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Topic: MOSFET ON by default when arduino is off. (Read 6742 times) previous topic - next topic

tauro0221

Hi,
I checked your schematic and attached it is one in the way I would do it.  It is almost the same as your are but less parts. If you remove the micro it will make the n mosfet disable and let the p mosfet keep charging the battery. I do not know if that is  what you was looking for. A high in the gate of the n mosfet  will disable the P mosfet. If you already fixed yours schematic just disregard it. 

juan3211

Hi,
I checked your schematic and attached it is one in the way I would do it.  It is almost the same as your are but less parts. If you remove the micro it will make the n mosfet disable and let the p mosfet keep charging the battery. I do not know if that is  what you was looking for. A high in the gate of the n mosfet  will disable the P mosfet. If you already fixed yours schematic just disregard it. 
Hi Tauro0221, thanks a lot for your schema.

May be I have not explain my schema and my project.

In this case, I have to design a little schema for a project that will be connected thought SIM900 module. It is powered by a Li-Ion 3.7V battery and solar panel as you see.

I want to program it this way:
1. if battery is > 4.1V, disconnect solar panel by short circuiting it with mosfet
2. If battery is < 3.7V, connect solar panel
3. If battery is < 3.5V send a SMS or HTTP GET to a WEB to call for help as the battery will be ruined if there is not more solar power to recharge it.

In this case,I dont mind or I dont want to include a cut off battery schema(if anyone want it, please see some post above).

And as the circuit/project will be on ALWAYS,I don't want to include the circuit that you said some post above to conect solar panel with battery when arduino has not being powered.

The objetive is:
0. keep it as simple as possible.
1. a simple switch on and off a solar panel with a a battery from an Arduino pin.
2. there is no need to have a low battery cut off system
3. there is no need to connect solar panel with battery when arduino has not being powered as in that case and because of it hasn't got a low battery cut off system, i will be always on until battery ruins or is changed or is recharged.

Do you think that my schema meets the requirements?

Regards,


tauro0221

Hi,


The objetive is:
0. keep it as simple as possible.
1. a simple switch on and off a solar panel with a a battery from an Arduino pin.
2. there is no need to have a low battery cut off system
3. there is no need to connect solar panel with battery when arduino has not being powered as in that case and because of it hasn't got a low battery cut off system, i will be always on until battery ruins or is changed or is recharged.


I think followed what you explained above what you need it is a voltage regulator that provide the voltage that you require from  the battery. The battery will be constantly be charging  by the solar panel.

juan3211

I think followed what you explained above what you need it is a voltage regulator that provide the voltage that you require from  the battery. The battery will be constantly be charging  by the solar panel.
HI Tauro0221, thanks a lot. I have made what you say some time ago. It is simply, yes, probably a LDO regulator, two capacitors and two resistor to set the voltage that the battery require.

But it has two problems:
1. there is a little or big voltage dropout  so you will lose some power from the solar panel.
2. this is the  main problem: you need to set a voltage to the voltage regulator. Let's set it at 3.9V for a LiIon battery (but it is the same if you put 4.1V or 3.7V). You will lose a lot of oportunities to recharge the battery. First, you need 3.9V PLUS the voltage dropout of the regulator, and also, you will not get more than 3.9V in your battery. Also, when your battery is low (3.6v), the regulator doesn't seem to do a good performance as the battery forces voltage to 3.6V, and regulator forces it to 3.9V.

As my schema is only some resistor, a transistor and a mosfet, I will prefer over the regulator solution.

Looking at my schema, do you think that is something wrong ?

Regards,

tauro0221

Hi,
I lost where we are so attached is the schematic that your are proposing. Is this the right one? I lost which one we are working on.

juan3211

#35
Apr 08, 2017, 09:26 pm Last Edit: Apr 09, 2017, 12:24 am by juan3211
Hi,
I lost where we are so attached is the schematic that your are proposing. Is this the right one? I lost which one we are working on.
Yes, of course. It is here attached. May be will it be simpler with a N channel mosfet and also SAFE for arduino ? (si2302) (see second attached file)

juan3211

Hi,
I lost where we are so attached is the schematic that your are proposing. Is this the right one? I lost which one we are working on.
Hi @tauro0221 what about my last post ?

Regards

tauro0221

Hi,
Sorry, but I have been too busy lately. Let's see if I can get sometime and check it out.

tauro0221

Hi,
I am trying to simulate your schematic using the second schematic  but the mosfet gate it is connected to the ground. The gate always be grounded.

juan3211

Hi,
I am trying to simulate your schematic using the second schematic  but the mosfet gate it is connected to the ground. The gate always be grounded.
Sorry, change R24 to 1 Ohm or delete it.

R25 is to pull gate down to GND when arduino is off (just in case.If arduino is off, I don't know if output pins are conected to GND or floating). If arduino is working, you will have an output with these two states:
1. HIGH (3.3V):mosfet gate 3.3V=> mosfet ON, so solar panel is shorted. No energy to the battery
2. LOW (0V):mosfet gate 0V=> mosfet OFF, so solar panel current goes to the battery.Charging process.

What do you think ?

tauro0221

Hi,
A we taking about the same schematic. I am using the second one as you mentioned in the reply. Any way attached is your schematic. Please check the mosfet gate you will see it is connected to ground. I think it should be connected to the regulator output.

juan3211

Hi,
A we taking about the same schematic. I am using the second one as you mentioned in the reply. Any way attached is your schematic. Please check the mosfet gate you will see it is connected to ground. I think it should be connected to the regulator output.
I have to control gate voltage to put mosfet on or off.

My schema put solar panel in short circuit when mosfet is on, and when arduino output is HIGH (gate voltage = 3.3v, and with the pull down R25 resistor, 0.33mA from output pin of arduino.).
My schema put solar panel to battery when mosfet is off, and when arduino output is LOW (gate voltage = 0V)

I don't know why you think that it won't work

Thanks

tauro0221

Hi,
Can you look at the schematic and tell how you can turn the gate to high. Right now it is connected to ground. How can you turn the ground high?


TomGeorge

#43
Apr 11, 2017, 03:37 am Last Edit: Apr 11, 2017, 03:40 am by TomGeorge
Hi,
Can you look at the schematic and tell how you can turn the gate to high. Right now it is connected to ground. How can you turn the ground high?


The 10K R25 keeps the gate to gnd but if R24 is 220R, the output of the arduino will be able to pull the gate above ground.

The circuit is called Shunt Bypassing, and can be done here because of the low power PV.
The MOSFET bypasses the PV current away from the rest of the circuit.
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

tauro0221

Hi,

Attached it is the schematic that I am using with the voltage that resulted from the circuitlab simulation. I am using the closed components available to simulate your circuit in the circuitlab. Please check it to see if the components used simulate your circuit. Also the simulation showed a zero volt at the mosfet gate. Let me know any changes that I need to do to simulate your circuit. The circuitlab  just have the right components necessary to be able to simulate a circuit. I have the limit edition.

 

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