Anet A8 external mosfet upgrade

I am trying to use the above mentioned mosfet for a special project. I have searched in vain for a part number to describe it but all I get is lots of information on how to put one on a anet 3d printer to replace the one on the motherboard.
I’m using one to operate an automotive throttle body. I have it working using a Nano to drive a small mosfet on a breakout board from Banggood. That works fine except the mosfet gets very hot from the load of the the DC motor in the throttle body. So I bought some of these larger 25 amp mosfet breakout boards with larger heatsink, screw lugs, etc. widely used for the Anet 3d printer. I have tried just a digitalWrite to pin5 and an analogWrite to pin 5 and both light up the blue, on board led. The red power light is on too. But the mosfet never transfers power to the output pins (labeled hot bed on the board). I made sure to put a diode and a 220 ohm resister on the the signal control wire from pin5, but no luck. I have used 2 or 3 TP120 mosfets before with no problems, but I can’t figure out what I am doing wrong with this board.
Any clues on what I am doing wrong?
Thank you in advance for any help you can provide me. Bruce

I am trying to use the above mentioned mosfet for a special project.

You will have to explain what that is - I don't see any "above mention". Also "some of these larger 25 amp mosfet breakout boards" is meaningless without a link to the product datasheet.

You may find that there is more information available on the RepRap Forum which specialises in 3D printing.

Or is your question really something to do with an automobile - "I'm using one to operate an automotive throttle body."

See How to get the best out of the Forum


As I mentioned earlier I can't seem to find what the part number is. Even the Banggood web site doesn't get specific with the product data, let alone a data sheet. Trust me I have tried all I know to find out about the item, but no luck.
IN general my use of the mosfet is just to drive a 12 volt DC motor in a throttle body. I already know how to do all the PWM stuff as I have mentioned earlier I have it working with a smaller mosfet (also from Banggood) but it is too small to be reliable, so I thought I could just swap it out for this larger one. If you search for Anet A8 mosfet upgrade you will see lots of examples of the very board I'm trying to use, but none of the info talks about how to wire or control the two wire control input to the mosfet board. I'm guessing that 5 volts and/or PWM would "trigger: the mosfet. But again, when I try any of those signals from pin 5 on the Nano (just like I did with the smaller mosfet) I get no output on the "HOT BED" screw lugs.
TFTTTR (thanks for taking time to respond)

I put this link in from my product order, but it went away!

I’m using the “add image link” (the blue computer screen picture above with the little green circle) here and the link just goes away when I post it. A little square box with some scribbling in it appears at the beginning of the line.
I’ll be glad to add any documentation I can if someone will tell me how to include them in my post. my links just keep disappearing?

If you want to post an image have a look at this this Simple Image Posting Guide - this Forum may not work the way you expect.

if you just want to post a link to a webpage with a datasheet use the "insert a link" button that looks like some chain links.

If you search for Anet A8 mosfet upgrade you will see lots of examples

I am lazy. I won't be doing any searching. That's your job. If there is something you want us to look at then post a link to it.


Banggood web site with mosfet

Ahhh... I doubt that. Anyone who responds to this forum is far from lazy. But I get your point and I have been frustrated trying to figure out how to post an image of the mosfet into this posting. I tried three times and the picture link just disappears when I hit post. So I tried a link to the web page where I bought the mosfet. I am more than willing to provide you any details of the problem. Perhaps you could tell me how to attach or include a picture from my phone into these postings. Some camera shots might go a long way to shows you what I am trying to do.
Again TFTTTR! Anyone who contributes to this forum is Grade A in my book.

I'm not going to offer advice about mosfets - they are above my pay grade.

However I reckon it is still unclear what exactly you want help with.

Are you trying to replace a failed mosfet on your Anet A8? If not, what are you trying to do?


Well now I get to tell you I'm lazy. Read my initial post and all will become clear to you..... Just kidding.
original small mosfet
If the above link works you will see a small mofset (less than 5A) that I have connected to a Nano to control the DC motor in a Jeep electronic throttle body. The DC motor opens and closes the "butterfly valve" in the throttle body to control air flow. The main problem is that I can't find documentation for the Jeep part to tell me how much current the throttle body would like. Some suggestions from the WWW say to expect to use about 10 Amps @ 12 volts. I think that might be way too much because I can get the throttle body to sort of work with a 9 volt battery. The little mosfet works, but just too hard. It gets really hot after a short use, but it does work with the PWM commands from the Nano. I can make the throttle body valve do anything I want. So I noticed that Banggood has a much larger mosfet on a breakout board that is sold to upgrade the onboard mosfet for an Anet A8 3D printer to power the hot bed.
I thought I could just use the larger (25 Amp) mofset to replace the smaller one in my project. But no such luck. I was hoping to find some help with why the larger mofset wouldn't work. I guess I'll have to dig deep into the A8 printer circuit (if I can find it) to see how they are driving the mosfet. When they upgrade to the larger external unit that I am trying to use, they don't make any changes to the printer's mother board. They just plug in the new unit.
Anyways, thanks for taking some time to see if you could help me. Much appreciated.

If the above link works you will see a small mofset (less than 5A) that I have connected to a Nano to control the DC motor in a Jeep electronic throttle body.

That's a lot clearer than your Original Post. May I suggest that a better title would be "help selecting Mosfet for DC motor to control Jeep throttle". If you edit your Original Post you can change the Title.


Well now I get to tell you I'm lazy. Read my initial post and all will become clear to you..... Just kidding.
original small mosfet

That's not a logic-level MOSFET, and its not a low-resistance MOSFET either, so unsuitable for two different

Earlier you mention "TP120 MOSFET" - did you mean TIP120? That's not a MOSFET, its a darlington.

MOSFETs are rated by load voltage, drive voltage and on-resistance. Ignore the current rating, you
don't want to be anywhere near that in practice (without a water-cooled heatsink!). To be driven
from a Nano you must use a logic-level MOSFET.

You calculate the dissipation from load current and on-resistance. (Or decide on a suitable
on-resistance from the max dissipation you can tolerate and the load current).

Thank you Mark! After a day of riddle me this, you provided me with a very good answer. I didn’t understand the different types of mosfets, but you explanation made much of it very clear. I had a feeling that this Anet A8 3D printer external mosfet for the hot bed was just being controlled by the on board mosfet for the hot bed. Yes, that is the case. It takes 12 volts to “trigger” this mosfet, but you are the only one that could tell me that. Thank you so much for helping me with this. I was only planning on using about 5 amps anyway, so I think the capacity would have been fine. As I mentioned earlier I was using a “less than 5 amp” mofset already and it was working ok, except for getting very hot. I understand what I need now so hopefully I can order something more suited to my needs. I do wish some of these vendors would provide more specifics on their parts, but in this case Banggood and Aliexpress told me nothing.
P.S. I’d love to know what you know! Thanks again.

I'd suggest looking in relevant datasheets and learn to spot the on-resistance specification.
This is normally given as a resistance together with a Vgs voltage (gate-source voltage) that
is required to switch to that resistance.

If the only Vgs mentioned is larger than 5V, its not logic level. Many logic level MOSFETs
use Vgs=4.5V (to allow for supply voltage variation). Some MOSFETs have even lower
Vgs values for the on-resistance spec - but usually these are surface mount devices.

Don't be confused by the threshold voltage, Vth or Vthr, that's only of use for analog circuits
using the MOSFET (which isn't common, power MOSFETs are principally designed for switchmode).

Do you need a high side switch to supply power to the load, or a low side switch to connect the load to Gnd?

N-channel MOSFETs are great low side switches, A0D424 is great for that with very low Rds at high currents and 4.5V on the gate.

Again Mark, great advice and thanks for the education. I have a much better idea if what to do.
Crossroads, good question. I am powering a small brushless DC motor. Specs call for a 5amp, 12 volt power supply. In the event of an emergency or problem I want to "chop" the power off to the motor but leave the power supply running for the status display circuits to remain running to indicate where the problem occurred. So I would think that the mosfet would control voltage supply side not the ground.
This project may require getting a patent. Don't know yet. So I can't be completely forthcoming about what I am doing. Once it gets past that stage I would love to discuss this further and even pay for your expertise to develop the circuits properly. For right now I'm just trying to get a prototype "proof of concept" working. And with the info you have given me I see the light at the end of the tunnel.
Again, thanks to everyone for taking the time to respond and educate me. Greatly appreciated.

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