upgrading my solar set-up

[reilym]

My 2016 PW Lexor came with three 95 watt Go-Power Carmanah roof solar panels with the following specs:

Cell type Monocrystalline
Rated power 95 W
Maximum power voltage 17.5 V
Maximum power current 5.45 A
Open circuit voltage 21.2 V
Short circuit current 5.85 A
Series fuse rating 15 A
Max system voltage 110 V

These feed into a Go-Power 30A PWM controller. PW recommends using the AGM settings for charging the 12V 200Ah LiFePO4 house batteries (there is no Li battery setting). This works fine, but I wonder if I can get more out of it. I assume the panels are wired in parallel since they are feeding a PWM controller with a max input voltage of 28V.

I'd like to upgrade the system with an MPPT controller with a proper lithium charging profile. From what I have read, I can just replace the PWM with an MPPT. Do people think this is worth the time and money investment? If so, can I get away with a 20A MPPT controller and should I go to the trouble to rewire the panels in series?

[booster]

Originally Posted by reilym

My 2016 PW Lexor came with three 95 watt Go-Power Carmanah roof solar panels with the following specs:

Cell type Monocrystalline
Rated power 95 W
Maximum power voltage 17.5 V
Maximum power current 5.45 A
Open circuit voltage 21.2 V
Short circuit current 5.85 A
Series fuse rating 15 A
Max system voltage 110 V

These feed into a Go-Power 30A PWM controller. PW recommends using the AGM settings for charging the 12V 200Ah LiFePO4 house batteries (there is no Li battery setting). This works fine, but I wonder if I can get more out of it. I assume the panels are wired in parallel since they are feeding a PWM controller with a max input voltage of 28V.

I'd like to upgrade the system with an MPPT controller with a proper lithium charging profile. From what I have read, I can just replace the PWM with an MPPT. Do people think this is worth the time and money investment? If so, can I get away with a 20A MPPT controller and should I go to the trouble to rewire the panels in series?

A 20 amp should be OK, but what I would recommend is making sure it is good for 65 volts so you can put the panels in series and drop the current to 1/3 of what they are in parallel. Less loss and the MPPT will use all the over charge voltage power without issue. You have to go 65volts max voltage to cover the 21-22 volt max output voltage of the panels, which very possible will hit with good sun and full batteries. You may also find the some solar converters will have different total wattage differences betweeen 12,24,36 volt panels so be sure to check that and go by watts not amps. Also try to find one with a lithium program that is voltage settable so you can stop before they get to the full voltage they usually claim at around 14.7v as holding at the voltage, or even going to it all the time isn't very good for lithiums. Many like to charge in the 13.8-14.1 voltage range as you minimize wear a tear and only loose a tiny bit of capacity because of the way the charge curve is shaped.

[Winston]

Our vote is to retain the parallel arrangement of panels and acquire a 30amp MPPT controller - - as Booster suggested, you're probably ok with 20 amps . . . but with 30 amps, you'll have a margin of safety and the flexibility to rearrange your solar panels in the future when you'll be thankful for having the extra capacity.

We prefer parallel for 'sun-shading' issues and your collective 15 ampere current (from the three panels) is small enough that loses should not be an issue.

But - - if you're not upgrading the panels - - we question whether your gains in efficiency warrant the trouble. We've never tested PWM vs MPPT, but it is our understanding that the differences are not great.

[booster]

Originally Posted by Winston

Our vote is to retain the parallel arrangement of panels and acquire a 30amp MPPT controller - - as Booster suggested, you're probably ok with 20 amps . . . but with 30 amps, you'll have a margin of safety and the flexibility to rearrange your solar panels in the future when you'll be thankful for having the extra capacity.

We prefer parallel for 'sun-shading' issues and your collective 15 ampere current (from the three panels) is small enough that loses should not be an issue.

But - - if you're not upgrading the panels - - we question whether your gains in efficiency warrant the trouble. We've never tested PWM vs MPPT, but it is our understanding that the differences are not great.

We have had ours both ways as we were series when we had two panels so 24v and now parallel because the controller can't handle the higher voltage. The theoretical is nearly 20% different assuming 100% conversion of the extra voltage above charge voltage, but we didn't see that much. Probably some because of inefficiency and some because of more voltage because of the higher current of 3 times higher. We netted about 10% less.



He won't be getting 5.45 amps per panel, I would bet, as that is max amps in perfect sun and the unit able to hold the max power point voltage which will probably not happen with lithium batteries like it might with lead acid.


Our panels are tight together in about a 60" square and we haven't really noticed much shading, but we do choose sunny sites if we are going to need the solar.



If the panels do turn out to not be able to hold much above charge voltage due to acceptance of the batteries, he would probably get a better harvest with his PWM controller as they often are a bit more efficient at charge voltage in than MPPT is, from what I have read.


Of course a controller with a settable voltage lithium program would be useful, I think.



The whole parallel vs series and MPPT vs PWM will probably be a personal preference and point of differences in opinion until flux capacitor chargers come along and replace them both.

[Winston]

Originally Posted by booster

. . . a settable voltage lithium program . . .

The "meaning" of that phrase could be the subject of its own, lengthy thread.

[SteveJ]

One thing gained by going with MPPT with a series setup is improved performance under sub optical conditions. The Victron controller will not start until it sees 5 volts over the battery voltage. This will significantly delay the startup if using those panels in parallel. With a lithium battery sitting at, say, 13.5 volts you will need 18.5 volts from the panels to turn on the controller. There will be quite a bit of wasted solar using the panels in parallel.

[booster]

Originally Posted by SteveJ

One thing gained by going with MPPT with a series setup is improved performance under sub optical conditions. The Victron controller will not start until it sees 5 volts over the battery voltage. This will significantly delay the startup if using those panels in parallel. With a lithium battery sitting at, say, 13.5 volts you will need 18.5 volts from the panels to turn on the controller. There will be quite a bit of wasted solar using the panels in parallel.

That I have not heard before, so very interesting indeed.



Why would they do that? Do they give a reason?


The only thing reason I can come up with is that they are trying to avoid the fairly common issue of the controller not having enough output due to poor sun conditions and hanging at less than full charge termination (either by volts or volts + amps) all day and overcharging the batteries. We see this occasionally with out system. If I notice it, I will shut off the panels until the next day as the batteries are normally full under those conditions so the output is going to the van but at a voltage the is a bit high for float and normally in the 13.8-14.1 volt range. I do set a bit lower termination voltage on the solar than on the shore and alternator chargers to make sure the solar goes to float on every full charge cycle.


The main problem with our is that the solar controller goes into what they Blue Sky calls "rebulk" mode if the voltage falls below the float setting for a bit of time. I did talk to them about that and they said their new tech director has told them to lower that threshold to normal full battery rested voltage of 12.8v for lead acid. This will take care of most of the issue I think, but our unit is not able to be upgraded as it doesn't have that capacity.

[booster]

Originally Posted by Winston

The "meaning" of that phrase could be the subject of its own, lengthy thread.

Oh yeah, definitely could cause that. There have been many spirited discussions on what the final cutoff voltage charge point should be on lithium. IIRC you use 13.8v? I think if I had lithium that is about what I would use and makes sense to me.


I have been interested that I have seen some information lately that charger manufacturers are starting to talk about using the combination of volts and amps together to terminate the charging of lithium batteries, like is done by some for lead acid. It may have to do with more common smaller lithium battery banks, perhaps, as they might be more likely to be able to supply more charge current than the acceptance of a small bank is as it nears full and thus over voltage the charging if the current isn't looked at.

[SteveJ]

Originally Posted by booster

That I have not heard before, so very interesting indeed.



Why would they do that? Do they give a reason?


The only thing reason I can come up with is that they are trying to avoid the fairly common issue of the controller not having enough output due to poor sun conditions and hanging at less than full charge termination (either by volts or volts + amps) all day and overcharging the batteries. We see this occasionally with out system. If I notice it, I will shut off the panels until the next day as the batteries are normally full under those conditions so the output is going to the van but at a voltage the is a bit high for float and normally in the 13.8-14.1 volt range. I do set a bit lower termination voltage on the solar than on the shore and alternator chargers to make sure the solar goes to float on every full charge cycle.


The main problem with our is that the solar controller goes into what they Blue Sky calls "rebulk" mode if the voltage falls below the float setting for a bit of time. I did talk to them about that and they said their new tech director has told them to lower that threshold to normal full battery rested voltage of 12.8v for lead acid. This will take care of most of the issue I think, but our unit is not able to be upgraded as it doesn't have that capacity.

Hiya Booster. I never thought to ask why Victron has a seemingly high cut in voltage. My portable panels are wired in 2S2P for a nominal 24 volt setup so really not a concern for us.

I'm currently using AGM batteries with preferred absorption of 14.4-15v and 13.5-13.8 float.

The Victron has what they call "adaptive" float charging. It senses the charged stat of the batteries at start up and decides how long to float charge that day. A gimmick? I dunno but it seems to have worked well for tje 2+ years we've had it. The adaptive is user switchable, it can be turned off for a timed absorb.

There is also a tail current settingthat I think overides both of the above. I have ours set at 3 amps for 200+AH. The reason for the plus is that Weize uses a 10 hour rating for measuring AHs instead of the "standard" 20 hour rate. The 3 amp tail current would seem to be a good guess what with a .6 to .7 amp parasitic load. I have the absorption set at 14.6 and float at 13.6

The rebulk setting on the Victron(100/30 smart solar) follows the float voltage setting. I have this set at 13.4(a .2v drop) as I don't think that I want to wait on bulk charging if needed. The magic in the controller does get it to absorb then float quite quickly in a rebulk situation.

It should be noted that the AGM batteries are a new install that replaced maintenance free L/A batteries that were still performing well with at least 90% of capacity(measured). We have not boondocked with them as yet but will be next month.

I replaced them early 'cuz I scored the Weize group 31 batteries for $149 at Amazon as batteries seem to have jumped hard in price lately. The group 31 "deep cycle" L/A batteries seem to have gone up to about $150 to 160 recently, hence the purchase of the $149 Weize batteries that are now $165.

[reilym]

Originally Posted by SteveJ

One thing gained by going with MPPT with a series setup is improved performance under sub optical conditions. The Victron controller will not start until it sees 5 volts over the battery voltage. This will significantly delay the startup if using those panels in parallel. With a lithium battery sitting at, say, 13.5 volts you will need 18.5 volts from the panels to turn on the controller. There will be quite a bit of wasted solar using the panels in parallel.

This was part of my thinking as well. With the higher voltage available from a series connection, even limited sun should have a high enough voltage to allow the charger to start providing current to the batteries. The amount of current will be small, but not zero. I was looking at the Victron 20A MPPT and like the features. I suppose that the concerns about overcharging lithium batteries is mitigated by the BMS, which will shut off the charging current once the batteries are assessed as full.

I need to do a little more research and measurement on my existing system before I jump into spending money upgrading a system that works.

[booster]

Originally Posted by SteveJ

Hiya Booster. I never thought to ask why Victron has a seemingly high cut in voltage. My portable panels are wired in 2S2P for a nominal 24 volt setup so really not a concern for us.

I'm currently using AGM batteries with preferred absorption of 14.4-15v and 13.5-13.8 float.

The Victron has what they call "adaptive" float charging. It senses the charged stat of the batteries at start up and decides how long to float charge that day. A gimmick? I dunno but it seems to have worked well for tje 2+ years we've had it. The adaptive is user switchable, it can be turned off for a timed absorb.

There is also a tail current settingthat I think overides both of the above. I have ours set at 3 amps for 200+AH. The reason for the plus is that Weize uses a 10 hour rating for measuring AHs instead of the "standard" 20 hour rate. The 3 amp tail current would seem to be a good guess what with a .6 to .7 amp parasitic load. I have the absorption set at 14.6 and float at 13.6

The rebulk setting on the Victron(100/30 smart solar) follows the float voltage setting. I have this set at 13.4(a .2v drop) as I don't think that I want to wait on bulk charging if needed. The magic in the controller does get it to absorb then float quite quickly in a rebulk situation.

It should be noted that the AGM batteries are a new install that replaced maintenance free L/A batteries that were still performing well with at least 90% of capacity(measured). We have not boondocked with them as yet but will be next month.

I replaced them early 'cuz I scored the Weize group 31 batteries for $149 at Amazon as batteries seem to have jumped hard in price lately. The group 31 "deep cycle" L/A batteries seem to have gone up to about $150 to 160 recently, hence the purchase of the $149 Weize batteries that are now $165.

Great details, it is always good to get the whole story in on shot and not piecemeal and/or inconsistent.


If the Victron has a tail amp setting, does it also have access to a shunt to see the actual amps at the battery. I ask because the first charger we had with tail amp settings was a Blue Sea that was a really good charger in general, but the tail amps were measured within the charger so any coach loads or any current going the the starter battery though the separator got counted. Those are variable loads so make it kind not a great feature to have tail amps.


I am not familiar with those batteries so will need to see what I can find on them. It is very possible they won't list the recommended tail amps as most of the time you have to contact manufacturers to get it. Lifeline is the exception to that and actually push the use of tail amp controlled charging. The most common tail amp settings I have seen or heard about are in the .5-1.0% of ah rating of the batteries. TPPL will have as low as .1%. Lifeline specs .5% but there batteries, especially when new will actually go much lower than that to .2% but it takes a long time beyond the already long (about 8-10 hours from 50% with a 80-100amps of charging available) so the .5 is probably a bit better to prevent excessive dry out. An interesting thing is too look at the float current when it goes to float after a full charge to tail amps. It will go negative first as the surface charge that is between the float voltage and absorption voltage comes off. Then our batteries, which are set at 2.0amps tail amps for our 440ah bank, show around .3amps at float at 13.1v where I like to float it long term to limit dryout. Over the next 48 hours that float amp reading slowly drops to about .05amps so I would say it did fill the batteries a bit more, I think. Many times if the van is in winter layup, I will then unplug it and let it sit a 4-6 weeks, then discharge it to 20% and recharge to full just to give some rest time and reactivation regularly. I have no clue if this better or worse than staying plugged in but it just makes sense to me.


If you are a data, and how does this work(?), junkie like I am you might want to put the charger into tail amp charging control if it is on a shunt and set the tail current very low to see how low it goes before it stops changing over some time. On ours if it went 4 hours without changing that is where I stopped, but 2 would probably be fine and maybe even better. Then move the tail amp setting above what you saw for amps above and watch the amps which will likely go negative and then positive. Let it run a while in float to see if it drops over time and where it ends. For comparison just run down the batteries a ways and set it to the settings you are using currently and run the same last part of the above test. It will automatically go to float at some time and just where the float voltage stabilizes quickly after going positive and how long it takes to hit the lowest float voltage. Compare the two tests and you should be able to tell if your current settings are good for your brand of batteries and charge voltages. The Lifeline chart in their tech manual shows 10hr rate gives about 7% less ah capacity rating than at 20hr rate. Yours are probably similar so you can adjust your rating to 20 hr for comparison the more common 20 hour rating for things like capacity, tail amps, run time, etc. In real world use our average (which is what counts) rate is closer to the 100 hour rate.


If you have shore charger that can also do tail amp controlled charging it really helps in being able to determine what to do with solar settings as you want to be certain that the solar is getting to float a bit before the shore charger does. The reason is if the solar is not tripped to float already by the tail amps when the shore goes to float the solar will keep charging until it trips on tail amps. Even if set to same setting this can happen as they may look at the time at the amps before tripping differently or slightly different calculations methods. If it still charging when other sources go off, and the conditions are right as described above, it can get the in between float and absorption voltage that it can stay in for way longer than full batteries should seen.



You are higher in both float and absorption voltage than I run and also could easily be a bit high on tail amps also. Tail amps do change with voltage by a bit so that can be a bit of oddness, and even lifeline doesn't specifically call out the suggested tail amps voltage point within their range. I stay at very bottom of the ranges for both float and absorption at 13.1v and 14.2v and use the recommended .5%C tail amps. It takes only a minimal amount of extra time to get a full charge at the low end absorption compared to high end and when you are talking about 8*10 hours anyway it is never an issue. The solar is set a .1v lower for absorption and 12.8v for float with the tail amps set .3amps higher. Alternator is set at 14.3v and 13.1v and I can force to float when I want while drive or shut off the coach charging from the alternator by looking at the amps on the ammeter I have in the cockpit.


I think the big deal, and which certainly is related to this thread is that getting all the parts to work well together and not do bad things is the hard part of it all and solar is probably hardest on to deal with because the output is so incredibly variable that it is hard have it always to do the right thing. It may be even more important with lithium as having it run all day locked in at near full charge voltage could be a bad thing on full batteries and getting it to always turn on to full voltage when needed might be a bit harder because of the low voltage drop with discharge % that lithium has.


Hopefully the OP will get a controller that reacts well to his other components or is at least on the conservative side. The overcharging issue is the reason, I am sure, that many solar controllers limit absorption voltage charging to a low time frame like 4 hours total per day.

[reilym]

Victron published an interesting white paper on MPPT vs. PWM. Among their conclusions is that a PWM performs within 90% of an MPPT over a fairly wide range of conditions, typically on smaller systems in warmer climates:

The PWM charge controller is therefore a good low cost solution for small systems only, when cell temperature is moderate to high (between 45°C and 75°C)*

An MPPT charge controller is the solution of choice if:
a) cell temperature will frequently be low (below 45°C) or very high (more than 75°C)*.
b) cabling cost can be reduced substantially by increasing array voltage.
c) system output at low irradiance is important.
d) partial shading is a concern.

*the cell temperature is typically 25C higher than ambient

Since solar harvest is low under non-ideal conditions (where the MPPT significantly outperforms the PWM), we still might only be talking about single digit amp-hours/day benefit for switching to MPPT.

If I do decide to make the switch, I like the Victron SmartSolar MPPT 100/20. It has a built-in LiFePO4 profile which is adjustable with a low temperature cut off. It collects data for up to 46 days.

I have to determine if the 3 CTI-95 solar panels have bypass diodes that will allow me to safely wire them in series to avoid partial shade issues. As SteveJ pointed out, the Victron requires >18V to start charging, so I think a series configuration would be important to ensure that the controller is working as much as possible.

[SteveJ]

Originally Posted by reilym

Victron published an interesting white paper on MPPT vs. PWM. Among their conclusions is that a PWM performs within 90% of an MPPT over a fairly wide range of conditions, typically on smaller systems in warmer climates:

The PWM charge controller is therefore a good low cost solution for small systems only, when cell temperature is moderate to high (between 45°C and 75°C)*

An MPPT charge controller is the solution of choice if:
a) cell temperature will frequently be low (below 45°C) or very high (more than 75°C)*.
b) cabling cost can be reduced substantially by increasing array voltage.
c) system output at low irradiance is important.
d) partial shading is a concern.

*the cell temperature is typically 25C higher than ambient

Since solar harvest is low under non-ideal conditions (where the MPPT significantly outperforms the PWM), we still might only be talking about single digit amp-hours/day benefit for switching to MPPT.

If I do decide to make the switch, I like the Victron SmartSolar MPPT 100/20. It has a built-in LiFePO4 profile which is adjustable with a low temperature cut off. It collects data for up to 46 days.

I have to determine if the 3 CTI-95 solar panels have bypass diodes that will allow me to safely wire them in series to avoid partial shade issues. As SteveJ pointed out, the Victron requires >18V to start charging, so I think a series configuration would be important to ensure that the controller is working as much as possible.

It's hard to argue with Victron, but...

I think in perfect conditions that the 90% number would come into play. However, once you start talking a day or more of haze or clouds, it's a whole other scenario. With that high kick in voltage the controller may not kick in all day with a parallel array where in series one would pick up something, even if it's only 10 or 20 AHs, much better than going backward all day. When dry camping for more than a couple of days at one spot this could very well be the difference between having to run a genny or not.

I had a PWM system on our Roadtrek and decided to go the MPPT route on our new to us Safari Trek. The improvement of the whole solar experience was noteworthy. Having had both I see no conceivable reason to go back to a PWM system, at least in an RV setting.

Have fun!

[scottdailey]

Originally Posted by Winston

The "meaning" of that phrase could be the subject of its own, lengthy thread.

I spoke with the folks at BigBattery DOT com, where I found a 170 Ah Lithium battery that just barely fits in the stock battery box of my 99Dodge190P. Highly recommended, thus far.

They referred me to their datasheet for charging parameters. They essentially recommend setting all the voltages in the Victron charge controller to 14.6 (!).

Interestingly, they said the concepts of Bulk, Absorption and Float are NOT Applicable to LiFePO4 batteries.

They said I should never need to disconnect the Solar, as the Victron will ensure battery voltage doesn't exceed 14.6V, and if it does, the battery's onboard BMS will kick in automatically.

He did say, that for long life, they recommend to discharge all the way down to 20% (~12.8V) every 6 months or so.

As they say: "Change My mind"

Thanks much for all the great discussion & facts here. Let me know if I should have started a new thread?

Cheers,

Scott
1999 Dodge 190P

[booster]

Originally Posted by scottdailey

I spoke with the folks at BigBattery DOT com, where I found a 170 Ah Lithium battery that just barely fits in the stock battery box of my 99Dodge190P. Highly recommended, thus far.

They referred me to their datasheet for charging parameters. They essentially recommend setting all the voltages in the Victron charge controller to 14.6 (!).

Interestingly, they said the concepts of Bulk, Absorption and Float are NOT Applicable to LiFePO4 batteries.

They said I should never need to disconnect the Solar, as the Victron will ensure battery voltage doesn't exceed 14.6V, and if it does, the battery's onboard BMS will kick in automatically.

He did say, that for long life, they recommend to discharge all the way down to 20% (~12.8V) every 6 months or so.

As they say: "Change My mind"

Thanks much for all the great discussion & facts here. Let me know if I should have started a new thread?

Cheers,

Scott
1999 Dodge 190P

There is a lot of information on this site about charging lithium and what they told you appears to be what we were hearing at the beginning of the lithium revolution.

A lot has changed since then and current best practices seem to be much different than a fixed 14.6v on full time.

Other members, like Avanti who is currently working with a custom van builder is putting together a system, will be filling us in on what he decided to do and what profiles he will aim for. I expect them to be far from being a turn in on at 14.6v and leave it on all the time and do occasional deep discharges.
Hopefully, Avanti can jump in and give a bit of an update for you at this point on what they told you.

[@Michael]

Originally Posted by scottdailey

They referred me to their datasheet for charging parameters. They essentially recommend setting all the voltages in the Victron charge controller to 14.6 (!).

Interestingly, they said the concepts of Bulk, Absorption and Float are NOT Applicable to LiFePO4 batteries.

This recommendation is now fairly common. My lithium battery mfg. says the same, claiming that their built-in BMS is smart enough to protect the battery against my abuse. I don't follow their recommendations, but rather a more conventional lithium charge profile.

[booster]

Originally Posted by @Michael

This recommendation is now fairly common. My lithium battery mfg. says the same, claiming that their built-in BMS is smart enough to protect the battery against my abuse. I don't follow their recommendations, but rather a more conventional lithium charge profile.

I think that the recommendation is probably more because it is easy and is still somewhat common. It was pretty much universal in the beginning so I would call in it kind of running on momentum. Most of the higher end systems use much different things like lower final voltage, full off charging, etc.


The way I look at the BMS limits is that they are last line of defense against very rapid failure, not necessarily at the best points for best service life, etc. Others are OK using it to cycle the charging it appears.

[reilym]

Originally Posted by scottdailey

I spoke with the folks at BigBattery DOT com, where I found a 170 Ah Lithium battery that just barely fits in the stock battery box of my 99Dodge190P. Highly recommended, thus far.

They referred me to their datasheet for charging parameters. They essentially recommend setting all the voltages in the Victron charge controller to 14.6 (!).

Interestingly, they said the concepts of Bulk, Absorption and Float are NOT Applicable to LiFePO4 batteries.

In the past 3 years of owning my RV, I have come to the conclusion that applying lead-acid battery theory to charging of LiFePO4 batteries has led me down a lot of rabbit holes. Of course these are batteries, but their properties and the now universal presence of a BMS makes them entirely different beasts that require some new terminology and approaches. I am seeing more and more information like you got from BigBattery that supports this.

I started this thread looking to move from PWM to MPPT and have learned a lot from this excellent discussion and others. The collective wisdom is to set the charger at 14.2-14.4, then let the battery cycle. Some argue for a step down to 13.2 after the initial charge, but given the nature of LFP, there is no harm done in skipping a "float" stage. Because of the required PV/battery voltage differential, it does not make sense to move to MPPT without putting the 3 panels in series and I am not quite ready to do that. I've ordered a Blue Sky SC30 PWM controller that will go into the same wall cut-out as my existing SCC, but will give me ability to customize every charging parameter. If I decide to upgrade my solar panels, I'll look to do a 2S2P with an MPPT controller.

This place is great!