dc-dc CHARGING

[Berend]

Hi all,

I am a bit confused about the charging profiles of many DC-DC chargers (and other chargers also). I can understand the bulk and absorption stages for a LiFePo4 battery. But why the float stage? It does not improve battery life or capacity. I would want charging to completely stop at 13,8 or 13,6 Volts. It seems that none of the chargers has this option.

Kind regards, Berend

 

[Supervstech]

Any quality LFP charger should have no float...

 

[Berend]

That's what I think. But the widely used Victron Orion-Tr Smart has a Float stage same as the CTEK D250SE. The only DC-DC charger I could find where the float stage could be disabled is the Enerdrive DC2DC but I can't find a European distributor for that one.

 

[Sabre36]

If you program float to below the 100% SoC point for LFP, such as 13.4V (3.35VPC) it will be off until a quiescent draw pulls the bank below 3.35VPC VPC. You could also choose 13.2V or 3.3VPC..

 

[Berend]

Still don't understand why they design for a float stage. Weird that we have to change the parameters for a so called "ideal Lithium" charger.

 

[grizzzman]

I think there needs to be a new term for LFP "float". It would be more accurate to say "Solar Load Share" as an example. Or perhaps "Charge Load Share" Where your charge source is being used instead of the battery. That said you need to be careful, especially with variable loads.

 

[John Frum]

Still don't understand why they design for a float stage. Weird that we have to change the parameters for a so called "ideal Lithium" charger.

For lifepo4 batteries float can be better understood as power assist.
The charger helps the batteries with the load.

 

[Berend]

What if there is no load? It will still be floating.

 

[John Frum]

What if there is no load? It will still be floating.

If there is no load and the battery voltage is equal to or higher than the float voltage then no current flows.
The added stress to the batteries is minimal because there is no added voltage stress.
If the float voltage is higher than the battery voltage then that is added stress.
Float voltage should be lower than the the full resting voltage of a battery.
Does that answer your question?

 

[Nol]

I am also worried when the battery is full and the charger keep charging, does that not damage the LifePo battery ?
This is what Renogy helpdesk wrote me :
It will not stop automatically when the LifePo4 is full. It will continue to charge with a small current if it keeps on charging.

 

[John Frum]

I am also worried when the battery is full and the charger keep charging, does that not damage the LifePo battery ?

If the charge current is below the full resting voltage of the battery it won't hurt the battery.
3.35 volts per cell is considered a safe float voltage for lifepo4.
@Nol is that clear?

 

[Nol]

Ik think so
Normal voltage when battery is in rest is 13,4V so if the charger is below 13,4V it is ok
But what if we drive and the alternator is 14,4V ?
What does the DC-DC charger do ?

 

[John Frum]

Ik think so
Normal voltage when battery is in rest is 13,4V so if the charger is below 13,4V it is ok
But what if we drive and the alternator is 14,4V ?
What does the DC-DC charger do ?

Depends if it has charge termination logic.
If it has charge termination logic it will go to float when it determines the battery is charged.
Look in the manual and see if it mentions float.

 

[Nol]

Thanks, I have not yet bought one but will buy a Renogy 20A because the Orion TR 12/30 is twice the price of a Renogy and I think it will do the same.

 

[John Frum]

Thanks, I have not yet bought one but will buy a Renogy 20A because the Orion TR 12/30 is twice the price of a Renogy and I think it will do the same.

Well the renogy is rated for 20 amps and the Victron is rated for 30.

 

[Nol]

I know but 20A is enough if I may believe Will Prowse
I have a 280Ah LifePo4 in my Ducato from 2011, no smart alternator.
LifePo can handle more amps but I don´t know if my alternator can handle that and to be save I am intent to buy the 20A version

 

[grizzzman]

If the Renolgy is in the lifepo4 mode, it will hold the voltage you set it to. (not good) you could control it with a voltage controller. Or set it to charge at 5 amps during travel.

 

[John Frum]

If the Renolgy is in the lifepo4 mode, it will hold the voltage you set it to. (not good) you could control it with a voltage controller. Or set it to charge at 5 amps during travel.

Since it has the capability to float it has charge termination logic.
So I'm not sure what you are driving at.

 

[grizzzman]

Since it has the capability to float it has charge termination logic.
So I'm not sure what you are driving at.

Not if it is set to lifepo4 settings

 

[John Frum]

Not if it is set to lifepo4 settings

Why would it not terminate a charge in lifepo4 mode?
It can terminate the charge whether or not it goes to float.