Bulk & Float Solar settings for LiFePO4 batteries

[john61ct]

Originally Posted by Kim Klaka

Drop-in 12V lithium packs with min/max regulator cost roughly 10-20% more than good quality AGMs.

Really? Victron, Redarc?

[asimba2]

Originally Posted by john61ct

Maybe lower 13.2V on the float, much better to just STOP when Absorb drops to .02C

Resting full - no charge or load for five hours - should be around 13.5-13.6.

This is where my question comes in. In my case my battery is 200 aH so .02C is 4 amps. If I were able to program my solar charge controller with these settings, would it not charge my battery to 100%, albeit the correct way with the tapering current. If instead I were to set a bulk charge to 13.8V and float at 13.2V, would that not charge my battery to somewhere in the mid-90% range (helping preserve long term battery capacity) and the 13.2V float will be there to pick up the loads up to the amount my solar panel is putting out? Long term battery capacity is a priority for me over getting every last amp hour out, but I'm not sure what charging regime is best for me. If I need the capability to program the %C where float is entered, I'll have to buy the much more expensive "the kid" charge controller along with the second shunt (Whiz Bang Jr) to get that %C capability.

[44'cruisingcat]

I'm running 13.9 bulk,13.4 float.

[john61ct]

Yes, much of the time, the ideal charge is not available. No ability to disable float is very common, and both of the above are likely making a small marginal difference given all the other factors.

The capacity "sacrifice" is I think miniscule between say 13.9 and 14.1 IF you are using end current to terminate.

Even between 13.8 and 14.2 I really doubt more than a few %, no way are you losing 10%, but I agree even if you were the longer lifetime is worth it.

Charging to a volts setpoint only, then variability of current level may give a larger difference.

I would "trust but verify" with accurate monitoring, ideally recorded logging what the output actually is, and tune settings conservatively.

And for those with pricey big banks and no BMS, personally I like the idea of multiple protection "layers" against primary device failure, OVD set higher, LVD set lower, low-temp shutdown.

And maybe a push-button timer that closes the bank's charge buss for say 12 hours, nothing worse if you forget to push it in the afternoon, and no need to remember to close it in the morning?

But a monitor that can trip a relay at 100% SoC would be even better.

[asimba2]

Originally Posted by 44'cruisingcat

I'm running 13.9 bulk,13.4 float.

Thanks, good to know I'm on the right track if I end up using the constant current then constant voltage method for charging.

So those of you solar charging LiFePO4 batteries, are you using voltage to terminate charging or are you using a configurable "end absorb" (usually a % of C) and what solar charge controller are you using to do it?

[john61ct]

EndAmps method best way to go IMO

Most need added cost harware for full access to custom programming

So far looking at:

Victron

Bogart Trimetric controlling SC-2030's if PWM is OK

Shunt-based ​MidNite Solar, KID with Whizbang Jr

MorningStar ProStar

Blue Sky

[SV THIRD DAY]

Most use voltage as an indicator of SOC for charge ending and back that up for confirmation with a good Amp Hour meter.

[asimba2]

Originally Posted by john61ct

EndAmps method best way to go IMO

Let's discuss this for a moment. If you're using End Amps it means you are filling your battery to 100% everytime (at least when there are enough sun hours via solar). What if I want to terminate charging before the battery reaches 100% to preserve battery life?

[SV THIRD DAY]

Originally Posted by asimba2

Let's discuss this for a moment. If you're using End Amps it means you are filling your battery to 100% everytime (at least when there are enough sun hours via solar). What if I want to terminate charging before the battery reaches 100% to preserve battery life?

That's easy.
Just set the charge voltage at a lower rate.
For example set your solar controller voltage at 13.4v or 13.5v and you won't get to 100%. At least not on a normal cruising boat not put away for storage.

[asimba2]

I think there is a fundamental of battery charging I don't understand. Bulk charging, to me, means you are cramming energy into the battery from the solar system as quick as possible, but float is confusing me. Using this generic curve, let's assume I want my "full charge" to be somewhere in the 80-90% of capacity range:


Let's say I decide on 3.45vpc or 13.8V on a 4S battery. I set the BULK setting in my solar charge controller to 13.8V. It's now 1:30pm and the battery hits 13.8V. If I were to disconnect the solar at that moment, I would expect battery voltage to be 13.8V at that moment and slowly (?) decrease and settle around 3.3vpc or 13.2v for the pack. Is this a correct assumption?

So continuing with my above scenario, at 1:30 pm my battery reaches 13.8V. If my FLOAT setting is set at 13.2V, what happens next?

[SV THIRD DAY]

Get out of Lead Acid battery charging thinking/mindset. You don't Bulk, adsorption, Float charge LiFePO4 batteries. So on my solar charger I set ALL stages for the same valve and bingo, done. I started out conservative 3yrs ago at 13.4v and have slowly walked up the voltage to 13.8v. Now, If I leave the boat for a week with no loads, I turn it down to 13.4v.

[asimba2]

Originally Posted by SV THIRD DAY

Get out of Lead Acid battery charging thinking/mindset. You don't Bulk, adsorption, Float charge LiFePO4 batteries. So on my solar charger I set ALL stages for the same valve and bingo, done. I started out conservative 3yrs ago at 13.4v and have slowly walked up the voltage to 13.8v. Now, If I leave the boat for a week with no loads, I turn it down to 13.4v.

I am seeing two distinct recommendations in this thread and the giant 382 page LiFePO4 thread. One recommendation is to bulk charge to 13.8/13.9V and float at 13.2-13.4V and the other is to set bulk/absorb/float all to 13.4-13.8V. I am attempting to understand what happens under each of the scenarios. My question above is what happens to the charge voltage and current from the solar charge controller under the first scenario and my other question is what happens under the second scenario when you're holding the voltage at 13.4-13.8V when the resting voltage of these cells is 13.25-13.3V.

[44'cruisingcat]

Originally Posted by SV THIRD DAY

Get out of Lead Acid battery charging thinking/mindset. You don't Bulk, adsorption, Float charge LiFePO4 batteries. So on my solar charger I set ALL stages for the same valve and bingo, done. I started out conservative 3yrs ago at 13.4v and have slowly walked up the voltage to 13.8v. Now, If I leave the boat for a week with no loads, I turn it down to 13.4v.

Sitting at 13.8 for a few hours, you'd be getting very close to100%. If it's only at 13.8 for a moment, then back to 13.4, that won't happen.

[44'cruisingcat]

Originally Posted by asimba2

I am seeing two distinct recommendations in this thread and the giant 382 page LiFePO4 thread. One recommendation is to bulk charge to 13.8/13.9V and float at 13.2-13.4V and the other is to set bulk/absorb/float all to 13.4-13.8V. I am attempting to understand what happens under each of the scenarios. My question above is what happens to the charge voltage and current from the solar charge controller under the first scenario and my other question is what happens under the second scenario when you're holding the voltage at 13.4-13.8V when the resting voltage of these cells is 13.25-13.3V.

What happens with our system, set at 13.8 bulk 13.4 float, is that when the batteries reach 13.8, the current from the solar goes to zero.

It'll stay at zero until a load such as a fridge cuts in, and the battery voltage drops below 13.4, at which point the current comes back up to match the load.

So what you have is that when the batteries have reached 13.8, charging stops and the solar controller is now just carrying house loads.

[asimba2]

Originally Posted by 44'cruisingcat

What happens with our system, set at 13.8 bulk 13.4 float, is that when the batteries reach 13.8, the current from the solar goes to zero.

It'll stay at zero until a load such as a fridge cuts in, and the battery voltage drops below 13.4, at which point the current comes back up to match the load.

So what you have is that when the batteries have reached 13.8, charging stops and the solar controller is now just carrying house loads.

I appreciate the time you guys are taking to reply. The above sounds like what I'm looking for but I appreciate hearing the pros and cons of the other method as well.