Any info on Transient voltage suppression diodes?

[roam]

I've recently been introduced to these TVS diodes by another cruiser following a conversation about voltage spikes ruining electronic equipment.
My non-technical brain is interpreting them as: matchstick sized gizmos that absorb any voltage spikes that can occur when a DC brushed motor is started - like the starter motor and the windlass instead of it shooting through my boat circuits. They appear to cost under a pound each, so would seem a very worthwhile addition to any boat.

So, can anyone help me determine what spec TVS i would need for a 12v 1000w windlass motor, for example?

My problem is that I cannot find any information on them that helps me to identify what spec diode i should get and ideally where they are best fitted. the data sheets are full of just that - data which unfortunately is just frying my brain: unidirectional/bidirectional, max clamping voltage/breakdown voltage/ peak pulse power. and no fitting instructions either!

i've done a search on these and other forums, but cannot find any mention of them.

many thanks

 

[captainboo]

See here for some descriptions and definitions.

http://www.vishay.com/docs/88436/appnote.pdf

http://en.wikipedia.org/wiki/Transient-voltage-suppression_diode

Generally you are looking for the breakdown voltage to be a few volts above the working voltage of the circuit but below that which would cause damage to certain electronics such as leds.

Unidirectional are used on dc, bidirectional on ac.

They look like a diode and are generally connected across the item you want to protect such that it dosn't conduct under normal conditions but does when the voltage spikes/rises.

 

[nigelmercier]

Any electronic equipment worth protecting will have a voltage regulator built-in. Even cheap LED lights can withstand the brief transient produced by a motor, so they won't help unless you have something that keeps failing.

 

[roam]

thank you guys.
I note the Vishay article says that $10bn worth of electronics are ruined each year due to transient voltage, so it would seem that a lot of equipment is NOT protected.
so if i err on the side of caution and assume that nothing has in-built protection, for the price of 2 or 3 quid i can put my mind at rest.

So what i know now is:
- for DC current, i need a uni-directional diode.
- the diode goes across the +ve and -ve terminals

what i still need to know:
- how to spec a suitable TVS diode for a motor
- which way around to fit it (does it matter?)

thanks in advance.

 

[nigelmercier]

- how to spec a suitable TVS diode for a motor

You don't specify it for the motor, you specify it for the gear you are protecting and build it into the circuit, not externally; at the very least it needs to be inboard of the fuse.

You would need a crowbar to cut the spikes from a big motor.

 

[pvb]

I note the Vishay article says that $10bn worth of electronics are ruined each year due to transient voltage,

But they would say that, wouldn't they? They're selling the TVS products!

 

[nigelmercier]

But they would say that, wouldn't they? They're selling the TVS products!

MRDA

 

[Hoolie]

MRDA

I don't know what you mean by that, so I looked it up:-

Mental Retardation Diagnostic Assessment
Mandy Rice-Davies Applies
Moldovan Research and Development Association
Multi-Resonant Dipole Antenna
Missouri Round Dance Association
etc. etc.

... and I don't think I'm any the wiser

 

[nigelmercier]

I don't know what you mean by that, so I looked it up:

Mandy Rice-Davies Applies.

Look it up again, with reference to the post I quoted, or see here.

 

[Hoolie]

Thanks!

Glad it wasn't to suggest a Mental Retardation Diagnostic Assessment