Crowbar Overvoltage Circuit to Protect Transceiver

I was looking for a simple circuit to protect my radio  and auxiliary equipment  from overvoltage and found a circuit diagram and full description on Phil Salas – AD5X site.

The voltage protector file including circuit diagram and full parts list is available for downloadable here – Vprotect.

The circuit is designed to ‘blow’ the supply fuse to the equipment in order to protect it, the protection is from reverse polarity as well as  transient spikes and damaging overvoltage.

The specification for the Kenwood TS-2000 is 13.8v +/- 15% ( Total Maximum voltage 15.87v), this circuit will only allow 14.8v to pass before the protection crowbar circuit operates.

The components are sizes for 40A, the Kenwood maximum current draw is 20.5A, so well within capacity.

SAM_5357 (Medium)

SAM_5358 (Medium)

The circuit board could have been made marginally smaller, but I was too lazy to trim it down!

SAM_5360 (Medium)

This shows the test setup with the power supply units (PSU) current trip set low in order to monitor the tripping voltage, on the left of the PSU in between the knobs marked CURRENT, their is a small LED with C.C. for Constant Current, the circuit is working passing 13.73v to the meter.

SAM_5362 (Medium)

The voltage from the PSU has now been increase past the crowbar limit of 14.8v and the C.C LED is ON showing that if this was a fuse it would have operated to protect the transceiver, 14.8v is the maximum voltage that will ever reach the transceiver, no matter what!

Parts: – These were from UK ebay

1.5KE 15 TVS Diode 1.5KW 15v DO-21 – £1.69

Thyristar 40A, 600v TO-220 TYN640RG – £3.19

IN5245B Diode Zener 15v 0.5w – £1.42

Radial Electrolytic Capacitor 1uF 50v – £0.99

Resistors 27k, 10 Ohm and Veroboard I had already

Less than £8 to protect an expensive radio, filtered speaker etc. pictures of completed unit is HERE.

4 thoughts on “Crowbar Overvoltage Circuit to Protect Transceiver”

  1. Hi There, Do you have a circuit diagram for this over voltage crowbar. I have just acquired a old power regulated 30A supply. I have check and it has short circuit protection, however nothing for over voltage.
    Could you please get back to me.

    Mike – ZL1MRC

  2. Hi Mike,

    Thanks for getting in touch, the original diagram link was broken which I didn’t know, I’ve added a link to the original author and as a backup, downloaded the article, so hopefully losing a link won’t lose the information.

    All the best with your construction.

  3. Hi!
    I was studying the original article, and noticed the author mention the capacitor value as 1uF in his text, but 10 uF on his schematic and on his parts list. I see 1uF has been used here. So it’s currently (no pun intended :D) a two all draw. Can we settle it on penalties? Which one is right? Or is it not too critical?
    I will be building this, as I once had a 13.8v linear PSU start putting 16.5v into a radio, and I only spotted it by how bright the light was on the signal meter.

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