24V panel, 10A CC, but want to run 12V lights etc.

[whazzatt]

Hi

This is a proper start to my solar energy experiment(s), so please excuse my lack of knowledge.

I was given a panel and ended up with a Steca 10.10F (10A) charge controller.

I have attached pictures for info and Voltmeter readings:

1) Panel
2) Panel info
3) V from panel
4) V to battery
5) V to load

The idea is to have a battery to remove when fully charged to take to a cabin at weekends. Can't leave the panel and battery etc. at the cabin due to theft threat.

But as I gather info I see that it's a 24V panel, but I wish to run 12V lights, and recharge a laptop off of a 12V car cigarette lighter connection, when I'm out at the cabin.

Am I correct in thinking that I could put 2X 40Ah 12V batteries in series to work with the 24V panel?

But then running the lights and laptop charger will have to be straight from one battery, right? But in this case, the batteries would deplete at different rates when used one at a time, causing recharge issues.

Also, what can be run from the load at the high V?

I bet someone is gonna suggest just getting 24V lights and laptop charger, but I didn't really want to be tied to 24V goodies...

Clearly I'm a bit confused. Okay, a lot confused. I've spoken to numerous people about this after calls to random companies dealing with solar and I'm none the wiser, so any help will be much appreciated.

Cheers,
dave

[whazzatt]

I suppose I could simply things by asking the following:

Considering my panel and my CC, what battery options do I have to charge a battery pack that will be taken to a cabin to power a few lights and a laptop charger?

Furthermore, how would the wiring work?

[dennis461]

You could do the lights, two in series connected to 24 VDC if they are the same type bulbs.
The laptop charger would need something like this, additional cost and power osses.

http://www.trcelectronics.com/View/Mean-Well/SD-100B-12.shtml

Why not use a 24VDC to 120 VAC inverter for the laptop charger?

What is the make/model of the charge controller in your picture?

[bcroe]

You might use an efficient MPPT charge controller into a larger 12V battery, or a cheap PW controller into a couple smaller 12V
batteries in series. Sticking with 12V means you could use a battery isolator to recharge from your vehicle if solar doesn't keep up
with your needs, similar to RV setups. Avoiding inverters will minimize large losses from idling, and multiple voltage conversions.
Bruce Roe

[PNPmacnab]

If you search ebay for "CC CV Buck Converter 8A" you can get a converter for about $4 if you can wait a couple weeks. Just get a couple and don't use them for more than half the rated power. I use them at my camp. Sometimes you should look a gift horse in the mouth. For years my power system was the vehicle battery, it was a truck with a second battery. Had a power cord out the grill and I just plugged it into my garage which had wiring to the house. Driving during the day would recharge it. You said you want portable. I can't see charging a battery with solar and taking it to a camp. I'd dump that charge controller and keep it 12V. Be aware, many cheap MPPT controllers are not real.

[whazzatt]

Thanks for the replies good people.

@dennis461: it's a Steca charge controller. 10.10F. Thanks for the idea to put two 12V bulbs in series. Maybe 3 sets of those could be dedicated to this system alone.

@bcroe: I already have a cheaper PW controller, so looks like I'll need to match the 24V panel to two 12V batteries in series. Then I could run a few strings of lights.

@PNPmacnab: point taken re. issues with portability. I'm rethinking things.

QUESTION: the output rating on my laptop charger is 19.5V. As pictured in my first post, the load V was 18.9 at full sun yesterday, and early this morning with thick cloud it was 18.6. Do you think I could safely connect the laptop straight to the load with a fuse on the wire to check if the under 19V from the load will work to charge the laptop battery?

Looks like I could use the system elsewhere for now (not at the cabin, as I originally hoped) to power 6 lights, and if the load to laptop works, then to charge that. Great opportunity to learn.

So it would be the 135W 24V panel; the 10A PWM charge controller; 2X 40Ah 12V batteries in series. Running 3 sets of 12V lights connected in series. And maybe a laptop charge direct from load.

Any thoughts?

[dennis461]

First, I totally missed the part in your post where you remove the batteries and then take them to a cabin to use.
If you will always do this (meaning no loads connected while charging) then you simply use one 12 volt battery until it becomes weak, then use the second 12 volt battery.
All 12 volt loads.

If on the other hand, you will have panel-controller-loads all connected; you cannot simply connect a laptop directly a DC source if it was not designed for it.
The laptop power supply (in the 120VAC connection cord) is matched to the laptop battery and no doubt has a variable output voltage and current profile, It may also communicate with the battery/PC (Dell uses a third wire, others communicate over the DC wires). It is not simply 195.V all the time.
If you want to test your idea, I have some old laptops laying around, I could plug one into my single panel and video-tape it for YOUTUBE

Since the laptop does not draw much power, you could connect the cigarette lighter-laptop charger to the 12 volt battery.
I am assuming you have a 12V power supply-adapter for the laptop, although I never found one for my Dell's

If you want variable voltage LED lighting, google this ...12v 24v work light.

[whazzatt]

First, I totally missed the part in your post where you remove the batteries and then take them to a cabin to use.
If you will always do this (meaning no loads connected while charging) then you simply use one 12 volt battery until it becomes weak, then use the second 12 volt battery.
All 12 volt loads.

Dennis, wouldn't this be problematic because the batteries may be depleted to different levels, which then have to be reconnected to each other?

If on the other hand, you will have panel-controller-loads all connected; you cannot simply connect a laptop directly a DC source if it was not designed for it.
The laptop power supply (in the 120VAC connection cord) is matched to the laptop battery and no doubt has a variable output voltage and current profile, It may also communicate with the battery/PC (Dell uses a third wire, others communicate over the DC wires). It is not simply 19.5 (corrected!) all the time.
If you want to test your idea, I have some old laptops laying around, I could plug one into my single panel and video-tape it for YOUTUBE

Sounds like a great idea - go ahead, I'll sure watch the video. But do remember that the panel is pumping out around 38V. I'm talking about the V from the load terminals on the CC, 18.6 to 18.9 ish, which is temptingly close to the 19.5 stated on the laptop power supply. And I'm in South Africa, so 220VAC).

Since the laptop does not draw much power, you could connect the cigarette lighter-laptop charger to the 12 volt battery.
I am assuming you have a 12V power supply-adapter for the laptop, although I never found one for my Dell's

Um, well, no, I don't have one but kinda assumed...

[whazzatt]

I sent off this email to Steca:

I bought a Steca 10.10F charge controller. I wish to connect this to a 24V panel. My question is, can I use a 12V battery and will the charge controller control the voltage so that there is compatibility between the 12V battery and the 24V panel? Or do I have to use 2 batteries in series to match the panel V to the battery V?[/QUOTE]

Reply:

yes it is possible to charge with a 24V panel a 12V battery. You have to keep the correct connection order in mind. Always connect the battery first ! So the charge controller detects the system voltage correctly and then can limit the incoming voltage from the panel (which you connect next), to charge the 12V battery properly. (Etc. - problems with copy-pasting rest of reply for some reason)

[dennis461]

Let's start over, your controller can be used to charge 12 or 24 volts battery with automatic voltage detection.
(Instruction manual says to connect battery first, then panel, then load.)
If I am reading the literature correctly.
So all the 12/24 volt battery discussion goes out the window...

http://www.steca.com/index.php?Steca-Solsum-F-en

I am using a similar device, CMTP02 with 24V battery bank.
If it warms up , tomorrow, I'll re-configure to two 12V batteries in parallel and try it out.
FYI, connecting batteries can get scary if done wrong

[whazzatt]

So all the 12/24 volt battery discussion goes out the window...

Yes. But I have got closer to action: I now know that one 12V battery is an option. And also that several lights and the occasional laptop charge is about all I can expect to power from this. Which is great in my opinion, considering that the panel was given to me and that the charge controller was cheap.

Now... what size battery to get...

[Sunking]

Everything you want to run is 12 volts right? Why are you using 24 volt battery? Just because you have a panel that says 24 volts does not mean you must use 24 volt battery. Any decent MPPT charge controller will work on a 12 volt battery just fine.

Secondly if you have to take the battery home with you, Solar is a complete waste of your money and takes way to long. Just buy a decent battery charger. A whole lot less expensive and does a lot better job in a few hours rather than DAYS.

[whazzatt]

Sunking, I never wanted to run a 24V battery, and as said in the first post, I am interested in 12V lights and chargers. However, I was under the impression (based on mixed feedback from different people working on solar shop-floors where I live) that I would have to match the 24V panel with a 24 battery bank. In fact, here's an email response from one person who was willing to communicate further with me: "According to the information I would suggest you connect your batteries in series which will give you 24V as per the whole system." And "I highly recommend sticking to a 24V system." His emphasis!

But now it's clear that I just connect the 12V battery to the CC first, and the 24V panel thereafter, and the V will sort itself out. And this with a decent PWM controller.

I'm aware of the issues with portability and recharging etc. but for me this is part of a learning curve. The cabin is on an off-grid plot, so eventually I'll need to get a bigger system. Gotta start somewhere. I'll use it at my current abode for a while and see what happens.

[Sunking]

highly recommend[/B] sticking to a 24V system." His emphasis!

How is that working out for you?

But now it's clear that I just connect the 12V battery to the CC first, and the 24V panel thereafter, and the V will sort itself out. And this with a decent PWM controller.

Do you know the consequences of your actions?

If you have a 130 watt 24 volt battery panel like you have, with a PWM Controller like you have, with a 12 volt battery like you have; you are the proud new owner of a 50 watt system. Not the 130 Watts you thought you had. However with a 24 volt battery with you rpanel and controler can get up to 90 watts from a 130 watt panel. That is what you get using cheap PWM controllers.

If you want your 130 watt panel to actually be a 130 watt panel will require a $200 MPPT Controller which can handle up 200 watt Panel of any voltage. With a 200 watt panel and MPPT controller gives you 15-amps of charge current. Both a 200 watt panel and 15 Amp MPPT Controller will cost you roughly $400 to $500. If the battery is sized properly will take 5 days to fully recharge the battery you are lugging around.

Or you could have spent less than $50 and bought a 20 amp 12 volt battery charger that will fully recharged the battery in 10 hours or less. Only down side is you would have more weight in your pockets from all the money you would have saved. Your salesman did a real good job. He took all that extra weight out of your pockets. Be sure to send him a Xmas card.

Here is some golden info for the next time. Some simple math.

For a PWM Controller Input Current = Output Current. Your panel maximum output Current = 4 amps. Power = Voltage x Current. So you have a 12 volt battery x 4 amps = 48 watts. Look at your Panel Specs, Vmp = 32.2 Volts and Imp = 4 amps. Do the math. 32.2 volts x 4 Amps = 128.8 watts

With a MPPT Controller Output Current = Panel Wattage / Battery Voltage. Do the math. 130 watts / 12 volts = 10.8 amps. Math is is fun and tells the truth every time. It is the only thing on earth that will not lie to you.

[whazzatt]

Sunking, thanks for the helpful info.

Not all of it is helpful though.

There is no salesman.

The panel was a gift from an acquaintance.

The CC was a bad purchase a couple of years ago. I see it's $55 on US amazon now. This is the total I have spent - my pockets feel fine.

I have not yet purchased a battery.

Sounds like you may need a Xmas card. Here's a start - cheesy but oh well:
sw-00485.jpg


The golden info is golden though - it will be used for next time. And no, I didn't know that the consequence was a 50W system. This forum process constitutes the figuring out of such things in this instance.

The battery charger from AC does indeed sound like a good idea. But remember that I'm dipping a toe into water here as far as solar goes. If I use an AC charger for the battery, I still have to get a battery, and pretty much for the cost of some cabling and clips I have the option of charging the batt off a 50W system, which is better than no system. In this case I only have to purchase one battery, again for the sake of experiment, maybe for the sake of some battery back-up (power outages are common here in South Africa). If I take the 2-batts-in-series route, I will have to purchase 2 batteries, which is not needed at this point, though I get that it would make the system more efficient. Anyhow, the pockets feel completely fine.

I am openly and admittedly a dumbass in this arena. I'm a humanities guy. I think it's comments like "math is is fun and tells the truth every time. It is the only thing on earth that will not lie to you" that must have been (and remain) instrumental in putting me off math somewhere along the line