I power all of my radio equipment from one large
Lamda 12V supply. While it does have internal
protection in the event the sereis regulator
shorts and dumps 20V on the 12V buss, I wanted
beter protection. The "Crow bar" Over Voltage
Protection has a fairly wide range and I wanted
to be able to set mine to 15.500V.

While doing some reserach for my work, the field
geeks have fried any number of sensitive electronic
instruments by powering them from a "standard"
automitive electrical system. There a lot of
spikes, both positive and negative, short term
over voltages of up to 18V that last for 4 to 5
seconds that lab equipment just can't cope with.
We used a analog storage scope to capture these
events. We tested all the work vehicals, and all
the staff's vehicals who would agree. I tested my
1991 Civic a lot.

This link points to a simple and effective OVP
unit that won't bankrupt anyone.
http://www.aeroelectric.com/articles/crowbar.pdf

We built enough for all of the sensitive equipment.
Since that time we have not had a single piece of
equipment damaged. Before at elast once a week
I got to repair something.

I used components from several surplus outlets and
built mine for about 4$ a unit. I added one to the
inside of all my +12V gear that had space. And the
OVP can be made pretty small. I built external units
for those that didn't have any spare space in the
mini Altoid tin boxes. I even built several in old
Buss metal fuse boxes.

I only made one change, I added a Si diode at the
input of the OVP to protect against reverse spikes.
I used 10A Si diodes, I suspect that 1N4001s would
work just fine.

Is this over kill? I don't know. But I do know that
several years ago a friends wife had car trouble and the
AAA "mechanic" managed to jump start the car with the
jump battery backwards. Fried the ECU, alternator, car
radio, and all of his ham radios that happened to be on.
Yes, she should have turned them off, but people make
mistakes, so this is cheap insurance to help prevent
that tragidy. AAA ended up replacing all of the damaged
equipment, but it took 18 months.

Terry

Thank you for the useful circuit.

wrote in message
oups.com...
I power all of my radio equipment from one large
Lamda 12V supply. While it does have internal
protection in the event the sereis regulator
shorts and dumps 20V on the 12V buss, I wanted
beter protection. The "Crow bar" Over Voltage
Protection has a fairly wide range and I wanted
to be able to set mine to 15.500V.

While doing some reserach for my work, the field
geeks have fried any number of sensitive electronic
instruments by powering them from a "standard"
automitive electrical system. There a lot of
spikes, both positive and negative, short term
over voltages of up to 18V that last for 4 to 5
seconds that lab equipment just can't cope with.
We used a analog storage scope to capture these
events. We tested all the work vehicals, and all
the staff's vehicals who would agree. I tested my
1991 Civic a lot.

This link points to a simple and effective OVP
unit that won't bankrupt anyone.
http://www.aeroelectric.com/articles/crowbar.pdf

We built enough for all of the sensitive equipment.
Since that time we have not had a single piece of
equipment damaged. Before at elast once a week
I got to repair something.

I used components from several surplus outlets and
built mine for about 4$ a unit. I added one to the
inside of all my +12V gear that had space. And the
OVP can be made pretty small. I built external units
for those that didn't have any spare space in the
mini Altoid tin boxes. I even built several in old
Buss metal fuse boxes.

I only made one change, I added a Si diode at the
input of the OVP to protect against reverse spikes.
I used 10A Si diodes, I suspect that 1N4001s would
work just fine.

Is this over kill? I don't know. But I do know that
several years ago a friends wife had car trouble and the
AAA "mechanic" managed to jump start the car with the
jump battery backwards. Fried the ECU, alternator, car
radio, and all of his ham radios that happened to be on.
Yes, she should have turned them off, but people make
mistakes, so this is cheap insurance to help prevent
that tragidy. AAA ended up replacing all of the damaged
equipment, but it took 18 months.

Terry