Help in reduce circuit losses

GH Crash · 2024-09-15T23:14:02-0700

Any suggestions on how to reduce the resistance of the attached circuit.

A supercapacitor (EDLC) is used to power a small motor. There is an ATTiny85 chip in the circuit that is used as a timer and a PWM controller for the motor. The problem that I'm loosing about half a volt between the capacitor's voltage and the voltage across the motor's leads. I need to minimize losses in the circuit as much as possible.

Can you suggest means to reduce voltage loses to the motor?

Diver300 · 2024-09-15T23:58:16-0700

That has got to be the result of the MOSFET and the wiring resistance. We need more details to know what losses you are getting, like motor current, MOSFET type and constructional details.

If you are using PWM, you should have a freewheel diode across the motor, and there shouldn't be a large capacitor across the motor. C5 will slow down the switching of the MOSFET a lot, so that will make the MOSFET stay in the linear region a lot of the time and get hot.

You've also got the wrong symbol for the MOSFET. The symbol shows a P-channel MOSFET, but the part number and the circuit layout are correct for an N-channel MOSFET

Nigel Goodwin · 2024-09-16T00:03:40-0700

Also, the FET is been driven very poorly - if you're just using it for simple ON/OFF it's OK, but for PWM losses in the FET will be high. Add either an IC driver, or a discrete one.

As always, I'd suggest using a battery rather than a 'super' capacitor - which are in no way 'super' - a battery is far more effective.

danadak · 2024-09-16T05:10:03-0700

What is V+ value for ATTIny85 ?

"Normally" the gate R for the MOSFET wants to be more like 50 - 100 ohms,
that will get it turned on a little quicker.

AnalogKid · 2024-09-16T06:11:03-0700

C6 and the ON resistance of T2 form a voltage divider. You never will see the peak voltage across the motor.

Also - to the TS - what do you think is the function of C5?

ak

AnalogKid · 2024-09-16T06:12:35-0700

danadak said:
"Normally" the gate R for the MOSFET wants to be more like 50 - 100 ohms,
that will get it turned on a little quicker.

Pending an answer about C5, in this circuit I would reduce R1 to 0 ohms and worry about possible EMI after the circuit is working.

ak

GH Crash · 2024-09-16T06:21:07-0700

Diver300 said:
We need more details to know what losses you are getting, like motor current, MOSFET type and constructional details.

I need more details before I can supply more details. Sorry for that, I don't know what kind of information, what specific information would be helpful to you. And sorry for the wrong MOSFET on the circuit digram. I'm a complete know-nothing when it comes to electronics.

Datasheet for MOSFET attached. The circuit is a commercially prepared circuit board measuring 20x20mm. Motor traces (leads) are 0.75mm, all others are 0.25mm. Photo of board layout attached. Capacitor connection to the right, motor connections to the left and MOSFET between M- pad and switch.

GH Crash · 2024-09-16T06:25:04-0700

Nigel Goodwin said:
As always, I'd suggest using a battery rather than a 'super' capacitor - which are in no way 'super' - a battery is far more effective.

Can't do. The whole purpose of this project is to use a capacitor to power a small coreless motor that will power a free flight model airplane.

Nigel Goodwin · 2024-09-16T06:28:19-0700

GH Crash said:
Can't do. The whole purpose of this project is to use a capacitor to power a small coreless motor that will power a free flight model airplane.

So range, duration, and speed aren't of any concern?.

GH Crash · 2024-09-16T06:29:06-0700

danadak said:
What is V+ value for ATTIny85 ?

"Normally" the gate R for the MOSFET wants to be more like 50 - 100 ohms,
that will get it turned on a little quicker.

V+ varies with the capacitor's voltage; normal range 2.1 to 5 volts.

I will change out the 1k for a 100 ohm.

GH Crash · 2024-09-16T06:34:52-0700

Nigel Goodwin said:
So range, duration, and speed aren't of any concern?.

Yes, they are a concern, but under the constraints that the power source has to be a capacitor.

Nigel Goodwin · 2024-09-16T07:32:40-0700

GH Crash said:
V+ varies with the capacitor's voltage; normal range 2.1 to 5 volts.

I will change out the 1k for a 100 ohm.

You need a proper driver - and probably a SM circuit to increase and regulate the drive voltage, as losses will increase massively as the capacitor rapidly drops in voltage, and at only 5V to start with it's pretty poor to begin with.

Nigel Goodwin · 2024-09-16T07:33:21-0700

GH Crash said:
Yes, they are a concern, but under the constraints that the power source has to be a capacitor.

I suspect you're going to be seriously disappointed.

alec_t · 2024-09-16T07:43:15-0700

GH Crash said:
the power source has to be a capacitor.

May I ask why?

GH Crash · 2024-09-16T08:04:52-0700

Nigel Goodwin said:
You need a proper driver - and probably a SM circuit to increase and regulate the drive voltage, as losses will increase massively as the capacitor rapidly drops in voltage, and at only 5V to start with it's pretty poor to begin with.

Can you explain, in dummy terms, what you mean by 'driver' and 'SM' circuit?

danadak · 2024-09-16T08:20:19-0700

GH Crash said:
V+ varies with the capacitor's voltage; normal range 2.1 to 5 volts.

I will change out the 1k for a 100 ohm.

I think yuour drive wikll be OK pending what current does motor need ?

GH Crash · 2024-09-16T08:26:58-0700

For those of you who question the use of a capacitor, the entire driving force behind this project is to make a device/circuit that will make a capacitor preform like a battery. Why? Because no one has done it.

In the aircraft modeling community, there are a group of people who are flying free flight airplanes using a capacitor as the power source. The circuit we are talking about is an attempt to improve capacitor powered flight by controlling the way the capacitor provides power to the motor.

GH Crash · 2024-09-16T08:29:16-0700

danadak said:
I think yuour drive wikll be OK pending what current does motor need ?

View attachment 147107

Max current will be under 3 amps.

danadak · 2024-09-16T08:46:42-0700

So where do you measure V loo\sr and how much is the loss in V ?

Nigel Goodwin · 2024-09-16T08:46:48-0700

GH Crash said:
Can you explain, in dummy terms, what you mean by 'driver' and 'SM' circuit?

A driver provides sufficient current to the FET to rapidly turn it ON and OFF, otherwise it get's hot and runs inefficiently, wasting power as heat, and potentially burning out. SM means 'switch-mode', a device for taking the rapidly falling low voltage from the battery, and increasing it to a higher regulated voltage.

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