Switching device suitable for controlling 30 A DC motor??

[gameelgamal]

switching 30a dc motor

Hi
I'm working on a 30 A DC motor
I wnat to just switch it on and off

my question is: what is the most suitable switching device should i use
MOSFET or BJT ????

please give me a specific number..
thanx..........

 

[Davood Amerion]

If you just want to switch on/off DC motor, you can use Relay (30A-40A relay).
In case of MOSFET you can use IRFP150A (43A, 100V).

 

[Siniša]

Re: Switching device suitable for controlling 30 A DC motor?

With IGBT you can expect ~1.5V voltage drop at 30A which will make dissipation in 45-50W range.
Mosfet would have 10-60mΩ at that current, so it will dissipate ~9-60W . For lower max voltages required Rds will be lower.
Mosfet is better choice for lower voltages, let's say 100V or lower. For higher voltages IGBT seems as only choice left.

And of course, if you have enough room and money and do not require frequent switching, relay is easy choise.

 

[rikie_rizza]

Use solid state....small size, logic controlled, and capable to handle current up to 60A continuous or 120A pulse.

 

[gameelgamal]

Re: Switching device suitable for controlling 30 A DC motor?

The Relay is expensive
I think MOSFET is the most suitable solution with my 12 V motor

But I have a question.....
Should I connect a resistance to the gate of the MOSFET, or not ??
As I know, The MOSFET has an isolated gate. But I have seen many designes with a resistance connected to the gate of the MOSFET!!!!
any comment

 

[Siniša]

Re: Switching device suitable for controlling 30 A DC motor?

Resistance is used to "slow down" switching characteristics of mosfet, so it reduces back EMF with inductive load and reduces emission of EMI. Make sure you have gate voltage at level that is stated for Rds-on (10-15V) and insert resistor in series with gate.

Good example would be IRFP064

@9mΩ Rds(on) and 30A it would dissipate 8.1W . You could further lower dissipation by paralleling more devices. It would require minimum 10V on gate to have that 9mΩ Rds. Few hundred ohms gate resistor would not hurt to reduce EMI and back EMF.
Don't forget diode anti-parallel to your motor for back EMF and to mount device on <6K/W heatsink.

 

[FvM]

Re: Switching device suitable for controlling 30 A DC motor?

The Relay is expensive
I think MOSFET is the most suitable solution with my 12 V motor

Hm. Simple automotive relays probably cost $0.5-$2. A MOSFET, even if oversized a lot, probably needs a heatsink at 30 A. Another point is inrush current, it may easily damage the FET, if it's unexpected high. Do you know the motors armature resistance and calculated the inrush current, did you check it with the FETs safe operation area? Also incomplete turn-on of transistor or oscillations can be dangerous.

 

[hkBattousai]

Re: Switching device suitable for controlling 30 A DC motor?

With IGBT you can expect ~1.5V voltage drop at 30A which will make dissipation in 45-50W range.
Mosfet would have 10-60mΩ at that current, so it will dissipate ~9-60W . For lower max voltages required Rds will be lower.
Mosfet is better choice for lower voltages, let's say 100V or lower. For higher voltages IGBT seems as only choice left.

And of course, if you have enough room and money and do not require frequent switching, relay is easy choise.

Sinisa is right. You had better using a IGBT. IGBT will cover your needs.

 

[Siniša]

Re: Switching device suitable for controlling 30 A DC motor?

I would agree with FvM that relay is much simpler and very likely cheaper solution for simple On/Off motor control. I would consider solid state solution only when number of On/Off cycles is over few thousand through desired life of your control.

 

[Davood Amerion]

In case of IRFP150A MOSFET
Rdson = 32 mili ohm
P diss = 0.032 x (30A ^2) = 29 W
for three paralell device, for example, power dissipation would be 10W which is high.
but in 40A relay, as i know, contact resistance is about 1-4 mili ohm,
and power dissipation on relay contacts not exceed 3-4W.

 

[FvM]

Re: Switching device suitable for controlling 30 A DC motor?

To learn, why an IGBT is very bad suited for control of a 12 V motor, just take a look at any available IGBT datasheet. The keyword is saturation or on-state voltage Vce(on). It's likely above 1 V, may be 1.5 - 2V. Very unpleasant.

 

[hkBattousai]

Re: Switching device suitable for controlling 30 A DC motor?

To learn, why an IGBT is very bad suited for control of a 12 V motor, just take a look at any available IGBT datasheet. The keyword is saturation or on-state voltage Vce(on). It's likely above 1 V, may be 1.5 - 2V. Very unpleasant.

Hmm, ok, I got the point.
Thanks.

 

[gameelgamal]

Re: Switching device suitable for controlling 30 A DC motor?

Resistance is used to "slow down" switching characteristics of mosfet, so it reduces back EMF with inductive load and reduces emission of EMI. Make sure you have gate voltage at level that is stated for Rds-on (10-15V) and insert resistor in series with gate.


@9mΩ Rds(on) and 30A it would dissipate 8.1W . You could further lower dissipation by paralleling more devices. It would require minimum 10V on gate to have that 9mΩ Rds. Few hundred ohms gate resistor would not hurt to reduce EMI and back EMF.
Don't forget diode anti-parallel to your motor for back EMF and to mount device on <6K/W heatsink.

Ok..I will add a resistance in series with the gate, but what is the suitable value of resistance should I use??
In other word, Is there a specific formula calculating the resistance value,or not??

Added after 6 minutes:

The Relay is expensive
I think MOSFET is the most suitable solution with my 12 V motor

Hm. Simple automotive relays probably cost $0.5-$2. A MOSFET, even if oversized a lot, probably needs a heatsink at 30 A. Another point is inrush current, it may easily damage the FET, if it's unexpected high. Do you know the motors armature resistance and calculated the inrush current, did you check it with the FETs safe operation area? Also incomplete turn-on of transistor or oscillations can be dangerous.

In my country, a 30 A relay is very expensive
it exceeds 50$.....
So..MOSFET is the winner

But I have a question...
Is there a way to know if the the MOSFET is completely turned on or not ??

 

[Siniša]

Re: Switching device suitable for controlling 30 A DC motor?

FET tutorial

 

[Davood Amerion]

Re: Switching device suitable for controlling 30 A DC motor?

But I have a question...
Is there a way to know if the the MOSFET is completely turned on or not ??

For this purpose you can refer to transistor specification and its curves.
As shown in attached curve, if you put 10 Volts on Gate-Source terminal it will turn on, and for 30A current about 0.22-0.24 volts drop on Drain-Surce terminal.
for Vgs=5Volts, we have higher voltage drop across DS terminal (0.5Volt), and consequently higher power dissipation on transistor.

Note: This curve belong to NTP75N06 N-Channel MOSFET transistor with 60V/75A voltage - current capability. which I think it is better than IRFP150A for you application.

 

[nandhu015]

Re: Switching device suitable for controlling 30 A DC motor?

If you use a mosfet, Ensure proper heat sink.

If mosfet heats a lot & get shorted you can't stop the motor and posibilities of your switching circuit affected. ( I got a bad experience with this once)

Nandhu