Tail Current and my Victron Blue Smart AC/DC charger.

[harpo]

Ok guys, I finally assembled my cells into a battery, equipped it with an Overkill BMS, Victron BMV-712 Smart Shunt and a Victron MPPT 100/30 charge controller and a Victron Blue Smart IP22 AC/DC charger.

In the testing phase and things going very well. Have the BMS configured how I want and the Bluetooth Ap running on my Android phone just fine.

Created a Victron network on the Victron Connect AP and have all three Victron components on line in the same phone thru that AP. Went thru the settings and feel confident I have the parameters set well to match my 280Ah battery and Overkill BMS, at least as a good starting point.

Here is the question I have and there was one just a couple weeks ago that was similar. I don't quite understand "Tail Current" its purpose and how I should set that parameter. All Victron has to say about it is: "Once the charge current has dropped to less than the set tail current (% of battery capacity) the battery is considered fully charged." Also: " Some chargers stop charging when the current drops below a set threshold. The tail current must be set higher than this threshold."

First off, according the IP22 Charger manual the charger never really shuts down or stops charging it goes into Absorption (14.2v) and then Float (`13.5v) in the LifePO4 mode.

What should I do with this Tail Current setting in the Smart Shunt? I don't even understand the purpose of it let alone know what to set it at. The default is set at 4% which is 11.2 amps. So in this case once the charging current goes below 11.2A there will be no more charging take place? Do I understand that correctly from the statement above which was taken directly from the Smart Shunt manual?

Do I set this parameter to something very low like .02% (.002 X 280 = .58A???)

I really don't know what to do with this setting and the Victron manual gives very little guidance or education about it. HELP.

 

[John Frum]

Here is the question I have and there was one just a couple weeks ago that was similar. I don't quite understand "Tail Current" its purpose and how I should set that parameter. All Victron has to say about it is: "Once the charge current has dropped to less than the set tail current (% of battery capacity) the battery is considered fully charged." Also: " Some chargers stop charging when the current drops below a set threshold. The tail current must be set higher than this threshold."

First off, according the IP22 Charger manual the charger never really shuts down or stops charging it goes into Absorption (14.2v) and then Float (`13.5v) in the LifePO4 mode.

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

Tail current for a big blue prismatic 280ah battery is .05c(14 amps).
In reality the tail current depends on the charge current.
The other problem with this is your charger can't tell the difference between a load and the battery.
So if you have a 15 amp load your charge will never terminate on tail current.

 

[Kemills1]

You can use the smart feature of your MPPT and BMV so that the MPPT uses the current reading from the BMV shunt so MPPT can see the actual current going into the battery. If you've a Victron smart charger, can it not do the same?

 

[Goboatingnow]

Tail current is the continuous system load on the battery while charging , the charge current the battery is receiving is the charge current -tail current. if you create a VE.smart network the smart shunt or BMV712 will feed battery current back to the Ve.smart chargers. In this case they can compute tail current as total charge - charge current.

Depending on the firmware , each victron unit will use the Bluetooth supplied current rather then a fixed value in the charger setup

 

[Kemills1]

The “tail current“ along with “Charged voltage“ and “Charge detection time” are parameters used by the smart shunt to determine when the battery is considered fully charged. When all the conditions are met, the SoC will be reset back to 100%. (Synchronized). The condition to be met for synchronization is, the BATTERY voltage must be above the set “Charged voltage” AND the BATTERY charging current must be below the set “Tail current” for the set period of the time “Charge detection time”. At this point the smart shunt will set the SoC back to 100%.
EDIT: I’ve just looked at the manual and the assumption below that the charger has VE smart networking is wrong. A very big oversight in my opinion, on the part of Victron and very misleading to calling it a ”smart” charger. It looks like your charger is not meant for in service battery charging.

If you are using your smart blue AC/DC charger to charge the batteries while they are still in service, the charger should be able to use the VE smart networking to “see” the actual BATTERY charging current i.e. the battery current measured by the smart shunt . It can then determine in the same way as the smart shunt, when the battery is fully charged and go to float.

 

[Goboatingnow]

The “tail current“ along with “Charged voltage“ and “Charge detection time” are parameters used by the smart shunt to determine when the battery is considered fully charged. When all the conditions are met, the SoC will be reset back to 100%. (Synchronized). The condition to be met for synchronization is, the BATTERY voltage must be above the set “Charged voltage” AND the BATTERY charging current must be below the set “Tail current” for the set period of the time “Charge detection time”. At this point the smart shunt will set the SoC back to 100%.
EDIT: I’ve just looked at the manual and the assumption below that the charger has VE smart networking is wrong. A very big oversight in my opinion, on the part of Victron and very misleading to calling it a ”smart” charger. It looks like your charger is not meant for in service battery charging.

If you are using your smart blue AC/DC charger to charge the batteries while they are still in service, the charger should be able to use the VE smart networking to “see” the actual BATTERY charging current i.e. the battery current measured by the smart shunt . It can then determine in the same way as the smart shunt, when the battery is fully charged and go to float.

Just to be clear

My system has a BMV712 a smart solar mppt and a mains smart 12/30

This does use the VE.smart Bluetooth networking and the charger will use bmv712 battery current to determine tail current

 

[mikefitz]

Because you are charging at a low current compared to battery capacity you can disregard tail current as a charge control . The chargers will reach the 'target ' absorbtion voltage of 14.2 volts. At this point the battery will, in effect, be fully charged, so any action due to tail current will have no influence on battery SOC. Tail current termination only occurs once the chargers are operating in the absorbtion phase, it does not prevent the charger entering float stage.
I suggest using the value of 4% for tail current.
It's probable with a modest solar system the current will be below this value durring the day anyhow.

Tail current charge termination is more useful when charging lead acid batteries with long absorbtion periods, perhaps several hours. For lead batteries 1% or even 0.5% tail current would be used.

Summary; set tail current to 4% and stop worring, you battery will charge OK.

Mike

 

[Kemills1]

Just to be clear

My system has a BMV712 a smart solar mppt and a mains smart 12/30

This does use the VE.smart Bluetooth networking and the charger will use bmv712 battery current to determine tail current

Sorry but I’m still not clear on one thing. Does your mains smart 12/30 support VE.smart networking and goes it have the tail current parameter?

 

[Kemills1]

At this point the battery will, in effect, be fully charged, so any action due to tail current will have no influence on battery SOC. Tail current termination only occurs once the chargers are operating in the absorbtion phase, it does not prevent the charger entering float stage.

If you don’t use the tail current feature, when does the charger go to float? I agree the feature is more useful for lead acid batteries as using a fixed or even adaptive absorb time is just a guess as to what the battery actually needs but terminating the absorb period on a LifePo4 battery using the tail current feature is still valid.

 

[Steve_S]

Tail Current is also called End Amps. The formula is 280AH*0.05 = 14A
The Bulk/Absorbe stops when the battery is only taking 14A and switches over to Float mode, which finishes off the charge process.
If you have 3 packs in a Bank, say 200, 272 & 280, you would use the Lower AH Battery to determine the TailCurrent. It has nothing to do with Lead Acid batteries.

 

[mikefitz]

if you don’t use the tail current feature, when does the charger go to float?

Your chargers will be set for absorption voltage and absorption time, the float stage will follow the absorption period.
With lithium, a charge voltage of 14.2, and low charge currents, a long absorption period is not needed.

but terminating the absorb period on a LifePo4 battery using the tail current feature is still valid.

It would be if the charge current was always constant and a high value compared with the tail current setting. However in this application its probable the charge current from solar will be lower than the tail current setting for 280 Ah battery.
As I pointed out, with low charge currents and 14.2 absorption voltage, tail current termination of the absorption period is academic, since the battery is charged by the time the absorption voltage is reached.

I agree that if charging at a constant 0.5C or higher, then tail current termination would be ideal.

Mike

 

[Kemills1]

It would be if the charge current was always constant and a high value compared with the tail current setting. However in this application its probable the charge current from solar will be lower than the tail current setting for 280 Ah battery.

Well, I have a 600Ah battery and I’ve set the tail current parameter to 1A (the max value you can set is 10A) and the absorb time is 15 mins. The charge current will drop below the 1A tail current setting before the 15 min absorb time has expired. I’m sure this strategy would work perfectly well for the OP’s system.

 

[Goboatingnow]

Sorry but I’m still not clear on one thing. Does your mains smart 12/30 support VE.smart networking and goes it have the tail current parameter?

Yes it’s ( blue start Ip22 12/30
) supports ve.smart networking and has a tail current parameter. It also synchronises charge states with the mppt controller over ve.smart

4. VE.Smart Product Compatibility

www.victronenergy.com

 

[Goboatingnow]

Because you are charging at a low current compared to battery capacity you can disregard tail current as a charge control . The chargers will reach the 'target ' absorbtion voltage of 14.2 volts. At this point the battery will, in effect, be fully charged, so any action due to tail current will have no influence on battery SOC. Tail current termination only occurs once the chargers are operating in the absorbtion phase, it does not prevent the charger entering float stage.
I suggest using the value of 4% for tail current.
It's probable with a modest solar system the current will be below this value durring the day anyhow.

Tail current charge termination is more useful when charging lead acid batteries with long absorbtion periods, perhaps several hours. For lead batteries 1% or even 0.5% tail current would be used.

Summary; set tail current to 4% and stop worring, you battery will charge OK.

Mike

Tail current is important to correctly terminate absorption mode. The next is be.smart networking or other methods which feed back actual tail current as the problem is many system can have considerable variation on tail current.

Hence for example my tail current jumps when the fridge comes on or other larger loads activate. Then it drops back to smaller values.

Too low a tail current figure and the charger never leaves absorption mode until typically a protection timer runs out , this leads to overcharging , to high a tail current and the absorption mode is terminated premAturely.

 

[Kemills1]

Yes it’s ( blue start Ip22 12/30
) supports ve.smart networking and has a tail current parameter. It also synchronises charge states with the mppt controller over ve.smart

4. VE.Smart Product Compatibility

www.victronenergy.com

Thanks, I was looking at the wrong charger.
Correction, I was looking at the right charger (Blue smart IP22) but the manual makes no mention of ve.smart networking. However, it is mentioned in the features list.

 

[John Frum]

Tail current makes sense with an inverter/charger and no pure dc loads.
While attached to shore power the mains power services the ac loads leaving the battery to take all the charge that the charger supplies.
Since no other load is being service by the charger, the charger can use tail current as a good deterministic way to terminate the charge when the battery is properly full but not overcharged.

The other scenario where tail current can make sense is if the load is constant enough to allow proper termination on tail current.

A typical solar setup either mobile or stationary doesn't usually fit the profile.

 

[Kemills1]

Tail current makes sense with an inverter/charger and no pure dc loads.
While attached to shore power the mains power services the loads leaving the battery to take all the charge that the charger supplies.
Since no other load is being service by the charger, the charger can use tail current as a good deterministic way to terminate the charge when the battery is properly full but not overcharged.

The other scenario where tail current can make sense is if the load is constant enough to allow proper termination on tail current.

A typical solar setup either mobile or stationary doesn't usually fit the profile.

Sorry if I have this wrong but you seem to have missed the point. Terminate charge using a tail current strategy in a in service system is only feasible if the charger can monitor the actual current going into the battery. This is where a smart charger and smart shunt can work really well. Via blue tooth, the smart charger can monitor actual battery current measured by the smart shunt and terminate the absorb cycle when the battery current drops below the tail current threshold set in the smart charger. Without a connection to the smart shunt, the tail current parameter is pointless.

 

[John Frum]

Sorry if I have this wrong but you seem to have missed the point.

I guess I did.

Terminate charge using a tail current strategy in a in service system is only feasible if the charger can monitor the actual current going into the battery.

I can't parse this sentence.

This is where a smart charger and smart shunt can work really well. Via blue tooth, the smart charger can monitor actual battery current measured by the smart shunt and terminate the absorb cycle when the battery current drops below the tail current threshold set in the smart charger.

I thought that level of integration in a Victron environment required a cerbo GX or similar and a wired protocol.

Without a connection to the smart shunt, the tail current parameter is pointless.

As I stated previously it depends on how deterministic the loads and charge sources are.

 

[John Frum]

Terminate charge using a tail current strategy in a in service system is only feasible if the charger can monitor the actual current going into the battery.

I can parse it now.
True in the common case but not a universal truth.

 

[Kemills1]

I can parse it now.
True in the common case but not a universal truth.

Agreed.