Solar controller for constant Voltage Lithium charging.

[Boyntonstu]

I have been using a 48.0 V lab quality power supply to charge my Lithium batteries in series at a  constant 48.0 Volts.

By limiting each cell to 4.0 V instead of 4.2 V, I have found that over hundreds of cycles, the cells hold up well and I have never needed to balance charge.

Back to solar:

Can you adjust your solar controller to output a constant  12.0 Volts so I can charge Lithium  the same way?

If you can do it, details please.

 

[John61CT]

It is very common for solar controllers to be fully adjustable and allow the user to customize the charging algorithm. So far as I would say any good model has that feature. The same is not true for Shore chargers

 

[Boyntonstu]

It is very common for solar controllers to be fully adjustable and allow the user to customize the charging algorithm. So far as I would say any good model has that feature. The same is not true for Shore chargers

Nice.  However they usually say, "Not to be used for Lithium charging".

I want a single setting, low or high, 12.0 Volts.

 

[John61CT]

Lawyers.

You're talking LiFePO4? "Lithium" is too general.

Prismatic? Do you have a BMS?

4 cells for nominal 12V should be charged at 3.45Vpc or 13.8V. Should stop at hitting the voltage, or worst case before trailing amps hits .02C, 2A per 100AH.

No need to get to full, in fact hurts longevity, but no automatic charge sources "just stop", so if you're not controlling manually, set Float to 13.2V.

Don't discharge too low or they're dead forever, same with trying to charge in freezing​ temps.

 

[TechScott]

I'm currently moding a fiberglass 5th wheel for full-time living.  Fiberglass trailers are challenging to install solar on due to limited space and mounting options so a lithium battery is crucial. I found this: https://www.amazon.com/Solar-Charge...=merchant-items&ie=UTF8&qid=1506886248&sr=1-6 MPPT controller that has a lithium charging mode and it's reasonably priced to boot!

 

[Boyntonstu]

Lawyers.

You're talking LiFePO4? "Lithium" is too general.

Prismatic? Do you have a BMS?

4 cells for nominal 12V should be charged at 3.45Vpc or 13.8V. Should stop at hitting the voltage, or worst case before trailing amps hits .02C, 2A per 100AH.

No need to get to full, in fact hurts longevity, but no automatic charge sources "just stop", so if you're not controlling manually, set Float to 13.2V.

Don't discharge too low or they're dead forever, same with trying to charge in freezing temps.

I use Lithium Ion 18650's and Lithium Polymer cells.  I never charge to maximum charge cell voltage.

If you use a constant Voltage chargers, they stop charging automatically at the desired Voltage.

I have left my CV chargers on for more than 24 hours and the cells measure exactly 4.0 V.

I have hundreds of cycles that proves the method.

For LiFePO4 I would charge to 3.2 V per cell or 12.8 V, no higher.

 

[TechScott]

I have been using a 48.0 V lab quality power supply to charge my Lithium batteries in series at a  constant 48.0 Volts.

By limiting each cell to 4.0 V instead of 4.2 V, I have found that over hundreds of cycles, the cells hold up well and I have never needed to balance charge.

Back to solar:

Can you adjust your solar controller to output a constant  12.0 Volts so I can charge Lithium  the same way?

If you can do it, details please.

The problem with charging 12v at a constant rate is that the battery will take much longer to reach a full charge. Lithium batteries can accept more of a charge (both in volts and amps) than their voltage rating.  Look at the manufacturers charge recommendations and set-up your controller for that amount.

 

[jonyjoe303]

If you adjust the absorb and float both to 12 volts (if they go that low) you should get the voltage you need, mppt controller can control the voltage better then pwm. Lower voltage means lower amps going into the battery. 

But I wouldn't trust any charge controller to charge lithiums, except maybe the electrodacus controller which can monitor the balance status of the battery. Its the only true lithium charge controller, all the others just monitor overall voltage but not the balance voltage which is where the danger is.

Its very easy for the battery to go out of balance while charging, and even if the controller stopped at 12.6 volts, one row of batteries might be severely over voltaged. Myself I wouldn't risk it and have charged both the li-ion and the lifepo4 batteries.

If you want to control that the battery doesnt go over a particular voltage, you can do what I do which is to put an overvoltage relay that will disconnect the panel from the controller when the voltage reaches 12 volts, this is how I do it. It works everytime. But even this isn't good enough for me because what if the battery goes out of balance, to me its more of a deadman switch.

I notice that if I set my ecoworthy mppt to 12 volts, my li-ion (11.1 volt battery pack never got charged, it just trickle charged at 3 or 4 amps).  My lifepo4 I had to raise the voltage to 15.5 volts to fast charge. You need higher voltages if you want to fast charge them. Lower voltages are much safer but I still wouldnt trust them unless the charger can monitor the balance voltage. The only time I saw my lifepo4 go under 12.9 volts was when it only had 30 percent power left, once it goes to 12.8 volts it will quickly go to empty.

When I want to fully charge my lithiums I have been using a 14 amp ISDT q6 balance charger, they use them in the RC world, it will hit the battery with maximun amps and make sure it don't go out of balance. My ecoworthy mppt, I only use it to slow charge my lithiums.

This controller is suppose to be lithium capable, and I tested it and it actually didnt stop the charge at 12.6 volts like it was suppose to. Thats why I would recommend a overvoltage relay on any lithium battery. Controller can fail or bms can fail.

 

[user 15722]

electrodacus, huh ?
I'll need to look for that one.
I'd like to go LiFePo4 one day, for all the usual reasons.
wheels

 

[John61CT]

I believe the 18650s are LiCoO2.

I would not for safety reasons recommend using any lithium-ion except LFP for large House bank use in a mobile context.

4.35Vpc or 13.8V isn't close to pushing the shoulder of the SoC curve, perfectly safe even at high current rates, long as you don't go higher and stop charging as soon as amps drops to .02C or earlier.

 

[John61CT]

> I still wouldnt trust them unless the charger can monitor the balance voltage.

With good quality prismatic LFP and in the context of House bank usage, much gentler current rates than say EV, just need an initial balance, check them say once a quarter.

They don't get unbalanced as long as you stay away from the shoulders at both ends, 5%-95% SoC charging no higher than 4.35Vpc / 13.8V

Charge rates at 1C or even higher are fine acceptance stays that high right up to 90+%, a full recharge in under an hour is easy NP.

 

[tripper]

> I still wouldnt trust them unless the charger can monitor the balance voltage.

With good quality prismatic LFP and in the context of House bank usage, much gentler current rates than say EV, just need an initial balance, check them say once a quarter.

They don't get unbalanced as long as you stay away from the shoulders at both ends, 5%-95%  SoC charging no higher than 4.35Vpc / 13.8V

Charge rates at 1C or even higher are fine acceptance stays that high right up to 90+%, a full recharge in under an hour is easy NP.

Thanks for the info. I currently have a 100 AH 12V LiFePo4 Auto battery from China (Ebay), has BMS built in and is in an automotive type grp 31 case. It says it has a low and high cutoff on it too.  I have been charging it using a standard Victron MPPT solar controller set to 14.0 volts for Absorb/bulk and 13.2 volts float.  So far it has been working well. The way the controller works is it may start off at high amps (60+) but then tapers down over time and eventually goes into float, it seems to be working just fine this way. I will drop the voltage down to 13.8 volts and see how it does. I am assuming temp compensation should be shut off for a LiFePo4.

I just best guessed the setup when I first installed it as there is very little info on doing this stuff in an RV. I have no way of knowing how charged/discharged the battery is other than I have a good idea of my power consumption and a voltmeter, the solar controller seems to be keeping it up just fine.

 

[frater secessus]

This controller is suppose to be lithium capable, and I tested it and it actually didnt stop the charge at 12.6 volts like it was suppose to. Thats why I would recommend a overvoltage relay on any lithium battery. Controller can fail or bms can fail.

Trebor and I both have shunt-style controllers like that.  Mine stops exactly on the setpoint.  Dunno about Trebot's, but we've PMed about them and he hasn't mentioned any voltage inaccuracy that I remember.

 

[Boyntonstu]

> I still wouldnt trust them unless the charger can monitor the balance voltage.

With good quality prismatic LFP and in the context of House bank usage, much gentler current rates than say EV, just need an initial balance, check them say once a quarter.

They don't get unbalanced as long as you stay away from the shoulders at both ends, 5%-95%  SoC charging no higher than 4.35Vpc / 13.8V

Charge rates at 1C or even higher are fine acceptance stays that high right up to 90+%, a full recharge in under an hour is easy NP.

"They don't get unbalanced as long as you stay away from the shoulders at both ends, 5%-95%  SoC charging no higher than 4.35Vpc / 13.8V"    

This has been my experience.

However, for my 48 V bike I am more conservative about staying away from the shoulders.

I have never measured imbalance.

This is my homemade jig for balance measurement:

[video=youtube]

 

[John61CT]

Yes any EV usage is very different from House storage, high %C discharge rates can make more frequent balance checking a good idea.

And really it's necessary to specify the type of chemistry for any meaningful discussion.

If it isn't LFP I avoid, but the profile I spec'd really is plenty safe.

Haven't found a "LFP ready charger" yet that gentle.

 

[John61CT]

> actually didnt stop the charge at 12.6 volts like it was suppose to. Thats why I would recommend a overvoltage relay on any lithium battery. Controller can fail or bms can fail.

Yes, with a very expensive bank it's worth investing in multi-layered security for LVD, OVD and often temperature.

I wish I could find a generic robust adjustable 4s BMS that had all three good for say 300A. That didn't do active cell balancing, I suppose alarm-only would be OK.

 

[John61CT]

> 100 AH 12V LiFePo4 Auto battery from China (Ebay), has BMS built in and is in an automotive type grp 31 case. It says it has a low and high cutoff on it too. 

aka "drop in" style. Make sure to never have this be the only charge target on an alt, or even with other sources with sensitive electronic loads on the circuit, the batt going offline suddenly can release the magic smoke elsewhere.


> I will drop the voltage down to 13.8 volts and see how it does.
You won't see any difference, only lose a couple percent capacity, but gain maybe many hundreds of cycles' lifetime.

Best to shut charging down completely, but if not that's a good Float.

Note you shouldn't leave them sitting full, only go that high if you've loads on going to start pulling it back down.

Storage at 10-20% SoC, but never let them go dead flat.


> I am assuming temp compensation should be shut off for a LiFePo4.

Yes

> I just best guessed the setup when I first installed it as there is very little info on doing this stuff in an RV.

Google the marine forums, especially "maine sail" aka CMS aka Compass Marine

> I have no way of knowing how charged/discharged the battery is other than I have a good idea of my power consumption and a voltmeter

Smartgauge doesn't work with LFP, but Victron 702-BMV or Bogart Trimetric. The latter can control up to 62A of solar controllers, sweet setup.