three terminal voltage regulators..changing the voltage.

[KeepItSimpleStupid]

A TVS is a better choice. They are faster and are designed to absorb spikes(uk supplier): https://uk.rs-online.com/web/c/semi...chTerm=tvs&sort-by=default&sort-order=default You might want a minimum breakdown of 16V. A Zener and a regular diode is better than nothing.

A Shotkey diode or a fast recovery rectifier with a breakdown of 400 V minimum and 1-3 amps for the reverse on.

Of course, a fuse.

 

[RogerJ]

If you put something in a car, the tansorb and reverse polarity protection is mandatory.

I've thinking about this aspect of LEDs in a vehicle and wonder if I can do the neccessary with some salvaged bits in a diiferent way. Havn't discovered how to post diagrams so, in text: Take a supply from a 7amp fuse (for all the lighting) and run it ito a ferrite choke. Across the choke input connect a 1uf cap and a reversed BYV29-300i n parallel to ground. On the "out" side connect a 10,000uf electrolytic. This then feeds onto voltage regs and various LED lights

The choke, salvaged from the ambulance, was the output trsfmr of the siren generator. it's a toroid 2.2 inches diameter and fully wound with about 2 layers 18swg wire. (the old windings I've connected in series) Resistance is too low to measure
The diodes are "very fast" and were snipped from the old flourescent light drivers that the LEDs are replacing. The caps are from the junk box.

How well might this work in removing spikes.? I also wonder how some of the voltages we concerned with can actually exist across the battery terminals. Surely the battery itself would sink them as I'm thinking of it a low impedance shunt regulator..What do you think ?

 

[4pyros]

I also wonder how some of the voltages we concerned with can actually exist across the battery terminals.

They are fast transit spikes thats why every one is saying to use a transorb if you are that concerned.

 

[RogerJ]

The thing that made me wonder about this because of the satnavs that plugs straight in a 12v socket. They seem to survive ok in spite of being on when cranking and turning headlamps on/of. Are they protected in the way suggested ?

Since I posted that I just found this interesting knockabout of ideas on the subject. admittedly qite old:

https://docs.google.com/viewer?a=v&...UQzfKW&sig=AHIEtbSLZuszvSBqRfZtF1Pd0f_keMIVZQ

 

[4pyros]

Yes I would think its built in before a SMPS.