choseing the corect diode.

[RoboWanabe]

Hi i need help with a project im doing involving 2 edf55 fan motors in series with a diode but i am haveing trouble on finding out what diode to use.

The voltage and current the fans will be subjected to are between 7.2v and 4.3A to 10.8v to 7.1A. These are the maximum and minum values can be used at, but im using a 12v battery and a mossfet with a micro to control it. In all honesty im getting quiet Bambozled by all this lol can some one try explain what im trying todo hear haha

 

[colin55]

Using PWM you can use the 10.8v motor and place two in parallel.
You only need a protection diode across the motor.

 

[Johnnythefridge]

Right doide ?

**broken link removed**

 

[Reloadron]

This should be a link to your motors. With 12 volts applied and the motors in series:

2 edf55 fan motors in series

Neither motor can ever see over 6 volts which depending on the exact motor would place the current between 3.0 and 3.3 amps. Placing a diode in series with the motors will only give you a 0.7 volt or so additional drop. Maybe I am missing something here?

I see you have the EM300H series so to correct the above, max current with the two motors in series would be 3.3 amps and max voltage either motor in series will see is 6 volts.

Ron

 

[RoboWanabe]

Cheers every one i think i was ment to say parallel instead lol im a doughnut. and to solve the problem i am now going to use Isolation 16A Schottky Barrier Rectifier which ive been told is more than adeqaute. so here we go wish me luck

 

[RoboWanabe]

does anyone know how to wire the Isolation 16A Schottky Barrier Rectifier from maplins its says its got 3pins but i cn only see 2?

 

[Reloadron]

Now it makes more sense.

Got a link to the diode and what do you want the diode to do?

Ron

 

[RoboWanabe]

its to protect the mosfets ive got linked to each mortor i think ive got it all working now, just putting it all together ive attached the schematic to this note just in case anyone is intrested in doing the same. Basikly im using a psoc to generate a pwm signal to operate the mosfets, which inturn turns the motors on any questions just ask.

 

[Grossel]

Hi. Off topic I know, but feel to say:

Why uploading a almost 2 meg jpg file (takes time to download) when a downscaled image that is easilly readable could be used as well. A replacement image can be way below 100kbytes. Some hints:

1. Physical size: Longest edge > 1000 px
2. Grayscale jpg
3. Irfanview/XnView/fsiv

[edit]
O' I forgot to answer the actual question. Well I'm not an expert on diode numbers so I have to leave the search work to you.

Here's what you should look at:

• Current: Look at the motor as an ideal inductor. Theoretically, the current spike from the coil may be as high as the current to the motor in the moment where the fet ceases to conduct. Remember that a motor where the axe is stuck the current will be much higher than when normally loaded
• Look at the fet's turn off time. The diode must be quicker than that time. That is the diode's turn on time < fet's turn off time.

 

[RoboWanabe]

not sure what you are saying about image? and thank you for your help that real helpfull now just need to remember lol

 

[Reloadron]

OK, they are used as flyback diodes. That should work as drawn.

Ron