Renewable energy: solar powerMppt connection

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Toilahyene
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Mppt connection

Unread Messageby Toilahyene » 18/02/20, 09:16

Hello
please help me, I have been working on it for 2 weeks and I have run out of ideas ...
a 10w solar panel connected to its 30A mppt charges a 12v, 33AH battery.
to the LOAD output is connected a 12V W1209 thermostat which activates a 12v fan when the temperature exceeds 23 ° C.
but once this value is reached, the fan receives an impulse, then the mppt drops to 5v, cuts off, then starts again on the same loop diagram.
with another weaker battery, same fault.
the mppt is set to 14,4v at maximum charge and 12,8v at maximum discharge for the battery.
Could someone explain the phenomenon to me and how can I fix it?

W1209-LED-Digital-Thermostat-Temperature-Control-High-Precision-Thermometer-Thermo-Controller-Switch-module-DC-12V.jpg
W1209-LED-Digital-Thermostat-Temperature-Control-High-Precision-Thermometer-Thermo-Controller-Switch-Module-DC-12V.jpg (37.79 KB) Viewed 399 times
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izentrop
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Re: mppt connection

Unread Messageby izentrop » 18/02/20, 09:38

Hello,
The 5 V indicates that your battery is completely flat.

A PV of 10 W at this time of year produces a maximum of 5, therefore 0,4 A on 12 V, but you are probably not located in France to have such high temperatures ...

A 33 Ah battery charges at 3,3 Ah at C / 10, remove this not at all suitable charger and connect the PV live to the battery with just a schottky diode in series and there, your fan will work without risk for the battery and without unnecessary losses.

Edit: you just put the image. This thermostat consumes too much for a small panel (2 hours of sun just to power the electronics), you would rather need a mechanical thermostat
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ENERC
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Re: Mppt connection

Unread Messageby ENERC » 18/02/20, 14:05

If the PV comes out in 12V, it can be connected directly to the fan. The fan will start to rotate slowly towards 6V then will increase in rotation speed with the increase in solar power.
If it is necessary to regulate the fan, put a MOS on the + with the grid connected to the thermostat. (it takes at least 5V to saturate the MOS, otherwise it will heat up).
For a battery system, a larger panel is required.
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Re: Mppt connection

Unread Messageby ENERC » 18/02/20, 14:15

ENERC wrote:If the PV comes out in 12V, it can be connected directly to the fan. The fan will start to rotate slowly towards 6V then will increase in rotation speed with the increase in solar power.
If it is necessary to regulate the fan, put a MOS on the - with the grid connected to the thermostat. (it takes at least 5V to saturate the MOS, otherwise it will heat up).
For a battery system, a larger panel is required.
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Re: Mppt connection

Unread Messageby izentrop » 18/02/20, 15:24

Wow !! It depends on the characteristics. For the mosfet, its threshold and the value of the rsd at this voltage.
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Toilahyene
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Re: mppt connection

Unread Messageby Toilahyene » 19/02/20, 08:37

izentrop wrote:Hello,
The 5 V indicates that your battery is completely flat.

the voltage at the battery terminal is 12,5v and when I connect the fan directly, it turns as hard on one or the other of my batteries
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Re: mppt connection

Unread Messageby Toilahyene » 19/02/20, 08:40

izentrop wrote:remove this not at all suitable charger and connect the PV live to the battery with just a schottky diode in series and there, your fan will work, without risk to the battery and without unnecessary losses.

the mppt is used to protect the battery so that it does not discharge beyond a certain threshold and does not charge too strongly.
the schottky diode cannot replace it, what will manage the reloading / unloading?
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Re: mppt connection

Unread Messageby Toilahyene » 19/02/20, 09:21

izentrop wrote: you would rather have a mechanical thermostat

that could be the solution however, for 12v?
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Re: mppt connection

Unread Messageby izentrop » 19/02/20, 10:14

Toilahyene wrote:
izentrop wrote: you would rather have a mechanical thermostat

that could be the solution however, for 12v?
He doesn't care about the tension, it's just a contact that opens and closes with the temperature. You can get it from an HS fridge by changing its calibration.
Toilahyene wrote:the schottky diode cannot replace it, what will manage the reloading / unloading?
It will prevent the battery from discharging into the PV at night.
You will not harm the battery, the maximum current that can deliver your PV is 10/12 = 0.8 A, 33 / 0.8 => it will take at least 41 h of full sun to recharge your 33 AH battery.

Then you must know the no-load voltage of PV at maximum solar. If it is 14 or 15 V, minus the 0.2 V voltage drop in the diode, you will have just enough to ensure the maintenance charge current. If it is 17 V, you can use an ordinary diode. https://www.ni-cd.net/accusphp/theorie/charge/plomb.php
We consider C / 30 as maintenance charge, 33/30 = 1.1 A, you will rather be at 1/60, even at 17 V.

Your MPPT charger is suitable for a charge of approximately 10 A and 100 AH of battery, largely oversized.
Toilahyene wrote:the voltage at the battery terminal is 12,5v and when I connect the fan directly, it turns as hard on one or the other of my batteries
Try it live on the battery (with a fuse in series, otherwise if you do a wrong maneuver it is the circuit that will smoke), but as it consumes 40 mA when empty and 80 when the relay is switched, it would be better to disconnect it out of use, otherwise like I said you lose 1 to 2 hours of charge per day, just to power this electronic thermostat.
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