Victron MPPT 250/100 Charging Over Set Voltage (24v AGM)

[PaleBlueDotFarm]

Hello! I just applied a new Victron MPPT 250/100 to a 24V bank made of 12x 2v 1000ah batteries.

The operating manual for the batteries does not list a bulk/absorption voltage, but lists 2.35V per cell (28.2V) as absolute max for a 'refresh' charge, and 2.25V per cell (27V) at 77F for float. The manual frequently says never exceed 2.35V (28.2V) per cell.

In entering these values in the VictronConnect app, all charging phases are 0.5-1V over the settings. The batteries are usually around 45F, so I imagine temp compensation might be playing a role.

How can I accurately set the controller so it doesn't exceed the operating manuals absolute max of 28.2 V, while still entering accurate settings? Will temp compensation always put me over - and is it OK to exceed manufacturers recommendations in this case?

Many thanks!

 

[RV8R]

You should set your charger up to the charging profile of your batteries (AGMs).

Can you post your battery charge parameters ,,, the pages of the battery manual or user guide ?

 

[sunshine_eggo]

Hello! I just applied a new Victron MPPT 250/100 to a 24V bank made of 12x 2v 1000ah batteries.

The operating manual for the batteries does not list a bulk/absorption voltage, but lists 2.35V per cell (28.2V) as absolute max for a 'refresh' charge, and 2.25V per cell (27V) at 77F for float. The manual frequently says never exceed 2.35V (28.2V) per cell.

In entering these values in the VictronConnect app, all charging phases are 0.5-1V over the settings. The batteries are usually around 45F, so I imagine temp compensation might be playing a role.

How can I accurately set the controller so it doesn't exceed the operating manuals absolute max of 28.2 V, while still entering accurate settings? Will temp compensation always put me over - and is it OK to exceed manufacturers recommendations in this case?

Many thanks!

I have the same controller.

What do you have reporting temperature to the MPPT? If you are using the built-in MPPT temperature sensor, it is not accurate enough for reliable temp compensation.

Please provide a link to the battery manual as well.

 

[PaleBlueDotFarm]

What do you have reporting temperature to the MPPT? If you are using the built-in MPPT temperature sensor, it is not accurate enough for reliable temp compensation.

I have a SmartShunt with a the add-on temperature probe sharing data.

Battery manual as best I can find. Purchased these used. Definitely not the best battery for a long-term off-grid set up apparently, but for the peanuts I paid, they've been rockstars!

 

[sunshine_eggo]

GX or VE.Smart network?

 

[PaleBlueDotFarm]

GX or VE.Smart network?

VE.Smart via bluetooth. In the app it says it's successfully sharing data, and the accurate temp reading is reflected in the MPPT profile display.

 

[sunshine_eggo]

Just making sure.

It looks like the batteries are quite particular about never exceeding 2.35V in any case.

I would consider charging purely by the float method listed in 17.2.

Set absorption and float to to 2.25V/cell or 27V.

Set temp comp to -26mv/°F

That should ensure you hit 2.32V/cell (27.84V) at 45°F

 

[PaleBlueDotFarm]

Just making sure.

It looks like the batteries are quite particular about never exceeding 2.35V in any case.

I would consider charging purely by the float method listed in 17.2.

Set absorption and float to to 2.25V/cell or 27V.

Set temp comp to -26mv/°F

That should ensure you hit 2.32V/cell (27.84V) at 45°F

My hero! Thanks for the review and confirming the particularity.

Is that temp comp in mv/F or mv/C? The app takes Celsius, hoping you might help me with the math if your calc is in F.

 

[sunshine_eggo]

My hero! Thanks for the review and confirming the particularity.

Is that temp comp in mv/F or mv/C? The app takes Celsius, hoping you might help me with the math if your calc is in F.

Set temp comp to -26mv/°F

Are you unable to see the "°F"?

equates to:

-46mV/°C

 

[RV8R]

Sounds like you got it resolved with @sunshine_eggo ?

 

[PaleBlueDotFarm]

Got it dialed in. With Absorb and Float set to 27, and -46mv/C, it’s now floating me at 27.85V (2.32v per cell) at the current 5C temp.

This is good, yeah? Many thanks

 

[sunshine_eggo]

Got it dialed in. With Absorb and Float set to 27, and -46mv/C, it’s now floating me at 27.85V (2.32v per cell) at the current 5C temp.

This is good, yeah? Many thanks

Based on my interpretation of the manual, it's operating within those specifications. I have a hard time using the word, "good." ?

Not a whole lot of margin to the downside. Just make sure the battery never goes above 28.2V.

And I would do an "equalization" charge per the manual as needed with temp comp disabled.

 

[PaleBlueDotFarm]

Following up since ya'll were so helpful!

According to the SmartShunt, I am only discharging down to at most 90% SOC (100 ah) on a daily basis. The bank is hitting absorb (27.8 @ 7C today) usually within 2 hours. Using the adaptive absorption time, it transitions to float at around 95% SOC (50 ah discharged) 2-3 hours later. In float, the bank is seeing 27.8V at ~5-8A.

This pattern leaves me at the end of the day with the SmartShunt reading ~97%. Resting voltages after a sunny day is 25.9ish. I can't see how the charging voltages could ever get me to 100% SOC per the shunt in a day regardless of a need for more panels.

Do I trust float and ignore the missing 'icing' between 97-100%?

24kw 2V 1000Ah EnerSys P100 AGM Batteries
1500W Panels

Settings:
Victron 250/100 MPPT
Absorb Voltage - 27.01
Float Voltage - 27.00
Temp Comp - -46mV/C
EQ Off
Absorb Time - Adaptive

Per battery manual, I am never to exceed 2.35V per cell (28.2V). Other charging instructions are difficult to gleam from the documentation, and were informed by this thread.

Many thanks for any help I can get!

 

[Rocketman]

One thing I have learned from my Lithium batteries is the Smartshunt is a mathematical model of what is happening to the batteries in the real world.

My (uninformed) guess is anything above 95% is full. Could you cram a few more electrons in there sure… but it may not be worth it. There are costs.

My guess is the Smartshunt reset to 100% earlier (a little before the battery was really at 100%). After that the conditions were not right to reset it again, even if the battery is still charging…

Good Luck

 

[sunshine_eggo]

One thing I have learned from my Lithium batteries is the Smartshunt is a mathematical model of what is happening to the batteries in the real world.

My (uninformed) guess is anything above 95% is full. Could you cram a few more electrons in there sure… but it may not be worth it. There are costs.

My guess is the Smartshunt reset to 100% earlier (a little before the battery was really at 100%). After that the conditions were not right to reset it again, even if the battery is still charging…

Good Luck

AGM batteries.

Following up since ya'll were so helpful!

According to the SmartShunt, I am only discharging down to at most 90% SOC (100 ah) on a daily basis. The bank is hitting absorb (27.8 @ 7C today) usually within 2 hours. Using the adaptive absorption time, it transitions to float at around 95% SOC (50 ah discharged) 2-3 hours later. In float, the bank is seeing 27.8V at ~5-8A.

This pattern leaves me at the end of the day with the SmartShunt reading ~97%. Resting voltages after a sunny day is 25.9ish. I can't see how the charging voltages could ever get me to 100% SOC per the shunt in a day regardless of a need for more panels.

Yep. These batteries are odd. Based on their specification, they are more appropriate for UPS-type activity, i.e., hold at full charge for several days and then discharge rapidly during a power outage for a few minutes until the backup generator turns on, then charge them to full over multiple days. They are turds for daily cycling.

Change to Fixed and 8 hour duration. Essentially, you never want to go to float, and it's going to be impossible to get to true 100% in a single day due to the nature of these batteries.

Do I trust float and ignore the missing 'icing' between 97-100%?

Pretty much unless you want to run AC charger overnight. Changing to a fixed absorption time might get a tiny bit more, but it's unlikely given the 0.01V difference between absorp and float.

Please provide your shunt settings.

 

[PaleBlueDotFarm]

Please provide your shunt settings.

Capacity - 1000 ah
Charged Voltage - 28.2V (Intended to avoid resetting SOC due to voltage alone)
Discharge Floor - 50%
Tail - 4%
Charged detection time - 50 min
Peukert - 1.25
Charge efficiency - 95%
Current threshold - 0.1A
Time-to-go Average - 12 min
Starts synchronized - off
Aux Input - Temp
Temperature coefficient - 0.0%cap/C

Will make absorb adjustments per your recommendation. I have a backup LP generator to run the inverter/charger at will, but can't determine a good frequency to use it if we're not dipping below 80% SOC.

They are turds for daily cycling.

Any tips on determining when the turd is starting to stink? I'm trying to get 12 months (24 would be amazing) out of these kids. My thought would be to do a weekly generator 'full' charge, and then check resting voltage after a few hours with no load. I'd love any ideas on how I might keep tabs on these strange, but in-hand batteries!

 

[sunshine_eggo]

I don't see any issues with the shunt settings.

While voltage isn't a great indication of SoC, it's value in similar conditions can definitely be useful in establishing trends.

Your shunt should record 45 days of the two trend values - make it SoC and voltage.

Periodically make a note of your daily minimum voltage and corresponding minimum SoC. If these diverge, it's either an indication of shunt accuracy wandering and/or capacity loss. Short term trends are more likely to be Shunt deviation, but long term variation is likely capacity loss.

This should be pretty accurate if your current is pretty consistent at the low voltage/low SoC point. If you have a lot of current variation, it will be more challenging.

If you're truly only discharging ~7%/day, I can't see how they won't last more than two years.