Victron smart 12.8v smart lithium battery

Yerf

> @Dave Angelini said:
> Just lurking... How did you get 400A @ 57V ?  A 25KW generator?  I would think the VICTRON BMS would limit overcharge but I guess it is not tied into the CC or charger on the Inv/Chg ?

Yes a 25 kw monster generator. She's old but she's powerful. It's a three phase generator. Connected to 3 quattro 10000kva inverters.

I set the BMS assistant up on the inverters, the BMS and the quattro s are connected through ve bus. When there is an overcharged cell the BMS cuts off the quattros. When there is a low voltage cell it also cuts them off to prevent under voltage damage.

The charge controllers are victron 150/70. Their old and don't have a remote off so they each have a cyrix li-charge so the BMS can cut them off in the event of a high voltage cell.

I believe each battery has its own individual BMS but not sure how they work.

Yerf

> @karrak said:
> The values are dependant on what you have set your charge controller to.
>
> The Charged Voltage needs to be slightly less say 0.1V-0.2V less that your Bulk/CV/Absorb voltage.
> The Tail Current needs to be set slightly higher than the charge current when it has tapered down just before the controller switches to float.
> I would set the Charged Detection Time to the minimum 1 minute.
>
> The SOC meter will reset to 100% when the battery voltage is still higher than the Charged Voltage and the charge current is less than the Tail current and these conditions must be met for at least the Charged Detection Time.
>
> What are your controller settings at the moment?
>
> Simon

I'm using the default lifepo4 setting on the victron blue charger 150/70.

Absorb 56,8V / 2h
Float 53,4V

So my settings would be 56,7v charged voltage, and 53,8v tail current? Detection time 1 minute.

Dave Angelini

I would definitely do what Simon wrote about limiting the current then.
You will kill these batteries or they will not last long.
There is no reason to hit them that hard offgrid. We want longevity and reliability.
In the LG Resu Lions BMS these high currents are logged and will void warranty.

karrak

At first glance the Absorb time of 2h seems somewhat excessive seeing that for longer life you want to keep the battery voltage high for as little time as possible. In most cases it takes less than 15 minutes of absorb time to finish fully charging an LFP battery. But when you look at page 12 of the manual is states that the absorb time is discounted dependant on the battery voltage at the beginning of the day. In most cases this means that with an LFP battery the absorb time will be 20 minutes or if the current drops below 2A.

The float voltage of 43.4V is a little lower than what I would use and will probably mean that the battery SOC will float below fully charged.

I would drop the Tail Current 2% of battery capacity and see how well it works.

It the tail current  is too low the SOC meter will never get reset, if it is set too high the meter will get set to 100% before the battery is charged to 100%. Same is true with the Charged voltage.

Simon

Yerf

Here are the absorb times for your reference on two different days.

karrak

Thanks for the information.

Interesting, on the 7th it looks like the current might have dropped down to 2 amps and terminated the absorb phase in 8 minutes.

On the 6th the absorb phase took 37 minutes

Was the 6th cloudy and the 7th sunny during the absorb phase?

Have you noticed if the battery voltages are becoming more balanced?

Simon

Yerf

Hi Simon

Sorry for the late reply.

Your settings for the battery monitor have worked perfectly so far. It even auto synced yesterday.

The batteries are definitely well balanced, although I am yet to check under load and charge.

It was sunny both on the 6th and 7th. The only difference is that on the 6th the system was under load. On the 7th it was also under load but very little. I have uploaded the charge controller voltage and amps on those days. Also a zoomed one of the voltage and amps at the end of the absorb phase on the 7th.

So it seems all is in order so far and the system is performing well. My slight concern is that the batteries have been discharged to around 30% on a couple of occasions. As far as I know this should be fine with lifepo4 batteries. Also the array charges them upto 100% on a daily basis. Do you guys think that this will harm the batteries?

karrak

Thanks for the information,

I am puzzled by the drop off in the voltage to round 16V, what is happening here, is it the charge controller going to sleep?

30%SOC is just fine for LFP batteries, had my battery down to ~18% yesterday, having said that it doesn't get down to this level very often.

A word of warning, if you are going down to a low SOC make sure your VE.bus BMS is correctly wired up and configured to kill the load if any of the cell voltages get too low.

Does your SOC meter ever go higher than 100%?

I think you could say that there is lots of commentary but few facts about how charging LFP batteries to 100% affects lifespan.

It is well known that the higher the SOC that you store LFP batteries at the larger the loss in capacity of the cells over time.

What is not so well known is what impact on capacity loss having the batteries at nearly 100% SOC during the day when they are in use is. I have read a credible explanation as to why having the battery in constant use would significantly decrease the capacity loss.

There are a large number of off-grid systems out there that run at nearly 100% SOC when there is enough sunshine who are seeing little if any change in the capacity of their batteries over a period of up to and over 5 years.

Reputable LFP manufacturers like A123  recommend charge voltages of 3.6V/cell  and a float voltage of 3.45V/cell which equates to an SOC of around 100%.

In your case Vicron recommends a charge voltage of 3.55V which is needed to balance the battery and a float voltage of 3.34V/cell. In reality you only need 3.45V/cell with a small absorb time to charge to nearly 100%SOC. I haven't seen any information to say whether this extra 0.1V/cell for the short period of time that the cells will be subjected to it will make much difference to the life of the battery. If you were to use a charge voltage lower than 3.55V/cell you will have to run an equilise cycle at 3.55V/cell every month or so to keep the battery in balance.

I run my battery with a maximum charge voltage of 3.45V/cell and drop to a float voltage of 3.35V/cell when the charge current has dropped to C/50.

Simon

Dave Angelini

Nice Simon! I can only add that LG and the other I am testing now (nice to have two in winter) count cycles in this way.
90% DOD = 1 cycle    5 days of 20% DOD equals 1 cycle  There was a spec for sitting (long term) full not cycling from LG that I can't find.
Probably because that never happens here

Good Luck Yerf

 Where are you BTW?

OldMan

I'm mighty suspicious of any Lithium battery without an on-board BMS. I've always thought Victron gear was overpriced. This does nothing to dispel the notion.