Solar Energy System which will power MacBook?

Technology and Internet
#1

I’m messing around with trying to build a solar energy system. I live in an apartment (on a top floor with lots of sun, though), and right now I’m very small. I’ve tried figuring out how to run the MacBook off of it. I already charge my iPhones and my extra USB charging batteries via solar. This is all experiments for when I plan to move into a tiny house in a year or so, and I want as much off-grid as I can manage.

Right now I have a camping, foldable 24 watt panel with three USB outlets, plus a new 25 watt normal panel. It came with a very small simple controller, and I got a USB/DC outlet (car outlet) for the system. I also got a CSB (Hitachi) Lead-Acid (I know Li-Ion is probably superior) 12 V/21 watt battery. I believe I can get the solar panel to charge the battery, and the battery to send electricity to the outlet, because it works with USB just fine, and if I put a car outlet to USB outlet dongle in, it also works to power the USB devices. But everything doesn’t seem to work all put together (Panel, battery, and outlet all hooked up the the charge controller), nor do I seem to be getting the power necessary to get the MacBook to recognise it is hooked up to a DC charger with a MagSafe end.

My assumption here is that given that the MacBook is Pro from Mid-2012 and the provided Apple adapter says 60 Watts, that some component in the system is not supplying even enough wattage to tell the MacBook it’s connected to a power source.

I was hoping someone else who might know a lot more about electrical systems than I do (as this is all a total experiment and new to me, so I’m teaching myself as I go) might explain where I went wrong. Is my battery too small at 12 V and 21 watt? Should I have gone with a 60 watt battery? And why would the solar panel charge the battery, and the battery charge what is plugged into the outlet, but I can’t keep the system connected in order to utilise the stored power? Doesn’t that defeat the entire purpose of having a system?

I’m a social sciences teacher. I barely passed my STEM classes in high school. I’m kinda lost.

#2

Batteries are generally rated in amp hours of capacity not watts.

I use a pair of 100 amp hour deep cycle flooded batteries that I got from super cheap auto (1st link below) fitted into super cheap auto battery boxes (2nd link below). I charge them with a folding 150 watt solar panel that I bought from the 4 wheel drive show in Melbourne (but it’s similar to the super cheap one I’ve linked below).

This gives me enough storage and enough charging capacity to be able to run a laptop computer and LED lights and a small fridge.

This system is much larger in capacity than what you’re running and my gut feeling is that you’ve simply under specified your system for your intended use.

But it’s also possible that the regulator your solar panel is fitted creates ‘dirty’ power (AC on top of DC) which the MacBook Power adaptor can’t handle. It would require hooking a scope to the output of the system to tell if that is what is happening.

N70T deep cycle battery
Battery Box
Solar Panels

#3

Watts = Voltage X Ampage . 60W = 12volt x 5 amp.
To achieve what you want you will need to supply a 12 volt, 5 amp 60 watt supply to your Mac.

You could do this a few ways.

By using your existing solar panel to charge a new deep cycle battery. 12 volt deep cycle batteries are usually labeled with Ah rating. This just means how many amps they can supply for one hour. i.e. a 5amp hour battery could in theory run your Mac for 1hour, although in practice probably half that time. Get a 100 maybe a 100ah battery and it should easily charge yor Mac.

Hooking a sine wave inverter http://www.supercheapauto.com.au/Product/SCA-12V-150W-Can-Modified-Sine-Wave-Inverter/326793?menuFrom=1021639 between the battery and your existing macbook charger would clean up the feed.

Use a more powerful solar panel
http://www.quickertek.com/products/solarJuicz.html

#4

Very true! Most common (and affordable) deep cycle batteries can only be discharged to the point where they’ve delivered roughly 50% of their rated amp hour capacity.

So the 100 amp hour battery from super cheap can only safely deliver about 50 amp hours of capacity or 5 amps at 12 volts for 10 hours (what the macbook pro requires).

I also run LED lights from that battery so I would only get about 8 hours of continuous use (the 2nd battery runs the fridge) before needing to recharge.

My solar panel (which is in theory 150 watts) on a sunny day generally only charges the battery at about 5 amps (due to losses in the panel regulator) and takes about 10 hours (or most of a sunny day) to fully recharge the battery.

Most days the laptop is only used for a couple of hours and the lights for a few so it’s not quite as bad as what I’ve suggested above. Generally a cloudy day will mostly recharge the partly discharged battery.

NB These are big heavy batteries, over 20 kg and they’re not designed to be used in an enclosed area.

If you want something you can use indoors it’s going to be significantly more expensive. You’ll need to buy AGM (roughly double the cost) or Lithinum Ion (much more again) instead of Lead Acid flooded. However bonus these types of batteries can be discharged somewhat further.

#5

It would be handy to know what this actually is. Maybe a model number or link to a data sheet? Geoff is correct that batteries don’t get measured in watts, which is an instantaneous measurement of power, but the capacity can be expressed in ‘watt hours’, which is a measurement of energy. If your battery is 21 watt hours, or 1.75 amp hours (21 / 12), it is tiny and wouldn’t run your MBP for very long at all. Think a couple of minutes.

That may not be your issue though. I haven’t been able to definitely determine the actual voltage output of an MBP power adaptor, but the battery seems like it might be 10.95 volts. A fully charged 12V battery will likely be sitting at 13 volts or so when charged. When being charged, by your solar panel for e.g., it will be higher. I would have thought that would be ok, but the computer might be rejecting it because it’s out of range.

It’s also possible, and certainly used to be the case, that the battery voltage in the MBP is more like 20V. I know the old PowerBooks used to be about that and apparently the new ones are too. If that’s the case, you aren’t going to be able to drive it directly with a 12V battery.

I’m also a little confused as to how you’re connecting all this stuff together. Some sort of diagram would probably help. Especially what the magsafe lead going to the computer is connected to and how.

Given that you’re not electrically inclined, you may want to think about doing this slightly differently and using an inverter. It’s less efficient, but a bit simpler in terms of plug ‘n’ play-ability. What you would have is:

Solar panel → regulator → battery → inverter → Apple AC power adaptor → MBP

Everything has to be sized correctly for the job, but that’s the case whatever you do.

1 Like
#6

This would work but make sure the inverter is a true sine wave inverter and not a modified sine wave inverter as computer power supplies (and computers) can be damaged by using a modified sine wave inverter to power them.

#7

Good advice - there are definitely things that don’t like modified square wave inverters - but those modern all-voltage power supplies tend to be pretty robust and tolerant in my experience. Plus they just chop the power up and reconstitute it at the end anyway. They’re not like old fashioned power supplies. The Apple ones are very sophisticated and laptops have an extra layer of separation with their external supplies.

Still, I would recommend using a sine wave inverter because you’ll likely avoid the cheapest and nastiest stuff that way.

#8

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I believe the battery is 7.2Ah or 7200mAh. Basically, I have solar panel, battery, and 12 volt DC car socket wired up to my charge controller. I have a 12 volt car plug with a MagSafe end. I have an inverter but I don’t know about the sine situation. Like many folks these days, I’m trying to practice and experiment before I need to build my tiny house and go off grid. Hence the reason I started really really small.

#9

Do you have access to a Multimeter? If so measure the outputs of your solar panels and your battery to findout what voltage and ampage you are getting. The problem with small Lead-acid batteries is under load the voltage can drop fairly quickly.

This does seem like the easiest pathway. Are there any 4-wheel drive and camping stores you could go to for advice. This is an area of the market they tend to cover, in Aus at least, not sure in your location.

#10

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That’s a good question. There’s a solar store nearby where I bought the battery. But other than for batteries, they’re pretty expensive. The guy at the store said Amazon was killing him, and he wasn’t aware of any other stores where an individual could buy small pieces. Most places won’t deal with someone like me; they’re for putting huge solar systems on top of big houses.

#11

Once a year there is a 4 wheel drive show in most states, there are always stands selling solar panels, chargers, regulators, battery boxes etc at discounted rates.

Entry is cheap.

Failing that try 4 wheel drive supercentre (they’re the discount kings of 4 wheel drive accessories and have some cheap gear).

#12

Geoff, I live in Tokyo. I’m not in Straya, and probably won’t be for a while. Haven’t been since 2011, actually. So while I appreciate the information, it doesn’t help me out.

BTW, looked at your links. Jesus that’s expensive. I could just order Voltaic Systems complete MacBook kit for cheaper than that.

The battery box looks like it has a DC out, though, right?

#13

Ahh ok… my bad.

The battery will have a +ve and a -ve terminal is that what you mean?

#14

Don’t worry about it. Fair assumption that if I’m on an Aus site, I’m likely in Australia.

No I mean the round thing on the left side of the picture. Looks like a car standard 12 volt DC port.

#15

I must be thick… I’m not seeing it.

I can see the rectangular connector at the rear of the solar panel but not a round one.

#16

If you want to drive your MBP without the inverter, i.e., as you have it set up now, you have to determine what voltage it requires.

If, as is possible and maybe even likely given that it’s not working, the computer needs around 20V at the MagSafe input, your setup just won’t work because it is outputting 12V. Assuming there are no faulty connections, adding an inverter will make this work as it is. It is a small battery though and won’t power your machine for long.

Re the solar panel connections, it’s never good to use two different kinds of panels into the same regulator/controller. It probably won’t break anything (no guarantees) but it’s not optimal. Personally, I would just disconnect the folding one for now. The less interactions in the system the better for fault finding. Maybe hook it up again once you’ve got it working.

Trying to do this stuff without a multimeter is a bit like trying to build IKEA furniture without an allen key in some ways. It’s very difficult to know what’s going on if you can’t at least measure voltage and continuity. I would also be determining the pinout of the MagSafe connector so I could, amongst other things, measure the output voltage of your AC adaptor. This will tell you straight away what voltage the MBP wants to see.

Once you have a multimeter and you know what pins in the MagSafe connector carry power, you should check your lead for continuity to make sure it’s working. The overriding principle with any sort of fault finding is to check everything - never assume something is working or not working, you must test it - and minimise complexity whilst you’re working through it.

All in all, it would be much simpler to just use an inverter, as previously suggested. To do what you want, you need one that will put out 60 watts continuously as a minimum. It is hard to get good small inverters, but I can give you an idea if you find something that looks suitable and you can post a link or make and model here, or a photo of the one you have. We use SEA Piccolo inverters for little stuff, but they’re pretty expensive relative to what you can get off eBay. The last one we sold was about $450 or so and I see the 12V Shop has them now for $467.

#17

Geoff:

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Richard,

Those two panels are independent systems. They are not connected.

Also that is way way way waaaaaaay beyond my budget. There’s no way I can afford spending that much on an inverter.

#18

That is a 12 volt socket (like a car lighter socket) with a weather resistant plastic/rubber cover.

The small red button is a momentary press switch used to activate the LEDs which indicate the battery voltage.

#19

Yes. That’s what I said. That’s exactly what I would need for my car socket (male) to MagSafe adaptor. Basically, if it works in a car, so it should work with that battery box, right?

#20

Basically yes, that’s why boxes like that are so popular.

But there is a current limit on the socket (I think it’s 10 amps).

Some car lighter sockets are rated to 20 amps.

Devices drawing more current than 10 amps should be hooked to the terminals at the front of the box.