CwazyWabbit Posted October 21, 2013 Share Posted October 21, 2013 I'm looking at fitting a second battery to the 110 to run a small computer. I'm planning on having the computer running 24 x 7 and don't want it to flatten the main battery hence the idea of fitting a second battery. On occasions the vehicle may go a week or two without being used. Initially the computer is likely to be running at less than 500ma, I know adding a 2nd battery and split charge for this sort of usage seems like overkill but there are plans that will probably result in increased drain in the future plus I hate the thought of having a flat battery Can anyone see any potential pitfalls with this scenario? I assume I would be better off with a leisure battery ... Anyway any comments? I can't see any problems with the idea but do wonder if I am missing something....... would rather not see the 2nd battery die an early death for some stupid reason. Quote Link to comment Share on other sites More sharing options...
ballcock Posted October 21, 2013 Share Posted October 21, 2013 Why not install a small solar panel to keep the second battery topped up if the drain is only small then the little ones Maplin supplies might be enough. Quote Link to comment Share on other sites More sharing options...
dirtyninety Posted October 21, 2013 Share Posted October 21, 2013 Yep, you can get solar panal trickle chargers fairly cheaply. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 21, 2013 Author Share Posted October 21, 2013 I shall do some googling this evening I think. Quote Link to comment Share on other sites More sharing options...
TSD Posted October 21, 2013 Share Posted October 21, 2013 0.5A load for 24hr/day = 12Ah discharge per day, so for 7 days life, you need an 84Ah battery. Ideally you shouldn't over-discharge lead acid batteries of any sort, so to avoid life shortening damage, you'd want something like 110Ah for a 1 week life. Caveat - I'm no solar energy expert, I just pulled a few numbers off the web out of interest. I suspect solar isn't a quick fix either, but a quick google session gives the following numbers :- Solar power in London averages 110W per sq. meter. (EDF Energy website) Wikipedia suggests a really decent photovoltaic might be around 20% efficient. So a 1m2 panel might average around 1.5A charging current, so on average you'd want a panel of around 0.5m2, but in reality sunlight hours vary through the year. The Met Office suggests a range of 50-200 hours month average, so you'd want to double that size to be reasonably confident of surviving through the winter months. A good quality 1m x 1m solar panel sounds expensive to me, especially combined with the charge controller and 200Ah worth of batteries you need to cover your 'couple of weeks' requirement. It would be much cheaper to turn it off when you aren't using it, or move to a lower power hardware solution. You haven't said what it's for, so can't make any suggestions there. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 21, 2013 Author Share Posted October 21, 2013 The actual plan is to monitor wireless signals and capture 802.11 probe requests and the associated mac addresses and then using zigbee wireless transmit the captured mac addresses etc back to my house. Edit: Cheers for the info TSD, it may be that I need to have a rethink, I also need to do some experiments when kit arrives to see actual power usage Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 21, 2013 Author Share Posted October 21, 2013 The basic idea is that smart phones are often associated with peoples home wireless and possibly work/friends wireless. When these phones are away from these wireless networks but the wireless is still turned on they send out probe requests that contain the mac address of the phone and the wireless network names of networks it has been associated with. These wireless network names can be looked up on some websites (populated by wardrivers) and will give the approximate locations of these networks. So if for some reason I need to know who has been hanging around my 110 I may have a chance of finding out ....... Oh and also as I'm a bit of a geek it might be fun Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted October 21, 2013 Share Posted October 21, 2013 Or it could look for your phone and unlock when you get within range. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 21, 2013 Author Share Posted October 21, 2013 Or it could look for your phone and unlock when you get within range. Unfortunately it's quite easy to spoof a mac address and as your phone would be broadcasting it most of the time it would be quite simple to bypass that....... probably not as easy as bypassing a Land Rover door lock though Quote Link to comment Share on other sites More sharing options...
TSD Posted October 21, 2013 Share Posted October 21, 2013 Embedded Wifi modules which draw around 1W maximum are available, Zigbee modules draw a bit less but don't need to be active anywhere near as often. Add in a decently pokey microcontroller and you'd probably manage to hit 1.5W when fully active. If you assume it takes longer than 2 mins to nick your truck, and less than 15 seconds to power up wifi and exchange mac addresses, then you get the average power down to around 200mW, or (say) 17mA @ 12V. Now your typical LR battery will run it for several months in theory, and certainly over a couple of weeks will not make a significant dent in the battery performance. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 21, 2013 Author Share Posted October 21, 2013 Very good point, hadn't thought about effectively just 'sampling the air' occaisionally. If the wifi module is in monitor mode it will never transmit so I assume it will never draw anything like maximum power. The Zigbee module will of course only need to transmit when I've seen something, I could also write the code so it only transmitted if it received a certain number of probe requests.... ie someone wasn't just walking by. Looks like I need to do some experiments capturing traffic to see how often different devices send out probe requests. Currently thinking of using a BeagleBone Black or one of the Raspberry Pi variants as the computing back end. I know the BeagleBone has a sleep mode itself so I wonder if that would be suitable..... Looks like more research for me to do. Thanks again for the ideas all Quote Link to comment Share on other sites More sharing options...
discomark10 Posted October 22, 2013 Share Posted October 22, 2013 is there much mapping done in the uk, quickly looked on a couple sites n it all seemed to be US plots Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 22, 2013 Author Share Posted October 22, 2013 is there much mapping done in the uk, quickly looked on a couple sites n it all seemed to be US plots Wigle.net shows UK to have 3rd highest coverage (about 5 million) behind USA and Germany, concentrations seem to be around major cities (probably as that's where most wireless networks are). Even if the network of interest isn't shown you can always go out for a bit of wardriving if there are a few areas that you suspect the people to have come from. It's not a perfect system but it's better than nothing. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 22, 2013 Author Share Posted October 22, 2013 The sleeping of the system is probably not going to work as I had forgotten that when monitoring the wireless it isn't as simple as just switching on and looking for probe requests as you have to scan through all the wireless channels (13 of them) looking on each channel. Sleeping of the zigbee wireless is of course feasible. Quote Link to comment Share on other sites More sharing options...
TSD Posted October 22, 2013 Share Posted October 22, 2013 Cant you be the 'AP' end of the link, and let the target mobiles do the hard work of scanning channels? Quote Link to comment Share on other sites More sharing options...
landroversforever Posted October 22, 2013 Share Posted October 22, 2013 Cool idea barry... looking forward to hearing how it works Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 22, 2013 Share Posted October 22, 2013 Daft question - if it's going to be talking to your house anyway, why can't you mount the gizmo in an IP-rated box on your driveway with a mains hookup? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 22, 2013 Author Share Posted October 22, 2013 Daft question - if it's going to be talking to your house anyway, why can't you mount the gizmo in an IP-rated box on your driveway with a mains hookup? Not a daft question at all, unfortunately no driveway and I often have to park up to 100 yards away from the house So I really need the box of tricks to be in the car to have a chance of picking up the right signals. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted October 22, 2013 Share Posted October 22, 2013 Pringles can on a wifi aerial? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 22, 2013 Author Share Posted October 22, 2013 Pringles can on a wifi aerial? A directional antenna that I point at the car along with the camera is an interesting idea. Quote Link to comment Share on other sites More sharing options...
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