Simple home made analog MPPT contoller
- Thread starter Warpspeed
- Start date
Warpspeed
Solar Wizard
Open circuit voltage is 49.5v which is definitely too high for the TL494.
Perfect for a couple of SM12's though. They are only a couple of dollars each, so well worth getting.
The results of running both my amp hour meters in series resulted in a difference of about 4.0% at the end of a bright sunny day, which is a much larger difference than I was expecting.
So funnily enough, when I first started comparing my own analog solar controller to a commercial Make Sky Blue mppt controller, my controller was being fed from solar panels that were about 3.7% better.
But the Make Sky Blue controller was being monitored with an amp hour meter that was being generous by about 4.0% so that almost exactly balanced out the difference !
Overall I think the difference in performance for all practical purposes is too close to call.
In the end it probably comes down to power conversion efficiency, and choice of the power components.
A few extra dollars spent on better mosfets and choke might get an extra couple of percent, but its probably not worth the trouble.
The Make Sky Blue is definitely going to be better in truly marginal conditions, where there is almost no worthwhile power to be gained anyway.
For me, the advantage of building my own controller is a definite cost saving, especially where there are multiple banks of solar panels pointed in different directions that require multiple different controllers.
A home brew controller is going to be very quickly and easily repairable, which in a SHTF scenario might be critical.
Perfect for a couple of SM12's though. They are only a couple of dollars each, so well worth getting.
The results of running both my amp hour meters in series resulted in a difference of about 4.0% at the end of a bright sunny day, which is a much larger difference than I was expecting.
So funnily enough, when I first started comparing my own analog solar controller to a commercial Make Sky Blue mppt controller, my controller was being fed from solar panels that were about 3.7% better.
But the Make Sky Blue controller was being monitored with an amp hour meter that was being generous by about 4.0% so that almost exactly balanced out the difference !
Overall I think the difference in performance for all practical purposes is too close to call.
In the end it probably comes down to power conversion efficiency, and choice of the power components.
A few extra dollars spent on better mosfets and choke might get an extra couple of percent, but its probably not worth the trouble.
The Make Sky Blue is definitely going to be better in truly marginal conditions, where there is almost no worthwhile power to be gained anyway.
For me, the advantage of building my own controller is a definite cost saving, especially where there are multiple banks of solar panels pointed in different directions that require multiple different controllers.
A home brew controller is going to be very quickly and easily repairable, which in a SHTF scenario might be critical.
Warpspeed
Solar Wizard
Yes happy to provide Gerber files so you can order your own boards.
Just not sure how to do that.
Any suggestions ?
curiouscarbon
Science Penguin
- Joined
- Jun 29, 2020
- Messages
- 3,022
Is it possible to upload as a resource? Since the normal forum posts are limited to common images.
Warpspeed
Solar Wizard
I have no idea, never tried to use the resource section of the Forum.
I will look into that.
But happy to provide all the information as a "free open source to anyone" project if that is possible.
I will look into that.
But happy to provide all the information as a "free open source to anyone" project if that is possible.
You can use https://wetransfer.com/ it's free and the size limit is far higher than anything you can need for PCB stuff 
The only downside is that the file is only kept for some time (a week IIRC).
By default it asks for an email address to send the link to but you can click on the three dots in the lower left and select "Get transfer link" instead, then once the file is uploaded you can copy-paste the link here.
The only downside is that the file is only kept for some time (a week IIRC).By default it asks for an email address to send the link to but you can click on the three dots in the lower left and select "Get transfer link" instead, then once the file is uploaded you can copy-paste the link here.
Warpspeed
Solar Wizard
I am really stuck with this problem.
I still cannot figure out a way to post Gerber files on the Forum.
HELP !!!
I still cannot figure out a way to post Gerber files on the Forum.
HELP !!!
A lot of people prefer GitHub for this reason. It lets you set up a proper project that you can maintain and update over time, including any related documentation. You can also track activity, and other people can contribute, work through issues, etc. Far better than trying to maintain static files on the forum.
Warpspeed
Solar Wizard
O/k I have enrolled at Github, I will investigate that further, but am a bit busy right at this moment.
stienman
Mostly Harmless
- Joined
- Jan 6, 2021
- Messages
- 476
Just a quick note: MPPT controllers have a distinct advantage over this one, which is that users don't have to set them up, nor change their settings if their array is changed. Plug it in and then ignore it. As your data shows, once you're close to MPP rating of the panel string the power difference between actively searching for it vs just sticking to the rating is very small.
Were you able to figure out github and put your files up? I'm going to check out the back shed forum as well, where it sounds like most of your design materials and discussions exist.
I like this design, thanks for sharing!
Were you able to figure out github and put your files up? I'm going to check out the back shed forum as well, where it sounds like most of your design materials and discussions exist.
I like this design, thanks for sharing!
SolarForU2
New Member
An interesting simple solution using the TL494, no CPU, excellent.
RV2 allows only a single battery voltage set point, did you consider adding an RV3 to allow an additional lower value float voltage, with some sort of electronic switch to select one or the other as required?
Cheers
Mike
RV2 allows only a single battery voltage set point, did you consider adding an RV3 to allow an additional lower value float voltage, with some sort of electronic switch to select one or the other as required?
Cheers
Mike
Warpspeed
Solar Wizard
Not on this very first prototype
Many changes, additions, and improvements are possible.
The TL494 is a rather old chip, but still readily available. Its pretty unique and ideal for this in having two excellent easy to use error amplifiers.
All I wished to do at this initial stage is to test that the basic concept works, which it does, and works better better than I ever dared hope for.
From here, its a case of building your own version to suit your own specific needs.
I just put together some power components that I already had on hand, which are not absolutely ideal, but good enough for proof of concept testing.
sun walker
New Member
Hi (just carrying on from our post on open source mppt's), I've read a couple of times your discussion on this thread & Open Source Microconverter, to understand your design as best as possible, in the hope of making some.
Its been a real learning curve, I have a basic concept of most of it, but chokes, drains, gates were new to me, I'm getting there.
So your present design for your system has 140 volts coming in, 100 volts coming out charging a 96V battery supplied from strings of 1kW banks of four panels ~7.5Amps. (I'm assuming your test exp. matches your home sys.) So I guess the 96v battery supplies your diy inverter that supplies 240v ac to your home wiring. & most of your parts are what you had at hand. Works best with a 30 amp toroidal (light dimmer) choke.
Lots of questions, but I'll limit them now, so as not to take up too much of your time.
Obviously I don't have the knowledge to modify your design, so best to repeat what you have done.
My system is 17 panels TW 415w, voc 38.08, 13A, North facing, 15 degree gable roof mounted, apart from cloud no shading.
Q. So for your 30A choke, is a 1kW string the maximum for your Mppt?
If I had 3 in-series panels = ~114v x 13A =1482w
that would be excessive, so I could only have 2 in series = 988w? Can I easily increase the choke amperage to accommodate 3 panels,1482w ?
Plus my 13 amps are > than your ~7amps, that could be a problem?
Q. You a have a 96v battery, but can I adjust the output to charge a 48v battery?
(On my present small 12v sys. my off grid home is wired for 12v, I plug inverters into this, next to the appliance. I was planning on having a 48v battery & running new 48v lines to new high load appliances (air con. etc) each with a dedicated inverter.)
Cost? I can't imagine how or from what I could salvage the chokes from, which at a glance seems to be the biggest cost.
ebay 2/5pcs 10A Power Filter EMC Common Modes Inductor Wire Choke Ring Inductance US $8.99/ea
Note ring needs to be hy2 iron powder (I think), not sure what these are.
I assume I can put these in series for higher Amps.(formula @ https://www.electronics-tutorials.ws/inductor/parallel-inductors.html )
ebay
Electric Welder 450V 470uF Aluminum Electrolytic Capacitor Volume 30x50
100% brand new and high quality
AU $6.32 each
Features:
The capacity is measured at around 470uf, which is suitable for welder.
Voltage: 450V
Capacity: About 470uF
Not sure if these are suitable or could be smaller? As a home build I'd like it as robust a reasonable.
I'll stop here, thanks for your time.
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Warpspeed
Solar Wizard
Those panels are rated at 415 watts only under standard laboratory test conditions of 1Kw per square metre.
The best that you are ever likely to see will be about 80% of that figure, or perhaps 332 watts of real power.
That is quite normal !
Estimated real life output at flat out max power might be something like 32 volts at 11 amps per panel loaded, and with 38v open circuit voltage.
Depending on battery type, a fully charged 48v battery might be roughly at somewhere around 56v as a guess.
These figures are all very approximate, but close enough to estimate some rough solar controller requirements.
If we run three panels in series, that would have an open circuit voltage of 3 x 38v = 114v max.
Under full load, the max power panel voltage might be about 3 x 32v = 96v at maybe 11 amps.
Max combined power 3 x 332w = 996 watts per string.
Battery charging current 996w divided by 56v, possibly about 18 amps give or take a bit.
So we need to select our mosfet and choke (and a heatsink) to handle possibly 18 amps continuously without burning up.
The mosfet and electrolytics must be rated for at least 150v for a good safety margin.
The two electrolytics across the solar voltage should each have a ripple current rating of about half of that 11 solar amps.
A 20 amp commercial light dimmer choke will usually have an inductance of about 600 microhenries which would be ideal.
That is a very rough outline of the whole thing to get started.
As there is going to be about 17 x 332w or 5.6Kw charging at roughly 56v, we are looking at possibly 100 amps charging current.
Much better to use multiple controllers for this, rather than one single 100 amp controller !!
sun walker
New Member
Thanks, those were my thoughts aswell.
So can I use more than 3 panel's per controller?
6 perhaps by increasing the ratings of mosfet, electrolytics & choke?
Warpspeed
Solar Wizard
Yes indeed !
The sky is the limit on the power components.
All I am really offering here is the basic concept, and a proven circuit for the control part of the system.
The sky is the limit on the power components.
All I am really offering here is the basic concept, and a proven circuit for the control part of the system.
sun walker
New Member
So I guess what I should aim for is 2 strings, 1 of 8 panels & 1 of 9 panels. That was the combo I was going for in the commercial mppt's. 17 panels 2 strings.
Warpspeed
Solar Wizard
Its important to realize how the ratings of the power components increase as you scale the whole thing up in voltage.
In the above example with three series connected solar panels, we are looking at about an estimated 996 watts, a voltage of 114v and a current of about 18 amps.
Two suitable mosfets should be able to do that quite efficiently.
If you were to string together nine panels in series, it comes to an estimated 2.988Kw, a voltage of 342v, and a current of 53 amps charging a 56v battery.
Higher voltage mosfets have a much higher rds-on than lower voltage mosfets, and to assemble enough of them to safely carry 53 continuous amps efficiently would not be an easy thing to do and be efficient and reliable.
Its going to take a lot more mosfets, be more expensive and much more difficult than building three of the lower voltage, lower power solar controllers.
If these nine series panels were for charging a 192 volt battery, that would be much easier, because the maximum charging voltage would probably then be something like 224v and at 2.988Kw the charging current might be only about 13 amps. That would be quite realistic.
Buck converters can be made to be very efficient, but only if the voltage step down ratio is fairly low, say 2:1 or 3:1
If you have a very high step down ratio like 20:1 (240v dc down to 12v dc) the switching device sees BOTH the high voltage and the high current, which makes it all vastly more difficult to specify switching devices large enough to do it.
You will find most commercial 48v solar controllers max out for input/output voltage ratios at about 3:1 or possibly around 150v or 160v maximum input.
People are continually asking why are there no 500 volt input 48v solar controllers made. That would be so nice !!
But its just not practical or economic to build such a monster using a buck converter.
Certainly possible, but it would require a topology much more complex and expensive than a simple buck converter to do.
Scaling up in current is much more practical and easier to do than scaling up in voltage.
But even then, one controller per string offers some redundancy and advantages where shading may be a problem, or where strings of panels face in different directions.
In the above example with three series connected solar panels, we are looking at about an estimated 996 watts, a voltage of 114v and a current of about 18 amps.
Two suitable mosfets should be able to do that quite efficiently.
If you were to string together nine panels in series, it comes to an estimated 2.988Kw, a voltage of 342v, and a current of 53 amps charging a 56v battery.
Higher voltage mosfets have a much higher rds-on than lower voltage mosfets, and to assemble enough of them to safely carry 53 continuous amps efficiently would not be an easy thing to do and be efficient and reliable.
Its going to take a lot more mosfets, be more expensive and much more difficult than building three of the lower voltage, lower power solar controllers.
If these nine series panels were for charging a 192 volt battery, that would be much easier, because the maximum charging voltage would probably then be something like 224v and at 2.988Kw the charging current might be only about 13 amps. That would be quite realistic.
Buck converters can be made to be very efficient, but only if the voltage step down ratio is fairly low, say 2:1 or 3:1
If you have a very high step down ratio like 20:1 (240v dc down to 12v dc) the switching device sees BOTH the high voltage and the high current, which makes it all vastly more difficult to specify switching devices large enough to do it.
You will find most commercial 48v solar controllers max out for input/output voltage ratios at about 3:1 or possibly around 150v or 160v maximum input.
People are continually asking why are there no 500 volt input 48v solar controllers made. That would be so nice !!
But its just not practical or economic to build such a monster using a buck converter.
Certainly possible, but it would require a topology much more complex and expensive than a simple buck converter to do.
Scaling up in current is much more practical and easier to do than scaling up in voltage.
But even then, one controller per string offers some redundancy and advantages where shading may be a problem, or where strings of panels face in different directions.
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