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Smoking Heat Sensor
#1
Video 
I have this drill that I am converting to 18650

When I pull the trigger it starts smoking, so I opened it up and it seems to be some sort of heat sensor.

You can see from the pic that the heat sensor chip is wired into the trigger, and sits on a heat sink.

Does anyone know of a more powerful one that is about the same size?

[Image: uLBlqe0.jpg]

CLOSE UP

[Image: she0czv.jpg]

FOLLOW WIRING

[Image: UxnH4MY.jpg]
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#2
The part no is for a MOSFET

https://www.mouser.com/ProductDetail/STM...%252BZo%3D
 later floyd
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#3
That isn't a heat sensor. That's the electronic switch for the drill.

What's the voltage of the battery pack?
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#4
As florydR says, it's a MOSFET.  The trigger just sends a signal (blue wire) to the MOSFET, which then lets through current to drive the motor.

If it's no longer working, the MOSFET is likely destroyed and needs a replacement.
If it's still working, but starts to smoke after a few seconds, (1) it either needs better cooling, and/or (2) be replaced with a device that can better handle the power.

(1) If it's just screwed on to the metal cooling block, sandwich a small amount of thermal grease.  It will dramatically improve the transfer of heat.  Also filling in the MOSFET<->block side gaps will help a bit.  If there is space, you could add another cooling block on top of the MOSFET to cool it from both sides.  But prolonged use without air flow and time to cool down may still lead to overheating.

(2) I find the choice of this MOSFET for this application extremely questionable.  But will need more data such as battery voltage to suggest an upgrade.


It may be nothing, but it looks like the wires are not properly soldered to the terminal.  If the connection is poor, it may be adding to the heat generated inside the housing.  Or even be the source of the smoke.


Same here.  The wire and conductor on the PCB is really thick/wide to handle big currents.  Yet the solder area connecting them together is tiny, probably adding more heat.
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#5
(05-09-2020, 12:51 AM)Korishan Wrote: That isn't a heat sensor. That's the electronic switch for the drill.

What's the voltage of the battery pack?

The voltage is 36v 20amps
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#6
Like said above, it's a MOSFET.
If you don't give the gate (control pin) of the MOSFET enough voltage (ie >~5VDC but max approx 20V) it may not turn fully "ON" & be in a resistive or oscillating state leading to high heat dissipation (what you're seeing). Spec for this one has the gate threshold voltage = approx 3V
You'll need to replace this one, it'll be damaged already. This exact one is old, there would be more recent equivalents.
Then figure out if there's something (like low gate drive or shorted motor windings) causing it to burn.
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#7
(05-09-2020, 08:49 AM)Redpacket Wrote: Like said above, it's a MOSFET.
If you don't give the gate (control pin) of the MOSFET enough voltage (ie >~5VDC but max approx 20V) it may not turn fully "ON" & be in a resistive or oscillating state leading to high heat dissipation (what you're seeing). Spec for this one has the gate threshold voltage = approx 3V
You'll need to replace this one, it'll be damaged already. This exact one is old, there would be more recent equivalents.
Then figure out if there's something (like low gate drive or shorted motor windings) causing it to burn.

How can a 36v drill have a max of 20v

what is threshold voltage, the amount it needs to turn on?

Any recommendations of something powerful enough?
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#8
Re the gate voltage max of ~20V, this is delivered by the control circuit part.
The MOSFET can switch much higher voltages across the drain & source pins, but the gate to source can only be max about 20V on most devices (this ones actually 30)

Yes threshold voltage is the gate voltage where the MOSFET starts to "turn on" & pass current, it varies. You don't what to "hover" around the threshold voltage in a switching application like your drill. Usually the gate is driven with 10-12V or so. The control circuit delivers varying width 12V pulses (PWM) as you squeeze the trigger more.

Part of this device's specs is to be able to handle the back emf spikes a DC motor makes when driven with PWM (the 500V Vds).
Key specs are: it's an N-ch device, Vds = 500V, Id (forward current)= 20A. Rds on (resistance when on) = 270mOhms & the package (body type) is a through-hole TO-247-3
This part no. should be a better performer: STW40N65M2 & wasn't too expensive & in stock
similar ones: STW48N60M2, STW42N60M2-EP
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#9
(05-09-2020, 09:45 AM)Redpacket Wrote: Re the gate voltage max of ~20V, this is delivered by the control circuit part.
The MOSFET can switch much higher voltages across the drain & source pins, but the gate to source can only be max about 20V on most devices (this ones actually 30)

Yes threshold voltage is the gate voltage where the MOSFET starts to "turn on" & pass current, it varies. You don't what to "hover" around the threshold voltage in a switching application like your drill.  Usually the gate is driven with 10-12V or so. The control circuit delivers varying width 12V pulses (PWM) as you squeeze the trigger more.

Part of this device's specs is to be able to handle the back emf spikes a DC motor makes when driven with PWM (the 500V Vds).
Key specs are: it's an N-ch device, Vds = 500V, Id (forward current)= 20A. Rds on (resistance when on) = 270mOhms & the package (body type) is a through-hole TO-247-3
This part no. should be a better performer:  STW40N65M2  & wasn't too expensive & in stock
similar ones:  STW48N60M2,  STW42N60M2-EP

Thanks I have ordered a STW40N65M2
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#10
There are lessons to be learnt from this project and still a few questions.

I was concerned about the smoking of the drill after replacing 30 NiCd cells with 20 x 18650 (10s2p).

So I removed two of the cells, the total of which were supplying 42v which still left it with 37v.

What I should have done was open up the drill to find out what was smoking

I have now received the STW40N65M2, the question is, can it manage the 42v and shoukd I solder them back into the battery?
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