Small DIY, Camping/Power Outage Solar System

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RileyB

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#195030 3-Apr-2016 15:36

Hi guys, I had a quick look, but not really sure what to search for, so sorry if there are already threads on this.

I'm looking to make a small Solar/Battery system to power things during blackouts/camping etc. I've seen a few off the shelf system, but they are either lack something I want, or are over the top expensive, or don't have distributors in New Zealand.

I want to be able to to charge phones, maybe have a couple small lights, and most importantly, charge camera batteries. All of those can be done off 12v, saving the cost and in-efficiency's of converting DC to AC, then back to DC again via an inverter.

My idea is to have an 12V SLA battery, 50-100W solar panel, solar charger, then have either a couple car lighter sockets, and use car lighter socket USB adapters, or just have 1/2 sockets, and make my own 12v-5V step down to USB sockets. Then add some kind of 12V DC powered LED lights on decent length cords, and build it all inside a plastic container of some kind.

First, am I being stupid?

Second, has anyone done something like this and can share there experience?

Lastly, some component questions:

-Any suggestion on the size battery I will need, and is it ok to run the same type SLA's in parralell

-Any recommendations on low power Solar charge controller, I've seen several on trademe/Jaycar etc.

-What sort of terminals should I use to hook all these things up?

-Is there such a thing as cheap 12V LED lights?

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#1525228 3-Apr-2016 16:06

You're not going to get cheaper than these for lights - http://www.aliexpress.com/item/Hot-Sale-High-Quality-E27-LED-Bulbs-Lamp-Home-Camping-Hunting-Emergency-Outdoor-Light-For-DC/32436456329.html and there are plenty of 12v PWM solar controllers all over there for a few bucks as well.

Friend tried that but ended up just using a DC to DC converter to charge SLA's up off their car, uses a portable car jumpstarter thing as it was half price at the warehouse, and comes in a carry case with a air compressor for tires and a ciggy lighter socket on it. Solar was just too slow to get anything into it. Their cable for charging off a car doesnt seem to get it full as it has a diode inside the jumpstart box and that means 0.6v less than the car is working at, whereas the DC to DC stepup will overcome that diodes loss and let you charge even when the car is not running and also off any wall wart you find like a laptop one.

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RileyB

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#1525239 3-Apr-2016 17:01

Those lights are definitely cheap!

I don't think my Bike would power anything for long:P

The idea would be that the battery itself would plenty enough for any short outage, and for anything longer that the solar panel could charging up all day. Power consumption shouldn't be to high, just 1-2 phones a day (2000-4000mAh @5v), couple hours of light at night (10 Watts for two lights) and maybe 1-2 camera batteries (2540mAh @11v)

Phone x 2 = 20 Wh

Camera Battery = 28Wh

Lights x2 x2 hours 20Wh

=68Wh before taking into account inefficiencies of chargers, DC to DC converters etc.

I currently have an 12V/7Ah battery lying around which should = 84Wh, although I was thinking of either getting a second, or getting one larger battery to give plenty of spare capacity.

raytaylor

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#1525399 3-Apr-2016 21:21

Standard sealed Deep cycle batteries should not be discharged more than 20% per daily cycle otherwise you will severly damage their life span.

I would recommend a 100 watt panel, mppt controller and 12v 120ah deep cycle battery.

This gives you 288 watt hours.

That equates to

- 2x 10 watt LED lights for 8 hours per night (160wh)

- 12 hours of running a tablet (5v 2ah = 120wh)

On a cloudy day, 8 hours overcast will give you 160 watt hours. So your battery could last 4 days before you enter damaging battery territory if you drop it below 50%

On a cloudy day, an MPPT controller gets double the output from the panel than a PWM controller.

Ray Taylor

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Dynamic

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#1525414 3-Apr-2016 22:12

For camping I bought the largest jump-start pack that I would find (gets used/tested/topped up every 2 months during the year) and a folding solar panel. Good for charging cameras and phones from 12v socket, not much capacity for running anything from an inverter.

For blackouts we have a small 800w inverter generator (The Warehouse jobbie for $400). Very quiet and good for running the fridge and deep freezer for an hour to keep them cold. Run it for half an hour each month to keep it in good order.

We just go to bed when it is dark but I do have 2 of these Energizer solar LED lanterns and a stock of D cells (rated at 150+ hours) http://www.amazon.com/Energizer-Solar-Rechargeable-9-LED-Lantern/dp/B003JIP8VG Very happy with the quality.

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timmmay

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#1525594 4-Apr-2016 10:11

I was thinking about this recently, but never got far with it. I got a couple of good value 30AH batteries, so they could be swapped around. If they fail because they were well used during a major outage, no problem, they'll have done their job.

I'd have gotten a solar panel in the 40 - 120W range from trademe or a local seller ($50 - $150), a cheap charge controller ($25 or so), and some cable. Where I came unstuck is getting this small panel somewhere useful to charge the batteries - though in an emergency I'd probably just lay it on the lawn or the deck, or prop it up somehow.

RileyB

247 posts

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#1525673 4-Apr-2016 10:54

I'll let you know if I get any further then the thinking about stage (no promises). I think I'll use the 7aH battery I have to build and test it, then use it to work out of big of an battery I'll need.

I'm guessing I'm also going to need to build some sort of voltage reader into this to make sure I don't over discharge.

If money wasn't an issue I would buy one of these with an extra panel or two : https://www.goalzero.com.au/shop/category/complete-kits/287

Seems like a great product, but a bit pricy for me.

timmmay

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#1525732 4-Apr-2016 11:47

Solar panel with simple charge controller and a battery much cheaper than that kit, but uglier and less portable. Doesn't really matter if you kill the battery, if you need it you need it.

RileyB

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#1525740 4-Apr-2016 12:03

timmmay: Solar panel with simple charge controller and a battery much cheaper than that kit, but uglier and less portable. Doesn't really matter if you kill the battery, if you need it you need it.

Yeah no way I'm paying that much, I'm hoping to build mine for ~$200.

Also the above packed is with a single 30Watt panel, you can use up to four for 120W, but they also charge about $250 per 30W panel which is very expensive.

timmmay

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#1525751 4-Apr-2016 12:19

I think it was @jeffnz from memory who can sometimes help with batteries. That, charge controller, and a $100 panel and you're good. Even if it's slow charge it should be enough to run phones and led lighting in emergency.

I got USB led camping lights from Amazon, my aa charger can run from 12V. For my led lanterns I have converters that let me put two aa cells into a d cell size, and I have dozens of aa cells from my flashes. Ufb stuff all runs from 12v DC ups, 8ah inline with a 33ah charged and ready to go.

Bring prepared is pretty cheap and takes little time, super useful in an emergency.

RileyB

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#1526063 4-Apr-2016 22:31

Been having a look around, and low Power MPPT controllers doesn't seem to be a thing, and from a bit of research, the 30% more power stated early in this post seems overly optimistic. Actual testing I've seen indicates about 8% more power in Summer, and 20% more at best in Winter.

My current dilemma is weather to spend a decent bit on an controller with fancy bits and bobs and decent bit of capacity...or get something cheap that essentaily does the same job:

http://www.mrpositive.co.nz/solar-battery-charging-regulator-12v-5a/ $25, 12V 5A (60Watts) -Takes power...puts it into the batteries......

http://www.mrpositive.co.nz/morningstar-sunsaver-4-stage-12v-6a-pmw-solar-controller-with-lvd/ - Essentially the same capacity (12v/6A) 4x the price, takes power...puts in battery, maybe a bit more elegantly. Status lights etc, and can turn off the load if battery voltage gets to low

http://www.mrpositive.co.nz/morningstar-sunsaver-4-stage-12v-10a-pmw-solar-controller-with-lvd/ - However at this point, I myaswell spend an extra $40 and get a decent chunk more capacity ($140 12v/10A)

Am I getting a bit carried away here......?

raytaylor

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#1526086 4-Apr-2016 23:51

For those that are interested.

The difference between MPPT and PWM controllers

Take a typical 100 watt (12v) panel and check out the specifications.

Typically the specifications will say something like 18.2v x 5.49 amps = 100 watts in full sunlight.

However if you connect that to a 12v battery using a PWM controller, the output of the panel is reduced to match the battery.

This means if your battery is about half charged, sitting around 12v, the panel will be operating at 12v 5.49 amps = 65 watts.

As the battery charges up, the speed at which it charges will increase. Getting closer to fully charged, the battery will be at 14v so 14v x 5.49 amps = 76 watts

But you will never get a usable 100 watts out of the panel.

This isnt a problem if you can fully charge the battery on a sunny day.
Note this isnt a summer vs winter issue - its a sun vs overcast issue.

Now when the sky is bright but overcast, you will get about 20% of your rated output. The voltage remains the same but the amps drops down.

The 100 watt panel becomes rated at 18.2v x 1.09amps = 20 watts
Connect that to a 12v battery and you get 12v x 1.09amp = 13 wattsAs the battery charges up, it gets up to 14v and so the panel runs at 14v x 1.09amp = 15 watts.

Like I say, no problem if you can still charge your battery up fully during the day.

==============================

Now an MPPT controller

They dont directly connect the panel to the battery. Instead they run the panel through a switchmode transformer. You loose about 1% through this process, but the gains are so much more important.

An MPPT controller can take our 18.2v 5.49 amp panel (100 watts) and step down the voltage, while raising up the amps. This means the power being pushed to the battery is constantly matched correctly, but more amps of power go into the battery. It becomes 12v 8.25 amps (100 watts). As the battery charges up, the MPPT controller changes the voltage and reduces the amps accordingly. 14v 7.07 amps (100 watts) as the battery becomes fully charged.

That is much more efficient at charging a battery. Again, its no benefit if your PWM controller could charge the battery fully in a day.

But how does this change things on a cloudy day???

Again if we assume the panel becomes 20% efficient, it outputs 18.2v 1.09 amps (20 watts)
The mppt controller will convert this to match the battery voltage. 12v 1.66 amps (20 watts)

Thats a PWM 13 watts -vs- MPPT 20 watts difference on a cloudy day.
And that can make a huge difference to your ability to recharge your battery on a cloudy day.

As the battery charges up, our PWM charger gets up to 15 watts, while our MPPT is still at 20 watts. A 25% improvement.

===========================

Further notes

If you use a sealed battery (highly recommended) then the voltage needs to be matched correctly to avoid damaging the battery. A PWM controller will disconnect the battery and reconnect it rapidly to prevent damage and too much gas build up which means you loose more efficiency. An mppt controller can manage the charging voltage by design.

So the question you ask yourself is when the power is cut, will it be a sunny day or a cloudy day? And do you want that extra performance out of the panel?

Ray Taylor

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raytaylor

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#1526088 4-Apr-2016 23:53

Oh if your going PWM then I highly recommend Steca
http://www.mrpositive.co.nz/steca-pr-3030-pwm-12-24v-30a-solar-regulator-with-lcd-display/

They also come under the brand name Fangpusun or something like that. Same company, just made in germany or made in china.

Ray Taylor

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RileyB

247 posts

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#1526156 5-Apr-2016 08:18

raytaylor:

For those that are interested.

The difference between MPPT and PWM controllers

Take a typical 100 watt (12v) panel and check out the specifications.

Typically the specifications will say something like 18.2v x 5.49 amps = 100 watts in full sunlight.

However if you connect that to a 12v battery using a PWM controller, the output of the panel is reduced to match the battery.

This means if your battery is about half charged, sitting around 12v, the panel will be operating at 12v 5.49 amps = 65 watts.

As the battery charges up, the speed at which it charges will increase. Getting closer to fully charged, the battery will be at 14v so 14v x 5.49 amps = 76 watts

But you will never get a usable 100 watts out of the panel.

This isnt a problem if you can fully charge the battery on a sunny day.
Note this isnt a summer vs winter issue - its a sun vs overcast issue.

Now when the sky is bright but overcast, you will get about 20% of your rated output. The voltage remains the same but the amps drops down.

The 100 watt panel becomes rated at 18.2v x 1.09amps = 20 watts
Connect that to a 12v battery and you get 12v x 1.09amp = 13 wattsAs the battery charges up, it gets up to 14v and so the panel runs at 14v x 1.09amp = 15 watts.

Like I say, no problem if you can still charge your battery up fully during the day.

==============================

Now an MPPT controller

They dont directly connect the panel to the battery. Instead they run the panel through a switchmode transformer. You loose about 1% through this process, but the gains are so much more important.

An MPPT controller can take our 18.2v 5.49 amp panel (100 watts) and step down the voltage, while raising up the amps. This means the power being pushed to the battery is constantly matched correctly, but more amps of power go into the battery. It becomes 12v 8.25 amps (100 watts). As the battery charges up, the MPPT controller changes the voltage and reduces the amps accordingly. 14v 7.07 amps (100 watts) as the battery becomes fully charged.

That is much more efficient at charging a battery. Again, its no benefit if your PWM controller could charge the battery fully in a day.

But how does this change things on a cloudy day???

Again if we assume the panel becomes 20% efficient, it outputs 18.2v 1.09 amps (20 watts)
The mppt controller will convert this to match the battery voltage. 12v 1.66 amps (20 watts)

Thats a PWM 13 watts -vs- MPPT 20 watts difference on a cloudy day.
And that can make a huge difference to your ability to recharge your battery on a cloudy day.

As the battery charges up, our PWM charger gets up to 15 watts, while our MPPT is still at 20 watts. A 25% improvement.

===========================

Further notes

If you use a sealed battery (highly recommended) then the voltage needs to be matched correctly to avoid damaging the battery. A PWM controller will disconnect the battery and reconnect it rapidly to prevent damage and too much gas build up which means you loose more efficiency. An mppt controller can manage the charging voltage by design.

So the question you ask yourself is when the power is cut, will it be a sunny day or a cloudy day? And do you want that extra performance out of the panel?

It's nice to know the theory, but just doesn't seem to be any low power MPPT chargers available. I'm pretty sure Winter-Summer does make a difference, firstly because there are tests that shows it does, and because in Winter, with the sun a lot lower, there is a lot more time where the sun is up, but not going to be directly hitting the panels, probably causing the same effect as it being overcast.

RileyB

247 posts

Master Geek

#1526169 5-Apr-2016 08:47

raytaylor:

Oh if your going PWM then I highly recommend Steca
http://www.mrpositive.co.nz/steca-pr-3030-pwm-12-24v-30a-solar-regulator-with-lcd-display/

They also come under the brand name Fangpusun or something like that. Same company, just made in germany or made in china.

That controller is a bit pricey for what I'm after, are the Steca lower end products still recomended (http://www.mrpositive.co.nz/steca-solsum-8-8f-pwm-12-24v-8a-solar-regulator-with-lvd/)?

RileyB

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#1526455 5-Apr-2016 17:55

Bought this one: http://www.mrpositive.co.nz/steca-solsum-8-8f-pwm-12-24v-8ahttp://www.mrpositive.co.nz/steca-solsum-8-8f-pwm-12-24v-8a-solar-regulator-with-lvd/

-solar-regulator-with-lvd/

Seemed like a good balance of price/capacity. $65 for 8A 12/24V

I haven't decided on an panel yet, but they have an 50 Watt unit $92 which seems like a reasonable price and size.

The controller appears to have screw terminals, is ok to just put stripped tinned wires straight in to these, or is better to put the U shaped spades on the cables? I also under stand it is good practise to put an fuse between negative battery terminal and the load connection on the controller?

Is there any other small things that an newbie like myself might overlook?

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