# Which diode to use to rectify AC into DC for motor drive?

Status
Not open for further replies.

#### garg29

Which diode to use ???

hi friends,
i'm designing a 3-phase, 440volts, 2hp, ac motor drive using IGBT's (6 of them, IGBT inverter bridge). which diodes should i use to rectify the AC into DC for this
application.

Thanks,

with regards,
Amit

#### IanP

Re: Which diode to use ???

I assume you will be using single phase supply ..
To have suficient safety margin I suggest the you use 25A bridge rectifier (example GBPC2506, Ifsm≈300A, 25A, 600V)

or 4x BY229-600 (TO220) or similar ..

#### garg29

Re: Which diode to use ???

thanks for replying but it is not single phase its a three phase supply.in that case which one to use?

thanks for replying but it is not single phase its a three phase supply.in that case which one to use?

#### IanP

Re: Which diode to use ???

As 3-phase rectifier blocks are rated for higher currents and are expencive you can use 6 x 4x BY229-600 (TO220) or similar ..

#### platonas

##### Full Member level 3
Re: Which diode to use ???

The diodes must also be able to stand at voltage level greater than (440×√2)×2 volts
That makes 1245v, minimum. You need a 1500v diode.

Also, P=√3×V×I×cosφ where cosφ is the power factor of the motor/load
V is the line voltage 440v in your case and
P= 2hp = 2×745W= 1490W
Hence I=1490÷(√3×V×cosφ) = 2.44A assuming cosφ=0.8

The starting current of the motor must also be consider and the full load current.
Further, consider the fact that the motom might start loaded which might increase the starting current further than that with no load. To be on the safe side I will suggest a 25A or more for the diode current rating.

Something I forgot to explain:
For a rectifier, the voltage across the rectifying diodes is given by 2×√2×Vac (Vac=V rms).
This is because the peak value of the voltage when rectified is Vr=√2×Vac but during the opposite cycle you have the diode facing twice this voltage. The output is at +Vr and the input when reversed bias is at -Vr, by adding them you have double the magnidute. This applies to any rectifier diode, single or 3-phase.

#### garg29

Re: Which diode to use ???

I've got a bit confused. please see the diagram in attachment. as i've said before i've to control 3-Phase 440 volt AC, 2Hp motor, please suggest the diodes for this application. i'm planning to use IRG4PH40UD IGBT's, have i chosen the right igbt's?

Thanks,

with best regards,
Amit

#### garg29

Which diode to use ???

Thanks a lot for repling "Ianp". Now, that means, after reffering the diagram, i should use only 6- BY229 diodes?.

Thanks once again,

With Best Regards,
Amit

#### IanP

Re: Which diode to use ???

I must admit that PLATONAS is right: you need a diode which can handle voltages of at least 2 x Vmax (pp) (1250V for 440Vac, 1070V for 380Vac) so this 1500V was not exaggerated.

In this case BY229 is not a proper choice..

So the diodes (depending on AC voltage in your installation) will have to be: 1500V (440) or 1200V (380) @ >20A ..

#### garg29

Which diode to use ???

oops, i'm confused again. now that means i should use 6 diodes with 1500 volt rating, each. Can you please advise me the number of such a diode.

With Best Regards,
Amit

#### IanP

Re: Which diode to use ???

You can try BY459-1500 (TO220, 1500V, 10A) - reasonable price.
or
40HF160 (Metal Stud, 1600V, 40A) available from Farnell ( www.premierfarnell.com )

#### garg29

Which diode to use ???

Thanks a lot. now i plan to use 3x6 = 18 (for 30A), BY459-1500 diodes. I think that will be fine.

#### IanP

Re: Which diode to use ???

That should be OK .. You may use 0.1Ω (oe less) resistor in series with each diode to equalize voltages ..

#### garg29

Which diode to use ???

thanks a lot.
with best regards
amit

Status
Not open for further replies.