Battery monitor and ???

[VanKitten]

Installed 2  - 345 watt panels.    LIFePo4 400amp,  Victron 150/70 tr mppt

The battery monitor has me stumped.  I thought the whole point of a battery monitor was to tell the user how much battery capacity it has left.   But, it seems that belief was wrong.    Once turned on..it displayed the amps charging the battery.   It subtracts amps being used on the load.   BUT..it does not tell me the thing I want to know...because it has no idea where the battery started!   Like having a checking account wit h the starting balance hidden!   Scary. 

When I started everything up...I was at 12.9 volts.    I know that volts mean pretty close to nothing with lithium...but...a steady 13.1 should be what I see if they are sitting between 80% full and 70-80% discharged.   So..I figure this means the batteries are starting to get low.

I reset the battery monitor, turned everything on.   The mppt showed going into bulk... staying there a couple hours.   The volts at the battery was showing 13.3.  ... doesn't that indicate I am on the high end?  Above the 80% full?  Since 13.1 is the voltage it will show for everything between. 
Then mppt dropped to absorption....followed by float.  Of course float means not charging with lithium.   So that was fast....but..volts at 13.3.    So called battery monitor showed 295 amps charged to batteries.  I think it is lies.    

As lithium is close to full...shouldn't the voltage be up near 14.? 

I've run the refrigerator steady.   Had the water pump running pretty steady too
I do not seem to be at risk of running out of power...but..I couldn't point to any data to prove that statement.

Someone...explain all this to me.   I don't really know what is happening.

PS.  Once I get to Ehrenberg I am going to get a clamp meter for DC   But..

 

[highdesertranger]

what battery monitor do you have? highdesertranger

 

[VanKitten]

JLD404 intelligent AH meter

It controls two relays as well...basically to cut off over charging or over discharging.

Both of those conditions have been tested and do work.

 

[John61CT]

That is not sophisticated enough to give very accurate SoC much over what you can tell from voltage.

A Victron 702-BMV would perform better for that, but your unit should be fine to manage your daily use LVD/OVD.

I seem to recall you don't have a separate BMS?

What cells do you have?

What is your target charging voltage?

What is your usual charge source's max charging amps rate?

You can easily determine 100% Full just based on V and A.

As long as the shunt is installed properly so no Loads, including monitoring gear bypass the AH counting, that should give a rough idea of declining SoC.

Cross-reference that with volts at the low end, what V are you defining as nominal 0% SoC?

What is your expected max discharge current?

 

[John61CT]

> whole point of a battery monitor was to tell the user how much battery capacity it has left

The term battery monitor is used for $5 E/F gauge, to a $15 display of just V and A, a $30 Watt's Up which is like yours but no relays.

All the way to the Victron unit I mentioned that actually tries to get accurate SoC%.

> it has no idea where the battery started!   Like having a checking account wit h the starting balance hidden!

You need to start from 100% Full, however you want to define that. Ideally from a quality shore charger and with all loads turned off to start with, let V settle down a few hours.

> 12.9 volts
> 13.1

You should have the 20-hour discharge chart showing SoC vs Voltage, that will vary somewhat from one mfg/model to the other.

Resting voltage will be very different from when cycling, charging pushes higher than resting, loads pull lower. The degree depends on Amps vs bank capacity.


> 13.3 if that is a charging voltage, while a charge source is active, it doesn't mean much without all the other above variables taken into account.

It certainly means far from Full.

Remember, it is unhealthy for the bank to be Full except momentarily while actively cycling, the mfg should store and ship them to you way below 50% depleted, ideally 20% or lower.

The user should "commission charge" them a few cycles, and follow breaking-in protocol in order to get them up to full peak AH capacity, usually with quality mfg, well over their rated AH.

Then ideally performing a benchmark 20-hour load test in very well-controlled conditions, to be able to verify State of Health as that capacity declines in future years.

Without that accurate number, no SoC gauge can be acvurate.


> Since 13.1 is the voltage it will show for everything between. 

Actually no batt's curve is flat, just that LFP is much flatter than lead, at least at moderate discharge rates like 20C.

dropped to absorption

With LFP, Absorb setpoint is the high point, where you usually stop charging. Make sure not to hold that past amps dropping past your endAmps point, your definition of Full.


> battery monitor showed 295 amps charged to batteries.  I think it is lies.    

What reason do you have for that thought? Do you think it is overestimating or underestimating?


> As lithium is close to full...shouldn't the voltage be up near 14.? 

Only while charging, but personally I would never let it get that high in normal daily usage, only for carefully controlled maintenance procedures.

 

[jonyjoe303]

On these monitors you need to fully charge the battery first and then program the amp hour of the battery. That way it has a an idea where it started.

But reading the website it says you have to calibrate the shunt also, it shows you the proper numbers you have to enter. According to the pdf file the password to set the amp hours is 0036.

Unless your tracking all the group of cells in your lithium (like I do) you never really know if your lithium is really fully charge. The only time I fully charge my lithium was with a balance charger. If the battery is out of balance its always going to stop charging early, the higher the charge rate, the faster its going to cutoff charging. Once a group of cells reaches 3.65 volts its going to cutoff (if you have a bms), even if the other groups are at 3.40 volts.

Your only going to see 14 volts when you have a charger connected and charging, once disconnected it will go back to 13.1 volts, 13.3 volts if you have no loads. At 12.9 volts your getting low, once you you start getting at these lower voltages its goes to zero quickly. If you see 12.8 volts, I start would start charging it back right away.

This is my lifepo4, I can tell its fully charge when all the LEDs on the right read 3.65 volts. But I been using a coulombmeter (amp counter) for daily tracking of battery status. As long as you have a good way to track amps going in/out you can get close enough to keeping you battery almost fully charge.

 

[deadwood]

I use the Trimetric and when I was setting it up you have to program in the battery you are using. Mine is a 260 Ah AGM so I followed the directions to set it so it knows that I have 260 Ah's to work with. Once the meter recognizes that the battery is full it will then be able to add or subtract amps going into and out of the battery.

The Trimetric (and I assume most meters) uses a shunt on the negative side of the battery. All of my negative connections are connected here. This is how the Trimetric can read things. When I hooked up a Voltage Sensing Relay the other day to add a secondary way to charge my battery I needed to make sure that the negative lead on the VSR was hooked up to the shunt side as well otherwise it would not be able to read the incoming amps and the meter would not have the right numbers.

I imagine there are all kinds of meters but to accurately measure state of charge to have a percentage of battery power left you need to be able to measure current in. Current out. And know how many Ah's the battery holds. After that the unit figures it all out pretty easily.

 

[John61CT]

Looking at the manual I didn't see a battery capacity setting?

 

[VanKitten]

Yeah...there isn't one.

Of course the 404 was set up. Both code 0036 and the relays code 0001.

Since the only BMS I was able to find would not handle 400 amps...I had to settle for separate functions. The system has 4 balancers installed...one each 12v 100amps ... then these relays to protect from too high and too low. And finally the temperature sensors with relays.

The reason I do not believe 295 amps is that the solar array can only deliver a top of 57 amps if everything was totally perfect.....and the monitor showed 295 amps charged after only a couple of hours. (Less than 3) and that was with a load...the refrigerator was running and a couple lights.

With everything off over night...I was down to 12.9. I wonder if something is bleeding the batteries.

The voltage I am measuring is at the batteries.... it agrees with the volts shown on the monitor.

I'll be lots happier when I have a clamp meter ... then I can know for sure what the amps are at the battery....quit guessing.

 

[jonyjoe303]

[font=Verdana, Arial, sans-serif]The system has 4 balancers installed...one each 12v 100amps. What are these? maybe they are always running and draining your battery trying to balance them?[/font]

[font=Verdana, Arial, sans-serif]I looked at the manual and saw a capacity setting, APvL setting is were you set the low side 0 amps, APvH is where you set the high side 400ah.  But looking at the manual it has too many settings people never use and gets everyone confused. Also you need to calibrate the shunt that would be the A-Sn setting.[/font]

[font=Verdana, Arial, sans-serif]Yes 12.9 is too low, I use my lifepo4 until 11 pm and it never goes below 13.1 volts, in the morning its actually backup up to 13.3 volts after sitting overnight unused. A fridge and some lights won't be too much drain on a 400 ah lithium battery pack unless they weren't being properly charged up the following day. [/font]

 

[Weight]

My Victron has a 500 amp shunt. I use at the most 200 amps during any one minute. Here are some instructions for setting monitors. Maybe you can adapt things for your LiFePo battery. https://marinehowto.com/installing-a-battery-monitor/ and this https://marinehowto.com/programming-a-battery-monitor/

 

[VanKitten]

The battery monitor is setup. The 404 was set up by the manufacturer....I walked thru all the settings with them originally to learn the setup and to ensure that they were going to be driving the relays correctly.

The Victron has a battery setting explicitly for LIFePo4. No other setting are available. Once the choice of that battery type is made...the rest are preset and not user defined.

My question is ... is 13.3 too low for a full battery? Shouldn't it be much more like 14 volts?

The Victron is dropping into float (which the manufacturer says is really a standby if the batteries are lithium) ... seems to happen way to fast...and batteries are at 13.3 volts when it happens.

I have the ability to cut off the whole system with a kill switch....maybe I will do that overnight tonight and see the state of the batteries in the morning....maybe the balancers are bleeding the batteries. If so..then I will have isolated it....as only the balancers are on the batterynside of the kill switch

 

[John61CT]

I would absolutely avoid any ongoing balancing, completely unnecessary in gentle House bank usage, that's an idea coming from the completely different EV world.

MaineSail/CMS is the #1 most knowledgeable LFP professional I've found sharing his many years' experience working with dozens of vendors' systems for hundreds of customers.

These systems cost many thousands of dollars with proprietary packaged BMS matched to their cells, and on his own boat, he made a big point working with the system vendor's engineer/designer to rip out the balancing functionality.

The complexity of live balancing is dangerous to longevity, they very often cause major problems, and the problem they are designed to "solve" turns out to **not be a problem** in this context.

Everyone following MS' longevity recommendations of keeping charge voltages low at 13.8V, and avoiding the top and bottom shoulders of the volt/SoC curve, has reported that when they check cell balance as part of periodic maintenance there is no appreciable imbalance at all.

Some after 3-4 years, not even any manual balancing required.

Also no decline in bank SoH, AH capacity, even in daily use, at 90% cycling, whatever, still higher than rated.

Other than taking out the balancers, I recommend for now putting your bank on shore power, never mind the solar input, isolate the loads, and do some commission charging cycles, measuring volts and amps with confirmed-accurate measuring tools.

Get to know your bank's behaviour, both while charging and at rest, document yourself the various V benchmarks so you can at least use that to estimate SoC from that.

And ideally also counting AH accurately.

I'd return that meter, not what I would call a Battery Monitor without an accurate SoC display.

Replace it with a Watt's Up on APP connectors for now, just watch out for amps getting high.

Consider investing in a Victron BMV.

And your Victron SC should allow custom adjustment of charging voltage using a PC or with the optional dongle from your smartphone.

 

[Weight]

LiFePo chemistry does nothing like lead acid. You can keep your bank at 13.3 volts.

 

[VanKitten]

This RV has ONLY solar charge ability for now. I plan to add wind this coming winter.

This is intended for off grid...Truely off grid.

I think once I get to Ehrenberg I will be able to order the clamp meter that does DC....then I will know finally the current available amps.

Weight, I seem to be unable to make them charge above about 13.4 I do not know why. I am talking to the Victron people .

 

[John61CT]

Yes, I understand "truly off-grid" for day-to-day use.

But the commissioning and periodic maintenance procedures that all batteries need for good longevity really should be done in well-controlled conditions.

Which means a quality adjustable power supply running off shore power.

You don't need to own the gear.

If you had cheap FLA and were an owner couldn't be bothered with proper care, never mind take your chances.

But that's not my perception of your situation as indicated by your posts.

 

[VanKitten]

JOhn, yes you are right.

I have "toyed" with the idea of the charger/inverter. Didn't mess with it because of the issue I had dealing with sorting out the relays. The reseller is basically useless and I ended up hiring an electrical engineer. (A long story). Now, I should go back and look into getting that charger setup and working....although, I do not know where I would be able to plug the thing in,

I leave tomorrow for Ehrenberg. I have no plans to be at an RV park in the foreseeable future

 

[John61CT]

A step at a time, no rush, remember LFP doesn't like to be at Full more than a few minutes anyway.

Paid campsites have got power of course, but if you keep yourself open to the locals not hard to find a kind soul let you park and run your extension cord for a time.

PS inverter's got nowt to do with it, avoid kombi units

 

[jonyjoe303]

13.3 volts while charging is too low for lifepo4, even for float. For a 400 ah battery bank you will deplete it after several weeks if your only seeing 13.3 volts. Your just not charging it back up everyday and giving it a little extra, at most your barely replacing what you been using.

People don't like to hear this but you need to crank up the voltage to fast charge your lifepo4, I have my mppt controller set to 15.5 volts, thats the only way to fast charge my 110 ah lifepo4 battery. At 14.4 volts, even at 15 volts, the controller goes into float mode too fast. I think everyone has some sort of voltage drop between the controller and the battery. If your controller sees 14.6 volts which means a full lifepo4 it will go to float, even if the battery actually only reads 14 volts, then you will have problems. Even at 15.5 volts it barely can get the battery to where I want it, I have to keep the float at 14.5 volts to top it off. 
I have an overvoltage relay that will shutoff the controller once the battery reaches 14.6 volts plus the bms also offers protection. In 4 months I haven't had the overvoltage relay trip even once, the bms has tripped 2 or 3 times because the battery was out of balance but overall voltage was 14.4 volts or less.

Once you do fully charge your lifepo4, it won't read 14.6 volts, it only reads that when charging. Once you disconnect the charger it will drop to 13.3 volts. But in the 13 volt range it could be full or at 50 percent, unless you count the amps going in/out of the battery you never really know. Even when I used a balance charger and got a verified full perfect 100 percent charge, voltage didn't stay at 14 volts when I disconnected the charger.  

You might have to go to manual mode on your victron if the lifepo4 setting aint getting the job done. If there is no voltage drop on your system, then the lifepo4 setting would work, but if you got voltage drop you will never fully charge your battery.

 

[John61CT]

Sorry man there's just so much wrong with all that I don't even know where to start.

For example, LFP should not be floated at all.

If the charge source can't just turn off, then a float setpoint of 13.1-13.2V is a distant second best compromise, the whole idea is to have 0A flow by staying below the bank's resting voltage.

I would never charge above 3.45Vpc or 13.8V for daily cycling.

I guess you only want your bank to last the rated 1500-2000 cycles?

They're able to go much, much longer, but not treated the way you're talking.

Worst is, you gain nothing of value your way, long as your source has the Amps, you can go from 5% SoC to Full in well under an hour, keeping to 13.8, no problem.