Does my MPPT SCC and 120V charger choice make sense for my LiFeMnPO4 batteries?

[ASprinter]

You are correct. To use a %C assumes you want to charge to 100% and that is the last thing you want to do with Lithium batteries. Let me rep[phrase, you can use a percentage of C to get to say 90% SOC but that will take a lot of work and experimenting.

You really want to just make your controller a CC/CV charger or in other words a Float Charger with Solar. You will use a voltage less than 100% SOC. The batteries will saturate and stop charging. From that point all power comes from the panels assuming the demand is equal to or less than what the panels can provide saving your battery power for night time use. Otherwise if you set up for Lithium to shut off charger, you go on battery despite that might be noon with bright Sun. Is that what you want?

I did not think so.

Correct, I do not need to charge 100%. I want to BULK charge to somewhere in the 90-95% SOC range and switch to FLOAT.

[Sunking]

It looks like I should forget about looking for a MPPT with the %C absorb customizable function and resort back to the original plan of the Victron 100/30 with 13.7V bulk and 13.5V float...

You are correct. To use a %C assumes you want to charge to 100% and that is the last thing you want to do with Lithium batteries. Let me rep[phrase, you can use a percentage of C to get to say 90% SOC but that will take a lot of work and experimenting.

You really want to just make your controller a CC/CV charger or in other words a Float Charger with Solar. You will use a voltage less than 100% SOC. The batteries will saturate and stop charging. From that point all power comes from the panels assuming the demand is equal to or less than what the panels can provide saving your battery power for night time use. Otherwise if you set up for Lithium to shut off charger, you go on battery despite that might be noon with bright Sun. Is that what you want?

I did not think so.

[ASprinter]

Without the Whiz-BangJr sense module and a Amp Shunt, the measured output via the KID also includes Loads and Battery amps. So unless you disconnect loads while charging, it's a no go. With Li, once you reach your Absorb Voltage, there is very little benefit (and a LOT of RISK) of spending more than a couple minutes in Absorb, reach Absorb, and then drop back to float, I would not use the Victon with Li battery if it has 1hr min Absorb.

That is precisely the type of information I was looking for, thanks. Disconnecting loads is a no-go and so is adding a second shunt (already have one).

It looks like I should forget about looking for a MPPT with the %C absorb customizable function and resort back to the original plan of the Victron 100/30 with 13.7V bulk and 13.5V float...

[Mike90250]

Without the Whiz-BangJr sense module and a Amp Shunt, the measured output via the KID also includes Loads and Battery amps. So unless you disconnect loads while charging, it's a no go. With Li, once you reach your Absorb Voltage, there is very little benefit (and a LOT of RISK) of spending more than a couple minutes in Absorb, reach Absorb, and then drop back to float, I would not use the Victon with Li battery if it has 1hr min Absorb.

[ASprinter]

Finally starting to pull together my solar components. The 300 watt LG Neon 2 (LG300N1C-G4) I've been looking for showed up locally and for a good price--this panel fits perfectly on the roof of the van. I was originally looking at the Victon 100/30 solar charge controller but was able to confirm with Victron that the minimum float time is 1 hour. I just discovered the Midnite Kid MPPT controller that has a Lithium battery setting and what looks like fully customizable battery profile. Can anyone confirm? I'd like the peace of mind to be able to enter float at 5% of C rather than rely on voltage.

[Sunking]

what would your SOC look like if you bulk charged to 13.8V and did not do a float at all?

A LFP fully charged rested battery is 3.45 volts or 13.8 volts on 4S. So it means it is possible if you set the charger to 13.8 volts, you can reach 100% SOC. That happens when charge current reaches 0-Amps and the battery is then fully saturated.

Example if for some reason you did not use much the night before, come sunrise you start charging and say by 10 in the morning you reach 13.8 volts, by afternoon your battery will reach 100%. Something tells me this will happen quite a bit in an RV that is not being used everyday.

[ASprinter]

Are you suggesting that because they are both floating at the same voltage, they must have the same SOC? If that were true, why would you bulk charge to 13.8 V at all? The path you take to float voltage matters because you are dealing with chemical reactions, and not instant transfers of energy. In scenario 1, as long as you have enough sun to drive current you get more productive time at 13.8 V (with the current falling as the reactions that can occur at that voltage taper off), which drives the SOC higher. In scenario 2, you only touch 13.8 before dropping down to 13.6, so those extra energy storage reactions don't occur and your SOC is slightly lower.

When charging terminates I recognize that the voltage will settle at a lower point, but I thought the 13.6V float charge was to essentially keep the batteries at a specified level and also to do the heavy lifting when loads are applied, rather than pull down the battery SOC. For another point of comparison, what would your SOC look like if you bulk charged to 13.8V and did not do a float at all?

[sensij]

I am having difficulty understanding how scenario 1 and 2 would produce different results. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

Are you suggesting that because they are both floating at the same voltage, they must have the same SOC? If that were true, why would you bulk charge to 13.8 V at all? The path you take to float voltage matters because you are dealing with chemical reactions, and not instant transfers of energy. In scenario 1, as long as you have enough sun to drive current you get more productive time at 13.8 V (with the current falling as the reactions that can occur at that voltage taper off), which drives the SOC higher. In scenario 2, you only touch 13.8 before dropping down to 13.6, so those extra energy storage reactions don't occur and your SOC is slightly lower.

[ASprinter]

I got that part, it's this part I'm confused about:

Originally posted by Sunking View Post
1. Set Bulk/Absorb to 13.8 volts, and FLOAT to 13.6 volts. Set Absorb time to 30 minutes initially. This method is going to require you to observe charge current for a week or so. What is going on is your Controller will stay into Constant Current phase until the battery voltage reaches about 13.8 volts, then at that point is Constant Voltage or Absorb stage begins. The charge current will start to taper off as the batteries Saturate to 13.8 volts. Ideally you would want to Terminate Absorb when the current tapers to 5% of C. Example if the cells are rated 100 AH, then 5 amps. Well your Solar Charger does not do that, it uses time. So what you have to play with it to find that amount of time it takes until you see the current taper down to around 5%. Don't sweat bullets trying to nail 5%, just do not let it go to 0 amps which would be 100% charged, you want to avoid that. Using this method gets to to mid/high 90's% SOC which is pushing your luck a bit. Once the timer times out the voltage switches to a lower FLOAT voltage of 13.6 volts and your batteries FLOAT while your panels supply power to loads until sunset.

2. Is my favorite because it is the no fuss or worry method. Just set Bulk/Absorb to 13.8 volts, ZERO minutes Absorb, and Float to 13.6 volts. Works exactly like above, except as soon as the Controller detects the charge current starts to Taper Off will lower the voltage to 13.6 volts and the batteries will Float. Like above the panels will provide power to the loads until sunset.

The difference between the two options is option 1 gets to to mid/high 90% SOC and option 2 gets you to high 80, low 90's% SOC.

I am having difficulty understanding how scenario 1 and 2 would produce different results. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

[Sunking]

I'm actually doing better than most with a 300W panel and 200ah of battery. I would say 200W of solar and 200 ah of AGM batteries is pretty typical

Yes that is typical for a lead acid battery. They cannot charge as fast as Lithium batteries. What might be part of your confusion is Pb batteries are sized for 5 day Reserve Capacity so you only discharge 20% per day. That gives you 2.5 days usable to stay above 50% on Pb. Pb batteries are charged at C/12 to C/8 with C/10 being perfect

Lithium is a different animal and you size them for 3 days with 2.5 days usable. It would take a 12 volt 335 AH AGM to equal a 12 volt 200 AH LFP. Both batteries require the same panel wattage of 450 to 500 Watts. The AGM charges at C/10 and the LFP would charge at C/6. LFP is good to C/2 or 100 amps in your case.

The 3rd generation 200ah GBS battery is a 4S config.....4 cells at 3.2V each.

OK my bad, I thought they were 100 AH, so you can only have 12 volts @ 200 AH

I am still hung up on my original question though...post 37 above, and how the scenarios would produce a different result.

Like you said, you did the Calcs wrong. 300 watts into a 12 volt battery generates 25 amps, and 25 amps on 200 AH battery is C/8. Again this has to do with you being a little light on panel wattage. 5% of 200 AH is 10 amps aka C/20. 25 amps is greater than 10 amps aka C/8. For GBS I think they specify C/33 or 3% or 6 amps on a 200 AH battery.

Do not get to hung up on all that. You are not charging to 14.4 volts when the charge current cut-off really matters. You are only going to 13.6 to 13.8. Your current taper to 0 and life is good. You wil just Float and use Solar Power until dark.

[sensij]

25 A is greater than 5% of C, right? If you manage to hit absorb in the middle of the day, you would have enough charge current available to see the tapering current at 13.8 V that indicates you are getting a higher SOC.

(Your peak sustained charge current is more likely to be 20 A with this panel, but even that might be enough to get some good from absorb if the timing works out)

[ASprinter]

OK you are quite a bit lite on panel power for such a large battery. If this was a 12 volt 200 AH battery would require a minimum 300 watt panel to generate a C/10 Charge Current. Lithium can run quite a bit higher wattage. Typically you would want C/4 on a lithium or 50 amps, and that would take 650 watts.

I'm actually doing better than most with a 300W panel and 200ah of battery. I would say 200W of solar and 200 ah of AGM batteries is pretty typical among Sprinter van owners, but the 300W LG Neon 2 panel is the same size as the 200w panel it replaced thanks to technology improvements. I will also have the advantage of the lithium battery's lower internal resistance, particularly above 85% SOC. There simply isn't any more room on the roof for more.

Now RELAX because with a MPPT Controller OUTPUT CURRENT = PANEL WATTAGE / BATTERY VOLTAGE. So do the math. 300 Watts / 12 Volts = 25 amps and on a 12 volt battery is 300 watts from a 300 watt panel.

You're right, I was doing the calc incorrectly.

So here is something to think about if you have not bought anything yet. You are going to have 8 cells configured 4S2P for 12 volts @ 200 AH. Consider 8S1P of 24 volts @ 100 AH. Gives you a lot more room to grow with on your Controller. Twice as much to be exact. Does not change battery capacity.

The 3rd generation 200ah GBS battery is a 4S config.....4 cells at 3.2V each.

I am still hung up on my original question though...post 37 above, and how the scenarios would produce a different result.

[Sunking]

SK--I am reading back through this thread making sure I understand everything you've written. One concept is still a little fuzzy to me...



I am having difficulty understanding how scenario 1 and 2 would produce different results. I am using a single 300W solar panel with a short circuit current of only 9.7 amps and a 200AH battery, which means current will always be less than 5% of C, essentially meaning that under scenario 1 my absorb time would be 0. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

OK you are quite a bit lite on panel power for such a large battery. If this was a 12 volt 200 AH battery would require a minimum 300 watt panel to generate a C/10 Charge Current. Lithium can run quite a bit higher wattage. Typically you would want C/4 on a lithium or 50 amps, and that would take 650 watts.

However you are missing an important characteristic of controllers. With a PWM controller INPUT CURRENT = OUTPUT CURRENT. So if you had a PWM Controller your output current would be around 8 amps and at 12 volts is 100 watts from a 300 watt panel.

Now RELAX because with a MPPT Controller OUTPUT CURRENT = PANEL WATTAGE / BATTERY VOLTAGE. So do the math. 300 Watts / 12 Volts = 25 amps and on a 12 volt battery is 300 watts from a 300 watt panel.

Do you feel better now? So if your controller is rated at least 25 amps, you are OK. FWIW you can calculate the maximum controller wattage input from the current rating and battery voltage.

Watts = Amps x Battery Voltage. Example an 80 amp Controller with a

12 volt battery = 1000 watts
24 volt battery = 2000 watts
48 volt battery = 4000 watts.

So here is something to think about if you have not bought anything yet. You are going to have 8 cells configured 4S2P for 12 volts @ 200 AH. Consider 8S1P of 24 volts @ 100 AH. Gives you a lot more room to grow with on your Controller. Twice as much to be exact. Does not change battery capacity.

Battery Capacity Watt Hours = Volts x Amp Hours.

12 volts x 200 AH = 2400 Watt Hours
24 volts x 100 AH = 2400 Watt Hours

Configured for 24 volts, the charge current drops to 300 watts / 24 volts = 12.5 Amps. Still the exact same charge rate of C8 either way.

[ASprinter]

SK--I am reading back through this thread making sure I understand everything you've written. One concept is still a little fuzzy to me...

1. Set Bulk/Absorb to 13.8 volts, and FLOAT to 13.6 volts. Set Absorb time to 30 minutes initially. This method is going to require you to observe charge current for a week or so. What is going on is your Controller will stay into Constant Current phase until the battery voltage reaches about 13.8 volts, then at that point is Constant Voltage or Absorb stage begins. The charge current will start to taper off as the batteries Saturate to 13.8 volts. Ideally you would want to Terminate Absorb when the current tapers to 5% of C. Example if the cells are rated 100 AH, then 5 amps. Well your Solar Charger does not do that, it uses time. So what you have to play with it to find that amount of time it takes until you see the current taper down to around 5%. Don't sweat bullets trying to nail 5%, just do not let it go to 0 amps which would be 100% charged, you want to avoid that. Using this method gets to to mid/high 90's% SOC which is pushing your luck a bit. Once the timer times out the voltage switches to a lower FLOAT voltage of 13.6 volts and your batteries FLOAT while your panels supply power to loads until sunset.

2. Is my favorite because it is the no fuss or worry method. Just set Bulk/Absorb to 13.8 volts, ZERO minutes Absorb, and Float to 13.6 volts. Works exactly like above, except as soon as the Controller detects the charge current starts to Taper Off will lower the voltage to 13.6 volts and the batteries will Float. Like above the panels will provide power to the loads until sunset.

The difference between the two options is option 1 gets to to mid/high 90% SOC and option 2 gets you to high 80, low 90's% SOC.

I am having difficulty understanding how scenario 1 and 2 would produce different results. I am using a single 300W solar panel with a short circuit current of only 9.7 amps and a 200AH battery, which means current will always be less than 5% of C, essentially meaning that under scenario 1 my absorb time would be 0. If both scenarios float the battery at 13.6V, wouldn't the ending SOC be the same under the two scenarios?

[Sunking]

Thanks again for all the help! I will be starting to buy parts soon and will report back.

You are welcome. Just make damn sure you have the time available when you go to bottom balance, like a free day. Start in the morning after your shower and breakfast. One thing about LFP batteries is the charge/discharge curve is very FLAT. For the most part 3.3 to 3.0 volts will go SLOWWWWWWWWWWWW and as exciting as watching grass grow. But once you hit 3.0 volts things go real fast and you are minutes away to 2.5 volts. Once you see the voltage drop and pass 3.0 volts, stop, and remove a couple of resistors to slow things down. By the end only 1 resistor so you can control what is going on. I will say this again, the resistors are going to be HOT, so make sure you have protection when handling. Remember when you were a kid and touched a light bulb? That kind of HOT. Stay on top of it and do not let it get away from you. Below 2 volts and you will damage them. Stop at 2.5 volts.

Good luck, and keep us posted.