I thought we were talking about efficiencies between PWM and MPPT? I am a retired electrical engineer as well.
Voltage change from panels to batteries
- Thread starter vdub
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rin67630
Solar Enthusiast
Which sums up to 600mAh or 7,8Wh a day. For nothing.
Consider a 20W ( nominal) panel in winter at 45° latitude under cloudy conditions, how much energy do you think you will harvest from it in a day?
We are talking about OVERALL efficiency considering all aspects of a solar panel, under realistic weater conditions, not about edulcorated advertising figures on a shiny prospectus.
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Sorry...pulled the incorrect spec. It's 10mA....exacty the same as the Renogy PWM controller. That is if you believe anything Renogy says.
The GoPower PWM uses 6mA so the Victron MPPT is 4mA more than that. Likely, the fact that the Victron has bluetooth is the reason for slightly higher power consumption.
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rin67630
Solar Enthusiast
No. A Victron 75/15 draws 25mA from a 12v Battery. Minimum. With Bluetooth active, it grows to 34mA.
LOL...this is silly. Worried about a 25mA draw in regard to overall efficiency?
I am the CFO and CTO of a small tech company in silicon valley. We manufacture small DCtoDC board mounted converter chips/modules. We have also built and sold power back up systems for cellular bases station sites. We designed an MPPT type of solar controller. PWM types were not considered at ALL because they are not efficient!
I am the CFO and CTO of a small tech company in silicon valley. We manufacture small DCtoDC board mounted converter chips/modules. We have also built and sold power back up systems for cellular bases station sites. We designed an MPPT type of solar controller. PWM types were not considered at ALL because they are not efficient!
rin67630
Solar Enthusiast
You just did not do the maths , obviously.
Yes....my company did the "maths"
rin67630
Solar Enthusiast
No. They did not at least not in the low-power solar segment.
It is probably not worth to try to explain that to you, but let me do it for the others, capable of understanding things a bit deeper than hammering simplistic paradigms:
Designing a low power outdoor off grid solar power using small panels is just a different challenge than claiming that this or that where always superior!
The right approach is to consider the worst case, being a succession of freezing winter days with only a few hours of scarce light.
The panel will only deliver a 5% maximum of its nominal power, and that for just around 4 hours a day, the rest of the time the circuit will be consuming power, so it is absolutely capital to get the minimum quiescent power drain at all.
During the few hours, where the panel provides power, it must feed enough power to recharge the battery for at least the next 20 hours, whilst keeping distributing power to your device all the time.
Under these conditions, MPPT is an underperformer: a 12V class panel will deliver a Vmp just slightly above the battery voltage and MPPT only works acceptably, when there is enough voltage gap available. 4v is the bare minimum, which is then not given the SCC will not even start, the whole day is lost.
On the other side, if you catch a sunny day, the battery will be fully charged at 11:00 and the SCC will be clipping power all the remaining time.
MPTT is then completely useless.
That is the very reason why I designed Soft Power to provide the two approaches in the same SCC:
-MPPT to be efficient for a couple of hours to be sure not to miss every sunshine minute for charging.
-PWM to run for the rest of the time, when the battery is fully charged or when there is not enough panel voltage available to run MPPT efficiently.
To gather experience, I am able to switch arbitrarily between both operation modes any time.
After two winters of data gathering, permanently analysing the charging process using different panels I came to the conclusion, that this overall complexity is not really necessary.
A plain simplistic PWM running all the time is almost as efficient.
MPPT generally requires a bigger panel, returned more days with an empty battery and is only running acceptably well in that context when using a 12 V class panel with a 6V battery.
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I agree.
Whenever I see a actual comparison by someone they come to the same conclusion...even Will!
Still one must understand the mpp of panels to get the most from their PWMs.
rin67630
Solar Enthusiast
In off grid-powering devices, there is no "one size fits it all" solution.
One must balance all opportunities.
12VoltInstalls
life passes by too quickly to not live in freedom
Interesting discussion.
I’m no EE but after 2-1/2 years running PWM with a winter interlude “test” where I plugged two 100W 12V panels in series using a WN P30L, I’m not against PWM. It worked, and well.
Now running 2S2P with 400W w/ mppt, I can’t really tell the difference between that and when I ran 500W 5P with the mppt. If that changes much when the days get short I may experiment some more. It will become important because this coming winter will be the first winter I’ll be living here November-March and not just April-Oct.
Anyway, I don’t know the consumption of the P30L but my batteries were always up last winter (I spent a number of overnights Dec-Feb). If I add 2 more panels I may run those through the old P30L and compare its daily watts with the Tracer just for fun.
I said all that for the setting of the stage.
PWM isn’t a terrible thing; it works. I might use PWM on my boat. The mppt does seem to recover the batteries better than the pwm did; and running the vacuum for 15 minutes in full sun exposure really ramps the amps and boosts the batteries during and after.
But the PWM still equalized the batteries 15V+ and I’ve seen it around 12A of charge a number of times when I only had 200W of panels. Math, specs, standby current: measurable, sure. However, they may not translate into something that makes a noticeable, practical difference in reality.
I’m no EE but after 2-1/2 years running PWM with a winter interlude “test” where I plugged two 100W 12V panels in series using a WN P30L, I’m not against PWM. It worked, and well.
Now running 2S2P with 400W w/ mppt, I can’t really tell the difference between that and when I ran 500W 5P with the mppt. If that changes much when the days get short I may experiment some more. It will become important because this coming winter will be the first winter I’ll be living here November-March and not just April-Oct.
Anyway, I don’t know the consumption of the P30L but my batteries were always up last winter (I spent a number of overnights Dec-Feb). If I add 2 more panels I may run those through the old P30L and compare its daily watts with the Tracer just for fun.
I said all that for the setting of the stage.
PWM isn’t a terrible thing; it works. I might use PWM on my boat. The mppt does seem to recover the batteries better than the pwm did; and running the vacuum for 15 minutes in full sun exposure really ramps the amps and boosts the batteries during and after.
But the PWM still equalized the batteries 15V+ and I’ve seen it around 12A of charge a number of times when I only had 200W of panels. Math, specs, standby current: measurable, sure. However, they may not translate into something that makes a noticeable, practical difference in reality.
rin67630
Solar Enthusiast
If you run 400W of panels, and aim to live off grid, the quiescent current of the SCC isn't the major part of the equation any more.
But that 400W will be an extreme limitation during wintertime, you will have to live like a monk with that.
Do your math with that: PV-GIS-Offgrid for your location and check the tab "Battery state" after "Visualize the results".
To give an example: with a 250W 30Vmp panel, MPPT SCC and two 100Ah FLA batteries, I can hardly power the 10W permanent consumption of my router + telephones + tablets.
If I were you, I'd buy a gas generator before September....
12VoltInstalls
life passes by too quickly to not live in freedom
I’ve run into Oct on solar without issue. But you are absolutely correct- light is a challenge here.
the point of my post was pwm does ok more than the math suggests
For my situation: I have a newly re-brushed 85A GM alternator, going to buy a ‘predator’ 5HP from HF. Been meaning to build that for years. Light weight.
Most of the manufactured smaller generators have really low 12V output- since I have four lead batteries parallel the 85A shouldn’t damage anything and still top up ok if needed.
Nov, Dec are generally dark here, as is part of Feb/March. The next property I buy is going to have a brook or other running water on it. For obvious reasons.
the point of my post was pwm does ok more than the math suggests
For my situation: I have a newly re-brushed 85A GM alternator, going to buy a ‘predator’ 5HP from HF. Been meaning to build that for years. Light weight.
Most of the manufactured smaller generators have really low 12V output- since I have four lead batteries parallel the 85A shouldn’t damage anything and still top up ok if needed.
Nov, Dec are generally dark here, as is part of Feb/March. The next property I buy is going to have a brook or other running water on it. For obvious reasons.
12VoltInstalls
life passes by too quickly to not live in freedom
W
Nobody said pwm was superior.
There was, however, a good discussion of the reasonably good performance of pwm with small systems for parts of the day in certain circumstances, and affirmation of how/why mppt is better generally- especially for higher volt systems.
Unless I imagined that?
Your hyperbole is in poor taste and unfounded.
Nobody said pwm was superior.
There was, however, a good discussion of the reasonably good performance of pwm with small systems for parts of the day in certain circumstances, and affirmation of how/why mppt is better generally- especially for higher volt systems.
Unless I imagined that?
Yes but he said PWM is almost as efficient...and it isn't.
He also claimed BradBill didn't do the "maths". Sounds like poor taste to me.
What is the deal with the PWM people that get butt hurt when people say that MPPT is superior? Seems especially true of the people that own the 1980s Bogart stuff that's out of date.
12VoltInstalls
life passes by too quickly to not live in freedom
A
In practical use pwm often performs much better than it should on paper. In some situations some charge is superior to little or no charging.
IMHO the negative diss on pwm isn’t the whole truth. When pwm output regularly exceeds daily demand, I for one am not disturbed at all that the batteries don’t know that they’ve been charged with inferior electrons.
It’s easy to argue that the new Corvette is superior to a C4 but dang! I’d drive a C4 happily if the 2021 ‘Vette was too much dough.
As was mentioned by someone else- even Will Prowse has a vid where a pwm had some pretty decent output. YES- the math/calcs clearly show mppt as superior: EXCEPT that is lab/theoretical superiority.
In practical use pwm often performs much better than it should on paper. In some situations some charge is superior to little or no charging.
IMHO the negative diss on pwm isn’t the whole truth. When pwm output regularly exceeds daily demand, I for one am not disturbed at all that the batteries don’t know that they’ve been charged with inferior electrons.
It’s easy to argue that the new Corvette is superior to a C4 but dang! I’d drive a C4 happily if the 2021 ‘Vette was too much dough.
12VoltInstalls
life passes by too quickly to not live in freedom
I’m Everday Educated. “EE” lol
I had series/parallel and ohms etc figured when I was like 12yo (unhealthy interest in audio production, plus had too easy access to a big public library after school every day in the 1970s) and learned a ton since then. I’m no expert but I can wire boats or fix automotive electrical pretty well. Campers, boats, etc- I’m pretty adept.
EDIT: ok I’m sorta expert at 12V compared to the average DiY. But I ain’t no guru or EE. /EDIT
I can’t look at a circuit board and tell you all the resistor values or mosfet specs though.
Oh. And currently I’m selling replacement windows for a major national company LOL
I had series/parallel and ohms etc figured when I was like 12yo (unhealthy interest in audio production, plus had too easy access to a big public library after school every day in the 1970s) and learned a ton since then. I’m no expert but I can wire boats or fix automotive electrical pretty well. Campers, boats, etc- I’m pretty adept.
EDIT: ok I’m sorta expert at 12V compared to the average DiY. But I ain’t no guru or EE. /EDIT
I can’t look at a circuit board and tell you all the resistor values or mosfet specs though.
Oh. And currently I’m selling replacement windows for a major national company LOL
I do.
It is cheaper and for my large number of converted to 12V panels scattered all around the yard to make the most of the winter sun between the trees, at different aspect angles because I've used existing structures as well as custom built frames an mppt charger would have trouble doing the mppt thingo!
.So may as well buy some $20 pwms from China, add a better heatsink, and watch my guppies swim around under solar powered led lights!
