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Forum Index : Electronics : unusual voltage drop

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Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 12:14am 24 Jun 2013
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My solar panels through a GSL MPPT feed 6 x 12 Volt, 100 Ah batteries, wired in pairs to provide 24 Volts. I have a 1500 Watt Pure Sine Wave Inverter providing 240 Volts AC.
At 1 am, 2 am or any time usually in the early morning, the batteries drop their voltage, say within 5 minutes from 23.50 to 19.80 Volts with the inverter beeping. My action is to turn off the inverter for, say, 15 minutes and watch the batteries Voltage recover. After this time, when I turn on the inverter, there is often even more voltage gain. The batteries recover to a healthy 23.80 or even as much as 24.2.

This is NOT a case of power drain. If it were, the battery would not recover to such an extent and then remain stable to provide power through to daylight.

Anyone had this problem or who knowss what might be happening?
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 09:47pm 26 Jun 2013
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Good one!

Maybe, try disconnecting the charger (GSL) after the sun goes down and see what happens.

I'd be putting a datalogger (to measure the ~24V) across the battery terminals with the inverter disconnected for a few nights. Do you need the inverter on stand-by during the night?

Are you measuring the battery voltage right on the battery terminals or via remote monitoring?



 
Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 03:37pm 27 Jun 2013
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Thank you davef for your reply. You are one out of ninety!

Your suggestion is a wise one, however, I have a cutout between the GSL and the batteries and it effects no improvement. I am interested in what is causing the syndrome,and I do need the inverter power all night, as I use the 240VAC.

However, I have solved it, even though we may never know the cause! I wait till midnight (voltage 24.5) and turn off the inverter front switch for 60 seconds. This eliminates an early morning voltage drop! I have ordered a 24 volt programmable timer to do the task at midnight.

Thanks for your reply.

PS. I would do a 24 volt disconnect (I have a manual 140 amp switch), but the relay contacts would have to be hefty! and the inverter switch-off does the trick.
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 10:54pm 27 Jun 2013
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The last question I posed.

Sounds like inverter is telling you the voltage has dropped, but has it really?
 
crez

Senior Member

Joined: 24/10/2012
Location: Australia
Posts: 152
Posted: 03:09am 28 Jun 2013
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If the problem happens early morning in winter, it maybe temperature related. As davef says, is the battery voltage really dropping or is it a measuring problem? Your 'fix' may be temporary if a problem is developing in the inverter. (not that I want to make you worry )
 
Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 05:14am 28 Jun 2013
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Thanks crez,

It may be a Winter problem (temperature related). It is not simply "this" inverter problem - it happened to the previous "not pure" inverter which had the voltage read-out on the front.

Of course, the strangest thing is that it is not a "load" problem, as the voltage recovers in seconds and the batteries continue healthily powering the system after switching inverter off and then on.

Thank you both of you for your thoughts.
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 10:13am 28 Jun 2013
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Are you reading the voltage on the current setup from the "front panel"?

 
Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 02:54pm 28 Jun 2013
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davef - No. My earlier inverter was a modified sine wave with a LED voltage on the unit. My present pure sine wave inverter does not have a voltage readout on it. I have separate LED readouts on each battery bank. All voltages, which feed the 24 volt inverter, seem to be (weirdly) controlled by the inverter when the voltage (artificially) drops. Switching the inverter off for a few seconds, then on, the voltage is restored to a healthy level which runs normally until morning.

I have discovered that I can turn the inverter off at the front switch for as little as 10 secs around midnight and there will be no voltage-drop syndrome overnight.

Thank you for your thoughts.Edited by Panelman 2013-06-30
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 07:57pm 28 Jun 2013
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I guess it will get weirder and weirder until the root cause is determined.

For the battery voltage readout to drop like that suggests that either there is a BIG load being put on the batteries, which would result is lots of heat/smoke OR the LED readouts are lying to to you (and to the inverter if they are connected to it).

Are these LED readouts connected in any way to the inverter?

Have you a multimeter of some description that you can verify the behaviour of the LED readouts?


 
Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 09:15am 02 Jul 2013
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Thank you for your thoughts, davef. The LED voltage meters are accurate and are across each pair of 12 Volt batteries (24v) which are then connected directed to the 24 Volt input to the inverter.

Lion battery techs have been very helpful in supplying a digital logger which logged the syndrome for four days. It does seem that it is a REAL momentary load. When inverter is switched off and on again, batteries recover to a healthy voltage, and the inverter continues to function as normal.
 
yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166
Posted: 10:47pm 03 Jul 2013
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panelman I see this a lot. It's like the flu for off grid systems.

lets get something straight for a start, the voltages you are quoting in the first post are not healthy for batteries that are not driving a heavy load at the time.

If there is NO LOAD on your inverter at the time, then a RESTING voltage of 24.1 is 50% capacity that is as low as you should be going regularly.

21 volts is dead battery territory. you need to establish if this is a true reading or not.

leave the inverter beeping and get your multimeter out and check the voltage back at the batteries and compare the two. If the voltage is higher(say 24.4+) then you are looking at dodgy connections between the bank and inverter on either the positive or earth wires.

Resetting the inverter will cause a current spike and a spark to jump across the dry joint and fry it a bit causing it to lessen the resistance across the fault for the rest of the night. The frustrating thing is it could be anywhere. I have found them in fuse holders, inside switches, lug connectors, in-between battery joiners, loose nuts and screws. Don't just tighten em, pull them to bits clean and sand or resolder it and reassemble.

I would fire up a hairdrier or something on the inverter and give it a good workout and go around looking for joints that are warm to touch and fix them first.


If the battery bank voltage is reading low the same as the inverters battery volts meter then you are in trouble.

That usually means the batteries are not charging correctly,

if you're lucky, it will be poor connections between the batteries getting the banks out of balance, easy fix with some sandpaper. if there is a voltage drop between the controller output terminals and the bank while it is charging then you can expect some battery damage from chronic undercharging.

Have a bit of a snoop around, take a few measurements first and see how you go.Edited by yahoo2 2013-07-05
I'm confused, no wait... maybe I'm not...
 
Panelman
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Joined: 27/09/2012
Location: Australia
Posts: 6
Posted: 01:54am 04 Jul 2013
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Thanks Yahoo2,

It has not happened for two days. I am looking at all aspects.

Thanks
 
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