency and likely accuracy, I think.


Most here are controlling lithium by voltage, but I will let them speak to that, but most sources are now saying it is best to stay a bit lower then the 14.6v for cutoff. Going a bit lower on the voltage and higher on tail current would still leave you in the knee of the curve but prevent charging to full regularly, which is no considered not good to do. With the once month to totally full you are covering the other oddities that are being mentioned these days. This will also assure you get a synchronize on each full charge cycle.


I don't understand the how the tail amps can be affected by load as the load should be carried by the charging source in a normal monitor installation that is measuring only battery amps in or out and never sees the load when on charge.


I am a fan of capacity testing periodically, and for lithium it should be pretty easy as you can run it to shut off on the BMS for a consistent low point, although that might kill the power to monitor and mess up the test

[themexicandoctor]

Booster,

I understood what you meant by the need to change the defaults.

However are you saying in essence that a Victron BMV712 works great up to a 20 hour/200amp battery bank but needs more fune tuning beyond this storage size?

I the above system.

[themexicandoctor]

CORRECTION TO ABOVE POST

Booster,

I understood what you meant by the need to change the Victron defaults to fine tune one's needs.

However are you saying in essence that a Victron BMV712 works great up to a 20 hour/200amp battery bank but beyond this storage size, even with fine tuning, it isn't perfectly accurate?

I thave a 20hour/200amp system.

[booster]

Originally Posted by themexicandoctor

CORRECTION TO ABOVE POST

Booster,

I understood what you meant by the need to change the Victron defaults to fine tune one's needs.

However are you saying in essence that a Victron BMV712 works great up to a 20 hour/200amp battery bank but beyond this storage size, even with fine tuning, it isn't perfectly accurate?

I thave a 20hour/200amp system.

I think you have a bit of confusion in relation to the terms being used, which seems to be getting very common these days because the manufacturers are doing the same thing, sometime nefariously.


* Amps are an instantaneous reading of the the amount of electrons going to a device. They don't tell you what amount of energy you are using.


* Watts are amps times volts and watts are what give you how much energy you are using at any instantaneous point of time.


* Watt hours are the accumulated energy used over time and is what we use to measure how much energy is stored in a battery. This is the number that really matters unless you a talking about a fixed voltage system like most RVs at 12v.


* Amp hours is just the watts hours divided by the voltage of the system/battery. It probably came into use in past days because they could measure amps pretty easily and read the time easily but they couldn't do watts directly. This is the common rating system used in deep cycle batteries to indicate how much energy they can store.


* Here is the one that I think is getting confused. The amp hour rating of a battery is not a fixed number for lead acid batteries because of the way they defined the capacity testing. The capacity test end point is amps sensitive and that makes the capacity change at different discharge rates. The 20 hour amp hour rating is just how much capacity has in amp hours if discharged completely at an amp amount that will take 20 hours to do that discharge. So 5 amps for a 100 amp hour battery for 20 hours. The 20 hour rating is the most commonly used, so that is what the monitor makers decided to use to set the capacity in the monitors. It may be the rate you discharge at and it may not, but it generally to the conservative side for most of our uses, so gives a bit of cushion.


So no the monitors are not limited to any particular size of battery bank as they normally can be set very high for capacity. They are also not tied in to using the 20 hour rate to set the capacity if you don't want to be. Our average discharge is more like at the 100-200 hour rate, so we could adjust our capacity based on those rates if we could find them or test to get them. It would be more accurate, but leave less cushion, so we don't do that.


So not limited to a 200 amp hour (20 hour rated bank) at all.


Based on the above descriptions of terms, I would point out there that the battery capacity is not rated in amps, it is in amp hours which are totally different. Amps in batteries is used to rate cold cranking and hot cranking specifications to give an indication of how well they can start an engine. Amp hours defines the capacity. Roadtrek started cheating on this spec quite a while ago be giving amps as a battery capacity but using the cold cranking amps for it so they looked like they had a lot more capacity than they really had. That may have been what started all this confusion as others have started doing the same thing.



Same thing is true when speaking of how much energy you used over a given time period. The only way you can define energy use is with a time included. If you want to tell someone how much power you use on a continuous basis, you might use one hour as a time frame and you use the term "amp hours per hour" as it needs to include power and time. It could also be "watt hours per hour" if you include the system voltage. We often list what our daily energy use is and the would just be "amp hours per day".



On the monitor you can normally read amps, amp hours since last recharge, in/out net amp hours (how far up or down the battery is), and also those readings with voltage included so in watts instead of amps.

[themexicandoctor]

Thank you.

My fingers are crossed that my existing 250watt Solar & Battery system will handle the demands of the Novakool R3800 well, after all this screenshot shoes how little demand there has been on my battery system on average.

I see the image was not clear but the deepest discharge # is only 36 amps without the future fridge.

[GeorgeRa]

Originally Posted by themexicandoctor

Thank you.

My fingers are crossed that my existing 250watt Solar & Battery system will handle the demands of the Novakool R3800 well, after all this screenshot shoes how little demand there has been on my battery system on average.

I see the image was not clear but the deepest discharge # is only 36 amps without the future fridge.

I would suggest to read the previous post. Discharge of 36 amps is meaningless, but discharge of 36 amp hr means energy was consumed at the current flow of 36 amperes for 1 hour, or 3.6 amperes for 10 hours.

My temperature this morning was 309.75, yes almost 310 degree. If you need a unit it is in Kelvin.

[markopolo]

Deepest discharge -36Ah
Min battery voltage 11.91V
Low voltage alarms 5

Time to get into the settings. The data you're getting now doesn't make much sense, IMO.

[themexicandoctor]

So 36amps would be divided by the time since last full discharge ie, battery was full from whatever source until it was recharged by the first source ie; 36 amps from 10pm to 7am would be 36amps ÷ 9 hours = 4amps per hour average?

[themexicandoctor]

Originally Posted by markopolo

Time to get into the settings. The data you're getting now doesn't make much sense, IMO.

I didn't even look at the low voltage alarms which is set for 12.2 volts.

The 11.91 volts minimum was caused by me starting the Generator one night when my voltage went down to 12.2 which is a phenomenon (or not) which I just detailed in this thread;

https://www.classbforum.com/forums/f5/stupid-question-generator-start-up-phenomena-10768.html

[markopolo]

The low voltage alarms indicate deep discharges, much greater than 36AH from 200Ah battery capacity. A 50% discharge would be 100Ah.

[themexicandoctor]

Its because I have them set for 12.2 volts.

Does that make more sense?

[markopolo]

Not to me.

12.2V is around 50% SOC. I'd expect that the "Deepest discharge" would therefore be 100Ah and not 36Ah, assuming your battery capacity is 200Ah.

A heavy load can cause a voltage dip but it seems to me that one or more of the low voltage alarms could be caused by lighter loads and the "Deepest discharge" should be greater.

Only 8 Synchronisations with Cumulative AH drawn at -2038Ah doesn't seem right either.

[themexicandoctor]

Originally Posted by markopolo

Not to me.



12.2V is around 50% SOC. I'd expect that the "Deepest discharge" would therefore be 100Ah and not 36Ah, assuming your battery capacity is 200Ah.

If i understand your statement correctly, then 50% SOC = 100amps of a 200amp hour system?

So perhaps my settings are incorrect?

I just went into the Meter & reset it for 200amp hours.

[markopolo]

Not amps. Ah is amp hour or ampere hour.

[themexicandoctor]

It makes it clear the default setting is 0200 ah.

I also reset the Auxiliary Input to the original TEMP versus the other options of Start or Mid Point.

Then the writing in the very next sentence is;

The BMV is now ready for use.

I rarely synchronize the unit, I was of the belief that if the batteries reached full capacity for a certain amount of time that the meter synchronizes itself.