Off grid charging problems

BigPhil

I should know better by now - our 31st year off grid. We upgraded our system about 5 years ago. Retired our 4 original "Exxon" 32W panels, 4 "Arco brownies" 32w. We installed 6 - 150w "Photowatt" panels. (they where manufactured 60 miles from us) a Xantrex 60amp charge controller, Prosine 2000w '"pure sine wave" RV inverter (cheap but can't be repaired) 8 - used Trojan L-16's. A year ago we replaced the Trojans with Interstate L-16 HCS. The system would be fully charged 14.8v/1hr. absorption by 2 pm or so. It has slowly degraded to the point where we added 2 - 140w Kyocera panels. That helped for a while but it's gotten steadily worse. Electrical problems make my head hurt! I've been inspecting the split bolts between the panels and the battery bank (utility room inside) all seems fine. The controller shows up to 82a,810w peak, but usually around 60a, 600w. We have a Vestfrost Danish refrigerator as our biggest ac draw - the web site says 15a but our inverter meter shows a maximum amp draw of 3a when both fridge/freezer compressors are running. We are running a Sears battery charger (60a setting) it will barely bring up the charge past 13.8 or so. ( when we added the 2 panels,we went to fully charged for several sunny days ) Any ideas where to start? I think in the a.m. starting at panels and checking all connections back into the house.

Photowhit

Re: Off grid charging problems

I think you mean "Prowatt" inverter since you called it cheap...

so I'm guessing a 12 volt system, so you have 4 strings of 2 batteries? Always difficult and a likely suspect.

You switched from Trojans to Interstate, did you also change your charging setting to include a maintanance equalizing? Trojans don't want you to equalize unless the specific gravity is well out of balance, while I'm pretty sure Interstate likes an equilizing every month or every other month.

westbranch

Re: Off grid charging problems

Welcome, I am thinking you have a deteriorating connection just off the top, BUT we really need to know the numbers as to what you are producing to and from the charge controller and a clamp meter set of readings for each panel and battery interconnection.... maybe a bad cell???
can you give cell SG's too?
hth

BB.

Re: Off grid charging problems

Welcome to the forum... And now to "pick your pocket";):

First, do you have a DC Current Clamp Meter (here is one that is "good enough" for our needs from Sears for ~$60).

Basically, you can clamp on each wire coming from a solar panel (or series string) and measure the DC current in the middle of the day (just one wire at a time to measure current in wire). You can quickly see if each panel is supplying the expected current or not (failed panel, poor electrical connections, etc.).

Next--Is this a XW MPPT type 60 amp charge controller or a C-60 PWM controller. There have been reports of C-XX controllers working well for years and then just stop charging (sounds like you are still getting current through the controller). Seeing a peak of ~82 Amps seems a bit high for either controller (XW 60 should never go above 60 amps--C-60 may go above 60 amps and then shut down as it overheats).

And when you talk about things going down hill--What is going down hill? Amount of charging current/hours on charge? Batteries taking longer to recharge (long time to reach 14.8 volts?), batteries dieing after a night of use? Are you measuring Specific Gravity?

Are your loads consistent, or your loads are growing over time?

Do you have any measurements of how many Amp*Hours or Watt*Hours per day your loads are?

Do you have a Battery Monitor (Victron another good brand)?

Also, using the DC Current Clamp Meter, you can measure the current flow into each battery (or series connected battery string). Also, use the DMM part to measure voltages across each 6 volt battery.

You are looking for "differences". Poor electrical connections, Open/Shorted Cells, etc.

Logging specific gravity of each cell over time should help you track the health of your battery bank. And weak cells may need equalization--and if they do not recover, you may need to replace that battery (or whole bank if all are low).

Lots of questions and can be very confusing on how best to proceed... Normally, I would suggest focusing on the battery bank.

• Rewire if needed to "balance" the charging current.
• Clean connections.
• Recharge battery bank to 100% full (should be to maximum SG reading on pilot cell, all cells should be equally bubbling). May need to assist with genset/AC battery charger (up to about 5 -13% of battery bank AH rated capacity--If I understand correctly, your bank should be ~1,680 AH @ 12 volts???? or around 84 to 218 amps of charging current--Trojan recommend ~10% or 168 amps).
• Focus on Specific Gravity... Logging each cell, if cells are more than 0.015 to 0.030 sg units apart, recharge at ~15 volts. Checking SG every 30 to 60 minutes, when low cells stop rising between readings, stop equalization. Log SG readings

Once the batteries are fully charged (and hopefully still functional), need to understand Solar array configuration (all panels in parallel?) and solar charge controller (C-60 vs XW 60 MPPT, etc.).

My guess is that you are significantly undercharging the battery bank (deficit charging) which will cause early sulfation. There is also a possibility that the batteries are not properly sharing current (need rewiring, poor connections, one or more failed cells, etc.). If you have open/shorted cells, you need to pull them out of the battery bank (same if you can identify severely sulfated batteries). And build a "good string" out of what is left.

At this point, I would suggest way too large (Amp*Hour) capacity battery bank for 12 volt system... At the very least you need a larger array and a second charge controller to get enough current to properly recharge your battery bank (looking at two 80 amp MPPT charge controllers).

Understanding your loads better will help... In some cases, too much battery bank is a problem--Not enough solar array to quickly recharge, and so much current needed you need several very expensive / high current charge controllers.

You could go to 24 or 48 volts (if you need this size battery bank for your loads), and then the charge controller current requirements would be cut by 1/2 or 1/4 (Power=Volts*Current--Double the bank voltage means 1/2 the current for the same amount of power).

Ideally, define your daily loads (and if they vary by season) first. Then define your battery bank AH size and bank voltage (i.e., roughly 1,200 watts peak power, 12 volt bank. 1,200 to 2,400 watt peak power look at 24 volt bank. Over 2,400 watts, start looking at a 48 volt battery bank).

Once the loads and the bank capacity has been defined, the rest is cook book sizing of array and charge controllers (vs wallet capacity).

Sorry for the confusing/complex post--Jumping into the middle of a problem battery bank is difficult. And, since a battery bank is easily damaged by charging problems or over discharging--Like to get the battery bank back to a healthy voltage/condition first (the longer the battery bank is discharged/has problems--the faster it will die).

-Bill

Cariboocoot

Re: Off grid charging problems

Wow is this ever a mess.

Here's a question: how does a 60 Amp Xantrex charge controller show "82 Amps"? The input isn't relevant; only the output which will not exceed 60 Amps.

60 Amps @ 12 Volts is 720 Watts. That would be a 935 Watt array on an MPPT type controller. I'll hazard yours is a C60, which is PWM. The six 150 Watt panels are about all that can take; the Kyoceras (if on the same controller) are doing nearly nothing unless the sun is low and all panel output likewise. For your total 1180 Watt array you'd need a MidNite Classic or Outback FM80 to utilize all the power.

Batteries. You have eight L16's which are at least 300 Amp hours, configured as four parallel strings of two. That's 1200 or more Amp hours of battery and your controller & array can't really handle that much. The 60 Amps maximum you have is <5% peak charge current. That's no good. Plus, Interstate has very high Absorb charge Voltage specs: over 15 Volts as I recall. Not a good choice for an RE battery really (many 12 Volt inverters can't take that). Chances are you don't have the batteries wired properly either, meaning they are sharing current equally.

Where do you start? You stop spending money. You re-evaluate the loads. Get some hard numbers from a Kill-A-Watt for everything you can. You need to know the maximum Watts at any given time (can't be too bad if a 2kW inverter can handle it) and the total daily Watt hours. My guess is you're in the common place: too much battery for the amount of panel. And you probably do not need all that battery.

Look at it from the base 900 Watt array POV:
900 * 4 * 0.52 = 1872 AC Watt hours per day.
900 * 0.77 / 12 = 57 peak charge Amps, enough for 570 Amp hours @ 12 Volts.
570 Amp hours @ 25% DOD = 142 * 12 = 1710 Watt hours.

Off hand I'd say the best thing you can do is check the SG of each battery, find the four best (equalize them if possible - although this requires a full charge first), and leave the others out of the system. Chances are you don't need them and they are only serving to interfere with charging. And see if you can't raise the Absorb Voltage to 15.

vtmaps

Re: Off grid charging problems

Welcome to the forum.
Like the others, I have more questions than answers. But I do have some comments.
You don't have enough panels or controller to charge a 1480 amphour battery bank.
If you did have enough, you would be doomed to failure anyway because 4 parallel strings of battery is at least 2 strings too many.
Your absorb voltage is correct for those batteries, but you need more than 1 hour of absorb time. Just because you get to 14.8 volts doesn't mean your batteries are fully charged.

Does your battery charger have a 6 volt setting? If so, try charging one battery at a time (it must be disconnected from the rest of the bank). And measure specific gravity! With any luck you will have 4 good batteries to use.

--vtMaps

SolarMusher

Re: Off grid charging problems

Coot,

That's 1200 or more Amp hours of battery

It's worst... UL16HC are 415Ah @ 20ah. So it's a 1660Ah battery bank.

Interstate has very high Absorb charge Voltage specs: over 15 Volts

Not specially, you can use 14.6V to 14.8V without problem and EQ these batteries from 15.5 to 16 if you need it.
BigPhil,
As all the guys before me have pointed out, too much 12VDC strings, too much Ah capacity, not enough solar panel.
Quickly check voltage of each 6V battery and check for leaks first then check SG... EQ at 16V as long as your SG rise.
Interstate is not a top quality RE battery manufacturer. I had mine since 4 years and that's not the best purchase I did in my life...
Good luck,
Erik

Cariboocoot

Re: Off grid charging problems

I scraped four years service out of some Interstates. First month I had them one needed replacing due to shorted plate. Performance afterwards was unsatisfactory too. Worst batteries I've ever had, and I've had a lot of batteries.

SolarMusher

Re: Off grid charging problems

Hi Coot,

I scraped four years service out of some Interstates. First month I had them one needed replacing due to shorted plate. Performance afterwards was unsatisfactory too. Worst batteries I've ever had, and I've had a lot of batteries.

Welcome to the Interstate Club!
I had one which was leaking after one year of service which caused me a lot of problems on the two strings. Had to buy two new ones which was not exactly the same type UL16HC versus UL16HCS. Put one in each string two years ago and it work (for now)... Not sure how long but... UL16HCS have a higher SG 1.300. Had no other choices.
I had recovered all my cells (1.275) exept one which hold a steady 1.250 and don't want to rise Still 3 or 4 years to wait to scrap this stuff.
In fact you'd better follow Rolls recommandations even with Interstate, that's what I did.
If someone is interested, I could sell a string
Good luck,
Erik

vtmaps

Re: Off grid charging problems

SolarMusher wrote: »

Welcome to the Interstate Club!

Thanks, I'm a bit nervous about being in that club.

Interstate L16s are very popular around here (good price, no freight charge if you pick them up at interstate dealer). I know several solar installers who recommend them and I have several off-grid friends who are their 3rd sets, having gotten 8-10 years from their previous sets.

Their charging profile makes no sense to a RE user (but that is true of many manufacturers).
see: http://forum.solar-electric.com/showthread.php?14738

Interstate recommends that on every charge cycle you bring them up to 15.5 31 62 volts for 2-4 hours! Equalization is 15.6 31.2 62.4 volts.

The installers around here recommend 14.8 29.6 59.2 volts for absorb. (I use 29.6 on my bank).

I'm curious... what do you get for end amps? If I set my absorb time to 'forever', the absorb current tapers down to about 2.5 amps (on a 370 AH bank). Based on what I have read about end amps, that's pretty low. If I followed Interstate's advice to charge at 31 volts, I suppose the end amps would be higher.

Wish me luck... I'm 3 years into my first set. --vtMaps

SolarMusher

Re: Off grid charging problems

Hi vt,
Don't be nervous, if you run them carefully you might expect 7 days, Oups excuse me 7 years of service. To be serious, I just think that if you don't have problems at their begining, there's no reasons to have problems later.

Interstate recommends that on every charge cycle you bring them up to 15.5 31 62 volts for 2-4 hours! Equalization is 15.6 31.2 62.4 volts.

Yes, just add eggs and bacon...
Don't follow Interstate recommendations and trust your hydrometer, it will be more accurate ... If they really had performed test on their batteries, they should know that one doesn't need these voltages to charge their batteries correctly.

The installers around here recommend 14.8 29.6 59.2 volts for absorb. (I use 29.6 on my bank).

I think they are right, 59.2V in winter and maybe a little 58.4/58.8V for summer with light discharge. 58.4V absorb/2hr with EA set to 4A (415Ah) will give you around 1.275SG everyday without consumming too much water. But if you need corrective EQ, you'd better use 64V for x hours (Rolls recommend the higher voltage your inverter/controller can supply).
Good luck and keep cool
Erik