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 Overvolt crowbar circuit. 
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Post Overvolt crowbar circuit.
Looking for a simple (simpler the better) circuit which could be fitted outboard of a PSU.
Looking for something to trip at 15V.

any help/circuits appreciated.

Roger G0IUW


Fri Jun 28, 2019 10:01 am
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
This is the circuit of mine I have built several of

http://g.zs5wo.net/construction-and-pro ... linear-psu

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Fri Jun 28, 2019 10:35 am
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
Sangoma wrote:
This is the circuit of mine I have built several of

http://g.zs5wo.net/construction-and-pro ... linear-psu

Thank you for that...looks like just what I need.
Any recommendations for the Thyristor?

73 Roger G0IUW


Fri Jun 28, 2019 11:00 am
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
G0IUW wrote:
Sangoma wrote:
This is the circuit of mine I have built several of

http://g.zs5wo.net/construction-and-pro ... linear-psu

Thank you for that...looks like just what I need.
Any recommendations for the Thyristor?

73 Roger G0IUW


Depends on the fuse/power supply, but be generous. For a 40A supply, use a 60A or 100A device.
You will see on the PCB there are two sets of three holes for different types, as I used the same board for all supplies, but different devices that had different pinouts.

Also, if it trips and blows the fuse, replace it, next time it might not switch :)

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Fri Jun 28, 2019 11:43 am
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
Here's the crowbar used in a variable 5amp supply I tend to use for many projects. Here it was part of an active extension speaker project, and the amp required 2amps @24V It's well over designed and would work in much higher current applications.

For a 15V limit, replace the 1N5632BG with a 1N5352BG. It had a 27V limit on this application... you'll want 15 for a radio PSU.

The Thyristor shown is rated at 20amps, which is good for up to a 10amp supply IMO. If you are building a 20amp supply, then replace with a TN4015 or other 40amp SCR. Basically, I always use twice the rated output.... these things are cheap.

https://i.imgur.com/FCYFDyC.jpg

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Sun Jun 30, 2019 9:38 am
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
Sangoma wrote:
This is the circuit of mine I have built several of

http://g.zs5wo.net/construction-and-pro ... linear-psu


Used that crowbar circuit as well and it works fine. Just use a proper fuse and not a blade automotive type as they're a bit rough and slow to blow!

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Sun Jun 30, 2019 5:47 pm
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
Thanks Guys,
I now have the parts on order.

GM0ONX mentions blade fuses...wonder why they are the choice for Yaesu and Icom? just wondering.

Roger G0IUW


Wed Jul 03, 2019 2:44 pm
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 Overvolt crowbar circuit. 
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Post Re: Overvolt crowbar circuit.
G0IUW wrote:
Thanks Guys,
I now have the parts on order.

GM0ONX mentions blade fuses...wonder why they are the choice for Yaesu and Icom? just wondering.

Roger G0IUW


A fuse is more use as fire prevention than protecting modern circuitry.

I've tested blade fuses, and they blow OK, with quite a big pop :)

If you want to go a stage further, use a mosfet in series with the supply, which is normally turned on, but as soon as the voltage goes high it turns off.

All my linears have one in the power line to the finals, and turn off fo any fault situation.

I think the crowbar is as effective as you will get, it will blow the fuse, and until the fuse has blown, it will keep the supply voltage right down.

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Wed Jul 03, 2019 3:25 pm
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