Battery powering options
-
Hi,
I have now reached a point where I have a software suite that works for me and I have six moteinos / anarduinos with RF69HW lying on my desk waiting to be used. I have a couple breadboard is order from eBay to do prototyping, but when I install the devices I want to do something a bit more compact/professional looking. I'm looking for the following:
- A good battery power option. Is two times AA enough? This provides 3 V, while the recommended input voltage is between 3.3 and 9 V
- A good mains powering option. I'm thinking of buying some cheap 5 V AC adapters on eBay together with some appropriate power jacks which I can mount in the sensor housing.
- A platform to which I can connect the various sensors I will use. It is difficult to get everything connected directly to the board, so I need some kind of expansion board to deal with the connections. I see there is some activity in this forum about doing your own boards, but I am by no means at that point. Maybe you know of some good options for Arduino mini pro compatible boards? The radio is sold direct to the board, so I do not need any special considerations for connecting this.
- A good case (some waterproof, some not) which can accommodate the expansion board and the optional battery solution.
I note might sound a bit lazy posting these questions here, but my challenge is that I am much more a software person than a hardware person. It would therefore be really helpful if I could get some advice on how to put together a decent "home production quality" sensor with a good wife acceptance factor.
-
@kolaf No, it doesn't sound lazy to me, we're all wrestling with these questions and I don't think any of them have been answered in such a way that they can be dismissed out of hand.
-
I guess two AA 1.5V alkaline batteries would work for the moteino (rechargeable of course self-discharge too fast, and LSD NiMH are a tad expensive). I think it's a fairly cost-effective solution too if the sensor allows it. The regulator seems pretty great, except that it requires 2.7-16V in. Hard to say how long 3V is going to last. Would have been better if it had started at 0.7-0.8 like some other regulators so you could have run it on only one AA battery. Perhaps you could run it on 3xAA? When I see the moteino I can't help but think that we're reinventing the wheel over here. Plus the range on these RFM69HW are phenomenal. Anyway. The anarduinos run on 5V right and are not designed for battery operation?
-
I'd be wary buying cheap AC adapters on Ebay.
http://www.righto.com/2012/03/inside-cheap-phone-charger-and-why-you.html
http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pricey.html
Perhaps you could look into buying some second hand brand adapters on Ebay. I bought two Nokia USB chargers (AC-10E) a while back from Germany and paid maybe 7€ each or so including shipping. They were originally meant to power Raspberries but I've since given up on buying more than one Pi and the one I have is powered by PoE using an aftermarket solution from Tp-Link. But I have a couple of sensors that I will need mains power for, like the powermeter ironically enough. I thought about buying something like this (between 12-24V 10-50W AC DC waterproof adapter) and then use buck converters in each enclosure to bring the power down to 3.3V or whatever. Starting at 12V and good gauge wire I should be able to run pretty long wires from one central transformer. But with all the problems with the NRF24 and bad DC quality I hesitate. I have some cheap ebay buck converters so I can try this before committing further resources though. At any rate, I'd avoid mains if I can. If you can get a year or more on a couple of AA and avoid radio problems, at least for those of us with NRF24, that seems cheaper and better to me. With AC-DC you have the cost of buying the adapters, the nagging feeling that they'll burn your house down, and that they'll interfere with your electronics. Plus the cost of running them. No idea what the efficiency is like here, but it probably varies a lot, around 75% if you're lucky, but that is probably at full load:
http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html -
No idea how to solve that gracefully and easily without making some custom board. Latching on some prototype board would be an eyesore on the moteinos etc.
-
It always comes back to these types of cases it seems:
http://www.ebay.co.uk/itm/191276960520
I've also bought a lot of the flanged model that may be more waterproof:
http://www.aliexpress.com/wholesale?SearchText=enclosure+waterproof
A bit ugly for indoor use though. Tried buying some without flanges, but got flanges anyway. I hope the Ebay ones above live up to the product picture at least. It's not that much to choose from.
People have been talking a lot about 3D printed cases but I'd be more interested in making wood enclosures of some type. A router and some router bits or whatever you'd need seems cheaper and more fun than 3D printing to me.
http://lifehacker.com/5640327/how-to-build-a-diy-wooden-hard-drive-enclosure
-
-
Now you've done it, after reading that information on the cheap phone charger I'm now questioning my purchase of these..
Looks like if I do wind up using these, I will need to include a temp sensor for some added protection..
-
@bjornhallberg Thank you so much for a very comprehensive answer.
Both the moteino and anarudino platforms run on 3.3 V, and all my devices are equipped with the RF69HW radio which gives me excellent range, as you say. I guess I could go with some regular RF69 radios as well for in-house use. I have ported MySensors to work with the Radiohead library (which supports a bunch of radios), so I can use the same library as you guys and benefit from the already developed software :-).
I guess 3xAA batteries are a good option, I just have to find a good three battery holder on eBay.
I think that most of my devices will be battery-powered, but there are a few devices that have to function as routers, so these should be mains powered. I guess I have a few cell phone charges lying around which I can cannibalise.
As for connecting all the sensor is, voltage dividers, and so forth, what is a good option when not using a breakout board? The data pins can mostly be soldered directly to the board, but to my mind power distribution is a major challenge. I also don't want to have a spaghetti of wires running all over the place. I guess this is the biggest problem facing when building the sensors.
-
@ServiceXp said:
Now you've done it, after reading that information on the cheap phone charger I'm now questioning my purchase of these..
Looks dangerously identical to the internals of my cable modem power adapter that broke down last week
Really!Looks like if I do wind up using these, I will need to include a temp sensor for some added protection..
And then what are you going to do when the temp sensor indicates burning? Dial the fire brigade automatically?
-
"And then what are you going to do when the temp sensor indicates burning? Dial the fire department automatically?"
Yep
J/K... I was thinking that I would at the very least shut the 2 relays down if running, and then send me a notification to throw the unit out the windows as soon as possible... 
.... but I get your point...
-
The title is about batteries, but the subject of using cheap phone chargers has come up.
Small note: Whenever I refer to "the regulator" below, I'm talking about the onboard regulator of the arduino variant you are using, not to any regulator chips inside the phone charger. Just to be very clear.
Safety:
If you ARE going to use cheap phone chargers, at least buy several and crack one open to look at the isolation on the PCB. (look at the pics on some web sites that have done this to get an idea what you are looking for) Then always unplug it before working on the sensor node - use an alternate high quality supply while programming and testing, Just In Case. And don't have any exposed conductors on your finished node, that could be touched.I would avoid the most compact ones with little room inside the case.
And you might want to test the temperature of the charger under load before deciding to use a given model.
Power quality.
At least measure the output with a voltmeter, under the loads you use.
If you try to run a 5V arduino (eg: APM = Arduino Pro Micro) from a 5V charger you could have problems (you must test). If you use Vin, you will likely have problems because there isn't enough voltage differential for regulation, a condition known as dropping out of regulation or drop-out. There are regulators with low drop out (LDO) specs that require less difference between input and output voltage, but those specs vary depending on the regulator and load. The ATMega chips have a lot of slack, so a 16 Mhz chip will probably still run fine if the output of the regulator is, say, 4.5v or maybe 4.0 volts so the voltage drop may not be critical. But the regulator may not be keeping the supply as stable when in drop-out - varying the voltage as load changes or passing through variations in the supply voltage (coming from a cheap charger).
So you may be tempted to just feed the charger 5v into the arduino's VCC=5V pin. That may work, but (1) some regulators don't like having power applied to their output pin only, so check that it doesn't overheat or remove it, and (2) the regulation on cheap chargers can sometimes be very bad - either off-voltage or with a lot of ripple and noise. Some are better than others. Expect the cheap ones to usually get flakey in these regards well under their nominal supply (eg: a charger which says 1A might work well only up to half that). And they may be poor even at low current. If you have a scope you can look at it (being careful about isolation and safety).
If you have a 3.3v arduino, you can probably feed the charger's 5v signal into its Vin and get a reasonably well regulated VCC=3.3v.
WIth the above qualifiers, some cheap chargers work fine in the right situation.
Of course, you should instead get a high quality power supply for each node. One problem is knowing that it is indeed a high quality supply - just paying more isn't a perfect predictor of that. Using a name brand may help, but there are plenty of reports of problems with name brand suppies too (tho we hope they are statistically less common). And a good supply may sometimes cost more than the node (3.3v APM = $3.50, nRF24L01+ = $1, dht-11 = $1, power supply = $10?)
