Author Topic: remote batts below 5V - will the MidNite begin charge when sun returns?  (Read 162 times)

familyfarm

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Hi all. I have a remote 24->12 V installation in a very cloudy area in winter. The constant loads depleted the batteries all the way down after major snowfall and cloudy days, but the batteries never were so low as now. Will the Midnite begin charging automatically when strong sunlight hits the panels again? In the past, the panels would go to 36V on a cloudy day but obviously not have enough current to charge. Will the MidNite operate when the panels have strong sunlight on the panels side but the battery voltage is below 5V? What can I expect? Thanks.
Remote Cabin 400 W 24V into six Duracell golf cart batteries = approx 660 AH @ 12V to power 2 Piper cameras and Pepwave Peplink cell connection. Classic 150 + WBjr.

ClassicCrazy

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #1 on: December 01, 2018, 12:06:13 PM »
I think there is a chance that the controller will shut off with too low battery  voltage ( not enough power to run the controller itself ) and then if the controller is not on there will be no battery charging happening. Depending on what kind of batteries you have,  going to such a low voltage for a long enough time can ruin them.  It does not sound good for your system there.

The solution for the future would be to use the controller to shut off loads below a certain voltage. You did not say if you are using a Kid or a Classic but they both have control ability to do that .

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Ron Swanson

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #2 on: December 01, 2018, 03:45:09 PM »
Batteries will often never recover after having been pulled that low, either.

The quick and dirty way to recover if the charge controller will not power up would be to temporarily wire the panels direct to the batteries in full sun until the batteries reach a reasonable voltage, but you would have to be on site to monitor and have good weather for a while to make this work.

Vic

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #3 on: December 01, 2018, 04:53:22 PM »
IIRC  MidNite Classics need about 10 or 10.5V battery voltage to wake-up.

Am not certain of what the KID Charge  Controller needs to operate.

Ron Swanson is correct.  Generally,   Lead Acid batteries are generally ruined when 12 V batteries get much below about 10 V.   This almost  always results in some battery cells going into cell-reversal,   and those cells get charged backward.   These cells will never recover.

It is not clear what MidNite hardware that you are using,   and (to me),  it is not quite clear,   just what the system battery voltage is.

Also  for batteries that are depleted,  the  temperature where battery electrolyte freezing occurs,   rises.  This could be a further source of damage to the batteries.   Do NOT  try to charge batteries that are frozen,  or that are likely frozen  --  this can be dangerous.

Good Luck,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

FNG

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #4 on: December 03, 2018, 12:23:19 PM »
As stated above, The Classic will not boot unless the battery is above 10v, You will need to get on site and wire the PV direct to the battery to get them charged a little and then the Classic will work

tecnodave

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #5 on: December 03, 2018, 07:10:39 PM »
Family Farm,

I have a suggestion on recovering batteries that are too deeply discharged.  First....control the current at about 3-5 amps with a higher than normal charging voltage. I use about 84 volts at 3 amps as supplied by 4 12 volt 36 cell panels in series. The panels will load down in voltage when connected to batteries. By limiting the current down to a few amps the batteries will not reverse polarize. Using the higher available voltage sulfation will be " burned off " the plates restoring their capacity to accept charge.  Maintain this charge rate until batteries are at 20 volts for set or 5 volts each. At that point normal charging should work.  I am using a set of Rolls-Surrette S-530's that were salvaged from a dead solar system that I bought for scrap prices. They were at 0.05 volts for the set. It took 30 days for the batteries to stabilize at 24.0 at that point a Kid was connected with 700 watts or so of panels.
The batteries are fully recovered and are in daily use.

Bottom line....batteries are limping along.....slow charging will recover some but not all. I am of the opinion that your set is recoverable but without testing and observation I can not answer for sure. I do know that if yor rush things and try to charge at 20% of capacity you have a good chance of destroying the batteries.

David
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 2 Suntech 280 24v AGM 105 a.h. Exeltech Inv.
#4 Kid/WBjr 2 Suntech 280 12v AGM 105 a.h.

familyfarm

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #6 on: December 03, 2018, 09:39:03 PM »
Thanks for the replies. Will be hiking in this weekend. I should have set a low volts cutoff and kept my small wind gen hooked up to kick start it. What happens with cell polarity reversal? I was thinking I’d just remove the heavy loads and let the batts charge over time and the sulfate ions will mostly go back into solution as long as not much time goes by.
Remote Cabin 400 W 24V into six Duracell golf cart batteries = approx 660 AH @ 12V to power 2 Piper cameras and Pepwave Peplink cell connection. Classic 150 + WBjr.

boB

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #7 on: December 04, 2018, 12:17:46 AM »
If the batteries are below the Classic's turn on point, here is what you can try if the sun is shining.

Bring a piece of wire with you.  Just a few inches. Maybe 12 gauge ?  16 gauge ?  Something...

Strip the ends.   Actually, a decent clip lead is probably better.  You know, wire with alligator clips on the ends.

Take the cover off of the Classic and connect the PV positive to the battery positive.  If it's a clip lead you might
be able to clip it to the screws or wires somewhere.

If the PV power is enough and the batteries are just really low, the Classic should light up and display the
battery voltage.  Watch this voltage rise and don't let it get TOO high. 15 volts maybe ?   

This would work better if the wire can sit there for a few minutes and the battery voltage slowly rise. 
Sometimes this doesn't work but most of the time it does work.

When the battery voltage is in the 12 to 14 volt range, remove the wire.  The Classic won't turn on
and try to charge when the PV input voltage and battery voltage are close to the same so this is why
this works.  You COULD disconnect the PV wire but shouldn't have to do that.

After the wire is removed and the Classic turns on and starts charging from the PV by itself, do NOT
connect the wire again !  This could be bad for the Classic to make that connection after it is running.

If the battery voltage comes up to turn on voltage, (around 9 volts), you will want to let it rise a bit more
because if you try to remove the boot wire too early, the battery voltage might drop too low before
the Classic can turn on.  It needs a few seconds of PV input being above battery voltage before it
will try to turn on.

Good luck !

boB



K7IQ

familyfarm

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Re: remote batts below 5V - will the MidNite begin charge when sun returns?
« Reply #8 on: December 11, 2018, 08:06:38 AM »
Ok, we hiked in and jumpered the MidNite Classic 150. It was an overcast day but the sun peeked out for a bit. We have our batteries wired as two sets of 3 at 6V per side. That night I checked the balance between the two sides and found one side was sitting at 3.8V and the other was about 5.8V. I disconnected the one battery that had been using more water than the others and the voltage rose to 5.3V. So I removed the culprit and replaced it with a good battery from the good side. In the morning the MidNite booted up and charged normally all day. Pulling a peak of 350W the batteries never got over 12.8V so that means to me that the resistance is low and it’s a good sign. Today is supposed to be sunny. We will see how the system settles.
Remote Cabin 400 W 24V into six Duracell golf cart batteries = approx 660 AH @ 12V to power 2 Piper cameras and Pepwave Peplink cell connection. Classic 150 + WBjr.