Guest 000 Posted December 10, 2016 Share Posted December 10, 2016 We are moving abroad the boat in a couple of days time for the next three months and I would like to get this tablet charging business sorted. I don't understand it. The tablet/battery operates on 3.7v. At home, my tablet mains charger has an output of 5.2 volts and 2 amps. On board my 12v charger has an output of 5volts and 2 amps. At home, the tablet charges in 5 - 6 hours, on board it takes 12 - 14 hours. Since the output in both cases is almost identical, why the difference? I have talked to a few people who are aware of the different charging times between 240v and 12v input but cannot explain why. Can anyone enlighten me or at least help me to fix it please. Quote Link to post Share on other sites
ex TL systems 63 Posted December 10, 2016 Share Posted December 10, 2016 if you have enough battery power just run a small inverter to power your 240 v charger? Quote Link to post Share on other sites
Farrari 4 Posted December 10, 2016 Share Posted December 10, 2016 Chris, are you plugging your tablet into the USB port on your boats 12V power supply by any chance? USB 3 specification only supplies 4.5W (0.9A @ 5V) maximum power. I have a DC/DC inverter for my laptop and it has a USB port on it but like you are experiencing, it is very slow to charge anything (phone or tablet). I do have a cigarette lighter socket USB charger and that works a lot better. You could try something like this (warning - this is not exactly the same as the one I use and I haven't had any experience with this specific one.) https://www.pbtech.co.nz/product/MPPMIX12313/Xiaomi-Mi-Dual-USB-Car-Charger-Silver5-Circuit-Pro The 230V power pack that comes with your tablet may have a USB looking port on it but doesn't adhere to the same USB specification and will usually supply 10W (2A @ 5V). Like ex TL systems says, one option is to use an inverter and your tablets 230V charger. This is quite inefficient however as the AC inverters are only circa 70-80% efficient. One other thing to be mindful of is that not all micro USB cables are made equal. Some of the cheaper ones will not support higher currents (thinner wires, higher resistance). You could try your genuine cable on your existing 12V boat charger and see if that helps. Quote Link to post Share on other sites
Island Time 1,220 Posted December 10, 2016 Share Posted December 10, 2016 Should be the same if output is, in fact the same. I bet it isn't. Many 12v usb chargers say 2a, some even 2.5a, but they have 2 usb sockets, and the 2a is divided between them, or its a total. Get a usb cable extension, strip the centre insulation from it, and use a multimeter to measure the current supplied. I bet it's 1-1.5a. There are lots of crap usb 12v adapters out there. Don't use the inverter - it wastes lots of battery power. Quote Link to post Share on other sites
Guest 000 Posted December 10, 2016 Share Posted December 10, 2016 I am plugging a little USB charger in a lighter type socket wired into the boats 12v system. Someone did warn me about the output amperage being divided across multiple outlets on USB chargers so I purposefully bought one with only one outlet. As to quality of the unit, I am unable to judge - it's a Harvey Norman supplied charger probably originating in China. Sometimes they tell porkies about their products. I have three same brand Chinese made soldering irons - a 15, 25 and a 40 watt. All put out exactly the same heat, so who knows what the charger output is in reality. I am using the same charging cable on board as I use at home to connect to the mains USB charger. Quote Link to post Share on other sites
Guest 000 Posted December 10, 2016 Share Posted December 10, 2016 OK, the latest (from the internet) Apparently, these smarty-pants phones and tablets are able to determine where their charging power is coming from. If they think it's from an AC charger then they go for it. If they think it's from a USB port then they throttle back to 500ma which is why the charge time is hugely extended. From the internet so this may or may not be correct. If it is then what is needed is some way to tell the phone or tablet not to be so fussy and to suck it up. Quote Link to post Share on other sites
Winter 42 Posted December 10, 2016 Share Posted December 10, 2016 This is correct Chris. Sometimes they can be fooled with a resistor of the correct value across the correct pins of the USB.. EG : http://www.instructables.com/id/Cheap-and-simple-USB-car-fast-charger-mod/ However it seems that Samsung/ Apple/ et all are all doing things their own way - so you'll need to find the correct method of tricking it for your particular device. One answer is perhaps just get a tiny inverter only big enough for your charger (or two) like a 150W job.. plug your AC charger in here. It will use more power than the equiv DC-DC, but at least it is plug and play. Quote Link to post Share on other sites
Guest 000 Posted December 10, 2016 Share Posted December 10, 2016 Thanks Winter. The slow charging issue lies in the realms of 'if I can fix it easily then I will.' I think it may be a little to complicated (and risky) for me to fiddle with. I suppose 12 hour charging is not too bad. Quote Link to post Share on other sites
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