Victron smart 12.8v smart lithium battery

Yerf

Hi

Can someone please explain how discharge and charge currents work for these batteries.

It says in the data sheet that the 100 A 12.8v lithium battery has a recommended charge current of below 50A and a recommended discharge current below 100A.

If I had a bank of 4x4 100 A batteries (4 in series 4 in parallel) so a 51.2 v 400 Ah battery bank what would my ideal charge and discharge current be?

BB.

Yerf, feel free to post a link to the battery pack.

50 amps per string, 4x parallel strings * 50 amps per string = 200 amps maximum rate of charge for proposed battery bank.

I do not know of any minimum charge rate (although, some rechargable battery chemistries have "odd behavior" when they are full--A slight drop in charging current, or even batteries get cold near full charge, etc.). In those cases, sometimes a minimum rate of charge is recommended so that those small changes, such as small voltage drop when full, are not missed. Many lithium batteries do not like to be over charged/trickle charged as this can dramatically shorten their life. Aiming for ~20-90% state of charge/cycling is common practice for many battery chemistries.

You need to know exactly what chemistry (Lithium) you will be working with... The operating voltage range needs to be programmed correctly to limit the chance of damage (or worse) to your battery bank.

-Bill

Yerf

Hi

These are the batteries in question https://www.victronenergy.com/batteries/lithium-battery-12-8v

I've attached a datasheet.

Can you also advise me on the size of the fuse for a battery bank consisting of 16 x 100Ah batteries in 4 strings

BB.

Regarding fusing, what peak charging/loads do you want to support.

In general, off grid systems discharge at c/8 to c/20 (long term average discharge rate) and charge at c/20 (5%) to c/8 (13%) to c/5 (20% genset) rate of charge.

Li Ion batteries usually support much higher charge/discharge rates than we need.

If you have different needs (power tools, etc.), then things would be different.

-Bill

Yerf

Hi

Charging at around 10 kw and load at around 15 kw

Estragon

FWIW - I think you need a total of 5 fuses/breakers. One would protect the inverter/charger and positive wire from there to where the parallel battery connections are made. The wire and breaker sizes should be spec'd by the inverter manufacturer.

The other 4 protect each connection from the 4 series string to the parallel connection so you don't get 3 strings feeding current into a short fault in any 1 string. With max recommended charge rate of 50a, a 63adc breaker seems reasonable to me. If polarized, I think (counterintuitively to me) the + breaker post would point away from the battery and to the parallel point, as that would be the source of current in a fault.

My thoughts only.

Yerf

OK this is exciting. Just recieved my batteries yesterday I have already charged two of them with the victron smart charger 12/7.

I charged at 7 amps. I have attached the results of the voltages of the cells of the two batteries. They seem unbalanced to me? What do you guys think?

Next I will try charging two more batteries at 2 amps each to see what kind of results I get.

I will connect 4 in series and 4 series connected batteries in 4 parallel so at 12.8v 100 ah each. Total 51.2v 400 ah . How should I choose which batteries to put together in series? Does it matter?

I have attached screen shot taken from my phone with the reading for the two batteries I charged at 7a. As you can see. Two very different results.

karrak

You really can't tell how balanced the batteries are until they are full with the cell voltages around 3.45V. The balancing circuitry in these batteries will not start working until the cell voltage gets to 3.55V (14.2V for a 12V battery) so it is important to charge and leave them charging at 14.2V for a few hours so they will balance themselves. I think this is mentioned in the manual somewhere. When you have charged and balanced each individual battery you can put them in series strings.

The battery at 13.06 volts is not fully charged and I would think the one at 13.47V is fully charged and the charger has turned itself off.

Ideally you would do a capacity check of each battery and put all the batteries with the similar capacity is the same series string, however I would be surprised if the variation in capacity of the batteries would be more than a couple of % so it is probably not worth going to all the trouble.

Make sure that you follow the guidelines in this article to make sure that the current is shared equally between the different strings.

Simon

karrak

Yerf said:

Hi

Can someone please explain how discharge and charge currents work for these batteries.

It says in the data sheet that the 100 A 12.8v lithium battery has a recommended charge current of below 50A and a recommended discharge current below 100A.

If I had a bank of 4x4 100 A batteries (4 in series 4 in parallel) so a 51.2 v 400 Ah battery bank what would my ideal charge and discharge current be?

I think a good rule of thumb for long life for LFP batteries is to limit the discharge current to 1C which is ~ 20kW for your battery and 0.5C (10kW) maximum charge current which matches the manufacturers recommendations.

My maximum charge rate is ~0.15C and maximum discharge rate is ~0.6C

Simon

Dave Angelini

Also keep in mind that discharge current needs to account for surges from motor starts. Hard to see and measure, but easy to shorten life on an expensive battery.

Yerf

> @karrak said:
> You really can't tell how balanced the batteries are until they are full with the cell voltages around 3.45V. The balancing circuitry in these batteries will not start working until the cell voltage gets to 3.55V (14.2V for a 12V battery) so it is important to charge and leave them charging at 14.2V for a few hours so they will balance themselves. I think this is mentioned in the manual somewhere. When you have charged and balanced each individual battery you can put them in series strings.
>
> The battery at 13.06 volts is not fully charged and I would think the one at 13.47V is fully charged and the charger has turned itself off.
>
> Ideally you would do a capacity check of each battery and put all the batteries with the similar capacity is the same series string, however I would be surprised if the variation in capacity of the batteries would be more than a couple of % so it is probably not worth going to all the trouble.
>
> Make sure that you follow the guidelines in this article to make sure that the current is shared equally between the different strings.
>
> Simon

Thank you for your detailed answer.

How can I make sure the current is shared equally between the different strings?

The funny thing is I left them both on charge with the same model charger (victron smart charger 7/12) and they were both finished when I took them off. And for some funny reason they had different voltages.

And another funny thing is that the charger won't charge in 14.2 V it's charging in 13.8 V. I wonder if its because the ambient temperature is 9 c.

What is the best way to finish off a battery that hasn't reached 3.4 Vdc per cell? Just put it on charge again? Do I risk overcharge? What is the ideal voltage per cell before connecting in series parallel? 3.55 Vdc?

karrak

The Victron Lithium Smart manual says the following

3.2 Charging batteries before use

The batteries are aproximately 50% charged when shipped.

When charging series connected batteries, the voltage of the batteries or cells with the highest initial state of charge will increase when reaching the fully charged state, while other batteries or cells may lag behind. This may result in overvoltage on the batteries or cells with the highest initial state of charge, and the charge process will be interrupted by the BMS.

We therefore recommend to fully charge new batteries before using them in a series or series-parallel configuration.

This can best be done by individually charging the batteries at a low rate (C/20 or less) with a charger or power supply set at 14,2V. An absorption period of several hours at 14,2V is recommended to fully balance the cells.

Parallel connecting the batteries and simultaneous charging is also possible. In this case every battery must be protected by a fuse and the recommended charge rate is again C/20 or less, with C being the capacity of one of the paralleled batteries. Alternatively, low current charging can be used: see the note in section 4.1

Unless you are using an external BMS like the Victron VE.bus BMS to shut down the charger or disconnect the battery from the charger if any of the individual cells goes outside its safe operating voltage range it is very important to follow these guidelines and keep the charge current below C/20.

The Victron Charger manual states that when charging in Li-ion mode that it will do a bulk charge and absorb at 14.2V and drop back to a float voltage of 13.5V when the absorb period has ended.

If you want to check if the battery is balanced you will have to look at the individual cell voltages during the absorb charging phase when the charge voltage has reached at least 13.8v. The individual cell voltages may be a bit ragged when the charge voltage first reaches 14.2V but should get closer together (more balanced)  the longer the charger is at 14.2V. If the individual voltages are still ragged when the charger switches to  the float voltage of 13.5V discharge the battery a few % and charge again.

To make sure you balance the battery current between the batteries use the guidelines here http://www.smartgauge.co.uk/batt_con.html I use method 2. With method 2 you need to make sure that the resistance of the interconnections is less than 1/10 of the internal battery resistance.


Simon

mike95490

Does the factory Victron VE.bus BMS, charge the batteries to 100% or to a longer life 90% full ? Is it adjustable ?

karrak

The VE.bus BMS is there as a safety device to stop any of the individual cells going outside their safe operating range. You cannot regulate the charge voltage with it, that is a job for the solar charge controller or battery charger.

I would like to see some evidence to back up the assertion that in use, charging LFP batteries to only 90% rather than 100% significantly increases their lifespan. This maybe true for LCO (lithium cobalt batteries) but each lithium battery technology has its own particular ageing characteristics. There have also been many advances in lithium-ion battery technology over the years which has improved the lifespan of lithium ion batteries.

I am responsible for two off grid systems with LFP batteries that are nearly five years old  which  show little if any sign of loss of capacity or any increase in battery impedance/resistance. I am one of many and probably the vast majority of people with off grid systems who charge their LFP batteries to nearly 100% on nearly a daily basis.

Storage of LFP and for that matter all lithium ion batteries at high SOC (State of Charge, 100%=full) is another matter. All lithium ion batteries should be stored with an SOC less than 50%. The data I have seen suggests that any extension of storage lifespan only occurs in LFP batteries at an SOC less than 70% and that there is no significant  difference in lifespan when they are stored with an SOC of 90% or 100%.

Simon

Dave Angelini

Definitely agree Simon. It would be hard to prove that a lower Soc will yield much in life in an offgrid application. I have been running the LG RESU10 for over a year now daily up to 99%Soc and I just now see a 1% drop in State of battery life. The Schneider Bridge just had firmware for lowering the mppt's and so I can drop the charge voltage to 57.5v and below now to dial in the Soc I want to end the day with. I really do not see any reason to drop the Soc lower and the engineers at Schneider agree. Use it or loose it and we cycle daily,  always!
The only thing they worried about was large motor starts and that was from problems with Victron and LG mating problems. Some of the blanks in the data below are waiting for another update.

We cycled quite a bit deeper this year running cooling all night during Bushfires/wildfires. It was really nice to know exactly how much charge was left from the internal battery monitor. Does the Victron get this data from it's BMS? I hope so as in this price range I feel it should be included!

Yerf

I put two batteries on charge and set the charger to lithium mode low current, which charges the batteries at 2 amps max. Left them alone for 24 hours and then took them off charge let them rest. These are the results. Are they fully charged? They look fully balanced and fully charged to me.

Dave Angelini

Did they get to 3.55v at any point? Is there a way to log it? What indication do you have that they are fully charged?

Yerf

> @Dave Angelini said:
> Did they get to 3.55v at any point? Is there a way to log it? What indication do you have that they are fully charged?

I don't know if they got to 3.55v. I set the charger and leave.

Not sure if there is a way to log maybe with pc software. I would need a pc with bluetooth. Which I don't have at the moment.

I think they are fully charged because the resting voltage is 3.33vdc. Also because the charger finishes the charging cycle and goes into storage mode. I may be so wrong.

karrak

The Victron Smart battery manual doesn't say anything about the Bluetooth interface.

Can you tell me if you are using the VRM app on your phone and if the VRM app is talking directly to the batteries, or through another piece of equipment connected to the battery?

Can you use the app when the battery is being charged by the charger?

A PC with Bluetooth wouldn't work unless Victron have written software to run on the computer to interface to your batteries.

Your screenshots look good but you really need to look at the individual voltage readings when the batteries are being charged with a voltage of 14.2V.

Simon

Yerf

Hi Simon

These are the new smart lithium batteries. They have low energy Bluetooth built-in. I use the victron connect app to get readings from them. You can use the app when they are being charged. I'm going to bring one home tonight and watch it to see how it charges. And look at cell voltages when it's charging at 14.2 Vdc.

They also have a windows version although I have not used it. But I presume you could possibly log the data on the windows version.

Regards

karrak

Dave Angelini said:

We cycled quite a bit deeper this year running cooling all night during Bushfires/wildfires. It was really nice to know exactly how much charge was left from the internal battery monitor. Does the Victron get this data from it's BMS? I hope so as in this price range I feel it should be included!

I am so pleased that you managed to get through the fire unscathed!! We are at the start of our fire season. I can't believe that you are still having large fires at this time of year, very worrying. I do not like summer!

I agree with you that it is one of the best features of lithium ion batteries to know with high accuracy just how much energy is left in them. We went from old locomotive NiCd batteries which we never knew when they were going to be empty to the LFP batteries where we know exactly how much energy we can use which is great as we don't have a backup generator.

I think you have to buy a separate  SOC meter and current shunt from Victron.

Simon

Yerf

> @karrak said:
> Dave Angelini said:
>
>
> We cycled quite a bit deeper this year running cooling all night during Bushfires/wildfires. It was really nice to know exactly how much charge was left from the internal battery monitor. Does the Victron get this data from it's BMS? I hope so as in this price range I feel it should be included!
>
>
>
>
>
>
> I am so pleased that you managed to get through the fire unscathed!! We are at the start of our fire season. I can't believe that you are still having large fires at this time of year, very worrying. I do not like summer!
>
> I agree with you that it is one of the best features of lithium ion batteries to know with high accuracy just how much energy is left in them. We went from old locomotive NiCd batteries which we never knew when they were going to be empty to the LFP batteries where we know exactly how much energy we can use which is great as we don't have a backup generator.
>
> I think you have to buy a separate  SOC meter and current shunt from Victron.
>
> Simon

Is there any special adjustment for the victron battery monitor for lifepo4 batteries? How does it know they are full exactly?

Dave Angelini

Thanks Simon!  We don't like summer either! We call it the mean season like the boaters do in hurricane season. What really scares me is all the years we made it and had a tenth of the clearance and combustible reduction we do now.

Being away from the coast we do not get the high winds with our fires that they are seeing now in Southern California. How about you, high winds with fires? 
They had 80 knots one night last week. That is about impossible to survive in the dense housing in those areas.

My Inverter shuts down at 10% and it did that a few times this summer. It was like smoking a pack of cigarettes a day my doctor said. Most of the time we just stayed off the roads as the sheriff would not let you go home if they caught you off of your property. Take care

karrak

Yerf said:

Is there any special adjustment for the victron battery monitor for lifepo4 batteries? How does it know they are full exactly?

Setting the battery efficiency at 99% and setting the Peukert exponent to 1.0-1.05 will work well with LFP batteries. It is a shame that you can only set the efficiency in 1% increments. The SOC meter knows the battery is full when the battery voltage gets above a preprogrammed voltage at the same time as the current having dropped below a certain value for a programmed amount of time. See the manual for more information.

Simon

karrak

Dave Angelini said:

Being away from the coast we do not get the high winds with our fires that they are seeing now in Southern California. How about you, high winds with fires? 

They had 80 knots one night last week. That is about impossible to survive in the dense housing in those areas.

We do get the high winds here, when the fire that went through our place destroyed the town of Yarloop the winds were very strong, we were lucky that we got the flank of the fire at night when the wind had died down. Still didn't stop the first embers that started the fire near our house travelling over 0.5km from the fire front.

Directly fighting a fire front with 80 knot winds is just about impossible. Just have to wait for the fire front to pass by and stop  the fires that are still burning after the fire front has gone through.

Simon

Yerf

Thank you for your answers.

This is a diagram of how I plan to connect the batteries. The batteries will be fused with 100 amp fuses each string and then connected in parallel to the battery bus bar from there connected to the common bus bar. The shunt will be connected on the minus side on the battery bus bar before going to the common bus bar.

I also want to put in a 100 amp breaker for each string before connecting to the battery bus bar on the plus side.

Can I improve it?

Dave Angelini

The worse part of the Santa Anna wind event in Socal is not just how strong the winds are,
the worst part is they often blow strongest at night.
Just like on a boat out on the ocean, it always seems to get bad at night.

Definitely fuse the strings Yerf and use the shunt that the Victron battery monitor requires. Network it all to the inverter and you should have a very nice system.

Yerf

So you think my connections are OK? Is it a good idea to use a battery bus bar seperate from common bus bar?

Also, I brought home a battery and put it on charge at 2 amps on lithium setting on battery. After 24 hours charging was complete and charger entered storage mode.

Not once did I see the voltage of the cells go above 3.35vdc. At the end of the charge all cells were 3.33vdc so I guess they are balanced right? But are they full? I don't know? What to do?

karrak

I think your idea of battery bus bars is a good one. Not sure that you need to then have a common equipment bus bar as well. If you make sure that all the cables interconnecting the batteries and going back to the two bus bars are all exactly the same length you should share the current evenly between the individual strings.

Do you need separate breakers and fuses on each string, I would have thought that the fuses would have been enough? Make sure the fuses have a high current interrupting rating (5000A+ should do it)

If your power generating and load requirements (10kW and 15kW) are accurate you will need some very heavy duty cable with the correct terminations. Are these peak surge ratings?

I would put suitably sized breakers in the line between each charge controller  and the batteries. Remember that you have to disconnect the charge controller from the solar panels before disconnecting it from the battery.

I find it a little puzzling that you aren't seeing the charging voltage rising to 14.2V within a 24 hour period. Can you measure the charge current with a multimeter. While the battery is charging the voltage will rise slowly from 3.35 V/cell to 3.40 V/cell (13.4V -13.6V) then very quickly up to 3.55V/cell (14.2V)



Simon


 

Yerf

OK so I put the charger in reconditioning mode and the voltages finally went up. One of the cells were really lagging behind at 3.43vdc while the others were at 3.6vdc.

I was getting worried and going to shut of the charger but then it started climbing. The chargers was in absorption mode for a long time. I shut it off manually in the end when all the cells got to 3.6vdc as I started getting worried because the charger had increased the voltage to 14.6 Vdc.

Still I am not sure if the cells are properly balanced or not. It took along time for all cells to get to 3.6vdc even though the battery had just been through a 24 hour charging cycle. After the 24 hour charge I put it in reconditioning mode for around 8 hours before all cells were 3.6vdc. I am not looking forward to doing this to the rest of the 15 batteries. Am I doing something wrong?

Yerf

Here is when the single cell was lagging. I still wonder how the battery was not full after a 24 hour charge cycle at 2 amps. And is it full now after another 8 hours?