Hi Eric,

Thank you for finding out the problem. The circuit indeed was designed to have hysteresis of approximately 2v-3v so that it does not start charging again until the voltage drops to around 52v. It was done this way to avoid oscillation in case of small voltage change in battery. But it seems, oscillation still exists. Kindly suggest how this issue can be solved.

Best,
DJS

@DJS
For your review I have attached both an .asc file and a screen capture (trace colors are noted to the right of the schematic). I believe the mods I show fix the problems I know of except: (a) There is no detection of a "shorted MOSFET". (b) There is no relief from the very many tolerances stackup that will make the "charger on"/"charger off" thresholds vary from unit to unit. Those tolerances include (a) the 12V PS, (b) R1:R2 divider, (c) R4:R7 divider, (d) large variation of Vtrig internal to the NE555, (e) large variation of Vthreshold internal to the NE555.
From your original circuit, changed or added components:
Added Q2, R3, R6, R5 to provide a high quality gate drive to the MOSFET, M1. Note the clean "on" and "off" periods.
Added D2, a necessary blocking diode that is sometimes built-in to a panel and sometimes must be added by the user.
Added R8, to better simulate a panel and keep the charging current to a reasonable value.
Removed the opto-coupler and associated components.
The TEST conditions: I set the panel voltage and battery voltage to simulate 2+ cycles of extreme high/low. The battery low voltage is set to 20V, rising to a max of 60V. The panel output (ignoring drop in R8) varies from 0V (dark) to 58V (noon).

I invite your review of the circuit. Of course, using the .asc file you can easily try other conditions than I have shown. Have fun!
EDIT: I just noticed that I failed to remove R6 from an earlier circuit variation; replace R6 with 0 ohms.
View attachment 186444

 

hi,
Downloaded your image.
I suspect the reason you occasionally have a problem with MOSFET's burning out is that controller is unstable, check thsi LTS sim image.
E

Hi Eric,
I am reviewing my circuit based on your findings. Could you please share me .asc file with your last findings of controller being unstable. I am not able to find LT model of some components that is there in the circuit diagram. Thank you.

Best,
DSJ

 

Morning DJS,
I am having a problem with LTS when using power MOSFET in the simulation.
LTS seems to get locked into a loop trying to solve the circuit.

I will ask @Bordodynov who is an expert in using LTS, to look at the problem.
Perhaps one his MOSFET models will suit the circuit.

I have looking into using a LM393 dual comparator in place of the 555.

E

EDIT:
This is bordodynov's library for LTS
https://yadi.sk/d/6nSSUmZiT9oCoQ


Update:
Added the problem asc file.

 

hi DJS,
After checking the operation of the circuit I can see why the circuits hangs when the MOSFET is trying to switch OFF.
The 12Vdc for the Opto transistor is powered from the 12Vdc, which is referenced to 0V.

When the MOSFET tries to switch OFF the Opto emitter loses its ground 0V reference, but instead it is referenced to the Solar negative line, so the MOSFET never gets fully switched OFF, its partially ON, this will cause instability ie; On/Off which will heat up the MOSFET.

In the SCC circuit they use a second MOSFET to isolate the Solar panel negative from the Source pin of the first MOSFET, so it gets a clean On/Off drive signal.

I will post a LTSpice circuit with this modification.

If the modification is agreeable , we can re-investigate the 555 switching action.

E

 

@DJS
For your review I have attached both an .asc file and a screen capture (trace colors are noted to the right of the schematic). I believe the mods I show fix the problems I know of except: (a) There is no detection of a "shorted MOSFET". (b) There is no relief from the very many tolerances stackup that will make the "charger on"/"charger off" thresholds vary from unit to unit. Those tolerances include (a) the 12V PS, (b) R1:R2 divider, (c) R4:R7 divider, (d) large variation of Vtrig internal to the NE555, (e) large variation of Vthreshold internal to the NE555.
From your original circuit, changed or added components:
Added Q2, R3, R6, R5 to provide a high quality gate drive to the MOSFET, M1. Note the clean "on" and "off" periods.
Added D2, a necessary blocking diode that is sometimes built-in to a panel and sometimes must be added by the user.
Added R8, to better simulate a panel and keep the charging current to a reasonable value.
Removed the opto-coupler and associated components.
The TEST conditions: I set the panel voltage and battery voltage to simulate 2+ cycles of extreme high/low. The battery low voltage is set to 20V, rising to a max of 60V. The panel output (ignoring drop in R8) varies from 0V (dark) to 58V (noon).

I invite your review of the circuit. Of course, using the .asc file you can easily try other conditions than I have shown. Have fun!
EDIT: I just noticed that I failed to remove R6 from an earlier circuit variation; replace R6 with 0 ohms.
View attachment 186444

Hello Teekay,
I simulated your circuit by replacing Q1 with opto coupler 4N25 as it was in my original design. The waveform is exactly same as yours. So i am not sure if your suggestion would work.

Sim image of both diagram is attached.

Best,
DJS

 

hi,
Try this simulation as per post #24.

 

hi,
Try this simulation as per post #24.

@DJS
Yes, the version with the opto-coupler works just as the version using the 2N3906 instead--they both work correctly, I believe. Explanation? Your original schematic (see your post#8), from which I worked, had an error that I corrected without realizing I had done so. The error? In your schematic, the signal driving the MOSFET gate does NOT connect to the MOSFET gate, but instead connects to the MOSFET source (leaving the gate floating). If you wish to use an opto-coupler rather than a PNP transistor, that is your choice.

 

hi,
Try this simulation as per post #24.

Dear Eric,
Tried simulation with Two MOSFET. Sim result looks ok but i noticed two MOSFETs are in series D-S-D-S. Is this configuration is for some kind of protection that if one MOSFET fails another will still work?

As i said in my previous post, good solar controller like morningstar has Mosfets connected in D-S-S-D. And i have not seen both MOSFET failing at the same time and charging is stopped if one fails.

Best,
DJS

 

Dear Eric,
This post is not related to my previous circuit but it is about the new Solar Charge controller circuit i found in net. If the problem of my original circuit cannot be fixed, then i can even think of making completely a new circuit as in the attachment. This new circuit is designed for MPPT 12V battery charging. Please take a look and suggest if moving forward with this new circuit would be a wise decision for 48V/50A by changing some components.

Best,
DJS

 

As i said in my previous post, good solar controller like morningstar has Mosfets connected in D-S-S-D. And i have not seen both MOSFET failing at the same time and charging is stopped if one fails.

Hi DJS,
The 'mod' has the MOSFET's in the same order as the SSC circuit.
Its as per post #4
When the MOSFET tries to switch OFF the Opto emitter loses its ground 0V reference, but instead it is referenced to the Solar negative line, so the MOSFET never gets fully switched OFF, its partially ON, this will cause instability ie; On/Off which will heat up the MOSFET.

In the SCC circuit they use a second MOSFET to isolate the Solar panel negative from the Source pin of the first MOSFET, so it gets a clean On/Off drive signal.

This is why the LTSpice would hang up at the switching point.

E

 

hi,
Ref post #29
The Vout max is quoted as 55V, will this be a high enough voltage overhead to force charge the 48V battery pack.??

It looks an elegant solution as a controller.

E

 

Hi DJS,
In the SCC circuit they use a second MOSFET to isolate the Solar panel negative from the Source pin of the first MOSFET, so it gets a clean On/Off drive signal.
E

Hi Eric, Your are not correct. In SCC circuit, MOSFETs are connected as D-S-S-D (Not D-S-D-S). I have seen this kind of configuration in other good controller (Like Morningstar) also.
Best,
DJS

 

hi DJS,
This is the SCC circuit you posted earlier, which I have used as reference.
E

 

[

hi DJS,
This is the SCC circuit you posted earlier, which I have used as reference.
E

Hi Eric,
You are mistaken again. The picture is little blur so it might have created confusion. It is indeed D-S-S-D. I have recreated the file. Please take a look at it again. Thanks.
Best,
DJS

 

hi DJS,
I can see the cause of my error, the person who drew the left hand BUZ11 has drawn the Gate connection 'upside' down.
Got so used to reading the MOSFET symbol and using the Gate symbol as a visual reference for the orientation.

What do you want to do on the next stage of your project.?

E

 

What do you want to do on the next stage of your project.?

Hi Eric,
I am still thinking what to do because i am little not confident about my original circuit that has problem of MOSFET shorting and then no control on charging. The solution that we have discussed to solve this problem is also not so promising yet.
The LT3763 based controller looks much better as it has short circuit protection (i tried sim by shorting the MOSFET and the result is perfect with "no charging") and is MPPT as well. I am just trying to understand what changes will be required in that circuit for 48V operation. If you have any ideas please kindly share.

Best,
DJS

 

hi,
OK, I will drop looking at the original circuit and run some sims on the LT3763, try some 48V modifications.
That diagram is for 14V at 5A
E

 

hi,
Run some sims on the LT3763, try some 48V modifications.
That diagram is for 14V at 5A
E

Good morning Eric,
Yes i would like to go ahead with LT3763 solution. For the MOSFET i will be using surplus IRFB4321. These MOSFETs used in Morningstar controllers for 48V/50A.

Best,
DJS

 

hi DJS,
As the Thread is moving towards a design project, I would recommend that you start a new Thread in the Projects Forum, this will hopefully bring other members into the discussion.
Post any relevant information to the new Thread , together with a draft design specification details.
You can also post a link there for this Thread.

E.
BTW: there is a Completed Projects Forum, so if you can finally get a fully working design we could move the Project.
It would help others working on the same type of project

 

hi,
I suspect the reason you occasionally have a problem with MOSFET's burning out is that controller is unstable, check thsi LTS sim image.
E

Hi everyone,
I would like to continue this thread again as i have some update. As mentioned about unstable controller, i also have strong feeling that at some very specific events (such as sudden change in sun intensity, bad batteries or something alike) the controller is not behaving normally making MOSFET partially ON and eventually burning it. Since this problem is intermittent it is very difficult to get it tested in Lab too.
As a last resort i am thinking to use some kind of MOSFET driver (IR2110 or TLP250) replacing the opto coupler 4N25. I have read somewhere that using MOSFET driver will significantly increase the MOSFET switching. But before going ahead with my plan i would like to hear suggestions from anyone who has experience using MOSFET drivers.

Best,
DJS

Edit: Referring to post 17 by Eric