So I've finally finished installing my backup system (just in time for load shedding it seems), and I've configured the ESS assistant. My question is this, are the voltages Victron have for the dynamic voltage cut-off extremely conservative?

I've left them at defaults, but I feel like I should be lowering them quite a bit: 0.005C = 52V, 0.25C = 50V, 0.7C = 49.2V, 2C = 48V. With the standard 1.2V delta, and 50V sustain.

My setup is a 48v system with the following components: Victron MP2 3000, 16x 120ah LifePo4 (https://lithiumbatteriessa.co.za/collections/cells/products/3-2v-120ah-lifepo4-lithium-ion-phosphate-battery-cell?variant=31983589359706), SmartSolar 150/35, 1640w PV array, BMV712.

Now my basic understanding is that the MP2 can't even pull more than around 55A (0.46C) from the battery at full load, and my typical load is only around 7-9A (0.05 - 0.08C). The defaults give me low battery warnings from as high as 85% due to this.

Does anyone have a suggestion as to what would be a more reasonable curve for my setup? Before I installed ESS I just had a the hard cutoff at 48V.

I'm thinking 0.005C = 50V, 0.25C = 48.8V, 0.7C = 48V, 2C = 47V, with a sustain at 49V.

 

27 minutes ago, igg said:

I'm thinking 0.005C = 50V, 0.25C = 48.8V, 0.7C = 48V, 2C = 47V, with a sustain at 49V.

I cant find the document now, but for Pylontech for example the Victron documentation recommends 46 Volt for all selections and 48 volt for sustain. Surely changes to the recommended values will also work and in principle your settings should work just fine.  

@igg just a tip, and take it form me. We already did the test on victron with all add-ons on the same batteries and if you using a Daly bms. Bulk charge 54.6v and float 53.6v. If you going to go over 55v you going to start get ripple warnings and errors spikes when the batteries getting full and the bms FITs cuts the charge. Got all the photos of it.

My system is running the same settings for over 5 months on the same lifepo4s and it's working. I adjusted the setting the other day just to check what it will do with a higher charge and the inverter when crazy because the mppt don't no what dc volts  it must charge when the bms FITs close the charging part. 

Solar MD runs the same charging volts on there units. 

2 minutes ago, Gerlach said:

@igg just a tip, and take it form me. We already did the test on victron with all add-ons on the same batteries and if you using a Daly bms. Bulk charge 54.6v and float 53.6v. If you going to go over 55v you going to start get ripple warnings and errors spikes when the batteries getting full and the bms FITs cuts the charge. Got all the photos of it.

My system is running the same settings for over 5 months on the same lifepo4s and it's working. I adjusted the setting the other day just to check what it will do with a higher charge and the inverter when crazy because the mppt don't no what dc volts  it must charge when the bms FITs close the charging part. 

Solar MD runs the same charging volts on there units. 

Thanks, yea; I went through a similar trial phase that resulted in me buying a bench PSU so I could top balancing all my cells. The cells were all resting at the same voltage, but most definitely did not have the same SoC, so I had some cells spiking to 3.7v while the rest were at 3.3v during charge. I settled on 54.5v bulk/absorb and 53.7v float after that, so almost the same as your numbers, and have been running without issue like this.

Also yes, using a Daly BMS, which I'm really not happy with... :(. It's a really expensive black box that has given me quite a lot of grief figuring out why it would just randomly disconnect the battery. It also causes the inverter to misread the voltage by +-1.5v during charge, so I ended up sticking the BMV between it and the battery to get accurate readings.

I only added the PV array with ESS this weekend, so still trying to figure out how to ensure the MP2 won't just randomly disconnect me under normal operation.

1 hour ago, Jaco de Jongh said:

I cant find the document now, but for Pylontech for example the Victron documentation recommends 46 Volt for all selections and 48 volt for sustain. Surely changes to the recommended values will also work and in principle your settings should work just fine.  

If I understand correctly, that means Pylontech recommends not using the dynamic curve and just set everything the same. So for a 16s the equivalent would be 49v?

35 minutes ago, igg said:

If I understand correctly, that means Pylontech recommends not using the dynamic curve and just set everything the same. So for a 16s the equivalent would be 49v?

Correct

 

Aaah late to the party 🙂

The Victron defaults are for 16-series batteries. Pylontech is 15s. So if you have Pylontech or Dyness batteries, you have to adjust them down.

The dynamic cut-off curve is only used while the grid is connected. When running islanded, it only switches off once the low-voltage cut-off is reached, or if the BMS disconnects the DC supply.

The dynamic cut-off curve is more important for lead acid batteries. For lead acid, a single cut-off voltage is not sufficient. A 12V battery that is at 11.5V with no load is almost completely empty while one at 10.5V that is doing a 0.2C discharge may be more than half full. The cut-off curve provides an intelligent way to to have a load-dependent cut-off point. It is not as serious with LiFePO4 since those batteries have much better current delivery capability.

When you have a BMS in the system that will disconnect, or send a DCL=0 request (Discharge Current Limit), you don't really need the cut-off curve. That is why the instructions call for just setting them all to some low voltage. It avoids reaching the cutoff unnecessarily.

It is important to not set the cut-foff too high. If you do that, the inverter will go into sustain mode too easily. For example, it might go into sustain at higher loads and 30% SOC, because the voltage starts drooping a bit too much.

(Sustain mode is when the inverter charges the battery at a low charge current to protect it from damage. Again, more important for lead acid batteries).

So given that you already have DCL control and a BMS that can disconnect the DC bus, it is okay to set the dynamic cut-off nice and low so it does not cause you issues lower down.

Note also that the inverter activates a pre-alarm once you get within 1.2V of the 0.002C value. If you set that value too high, you will get a pre-alarm even though the battery has plenty of juice left. So that is another reason to set it nice and low.

Edited July 10, 20205 yr by plonkster

On this topic, I had a support case one day of an inverter that was permanently stuck in sustain. It turns out that the sustain voltage was configured to the same voltage as float. Since you need to go 1.2V above sustain to get out of it... it simply couldn't ever get there. After lowering the sustain voltage, the system started operating correctly.

10 hours ago, igg said:

Thanks, yea; I went through a similar trial phase that resulted in me buying a bench PSU so I could top balancing all my cells. The cells were all resting at the same voltage, but most definitely did not have the same SoC, so I had some cells spiking to 3.7v while the rest were at 3.3v during charge.

Just as I sending mt msg the server went bbbbbblllaaaa. Server offline. Hahhaha

Jip. I had the same story. My first set of sells wasn't all the same SOC. I got them sorted the other day by leaving them for 10 days on bms ballancing and then charge them for 2 days at 5 amps that it can active balance all the sells. That help allot.  My second set i connected last week where standing for 4 months connected parallel waiting for there bms. They are dead on in SOC. That helped alot. 

I'm running a Smart Ant BMS that i check all the stuff via it's screen and i can connect to the bms via Bluetooth and adjust all the settings and check what the bms is doing. It works super nice and even Revov is using them on there 24v units. 

I will drop you a PM. 

15 hours ago, plonkster said:

Aaah late to the party 🙂

The Victron defaults are for 16-series batteries. Pylontech is 15s. So if you have Pylontech or Dyness batteries, you have to adjust them down.

The dynamic cut-off curve is only used while the grid is connected. When running islanded, it only switches off once the low-voltage cut-off is reached, or if the BMS disconnects the DC supply.

The dynamic cut-off curve is more important for lead acid batteries. For lead acid, a single cut-off voltage is not sufficient. A 12V battery that is at 11.5V with no load is almost completely empty while one at 10.5V that is doing a 0.2C discharge may be more than half full. The cut-off curve provides an intelligent way to to have a load-dependent cut-off point. It is not as serious with LiFePO4 since those batteries have much better current delivery capability.

When you have a BMS in the system that will disconnect, or send a DCL=0 request (Discharge Current Limit), you don't really need the cut-off curve. That is why the instructions call for just setting them all to some low voltage. It avoids reaching the cutoff unnecessarily.

It is important to not set the cut-foff too high. If you do that, the inverter will go into sustain mode too easily. For example, it might go into sustain at higher loads and 30% SOC, because the voltage starts drooping a bit too much.

(Sustain mode is when the inverter charges the battery at a low charge current to protect it from damage. Again, more important for lead acid batteries).

So given that you already have DCL control and a BMS that can disconnect the DC bus, it is okay to set the dynamic cut-off nice and low so it does not cause you issues lower down.

Note also that the inverter activates a pre-alarm once you get within 1.2V of the 0.002C value. If you set that value too high, you will get a pre-alarm even though the battery has plenty of juice left. So that is another reason to set it nice and low.

Thanks for this. Are you sure that the dynamic cutoff is only used in when grid connected, the ESS docs seem to imply otherwise (https://www.victronenergy.com/live/ess:design-installation-manual#dynamic_cut-off) 

• The Dynamic cut-off mechanism effective both when mains is available and during a mains-failure (system is in Inverter mode).

The primary scenario I'm trying to avoid is having the battery sitting at 40%. Then turning on a microwave for 2 minutes resulting in a cut-off due to a voltage droop. If this happens during no grid supply, I assume I'll unnecessarily lose power to everything.

The BMS I'm using is a Daly, so it will only disconnect the DC bus when a cell hits 2.5v, which I believe is too low for typical operation. So I assume a flat curve from 49 down to 48 should be good for my needs to get rid of the pre-alarms and have it cutoff at safe levels.

8 hours ago, Gerlach said:

Just as I sending mt msg the server went bbbbbblllaaaa. Server offline. Hahhaha

Jip. I had the same story. My first set of sells wasn't all the same SOC. I got them sorted the other day by leaving them for 10 days on bms ballancing and then charge them for 2 days at 5 amps that it can active balance all the sells. That help allot.  My second set i connected last week where standing for 4 months connected parallel waiting for there bms. They are dead on in SOC. That helped alot. 

I'm running a Smart Ant BMS that i check all the stuff via it's screen and i can connect to the bms via Bluetooth and adjust all the settings and check what the bms is doing. It works super nice and even Revov is using them on there 24v units. 

I will drop you a PM. 

I assume it's this one: https://www.aliexpress.com/item/32997552090.html?spm=a2g0o.productlist.0.0.98612689xH5UV9&algo_pvid=9c57c7d2-d767-49c6-88f7-452a1dc47064&algo_expid=9c57c7d2-d767-49c6-88f7-452a1dc47064-5&btsid=0ab6f83115944754191536779e56d5&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

I looked at that and then went and got the Daly instead... oh well, hindsight and all that.

I actually had the batteries resting for a month on the Daly BMS, but I guess since they do voltage balancing and my cells all like to rest around 3.3v the balancing function would never have worked for SoC. The 20ma balance is way too small to do anything during charge. Hence the process of putting them all in parallel and slow charging them with a bench PSU for a few days. So now the Daly is just relegated to doing the high/low voltage cell protection.

That's the ANT, yes. 

I have this Smart BMS https://www.aliexpress.com/item/32954859072.html
Also have a BT app and you can set all the settings (in the enterprise version). 

I also left my cells connected parallel for a few weeks, but one cell still gets ahead of the rest. Just limiting the charge voltage seems to keep it in check. I'm watching to see if it will stabilize over the next few weeks. As this is a 15s I have set mine to charge at 50.8v and float at 50.25v on my Multi II (5A limit)

2 hours ago, igg said:

The Dynamic cut-off mechanism effective both when mains is available and during a mains-failure (system is in Inverter mode).

Mmmh. Could be. Well, as I say to others, when in doubt... test it 🙂

(That means I need to test it to be sure).

4 hours ago, igg said:

I actually had the batteries resting for a month on the Daly BMS, but I guess since they do voltage balancing and my cells all like to rest around 3.3v the balancing function would never have worked for SoC. The 20ma balance is way too small to do anything during charge. Hence the process of putting them all in parallel and slow charging them with a bench PSU for a few days. So now the Daly is just relegated to doing the high/low voltage cell protection.

The Dali don't really do active ballancing. It only balance top end when it hits a sell that runs away. With Ant BMS, it can balance when there is no charge and no discharging, basically just standing, then it ballance. When you charging under 10amps, then it starts ballancing. When it gets fully charge and there is a sell that hits the top end volts that i adjusted on the bms, then it start shifting power arround the sells. It moves about 200ma arround. The BMs shows Cell Difference Ballancing then. What i did was, i fully charged the unit, then disconnect the inverter and left the bms doing it's job while we where away for holliday. Came back, connect the inverter and adjust it to run 5amps charge and left it. After that the sells run way stable. 

With 2nd set it was really easy. Leafing them for 4 months help alot. Bit it's handy to havea bench charger. I got a 6 amp charger that you can adjust for different tipes of batteries. Where did you buy your bench charger. 

Thank you for all the contributors to this topic.   i have had many days of frustrations trying all the permutations of various settings but couldnt fix the set of problems as mentioned above..   learnt new insights.    

One question though: on VEConfigure on the charger tab, i have the "configured for VE.Bus BMS" unchecked.  seems to be working fine as is .  

Would like to know the settings of other users...

System:  Victron components with BV26V mini batteries

On 2020/07/10 at 11:40 PM, ___ said:

Aaah late to the party 🙂

The Victron defaults are for 16-series batteries. Pylontech is 15s. So if you have Pylontech or Dyness batteries, you have to adjust them down.

The dynamic cut-off curve is only used while the grid is connected. When running islanded, it only switches off once the low-voltage cut-off is reached, or if the BMS disconnects the DC supply.

The dynamic cut-off curve is more important for lead acid batteries. For lead acid, a single cut-off voltage is not sufficient. A 12V battery that is at 11.5V with no load is almost completely empty while one at 10.5V that is doing a 0.2C discharge may be more than half full. The cut-off curve provides an intelligent way to to have a load-dependent cut-off point. It is not as serious with LiFePO4 since those batteries have much better current delivery capability.

When you have a BMS in the system that will disconnect, or send a DCL=0 request (Discharge Current Limit), you don't really need the cut-off curve. That is why the instructions call for just setting them all to some low voltage. It avoids reaching the cutoff unnecessarily.

It is important to not set the cut-foff too high. If you do that, the inverter will go into sustain mode too easily. For example, it might go into sustain at higher loads and 30% SOC, because the voltage starts drooping a bit too much.

(Sustain mode is when the inverter charges the battery at a low charge current to protect it from damage. Again, more important for lead acid batteries).

So given that you already have DCL control and a BMS that can disconnect the DC bus, it is okay to set the dynamic cut-off nice and low so it does not cause you issues lower down.

Note also that the inverter activates a pre-alarm once you get within 1.2V of the 0.002C value. If you set that value too high, you will get a pre-alarm even though the battery has plenty of juice left. So that is another reason to set it nice and low.

Thank you very much! You guys helped me a lot. Was wondering wth was going on as I was constantly getting low voltage warning light on 80% SOC on my multiplus II.