Constant Current/Constant Voltage Without Cutoff = 14.4V Float?

[orangeminnie]

Constant Current/Constant Voltage Without Cutoff = 14.4V Float? Everything Much of what I've read suggests that floating at 14.x volts is a bad idea for long term survival maximum lifespan of LiFePo4 banks. So why do some of the well-respected charger brands do this, and some of the well-respected battery suppliers say it's OK?

 

[John Frum]

Citation please.

 

[orangeminnie]

I haven't saved the original source documents, but here are a couple of articles.

DIY LiFePO4 Batteries On Boats - Marine How To

DIY LiFePo4 On Boats Last edit;3/26/23:The base of this article was written a number of years ago (2010) but this does not mean the information here is outdated. We have been keeping it updated and have added to it when ever we had the time. This article deals

marinehowto.com

Charge, Float and Cutoff Voltages for Large LiFePO4 Cells

First, this is a great site with incredible participation by some very knowledgable folks, thanx!

forum.solar-electric.com

Victron and BB recommend float voltages, if used, to be not higher than 13.6V... Kilovault & Trojan: 13.8... Relion: not higher than 13.8...
Renogy recommends floating at 14.4... These brands are using at least three different topologies of 3.2V cells.

I don't claim to be a battery expert. Just asking questions and trying to learn.

 

[offgriddle]

Constant Current/Constant Voltage Without Cutoff = 14.4V Float? Everything Much of what I've read suggests that floating at 14.x volts is a bad idea for long term survival of LiFePo4 banks. So why do some of the well-repsected charger brands do this, and some of the well-respected battery suppliers say it's OK?

The specifications for my lifepo's have a charge cut off of 14.65 volts with no float voltage specified.

Life cycle 2000-5000, (that's a broad range, maybe the 80/20 charge/discharge = 5000 cycles)?

My lifepo shore charger voltage specifies 14.4 - 14.6, (maybe that's the float)?

If that helps.

 

[John Frum]

I'm not surprised by float voltages in the 13.6 to 13.8 neighbourhood.
I am surprised by 14.4.
If the float voltage is = or < the resting voltage of the battery then it will not receive charge.

 

[offgriddle]

I'm not surprised by float voltages in the 13.6 to 13.8 neighbourhood.
I am surprised by 14.4.
If the float voltage is = or < the resting voltage of the battery then it will not receive charge.

Well the specification didn't specify a float voltage but I know what you mean, it would make sense for the charger to back off and rest before kicking in within only a couple of tenths of a volt drop.

 

[John Frum]

I couldn't force myself to read the links, I really tried.
Lifepo4 is charge cc=constant current/cv=constant voltage.
The cc part is current limited by the charger
The cc part ends when the current is limited by the battery.
The cv part ends when the current approaches zero.
CC ~= bulk
CV ~= absorb
Float is not part of the equation.
However if float voltage < the resting voltage then the charger and the battery share whatever load there might be.

 

[orangeminnie]

agreed

 

[Sgt Raven]

Here is the presets for Lithium batteries in my DC-DC/MPPT...... It's a Kisae DMT1250..
Bulk/Absorption... 13.9-14.6V(0.1Vstep)
Float.................... 13.5-14.2V(0.1Vstep)
Note 1 applies when in Float, any battery type.....
Note 1:Charger is acting as a power supply with selected constant output voltage and preset maximum output current.
Note 3 applies only to Lithium batteries...
Note 3:Charger will terminate charging when charging current drops to below the set charger termination value.

I can also program custom settings, too.
I still haven't wrapped my head around all of this...

This is the manual for it.....
https://www.donrowe.com/v/vspfiles/pdf/dmt1230_dmt1250_owners_guide.pdf

 

[offgriddle]

"However if float voltage < the resting voltage then the charger and the battery share whatever load there might be".
[/QUOTE]
Cool

 

[orangeminnie]

If I understood correctly what Denis at BB said in interviews: Ideally, a charger would not rebulk until/unless the battery is drawn down to about 75-80% SOC. Presumably this is to cut down on the number of short-cycles. Does any charger completely disconnect (with no float) until such a drawdown occurs? I my mind, an ideal charger might not rely on voltage, but would compute the Ah's consumed, when making a decision on when to rebulk.

 

[orangeminnie]

Regarding short cycles: there was an article that mentioned that chargers with excessive AC ripple unnecessarily age Lithium batteries. In essence, it's like having 60 mini-cycles per second. The take away, as I recall, was that for longer life, it's arguably better to have a few medium cycles, than hundreds of short cycles.

 

[Sgt Raven]

Regarding short cycles: there was an article that mentioned that chargers with excessive AC ripple unnecessarily age Lithium batteries. In essence, it's likely having 60 mini-cycles per second. The take away, as I recall, was that for longer life, it's arguably better to have a few medium cycles, than hundreds of short cycles.

I have read some posts saying that some people with RVs that spend a lot of time on shore power, keep an AGM battery to use when on shore power. This is in rigs that have to show some battery voltage for things to work. Just switching the LFP batteries out of the circuit doesn't work on those ones.

 

[orangeminnie]

I have read some posts saying that some people with RVs that spend a lot of time on shore power, keep an AGM battery to use when on shore power. This is in rigs that have to show some battery voltage for things to work. Just switching the LFP batteries out of the circuit doesn't work on those ones.

I had considered doing that. I want the big investment in lithium to be my last...

 

[Sgt Raven]

I had considered doing that. I want the big investment in lithium to be my last...

It shouldn't be that hard. Just a simple A-B switch. If you haven't charged the AGM in a long time,
I doubt throwing a quick charge on it under the LFP settings would kill it either.

 

[John Frum]

If I understood correctly what Denis at BB said in interviews: Ideally, a charger would not rebulk until/unless the battery is drawn down to about 75-80% SOC.

Can you provide a link to one of the interviews?
Makes sense to me but I have not been able to find anything authoritative.

Does any charger completely disconnect (with no float) until such a drawdown occurs? I my mind, an ideal charger might not rely on voltage, but would compute the Ah's consumed, when making a decision on when to rebulk.

I believe my $14.00 aliexpress charger did this but its broken right now so I can't test it.
From memory the led went from flashing orange to solid green and the current flow stopped.