A year to figure future storage

[Madscientist267]

I actually ran mine in series (as "24V") intentionally, but ending up in a 12V battery.

This was a two part thing; one I had bypassed two bad cells in one panel, so they no longer matched voltage wise. The other was that I got half the loss on my run into the house; they go through the buck converter before hitting the battery.

Guess that's a 'hybrid' approach?

Steve

[ChrisOlson]

The other was that I got half the loss on my run into the house; they go through the buck converter before hitting the battery.

On my setup, I actually get the full 600 watts into each half of my battery bank on a nice clear day with the panels split into two 12 volt strings - usually around 42 amps per bank.  So I'm not going to complain about that too much.  I discovered quite by accident that I was only getting 39 amps out of the panels on 24 volt and that by splitting them I could get 42 amps.  Not a lot, but 85 watts is 85 watts and I can use every one of them.

If you have a DC->DC converter, then it doesn't make any difference.  I think that's what a MPPT controller does.  The solar guy told me that if I would buy the controller he wanted to sell me that I could run those panels at 90 volts and wouldn't need all the wires going into the solar combiner.  But since I already had it installed that way, and it works, I decided I can spent the 500 bucks for a controller on something else.
--
Chris

[Madscientist267]

Yes, essentially it's just a manual MPPT:



Tweaking the pot adjusts the regulation of the input voltage, resulting in peak power output from the panels.

The fan is there in case things get a little bit too warm, and doesn't normally run.

Automatic would be better (a true MPPT), but isn't really necessary for what I'm doing. I get very close to rated panel output with this under the right circumstances. I've calculated the converter itself at ~90%+ efficient.

Steve

[ChrisOlson]

Automatic would be better (a true MPPT), but isn't really necessary for what I'm doing. I get very close to rated panel output with this under the right circumstances. I've calculated the converter itself at ~90%+ efficient.

Well, see, that's the other thing I sort of wondered about a MPPT box.  The thing isn't 100% efficient.  So being I already get 1200 watts out of those panels in direct sun on a good clear day, is a MPPT box going to get me more power yet after you factor in the loss in the box?  Will the MPPT box get more power from the panels on cloudy days and when the sun is not directly overhead?

The solar installer from the company I got the panels from said it would.  But he wouldn't demonstrate one to me to prove it.  I told him that for $500 for that controller I can just about add two more panels to the array.  And if he could demonstrate to me that the controller will make more power per dollar than adding two more panels, I'd think about buying one.  He gave me a line of technical BS that I don't think even ghurd would understand and the bottom line was he'd sell me a controller but he was NOT going to hook one up and demonstrate it.
--
Chris

[Madscientist267]

Its a fine line, really.

I see peaks of 4.15A @ 14V when the sky is playing with me. Steady sunshine I don't get near as much, because the panels warm up and lose efficiency.

The 4x14 thing works out to 56W, which the panels are rated for 60 (less the two bad cells).

This is with 35V @ 1.7A in, which is what brings the efficiency of the converter in at 90+.

But with only the panels (wired in parallel), I would be seeing ~3.4A (ish), so there aren't necessarily a whole ton of gains to be gotten, but they're there.

So does it technically improve output? Yes. The biggest gain I think though is the fact that the current is less than half of what it would be if they were wired direct, so the losses are less in the lead-in cable.

I'll have to sit down with it one day and run it through the ringer; there are a few optimizations that could be made here and there, but I haven't gone through all of them yet.

Steve

[ChrisOlson]

So does it technically improve output? Yes. The biggest gain I think though is the fact that the current is less than half of what it would be if they were wired direct, so the losses are less in the lead-in cable.

Do you have a solar combiner box?  Each pair of my panels came with a 50 foot roll of 10 AWG wire.  So I used it all.  Each pair had a 10 AWG positive and negative lead coming in, and the positive from that pair goes to a breaker in the box.  Set up that way it would do 83 amps @ 14.5 volts on a good day.

When I set them up for 24 volt I went up on the roof and wired each pair series.  Set up that way it would do 39 amps @ 29 volts.

When I split the panels into two strings of five I ran five more wires so each panel has it's own 10 AWG wire to the combiner box.  But it didn't make any difference adding the extra wires.  Each group of five still puts out about 42 amps into its respective side of the battery bank on a good day.
--
Chris

[Madscientist267]

Solar combiner, not really. Kinda happens at the panels. I only have the two ATM.

Also, in response to the "directly overhead" question, I think it makes a difference, as the panels have a tendency to head toward full voltage in indirect light,  so in theory, there is potentially more power to be had since the current seems to be what is most affected. I don't have any hard proof of that in terms of testing, but do have reason to believe this is the case. In completely overcast skies, with some bright spots (but no solar disk visible), I can get up to an amp or so from the buck by pointing the panels straight up. I'm pretty sure that the current at the input to the buck is considerably less, and the difference being made up in the higher voltage.

I have to adjust the buck for both temperature and light to get the most out of it. Unfortunately, I'm only measuring output current from the buck and battery terminal voltage, so my picture is not complete... I don't have 4 meters to measure it all simultaneously, and conditions change constantly, so switching back and forth wouldn't tell me a whole lot.

I can however do some direct OTV and Isc measurements in various conditions and come to a slightly better conclusion than theory alone can provide, just might take a few days for enough 'samples'.

Probably should get the metrics even for my own use, but they can probably find use as well for others...

Steve

[ChrisOlson]

Also, in response to the "directly overhead" question, I think it makes a difference, as the panels have a tendency to head toward full voltage in indirect light,  so in theory, there is potentially more power to be had since the current seems to be what is most affected.

Well, this has sort of gotten off topic from the system voltage thing.  But it sounds like you have a lot more experience with getting more power out of solar panels.  I barely know how to hook 'em up, and if the amps aren't enough I hook 'em up different and try that to see if it works.  I've never understood why a 12 volt panel is rated at 17 volts, and so on.  But if it says 123 watts and I get 123 watts out of it hooked up to 12 volts, then I figure it's hooked up right.  I do know that I can't get the full 1200 watts out of my solar panels unless the voltage of my system is close to 28 or 29.

From the way the solar guy talked that I dealt with, those panels will put out more than 123 watts with a MPPT controller.  I wondered if that was true or not.  I think the MPPT controller would help when the bank is at 25 volts.  But again, I wonder if the cost of it will yield enough extra power vs just spending that money on more panels and hooking them up direct.

It's kind of like if you have a diesel engine driving a pump and the engine doesn't have enough power.  You can put a turbocharger on it and turn the smoke screw to get more power.  Or you can just put a bigger engine on the pump.  Usually, it's better to just go with the bigger engine.
--
Chris

[rossw]

On my setup, I actually get the full 600 watts into each half of my battery bank on a nice clear day with the panels split into two 12 volt strings - usually around 42 amps per bank.

Specs I can see for 123W sharp modules says I(mp) = 7.16A (at 17.2V). with I(sc) of 8.04A.
How may panels do you have in parallel in each array?  If you have 5, that should make a fraction over 40A (40.2) *short circuit*, neglecting any cable losses.

At 12V, even assuming you have the full 40A they're theoretically capable of (short-circuit current) thats 480W.  (504W if you actually had 42A). If you had an MPPT you'd get 615W (input) max, even assuming only get 90% efficiency from your MPPT, thatd take you to 553W into the batteries. Times two if you count both arrays. Thats a minimum of 140W additional power - or more than a whole extra panel.

Not a lot, but 85 watts is 85 watts and I can use every one of them.

Yup. Or more, if you want it.


This thread from 6 months ago is particularly relevant: http://www.thebackshed.com/forum/forum_posts.asp?TID=3049

[ChrisOlson]

Specs I can see for 123W sharp modules says I(mp) = 7.16A (at 17.2V). with I(sc) of 8.04A.
How may panels do you have in parallel in each array?  If you have 5, that should make a fraction over 40A (40.2) *short circuit*, neglecting any cable losses.

I don't know how they come up with those specs for sure.  I only know that five of them puts out 42 amps with the bank at 28-29 volts and the Doc Wattson says right around 600 watts out of each string of 5 panels.

I have tested one single panel before direct hooked to a 12 volt battery and it will put out just about 8.5 amps with the battery at 15 volts.
--
Chris

[Tritium]

I run 12V because it is what I could get cheaply and I had inherited a number of modified sine wave 12V inverters. I did set up my arrays with Outback MPPT controllers. 1 array is 56V and the other is 110V so I can switch to higher battery voltage when it becomes necessary and affordable. I have already spent the money on 4/0 cables from the bank to breaker box/inverter so I am set for any higher voltage bank with a very much larger inverter than the one I have now. I use about 6 Kwh a day now but plan to move most household loads to a big sine wave inverter in the future when I have about 4 or 5K to spend on inverter and battery bank. I am on grid but I hate when it goes down when I need it most and would rather use it a a backup to my system and for irrigation water pumping.

Thurmond

[rossw]

I don't know how they come up with those specs for sure.  I only know that five of them puts out 42 amps with the bank at 28-29 volts

I thought you said above that you could only get 39A in 24V mode, but 42A (ea) in 12V? Now you're saying 42A in 24V?

The mismatch becomes *significantly* less as your battery (terminal) voltage (as opposed to nominal array voltage, just so we're not getting confused here) rises.
Look at my post (first reply) in the other link I posted.

At 28/29V (equivalent to 14 or 14.5V on a 12V system) you will be throwing away much less potential power than if your cells were down to 12V or less.
Eg, at Mp for your panels, 172 watts is 10A.  If you're sitting at 15V, your "realised" power is near enough 150W. At 12V it's down to just 120W.

I have tested one single panel before direct hooked to a 12 volt battery and it will put out just about 8.5 amps with the battery at 15 volts.

One of several things.
* What temperature are your panels at? If they're at less than 25C, you will see higher outputs.
* How old are they? Many manufacturers specify mid-life power, not start-of-life power, so if your panels are fairly new, they may still be outputting above "specified" power.
* Weather conditions and altitude. Under several conditions, you get atmospheric magnification of sunlight, resulting in higher output from your cells. (Eg, "cloud edge effect" often shows 25% above "normal maximum" for my panels)

[fabricator]

I run 12V because it is what I could get cheaply and I had inherited a number of modified sine wave 12V inverters. I did set up my arrays with Outback MPPT controllers. 1 array is 56V and the other is 110V so I can switch to higher battery voltage when it becomes necessary and affordable. I have already spent the money on 4/0 cables from the bank to breaker box/inverter so I am set for any higher voltage bank with a very much larger inverter than the one I have now. I use about 6 Kwh a day now but plan to move most household loads to a big sine wave inverter in the future when I have about 4 or 5K to spend on inverter and battery bank. I am on grid but I hate when it goes down when I need it most and would rather use it a a backup to my system and for irrigation water pumping.

Thurmond

If your MSW inverters run your loads now you don't need to spend 4-5k on a big sine sine wave inverter, a higher capacity quality MSW inverter will do the job just fine, then you an spend more money on batteries, these MSW inverter are high quality, my freezer, refrigerators and water pump motors work perfectly on them.
http://www.theinverterstore.com/the-inverter-store-product.php?model=pwrinv5k-front-rgb

[Madscientist267]

I don't know how they come up with those specs for sure

Every company seems to have a different method by which they rate their panels. Seems like Sharp has a better grasp on 'real world' usage than some. It's kinda like a car rated at 40MPG. How did they come to that? Downhill, drafting behind a semi, with a 90 pound driver and a 1/10th tank of gas? Not really a very useful rating, unless you're comparing it to cars that are rated the same way.

I suffer the same problem with my panels. Even though they're rated at 60W (30ea), I only can get 45 out of them on a continuous level because of the efficiency losses when they warm up. But I can't exactly call them liars either since I can see surges of 56W when conditions are right.

The panel voltages are higher so that in weaker light, they can still charge a battery. But that's apparently where the MPPT really starts to do it's thing. Current is nearly flat from a panel until you get close to OTV, then it starts to fall off rapidly. This is why you see the 'full output' from your panels when the batteries are full. Since the current doesn't change (appreciably), the higher voltage translates to more power. That's what makes the MPPT do it's thing. It hunts for the highest terminal voltage it can get from the panel without the current falling off, resulting in maximum power output.

I agree, I didn't mean to assist in the hijacking of the thread, although I can somewhat foresee this kind of thing possibly playing a role in someone's decision as to which system voltage to use. The higher the system voltage, the greater the difference between panel and battery OTV, potentially affecting efficiency. Although I can't really say from personal experience just how much. I only can go with what I've seen at 12V.

Steve

[ChrisOlson]

I thought you said above that you could only get 39A in 24V mode, but 42A (ea) in 12V? Now you're saying 42A in 24V?

That is correct, Ross.  Let me try to explain.

When I installed the panels I wired pairs in parallel and each pair had a 10AWG + and - coming into the solar combiner box.  5 pairs of panels.  The power from the combiner to the bank was typically from 83-84 amps on a good day, at peak.

When I bumped up to 24 volt I went up on the roof and wired each pair series.  That would put out 39 amps or so at peak.

I decided I wasn't getting the power at 24 volt that I got with 12.

So I split the panels into two groups of five each.  Each panel now has it's own 10 AWG + and - coming to the combiner.  My battery bank consists of 24 Group 29 batteries and two Group 8D batteries.  I have a four bar bus.  12 of those batteries plus one group 8D feeds two bars in the bus at 12 volt, and the other 12 plus the other 8D feed the other two bars at 12 volt.  There's only one series connection and that's from the N1 <-> P2 bars in my bus box.  24 volt power is taken from P1 <-> N2 in the bus.

One group of five panels feeds one 12 volt bank, the other group of five feeds the other side of the bank at 12 volts.  I now get right around 42 amps on a good day with the system at 29 volts.

It's important to realize that when you charge a series bank or connection, whatever the ammeter says for current is going to BOTH sides of that series connection.  So feeding 42 amps to each 12 volt side of a 24 volt bank is the same as charging that bank at 42 amps @ 24 volt.

The bottom line is that I get roughly 80 watts more out of those solar panels with the panels in a parallel configuration than I do with them in series.
--
Chris

-edit-
I didn't explain the above very good after I re-read it.  So here's a picture:


I have two big 12 volt battery banks.  One bank feeds the left two bars, the other feeds the right two bars in that bus.  There's a series connection in the bus between the center two bars.  The turbines and inverter are hooked to the outside bars at 24 volt.  The solar panels are hooked to the two left bars and the two right bars at 12 volt.

In other words I can have both 12 and 24 volt incoming power sources as long as I keep the 12 volt incoming sources equal on both sides of the bus.

dbcollins, in another thread on Fieldlines said my system is "cobbled together crap".  He sells Outback inverters and I don't have an Outback screwed to the wall.  But my system stores 34 kWh of usable power from the batteries at full charge down to 50% charge, and it will run my house on battery power alone for three days with no sun, no wind, no generator.  Despite it being "cobbled together crap" it frickin' works, and that's what counts.

[TomW]

In the interest of getting  this thread at least partially back to topical, please take this solar wiring discussion to another, new thread. This one has been hijacked far enough.

Thanks.

Tom

[ChrisOlson]

In the interest of getting  this thread at least partially back to topical, please take this solar wiring discussion to another, new thread. This one has been hijacked far enough.

Well, I'll try to get it back on topic about the pros and cons of various system voltages.

One thing I found out when I went to 48 volt with the Xantrex inverter, and now to 24 volt after being on 12 for so long, is that it's almost impossible to keep batteries perfectly balanced in series strings.  I got my Group 29's connected in groups of four for each parallel string, then that string feeds its respective side of the bus.

Once every two months I pull each string out and check electrolyte, measure the at-rest voltage, then apply a 40 amp load to each battery with my Sun AVR and measure the loaded voltage after one minute.  I record the results on a piece of tape stuck to every battery like this:



I just tested this string and you can see the at-rest was identical and the load test was within .06 volts.  This string of batteries is nine years old this coming June.  Compared to the newer ones that are under 2 years old, they test 11.88 to 11.92 on the load test.  So there's not a lot of difference between the nine year old ones and the newer ones.  When and if I ever find one that falls flat on its face during the load test, or its at-rest voltage is out of whack, I'll pull it out of the bank and charge it individually and restest it.  If it doesn't pass I'll replace it.

But what I've found with series charging is that the two sides of the bank get out of whack by up to .25 volts.  Sometimes it's one side of the bank, sometimes its the other and I haven't found a good explanation for it other than series charging of batteries is not recommended by any battery manufacturer that I know of.

To compensate for my banks getting out of whack with the 24 volt system I bought a marine dual-channel battery charger that I can run off the AC genset.  The dual channels "test" each half of the bank and equalize them.

A long time ago when I emailed my battery supplier about how I should connect batteries, this is what they wrote back to (in part):
First, a parallel system allows more convenient sizes which yields a greater range of systems. For instance, a 100 Ah battery can be placed in parallel with a 200 Ah unit to obtain a total of 300 Ah. Charging proceeds as expected, with each battery receiving its share of the charge current, and each reaching a full charge at the same time. On discharge, each battery supplies current according to its relative capacity, and both batteries maintain the same percent depth of discharge.

Contrast this with two 6 Volt units. With series connected units, each battery must be of equal capacity. That means that you can only build banks in the capacities that the manufacturers decide to build. Despite close manufacturing tolerances, each supposedly identical battery has different capacity and when the specific gravity is different in each, capacity is further affected. Deep discharges of series cells can cause the weaker cell to be reverse charged. A weak cell in a series string can cause other cells to be overcharged. An open cell in a series string results in a total power loss. For best results, 6 Volt batteries should be periodically charged individually and should definitely be equalized individually with equalizing resistors across each 2 Volt cell. This argument extends to 2 Volt cells when they are packaged individually.

In a series connected bank, an open circuit would mean the total loss of power, but a parallel bank will still function, albeit with less capacity. You'd still have enough power for an emergency with a parallel bank. In fact, the failure might be transparent in a poorly instrumented system until a prolonged heavy discharge occurred.

They went on and on, but the bottom line was, avoid series connections in battery banks like the plague.  That makes 24 volt and 48 volt systems extremely expensive because it's hard to find 24 and 48 volt batteries at any decent price.  Parallel connected batteries will last up to 20 years properly cared for.  You'll never get that sort of life from series connected batteries.
--
Chris

[Volvo farmer]

They went on and on, but the bottom line was, avoid series connections in battery banks like the plague.  That makes 24 volt and 48 volt systems extremely expensive because it's hard to find 24 and 48 volt batteries at any decent price.  Parallel connected batteries will last up to 20 years properly cared for.  You'll never get that sort of life from series connected batteries.
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Chris

You realize that each one of those group 29 batteries you own is comprised of six 2V cells in series, don't you?  If you really want to avoid series strings like the plague , you need to build a 2V battery bank. Unfortunately, I have never heard of a 2V inverter, or charge controller. Do you think series strings of cells are OK as long as they are all contained in one plastic case? Because that appears to be what you are saying here.

[ChrisOlson]

[Do you think series strings of cells are OK as long as they are all contained in one plastic case? Because that appears to be what you are saying here.

I didn't say it.  I'm just telling you what Interstate Battery told me.  The interconnects in the cells of a battery are probably better than what you can do externally and keep the cells balanced.  Show me one single battery manufacturer who recommends charging multiple batteries in series.  There's a reason marine-duty battery chargers have two, three or more channels to charge the series battery banks in big boats.
--
Chris

[Madscientist267]

Its not so much an issue of series in and of itself. It's the lengthy strings that cause problems.

A weak cell and a strong cell in the same string will interact negatively with each other. Every cell you add to a series string increases the chances that you'll have a weaker or stronger cell that doesn't play nice with the 'normal' cells.

When you break down a string into smaller strings to charge them, each set of cells gets a more 'comprehensive' (lack of a better word) charge, and this helps minimize balance issues.

IOW, in a string of 24 2V cells (for 48V nominal for example), the odds that all of them are close to 'ideal' is nil. There might be as many as 5 or 6 in the mix that don't quite conform to the rules that the rest of the string is following. Chances are, they're spread out amongst the entire string, so isolating just the cells that need attention isn't practical.

Cutting the string into sets of 6 or smaller cuts down on the interaction between the misbehaving cells, theoretically enhancing overall string performance; 6 cells are MUCH more manageable than 24.

Steve

[rossw]

Show me one single battery manufacturer who recommends charging multiple batteries in series.

A "battery" is litterally "a multiple of series-connected cells". A 12V car *battery* is 6 series cells. A 6V cart *battery* is 3 series cells. A telco site *battery* is 24 series cells. Given that I've never actually seen a battery supplier recommending the disassembly of a battery down into its component parts for charging in a day-to-day application, I'd say I've never seen a single manufacturer who recommends OTHER than charging cells in series.

There's a reason marine-duty battery chargers have two, three or more channels to charge the series battery banks in big boats.

In the telco industry (arguably the largest single user of deep-cycle and standby batteries in the world), 48V battery strings are the norm. Virtually everything works from 48V. Larger sites seem to invariably use 24, 2V cells in series. Small racks (like usually installed at customers sites to keep fibre and other switching gear active) have 4, 12V SLA cells.

In all my years, I've never, ever, seen a single charger that attempts to break these down into smaller chunks. Never seen a charger that attempts to charge a 48V string in 4 12V substrings, or 24 2V cells.

The telco industry makes extensive use of cells that cost $600 and above *per 2V cell*. They also replace them periodically (at manufacturers recommended intervals) even though they appear to be fine. *IF* there was a problem and the manufacturer knew of it, do you think these people wouldn't jump at the chance to get another year, or two, or ten, out of their investment by simply charging them in a "better" way? I mean, telco chargers are generally pretty expensive, clever, precision gear. Far from a transformer, a diode bridge and an ammeter. Temperature corrected, precision monitored and controlled.

I think you're perhaps making a problem where none exists, or making a very minor problem sound like it's the best reason to stick with 12V or lower, when whatever small problem (real or perceived) is far less than the higher current of a comparable power but lower voltage system, would present.

[Madscientist267]

In all my years, I've never, ever, seen a single charger that attempts to break these down into smaller chunks.

It's actually a little more typical of the marine environment, where vibration and other environmental extremes compound the balancing issues.

They're not generally marketed as such, but its fairly common to see them used that way. Each output is isolated from the others, typically as 12V, and so they can be used in close to any configuration imaginable.

In telco, the batteries are in a significantly more controlled environment.

Steve

[ChrisOlson]

In all my years, I've never, ever, seen a single charger that attempts to break these down into smaller chunks.

Well, then I would say you've probably never seen a marine 12/24/36 volt battery charger:
http://marineengineparts.com/shopsite_sc/store/html/page318.html

The telco industry is probably the most wasteful industry there is and they are no model to go by for battery power systems.  They don't run batteries anywhere near as long as off-grid home power systems are going to want to run them.

I think you're perhaps making a problem where none exists, or making a very minor problem sound like it's the best reason to stick with 12V or lower, when whatever small problem (real or perceived) is far less than the higher current of a comparable power but lower voltage system, would present.

Not really, just pointing out problems I've seen with the higher voltage system after being on 12 volt for years and my batteries stayed from being perfect to no more than .05 volts difference during servicing and load testing individual batteries.  For the last three days we've been having power brownouts in our house because the turbine hits 120-130 amps and sometimes over 140 in 55-60 mph gusts, plus 40 amps or so from solar.  During the spikes, due to bank balance issues at at high power flow rates, the inverter goes over-voltage in the .2 seconds it takes for the controller to bring 3 kW water heating elements online for 15 minutes.  The inverter flips out at 34 volts, and the bus hits 40+ before you can snap your fingers when the turbine is pushing 140 amps.  The controller shuts the solar off and applies the turbine brake to bring the voltage back down.  Then the inverter comes online, the water heater comes online, the controller turns the solar back on and releases the turbine brake.

This has been going on steady here for three days.  I never had any of these problems on 12 volt and I handled one hell of a lot more amps on my 12 volt system than I got coming in on 24.  My voltage operating range on 12 volt was only 12.0 nominal to 15.0 peak - 3 volt range.  With that damned series connection in there it's 24.0 nominal to 30.0 peak.  And when the turbine hits high amps the system voltage climb is twice as fast on the 24 volt system, compounded by the series connection.
--
Chris

[rossw]

In all my years, I've never, ever, seen a single charger that attempts to break these down into smaller chunks.

Well, then I would say you've probably never seen a marine 12/24/36 volt battery charger:

No, and I don't much care to. The closest sea is 350km away. And I wasn't talking about 12/24/36V chargers, OR marine chargers.

The telco industry is probably the most wasteful industry there is and they are no model to go by for battery power systems.

Thats an emotive, argumentative and just plain wrong statement.

They don't run batteries anywhere near as long as off-grid home power systems are going to want to run them.

Not because they don't *WANT* to.  They replace cells because they are *REQUIRED* to. Unlike your home, where you can sit and use your laptop until its battery is flat, and eat by a candle-light, telcos have legislative requirements in terms of uptime and system availability. Unlike your battery bank at home, if it goes flat, people don't *DIE*. Telco-land is different. People can and DO *DIE* if their batteries fail.

pointing out problems I've seen with the higher voltage system.
...
For the last three days we've been having power brownouts in our house because the turbine hits 120-130 amps and sometimes over 140
...
During the spikes, due to bank balance issues at at high power flow rates, the inverter goes over-voltage

So you have 12KW of turbine... and what size battery? Sounds to me like you're blaming "bank balance issues" for "inadequate system" design.

This has been going on steady here for three days.  I never had any of these problems on 12 volt and I handled one hell of a lot more amps on my 12 volt system than I got coming in on 24.

You seem to be misunderstanding "watts" and "amps".

You will argue I'm wrong, but I rather suspect that what was happening is that when you had 12V, the cable resistance to your turbine had a MUCH higher effect than you counted on. When the amps went up high, the voltage drop across your cables went up *EXPONENTIALLY*. That is, your spikes were being "softened out" by losing more in your cabling. I suspect *THAT* is the *REAL* reason you are now having problems that you didn't have before.

I don't have 12KW of turbines. But I do know when I run my genset (on those days where I get no wind and little usable sun), I can poke those sorts of power into my batteries and they don't move much further than about 56V at 70A (so thats roughly equivalent to 140A in your 24V system).

My voltage operating range on 12 volt was only 12.0 nominal to 15.0 peak - 3 volt range.  With that damned series connection in there it's 24.0 nominal to 30.0 peak.  And when the turbine hits high amps the system voltage climb is twice as fast on the 24 volt system, compounded by the series connection.

So tell me how 12-15V range on 12V is ANY DIFFERENT to 24-30V in a 24V system? I'd argue that your 12-15V is actually WORSE than my 48V system that only goes up to 56.4V during heavy charging (equivalent to 14.1V). After a 25% discharge my volts have dropped to 47.8V (equiv to 11.95V per 12V chunk).

I'm only a n00b in this game, having lived totally off-grid only since the end of 2004. In that time however, I've had zero downtime as a result of the battery over or under voltage issues you cite. Also, with the arrangement of system components I have, I've been able to completely remove and replace my battery bank *SAFELY* without losing power to the house.

Its as has been said time and again - it depends on what you want to do, how you want to do it, how much you're prepared to spend on it and what your expectations are, as to what's the "best" choice of system voltage. For my money, it was 48V. For my *CUSTOMERS* money, where I am being asked to work on *THEIR* expensive equipment, MSW was never going to happen.

Just because *I* went that way doesn't make it "the right way" for anyone else (even you!). However as has been said before, just because something works *for you* doesn't mean it's automatically the right choice for anyone/everyone else.

Your "mate" before was "advising" to not spend money on a proper inverter, that msw (marketing lie for "barely better than squarewave") was quite good enough, and spend the extra cash on batteries. A very ill-advised suggestion in my view - without knowing exactly what the requirements were.

[ChrisOlson]

No, and I don't much care to. The closest sea is 350km away. And I wasn't talking about 12/24/36V chargers, OR marine chargers.

For pete's sake, Ross.  First off, here in the US my "mate" is my wife.  And she could care less about what sort of sine wave the inverter has as long as the lights come on and her Super Turbo Pro Megwatt hair dryer (by Revlon) works.

You said you'd never seen a charger that breaks a bank down in "chunks" to prevent series charging.  So I just pointed out a link to several of them for smaller boats.  And now you don't want to see it because the nearest sea is 350 km away?  JFC.  I give up.

Where I come from we got a little phrase that describes that; "You can lead a horse to water to but you can't make 'em drink".

So you have 12KW of turbine... and what size battery? Sounds to me like you're blaming "bank balance issues" for "inadequate system" design.

I have 2,860 amp-hours @ 24 volt, which is 68 kWh total storage, 34 kWh usable from full charge to 50% capacity.  My batteries are designed for 50% DOD and I never run them below that.  My turbine is not 12 kW.  It's 2 kW but sometimes it puts out more than that.  12 kW @ 24 volt nominal would be 500 amps, for pete's sake.  Then I WOULD have problems.  LOL!
--
Chris

[rossw]

You said you'd never seen a charger that breaks a bank down in "chunks" to prevent series charging.  So I just pointed out a link to several of them for smaller boats. 

Recheck my quote. I was talking about *THE TELCO INDUSTRY* where strings are almost always 48V.

My turbine is not 12 kW.  It's 2 kW but sometimes it puts out more than that.  12 kW @ 24 volt nominal would be 500 amps, for pete's sake.  Then I WOULD have problems.  LOL!

Dunno where I got 12KW. Doing too many things at one time probably.
If you've got 68 kWh of batteries, thats very similar to what I have. (62 cells, 2V/500AH each).
My current turbine is only 1kW, but one day I'll get this 2.5kW flying, and the 3.5kW of PV is adequate. Either way, I often see over 80A going into my bank, which is within 5% of yours, only configured for twice the voltage. So why do *YOU* see such substantial changes in battery voltage at even lower per-cell currents than I do?

TomW has a 24V system, I recall him saying his new bank is very much "stiffer" than his old bank - I can't help but wonder if either your cells are not in the condition you think they are, or if there are high resistances there somewhere you don't know about?

[ChrisOlson]

So why do *YOU* see such substantial changes in battery voltage at even lower per-cell currents than I do?

The problem arises at times of continuous high output of the turbine so the bank is close to fully charged and hanging right around 28 volts with normal loads on in the house.  My wire run was originally sized for high-output 12 volt turbines and the resistance is under .1 ohm.  My turbine pushes well over 100 open volts at the generator rpm for 130-140 amps.  So when it gets hit by a 60 mph gust the voltage of the bus skyrockets due to the batteries being fully charged.

It takes my controller .2 seconds to react and get the first 3 kW of load online to control it and by that time the bus voltage is already over 40 and the inverter is kicked out.  So at that point the controller shuts the solar arrays off and kicks the brake on on the turbine to stop the voltage climb.  Then the inverter comes back online, the heating load is switched in, the solar comes back on and the turbine brake gets released.

Without that controller shutting off the solar and applying the turbine brake my system would've already been burnt.

My turbine has a geared generator and it builds voltage and amps very fast with just small increases in rotor rpm.  And that's part of the problem.  High-output battery charging turbines in high winds are a whole different ballgame than gensets or solar panels.  Even grid-tied Bergey Excels kick their inverter out in powerful gusty winds and run unloaded with the inverter flashing an overload fault.

I'm just going to have to change my controller timing and thresholds so it starts adding incremental heating load long before the system gets to 29 volts.
--
Chris

[rossw]

My turbine has a geared generator and it builds voltage and amps very fast with just small increases in rotor rpm.  And that's part of the problem.  High-output battery charging turbines in high winds are a whole different ballgame than gensets or solar panels. 

So you're saying that turbine amps are somehow more effective/powerful than genset/PV amps???

*reality check*

I'm just going to have to change my controller timing and thresholds so it starts adding incremental heating load long before the system gets to 29 volts.

Well, yeah. I'd say so. "Proper system design" should take ALL these things into account, otherwise you get exactly these sorts of things happening. That, in my view, isn't a problem inherent with any particular voltage, it's because "all the bits don't play nice together". The whole is more than the sum of the parts, and you need to consider the whole thing while being mindful of each individual part.

[joestue]

i'd like to see some evidence that 4 batteries connected in parallel perform any differently when overcharged beyond the 8 hr rate than they do in series at the same 8hr rate.

complaining that the series connection "doubles" the voltage rise... really?

[Do you think series strings of cells are OK as long as they are all contained in one plastic case? Because that appears to be what you are saying here.

I didn't say it.  I'm just telling you what Interstate Battery told me.  The interconnects in the cells of a battery are probably better than what you can do externally and keep the cells balanced.  Show me one single battery manufacturer who recommends charging multiple batteries in series.  There's a reason marine-duty battery chargers have two, three or more channels to charge the series battery banks in big boats.
--
Chris

the interconnects in the battery is not what keeps them equalized.
even in the case of non identical batteries kept in series parallel strings, it doesn't make any difference.
the batteries will share the current based on internal resistance between the parallel strings but within the series string there will be equal amp-hours gain/loss.
if the stronger cell wears out faster than the weaker than it will essentially normalize.
during the equalizing process you have to dump a significant number of amp hours into the battery, the weaker cells will become fully charged and gas.
this could essentially be an entire 12v battery due to manufacturing limitations, but unless there's a significant (ie 10% difference in amp hours) then it isn't a problem, it just means that equalizing the battery will require that many more amp hours.
If you want to mix and match batteries in parallel strings for an invested situation (ie, you need them to last 10 years), i'd check to see that the short circuit amps per amp hour is the same. this will guarantee that the internal resistance of the batteries are the same, thus they will share current equally.
I would not parallel batteries of different manufactures due to the differing specific gravity, but I would run them in series.
in fact, i'd go ahead fully charge them all.. and dump the acid out, mix it all up, send a sample off to the lab to check for iron, copper, nickel, and other contaminates and then fill them all back up.

no two cells have exactly the same amp hours, but if you parallel enough of them they will average out, this is where cheap batteries will differ and may cause problems.
the technology is 120 years old. about the only thing they do on the line is load test and charge them.
i could see the same amount of acid to the milliliter being injected into each cell of a car battery, but beyond that the only reason you have to limit the number of batteries in series is just a simple case of reliability and statistical failure.

[TomW]

***SIGH****

Apparently thread hijacking is the new Fieldlines Sport.

My apologies to the Original Poster.

Tom

[Madscientist267]

Its bad enough that there's a pissin' contest...

But then there are other posts that make no sense to further cloud the issues.

People, do your homework before laying something out as fact, huh? And READ before you post! Don't just reword something and then think that you're original!

Sorry,  Tom. I don't mean to further hijack this, but it's already FUBAR and doesn't appear to be heading back in the direction of the original post.

Unfortunately, it looks like nominal system voltage belongs on the 'taboo' list after all.

Steve

[TomW]

Thirteen;

My opologies that the supposed adults here cannot understand the simple concept of staying on topic.

I am closing this as a lost cause.

Feel free to re ask this in another thread and we will see if the children can behave.

Tom