Diode cutout

[Nick Salmon]

I have been asked by an A7 owning friend, who is allergic to computers, to ask if anyone has experience of using the smart diode cutout that is sold by the Magneto Guys.

I know this was something covered in the forum back in 2021 but some up to date info would be appreciated so as to get some idea of reliability and ease of installation on a Seven.

[Ruairidh Dunford]

Yes, I have fitted around 20 now.

Very good and inexpensive bit of kit.  I shall actually be fitting another one today.

[Howard Wright]

+1 for the Magneto Guys diodes. One on each of my three cars.

Howard

[`Gordonhbm]

I am unclear whether the diode is mounted on a heat sink as the diode will heat up when passing current. The more current and the longer the time it is flowing the greater the heat build up. You obviously increase reliability by keeping the diode as cool as possible. Can any voltage spikes from the car electrical system get through to the diode? If that was the case then the max voltage rating of the diode may not be adequate. Much higher rated schottky diodes are available and are inexpensive.
Does anybody know the failure rate of these units that the Magneto Guys have reported?

[John Cornforth]

Hi

I believe these smart diodes are based on the Texas SM74611 chip, originally developed for solar panel applications. The forward voltage drop is about 30 mV at 10 Amps at 25 degrees C, rising to 50 mV at 85 degrees C. The power dissipation is therefore only a fraction of a watt and no elaborate heatsinking is necessary. A "Normal" heavy duty schottky diode will drop more like 600 mV and dissipate several watts with 10A flowing, a heatsink is essential for these.

I suspect that in practice voltage spikes are not an issue, or we might have heard tales of woe.

[`Gordonhbm]

Hi John,
Thanks for your input. I appreciate the sense of what you say and agree that for the diode you've quoted heat build up should not be an issue.