8 Channel High Current MOSFET circuit for 12V switching using arduino

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
Hello, I am in need of some help designing a 8 channel "relay" board using mosfets. I basically want to recreate those cheap sainsmart 8 channel relay boards but using something solid state. I've narrowed it down to what i believe is an acceptable MOSFET the FQP30N06L. In the end i want to be able to have 8 channels from the arduino control 8 channels out with a shared power source (optional but wanted). I understand the basics of how this should theoretically be setup but am having issues coming up with the full circuit and then i don't know what PCB settings are capable of withstanding the high currents. Anyone able to help out on the circuit design process would be much appreciated.

Basically what i want to recreate:

https://smile.amazon.com/gp/product/B00KTELP3I/ref=ppx_yo_dt_b_asin_title_o02_s01?ie=UTF8&psc=1

Most channels will only see around 20-30W at 12V but one will see around 300W at 12V so might aswell beef them all up.
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
I should have added I don't know if it is possible but i would like to control the positive side of the device as they already have a common ground and it is much easier to control the positive side rather than the ground.
 

djsfantasi

Joined Apr 11, 2010
6,432
The FQP30N06L is a N channel device; you need a P channel device. However, it could handle the current. It is rated for 60V and 32A. 300W is 25A.

Note that a P channel device will need an N channel driver. A 2N7000 can be used to be drives by the Arduino and to drive the P channel MOSFET.

What do you mean by ‘shared power supply’? Are you saying that the 12V supply operates the Arduino and is switched by the MOSFETs? You’re switching 21A for the low-current devices and 25A for the one high-current device, for a total of 46A. I’d recommend at least a 12V 50A supply.

That’s a lot. I didn’t bother adding the 200mA for the Arduino.

The other thing that’s not clear is the emulated relay contacts. Are you just switching on? Or do you need a NO / NC set to be switched?

PCB Trace sizing is a little more complicated. This AAC thread discusses your problem which another member also had.
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
The FQP30N06L is a N channel device; you need a P channel device. However, it could handle the current. It is rated for 60V and 32A. 300W is 25A.

Note that a P channel device will need an N channel driver. A 2N7000 can be used to be drives by the Arduino and to drive the P channel MOSFET.

What do you mean by ‘shared power supply’? Are you saying that the 12V supply operates the Arduino and is switched by the MOSFETs? You’re switching 21A for the low-current devices and 25A for the one high-current device, for a total of 46A. I’d recommend at least a 12V 50A supply.

That’s a lot. I didn’t bother adding the 200mA for the Arduino.

The other thing that’s not clear is the emulated relay contacts. Are you just switching on? Or do you need a NO / NC set to be switched?

PCB Trace sizing is a little more complicated. This AAC thread discusses your problem which another member also had.
I want to switch some led bars for an offroad vehicle. Some are small LED pods and Some are full 50inch light bars. I have a setup right now that is using an 8 channel relay board but the noise is quite annoying. The lights are powered from the cars battery and the arduino now is using a DC-DC converter to step the voltage down to 5V and to trigger the relay coils. I don't have a use for NO/NC set just care about ON/OFF.

https://www.4x4spod.com/bantam_w_hd_smart_panel
this is what i want to recreate using an arduino.
 

djsfantasi

Joined Apr 11, 2010
6,432
I want to switch some led bars for an offroad vehicle. Some are small LED pods and Some are full 50inch light bars. I have a setup right now that is using an 8 channel relay board but the noise is quite annoying. The lights are powered from the cars battery and the arduino now is using a DC-DC converter to step the voltage down to 5V and to trigger the relay coils. I don't have a use for NO/NC set just care about ON/OFF.

https://www.4x4spod.com/bantam_w_hd_smart_panel
this is what i want to recreate using an arduino.
So, your requirement is pretty straightforward.

A GPIO pin from the Arduino is wired to an N-channel MOSFET gate with a pull down resistor. The drain is connected to the P-channel MOSFET gate with a pull up resistor to 12V. And the P-channel MOSFET switches 12V to the load. Repeat 8 times.

I wouldn’t use the DC-DC converter to get 5V. The Arduino runs off 7-20VDC, but the 12V isn’t stable since its from a car battery. The Arduino has a power sweet spot of 9V. So use a 9V DC-DC converter instead.

Are you comfortable programming the Arduino and loading your sketch onto it? And what are you going to use as input(s) to the microprocessor?
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
So, your requirement is pretty straightforward.

A GPIO pin from the Arduino is wired to an N-channel MOSFET gate with a pull down resistor. The drain is connected to the P-channel MOSFET gate with a pull up resistor to 12V. And the P-channel MOSFET switches 12V to the load. Repeat 8 times.

I wouldn’t use the DC-DC converter to get 5V. The Arduino runs off 7-20VDC, but the 12V isn’t stable since its from a car battery. The Arduino has a power sweet spot of 9V. So use a 9V DC-DC converter instead.

Are you comfortable programming the Arduino and loading your sketch onto it? And what are you going to use as input(s) to the microprocessor?
Ok thanks ill give it a shot, i wasn't aware the arduino could accept that kind of voltage.
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
So, your requirement is pretty straightforward.

A GPIO pin from the Arduino is wired to an N-channel MOSFET gate with a pull down resistor. The drain is connected to the P-channel MOSFET gate with a pull up resistor to 12V. And the P-channel MOSFET switches 12V to the load. Repeat 8 times.

I wouldn’t use the DC-DC converter to get 5V. The Arduino runs off 7-20VDC, but the 12V isn’t stable since its from a car battery. The Arduino has a power sweet spot of 9V. So use a 9V DC-DC converter instead.

Are you comfortable programming the Arduino and loading your sketch onto it? And what are you going to use as input(s) to the microprocessor?
I'll give this a shot thanks. Have any P mosfet reccommedations for 12v at around 30A?
 

djsfantasi

Joined Apr 11, 2010
6,432
Google
p channel mosfet 25v 30a​

You want a little headroom. Once you do a couple of searches, you see what search terms are best.
 

crutschow

Joined Mar 14, 2008
24,980
How does a FQPF47P06 sound?
That will work but it has an on-resistance of 26 mΩ max which will dissipate 23W @ 30A.
To eliminate the need for a heatsink at 30A, the device should have an on-resistance of no more than about 1.1mΩ.

The relays you are replacing are 10A.
Why do you need 30A?
How's this look?
Not very good.
Take another look at my circuit.
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
That will work but it has an on-resistance of 26 mΩ max which will dissipate 23W @ 30A.
To eliminate the need for a heatsink at 30A, the device should have an on-resistance of no more than about 1.1mΩ.

The relays you are replacing are 10A.
Why do you need 30A?
Not very good.
Take another look at my circuit.
i messed up the first one and i didn't realize till after i posted, i'll attach the one i think is ok. I'm pretty sure im over the limit for those relays on atleast 1 of the channels with the 300W ~21A. So far they have been ok but also not sure how long they will last part of the reason i want to update the system. Ill keep looking for a better P-channel in the mean time. Again huge thanks

Schematic.PNG
 

djsfantasi

Joined Apr 11, 2010
6,432
i messed up the first one and i didn't realize till after i posted, i'll attach the one i think is ok. I'm pretty sure im over the limit for those relays on atleast 1 of the channels with the 300W ~21A. So far they have been ok but also not sure how long they will last part of the reason i want to update the system. Ill keep looking for a better P-channel in the mean time. Again huge thanks

View attachment 204842
Ummmm...... where did you get 300W 21A from?

I mentioned 21A but that was for the 7 channels at 30W. And I made a mistake; it should have been 17.5A.

However, the 300W channel draws 25A; not 21A.

For a total of 42.5A. A bit of current.
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
Ummmm...... where did you get 300W 21A from?

I mentioned 21A but that was for the 7 channels at 30W. And I made a mistake; it should have been 17.5A.

However, the 300W channel draws 25A; not 21A.

For a total of 42.5A. A bit of current.
the biggest light i have is rated for 300W i assume thats at 14.4 V so 20.8A. Thats the biggest largest load so 1 channel needs to handle that.
 

djsfantasi

Joined Apr 11, 2010
6,432
the biggest light i have is rated for 300W i assume thats at 14.4 V so 20.8A. Thats the biggest largest load so 1 channel needs to handle that.
You don’t want to calculate the current at the highest voltage. That value will be its lowest value (Ohm’s Law)

300W /12VDC = 25A​
 

Thread Starter

Mr.Incredible

Joined Apr 19, 2020
17
You don’t want to calculate the current at the highest voltage. That value will be its lowest value (Ohm’s Law)

300W /12VDC = 25A​
ah you are totally right either way i wanted to do 25A a channel as a minimum was hoping for more like 30A a channel but finding this P-channel mosfet is proving to be the end of me
 
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