Need guidance on design of tiny, but complicated, remote 12V solar system

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Need guidance on design of tiny, but complicated, remote 12V solar system

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Started 6 years ago by karmacoma
Latest reply from karmacoma

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karmacoma
Member

I'm getting ready to stay a while in my wife's remote Pacific Island village. I want to add to the tiny 12V solar system we already have there. I know what the goal is, but I am not certain about what I need to do. I would love some comments.

What we have: 40W 12V panel supplying about 10W LED lights, via an old Plasmatronics 1206 6A regulator (on a fused switchboard with voltmeter and ammeter) and car battery. Car batteries are all we can get there, and even they are expensive. It's run for four years like that and the battery is still holding up ok. Obviously with such a wrong battery, it's a delicate system, and I don't want to disturb its life chances.

What we want to do: take over two permanent magnet 18V 36W fans, a 100W panel, a 9.5V 24W netbook (old tiny laptop) and maybe a 7.2Ah SLA battery dedicated to the netbook. The old 6A regulator won't cope with 140W panel output (or whatever we really get - but I guess it would be up around 10 or 11A sometimes). Could buy a new regulator, but I'd prefer not to. Same with more batteries - prefer not to. So it gets a bit devious here.

What I'm thinking (here's where I need some feedback):

1) run the two fans direct from the 100W panel. When it shines they go like blazes, when it's dull, they stop. We don't need them running via a regulator and battery. They soak up energy, so that even if the 100W panel is also connected to the existing 40W panel, the balance of the current after the fans (about 70W) can still all run through the 6A regulator (if I have to, I'd buy a 10A Plasmatronics 1210 regulator, easily installed because it has the same form factor as the old 6A one - just for headroom in case the fans stop working as a load dump). Is my logic correct here?

2) Run the netbook via its 9.5V DC charger which plugs into the 12V 7.2Ah SLA battery, which is itself charged from the car battery. I'm hazy about this. I know I don't want to load the fragile car battery with extra night-time demand. Hence the 7.2Ah SLA, which can be charged daytime but can be isolated from the system at night if I want to use the netbook. Would I need to regulate the charge from the car battery to the 7.2 SLA? Or would it be happy just connected directly to the car battery terminals? Is there anything else that's wrong with this idea, or that I need to know?

I'd really appreciate some guidance.

Posted Wednesday 26 Aug 2015 @ 1:45:35 am from IP #
scott drew
Member

Comment on point 2. Are you manually connecting bith batteries together so you can manually disconnect them for night time use of computer leaving the original battery alone at night?

May it be feasible to include an automatic solenoid type dual battery charger into the system? That way you permanently connect the two batteries together with the dual battery charger and when not charging both batteries the second battery will be automatically disconnected from the first.

4wd places will have these dimple devices or I csn recommend a website via PM to a guy who deals in 4wd electronic 12v gear. He's based in queensland and oosts items wuickly and is reasonably priced.

Posted Wednesday 26 Aug 2015 @ 4:57:17 am from IP #
karmacoma
Member

Scott, although those are convenient devices, I won't get one at this stage. We have to keep the system as simple as can be, and that will mean manually isolating the SLA battery at night, if running the computer. That is, if what I'm proposing will work.

Posted Wednesday 26 Aug 2015 @ 6:35:50 am from IP #
scott drew
Member

Yep fair call. Unfortunately im unable to help with point 1 though. Maybe you could call the ata office and see if they will be able to contact someone that can help? This situation is similar to what the ata was/is doing overseas. Can't exactly remember but Timor comes to mind?

Not sure if there's some threads of similar topics where you could PM someone too.

Posted Wednesday 26 Aug 2015 @ 10:33:01 pm from IP #
karmacoma
Member

Thanks Scott. I think my question would have attracted more interest back when very small solar was in vogue back in the 80s and 90s. Unfortunately it now seems to be outside most people's concerns here in Australia - nobody has to do anything on a shoestring anymore (we are all rich now) and nobody bothers with car batteries and sub-1kW systems. I'll just have to cross my fingers and hope it works. Thanks for your interest!
Ian

Posted Thursday 27 Aug 2015 @ 9:36:38 pm from IP #
rockabye
Member

Actually karmacoma there is still plenty of interest in small simple solar it's just that larger systems are so inexpensive compared to a few years ago. The shoestring approach is what we need more of. So much power is wasted we could run another country with what goes down the drain.

Your idea with a separate SLA 12V battery is good as these are usually very reliable and often take a lot of punishment which is exactly what you need where you are going. They don't like overcharging though so a regulator is needed. I use these everywhere including on an ebike, running cordless drills with a non replaceable battery, USB charging via adaptors, you name it.

I'll think on this a little more and follow up.

Posted Thursday 27 Aug 2015 @ 9:48:40 pm from IP #
rockabye
Member

Solar systems are simple in principle but a lot of info has to be 'known' before good decisions can be made. There are entire books written on this subject and the ATA webshop may sell some or you can go to the library. It just isn't possible to deliver the amount of information you actually need in this type of forum however here is a small taste of where to begin.

First up your post has a heading relating to 'guidance on design.....' of a small 12V solar system. Fortunately the basis of solar system design is quite similar whether it be large or small. A grasp of the maths involved goes a long way towards determining what to do and what to buy.

You have already decided what you want to run from the system and what can seem like small system loads often end up being much bigger than a 'small' system can deliver. Step one is to try and keep all units of measurement the same for each part of the system. Step 2 is to determine how long each load is going to run. An example of calculating loads is given below.

The specified 24W netbook is being supplied from an 85Wh (12V X 7.2Ah theoretical maximum) battery. In practice this should give around 2 hours at 24W of safe use (48Wh) before needing to be recharged. However to recharge the battery at least 60Wh will be needed to account for conversion and recharging losses. If a longer runtime is needed it would be preferable to either have a larger SLA battery or use it when it is connected to a charging source such as a solar module.

Posted Friday 28 Aug 2015 @ 5:36:21 am from IP #
karmacoma
Member

Thanks Rockabye. I'm a little bit ok with basic design of a 12V PV system - the original system we have of a 40W panel driving a few LED lights (I forget the total wattage of those lights - I think it was about 5 or 6 watts all up), and a design load of 3 hours a night if it has been reasonably sunny, and less if it's cyclonic conditions (little sun) was all formally calculated by me to keep the car battery >80% charged, and the result has been 4 years of running from the 140Ah car battery. Wasn't supposed to get that kind of life from the kind-of-battery-one-shouldn't-use, but it has. And that included training the users, none of whom had been fortunate enough to get more than primary school education, in the concepts of balancing charge and discharge, and what decisions to make based on voltmeter readings. So I pass PV 101.

But the problems I face now are not the textbook straightforward situation like that described above. I doubt I'm going to find a textbook that addresses these problems, they are too one-off.
- Firstly, that thing about splitting the daytime load between fans (a load dump), and a 10A regulator into batteries. But the more I think about it, I can't see why not do that. The panels will together generate total of 11.7 amps in ideal conditions, probably less, fans use maybe 5A of that, and the rest goes through the 10A regulator to the battery. So unless I've overlooked something, I take it that will work.
- Secondly, charging the 7.2Ah SLA battery (I can't get a bigger one into my aircraft cabin bag, that's prescribed by regulations - it will have to do) from the car battery, for evening use. I assume that the SLA won't see the fluctuating voltage from the panel, because that's already smoothed out by the PV regulator. So the issue with it is probably only that the battery specs say the charging current must not exceed 1.2A, so I will need to put in a calculated resistance. I've been given an idea to use a small light bulb, the wattage being about 10% of battery capacity x 12V, and disconnect the SLA when the light bulb goes out (voltages then being equal, so means SLA battery is charged). That's all I will do if I get no further feedback, but again I may have missed something.

Posted Friday 28 Aug 2015 @ 10:22:22 am from IP #
rockabye
Member

karmacoma said:
Thanks Rockabye. I'm a little bit ok with basic design of a 12V PV system - the original system we have of a 40W panel driving a few LED lights (I forget the total wattage of those lights - I think it was about 5 or 6 watts all up), and a design load of 3 hours a night if it has been reasonably sunny, and less if it's cyclonic conditions (little sun) was all formally calculated by me to keep the car battery >80% charged, and the result has been 4 years of running from the 140Ah car battery. Wasn't supposed to get that kind of life from the kind-of-battery-one-shouldn't-use, but it has. And that included training the users, none of whom had been fortunate enough to get more than primary school education, in the concepts of balancing charge and discharge, and what decisions to make based on voltmeter readings. So I pass PV 101.

*** That's a relief Actually what you have discovered is that with good measurement and battery management any battery life can be extended. My refrigerators run on a 24V system with batteries long past their use by date.

But the problems I face now are not the textbook straightforward situation like that described above. I doubt I'm going to find a textbook that addresses these problems, they are too one-off.

*** All problems are one off but the maths and principles involved are identical. Calculate the watts in/out as required. Minimise the loads using the most efficient method ie LED lights +1, maximise energy in.

- Firstly, that thing about splitting the daytime load between fans (a load dump), and a 10A regulator into batteries. But the more I think about it, I can't see why not do that. The panels will together generate total of 11.7 amps in ideal conditions, probably less, fans use maybe 5A of that, and the rest goes through the 10A regulator to the battery. So unless I've overlooked something, I take it that will work.

*** Sounds simple but some 'experimentation will be needed here. The fans will draw down the solar 'output' if placed before the regulator. First up a diode is required to each fan and as silly as it sounds a long run of wire to each fan will act as a current limiter to them making them run a little slower. The thinner the wire the more resistance = less current/watts. Make sure a switch and fuse is in series with each one so you can turn them off individually as required to see what effect each one has.

- Secondly, charging the 7.2Ah SLA battery (I can't get a bigger one into my aircraft cabin bag, that's prescribed by regulations - it will have to do) from the car battery, for evening use. I assume that the SLA won't see the fluctuating voltage from the panel, because that's already smoothed out by the PV regulator. So the issue with it is probably only that the battery specs say the charging current must not exceed 1.2A, so I will need to put in a calculated resistance. I've been given an idea to use a small light bulb, the wattage being about 10% of battery capacity x 12V, and disconnect the SLA when the light bulb goes out (voltages then being equal, so means SLA battery is charged). That's all I will do if I get no further feedback, but again I may have missed something.

*** The same physically sized battery is available in 12V 9Ah capacity. Slightly heavier of course but I use these in preference to the 7Ah. Every little bit is going to help in your situation. Take 2 if you can.

It is possible to charge these simply by connecting them in parallel with your car battery with a couple of small jumper leads. Disconnect them once the system voltage gets to 14V or more.

Once again some more experimentation. Yes a 21W 12V incandescent light bulb will do. This is a 'current limiter' but isn't really necessary unless the battery is completely flat. You can buy these as a 12V work light with alligator clips from auto shops. Once the light dims connect the battery directly to the big one to maximise the charge voltage.

By the way these devices are fantastic and cheap to buy without the Anderson plugs. I use them everywhere I can.

http://www.ebay.com.au/itm/ANDERSON-PLUG-12V-4X4-VOLT-METER-BATTERY-CAR-FRIDGE-MONITOR-SOLAR-AGM-WATTMETER-/121452965286

http://www.ebay.com.au/itm/Jayco-LED-Volt-Watt-Current-Meter-12V-Battery-Solar-Caravan-4x4-Camping-4WD-Boat-/261517831159?hash=item3ce3ad6bf7

Solar 101 - If you can't measure it you can't manage it.

Posted Friday 28 Aug 2015 @ 9:42:24 pm from IP #
rockabye
Member

Remote control speed controller looks like a handy thing as well. Voltage variable up to 24V and 12Amps load control.

http://www.ebay.com.au/itm/LED-RF-WIRELESS-REMOTE-DIMMER-12V-BATTERY-JAYCO-CARAVAN-CAMPING-/261451629747?hash=item3cdfbb44b3

Posted Friday 28 Aug 2015 @ 11:10:58 pm from IP #
karmacoma
Member

Thanks Rockabye. What you say about adjusting the fan current to ensure the regulator sees some current checks out. The fans have rotary potentiometers for speed control that also act as on/off switches. I have an ammeter on the system control board that monitors regulator input current, so I should be able to adjust the load nicely. But maybe I should take a handful of 2A fuses for the fans, until I get the hang of it. If that's what you were getting at, its a good point.

Worst-case, I am just hoping that if both fans go offline while the panels are producing maximum power that the 10A Plasmatronics 1210 regulator will handle it. I'm assuming the "140W" of panels will in reality never produce more than a bit above 10A (temperature, aging, dust). But its a pity Plasmatronics haven't kept up with the availability of now-cheap high output 12V PV panels, by adding a 20A version to their range of basic resin-block regulators.

I will need (actually, already have, in the control panel with the regulator) a reverse blocking diode on the battery +ve for prevention of night-time discharge through the panel, but what would be purpose of a diode to each fan? I don't understand that.

The plane company has a rule that SLA batteries must be ≤12V and ≤100Wh, so 9Ah would exceed the limit. They do allow two batteries though and I will consider whether to take two. Low Energy Developments in Preston Vic have cheap ($20) 12V 7Ah that, by their figures, would over the long term handle 1 hour each at 2A, so with two I'd get two hours netbook time at night.

Thanks for all your considered input, I really appreciate it. Its so good to be able to bounce ideas off someone.

Posted Friday 28 Aug 2015 @ 11:36:41 pm from IP #
karmacoma
Member

Rockabye, those low-voltage wattmeters that you have linked to on eBay look superb.

Posted Friday 28 Aug 2015 @ 11:45:46 pm from IP #
rockabye
Member

karmacoma said:

Worst-case, I am just hoping that if both fans go offline while the panels are producing maximum power that the 10A Plasmatronics 1210 regulator will handle it. I'm assuming the "140W" of panels will in reality never produce more than a bit above 10A (temperature, aging, dust). But its a pity Plasmatronics haven't kept up with the availability of now-cheap high output 12V PV panels, by adding a 20A version to their range of basic resin-block regulators.

***** The Plasmatronics PL20 is still available. It includes a digital display and data logging built in. I have been using one since 1998 and no problems yet. Expensive but good quality. Load terminal is programmable for low volts cutoff or gen control etc

http://store.energymatters.com.au/pl20

I will need (actually, already have, in the control panel with the regulator) a reverse blocking diode on the battery +ve for prevention of night-time discharge through the panel, but what would be purpose of a diode to each fan? I don't understand that.

**** The diodes will act as a crude isolator for each fan stopping back EMF if any.

The plane company has a rule that SLA batteries must be ≤12V and ≤100Wh, so 9Ah would exceed the limit. They do allow two batteries though and I will consider whether to take two. Low Energy Developments in Preston Vic have cheap ($20) 12V 7Ah that, by their figures, would over the long term handle 1 hour each at 2A, so with two I'd get two hours netbook time at night.

****** The 9Ah batteries are really 100W in practice but it's up to you.Can't beat that price. Buy 3

Thanks for all your considered input, I really appreciate it. Its so good to be able to bounce ideas off someone.

Posted Saturday 29 Aug 2015 @ 6:32:11 am from IP #
Oilburner
Member

karmacoma said:

The plane company has a rule that SLA batteries must be ≤12V and ≤100Wh, so 9Ah would exceed the limit.

Can you not post or courier a larger battery? I appreciate it may not be cheap but I would think the cost may be well offset by the benefits and advantages.

What about Lipo's? Lot of capacity for the weight and not all that exy now either.
They sell them on fleabay so get them sent direct.

Posted Saturday 29 Aug 2015 @ 8:22:49 am from IP #
karmacoma
Member

That tip about diodes on the fans to prevent back EMF is exactly the kind of thing I would never think of. Great, thanks.

What diodes would you use for the fans? I see 1N5400 and 1N5822 diodes, but wouldn't know which is better - or maybe I should be getting something else.

It occurs to me too that I will need to upgrade the blocking diode to the panels because it is about to become a "12A" system (or 10A anyways). I've searched Element14 (I have to order various other unrelated bits and pieces, might as well get the diodes from them too), but not finding anything, due to not getting the right keywords. Any clue what to look for there?

Posted Saturday 29 Aug 2015 @ 8:59:33 am from IP #
rockabye
Member

The 1N5400 should be ok to 3A which is just big enough.

Unfortunately the 15A 45V Schottky Diodes are all from China on ebay so a delay in getting them.

http://www.ebay.com.au/itm/5PCS-15A-45V-15SQ045-PEC-schottky-barrier-diodes-for-DIY-Solar-Cells-panels-/261838492583?hash=item3cf6ca53a7

Are you committed to a 140W module?

Then again maybe these.

http://au.element14.com/multicomp/mur1520/fast-recovery-diode-15a-200v-to/dp/1857531?&CMP=KNC-GOO-DSA-e14&mckv=sY4krAXrl%7Cpcrid%7C83439950088&gclid=CNb-sridzscCFUhvvAodlWUOWA

http://www.farnell.com/datasheets/1239100.pdf

More reading here suggests they are ok.

http://www.eicsemi.com/back-office/downloads/Solar_v2A.pdf

Posted Saturday 29 Aug 2015 @ 11:51:47 am from IP #
karmacoma
Member

Following your lead, I found a few pdf datasheets for 'solar' Schottky rectifiers. The best is called "15SQ030 thru 15SQ100 Photovoltaic solar cell protection Schottky rectifier"
(http://bruckewell-semi.com/pdf/15SQ030-15SQ100.pdf)

This one was also interesting: "Solar Cell Bypass Diodes in Silicon Crystalline Photovoltaic Panels" (http://www.vishay.com/docs/89398/solarcell.pdf)

Mostly these publications talk about blocking diodes. However there was this helpful note in "Power Rectifiers for Solar Photovoltaic Applications"
(http://cms.nacsemi.com/FranchiseDocs/TaiwanSemi/PowerRectforSolar.pdf)
"Blocking diodes and Bypass diodes are NOT the same application. Often the actual diode type is the same, but serves different purposes."

I take it then that I can use a Schottky bypass diode as a blocking diode. So I found two similar axial types that appear to fit the right specs at Element14:
1. http://au.element14.com/vishay-semiconductor/vsb1545-m3-73/diode-rectifier-15a-45v-p600/dp/1864886
(and see its datasheet "Vishay VSB1545-M3 Photovoltaic Solar Cell Protection Schottky Rectifier", http://www.farnell.com/datasheets/1839052.pdf )
2. http://au.element14.com/taiwan-semiconductor/sr1504/diode-rectif-40v-15a-r-6/dp/1863151

Posted Saturday 29 Aug 2015 @ 1:32:42 pm from IP #
rockabye
Member

You may also be interested in these devices to 'simplify' you solar system. Something I also use to run DC devices like laptops wanting 19V etc. Very cheap to buy.

Basically these will run very efficiently from your 12V battery and allow for higher voltages to run your 18V fans or even recharge your SLA batteries.

http://www.ebay.com.au/itm/High-Quality-10-32V-Step-Up-to-12-35V-DC-DC-Boost-Converter-Voltage-Regulator-/281686153518

Posted Sunday 30 Aug 2015 @ 10:07:21 pm from IP #
karmacoma
Member

I had one of those DC-DC step-up power supplies - an expensive one - running my 19V laptop (my other laptop) off 12V batteries in Solomon Islands a while ago. It got so hot you could fry eggs on it. In the event, it just fried the battery - i.e. it consumed too much power. That is why I am going through all the contortions of direct-supply to the fans and using a 9.5V laptop, to avoid things like inverters and DC-DC switchmode devices.

Mind you, it remains to be seen if the 12V to 9.5V charger I am making for my netbook (a NZ design - https://web.archive.org/web/20130511024750/http://www.marlwifi.org.nz/projects/asus-eee-car-charger ) will be all that much more efficient.

Posted Monday 31 Aug 2015 @ 12:32:41 am from IP #
rockabye
Member

Yes they can run hot but if you keep the load below 20-30 watts they work well especially at that price. Ideal with one of those watt meters on the input side to measure actual watts used and amp hours out of the battery.

For a laptop I use a Macbook air which runs on about 8 Watts all thought the newer ones use even less. And it only weighs 1kg so is ideal for travel. This is where efficiency really starts to come in to play. Even charging from AC it is only using around 15W.

An ipad is even better and charges from a usb port.

I agree that the simpler the better though.

Posted Monday 31 Aug 2015 @ 3:20:58 am from IP #
karmacoma
Member

The future seems bright for tablet devices that will run a full desktop OS, at low power and voltage. I imagine I'll eventually end up with one once they become mainstream. So the writing is on the wall for my old 9.5V netbook, but it will have to do for now.

Posted Monday 31 Aug 2015 @ 8:16:50 am from IP #

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