• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Working AC Crowbar Circuit Anyone?

Status
Not open for further replies.

ACharnley

Member
Apparently the triac can do it, only google has no circuit diagrams. I can only find the one (which many reposted) and it doesn't work (it's DC).

ArticlElectronic-Crowbar-For-Ac-Or-Dc-Lines_200362200.jpg
 

crutschow

Well-Known Member
Most Helpful Member
Exactly what do you want the crowbar to do?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Your schematic looks like a typical AC dimmer. Definitely not a crowbar. AC or DC might be referring to Universal motors which can operate on AC or DC.
 

ACharnley

Member
Agreed. So many comments on the web saying a triac can crowbar AC... no schematics to back it up.

crutschow ... short the AC on over-voltage.
 

crutschow

Well-Known Member
Most Helpful Member
short the AC on over-voltage.
So it will blow a breaker or fuse when that happens?

Do you want to trip on the the peak of the waveform or its average value for the overvoltage detect point?
Tripping on the peak would make it susceptible to noise spikes.
 

eTech

Active Member
A voltage on the wave over a determined level, noise spikes are fine. That's correct on the fuse.
Hi

Here's my attempt at a demo
The simulation shows a sudden rise in line voltage between 50-70ms. The fuse blows as shown by the sudden drop of current thru the load.

See OnSemi app note AND8012/D.

eT

OVProtectionDemo.png
 

tomizett

Active Member
First circuit looks fine to me - esenntially the same as eTech's in #7. You can adjust the value of the 0.1u cap to trade off noise immunity vs. response time.
It is essentially the same as a dimmer, just that there is no load in series with the triac (except for the fuse).
 

alec_t

Well-Known Member
Most Helpful Member
LT Spice keeps getting stuck.
Have you got the latest LTS executable update? My LTS was randomly freezing until I updated it yesterday.
 

ACharnley

Member
Build: July 3, 2018 (latest)

It's not randomly freezing, it's going very, very slow!

I've attached the asc file (it's a bit different as I've been playing around to try and make it simulate).

I also wonder why LTSpice copies all the models/symbol files into the users home directory and doesn't sync them.
 

Attachments

Last edited:

eTech

Active Member
Build: July 3, 2018 (latest)

It's not randomly freezing, it's going very, very slow!

I've attached the asc file (it's a bit different as I've been playing around to try and make it simulate).

I also wonder why LTSpice copies all the models/symbol files into the users home directory and doesn't sync them.
Hi

I had to use a modified version of the triac library and symbol.
I’ll post later this afternoon.

eT
 

gophert

Well-Known Member
Most Helpful Member
Thought so, any input to the gate caused LTSpice to die. :)
Try adding a few ohm resistor in place of the fuse in the model because spice models don't like infinite current circuits. The crowbar is supposed to represent throwing a crowbar across the bus bars - infinite current and blown fuse.
 

Aswinth_Raj

New Member
I also had a very bad time trying to simulate the circuit on LTSpice of even Proteus for that matter. Finally decided to give the hardware directly a try since it had only minimum components. I also used a much more simple circuit that only employs a thyristor and zener. You can find detials of it here
https://circuitdigest.com/electronic-circuits/crowbar-circuit-diagram

Needless to say you have to use a TRIAC in place of Thyristor if your supply is AC. Also do people still use these circuits? I mean there are better options available not considering the cost though
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top