Go Down

Topic: Powering a Heating Element (Read 1 time) previous topic - next topic

Jasonchildress

@TomGeorge, I'll take a pic tonight when I get home and after I've cleaned up the breadboard so it will be easier to visualize.

As for doing what happened in post #27, I ran into a soldering problem with the body of the heating element and decided to call it a night (solder not sticking to smooth, curved metal). But I'll get it soldered up later tonight and report back.

Jasonchildress

@JCA79B, I tried what you suggested and I was experiencing similar results, although the voltage drop wasn't as bad. Instead of getting 0.1v with the heating element connected, I'm getting roughly 0.6-0.8v. Here's a pic of the setup:


@TomGeorge, here are some pics of the breadboard. I cleaned it up a bit to make it easier to see. I verified that I'm getting the same results.

Here you can see a decent voltage without the heating element:


And then the voltage drop with the heating element:


Here's a close up of the wiring:


Some notes:
  • After cleaning up the breadboard and reducing the # of rails carrying a pos/neg load, down to just one rail, I'm seeing a higher voltage across the element then having all the rails of the breadboard hooked up. But its still not enough to produce any heat.
  • The battery power to the heating element was isolated from the ESP32. I powered the ESP from USB.

TomGeorge

#32
Mar 26, 2019, 10:25 am Last Edit: Mar 26, 2019, 10:27 am by TomGeorge
Hi,

In this configuration, can you please measure the voltage from gnd to the gate of the MOSFET please?
And from gnd to the output pin of the ESP32 PCB?
And the battery voltage?

What is the part number of the MOSFET?
Gate voltage of 3.3V is probably not enough to turn the MOSFET completely ON.

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Jasonchildress

@TomGeorge, thanks, I'll get those readings when I get home from work tonight.

The MOSFET is part #: P30N06LE

JCA79B

What was the battery voltage when you were getting 0.6V across the heater?

Jasonchildress

@JCA79B & @TomGeorge

Here are some more measurements:

With the Original P30N06LE MOSFET:
  • Battery Voltage: 3.8v
  • Ground to MOSFET Gate (pin on): 3.29v
  • Ground to MOSFET Gate (pin off): 0v
  • GND to ESP32 Output Pin: 3.29v

I tried a IRF3708 MOSFET and was getting a slightly higher voltage to the heating element. Roughly 1.6v versus 1.3v. But still not enough to heat up the element.


dave-in-nj

Did you say you were able to connect the battery to the heater and get it to work ?

if you did, then you might need re-think how you need to control the FET.

if you are using a USB to power the unit, you have 5v available.

you might also look at getting an  IRL  FET. one that switches with low input voltage.





WattsThat

OP mosfet is logic level. datasheet

Perhaps the gate resistor is the wrong value or bad. You should be measuring point C right at the gate of the mosfet, not at the esp32 output pin. Gate voltage should be 3.3 volts.

Another possibility is voltage drop in the breadboard which you've already seen. But, overall, I question if a 400mAh battery can supply a 2000mAh load for any length of time.
Vacuum tube guy in a solid state world

TomGeorge

Hi,
It looks like  MOSFET cannot turn fully ON with 3.29V on the gate.

What is the gnd to source voltage with gate ON and OFF?

If you disconnect the gate resistor from the ESP32 and connect the resistor to the Lipo positive. So the MOSFET gate is connected to the Lipo positive.
What voltages do you get?

Thanks.. Tom.. :)

Everything runs on smoke, let the smoke out, it stops running....

Blackfin

According to the datasheet for that MOSFET it should be more than on enough for the OP's load. Something else is up.

OP, can you measure:

- voltage at the drain (centre pin) with respect to battery ground
- voltage at the source (right-most pin) with respect to battery ground
- and/or verify continuity between source of MOSFET and battery ground
- verify: you are driving that digital IO on the ESP to "HIGH" and not PWMing it
- can you disconnect the resistor from the ESP and connect the gate directly to battery +ve; verify heater works

Jasonchildress

@dave-in-nj, I was able to connect the heater directly to the battery an make it heat up really well. Just not when using the FET. The project will be battery powered, so I'm avoiding using the USB's 5v as an option.

@WattsThat, For the measurements, I measured both, directly on the ESP32 pin's (on the actual pin/soldering), and Right on the MOSFET's gate pin. As for the battery, I see the same exact results when using a beefy Samsung 18650 battery.

@TomGeorge, GND to SOURCE voltage (directly on the pin) is 0.4v when om, 0.0v when off. With the BATT + () connected to the MOSFET gate and resistor removed, I'm getting 1.0V

@Blackfin:
- voltage at the drain (centre pin) with respect to battery ground = 1.45v PIN HIGH - 3.65v PIN LOW
- voltage at the source (right-most pin) with respect to battery ground = 0.85v PIN HIGH - 0v PIN LOW
- and/or verify continuity between source of MOSFET and battery ground = CONFIRMED
- verify: you are driving that digital IO on the ESP to "HIGH" and not PWMing it = HIGH, NOT PWM
- can you disconnect the resistor from the ESP and connect the gate directly to battery +ve; verify heater works = Works, but with lower voltage 1.0V.

Thanks again everybody for all of the support.

TomGeorge

Hi,

Quote
@TomGeorge, GND to SOURCE voltage (directly on the pin) is 0.4v when om, 0.0v when off. With the BATT + () connected to the MOSFET gate and resistor removed, I'm getting 1.0V
Your source to gnd wire is faulty or protoboard connection not good, the drop should be zero in both cases, because source is connected to gnd.
This will take 0.4V of gate level away from your MOSFET.

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Blackfin

Hi,
Your source to gnd wire is faulty or protoboard connection not good, the drop should be zero in both cases, because source is connected to gnd.
This will take 0.4V of gate level away from your MOSFET.

Tom.. :)
I agree. This is suppported by "voltage at the source (right-most pin) with respect to battery ground = 0.85v PIN HIGH - 0v PIN LOW". The source should simply be connected to ground all the time and the voltage drop should be minimal.

OP, IIRC the pins on a TO220 have a rectangular cross-section, wider when viewed from the front or rear than when viewed from the side. When you insert that into the protoboard you may be spreading the contacts into a 'V' shape resulting in holes adjacent making poor or intermittent contact. Consider moving the black wires for the drain and source to the "other end" of the slot -- the last holes, furthest away from the TO220, where the 'V' would be narrowest.

You might also re-orient the TO220 so the pins go in with the narrow axis spreading the contact; this would mean bending and staggering the pins so they each have their own row. The contact-spreading problem would be lessed. Maybe it's time to move to plated-hole perf-board for the power-section of your prototype...

Jasonchildress

Sorry for the delay in getting back to everybody, I've been busy with work and family events.

But good news, I took Blackfin's advice and moved this onto a small protoboard to avoid the breadboard and its now working as expected. The heater heats up well (really hot actually), and now I'll try using PWM to control the heat.

I just want to thank everybody who took time to help me identify my problem and offer solutions that helped me out. My project would have been stuck without you guys. :-)


Go Up