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I asked a question the other day but am still unsure, I just bought a 0-30v 0-5A dc regulated power supply today and want to use it to play around with various DC motors, I was told I didn't need to worry about a fly back diode with a straight motor one the other question but the store I bought it from still recommended and sold me a 10A07 diode, the data sheet is in this link http://pdf.datasheetcatalog.com/datasheet/mcc/10A07.pdf

My question is, is it really needed?, the guy at the store said its just safer to use one so i figured why not. After looking at the data sheet it seems it can handle up to 1000V reverse voltage so im assuming its good.

The power supply is only a cheap $150 AUD one so im not to sure if it would have the proper protection but I have read that fly back diodes are mainly used with transistors, Is that true and did I get sold something I don't really need or would it still pay to use it anyway? Im completely new to electronics so any help would be appreciated.

Thanks in advance

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  • \$\begingroup\$ Use a diode anyway. The PS might not be protected and it will have transistors on the output. \$\endgroup\$ – Leon Heller Jun 15 '17 at 10:36
  • \$\begingroup\$ Better prevention than cure. Industrial electronic circuits are made with every potential fail-safe option, like reverse polarity, isolation and so on. It is very good practice to add a flyback diode whenever we deal with inductive loads \$\endgroup\$ – Prasan Dutt Jun 15 '17 at 10:38
  • \$\begingroup\$ Definitely use a diode. The inductors in the motor will output whatever voltage is necessary to keep the current flowing (e=L*di/dt). I'd go further and suggest to also put a capacitor, otherwise you could hear interference in your radio (this used to happen in old cars when you turned on the fan) \$\endgroup\$ – Andrés Jun 15 '17 at 10:40
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but the store I bought it from still recommended and sold me a 10A07 diode, the data sheet is in this link

The motor can be supplied up to 5 amps so all you need is a diode that can handle a peak of 5 amps (not continuous) and has a reverse working voltage that is at least 40 volts (a bit more than 30 volts).

A 10 A continuous diode capable of a reverse voltage of 1000 volts is of course perfectly usable but i question why a 1N400x wasn't recommended: -

enter image description here

It can stand-off 50 volts and handle a peak of 30 amps and probably cost a fraction of what you paid for the heavy duty diode (that can handle up to 600 amps of peak current).

Yes, I would still fit a reverse diode.

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  • \$\begingroup\$ Thanks for your help, im sure he just sold me the most expensive just for a bit extra money lol, cost me around 6.80 AUD but atleast i know it will do the job. Now i just need to figure out how to wire it correctly, reverse bias im pretty sure? so backwards, the anode of the diode to the anode of the psu? and the cathode of the diode to the negative of the motor if i remember correctly. any further help would be greatly appreciated :) \$\endgroup\$ – PyNuts Jun 15 '17 at 10:59
  • \$\begingroup\$ The 1N400x series should cost pennies. learningaboutelectronics.com/images/… \$\endgroup\$ – Andy aka Jun 15 '17 at 12:23
  • \$\begingroup\$ Thanks again bud, if the one i bought is safe i might aswell use it, gives me enough protection for pretty much all motors the psu could run. \$\endgroup\$ – PyNuts Jun 15 '17 at 12:25
  • \$\begingroup\$ One more quick question, in that diagram, why have you used a ground lead aswell as a negative going to the battery? am i miss reading it or is there something else i should know? \$\endgroup\$ – PyNuts Jun 15 '17 at 12:27
  • \$\begingroup\$ The ground symbol needn't be regarded as actual hard ground - it's not a requirement that motors be grounded or that reverse protection relies on a hard ground. It's probably meant more as a symbol implying 0 volts. I didn't do the diagram I just stole it from google images when I did a quick google for pictures that show how it's connected. \$\endgroup\$ – Andy aka Jun 15 '17 at 12:31

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