Charging LIFePo4

[VanKitten]

So, this question occurs to me...

 If I use a solar charge controller that is not intended for LIFePo4.... as long as I can set it to stop charging above 14.6 volts....it should work just fine for my batteries?

Are there other settings I would have to "fix" to accommodate these batteries?  

I have a relay that will shut off charging at 14.8.  By disconnecting the battery from the charge.   But, that is a last ditch save the batteries situation...

 

[willprowse]

Depends on BMS or cell balancer. What does yours recommend? Different LiFePo4 batteries like different input voltages depending on how they are designed.

Is it a drop-in lead-acid replacement? Or bare cells without a BMS?

 

[jonyjoe303]

Yes the overvoltage regulator is a good thing to use I have it on mine to shutoff at 14.6 volts. The actual relay is connected between the solar panel and controller, thats the perfect place to put it, when it triggers the controller goes into sleeping mode. The overvoltage relay need to get the voltage reading directly from the battery so it has the true reading (no voltage drop).

The controller itself won't stop charging even if you set it to 14.6 volts, it might go to float. You can set the float so low, that the battery won't receive any amps.

The only thing I notice is that the controller see's a lifepo4 as a full battery and will not charge at maximum amps when set to 14.6 volts. I need to set mine to 15.5 volts to fast charge it. The only time I set it at 14.6 volts is when I just want to trickle charge the battery when its already at 90 percent or higher. 

I don't think there is such a thing as a lifepo4/lithium solar controller, unless the controller can balance a lithium it doesnt really know if its full. A lifepo4 can read 14.6 volts and be severely out of balance were one group of cells exceeded its max limit (that happens if the bms fails). I seen it happen thats why I monitor each group of cells.

If your lifepo4 has a balance lead, you can easily check the condition of the battery with a (10 dollar) 3in1 lipo checker.

 

[VanKitten]

Well.. there is no BMS on this system. (Long story )

I have balancers sitting right on the batteries. I have two relays.
One cuts off high voltage. This cannot sit between the Panels and the controller...because it must handle ALL the possibly charge supplies in the system..not just solar. The other sits on the load panel and cuts off when voltage is to low.

So...back to the solar charge controller...... I want to use an MPPT but it doesn't necessarily support LIFePo4. The battery manufacturer says the charge limits is 14.8 then cut off...the discharge limit is 11.8 then cut off.

Ok, so my question is.... can I set the charge controller to 14.6 .... what lie do I need to set for lithium instead of lead acid?

 

[blars]

Yowch. I was being aggressive and charging my LiFePO4 to 14.0 volts. Current recommendations for house battery use are 13.8v max. Unlike lead, you should not hold a LiFePO4 at full charge, it will reduce the life. You can get over 98% charge at 13.8v. "Float" should be at 13.2v or less. Balance is mostly only an issue if you use the battery destroying top or bottom end, keep you cells in the 10% to 90% state of charge range and it won't be an issue.

At 14.6v, don't expect your LiFePO4 to last more than a few hundred cycles, maybe much less.

 

[John61CT]

Thank you. I was just going to sit this one out, since I've tried to get through to OP a few times now.

No one should be accepting vendor claims that LFP is OK with charging Full to over 14V.

Even 14V is not optimal for longevity, my limit is 13.8.

 

[John61CT]

Just for giggles, here's my "boilerplate" LFP summary

____
Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Note nearly **every** vendor, also those of ancillary hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My (conspiracy) theory is that manufacturers would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc which = 13.8V max for "12V".

Either stop when voltage is hit, or if you want another couple % SoC capacity, stop when tailing amps hits endAmps of .02C, or 2A per 100AH. Note even at the "low" max charge voltage, letting the charge source continue to "push" even low currents long past the endAmps point is **over-charging, and will** greatly reduce lifecycles.

If you can't then "just stop", set Float at 13.1V, but that is a compromise, and *may* shorten life cycles.

With LFP, you don't need to fill up all the way at all, as far as the cells are concerned, in fact it is bad for them to sit there more than a few minutes. Therefore only "fill up" if loads are present, ready to start discharging, ideally right away.

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly). Letting the batts go "dead flat" = instant **permanent unrecoverable** damage. 

Same with charging in below 32°F / 0°C freezing temps.

Persistent high temps also drastically shortens life.

Charging at 1C or even higher is no problem, as long as your wiring is that robust, vendors may spec lower out of legal caution.

Going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve. And of course, we're taling about gentle "partial C" House bank discharge rates, size appropriately and be careful feeding heavy loads like a winch or windlass.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers of protection are advised if it is a very expensive bank, don't rely on any one device to work.

Check cell-level voltage balance say monthly to start, then quarterly, finally every six months if there are no imbalance issues, but only if that seems safe to you.

This thread is long but informative
LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks , make sure to give both Maine Sail and Ocean Planet your close attention.

Also MS' summary notes here
http://www.pbase.com/mainecruising/lifepo4_on_boats

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor. His new site under development transitioning the pbase content is here

https://marinehowto.com

Best of luck and do please report back here.

 

[John61CT]

So, this question occurs to me...

 If I use a solar charge controller that is not intended for LIFePo4.... as long as I can set it to stop charging above 14.6 volts....it should work just fine for my batteries?

Are there other settings I would have to "fix" to accommodate these batteries?  

I have a relay that will shut off charging at 14.8.  By disconnecting the battery from the charge.   But, that is a last ditch save the batteries situation...

Well great we've come this far.

Your SC should be adjusted to 13.8V max, minimum Absorb hold time (none is best) float at 13.1V (just stopping is better.

Your relay should trigger to open (isolate) at 14V.

There are no charge sources that actually take care of LFP properly out if the box. In fact most that claim LFP ready are much worse than those that don't.

Best you can get is as much user-adjustability setting up a custom charge profile.

 

[John61CT]

Different LiFePo4 batteries like different input voltages depending on how they are designed.

Not in practice, just that some vendors are more shameless than others in claiming it's OK to adopt LFP into an infrastructure designed for lead.

The actual chemistry dictates how to treat it if longevity is your goal.

 

[Trebor English]

I want to use an MPPT but it doesn't necessarily support LIFePo4.   The battery manufacturer says the charge limits is 14.8 then cut off...the discharge limit is 11.8 then cut off.    

Ok, so my question is.... can I set the charge controller to 14.6 .... what lie do I need to set for lithium instead of lead acid?

I have no experience with lithium batteries but, from reading about it I have been led to believe there is an issue.  Charge controllers do not have linear regulators on their outputs.  For example, my PWM controller connects the panel to the battery with an on/off low resistance switch.  The voltmeter connected to the lead acid battery shows an average of 14.2 or whatever volts.  It is actually pulses of panel voltage with a momentary battery voltage quite a bit higher than the average.  Lead acid doesn't seem to care but from my reading it seems that LiFePo does care.  MPPT will have a similar effect with the amount varying from one controller to the next.  

I would expect that a "lithium" controller would have a different design to limit this effect.  Shortening the magnitude and duration of the pulses is a start.  Most of the charging is done with the battery far enough from full to avoid this problem.  

If it were my battery I would have the controller shutting off well lower than a potentially damaging level.

 

[John61CT]

Interesting idea of the pulsing being an issue. Any links on that?

It is true I've never heard of any LFP prismatic bank owners using PWM, someone spending thousands on the bank isn't going to try to save a few hundred on their controllers. 90% of them these days are using Victron specifically.

But I never came across any statement about that issue you raise being a reason, just the usual "MPPT is better" assumption.

As for "damaging voltage levels" this is as usual a question of semantics. Any "damage" from lead-based charge sources is unlikely to show up for at least five years.

The difference between charging bank A at 13.8V as opposed to say 14.4 on bank B may be mean that B only lasts for 1-2,000 cycles, but A is still showing 95% rated capacity at 4,000 cycles fifteen years later.

But paying 5-7 times more per AH than lead is usually only justified by that longevity factor.

I myself do think of charging voltage as "damaging", but prefer to use more nuanced terms like "suboptimal" or "harmful to longevity".

 

[jimindenver]

In the bottom of a MPPT controller is a "PWM". The difference is how the power is presented to that PWM unit as in all of the available panel power at a acceptable voltage vs the fraction of the power a normal PWM allows for due to battery voltage limitations.

Kats controller is maxing at 7.8 amps no matter it it is trying to raise the voltage or running her induction burner. Her two 345 watt panels are wired in series and I checked to make sure they had output. Oddly connected they are reading 58-60 volts as what I would read as a working voltage which should be around 30v or so per panel. The Voc per panel is 48v or 96Voc in series. The voltage of the bank never rose above 13.3v for the while I was there and dropped to 13.1v with the induction burner boiling water. It was very sunny yesterday.

The high working voltage concerns me because that would be the working voltage of a 48v bank which might explain the low amps. Unfortunately she does not have the dongle or a remote display so I am working blind in a sense.

She has a Morningstar TS-MPPT-60 that I can easily connect a computer to and set a custom profile that will use whatever voltages are deemed proper.

 

[tx2sturgis]

 Her two 345 watt panels are wired in series and I checked to make sure they had output. Oddly connected they are reading 58-60 volts as what I would read as a working voltage which should be around 30v or so per panel. The Voc per panel is 48v or 96Voc in series.

Were you able to check each panel individually?

Voltage AND current?

It sounds like one of the panels may have low output for some reason.

If possible, try connecting each panel to the controller individually, see what you get from each one.

 

[jimindenver]

I didn't take the system down to that point but rather just checked the voltage with the controller connected, ie working voltage at 30 volts each would have been where I was seeing 60 volts. It is too cloudy to test much today and I think I am going to have to gas up the little generator or run a shore cord over to her to keep the fridge running. Tomorrow I will get back up there for more resting and possibly set the panels in parallel.

John

How does the Victron decide what voltage the bank is at?

 

[John61CT]

Sorry do you mean Kat owns a Victron device of some kind? Or just hypothetical, their MPPT as opposed to what Morningstar does?

The voltage of the circuit as a whole will be "negotiated" between the loads, bank SoC and what the SC is putting out.

I would take all loads off the circuit completely while trying to figure out what's going on between the solar and the bank.

And get the bank to full via a shore power supply, i.e. 13.8V or close as possible not too high. But as much current as you like up to say 30A.

If you do go over 14, stop when you get to the target voltage, and start discharging right away, it's not good for LFP to stay **that** full more than a few minutes.

But as a test, do record "resting" volts after say one hour, if you are able do the "13.8 & stop" routine.

Note it is possible to damage the bank by overcharging between 13.1-13.8 too, so best as a double check make sure trailing current doesn't drop below 2A regardless of voltage.

What is the battery model again?

Panels?

 

[John61CT]

Her two 345 watt panels are wired in series and I checked to make sure they had output. Oddly connected they are reading 58-60 volts as what I would read as a working voltage which should be around 30v or so per panel. The Voc per panel is 48v or 96Voc in series. The voltage of the bank never rose above 13.3v for the while I was there and dropped to 13.1v with the induction burner boiling water. It was very sunny yesterday.

The high working voltage concerns me

Do you mean at SC input?

That controller is OK up to total 150Voc, so plenty of headroom there, dropping to lower V going parallel would like drop total output right, less for MPPT to work with.

Remember the internal BMS here too, this is a Drop-in type not bare prismatic cells.

 

[jimindenver]

John

How does the Victron decide what the voltage of the battery bank is? As in 12v/24v/36v/48v

Working voltage of a panel is the lower voltage you see on the name plate. It can be adjusted by the MPPT controller so when I checked yesterday hers were at a working voltage of near 60v. I would have had to disconnect or at least shut down the controller to check the Volts open circuit.
Kat said she talked to you last week or so and to bring some of the good stuff with you, hehe

 

[tx2sturgis]

John

How does the Victron decide what the voltage of the battery bank is? As in 12v/24v/36v/48v

I'll address this since I know the answer.

When you first hook up the controller to the battery (or batteries) the controller measures the voltage. It assumes a standard battery voltage based on what it sees when you hook it up to the batteries. It will remain at this reference voltage from then on, unless it's disconnected for some length of time.

Of course this assumes the battery bank is somewhere close to its normal operating voltage when the controller is connected.

 

[John61CT]

How does the Victron decide what the voltage of the battery bank is? As in 12v/24v/36v/48v

Again, what Victron unit? A battery monitor, isolator? You stated she has Morningstar SC.

In any case automatic "nominal" detection happens when the SC is hooked up to the bank, which is supposed to happen before the panels get attached. Which is what Kat's been doing, right?

Some older units required user to select manually.

AFAIK the smaller Victron SCs are 12/24 only, haven't much experience with higher than that, IMO for propulsion only.

Working voltage of a panel is the lower voltage you see on the name plate.

Who, me personally? Have I missed some photos? Plate on what, panels?

It can be adjusted by the MPPT controller so when I checked yesterday hers were at a working voltage of near 60v.

If you mean between the panel and the SC, I didn't think that was adjustable by the user. Output after the SC charging the bank should only be adjustable between a range appropriate for the bank nominal V, e.g. for "12V" between 11V and 17V

 

[John61CT]

When you first hook up the controller to the battery (or batteries) the controller measures the voltage. It assumes a standard battery voltage based on what it sees when you hook it up to the batteries. It will remain at this reference voltage from then on, unless it's disconnected for some length of time.

Of course this assumes the battery bank is somewhere close to its normal operating voltage when the controller is connected.

Yes to all that,

but a batt could only show lower, not higher right?