Author Topic: Should i measure idle voltage with or without load ?  (Read 2946 times)

0 Members and 1 Guest are viewing this topic.

pguillem

  • Newbie
  • *
  • Posts: 22
  • Country: co
  • A full time curious inner kid
    • Ethervoice
Should i measure idle voltage with or without load ?
« on: December 04, 2013, 06:23:59 PM »
Hello my fellow energy geeks!

We have a hybrid solar/wind system storing power at 48v in 12 deep cycle batteries, arranged in 3 sets of 4 batteries each.

Both the storage and the 10Kw inverter is designed for 48V. Meaning whenever i use 4 amps in 110VAC i will be draining nearly 10 amps from the batteries, having a 2.5 to 1 DC/AC conversion ratio.

Each battery is rated 150Ah and the whole set should last for 12 hours draining 30 amps permanently using less than 70% of the available charge.

Whenever we put a load to the inverter (air conditioning, fridge, etc) the battery voltage drops from 54 to 50 and slowly discharges.

We are confused on how to measure the idle charge, as when we reach 47.5 volts and release the load, the voltage goes back to 49.

Which reading should we trust to test for idle charge ? Measuring the voltage with full load ? Or with no load at all ?

Also, we noticed after 1 year of use without draining below 47.5V, the batteries are reaching this theshold faster, but they are practically new. According to the manufacturer if we never drain more than 30% of the  batteries, they should last for 1200 cycles or so. Could you guys suggest a good way to test if a battery of the set is damaged or worn out?

Pedro




« Last Edit: December 04, 2013, 06:30:08 PM by pguillem »
The secret of happiness remains in finding something in which to become an enthusiast.

Jesus María Guillem (1913 - 2002)

birdhouse

  • Hero Member
  • *****
  • Posts: 919
  • Country: us
  • Portland, OR USA
Re: Should i measure idle voltage with or without load ?
« Reply #1 on: December 04, 2013, 08:21:13 PM »
pedro-
resting voltage is what you are after.  while a load is being pulled the batts show an artificial lower voltage than actual.  it's the same but opposite as when charging.  you probably notice the volts go pretty high while charging, and once the charge is removed, they settle back down to an actual voltage point. 

i think true resting voltage is measured 24 hour after all draws and or charging has been done. 

do you ever equalize the batts? 

you can do controlled tests periodically to see how good they are now versus then kind of thing, but they must be controlled very well, including battery temperature. 

adam

pguillem

  • Newbie
  • *
  • Posts: 22
  • Country: co
  • A full time curious inner kid
    • Ethervoice
Re: Should i measure idle voltage with or without load ?
« Reply #2 on: December 04, 2013, 10:01:16 PM »
Dear Adam

Thank you very much for taking the time to respond. Your explanation makes perfect sense and we do see the floating voltages behaving as you mention. Thank you for addressing that info.

We will perform the resting voltage test in the following days to measure it as you suggest.

We have never equalized the batteries since we installed them. Now that you mention it, we are not quite sure what  equalizing means or how it is performed. Could you give us a hint or point us to some docs?

One more question thou.

8 of our batteries are deep cycle sealed-GEL, the remaining 4 are marine deep cycle lead-acid. We have not seen issues with this setup in over a year... but we have read it is not recommended to mix different chemistries, even if they are rated for the same output/duty.... do you agree we should not mix this 2 types of deep cycle batteries?

Can we equalize both types with the same technique?

Regards
Pedro
The secret of happiness remains in finding something in which to become an enthusiast.

Jesus María Guillem (1913 - 2002)

Frank S

  • Hero Member
  • *****
  • Posts: 1901
  • Country: us
  • Home with a view of Double mountain
Re: Should i measure idle voltage with or without load ?
« Reply #3 on: December 04, 2013, 10:11:06 PM »
  This could be the key point of your bank not having as long of usable charge as it had in the beginning.
 SLA or sealed lead acid gel batteries will take a faster charge than the  FLA or flooded lead acid
 your 4 batteries that are flooded acid may not be getting fully charged and are becoming sulfated.
I live so far outside of the box, when I die they will stretch my carcass over the coffin

birdhouse

  • Hero Member
  • *****
  • Posts: 919
  • Country: us
  • Portland, OR USA
Re: Should i measure idle voltage with or without load ?
« Reply #4 on: December 05, 2013, 01:01:32 AM »
pedro-
if i were you, i would try and see if one battery bank is far better than the other, and keep the better one.  OR, put the two types in separate banks with marine type switches to allow one bank to charge while drawing from the other.  ect. 

basically, the two different type of batteries take totally different care.  equalize is hitting you bat bank with high voltage and decent amps.  it makes them boil a bit.  you CAN NOT do this with GEL bats.  or at least not as hard as you can do with FLA.

adam

Simen

  • Sr. Member
  • ****
  • Posts: 479
  • Country: no
  • Grimstad, Norway
Re: Should i measure idle voltage with or without load ?
« Reply #5 on: December 05, 2013, 02:17:43 AM »
I agree with Adam.
The SLA batteries are not as prone to sulfation as FLA, and the SLA picks up the charge a bit faster than the FLA.
You should separate the two banks and charge them separately, and then give the FLA bank a  proper equalize.

We talked about equalizing in another thread here;
http://www.fieldlines.com/index.php/topic,147989.msg1025457.html#msg1025457
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)