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adamekw avatar image
adamekw asked

just Installed bmv 712 and smartsolar mppt 100/30. something's not right.

I just installed these components, hooked up to 2x 155 ah agm batteries (310 ah total). the batteries are new. here are some current displays from both the bmv and the charger: my question is this: why does the charge controller say bulk charging when the bmv says 99%? I thought bulk was supposed to be up to 80-90%.


I am pretty sure the bmv synched yesterday after I installed everything. it was sunny and the controller did briefly have the 'float' light on, so I think the batteries reached 100%.


honestly, I don't really understand the charging stages or settings at all. my current settings on each device are:as far as I understand these settings are correct. what is going on? a full agm battery should have a voltage of around 12.85, so why is it that absorbtion starts at 14.x??? and why is float voltage LOWER than absorption if float starts at a higher batt percentage? ugh

MPPT ControllersBMV Battery Monitor
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3 Answers
Rob Fijn avatar image
Rob Fijn answered ·

Hello Adamekw, assuming that all the Victron parts/equipment is correctly... then need to know how you made all the connections.
Maybe you can post a simple drawing of your connections?
Also important to know if the load that you connect to this system.

best regards,

rob

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adamekw avatar image adamekw commented ·

it is wired correctly. all loads and charge controller go to correct side of shunt, and the bat side of shunt only goes to most negative battery. batteries are wired in parallel. charge controller is wired correctly.

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Justin Cook avatar image
Justin Cook answered ·

@adamekw, a couple of things:

1. Since you have AGM batteries, I would recommend setting your charge controller to an AGM profile rather than the Gel profile you currently have set.

2. The charge controller appears to either have its negative connected to the wrong side of the shunt (since the shunt reads -A for the charge being put into it from the controller) or you have roughly 2.6A of loads currently running, with 1.2A of the load coming out of your battery and 1.4A being powered by the charge controller. One of the two is true, but without seeing your actual installation I can't tell which.

3. The charge controller may stay in "Bulk" if you have loads currently on the batteries; this keeps the batteries topped off while providing power for the loads.

4. Bulk charging voltages are higher than battery resting voltage because (to vastly oversimplify the mechanics of battery charging) the higher voltage is "pushing" the charge into the battery's lead plates.

5. Float voltage is also higher than battery resting voltage for the same reason; float is intended to maintain a higher surface charge than the battery resting voltage.

6. I see you manually set your battery SOC to 99.1% in the BMV at some point; this manual setting may well be throwing off your current SOC reading by a minimal percentage.

7. The BMV will automatically synchronize SOC at the top of a complete charge cycle; to register a charge cycle, however, the batteries need to be drawn down to ~70% and charged back up to 100%. Shallow charge cycles (100% to 90% to 100%, for instance) do not register as complete cycles and the BMV will not automatically synchronize after this type of cycle because (again, dramatically oversimplifying the algorithm) it can't get any meaningful data about the battery performance from a shallow charge cycle.

Bottom line: check that your charge controller's negative is attached to the "loads and chargers" side of the shunt (must be attached to the bolt at the top of the shunt, not the PCB mounting screw at the side) or verify your current loads (if everything is truly connected properly at the shunt, the readings you're showing should indicate ~2.6A of loads running at the time these screenshots were taken), change your controller charge profile to an AGM profile, and leave the setup alone for a while. As long as they're connected and configured properly, these components are smarter than all of us, so sometimes it's best to not overthink them too much.

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adamekw avatar image adamekw commented ·

thanks Justin. yes, I was running my fan when these screenshots were taken, and it is very cloudy out hence the low solar output. as far as I understand, my controller is set to an agm profile. victron just calls this one gel for some reason. each relevant input matches my battery manual's recommended ranges.


the controller is wired correctly. it still is bulk charging my batteries when I am not drawing any load from the batteries. I will try draining the batteries to 70 percent or so and recharging to see if things work normally.


I am still concerned however, because these batteries should be at 100% or close to it. I just received them from the manufacturer, who has confirmed they charge their Batts to 100 before shipping. so Im saying I think the bmv percentage is correct or very close, and so I'm concerned that my controller is still bulk charging despite the near 100% batt status.

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Justin Cook avatar image Justin Cook ♦♦ adamekw commented ·

The controller won't switch to the absorption stage until it reaches the absorption voltage setting, which is (under your current settings) 14.4v, and your batteries are currently (when these screenshots were taken) at 12.74v, which is -by normal AGM standards- still a good ways below 100%. So the controller will keep sending as much current as it can into the batteries in Bulk until they reach your absorption voltage, then it'll switch modes.

I would be extremely surprised if the battery manufacturer/distributor charged them to 100% right before they shipped them... ~90% would be more likely. And with a bank of this size, it's going to take a long time in Bulk (especially with only a couple of amps going in) to get their voltage up to 14.4.

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adamekw avatar image adamekw Justin Cook ♦♦ commented ·

yeah I don't totally get that concept. it is my understanding that an agm battery at 100% will read something like 12.85v if you use a multimeter. so why are the charging voltages so much higher than that?

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Justin Cook avatar image Justin Cook ♦♦ adamekw commented ·

See above - the simplified version is that charging voltage has to be higher than resting voltage to force current into the lead plates. I suggest a quick Google search on the topic of charge profiles and how various battery chemistries charge/store energy so that you acquire an understanding of how/why your system is working. A good place to start is Victron's Technical Information section, which has entire books for your to study on the subject:https://www.victronenergy.com/support-and-downloads/technical-information

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adamekw avatar image adamekw Justin Cook ♦♦ commented ·

I understand this. but how does the controller know when to go into each stage? I thought it was being 'triggered' to switch charge stage by the battery voltage, which is why I was confused about the high voltages

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spirou avatar image spirou adamekw commented ·

Voltage, current, time at each phase... As said before, in very simple terms that is how charging works. As far as I can tell, there is nothing wrong with your situation. Batteries are being charged because they are not full or under a significant load or both.

I find the % display is the least useful part of a BMV as it depends on presumptions in settings.

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adamekw avatar image adamekw spirou commented ·

the % display is a large part of what separates the bmv from a 10$ "battery monitor". I spent a lot of money on victron components so that i could closely monitor my system and know exactly what was going on. Clearly, something is not right. there is no way my battery is close to 100% if my charger is bulk charging. or, if they are at 100%, then something is wrong with the controller. hopefully, a larger discharge and sync to 100% will solve this. Your condescension certainly won't. merry xmas.

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spirou avatar image spirou adamekw commented ·

If you think any of the replies were condescending thats your problem, not of those who tried to help and explain.

You bought something you don't understand and now desperately want it to work the way you think it should rather than learning how it actually does. The % display cannot be accurate unless you find the correct settings (plural) for your specific battery setup and even then it will change over time and other conditions. What you currently have are approximate parameters which may or not be close to accurate. It certainly won't magically know when your battery is actually full without some of your input. Or let the charger/regulator know to switch off. These are entirely independent units even with data sharing in the so called smart network.

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adamekw avatar image adamekw commented ·

also, I never manually set the SOC to 99.1. that's just saying it is currently at 99.1 and if you click that area you can manually set it.

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JohnC avatar image
JohnC answered ·

Hi Adam.

For your BMV's SOC to make sense, you'll have to 'tune it in'. The default settings it comes with won't do, as the factory doesn't know your batts. As a start point, try changing 'Charge efficiency' to 95%, and 'Peukert' to 1.25. That will be closer to reality for agm's, but will still need closer attention/time to be accurate enough to rely upon.

Settings like this means accepting your batts are quite inefficient in overall round-trip-efficiency. If that disappoints, do what I did - take a deep breath and suck-it-up. Mine go like 76% Wh out vs in. Such are pb's, even when new.

Watching batt V is akin to waiting for a chemical reaction to finish when under charge or load. So they really need to 'stand' for a few hours to determine their condition from V. Experience will help you judge that from day to day without much (if any) standing time, and I don't even bother with soc myself to see what I need to see.

Not saying the BMV isn't a great device to have, because it is. But my VRM graphs are a personal preference..


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