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How to / DIY => Everything else => Topic started by: veggie on August 17, 2019, 01:54:57 AM

Title: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 17, 2019, 01:54:57 AM
Hi All,

I came across this video where a fellow uses a small buck converter to match a 24 volt (28 -34 vdc) solar panel
to a 12 volt charge controller to charge a small gel cell battery.
https://www.youtube.com/watch?v=AD7g5BNy5fM (https://www.youtube.com/watch?v=AD7g5BNy5fM)

This interested me because I have a few 50 watt (24 volt) panels and I would like to use them on some protects involving 12 volt gel cell batteries and a microprocessor. I also have a few cheap Ebay buck converters kicking around.
Now granted, this may not be the best accepted practice, but if one has the components sitting around collecting dust, maybe it's ok.
So my question is...
Does anyone see a problem with this setup when used for small batteries and low amperage?
I'm not really concerned with efficiency. I just want to use a surplus 24 volt panel to charge a small 12 volt battery using a 12 volt charge controller.
The microcontroller would run 24/7 so it will draw from the battery constantly.
Battery charges in the day and draws down at night.
I am aware of the necessary depth of discharge limitation that I must consider with the microcontroller draw.
I have multiple 50 watt, 24 volt panels if needed.


Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: BruceM on August 17, 2019, 04:25:34 AM
As long as the solar charge controller can manage with the high EMI and ripple of the buck converter, I see no problem.  A PWM type charge controller will be likely to do fine since it was already coping it's own rather substantial EMI. 

Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 17, 2019, 05:34:16 AM

I would ask why even bother with the charge controller in the first place?

The buck converters I have seen all have output ajustment  over a fairly wide range. If you set them to a max limit of 14.5/ 14.8, whatever you like your batteries to flat at, then a charge controller is unnecessary because they will never go above that.
If you load them up the voltage will drop and the Buck converter will flow more power up to it's and the panels limit ( no reason you can't series the panels if the Buck will handle it) and get more output. If you have multiple panels, I'd series them in an east, west and flat configuration. that way you will get the earliest charge into your batteries, the latests and the best possible in  crappy weather.
Angling the east/ west panels at 60O will also allow you the most CONSTANT and even charge into the batteries which is what you want over the highest output especially if the batteries are small.

As you have the Buck set to 15V in the diagram, turn it down a fraction more and that's it.  Once the battery hits that voltage the buck will only supply the MA it needs to float and anything else the load requires.

The PWM controllers will pull the panel voltage down to the battery and are no different to direct connection EXCEPT for the cut off. I have a panel hooked to the exact charger in the vid which aren't bad for the cheap thing they are but My Buck controller is a High amp Fixed output. You would have to be sure the Buck converter would cope with the potential draw of the Charge controller  but again, I don't see the need for one.

If you measured a lot of ripple from the Buck, just add in a nice fat capacitor or bank thereof.

I have a battery charger I use as a power supply and it's low output works on the half wave from the rectifier which gives terrible ripple and some devices wouldn't work because of it.  A 370UF 330V Cap ( was what I had)  Smoothed it out very nicely and still gives lower power but a lot cleaner DC than before.  When using it as intended as a battery charger, the batteries themselves too care of the ripple.

I see no problem, I just wouldn't worry about the charge controller to start with and maybe throw in a cap on the output side but I don't see it will be needed unless you are running  like a 2Ah battery or similarly tiny.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 17, 2019, 02:31:09 PM

Thanks for the guidance fellas. I'll give it a try.  :)
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: BruceM on August 17, 2019, 02:50:26 PM
Glort's got it right and I missed the obvious. No need for two stages of pulse regulation when one will do.  Set the buck regulator output voltage depending on the type of battery and typical daily depth of discharge and time to charge. 

 You might be able to find a 24/12V PWM controller that can do directly what you want, and is smart enough to go to float charge voltage when charge current tapers off.  That will increase battery life somewhat, perhaps adding a year.  You can either do a seasonal average temperature adjustment on the charge voltage yourself or better select the charge controller for one that does it automatically for you.   That will add a year or two to battery life.  Few (lead acid) batteries die, most are murdered before their time.




Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: mike90045 on August 17, 2019, 04:07:56 PM
Watch out for the simple Buck converter not being able to start or be stable with the variable output from the PV panel. if it hangs up, you won't get charge
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 17, 2019, 04:41:28 PM

 You might be able to find a 24/12V PWM controller that can do directly what you want,

Why do you think the PWM controller would not give max battery Life Bruce.?  If the max voltage was set to the point you want the battery to Float, why would it go over? I would think it would be just a matter of hooking everything up and setting the controller with a Multimeter to keep the battery where you wanted it.  I would assume that the "charge" current would taper off as the voltage got higher which would be exactly what one wanted.

In any case, I got a couple of these on order that should do the Job:

https://www.ebay.com.au/itm/5A-MPPT-9V-12V-24V-Solar-Panel-Regulator-Controller-Battery-Charging-Auto-Switch/282624044890?_trkparms=aid%3D555021%26algo%3DPL.SIMRVI%26ao%3D1%26asc%3D20190711100440%26meid%3Df9c476a752e84f6382173eb02ddf7d28%26pid%3D100752%26rk%3D2%26rkt%3D16%26mehot%3Dag%26sd%3D233167705792%26itm%3D282624044890%26pg%3D2047675&_trksid=p2047675.c100752.m1982 (https://www.ebay.com.au/itm/5A-MPPT-9V-12V-24V-Solar-Panel-Regulator-Controller-Battery-Charging-Auto-Switch/282624044890?_trkparms=aid%3D555021%26algo%3DPL.SIMRVI%26ao%3D1%26asc%3D20190711100440%26meid%3Df9c476a752e84f6382173eb02ddf7d28%26pid%3D100752%26rk%3D2%26rkt%3D16%26mehot%3Dag%26sd%3D233167705792%26itm%3D282624044890%26pg%3D2047675&_trksid=p2047675.c100752.m1982)

Being MPPT they should handle the 24 to 12 Down rating and are also adjustable for the desired end voltage.

There are also these Boards  https://www.ebay.com.au/itm/DC-DC-Buck-Constant-Voltage-Current-Converter-DIY-Lithium-Battery-Charger-Board/112546564848?hash=item1a344c4af0:g:fB4AAOSwuq9ZY04k&frcectupt=true (https://www.ebay.com.au/itm/DC-DC-Buck-Constant-Voltage-Current-Converter-DIY-Lithium-Battery-Charger-Board/112546564848?hash=item1a344c4af0:g:fB4AAOSwuq9ZY04k&frcectupt=true)

And the same with a readout: https://www.ebay.com/itm/Solar-Panels-MPPT-Controller-5A-DC-buck-Step-down-Constant-Voltage-Current-Modul-/191927867733 (https://www.ebay.com/itm/Solar-Panels-MPPT-Controller-5A-DC-buck-Step-down-Constant-Voltage-Current-Modul-/191927867733)

Plenty of cheap solutions in any event.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 17, 2019, 10:31:43 PM

 You might be able to find a 24/12V PWM controller that can do directly what you want,

In any case, I got a couple of these on order that should do the Job:

https://www.ebay.com.au/itm/5A-MPPT-9V-12V-24V-Solar-Panel-Regulator-Controller-Battery-Charging-Auto-Switch/282624044890?_trkparms=aid%3D555021%26algo%3DPL.SIMRVI%26ao%3D1%26asc%3D20190711100440%26meid%3Df9c476a752e84f6382173eb02ddf7d28%26pid%3D100752%26rk%3D2%26rkt%3D16%26mehot%3Dag%26sd%3D233167705792%26itm%3D282624044890%26pg%3D2047675&_trksid=p2047675.c100752.m1982 (https://www.ebay.com.au/itm/5A-MPPT-9V-12V-24V-Solar-Panel-Regulator-Controller-Battery-Charging-Auto-Switch/282624044890?_trkparms=aid%3D555021%26algo%3DPL.SIMRVI%26ao%3D1%26asc%3D20190711100440%26meid%3Df9c476a752e84f6382173eb02ddf7d28%26pid%3D100752%26rk%3D2%26rkt%3D16%26mehot%3Dag%26sd%3D233167705792%26itm%3D282624044890%26pg%3D2047675&_trksid=p2047675.c100752.m1982)

Being MPPT they should handle the 24 to 12 Down rating and are also adjustable for the desired end voltage.


Nice find Glort !
 I ordered a couple for myself.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: BruceM on August 17, 2019, 11:07:18 PM
Nice find Glort. That does look like it will take a 24V panel input to a 12V battery as Veggie desires, though I couldn't find specs or manual that specifically elaborates that. 

The only concern with a fixed voltage converter of either PWM or MPPT is that never going to float or never going to bulk charge voltages in some cases can limit lead acid battery life.  You can deal with it by lowering the fixed voltage if it's mostly in float, or raising it if it's going to be discharged more over night.  I do it myself on my PV linear regulator for the car, even though it does shave a year off the battery life for overcharging and drying out the AGM battery.  I didn't have room for more circuitry, was trying to squeeze it on a nice surplus heat sink I could slip in next to the battery.  So I just do a seasonal fixed voltage adjustment, lowering it for summer, raising for winter.

I think PWM vs MPPT is irrelevant.  MPPT is mostly hype and I certainly don't give a hoot  about the last 15% of PV power under certain low light situations.  PV is so cheap now that it's nuts not to design for plenty of extra PV for winter/cloudy days. 

While I was sitting here, my 1 hp air compressor is topping off my 500 gallon tank.  I know it's still pumping as there's a bug in my battery charge controller which causes it to go to bulk charge voltage when there's a big load on the inverter.  It's a handy bug- I can tell when the well pump or air pump is finished when it goes back to float, but I'm trying to fix it anyway.  I just added a resistor and capacitor on one critical signal that had some ripple, but alas, it apparently wasn't the one that was causing it to trip out of float.  The other is a stinker, the trace that must be cut is completely under the IC.  Grrr.  I'm trying to get it finalized so I can have new clean PCBs made; it's my original prototype and it's got lots of rework on it. 






 



Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 18, 2019, 01:39:33 AM
Nice find Glort. That does look like it will take a 24V panel input to a 12V battery as Veggie desires, though I couldn't find specs or manual that specifically elaborates that. 

No, I couldn't either but as it does not specifically say it won't do the 24/12 and knowing other MPPT controllers can, just have to give it a go. If the magic smoke comes out, I'll claim a refund.
I have seen descriptions of  things like this that one either ends up having no clue whatsoever as to what the thing actually is for , or, The impression given to everyone who reads said description is completely and utterly opposite to the actual function of the component!

Funny enough, when I was looking at these different boards the other week, I was specifically after some that were NOT MPPT.  I came across several that were described as PWM  but the picture clearly showed the inductor that told me they were MPPT which wasn't what I wanted.
Of course the number of PWM controllers that are described ( and Priced) as MPPT  is well known.
The Chinese are anything BUT ethical or honest Business people.

Quote
The only concern with a fixed voltage converter of either PWM or MPPT is that never going to float or never going to bulk charge voltages in some cases can limit lead acid battery life.

Hmm, equalising charge.  I guess one could always have a second Controller set higher and switch that one in now and then to give the battery a boost. Matter of fact a Timer board could be put on said controller so it kicked it in automatically every so often for a given time to raise the voltage.  Plenty of the little timer boards that will do week intervals now.

Quote
I think PWM vs MPPT is irrelevant.  MPPT is mostly hype and I certainly don't give a hoot  about the last 15% of PV power under certain low light situations.  PV is so cheap now that it's nuts not to design for plenty of extra PV for winter/cloudy days. 

I think it depends on the application.
PWM will normally  pull the panels down to battery voltage rather than keep them at their Pmax which can be important is some applications. If the array is dragged down, it will certainly kill the efficiency not just at the beginning and end but right through the day.  Of course depends if you can use all the array's output and for how long.  On big systems and in bad weather, that might be important to some people.

In playing with the idea of a solar only direct control water heater, PWM is fine but it does need to take into account the sweet spot in the panels.  It's a real annoyance to have 2KW of panels hooked to an element and get 500W output if you are lucky.  Resistance matching leaves a lot to be desired as well.  No matter how many panels one has, it's nice to get some semblance of correct operation out of them.
I can have an array hooked directly to an element and get Diddly out of it. I then take that same connection and put it into a GTI and hook the element to that and get 5X more power output.
Not so much a matter of cost of panels for me, it's now a matter of space to put them all!  :0)

What I want to do is use the simple PWM but have control parameters on it so it will run in the panels happy place.  With that accomplished, I agree, MPPT is largely a waste of time in most applications.  My axiom with solar  from early on is inefficient is efficient when the cost of getting efficiency out of something is weighed against just throwing more brute force at it.
In the case of PWM with things like an element, that may not be the case always.

I certainly agree with the idea of over designing for the low radiation periods. All my arrays are pretty much double the inverters capacity or more.  I realised over winter that the output from the solar wasn't that much down through the main 4 Hours, it was just the things were only at the good end of production 4 Hours instead of more like 8 in summer. It wasn't so much an output thing as a time problem.

I also noticed on cloudy days the output from a 2KW inverter could be virtually the same or even better than a much larger one.  More dependent on what it was hooked to rather than the size of the inverter itself.

The system I put up at my fathers place is a design disaster in effect.  Wrong direction, terrible shading, wrong tilt..... But the Little inverter it's on is overclocked to hell.  The output is pretty useless when the the panels NEVER see direct light but the other 9 Months of the year, It's halved his bill and the output is better than I would have expected by a long margin.  The extra panels make a BIG difference to what the thing would do if set up as our regs allow with only 30% over drive. 


Quote
While I was sitting here, my 1 hp air compressor is topping off my 500 gallon tank.  I know it's still pumping as there's a bug in my battery charge controller which causes it to go to bulk charge voltage when there's a big load on the inverter.

Ummm, how is that a Bug?
Load comes on, battery voltage will drop presumably enough to trigger charge into bulk state, Charger kicks in hard and basically supplies load direct at least to the max it can so when load kicks off, battery's recharge to float voltage maybe in minutes or certainly a lot quicker than they would have if all the load was borne by them alone.

What do you see as the problem and what would you like to happen?

Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: BruceM on August 18, 2019, 05:27:13 AM
You may be right that some cheap PWM units aren't true buck converters.  In that case, the PV array voltage must match the battery well or true, it won't work worth a damn.  Probably MPPT is the best way to insure that you're getting at least a decent DC-DC Buck coverter even if not true MPPT.  MPPT assures that someone might have at least thought about the panel voltage/amps curve, and will do a proper Buck (downward DC to DC) conversion (with inductor as you mentioned) with decent efficiency so is probably best for most consumers, who unlike me don't give to shits about conducted or radiated EMI.

For my 12V and 6V batteries, I have a cheap adjustable 5A DC power supply (switcher) for equalization charging.   My 120V bank controller does equalization on demand, with a 5 hr timeout. Each 12V battery in series is held at the proper equalization voltage by it's individual battery shunt regulator.  I do it the end of the month on a clear day.   I avoid electric cooking that day as 153V is a bit much, though it does heat a 115V rated soldering iron quite fast!

The bug in my 120VDC charge controller is that it should stay at float voltage (136- ish volts depending on temperature) as there's ample PV power to run the inverter and maintain other minor loads. While I have found the bug useful it's still a bug.  When I filter the netcharge signal tomorrow, that should fix it.









Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 18, 2019, 04:40:34 PM
 I couldn't find any specs either, however there are a few videos (if your Russian is good)
Here the fellow looks to be feeding 24 VDC and tuning the output to 12 VDC
https://www.youtube.com/watch?v=3btBG0DtSEs (https://www.youtube.com/watch?v=3btBG0DtSEs)

Here a fellow is testing the unit with instuments.
No dialog, but maybe BruceM and Glort will understand what the heck is going on.
Part 1:
https://www.youtube.com/watch?v=h0G2XQceHCM (https://www.youtube.com/watch?v=h0G2XQceHCM)
Part 2:
https://www.youtube.com/watch?v=ROOU8c9TgM0 (https://www.youtube.com/watch?v=ROOU8c9TgM0)
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: BruceM on August 18, 2019, 05:15:05 PM
Interpreting the videos without any diagram or verbal explanation of his test setup requires psychic abilities I lack.   Youtube at it's lowest.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 19, 2019, 06:52:03 AM

My Russian is more Corroded rather than rusty however in the first vid the guy is definitely feeding the board 36Volts so it will handle that at least. He says he first feeds it 73 V from what I can make out but that seems kind of high although maybe it's just momentarily as a stress test. The light bulb he is testing it with however is 24V so that does not tell us if it will do the 24>12 conversion but adds hope it should if it will pull down from 36.

 He shows the first board and compares the heat sinks to the blue one he calls grey?? and says he fried the first one running it flat out and the heat sink is too small. He compares the heat sink on the second one and comments how much larger and capable it is. oh, he may be referring to the heat sink being grey on the first one. It's definitely too small for his liking. He says he fried the thing at 12V because the amps were too high and running it at 19V is better and will charge a 18V battery down to a minimum of 21V input.
He tests the various settings on the pots and concludes the thing does do  true MPPT and will start up down to 11V but one of the pots adjusts that kick in voltage.  He says after setting the pots, in practice with a load they are about 20% out to what he set them to with the 24V bulb as a load.


The second guy is looking at the MPPT function and determines the board does do true MPPT and will Buck and boost. He tests the ripple which is low, under .5V 
He tests  the startup function as with a dead battery and determines it will trickle charge the battery first then kick in the full charging and then taper off the last 15% of the charge and gradually decreases from there. He demonstrates it will do full MPPT and hole the panels at voltage while varying the output.

In the second Vid he tests the ripple at high power and it is still good but cooling the IC makes the thing over shoot a little.
Driving the thing at full load makes it overheat after a while and it would be better at 3a unless a cooling fan is used on it.

Seems the board for once works as advertised and does a good job.  Someone in the China factory making these obviously slipped up and did something right!

What I would like to do is use this board to control a Bigger Mosfet that will hold the panels at the set voltage while allowing the board to be the base controller to drive a higher voltage and amperage load. The buck and boost would be irrelevant, just use it to hold the panels in a 10V range where they will still be outputting 95% of their power.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 19, 2019, 05:38:38 PM

Thank you for the translation "Mr Glort Yakimov"   ;D
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on August 28, 2019, 02:23:04 AM
Glort, did you receive your eBay MPPT converters yet?
I'm curious to see how they work.
Mine are still 4 weeks away.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 28, 2019, 04:19:15 AM

Yes mate, I have got a whole bunch of the things. I forgot how many different ones I ordered!
The last lot arrived yesterday but I haven't tried any yet.
I might go try something this afternoon now I am finished Mining in the Kitchen floor.

I hooked up 4 175W panels directly to a 3600W element and put that in a 25L tank in the fridge I am using for raising seedlings.  I boiled the water! :embarassed: Certainly the day have been sunny but I didn't even calculate and grossly over guestimated the power required.

Pulled it back to 2 panels and seems plenty hot.  I read a guy on YT going on about his controllers and being able to make 6 gallons of hot water which is less than 25L .  I wonder why the hell you wouldn't just throw a couple more Panels at it and be done with it? With 4 panels maybe paralleled/ series connected and a Controller, I reckon 125L might be more feasable.  I have been playing with 100L + and sort of missed how relatively easy a small amount like 25L would be to (over) heat but I think it's pretty dam useless for domestic purposes.
There is a 30L heater at my holiday house and it's a one shower job at best. Being on mains it takes about 45 Min to heat back up so isn't unworkable for that use.  A warm wash here at home would probably kill it though.

First thing I want to do with the controllers is see how much better I can make the output of the panels by bringing them back to power point which I'll do manually. Then I'll add a cap bank and see how that goes. the last thing will be to make the automatic PWM switching. I have the boards I'm going to plat with that as well which also arrived yesterday.

I like getting this stuff in the mail.  It's like Christmas only better because you get stuff you actually want rather than having to smile, say " Oh wow" and at the same time be thinking " What the F.. am I going to do with this shit?"

Today was a GOOD present. I bought myself this head light thing after getting one at bunnings the other day and finding out how dam helpful they are.
It has 3 Lights which can be single, double or all 3 and came with 18650 Batteries, a charger, cable and a Mounting which I think is for bike handlebars.
I unpacked it, put the batteries in, put it on, turned it on through the various modes  and then sat back down and ordered 3 More of the things.
For $10, best buy I think I have made in a while. 

More presents to arrive next week Now!   :laugh:
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on August 29, 2019, 06:48:05 AM

being a man of my word, ( on rare occasions) I went out and tested the PWM controller on the panels and heater element.

Unfortunately yesterday was bright and sunny and when I went out it just so happened that the voltage I was getting off the 3 panels I had hooked up matched the element impedance  within .9 of an Ohm.  As such the PWM could not make any improvement on a direct connection.
Today is the opposite and so cloudy that the panels aren't making enough to even get on their  Curve within anything I can adjust for or more over, accurately measure.

I haven't used the cap bank yet, no doubt today it would make a difference although probably a slight one due to the fact the PWM cycles would I think be firing way too fast. Something with a much slower pulse like an arduino driving the pulses would no doubt be much better for this low an output.

I'll try again tomorrow but the nut shell is having an array of panels and dividing the voltage between them to stay on the power point of the panels to give the most efficiency.

Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on September 05, 2019, 01:43:13 AM

I have Given the PWM controller a few more tests and not come up with anything real exciting.
It seems the benifit when direct connected even with matching the sweet spot of the panels is not very significant at this level. I have tried 2 and 3 panel setups with the 3600W element but it's a real fine line for the peak efficiency at  this low output. I doubt at the nd of the day there would be much difference in and reasonable amount of water with and without the controller.
If it was ramped up to a total of KW instead of hundreds of watts, then I expect the difference would be more but that's beyond the scope of the controllers available without modification.

I haven't tried using a cap bank and am hoping that makes the difference.  I'll try to get a DC watt meter because working out every equation with volts Vs amps is not practical. If I had a watt meter and can just see a higher number I'll know where I'm at. I thought... I'm sure I have a DC wattmeter somewhere on something but I can't think what it was. Might have been my solar battery inverter setup. I'll go dig it out and look.

One thing is pretty clear though, if you get lucky with the panels and element you are using you are going to be pretty close in the ball park to start with.

Seems I might have hit the magic numbers at the one time I prefer not to. Next I'll try the caps and then changing the panels for something else.
Can't be annoyingly lucky twice!
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on September 05, 2019, 02:46:26 PM
Thanks Glort,
I assume you are talking about the module shown in the picture below...
From what you have seen, will it work as a crude charge controller with my 24-34vdc panels charging a small 12vdc battery?
I have a 50W (24vdc) panel and wish to solar charge a small gel-cell battery which powers a micro-controller at a remote site.

Mine have still not arrived  :-[
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on September 05, 2019, 11:39:13 PM

Hi Veg,

The one you showed was the one I DIDN'T order!   :0)
For what I want to do it's not suitable as it's MPPT rather than PWM and I can't externally drive a Mosfet with it.

For what you are describing you want to do with it however, I'd say it's perfect.  It has an Inductor coil ( which was why it was no good for my purposes) so will allow the Voltage Mismatch of the panel and the Battery.  I might order a couple of them myself actually, I found a good small Panel I was given a while back and I  thought about putting it up the back in the machinery shed and putting it on the  tractor as the regulator is not working on that and I am just recharging the battery every so often which isn't great for it.
  In any case sometimes it's a couple of weeks before I use the thing so having a charger on it would be much better.

I have a STACK of different controllers sitting on my desk in front of me to try out, modify and build into circuits for this idea.
The controller I'm playing with atm is a 90V, 15A capacity unit which was the highest pre made board I could find.  I was thinking I could upset the impedance match I have with the panels and the element by adding another set of panels in parallel with the first ones.
This will halve the impedance of the panels and -may- give me more power as well depending on the setup.
Again I think to make that work I'm going to have to bring in the capacitor bank  to store the panel energy between pulses.

I'm also beginning to wonder if I have gone the wrong way all together and for real low outputs it would be better in the long run just to buy a low Voltage element and be done with it?  Being a tight arse and being able to get AC elements anywhere for Nix, that was the route I preferred to take.
One the 3rd or 5th hand, what ever I am up to, the low voltage elements I have seen are all pretty low output, 6 or 900W.
I was pulling1800W out of a bunch of panels on another array yesterday on a 3600W element hooked to 3.75 Kw of panels in series.
Might sound bit of an inefficiency but given the season here and the fact the array is way off ideal tilt, I thought it was pretty good being they are never going to produce perfect efficiency to start with. I might if I get a chance test what I get with the array direct coupled and what I get when Hooked to the GTI.  At some times it should be very similar, at others the GTI will be miles more efficient as that's what it's there for in the first place.

Certainly 1800W is going to heat a decent amount of water up a lot faster than 900.

I have another idea yesterday for matching the impedance of the panels. 
At different times of the day the panel output and impedance ( resistance ) will vary.  If multiple elements were used and switched in and out, the impedance could be varied higher or lower and a better match for the panels at that time would be created.
I'm thinking this would be best done by voltage monitoring and would give a similar effect to the PWM of the panel voltage to keep them in the sweet spot which is what we are trying to do. It would be far more staged but none the less give a decent efficency improvement.
I could possibly switch the panel arrays from Series to parallel and Daisy chain the elements also which could give 8 stages pretty easy I think.

Most water heaters will only take a max of 2 elements here but if a custom external element pack was built with say 2 more elements and a solar Circulation pump used, then this could be incorporated fairly easily. I do remember seeing something similar on the net some years back where a guy had something like 20  500W cartridge heaters in a pipe and was switching them with a load of SSR's .  Rather expensive setup but this was probably what he was doing. I do remember him being questioned as to why such a big heater setup and he had a massive amount of panels as well and the reply was he was running a guest house / small holiday resort and had a large hot water demand.
If I can work out how to stage the panels, then a twin water heater element should give a minimum of 4 stages and If I had 4 arrays, might be possible to again have 8 stages of resistance which would allow pretty tight matching.  I'll have to do the mental and practical arithmetic on this  but it should just be swtching.  The control part would be the trick as always.

I did get I think it was a thermostat board with staged outputs I was going to look at converting  to a voltage input signal which is what a thermo couple would work on anyway  but given the voltages used, It will take some real accurate setup to make it work.

All I need to test and work through all this is a completely parallel life with nothing else to do.   :embarassed:
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on September 05, 2019, 11:52:26 PM

Thanks Glort,

I might order a couple of them myself actually, I found a good small Panel I was given a while back and I  thought about putting it up the back in the machinery shed and putting it on the  tractor as the regulator is not working on that and I am just recharging the battery every so often which isn't great for it.
  In any case sometimes it's a couple of weeks before I use the thing so having a charger on it would be much better.


That's the exact reason I bought two.
My tractor can sit for months before I use it. I want to use my second 50 watt panel to keep the battery charged.
However, I'm not sure that this little controller is smart enough to scale back when the battery is full.
Will have it investigate.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on September 06, 2019, 02:04:31 AM

Being MPPT and the tests I looked up on the net say it is a true MPPT  and a good one at that, I don't think you need to have any concerns at all. I'm sure it will do exactly what you want.

From what I can see, you may have to set the thing up initially.  The instructions say to charge the battery and keep an eye on the voltage and ajust the trimpots to give the cutoff voltage you want.  Seems to me nearly everyone has their preferred end/ cutoff voltage  so you can set the controller to give you what ever you want.

I'm thinking it's likley to be set up for 12V out the box but whether you want 14.5 or 14.8 or something else is up to you. I don't think there is any question it's smart enough to know the end voltage, from what I saw the thing does a very good job in all aspects.
The thing will be just to initially check it and ajust the settings to what you like.

In my experience those little trimmers either take 5 turns to adjust something a volt or they adjust 10V if you breathe on them.  :0)
You should only have to do an initial setup and then they will be fine. This is the same as some better solar battery controllers I have with an LCD readout. They  all have settings for low voltage cutoff and end charge/ Float voltage.

From what I have seen, you have bought the best boards available for the job and should work very well for you.  :0)
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: veggie on September 06, 2019, 02:54:02 PM
Well ... if that's the case then I would say that a price of $10 for these little units is the best bargain out there.
An adjustable MPPT charge controller for small batteries (or maintaining a vehicle battery) for this price is a great deal.
Having said that, I am mindful of where it is made. I will report back once my charging system is active.
Title: Re: Solar - 24vdc Panel with 12vdc Charge Controller
Post by: glort on September 06, 2019, 04:41:27 PM

Like I said, everything I found on them, and I did do a reasonable amount of homework as usual, said they were really good.
I don't believe in writing everything Chinese off either. I think there is a lot of bias and out of date thinking there.
Certainly there is some real crap but then again, I can point to some real crap coming from anywhere in some product or another and much of it isn't too cheap either.

In my game, a LOT of Japanese and european gear has been almost completely given up on for Chinese stuff.  Initially they ripped off the OEM  products as they do and they did them very well and very cheap. Now they have just picked up the ball and run so far and so hard with it, people look at the OEM stuff as hoplessly under featured and severely over priced.

 I remember buying some of the Chinese gear when it first came out. I wanted it for what I thought was akin to a Suicide mission. I got lambasted on forums as being  a cheap arse, which I certainly am, but the stupid and other things turned out to be others not me when everyone soon woke up the stuff was in many ways better than the OEM and so cheap it was virtually disposable... except that no one ever seemed to break the things.
My Suicide gear came though without a proverbial scratch even though exactly what I thought would happen did.  Many others including the OEM flag wavers even admitted they would not expect the brand name gear to survive what I showed the Chinese gear had.  Still have the stuff today and use it occasional although it's way under featured compared to what is now available... for literally a 5th of the less featured OEM offerings.

My experience and that of other people I know with a considerable amount of Chinese machinery, easily over 60 different items, has been fantastic.
I only know of 3 failures and they were all operator error that has caused thousands of brand names to fail. Engines just don't like being run without oil  and chainsaws have this aversion to running again when you drop them 30Ft  out the basket of your boom lift. Apparently the Chinese gear is a bit weak when being run over by 26ton excavators as well.   :0)

I have several Chinese Solar battery charge controllers ( Only have Chinese controllers ) and can't fault them either.  Yeah, some are as simple, cheap and basic as they come but they do work as advertised.  My better ones are bloody brilliant. There are many MPPT controllers and some of the higher end Chinese controllers are now well preferred by the off gridders than anything else. Hundreds of YT vids on the different units.

The other thing of course is how many brand names people swear by are made in China now.
There isn't much made anywhere else.
A guy I am friendly with imports a LOT of stuff from China and goes there 4 times a year.  His opinion is you get what you pay for with them. If you are after lowest price, that's what you get with lowest quality as a bonus.  If you want quality and tell them that, that's exactly what you get for surprisingly little extra.  He laughs and tells me how people he sees there asking about making replica parts will give him a price to make the same thing, a lower price to make cheapest and then another price where they will point out design flaws and failure points and tell him they can give him a product that will eliminate all that for a buck or 2 more like it's 100 bux on a $50 part. He said the only problem with getting the good quality is you never sell them again because they outlast what they are put on.

I think you are going to be pleasantly Surprised with these things mate.