Power One Supply 'power down' issue

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deveng

Well-known member
Joined
Jan 11, 2005
Messages
371
Location
California
I installed a Power One HDD-15-5A power supply on my console and have an issue on power down.  The negative rail takes longer to drop than the positive rail.  So, when you shut the supply off the console VU meters slam for just a moment.  Does anyone else have a console powered by this supply and do you have the same issue?  I've been running it for quite some time now but have now been concerned about the possibility of damaging all the VU's.  It appears to be characteristic of the design.  I'm curious if anyone else has encountered this.

Regards,
Jeff
 
Svart,

I'm fairly confident its about the same since the original supply never had this problem.  I found the slow drop of the negative rail also happens with no load.  With the console load it drops in about 1-2 seconds, with no load the negative rail stays high for 29 seconds before it starts dropping.  I believe its due to the design of the supply.   I'm just curious if anyone else using these supplies notice the same thing.  It may be this revision of the design.  I bought these off Ebay (both never used) and they may be older versions.

regards,
Jeff
 
Yikes, I just bought an HDD-15-5A to use as a psu for a 22 channel gssl unit I'm building for another studio.  I'm about a week or so from wiring it up.  I'll let you know if mine does the same thing.
 
Yep, it happens on both units with or without load.  When its loaded of course the dissipation time is quicker but still not the same on both rails.  I bought 2 never used power supplies so I'd have a spare.

Curious John,  you can easily test yours by powering it up on the bench.  Put a couple of voltmeters on the rails and turn the supply off.  If you have the same issue you'll see the negative rail take as long as 45 seconds to drop to zero.  I'm hoping I have an older version and yours don't do this!

I'd be interested to get Jim Williams' input on this since he's the one who recommended these supplies and uses them when upgrading many Soundcraft consoles.  I suspect if he had this issue he would have mentioned it.  

Since I've already got these supplies mounted and interfaced (and paid for!) I may need to go another route.  I may need to quickly design and build a timed meter disconnect circuit using relays.  It would not be difficult to design but just a pain to squeeze into the meter bridge and also a bit time consuming.  Let me know how your supplies behave!

Regards,
Jeff
 
Finally got sick and tired of the VU meter slam when I powered my console off.  I ended up using relay's to disconnect the +/- rails.  I purchased a couple of Sparkfun beefcake relay boards.  I changed out the relay to a 48V high current relay.  Then changed the relay control resistors to run off my 48v phantom.    I added a switch to the front of the power supply chassis.  So now, I turn on the supplies with one switch and use the disconnect switch to turn on/off the console.  Works great, no more slam! 

Regards,
Jeff
 
Sorry, but you have been worrying about something that really doesn't matter. And now you have introduced the impedance of relay contacts into your supply rails.
 
pucho812 said:
Are you referring to the coil or to the switching contacts?

Probably contacts.
I use relays with silver contacts (contactors) and have not had a problem.
Just make sure the contacts are WAY overrated.
YMMV
Best,
Bruno2000
 
Well, switches do have resistance, as do relay contacts. And it goes up as they age. It might start out fine, and ten years down the track be causing all sorts of problems. All contacts have resistance. Look at the dreaded Molex in Eventide devices problems.
 
Many of the power supplies in the past go into protection upon turn on and don't RESET.  I had to add delay to the controller chip on many supplies to fix the TURN ON CURRENT LIMITING problem.  I hope this will help understand the problem.
Duke
 
Relay contact resistance is listed at less than 0.075 ohm and is rated for 30A switching.  I bought an extra pair just in case they give me any trouble down the road.    Shouldn't be an issue.    Some VU's are sensitive to slamming while others can be slammed for years and never have a problem.  I wont' take the chance of replacing 12 VU's (cost and time).  The relays are relatively cheap and easily replaced.

Regards,
Jeff
 
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