whatever happened to crowbars?

[Bruce Varley]

Maybe I'm not looking hard enough, but it's a long time since I saw a power
supply design including a crowbar. Is it just an idea that's just come and
gone? If that is the case, any idea why? It seems like a good last-ditch
protection mechanism for gear with a small overvoltage margin, which
includes nearly all digital stuff.

Is there another protection mechanism against regulator failure that's
applied nowadays, or it just a case of wearing the risk?

 

[Phil Allison]

"Bruce Varley"

Maybe I'm not looking hard enough, but it's a long time since I saw a
power supply design including a crowbar.

** Many plug-pak style SMPSs have zener crowbars on the output.

The zener is intended to fail short if the output voltage goes high and so
protect the load.

Is it just an idea that's just come and gone? If that is the case, any
idea why? It seems like a good last-ditch protection mechanism for gear
with a small overvoltage margin, which includes nearly all digital stuff.

** Still common enough to see damaged ( written off) digital devices when
the SMPS goes haywire.

I have personally added SCR crowbars to the +5 volt supply on Yamaha digital
effects processors - notably SPX90s and REV5s cos the SMPS is a notorious
lemon.

Most PC power supplies have over voltage protection in the form of DC rail
monitoring and shut down if out of range.



..... Phil

 

[Barry OGrady]

On Thu, 11 Aug 2011 18:41:20 +0800, "Bruce Varley" <bv@NoSpam.com>
wrote:

Maybe I'm not looking hard enough, but it's a long time since I saw a power
supply design including a crowbar. Is it just an idea that's just come and
gone? If that is the case, any idea why? It seems like a good last-ditch
protection mechanism for gear with a small overvoltage margin, which
includes nearly all digital stuff.

Is there another protection mechanism against regulator failure that's
applied nowadays, or it just a case of wearing the risk?

I had a Data General minicomputer which had a built in UPS with
crowbar over voltage protection.
It had eight 2 volt Gates cells in series parallel to give 8 volts
which was series regulated down to 5 volts through 14 power
transistors in parallel. It had a 200 amp HRC fuse in line with
the buss bars and across the buss bars was a large SCR.
It had a switch mode power supply rated at 5 volts at 135 amps.

 

[Franc Zabkar]

On Thu, 11 Aug 2011 23:44:07 +1000, Barry OGrady
<atheist@hotmail.com.au> put finger to keyboard and composed:

I had a Data General minicomputer which had a built in UPS with
crowbar over voltage protection.

Nova? Eclipse?

It had eight 2 volt Gates cells in series parallel to give 8 volts
which was series regulated down to 5 volts through 14 power
transistors in parallel. It had a 200 amp HRC fuse in line with
the buss bars and across the buss bars was a large SCR.
It had a switch mode power supply rated at 5 volts at 135 amps.

I still have several of those PSUs, although mine have +/-12V and -5V
rails.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Franc Zabkar]

On Thu, 11 Aug 2011 18:41:20 +0800, "Bruce Varley" <bv@NoSpam.com> put
finger to keyboard and composed:

Is there another protection mechanism against regulator failure that's
applied nowadays, or it just a case of wearing the risk?

Many devices have overvoltage protection in the form of TVS (transient
voltage suppression) diodes. These work like zeners, but they respond
much faster. In fact I answer about 3 questions per week in various
forums where the OPs have overvolted their external hard drives with a
19V laptop adapter. The fix in the majority of cases is to simply cut
out the shorted 12V TVS diode.

See http://hddscan.com/doc/HDD_from_inside.html

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Barry OGrady]

On Fri, 12 Aug 2011 06:02:10 +1000, Franc Zabkar
<fzabkar@iinternode.on.net> wrote:

On Thu, 11 Aug 2011 23:44:07 +1000, Barry OGrady
atheist@hotmail.com.au> put finger to keyboard and composed:

I had a Data General minicomputer which had a built in UPS with
crowbar over voltage protection.

Nova? Eclipse?

I don't recall the model but it was a rack style with two
"washing machine" hard drives.

It had eight 2 volt Gates cells in series parallel to give 8 volts
which was series regulated down to 5 volts through 14 power
transistors in parallel. It had a 200 amp HRC fuse in line with
the buss bars and across the buss bars was a large SCR.
It had a switch mode power supply rated at 5 volts at 135 amps.

I still have several of those PSUs, although mine have +/-12V and -5V
rails.

Mine had a separate power supply for the 12 volts.

>- Franc Zabkar