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tiannasins asked

150/70 MMPT not fully charging batteries and staying in bulk mode


19 days ago my system started only bulk charging and only charging up to 13.56-13.59. It will not go into float or absorption. The only thing different I have done is updated the firmware when alerted to do so. The charge controller has had these symptoms once before and resetting the controller fixed the issue.

There are currently no significant energy draws on the system and I've had a full day of sun to test. My feeling is it's a faulty controller. Does anyone have any other recommendations on what could be going on??

Actions taken:

Reset charge controller on 3 occasions

Tested batteries - Good

Tested solar panels - Good

Disconnected battery sense - no change

Checked all fuses - no blown fuses

Reset charge controller to factory defaults - no change

System Details:

(2) 24 volt 320 watt solar panels wired in series

(4) 100 ah 12 volt batteries

150/70 Smart solar Victron MPPT

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MPPT Controllersbattery chargingMPPT SmartSolarsmart solar charging behaviour
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snoobler avatar image snoobler commented ·

I doubt it's the BMS. You don't indicate use of a GX, and standalone 12V with BMS can't throttle current. They can only disable charging cutting current to 0.

IMHO, your battery is at a pretty low state of charge (50%-ish), and

Recommend you go to user type and configure as follows:



"Smart Lithium" are victron batteries, and you don't have those.

The vast majority of LFP battery charging occurs between 13.2 and 13.8V. Assuming you get perfect sun maxing out your panels to their 320W rating, you're going to need over 8 hours of full array output charging. That's likely going to take you 2-4 days depending on solar conditions.

If you're in the Northern hemisphere, the sun is about as far South as it gets, so your daily kWh is going to be notably less than ideal.

You have 5.12kWh of battery capacity, and based on your array performance, it's going to take you > 5 days to fully charge.

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tiannasins avatar image tiannasins snoobler commented ·

Great info Snoobler! I have smart lithium batteries from Renogy and this was the previous setting when it was working correctly. I have two 320 watt solar panels for a total of 640 watts. 20 days ago the weather was not as sunny and I was reaching a fully charged battery state.

Today during testing regarding the BMS (which wasn't the issue as you had indicated), I was watching my charging like a hawk. My volts went up to 13.48 (it's a mostly sunny day) and then it starts to drop. It goes back down to 13.28 for some reason even when it's receiving 110 watts of solar. I've turned off all 12 volt and there is nothing drawing power currently. This is the behavior it's been exhibiting over the last 20 days. :(

I will try your custom setting and see if that helps at all. Thank you for your suggestion!

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snoobler avatar image snoobler tiannasins commented ·

Again, you're just behind the curve. You've used more battery capacity than you can replace with solar in a single day, and it's likely been cumulative over time. Since you don't have a battery monitor, you have no idea what your state of charge is. Here's a set of charge and discharge curves:


I have added red lines for 3.3V and 3.4V/cell levels (13.2V and 13.6V, respectively)

The solid red line is a 0.05C charge current. In your MPPT cap above, you are charging at 5.6A. This is 5.6/400 = 0.014C, so you're not even charging at this rate - meaning your charge voltage will be even lower than the chart indicates.

It's very important to realize that only a 0.4V change in battery voltage covers 60% of the battery capacity... LFP voltage is very consistent even with large changes in charge.

To say it other ways:

If you're charging at 20A, then you will indicate 13.6V or lower until you hit 95% charge.

If you're charging at 40A, then you will indicate 13.6V or lower until you hit 80% charge.

If you're charging at 20A, then you will indicate 13.2V or lower until you hit 20% charge.

If you're charging at 40A, then you will indicate 13.2V or lower until you hit 17% charge.

Given that you're showing < 13.12V and charging at an even lower current, your battery is at an extremely low state of charge.

You likely need at least 2-4 days of excellent solar conditions (no shading from sunrise to sunset with array at optimal orientation) with ZERO loads of any kind before you can fully charge your battery.

Look at the Wh your array is producing. If you use more than that on a daily basis, you will eat away at your battery state of charge.

On days 20 and 21, you generated a total of about 1100Wh or 550Wh/day average. Looking at days 9-13, you are producing more than this on average, yet you are unable to attain peak voltages. This indicates you are using more than you are taking in.

Recommend you get a smartshunt, so you know your actual state of charge for the future.

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tiannasins avatar image tiannasins snoobler commented ·

This is great additional info and I'm picking up what you're laying down. I'm going to do some additional testing to try and fully charge the batteries via a different method.

I do have a smart shunt. I'm using the Pico Blue SC503 (I don't recommend it at all). My usage is very nominal since I'm not currently using the space to live in yet. I'll look into what additional items I may have added that could be drawing more power these last couple of weeks and use the shunt to watch the amps. The Pico lacks reporting. :/

Stay tuned!

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snoobler avatar image snoobler tiannasins commented ·

Proper configuration of a shunt is critical. Many specify a charged voltage based on float. This is only appropriate with AC charging that provides reliable current. If charging with solar, the variable and often low current nature of solar charging will produce false syncs to 100%.

When charging with solar, Victron recommends you set charged voltage to 0.2V below absorption. In your case, with 14.2V absorption, you would set charged voltage to 14.0V and tail current to 5%.

After charging for the day, I recommend you disconnect the battery for 15 minutes, so there is no charge or discharge of any kind. Check open circuit voltage against this chart:

interpolate as needed and manually set SoC. It's not terribly accurate, but it's way more accurate than if your shunt is triggering false sync.

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tiannasins avatar image tiannasins snoobler commented ·
There is something definitely up with the charge controller. I have a Victron DC to DC charger and I was able to go for a drive last night and it would only charge the battery up to 13.4 volts. Arrrrg.

Is there a way to go back to an older firmware version to test that it is in fact the upgrade I did?

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snoobler avatar image snoobler tiannasins commented ·
How does this support the idea that there's a problem with the charge controller? You now have a second charger that is only charging to 13.4V, which is still a low state of charge.

This new information with the DC-DC only supports the conclusion that your battery is at a low state of charge, and that's why you're not getting higher voltages during charging.

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tiannasins avatar image tiannasins snoobler commented ·
It supports the fact that something is stopping it from charging past 13.4. It should have kept charging while driving and gone into float but it stops at 13.4 even with continued charging. Am I missing something?
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snoobler avatar image snoobler tiannasins commented ·
Yes. You keep missing that your battery is at a very low state of charge, and this is normal. If you are saying it hit 13.4V and the Amps went to ZERO, then I would say something is wrong, but if Amps were still going into the battery at 13.4V, you just need to keep charging.

"Stops at 13.4V even with continued charging" tells me you were still sending current to the battery.

LFP voltage changes very little with state of charge.

Recommend you re-program the shunt SoC per the instructions above and keep charging.

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Alexandra avatar image Alexandra ♦ commented ·
Could be the temps we are seeing there the battery bms affecting the charge.
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tiannasins avatar image tiannasins Alexandra ♦ commented ·

Thank you for your suggestion! I will investigate and report back once I've followed directions to reset the BMS.

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tiannasins avatar image tiannasins Alexandra ♦ commented ·
No dice on the BMS. Bummer.
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1 Answer
tiannasins avatar image
tiannasins answered ·

It does seem to be the BMS malfunctioning. I'm working with Renogy right now to fix the issue. Thank you for everyone's help! I'll reply back with the solution once I find out.

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