DLTooley
Well-known member
Also if/when you upgrade I’d urge you to consider handing down your components that you no longer need to deserving newbie at an RTR. Selling a lead acid bank for the cost of the core is good karma.
MPPT vs PWM test
- Thread starter jimindenver
- Start date
Help Support Van Living Forum:
> With lead acid systems peak charging results in a voltage drop (volts not watts).
If by "peak charging" you mean the point of highest amps acceptance by the bank, that is during the initial Bulk/CC stage when volts are low.
> As such panels are engineered to produce near optimal voltages during peak charging.
Again, no idea what you're trying to say there. Panels put out a certain narrow V range, PWM just discards higher volts. MPPT manipulates panel voltage to get maximum watts.
> I believe this is the functional definition that f the absorb state.
Absorb is the stage after V hits the setpoint, aka CV. The SC regulates output to keep V from climbing, the batteries' resistance as SoC climbs reduces amps accepted.
> On that THEORY I would not upgrade from a PWM on a lead acid bank.
No idea of the reasoning there. It's just a matter of higher up-front cost to extract more power from your panels.
> Two exceptions would be overpaneling on a bank(the voltage drop will be less)
What voltage drop? And overpaneling is about watts not volts.
> and when you are using non battery power post absorb.
No idea what that means, just word salad.
> I suspect MPPT may hav additional benefits in cloudy conditions but can’t figure out how to test.
Two identical panels and batteries at 50% SoC, only difference is the SC in between.
Compare watts output and time it takes to get to 100% SoC
If by "peak charging" you mean the point of highest amps acceptance by the bank, that is during the initial Bulk/CC stage when volts are low.
> As such panels are engineered to produce near optimal voltages during peak charging.
Again, no idea what you're trying to say there. Panels put out a certain narrow V range, PWM just discards higher volts. MPPT manipulates panel voltage to get maximum watts.
> I believe this is the functional definition that f the absorb state.
Absorb is the stage after V hits the setpoint, aka CV. The SC regulates output to keep V from climbing, the batteries' resistance as SoC climbs reduces amps accepted.
> On that THEORY I would not upgrade from a PWM on a lead acid bank.
No idea of the reasoning there. It's just a matter of higher up-front cost to extract more power from your panels.
> Two exceptions would be overpaneling on a bank(the voltage drop will be less)
What voltage drop? And overpaneling is about watts not volts.
> and when you are using non battery power post absorb.
No idea what that means, just word salad.
> I suspect MPPT may hav additional benefits in cloudy conditions but can’t figure out how to test.
Two identical panels and batteries at 50% SoC, only difference is the SC in between.
Compare watts output and time it takes to get to 100% SoC
frater secessus
Well-known member
What???
Edit: John beat me to it.
Edit: John beat me to it.
Every test I have found has results of MPPT having the advantage over PWM during bulk charging, only. That is with lead chemistries. Careful use of my large AH bank results in smaller % use of the bank. Not as much time spent in bulk charging.
jimindenver
Well-known member
- Joined
- Dec 20, 2014
- Messages
- 5,266
- Reaction score
- 51
Hehe
Can you show links to these test? I will enjoy talking to the authors.
The excess power of the voltage clipped by a PWM controller is available in all modes with a MPPT controller. Just because the bank has gone to absorb does not mean it can not absorb the full value of the panel, in fact it will do so until the battery starts reducing the acceptance rate. That could be a while meaning the PWM controller is extending the absorption cycle. Once the reduction of acceptance is started the rest of the power available is still usable to run loads.
In float my system allows me to use its full 80a output even if my bank is accepting nothing. It is how I can run my A/C without lowering the voltage of the batteries. A PWM system can do the same thing but just with a smaller A/C because it can not produce as much power and the bank will start dipping if asked to run as large of a load as the MPPT controller can run.
Now if you have a system that over powers your needs, you are lucky. Not everyone is so lucky out here and they need every bit of power that they can get in all modes. Not all solar systems are just battery chargers, like mine it can be treated as a power plant that just so happens can charge batteries too.
Can you show links to these test? I will enjoy talking to the authors.
The excess power of the voltage clipped by a PWM controller is available in all modes with a MPPT controller. Just because the bank has gone to absorb does not mean it can not absorb the full value of the panel, in fact it will do so until the battery starts reducing the acceptance rate. That could be a while meaning the PWM controller is extending the absorption cycle. Once the reduction of acceptance is started the rest of the power available is still usable to run loads.
In float my system allows me to use its full 80a output even if my bank is accepting nothing. It is how I can run my A/C without lowering the voltage of the batteries. A PWM system can do the same thing but just with a smaller A/C because it can not produce as much power and the bank will start dipping if asked to run as large of a load as the MPPT controller can run.
Now if you have a system that over powers your needs, you are lucky. Not everyone is so lucky out here and they need every bit of power that they can get in all modes. Not all solar systems are just battery chargers, like mine it can be treated as a power plant that just so happens can charge batteries too.
frater secessus
Well-known member
Weight said:
MPPT has an advantage when the system needs more power than the panel can generate at the battery's present voltage.
Yes, that does happen during Bulk when Vbatt is at its lowest. It can also happen anytime a significant load is imposed on the system.
I continued this line of thought with examples in this blog post.
Quote jimindenver.
Here is one carefully conducted test. Remember Rod found 205 gain with MPPT over PWM, but using LiFePo battery. Can stay in bulk longer.
Most of us have small solar systems as that is what will fit on our van. I don't think MPPT makes all that much difference with any loads we may have during the day. I will be glad to see any contrary testing information you can provide. I myself, made the choice to buy an expensive, quality PWM rather than a cheap less-quality MPPT.
Here is one carefully conducted test. Remember Rod found 205 gain with MPPT over PWM, but using LiFePo battery. Can stay in bulk longer.
Most of us have small solar systems as that is what will fit on our van. I don't think MPPT makes all that much difference with any loads we may have during the day. I will be glad to see any contrary testing information you can provide. I myself, made the choice to buy an expensive, quality PWM rather than a cheap less-quality MPPT.
I'm trying to post a link. But for some strange reason i'm having trouble. here we go again. https://marinehowto.com/mppt-vs-pwm-solar-controllers/
jimindenver
Well-known member
- Joined
- Dec 20, 2014
- Messages
- 5,266
- Reaction score
- 51
I shall really enjoy having a conversation with this one.
He is incorrect in thinking that the excess voltage can not be used in absorb or float. The battery may not want it but you don't have to sit on your thumbs while the battery is only accepting small amounts of amps. You can turn on a load and still get the full power of your array in absorb and float.
Weight, I am not trying to convince you to buy a MPPT controller. Your system works well for you. That doesn't mean you could not get more out of it if your needs ever grew. You could see 6 extra amps if your bank was low, 4 in absorption and float. Those numbers sound small but in the course of a day it is enough to recharge another battery or in my case run both of my exhaust fans or my 12v Engel in freezer mode all day long without touching the battery. In the case of a system like mine it represents 18 extra amps early and 12 as the voltage comes up. The excess alone is a decent sized system and I can find lots of ways to use it.
As for more test, naw, I do not have room to carry the gear and I already know that all of the test, pictures, graphs and such that I have posted for five years will not change someones mind. The only thing that will is if someone gave them a MPPT controller so that they could see the benefit themselves. I can't do that either.
He is incorrect in thinking that the excess voltage can not be used in absorb or float. The battery may not want it but you don't have to sit on your thumbs while the battery is only accepting small amounts of amps. You can turn on a load and still get the full power of your array in absorb and float.
Weight, I am not trying to convince you to buy a MPPT controller. Your system works well for you. That doesn't mean you could not get more out of it if your needs ever grew. You could see 6 extra amps if your bank was low, 4 in absorption and float. Those numbers sound small but in the course of a day it is enough to recharge another battery or in my case run both of my exhaust fans or my 12v Engel in freezer mode all day long without touching the battery. In the case of a system like mine it represents 18 extra amps early and 12 as the voltage comes up. The excess alone is a decent sized system and I can find lots of ways to use it.
As for more test, naw, I do not have room to carry the gear and I already know that all of the test, pictures, graphs and such that I have posted for five years will not change someones mind. The only thing that will is if someone gave them a MPPT controller so that they could see the benefit themselves. I can't do that either.
DLTooley
Well-known member
JiminDenver has a sense of what I am getting at. I have seen different definitions for bulk and absorb and that may be part of the problem.
In spite of all the criticism no one has addressed the observation I’ve based it on, that there is a voltage drop early in the charge cycle. I am positing that the voltage drop is when the ‘acceptance rate’ of the battery Goes down
If you don’t see a voltage drop that may be because you have an overpaneled bank.
I suspect the original test may have been faulty if the mppt pwm comparisons were made on a bank at different phase. One thing for sure, pwm is a lead acid charger only.
AC run straight from the charger is an excellent reason to go MPPT.
In spite of all the criticism no one has addressed the observation I’ve based it on, that there is a voltage drop early in the charge cycle. I am positing that the voltage drop is when the ‘acceptance rate’ of the battery Goes down
If you don’t see a voltage drop that may be because you have an overpaneled bank.
I suspect the original test may have been faulty if the mppt pwm comparisons were made on a bank at different phase. One thing for sure, pwm is a lead acid charger only.
AC run straight from the charger is an excellent reason to go MPPT.
I am trying not to be too "critical" but feel it is important to let you know when what you are trying to communicate is not getting through, try to help you be more precise in your terminology.
> I have seen different definitions for bulk and absorb and that may be part of the problem.
Vendor manuals are the worst offenders in this. Universal standard definitions nowadays are:
First comes Bulk, aka CC constant current, voltage is below setpoint.
Second is Absorb, aka CV constant voltage, has reached setpoint, V now limited by regulator, after a while current falls until batt Full
Float is last stage, no more charging, just counteract self-discharge while no cycling.
> there is a voltage drop early in the charge cycle.
If not explained by the above, what drop do you mean? From what level to what level and measured where? or between what two physical measuring points?
> I am positing that the voltage drop is when the ‘acceptance rate’ of the battery Goes down.
No, current only starts to drop after voltage has started climbing, and drops the most toward the end after V is being regulated.
> If you don’t see a voltage drop that may be because you have an overpaneled bank.
Again, this makes no sense, at least not using the usual meaning of overpaneling as outlined above.
> I suspect the original test may have been faulty if the mppt pwm comparisons were made on a bank at different phase.
No, there are hundreds of such tests out there and only very very rarely in very specific conditions does PWM come close to MPPT ouput.
> One thing for sure, pwm is a lead acid charger only.
Again, not true, I have installed Bogart SC-2030s controlled by Trimetric BMs that are doing an excellent job with LFP banks, could work with NMC or LiPo as well just fine, you just need to adjust the charge profiles to suit the chemistry.
I agree it would make no sense to pair super-cheap poor quality SCs of any type with a sensitive bank costing thousands of dollars, but there are plenty of high quality PWM SCs still on the market.
> I have seen different definitions for bulk and absorb and that may be part of the problem.
Vendor manuals are the worst offenders in this. Universal standard definitions nowadays are:
First comes Bulk, aka CC constant current, voltage is below setpoint.
Second is Absorb, aka CV constant voltage, has reached setpoint, V now limited by regulator, after a while current falls until batt Full
Float is last stage, no more charging, just counteract self-discharge while no cycling.
> there is a voltage drop early in the charge cycle.
If not explained by the above, what drop do you mean? From what level to what level and measured where? or between what two physical measuring points?
> I am positing that the voltage drop is when the ‘acceptance rate’ of the battery Goes down.
No, current only starts to drop after voltage has started climbing, and drops the most toward the end after V is being regulated.
> If you don’t see a voltage drop that may be because you have an overpaneled bank.
Again, this makes no sense, at least not using the usual meaning of overpaneling as outlined above.
> I suspect the original test may have been faulty if the mppt pwm comparisons were made on a bank at different phase.
No, there are hundreds of such tests out there and only very very rarely in very specific conditions does PWM come close to MPPT ouput.
> One thing for sure, pwm is a lead acid charger only.
Again, not true, I have installed Bogart SC-2030s controlled by Trimetric BMs that are doing an excellent job with LFP banks, could work with NMC or LiPo as well just fine, you just need to adjust the charge profiles to suit the chemistry.
I agree it would make no sense to pair super-cheap poor quality SCs of any type with a sensitive bank costing thousands of dollars, but there are plenty of high quality PWM SCs still on the market.
DLTooley
Well-known member
I’m on my phone and not able to cut and paste your comments. I’m ignoring most of them because they are not responsive. You’ve come to the conclusion my reasoning is faulty and proceeded on that basis without any further effort to understand my thinking
Charge does happen in float, that is the ‘tail’ and is crucial to getting a bank to 100%.
I cede your point on programmable pwm, but all you are doing is programming away the lead acid charge state set points.
Charge does happen in float, that is the ‘tail’ and is crucial to getting a bank to 100%.
I cede your point on programmable pwm, but all you are doing is programming away the lead acid charge state set points.
I'm not saying your reasoning is faulty.
I am giving you some "if this then maybe it's that" explanations for possible scenarios that may or may not fit, since I have yet to understand exactly what it is that you are observing.
I have asked specific questions to try to clarify that, but which you have not answered. Please help us help you by answering as specifically as possible, or we're just wasting our time.
If any charge still happens in Float that is because the controller dropped out of Absorb prematurely. Absorb should hold until the endAmps spec is reached, often for 4+ hours, that is the definition of the long tail.
Float should only be after charging is finished, there is no reason to slow current down 90% by dropping voltage before then.
An adjustable charger can be set back and forth between different profiles as needed, even multiple times per day, nothing is getting "programmed away".
I am giving you some "if this then maybe it's that" explanations for possible scenarios that may or may not fit, since I have yet to understand exactly what it is that you are observing.
I have asked specific questions to try to clarify that, but which you have not answered. Please help us help you by answering as specifically as possible, or we're just wasting our time.
If any charge still happens in Float that is because the controller dropped out of Absorb prematurely. Absorb should hold until the endAmps spec is reached, often for 4+ hours, that is the definition of the long tail.
Float should only be after charging is finished, there is no reason to slow current down 90% by dropping voltage before then.
An adjustable charger can be set back and forth between different profiles as needed, even multiple times per day, nothing is getting "programmed away".
jimindenver
Well-known member
- Joined
- Dec 20, 2014
- Messages
- 5,266
- Reaction score
- 51
John
Charge in float was one point that sternwake and I had issues with. Float is the reason we tell people that you can not practically charge with a generator. You can not force the last 10% into a FLA bank with higher voltages. It takes a long time to finish it off and if you don't allow it to happen you get progressive capacity loss. My Lifelines are AGM and are suppose to be done once the acceptance rate drops to a certain point in absorb.
Charge in float was one point that sternwake and I had issues with. Float is the reason we tell people that you can not practically charge with a generator. You can not force the last 10% into a FLA bank with higher voltages. It takes a long time to finish it off and if you don't allow it to happen you get progressive capacity loss. My Lifelines are AGM and are suppose to be done once the acceptance rate drops to a certain point in absorb.
Canine
Well-known member
With my set up my batteries take a little longer to drop from 12.7 to 12.6 when it hangs around in float mode for a while. It will even hang out at 12.8 for a bit with no sun after being in float mode for a while. If it goes from acceptance to float then in 10 minutes the sun goes down enough to reduce charging enough, it will drop right to 12.7. It is a minor difference that I would have never noticed if the volt meter wasn't there to give me a visual reading. Practically, the extra energy is meaningless to me even though there is a tenth of a volt difference for a half hour or so. However, it will make a difference in keeping the plates clean; therefore, making the batteries last longer. It's literally equalizing the battery, but at a much lower voltage. It still helps with longevity.
> Charge in float was one point that sternwake and I had issues with. Float is the reason we tell people that you can not practically charge with a generator.
It is silly to try to get past even 90% burning dino juice unless the engine's running anyway.
But with whatever charge source, there is no reason to drop to Float until you reach endAmps. The fact that so many regulators can't be adjusted to do so is a design flaw, and good reason to buy one that does.
> You can not force the last 10% into a FLA bank with higher voltages.
Nothing to do with force. If you drop to Float prematurely it takes a lot longer, maybe never get there in practice.
And there is no positive reason to drop voltage early, as you say longevity harmed so why do it?
> My Lifelines are AGM and are suppose to be done once the acceptance rate drops to a certain point in absorb.
Exactly!
That's the endAmps setpoint, and they need to get there at least 2-3 times a week for good longevity.
From my past notes:
> with a .4C charge rate (40% of Ah capacity or 100A for a 400AH bank), from 50% SOC, a Lifeline bank gets to approx 97% SoC in about 2 hours.
> It takes almost another four hours to get to 100%, and that last 3% is critical for overall health.
This is why if solar by itself is not sufficient, the supplemental dino juice source must be run in the morning before insolation really kicks in.
Then solar can finish the long tail, but only if the owner makes sure it is adjusted right so it doesn't drop to Float before trailing current drops to the endAmps spec, .005C, or half an amp per 100AH.
The ideal SCs work in conjunction with a shunt batt monitor to control the transition based directly off the acceptance rate.
Second best is full adjustability of the eggtimer algorithm, but then it needs to be checked and adjusted as usage patterns change.
PS do equalize those Lifelines when you get the chance, ideally monthly? They're the only AGM vendor still specs that.
It is silly to try to get past even 90% burning dino juice unless the engine's running anyway.
But with whatever charge source, there is no reason to drop to Float until you reach endAmps. The fact that so many regulators can't be adjusted to do so is a design flaw, and good reason to buy one that does.
> You can not force the last 10% into a FLA bank with higher voltages.
Nothing to do with force. If you drop to Float prematurely it takes a lot longer, maybe never get there in practice.
And there is no positive reason to drop voltage early, as you say longevity harmed so why do it?
> My Lifelines are AGM and are suppose to be done once the acceptance rate drops to a certain point in absorb.
Exactly!
That's the endAmps setpoint, and they need to get there at least 2-3 times a week for good longevity.
From my past notes:
> with a .4C charge rate (40% of Ah capacity or 100A for a 400AH bank), from 50% SOC, a Lifeline bank gets to approx 97% SoC in about 2 hours.
> It takes almost another four hours to get to 100%, and that last 3% is critical for overall health.
This is why if solar by itself is not sufficient, the supplemental dino juice source must be run in the morning before insolation really kicks in.
Then solar can finish the long tail, but only if the owner makes sure it is adjusted right so it doesn't drop to Float before trailing current drops to the endAmps spec, .005C, or half an amp per 100AH.
The ideal SCs work in conjunction with a shunt batt monitor to control the transition based directly off the acceptance rate.
Second best is full adjustability of the eggtimer algorithm, but then it needs to be checked and adjusted as usage patterns change.
PS do equalize those Lifelines when you get the chance, ideally monthly? They're the only AGM vendor still specs that.
jimindenver
Well-known member
- Joined
- Dec 20, 2014
- Messages
- 5,266
- Reaction score
- 51
Believe me John, if anyone knows how to take care of my seven year old Lifelines, I do. I also knew how to handle my Interstate FLA that was still good at 6 years old when I gave it away. In both cases a near 2-1 solar system kept them happy without the need for the morning generator run. Are they what they were in the beginning? Of course not. Then again neither is sternwakes according to him.
The thing is my Lifelines are not your basic FLA nor are they charged like it either. That's why sternwake and I differed on the topic. He took the concept of charging AGM's ( and not even all AGM's) and applied it to all batteries. Cooking a FLA isn't going to speed up the process else wise the manufactures would have us boiling them like eggs. I haven't seen any manufactures of FLA not suggest float for the tail, maybe they know what they are talking about considering they built the battery.
The thing is my Lifelines are not your basic FLA nor are they charged like it either. That's why sternwake and I differed on the topic. He took the concept of charging AGM's ( and not even all AGM's) and applied it to all batteries. Cooking a FLA isn't going to speed up the process else wise the manufactures would have us boiling them like eggs. I haven't seen any manufactures of FLA not suggest float for the tail, maybe they know what they are talking about considering they built the battery.
DLTooley
Well-known member
Is managed pwm better at absorption? I chose the Victron mppt because it manages absorption based on acceptance. The other mppt controllers all do it based on adjustable time. Iirc default was two hours.
