whatever happened to crowbars?

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
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?



Re: whatever happened to crowbars?

"Bruce Varley"
Quoted text here. Click to load it


** 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.


Quoted text here. Click to load it


** 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






Re: whatever happened to crowbars?

Quoted text here. Click to load it

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.


Re: whatever happened to crowbars?
On Thu, 11 Aug 2011 23:44:07 +1000, Barry OGrady

Quoted text here. Click to load it

Nova? Eclipse?

Quoted text here. Click to load it

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.

Re: whatever happened to crowbars?
On Fri, 12 Aug 2011 06:02:10 +1000, Franc Zabkar

Quoted text here. Click to load it

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

Quoted text here. Click to load it

Mine had a separate power supply for the 12 volts.

Quoted text here. Click to load it


Re: whatever happened to crowbars?
finger to keyboard and composed:

Quoted text here. Click to load it

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.

Site Timeline