New to Pv, looking for advice

[vtmaps]

I didn't even know there were different ratings for clamping different strand types. I've only been aware of differences between solid and stranded connectors.

A recent thread over at NAWS may be of interest to you:
http://forum.solar-electric.com/showthread.php?26114

Also, this Home Power article:
http://www.homepower.com/articles/solar-electricity/design-installation/inverter-battery-cables

--vtMaps

[vtmaps]

I did use the string sizer setting up 12 of my panels in 2 strings and it said it was ok on the Classic 150 down to (IIRC) -8F which is unlikely in this part of Florida. But "ok" and "optimum" I know are different things. 5+5 may be fine for me, I'll need to re-do some math to figure it out.

Actually, optimum (for a 12 volt system) would probably be three of those panels in series.  How long a run is it from the panels to the controller?

--vtMaps

[kf4hzu]

A lot of information since my last visit, thanks! This may be a bit long of a post...

Please, do not try to use any Equalize settings on your AGM batteries.   Go to the Mfg's website and look up the maintenance charge voltages.
When charging AGM, once you exceed the internal gas recombiner, it Vents gas, and therefor you loose electrolyte that can not be put back.

Yep that seems to be what everyone says. I did read the spec sheet; that information is in my original post.

For most folks, by the time they realize something is wrong with their parallel batteries, serious damage has been done.  You seem to be more on top of it than most folks.... you have a clamp meter and use it, and you are sensitive to tenth-of-a-volt differences.  You might be able to rescue your bank.

Thanks, I hope so. After all the reading I've done over the last few weeks I plan to use the clamp meter (which I've found to be very accurate) to check the voltage and charge/discharge amps from each battery every week going forward.

What you MUST do is separate those batteries and charge them and evaluate them one at a time. 

Some AGM manufacturers do recommend an "equalization" when needed... but it's usually just an extra long absorb, or its very few tenths of a volt higher than a routine absorb.  I think you mentioned that you have interstate batteries... they're OK batteries (in my opinion) but you must understand that Interstate's tech support folks are clueless, and have no clue that they're clueless.  If you can find out who made those particular batteries for interstate, you can look up that manufacturer's recommendations for the battery.

For safety reasons it is a good idea to put a fuse or circuit breaker in each string of a parallel battery bank.  If you had done that it would be very easy to switch in or out any particular battery in your bank.  Of course, all the extra connections involved in fusing each string add connections (which are points of failure) to the battery wiring.  You seem to understand some of the issues with parallel batteries.  Do you know that the problems are exacerbated with AGM batteries?  This is because their lower internal resistance makes the resistance in the wiring relatively greater.

Since I kept it a 12V system, I can actually remove the entire bank from the system and replace it with a 12V 35AH AGM battery I have allowing me to do any charge/eval cycle needed on them. What do you suggest I do, and what results should I look for?

I've looked for who may make the PowerPatrol SLA1165 batteries but only find spec sheets that don't even have the word "Equalize" in them. I do believe the tech support people don't know what they are talking about, which is why I asked here

I actually bought fuses and fuse holders to go between the batteries as you suggest. I decided not to put them in because I was concerned about adding resistance and increasing my voltage sag during heavy load. Do you feel it is best to put them in anyway? If so, is it fine to only fuse the positive leads?

I recently learned my AGM batteries are the worst for parallel banks. Wish I would have known before I spent the money on them. I just need to get some more time out of them before I can buy another bank that is designed properly. Maybe LiFePO2?

A recent thread over at NAWS may be of interest to you:
http://forum.solar-electric.com/showthread.php?26114

Also, this Home Power article:
http://www.homepower.com/articles/solar-electricity/design-installation/inverter-battery-cables

Ugh, none of that is good news for me. The only thing I have that meets compliance are the rings that powerwerx.com used, which ARE UL listed. The cable doesn't have the required markings on it to pass. The future cost of this system is going to exceed the budget I've allocated to it. 

Actually, optimum (for a 12 volt system) would probably be three of those panels in series.  How long a run is it from the panels to the controller?

It is a 50' run from the roof, not counting the short interconnect cables on the panels. (I put that all in my first post)

Using Vmp (18.9V) and Imp (5.29A) for the math, building it out the way you suggest, http://www.calculator.net/voltage-drop-calculator.html says I would have about a 2.35% loss. My original design of 6x2 would be 0.58% loss. At 1200W, that would be an increase of 21W of loss if my math is right. I've read a lot of articles suggesting to keep cable loss at or below 1% if possible. Would having a 3x4 configuration with that cable loss be better due to the Classic's losses in converting down from ~113.4V on a 6x2 configuration? I know I'd need to change out the fuses for the Pv side since I only have 20A fuses now.

I purchased the Classic because I thought it could easily and efficiently handle the 6x2 configuration I had planned when I reach 1200W of Pv. The string calculator on the site said it was ok. There was no mention of estimated losses in the controller itself due to the configuration. Maybe this should be added to the calculator if it really does make a significant difference in losses which also increases heating of the controller, reducing its lifespan. Perhaps someone from MidNite can chime in on this one?

On a good note, another 100W panel is on the way! My wife decided it would make a good birthday present. So at least I will be at the 10% charge amps previously mentioned in this thread on a good day.

Thank you all for the info so far! Still a lot to learn...

[kf4hzu]

Thought I'd attach another graph. I put too much load on it so never even reached Absorb. Shed some load last night and full 2hr absorb with a little over an hour of float today! With the 4th panel coming I should be good at the current load levels. Just need to repair the battery bank issues.

I have noticed something that may be an issue. The relay in the charge controller clicks every few minutes in the morning and evening when the light levels are low. In the morning it switches between BULK MPPT and RESTING (Low Light). This evening it is switching between FLOAT MPPT and RESTING (Low Light). The output watts is zero in both modes when this is going on. Is this normal? I'm guessing the relay has a lifetime max cycles. Any reason SSRs weren't used?

[Westbranch]

You can set the time between sweeps on a Classic.

The sound is normal so don't have it beside your bed unless you want to get up with the sun...

[kf4hzu]

Well I know the sound is normal, just didn't think it would be that frequent. It is in a closet far away from our bedroom so no problem there

My only concern is the lifespan of the relay. Would it be a good idea to increase the sweep to 5 minutes, or 10? I figured lower was better so as conditions change it can adapt quickly. But I'd also like my CC to last many years, at least longer then the 25yr warranty of the panels.

[Westbranch]

FYI, found this quote from boB from about a year ago about sweep... emphasis added

As for the sweep interval time on the Solar mode, 3 minutes is the default time
but that is a "must sweep" time interval.  There are times, in Solar mode, that the
Classic may sweep before that time interval.

I know my MX60m designed by boB, lasted for >5 years clicking away and it is now over at the neighbours... clicking on..... so I think you don't have to worry  about longevity

[kf4hzu]

Just a quick update; I now have 4 panels for a total of 400W hooked up in series.

This weekend I plan to work on the battery bank issues since it will be very sunny according to the forecast.

[WizBandit]

I didn't read how you have your four 12V batteries connected.  This is a big deal for AGM's
See the attached drawing, ignore the NEG going to Ground, this is how RV batteries SHOULD be wired and most are not and RV owners replace batteries every year. Getting the power IN/OUT off one end of a paralleled set of batteries will kill the far ones.

[vtmaps]

I didn't read how you have your four 12V batteries connected.  This is a big deal for AGM's
See the attached drawing, ignore the NEG going to Ground, this is how RV batteries SHOULD be wired and most are not and RV owners replace batteries every year. Getting the power IN/OUT off one end of a paralleled set of batteries will kill the far ones.

You can do much better than your diagram shows:
http://www.smartgauge.co.uk/batt_con.html

However, the most important thing to know about having four batteries in parallel is that it is a poor design choice to have so many batteries in parallel, even if they are wired to perfection. 

The batteries are, at best, in an unstable equilibrium.  Usually they are not even at equilibrium. 

Getting the current to divide equally among four batteries is like trying to balance a pencil on its point.  They are both examples of unstable equilibrium. 

Suppose, that for any reason, one battery gets a bit more current flow than the others.  That makes it warmer.  If it is warmer it gets more current flow than the others.  If it gets more current flow, it gets warmer than the others... get the point?  It's like balancing a pencil on its point... if it leans just a bit one way, the forces on it will pull it further in that direction which will increase the forces pulling it in that direction... get the point?

Each of four batteries in parallel should be fused.  The problems I just mentioned become dangerous when a cell in one battery shorts out.  Of course, adding all those fuses means adding many more connections which are all potential points of failure.  Because of the issues with monitoring and maintaining four parallel batteries, it is a good idea to include some switches (or circuit breakers) to be able to switch in or out any particular battery.

The life of a battery bank is equal to the life of the shortest-lived cell.  The lifespan of the cells is a Gaussian curve (bell shaped curve).  With four 12 volt batteries, there are 24 cells.  Hopefully, none of your 24 cells is in the lower tail of that curve, because it doesn't matter what the average lifespan of your cells is... all that matters is that one of your cells will pull down the whole bank when its time is up.  If you had just 6 cells to make up your 12 volt battery, you would have a much greater chance of NOT having an outlier short-lived cell.  In fact, you would even have a 1 in 64 chance of buying 6 above average cells.

--vtMaps

[kf4hzu]

I didn't read how you have your four 12V batteries connected.  This is a big deal for AGM's
See the attached drawing, ignore the NEG going to Ground, this is how RV batteries SHOULD be wired and most are not and RV owners replace batteries every year. Getting the power IN/OUT off one end of a paralleled set of batteries will kill the far ones.

I did take a picture of the connection and posted it earlier on this thread, but I made this diagram to help describe it. The 4AWG cables are within 1cm of each other in length.

[kf4hzu]

You can do much better than your diagram shows:
http://www.smartgauge.co.uk/batt_con.html

However, the most important thing to know about having four batteries in parallel is that it is a poor design choice to have so many batteries in parallel, even if they are wired to perfection. 

The batteries are, at best, in an unstable equilibrium.  Usually they are not even at equilibrium. 

Looks like I used Method 3 - but yes it is still not a good thing. However it is all I have for now until the batteries are completely shot and then I will replace them with a proper design.

Each of four batteries in parallel should be fused.  The problems I just mentioned become dangerous when a cell in one battery shorts out.  Of course, adding all those fuses means adding many more connections which are all potential points of failure.  Because of the issues with monitoring and maintaining four parallel batteries, it is a good idea to include some switches (or circuit breakers) to be able to switch in or out any particular battery.

I have fuses I can add. Is adding to just the positive leads acceptable?

The life of a battery bank is equal to the life of the shortest-lived cell.  The lifespan of the cells is a Gaussian curve (bell shaped curve).  With four 12 volt batteries, there are 24 cells.  Hopefully, none of your 24 cells is in the lower tail of that curve, because it doesn't matter what the average lifespan of your cells is... all that matters is that one of your cells will pull down the whole bank when its time is up.  If you had just 6 cells to make up your 12 volt battery, you would have a much greater chance of NOT having an outlier short-lived cell.  In fact, you would even have a 1 in 64 chance of buying 6 above average cells.

This is why my next battery bank will be designed using 4V or 6V SLA batteries. If I am lucky, maybe LiFePO2 batteries!

I do think I have a serious problem with the bank. I hope it isn't a bad cell, but I'm also not sure where to start troubleshooting. I just know, as I've said previous, that two batteries charge/discharge at different rates then the other two. By ruff math it is about 15% difference. Whatever is going on is causing bank voltage to drop off quickly even with minimal load. It seems better after I tried doing an "equalize" charge, at the same voltage as Absorb, for 4 hours. The bank actually stayed at 12.9 for over an hour which it used to do for several hours.

I know there are problems with my design, both performance and NEC-related. I just need to fix what I can for the least amount of money right now and try to get another year or two out of the batteries before they are scrapped for a new bank. Any advice to help make this happen would be very helpful. I really appreciate all of the information everyone has provided on here, I just don't have a solution yet unless I missed it somewhere.

[vtmaps]

I do think I have a serious problem with the bank. I hope it isn't a bad cell, but I'm also not sure where to start troubleshooting.

As I mentioned earlier in this thread, you need to separate the batteries and try charging them one at a time.

It would be useful if you had a DC clamp ammeter... you could easily see how the current is dividing among the batteries while they are in parallel.  That will help with the diagnosis.  Of course, you will still need to separate them to achieve a cure.  The inevitable cure may involve amputation of one battery from the bank.

When batteries get really out of balance, you may have some batteries discharging into other batteries when you turn the charger or controller off.  You can see that with a DC clamp ammeter. 

--vtMaps

[kf4hzu]

As I mentioned earlier in this thread, you need to separate the batteries and try charging them one at a time.

It would be useful if you had a DC clamp ammeter... you could easily see how the current is dividing among the batteries while they are in parallel.  That will help with the diagnosis.  Of course, you will still need to separate them to achieve a cure.  The inevitable cure may involve amputation of one battery from the bank.

I do have a DC clamp meter; that is how I figured out that I have a problem with the differential in charge/discharge rates. I think I mentioned that. Once I separate them, what should I do? Should I leave only one connected to the Classic per day for 4 days and then reconnect them all? Or should I charge them individually with an AGM charger that plugs in to regular power? It only outputs 7 amps max and these are 55AH batteries.

When batteries get really out of balance, you may have some batteries discharging into other batteries when you turn the charger or controller off.  You can see that with a DC clamp ammeter. 

How did I not think about this! I have yet to try that, but it makes complete sense, thanks! I'll do that today/tonight. The batteries are already in Absorb after only 3 hours of sun (11:50AM local time here). Should I pull all load and disconnect the CC, then test immediately, or wait until Float and then pull load/CC and test immediately?

[kf4hzu]

Ok I waited until the batteries were float charging to test, so full 2.5hrs of Absorb at 14.7V and then float at 13.8V for about 2 hours.

I disconnected all load, got the clamp meter ready, and disconnected the charge controller. I immediately tested each battery lead several times to get the best reading. I found the highest power flow between the batteries was from the one I just happened to have connected the temperature probe from the Classic. 200mA was flowing out of it in to the other batteries at different rates. One was absorbing 100mA and the others were both alternating between 40mA and 70mA.

I then decided to do a load test on the system and see the differences, checking the outflow of power from the batteries out to the inverter. I connected a 350W pure sine-wave inverter and ran two laptops along with a small heater which was a little over 300W of load.

The biggest issue after only about 10 minutes ended up being heating on the wiring seemingly surrounding the 80A fuses. The highest reading was closest to the fuses at 112f/44.4c which seems fairly high for only about 25A of power draw from the batteries. This is very concerning since I have never had heating of the cables before. All my connections are crimp, and were very tight when I made the cables. Now I'm questioning all of it. Should I take everything apart and re-make it, or is there a better way?

Back to the original issue, the two outside batteries of the bank were reading ~5.5A draw, where the two inside batteries were reading ~6.5A draw. So just confirming I have an issue, and it could be two batteries.

Should I disconnect all 4 batteries and charge them separately? What would be the best next steps to help the battery balance issue, even if only temporarily?

Obviously I need to fix the wiring issues now too. Luckily none of the battery interconnects were warm at all. For reference, it is 68f/20c in the room and the batter interconnect cables felt just as cold as other surfaces in the room, including the 1/0AWG cables that were not in use at the time.