MPPT solar battery charger

[theFob]

Hi iw,
I'll be glad to do this Had no such fun from long time.
I need the nominal voltage and maximum current values of the panel or just the model.
I noticed the lack of general decoupling diode in your circuit. Is needed for reverse current protection. May be the panel have such internally.
Also a small input filter will be good idea, because the input current of the buck is trapezoidal and is very stressful for the panel.
So the preferred converters are boost (when is possible) or sepic. The input currents there are triangle in continuous mode.
I allowed myself to check your CQ on the net. How far you've come with SG3525 inverter ? I guess it will work with this converter .... ?

Regards

[iw2fvo]

TheFob:
panel data are:
max power 50 w
open circuit volt: 21.6 Vdc
short circuit current : 3.04 A
Max pp volt: 17.6 Vdc
Max pp current : 2.84 A
There is a reverse protection diode ( see D1 on buck converter schematics ).
There is 220 uF at the buck input . Could it be too small ?
The panel keeps the SLA battery charged and so I do not have any inverter to produce line alternate power. I just need 12 VDC nominal.
CQ: >> I have a fully working homemade SDR rx tx for the HF. I have to re_install the antenna that went out completely during the last windy thunderstorm.
I plan to do that at the beginning of the next month.
Thanks.
73, IW2FVO.
Ambrogio

[theFob]

No, you have no panel protection diode. there must be a diode right after the panel, before the point C. It is essential.
If the sun goes down and you have no load at the moment, the input capacitor will return current which can destroy the junctions in the panel.
Diode D1 protect only the buck from the battery. Also the input capacitor is good to be bigger. At least 2200uF in my opinion.
Plus ~1uH inductance after the diode - will help a lot against noise. Few turns on the fly.
SDR sounds interesting, it is something new for me.

[iw2fvo]

Thanks.
I have learn now the need for a panel diode. I will move D1 to the panel input. I will also install a 2200 uF low ESR at panel input and after the diode.
The RF choke is a good idea too.
Ambrogio

[EarlyBird2]

Thanks Ambrogio for this very interesting and informative thread.

When I first read this thread I wondered why make your own Solar Regulator when I buy them for 20€ but obviously now I realise the models I use are not MPPT. The MPPT version costs 250€ so making your own is not only an interesting project but saves lots of cash.

I also realise that your design allows for Solar or Mains power which makes it even more interesting but I could not work out how the program/micro does the switching between the two power sources.

[iw2fvo]

Steve,
the program controls both the load disconnection and the external power .
You can set the voltages at your choice.
Here is the piece of code. The whole code is not optimized : I am not a software expert as I told at the beginning. There are a lot of comments on the program.
I think that a software guy could improve the code in a significant way. BTW it is still working at my home.
regards,
Ambrogio
iw2fvo

' LOW VOLTAGE PROTECTION ...and load control..................................

IF ( VB<11800 ) THEN ' BATT LOWER THAN 11.8 Vdc
U_VOLT=1 ' SET UNDER_VOLTAGE FLAG
LOW LD_EN ' DISABLE LOAD
LOAD=0
U_FLG=1
ELSE
IF ( VB>12600 ) THEN ' IF VBATT MORE THAN 12.6 Vdc
U_VOLT=0 ' RESET UNDER_VOLTAGE FLAG
IF U_FLG=1 THEN
HIGH LD_EN ' ENABLE LOAD
LOAD=1
U_FLG=0
ENDIF
ENDIF
ENDIF

IF (U_VOLT=1) AND (EXTPWR_OK=1) THEN
LOW EXT_PWR_RLY ' ACTIVATE EXT POWER RELAY
EX=1
ELSE
IF U_VOLT=0 THEN
HIGH EXT_PWR_RLY ' RELASE EXT POWER RELAY
EX=0
ENDIF
ENDIF

IF U_VOLT=0 THEN
IF PB_3=0 THEN
if LOAD=0 THEN
LOAD=1
ELSE
LOAD=0
ENDIF
IF LOAD=0 THEN
LOW LD_EN
ENDIF
IF LOAD=1 THEN
HIGH LD_EN
ENDIF
WHILE PB_3=0 : WEND
ENDIF
ENDIF

[EarlyBird2]

My rules for programming in order of importance.

1 It works
2 It is easy to follow
3 It is easy to modify

My definition of a good program is

It works

Which yours does except for one minor detail. So the question is whether to rewrite the program or not to solve this cloud issue? Personally I would rewrite the program because I would learn by doing so. I only wish I had the hardware.