×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

DC voltage dip

DC voltage dip

DC voltage dip

(OP)
We have a bank of lead acid batteries providing substation dc power.

Recently, during an event,  we had a dip in our station power, which of course caused a dip on the input voltage to the charger.

At the exact same time the station power dipped, our DC voltage dipped from 134v to 78v, but for only 10 cycles, then recovered to full voltage.


Comments?

HP

RE: DC voltage dip

No storage capacity left in the batteries, running only on the charger?

RE: DC voltage dip

I would agree.  Batteries toast?

RE: DC voltage dip

It sounds like batteries. Take a deep breath and turn the charger off for a few seconds. Be careful, we just had a discussion about batteries exploding when they're in bad shape and running on the charger.
yours

RE: DC voltage dip

Knackered batteries and a charger trying to recover its output voltage during the dip?

Was the dip longer than 10 cycles? What kind of charger is it: switchmode or thyristor? The switchmode types are usually more forgiving of input disturbances because they can react very quickly and typically have very broad input voltage ranges.

Invest in a load discharge test for your battery. A fault in a substation whose breakers have no tripping power could turn ugly very easily. If people argue over cost of the test and probably a new battery too, enquire whether their budget stretches to a new substation.

----------------------------------
  I don't suffer from insanity. I enjoy it...

RE: DC voltage dip

(OP)
The AC dip was for slightly more then 50 cycles. The DC dip was only for 10 cycles.

The bank was just recently tested and all was good. It was not however discharge tested or load tested.

Have any of you heard of the term " Coup De Fouet "


HP

RE: DC voltage dip

How can the bank have been tested if it wasn't at least load tested?

RE: DC voltage dip

Hi itsmoked.
Probably the insurance carrier told management that the batteries must be tested but did not specify the test procedure on the same page. Management issued a directive,
"Check the batteries but don't take too much time and don't take anything out of service."
I believe it's called "Checking the boxes."
I often don't know if I'm a cynic or a realist.
yours

RE: DC voltage dip

(OP)
When the batteries are only 3 years old, and its your ONLY bank, then strap and spG reading are the extent of testing.

HP

RE: DC voltage dip

Hello HighPotter
I apologise. I understand your restraints. Is it possible to turn off the battery charger and monitor the voltage for long enough to see if the voltage drop is excessive?
yours

RE: DC voltage dip

Number of banks should not affect the testing schedule. Criticality of the load should. I would suggest cell and interconnection resistance or impedance testing, and IR scans. 20 year rated VRLA batteries have been known to die in three years, although your spg comment suggests you have flooded cells. See IEEE standards for recommended maintenance and intervals. My French is long gone, please explain the term.

RE: DC voltage dip

Certainly you should be able to turn off the charger and watch the results.. Otherwise disaster WILL occur.   And if you can do this, then you should be able to hang some sort of load out there to really test the capacity.  Otherwise you're really flying blind.poke

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources