what happens with LiPO4 is full by solar?

[Sailorman Ed]

I understand how a 110v charger tapers off when the LiPO4 battery is full but how does it work with a solar controller? The solar panel is still putting out power. How does the MPPT controller handle this? What happens to the solar panel amps when the battery is full? It doesn't hurt the panel to do nothing under full sun?



And I remember reading that a LiPO4 battery should be kept at 80%. I don't see a way to accomplish this except by turning the MPPT off???
thanks in advance for my education.
Ed

[donradcliffe]

Most solar controllers reduce current by reducing the width of DC pulses. Some interrupt the entire circuit. The solar panels don't care.

[K_V_B]

This is why solar can kill your lithium batteries.

What you need is a way for the battery to turn the solar charger off when it is full. In lithium system the batteries are the master, and they tell the chargers to charge, or not to charge.

[wholybee]

The first thing to understand is that no charger produces Amps and pushes them into a battery. And no charger reduces Amps perse. The current is a result of the voltage difference between the charger and battery, and the resistance in the circuit by ohms law. The only thing a charger can do to reduce current is to reduce voltage.

With that in mind, the requirement for LFP is to charge the battery till full, then stop. There are different ways to estimate when the battery is full(and that is another discussion), but the most common is to choose a voltage (say, 14.1V) and consider the battery full when that voltage is reached. Typical Solar controllers do this just fine, by setting the "float" voltage lower than the resting voltage of the LFP. A 12V nominal LFP will be at 13.8V resting when it is full. So, setting the float voltage to lower than that (usually 13.5V) will cause the charger to completely shut off after the battery is full.

Nothing more needs to be done. There is a whole lot of overthinking and over worrying about LFP. LFP is actually pretty hard to damage. You don't need to keep it at 80%. In fact, one of the main advantages is that you don't need to keep it at 80%, and can use the whole thing, from 100% till 0%. You don't need to worry about keeping the SOC in any range, or getting it fully charged once per week(though you should be sure to keep them balanced), or any of the worries we are used to with Lead Acid. Just set up the chargers as I said above, and forget about it for 15-20 years.

There is no need to taper off the current (which is really lowering the voltage) at the end of charge. If you have a big A/C charger that charges at a 1C rate, there might be a need, but solar chargers are much lower current to begin with, so it would serve no purpose.

https://www.youtube.com/watch?v=1G8WxY_jcUM

[Rohan]

Originally Posted by Sailorman Ed

And I remember reading that a LiPO4 battery should be kept at 80%

The only context in which I've heard of keeping batteries at 80% is for some electric cars, as a way to increase the life of the main battery. But experts disagree, there really isn't consensus over that idea, and any advantage gained would be extremely slight in any case. And we are talking about massive battery packs that cost 10k or more to replace.

LiFeP04 batteries for boats are extremely cheap now. Charge them to 100% and get your full money's worth.

[Johan Leopard51]

Amps are taken not given.

[barnakiel]

Originally Posted by K_V_B

This is why solar can kill your lithium batteries.

What you need is a way for the battery to turn the solar charger off when it is full. In lithium system the batteries are the master, and they tell the chargers to charge, or not to charge.

How about a voltage driven relay ?


Sense the battery voltage and place into the panel / to / regulator cable.



b.

[Cheyne]

LFP will calendar out way before charge cycles kill them. Shoot I would bet over 90% will be in landfills and replaced with the next great thing before they even come close to calendaring out.

Cheyne

[barcoMeCasa]

Originally Posted by K_V_B

This is why solar can kill your lithium batteries.

What you need is a way for the battery to turn the solar charger off when it is full. In lithium system the batteries are the master, and they tell the chargers to charge, or not to charge.

Which is exactly what Victron does, the regulators get told what the actual real battery voltage is from a smartshunt over bluetooth then reduce the voltage when it hits (in my case) 13.8v. Some people like to keep the voltage up into 14+v every time for a while to kick in a balancer though with no BMS mine are still within a few mV after nearly 2 years so suspect the "must balance every time" might be unnecessary, with good cells anyway.
From a SOC point of view there isn't really much point going any further, 13.8v from solar is well up the top voltage knee & close enough to fully charged that going any further won't be noticed in the real world.

[Sailorman Ed]

Thanks all. I should have been more clear that I was curious about what happens to the solar panel sitting in the sun with no load when the battery is full. Looks like nothing happens.


wholybee - I did actually watch Will video several weeks ago but good to watch again now my system is all connected - thanks.


Rohan - exactly what Will Prowse is saying


donradcliffe - I need to watch the current flow when my Balmar meter says 100% SOC and monitor the voltage output of the MPPT. I just haven't been able to catch it so far.

[barcoMeCasa]

Originally Posted by Sailorman Ed

donradcliffe - I need to watch the current flow when my Balmar meter says 100% SOC and monitor the voltage output of the MPPT. I just haven't been able to catch it so far.

This is what victron does with regulators being told what the battery voltage really is. Regulators go to float when the voltage hits 13.8, though looks like I had it set higher on that day, no point going up the knee very far unless you want to balance every single charge cycle.

[newhaul]

Originally Posted by Sailorman Ed

I understand how a 110v charger tapers off when the LiPO4 battery is full but how does it work with a solar controller? The solar panel is still putting out power. How does the MPPT controller handle this? What happens to the solar panel amps when the battery is full? It doesn't hurt the panel to do nothing under full sun?



And I remember reading that a LiPO4 battery should be kept at 80%. I don't see a way to accomplish this except by turning the MPPT off???
thanks in advance for my education.
Ed

Absolutely nothing will happen to the solar panels .

My opinion is this set my mppt to 13.8v bulk and set float to 13.2v
Shuts off charge at 13.8 or about 90% and turns back on charging at 13.2v
After controller says battery full then I run the watermaker or the rice cooker.
And the holding plate fridge..

[m0ggy]

Once the solar controller stops charging the li-po, the solar voltage goes up slightly and the panel no longer generates any power. At least that's what happens with my setup. Been charging to 99% or even 100% regularly and also down to 0% quite often in the winter. I have found that Wholybee is completely correct. Once in a while my bank does need balancing as 40% difference in state of charge (SoC) is too much loss. I have 2 200a and 1 300a Li-Po batteries. And I live on my yacht all year round for the last 7 years.

[newhaul]

Originally Posted by m0ggy

Once the solar controller stops charging the li-po, the solar voltage goes up slightly and the panel no longer generates any power. At least that's what happens with my setup. Been charging to 99% or even 100% regularly and also down to 0% quite often in the winter. I have found that Wholybee is completely correct. Once in a while my bank does need balancing as 40% difference in state of charge (SoC) is too much loss. I have 2 200a and 1 300a Li-Po batteries. And I live on my yacht all year round for the last 7 years.

I hope you have lifepo4 banks .

[Johan Leopard51]

Do all boat-size LifePO4 have BMS? Yacht PS is still on AGM battery so I don’t know 12V and my home backup system is 48V with BMS and my factory is a big 600kWh system.

In both home and factory the solar inverter is grid-tied but at factory that “grid” is in effect established by my isolation transformer, not the utility.

Point is, in both cases the inverter that manages solar MPPT is not the one doing DC with the battery BMS - it outputs AC. Managing DC is the job of the battery inverter and BMS communications.

For boat I’d go for MPPT controller that manages the solar to a DC combiner. The hybrid inverter sets the party rules on the DC combiner. MPPT would if batteries need more, supply more, because the hybrid inverter is in charge and presents demand at the DC combiner.