Master Anti-spike Diode Part Number

[mfshook62]

I am interested in the anti-spike diode part number that is supplied with the Vans master relay. (Not the Vans pn, the actual diode pn) I want to purchase some replacement diodes from an electrical parts warehouse like Mouser. Some threads in VAF list personal diode preferences and recommendations that cost from $2 to $30 each and are either shottky or silicon diodes. I am just interested in the replacement part number or the specs for the diodes that come in the Vans kit.

Also, these are listed as anti-spike diodes, can anyone explain to me how they clamp spikes. I really am not interested in speculation, just how they actually work.

Thanks,

Mike Shook
RV9a
942WG

[fl-mike]

A 1N5404 or 1N4004 will do what you want.
I've got a few hundred. Save your money. Shoot me an address and I'll mail you some.

When you open the switch to the relay coil, the large inductance of the coil creates an voltage "kickback". Here is an explanation:
http://www.coilgun.info/theoryinduct...vekickback.htm

[Jeff R]

Most any silicon or Schottky diode with a voltage rating of 100 volts or more and a current rating of 1 to 3 amps or more ought to work just fine. Just be certain to connect it properly. If you install it backwards, you will probably destroy it and, thus, lose its protective features.

[hcccs]

I saw an interesting entry on Wikipedia concerning diode protection of inductive loads. It says:
In some DC circuits, a varistor or two inverse-series Zener diodes (collectively called a transorb) may be used instead of the simple diode. Because these devices dissipate significant power, the relay may drop-out faster than it would with a simple rectifier diode. An advantage to using a transorb over just one diode however, is that it will protect against both over and under voltage if connected to ground, forcing the voltage to stay between the confines of the breakdown voltages of the Zener diodes. A Zener diode connected to ground will protect against positive transients to the value of the Zener breakdown, and will protect against negative transients greater than a normal forward diode drop.
The entire article is here http://en.wikipedia.org/wiki/Snubber.

I can't figure out the values and wiring of these diodes but I'm sure there are builders on the forum who can. Comments?

[foka4]

The voltage rating on suppression diodes is often the breakdown voltage, or the voltage at which the diode will allow current to pass through it "backwards".

I'm no expert in transient suppression, but my understanding is that a lower breakdown voltage (i.e., 24 - 50V) will provide better protection, as it means the diode will begin suppressing the spike sooner.

Sorry to inject confusion into the matter - I'd love for an expert to weigh in.

For purposes of discussion, have a look at a 1N5359BG, available from Jameco.com (and other places, I'm sure).



m

[nucleus]

http://www.periheliondesign.com/suppressors.htm

[loopfuzz]

Just curious, does anyone know if the diodes vans sells is a 1N5404 or 1N4004 diode?

[Daniel Hooper]

Originally Posted by foka4

The voltage rating on suppression diodes is often the breakdown voltage, or the voltage at which the diode will allow current to pass through it "backwards".

I'm no expert in transient suppression, but my understanding is that a lower breakdown voltage (i.e., 24 - 50V) will provide better protection, as it means the diode will begin suppressing the spike sooner.

That is true for a Zener, but not true for a normal silicon diode. My initial impulse for adding diode protection to a relay is to add a silicon diode across the relay control terminals with the arrow pointing toward the positive supply of the relay. The diode blocks current while energizing the relay, allowing it to go through the relay, but it conducts the "circulation current" when the magnetic field collapses when the relay is de-energized.
When you stop providing current to the coil in the relay, the magnetic field that has built up to physically pull in the contacts, that energy needs to go somewhere. When you cut the current, the field collapses, resulting in a 'current source' that wants to keep flowing in the same direction. The current will keep flowing at any voltage, up until it arcs across something. The silicon diode shorts the 'current source' to itself, allowing the magnetic field to collapse and dissipate that energy resistively in the coil.
Silicon diodes have a forward voltage Vf, which is the voltage drop when current is flowing in the direction of the arrow. This is related to both the reverse voltage rating and the power rating. It is not that important in this situation. The reverse voltage rating is the voltage that will destroy the silicon diode, against the arrow. The reverse voltage rating needs to be large enough to handle any voltage spikes, no matter how short in duration (milliseconds or microseconds). In large relays, it's important to make sure it can handle the larger energy from the collapsing field. So, larger diodes with bigger power ratings for larger relays.
There are other considerations that might lead you to choose a Zener or a Schottky, but that is much more complex.
All in all, better to copy a working design!

[loopfuzz]

ok, found out by pealing back the heat shrink on on the master switch diode that van sells. Its a 1N5407 diode they sell.

Note: The starter switch diode may be a different one. not sure.