Solar novice questions

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Rikkitic

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#213847 14-Apr-2017 21:02

I have decided to dip my toes into solar energy for the first time and have a couple questions relating to my intended project. To start with, I only want to use a small panel to trickle-charge a car battery to operate two small electronic devices. The devices in question are my Huawei B315 RBI router and an IP phone adapter. The Huawei needs 12 volts at 1 amp and the phone adapter requires 5 volts at 2 amps.

To keep things simple, I just want to run the Huawei and phone adapter from a 12-volt car battery and use a solar panel to top the battery up. At this stage I don't want to get into UPS devices or various switching circuits or other automated paraphernalia. Cost is also a factor.

If the power fails, the router and adapter could be manually switched over to the solar system or they could run from that all the time. I haven't decided but the latter case would probably require a larger solar panel to keep the battery from running down at night.

The system would also require a voltage regulator and this is one of my questions. Devices like the Huawei and the phone adapter are sensitive electronic devices. Batteries require charging voltages higher than the battery's nominal 12 volts. Does the regulator ensure that the equipment receives the correct voltage regardless of what the solar panels are doing? I don't want to fry something.

Suggestions and other ideas are welcome. I am kind of feeling my way along here.

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#1764536 14-Apr-2017 21:23

This may help. I have one. Works well.

I also have a solar panel, solar regulator, and small bank of batteries. They're not connected to the Sentry lite, but if the power goes off I could carry them in. I could connect them, but I don't want to. I suspect if you use the device above, a solar panel, and a solar regulator it should be ok - but I'm half guessing.

I have this, 40W version of this, plus cables and connectors. Mine sits in a window, but if you want to maximise power it needs to get full sun.

Rikkitic

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#1764627 15-Apr-2017 09:27

Thanks for the links Timmmay. This is useful information.

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timmmay

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#1764703 15-Apr-2017 13:23

Let me know if you have questions, will reply sooner or later, bit busy this weekend. I know a little.

Rikkitic

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#1764732 15-Apr-2017 14:05

Thanks for the offer. I expect most people are busy over Easter so I'm not in a hurry for responses but I do have a question to start with.

You have pointed me in some good directions and I have already learned a lot as a result. I think my preferred set-up would be a battery receiving a constant charge from the solar panel. I would then want the battery to be constantly supplying the router and phone adapter. This way everything works all the time and nothing has to be manually switched. The devices don't require a lot of current so it should not be difficult to come up with a battery/panel combo that would supply enough charge to get through a night or two and a few days of cloudy weather. If the battery voltage drops too low, it is an easy matter to simply plug the devices into the mains until things improve. This seems like a pretty good compromise between the practical and the ideal.

The problem I have run into is that the delicate electronic devices require a steady supply voltage and even if they are connected to the load output on the solar controller, they will still probably see the same voltage fluctuations that the battery does as it charges. A 12 volt solar panel may go as high as 14 volts and this would not do the electronics any good. So I need a voltage regulator to protect them.

I thought that would be a simple matter but every voltage regulator I can find only works if the supply voltage is at least 1-1.5 volts higher than the output. That would be okay if the voltage on the battery actually is 14 volts, but most of the time it will be lower, especially if the battery is charged. Normal operating voltage is only about 12.6 volts I think, and that is too low for any 12-volt regulator I can find. The only thing that would work is a low dropout regulator, but I cannot find any operational devices, just components. I really don't want to have to try to build this myself so that is my question. Where can I buy a working ldo regulator or is there another answer?

Something to think about over Easter maybe. Thanks again or any help.

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huckster

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#1764736 15-Apr-2017 14:28

I have a similar setup but the goal was to power a Raspberry Pi which is 5v.

An alternative would be to go for a 24v solution (PWM and battery) with a DC converter to take the 24v down to 12v.

Then there are things like...

https://www.jaycar.co.nz/12vdc-3a-car-power-adaptor-with-usb-outlet/p/MP3671

andrewNZ

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#1764742 15-Apr-2017 15:01

Time to look at some ~~real~~ numbers. I started looking into solar a year or two back, but so all of what I have to say is only theoretical. I haven't to date built the planned project. I'm also going to use maths friendly numbers for calcs, because it's easy and because I cant be bothered finding out the real ones ATM.

First, your devices won't draw what their power supplies are rated for. If they did, you'd be looking at somewhere in the vicinity of 2Amps at 12Volts. If you're lucky, you'll need 1A, but probably closer to 1.5A. Lets work on 1A for these calcs.

At 1A, in a 24 hour period your gear will use 24Ah (Amp hours). So we'll start with a 24Ah battery for giggles. That'll get 24hours running with no charging.

A solar panel will need to supply the devices and charge the batteries during sunlight hours. Let's say the solar will have the equivalent of 12 hours of full rate charging in the summer. You'll need a panel good for 2A just to keep up.

In the winter panel output drops to 20%, so now you need a panel good for 10A to keep up with device draw and charging.

On cloudy days panel output drops to 20%, that's 5% output on a cloudy winter day, so to keep up with that the panel would need to have a 50A output.

Of course there is the option of increasing the battery size, that will take the sting out of the crap days. So you have to work out what a good balance between batteries and solar is.

For my project, I said I wanted to tolerate 5 crap days in a row, and recover fully from that in 3 days.
So. In your case, that'd be a 120Ah battery (a car battery is about 50Ah), and a panel good for 16A charging thats 200Watts of panels.
(All assuming 1A at 12V draw)

Using my dodgy numbers and maths, we can do some quick pricing off AA Solar (cause thay're easy to find prices). You're looking at around:

$300 for a 200W panel
$200 for a MPPT charge controller
$320 for a 130Ah battery
$820 total

Edited for clarity

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andrewNZ

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#1764743 15-Apr-2017 15:07

huckster:
I have a similar setup but the goal was to power a Raspberry Pi which is 5v.

An alternative would be to go for a 24v solution (PWM and battery) with a DC converter to take the 24v down to 12v.

Then there are things like...

https://www.jaycar.co.nz/12vdc-3a-car-power-adaptor-with-usb-outlet/p/MP3671

Keep in mind, every conversion is inefficient. Solar-24v-12v-5v will be less efficient than Solar-12V-5V

DarthKermit

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#1764745 15-Apr-2017 15:36

Why do you actually need the solar component?

You could trickle charge a 12 volt battery from the mains as your backup to keep the interwebz and phone working when the mains goes out.

huckster

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#1764747 15-Apr-2017 16:04

andrewNZ:
huckster:

I have a similar setup but the goal was to power a Raspberry Pi which is 5v.

An alternative would be to go for a 24v solution (PWM and battery) with a DC converter to take the 24v down to 12v.

Then there are things like...

https://www.jaycar.co.nz/12vdc-3a-car-power-adaptor-with-usb-outlet/p/MP3671

Keep in mind, every conversion is inefficient. Solar-24v-12v-5v will be less efficient than Solar-12V-5V

Poster wanted 12v to 12v but there is concern about keeping a good 12v signal to the router etc.

I have a setup where it is 12v to 5v for a different reason.

Cheapest option is a UPS but it's not as much fun as running the risk of electrocuting yourself whilst believing you are helping the environment.

kiwirock

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#1764749 15-Apr-2017 16:20

You can probably get $15 dc-to-dc 2A regulators with user selectable voltage, the size of a match box as a module. They'd be good with a small 24v panel and two small 12v batteries wired in series as they usually require the input voltage to be 1.5v higher.

I use two of these finished units in the car for 5V and I run everything, GPS, phones, lights etc... off them: 12v to 5V USB

For a 12v router, I use Mikrotik gear with its own regulator built in. But they can suck a couple of amps.

edit: If you use cheap lead acid batteries, you don't want to run them down passed 50% or it'll shorten their life a lot. Double the battery capacity you want and use a low voltage disconnect to protect them. Once you start doing this, you'll probably want more than a trickle charge and panels you would normally want double the size of the charge current you want.

SCUBADOO

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#1764754 15-Apr-2017 16:32

I agree with andrewNZ. Ignore the power rating on any appliance. Actual measurements are necessary.
We have been "off grid" for two years of full timetravel in our motorhome. All solar. No mains power connection.
e.g. all at 13.2VDC nominal from our 300Ah LiFePO4 battery pack.
Huawei B315 -power pack 1A - measured 220mA
Akai 24" TV - label 220W - measured 27W
i5 & i7 notebooks - permanently wired step up converter - power pack label 4.75V @ 19V (90W) - typical movie watching etc. <30W
Toaster - inverter powered - label 850W - measured 742W
Samsung 255l digital 230V inverter fridge - label 90W - accurate maximum - average over two years 33W
and so on.

All devices have operated perfectly from our battery. The voltage range here - 13V-14.2V. No smoke yet.

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Rikkitic

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#1764756 15-Apr-2017 16:34

DarthKermit:

Why do you actually need the solar component?

You could trickle charge a 12 volt battery from the mains as your backup to keep the interwebz and phone working when the mains goes out.

Bingo. That is also the conclusion I came to. I think one of the problems with solar and other alternatives is that people tend to develop an all or nothing mentality. I spent the whole day breaking my head over this and ended up just about where you suggest, with a couple of additions.

First, as you point out, it doesn't have to be 100% solar 100% of the time. So no $300 battery, just a cheapo $60 Japanese job is sufficient, with just a small panel to trickle charge it when conditions are favourable. Second, this is an emergency solution so when the power goes out you don't keep the router and phone running 24/7. You just turn them on a couple of times a day for a half-hour to conduct essential communications. Third, if the disaster goes on so long that the battery runs out anyway, you can still charge it with the solar panel, even if it takes a week or you have to wait for good weather. And fourth, we have a generator anyway, though it isn't particularly handy. But we could always dig it out to charge the battery if absolutely necessary (or even just run a car).

The first link Timmmay gave me is to a neat device that can power our router and phone adapter while charging a small fall-back battery. Any time the power goes off it automatically switches over. That would solve 90% of anything we would ever encounter. I only run into the problem of the regulator if I want to use solar to supply it. I am still working on that one. But as you point out, it may not really be that necessary.

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Rikkitic

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#1764760 15-Apr-2017 17:05

SCUBADOO: I agree with andrewNZ. Ignore the power rating on any appliance. Actual measurements are necessary.
We have been "off grid" for two years of full timetravel in our motorhome. All solar. No mains power connection.
e.g. all at 13.2VDC nominal from our 300Ah LiFePO4 battery pack.
Huawei B315 -power pack 1A - measured 220mA
Akai 24" TV - label 220W - measured 27W
i5 & i7 notebooks - permanently wired step up converter - power pack label 4.75V @ 19V (90W) - typical movie watching etc. <30W
Toaster - inverter powered - label 850W - measured 742W
Samsung 255l digital 230V inverter fridge - label 90W - accurate maximum - average over two years 33W
and so on.

All devices have operated perfectly from our battery. The voltage range here - 13V-14.2V. No smoke yet.

I would be interested to know more about your experiences. Are you operating your electronic devices from 12 volts or via an inverter? I don't think an inverter is bothered by slight source variations but my concern is running 12 volt devices directly from a variable source.

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richms

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#1764775 15-Apr-2017 17:53

They are not 12v devices, they will be 3.3 or 1.8 or something like that, with a switchmode step down to take the wall wart power down to that inside them. The reason they dont use 3.3v wall warts directly is because the internal DC converter gives them another layer of protection and there would be voltage drop concerns over the cable of the wallwart.

If you are concerned, there are buck/boost 12v output boards available on the usual sources for about $3 or so. Just watch the max current on the inputs as that is where they usually fall down and cant do a signifigant boost at their rated wattage.

I have run routers and switches off a 12 SLA that was under charge at 14ish v fine for about a year with no change in performance. When the charger blew up and they ran flat, it was at about 7v when the internet finally died. I wouldnt bother with anything to stabalise it further than what a battery itself does.

Richard rich.ms

Rikkitic

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#1764776 15-Apr-2017 17:59

Thank you @richms. That was my question.

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