Bowie69 Posted August 7, 2017 Share Posted August 7, 2017 a.n.other solution, get a booster pack, and put it somewhere handy, ensure the cigar lighter socket is ignition switched and charge your devices off that, if you must. https://www.britpart.com/all-parts/da1239/ Already got built in USB ports.... Quote Link to comment Share on other sites More sharing options...
landroversforever Posted August 7, 2017 Share Posted August 7, 2017 Something that hasn't been mentioned is some kind of powerbank for charging phone/iPad? That's probably the simplest option. Have it plugged in and charging when you drive and then use it to charge the phone/iPad off-grid. 1 Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted August 7, 2017 Share Posted August 7, 2017 Ehem @landroversforever, look one post up Quote Link to comment Share on other sites More sharing options...
Davo Posted August 8, 2017 Share Posted August 8, 2017 "Great minds", and all that . . . 1 Quote Link to comment Share on other sites More sharing options...
landroversforever Posted August 8, 2017 Share Posted August 8, 2017 Ahh I read that as a jump start pack rather than specifically for charging 1 Quote Link to comment Share on other sites More sharing options...
Anderzander Posted August 8, 2017 Author Share Posted August 8, 2017 Well crikey ! I've been away a couple of days and had no idea I'd get 2 pages of suggestions ? I have thought about the twin battery route - but I wasn't sure if it wasn't huge overkill for charging a tablet whilst we sleep in a tent .. the other scenario being my 5yo daughter has plugged her tablet in and I've not noticed. Though that's harder to legislate against. What I seem to be taking away is that of my battery is in good nick - I should comfortably be able to charge a phone overnight. A split charge will gurantee I won't have misjudged the health of my battery / the drain of my charging device - but costs a lot more than an external battery pack to charge it ... The other idea was to run a timing relay in there. That sounds interesting - l'll have a look at how that might work. Thank you everyone though - I'll have a read through again and make sure I haven't missed anything. Quote Link to comment Share on other sites More sharing options...
mickeyw Posted August 10, 2017 Share Posted August 10, 2017 Last summer we went camping with the 110. I have a 110Ah battery (Numax CXV31MF I think) as my only battery, and we left both our phones and two tablets charging overnight in the truck. No problems starting the next day. I think many of us have a tendency to overthink these things Quote Link to comment Share on other sites More sharing options...
Snagger Posted August 10, 2017 Share Posted August 10, 2017 17 minutes ago, mickeyw said: Last summer we went camping with the 110. I have a 110Ah battery (Numax CXV31MF I think) as my only battery, and we left both our phones and two tablets charging overnight in the truck. No problems starting the next day. I think many of us have a tendency to overthink these things That wasn't how I the original post was presented, though - it was a situation where a vehicle had suffered battery flattening from a fitted system, possibly a bad stereo, a couple of times, and in the future will additionally be used to charge devices over extended periods without being run. Overnight with no suspect drains is not going to be an issue for for a 70AHr battery, let alone 110. Quote Link to comment Share on other sites More sharing options...
AMB Posted August 10, 2017 Share Posted August 10, 2017 (edited) As stated above – it all depends! Why complicate the issue? Most tablets and phones are around 3Ah capacity and will run on standby for something like 200hrs or more, especially if automatic battery savers are installed. That gives a nominal internal battery drain of 15mA. Work on 75% charger efficiency and 20mA average from the vehicle battery should keep any phone charged. Depending on model etc you can probably have a main vehicle battery of at least 65Ah capacity when fully charged. Assuming that you need at least one third capacity to guarantee starting with a little margin in hand and commencing with a moderately charged battery, you will probably have at least 30Ah in hand to run theft alarm, phone charger and anything else left on. Starting from a fully discharged phone, you would take 4Ah (ie 3Ah at 75% efficiency) in the first 3 hours or so to take you to fully charged, another 0.5Ah a day to keep that charge topped up and so on. I’d be quite happy to leave that phone quietly charging in my car for at least a couple of weeks without running the engine - it's far less than the self discharge rate of a lead acid battery. Edited August 10, 2017 by AMB Quote Link to comment Share on other sites More sharing options...
HoSS Posted August 10, 2017 Share Posted August 10, 2017 Theres a lot of windy replies here which don't actually answer the OP's question (and some total rubbish from an electrical POV). You can't work directly from the Ah of the battery as that doesn't account for real world factors such as internal resistance, chemistry, temperature, quality. You will need to find the discharge curve for your battery. A generic example for a battery of the same size will give you a reasonable approximation. (example attached, although i believe from a 12Ah model) In this example you can see that you could draw 0.6A (600mA) for about 15 hours before getting down to 12v. Your battery is likely 80+ Ah, so you will get much more than this example. It depends a lot on temperature, and what else is drawing current e.g. alarm Quote Link to comment Share on other sites More sharing options...
AMB Posted August 10, 2017 Share Posted August 10, 2017 4 minutes ago, HoSS said: Theres a lot of windy replies here which don't actually answer the OP's question (and some total rubbish from an electrical POV). You can't work directly from the Ah of the battery as that doesn't account for real world factors such as internal resistance, chemistry, temperature, quality. You will need to find the discharge curve for your battery. A generic example for a battery of the same size will give you a reasonable approximation. (example attached) In this example you can see that you could draw 0.6A (600mA) for about 15 hours before getting down to 12v. It depends a lot on temperature, and what else is drawing current e.g. alarm I agree in principle, but, in practice, you only need to take that all into account when trying to work into the margins of performance and heavier loads. My point was that you would not be working into that margin unless you have a cr@p battery or a much greater load, Your curve shows that the lower the current drain, the higher the useful capacity - a 30% difference between 7.2A discharge and 0.6A. 20mA is less than self discharge on a standard vehicle lead acid battery and almost certainly less than the standby load on the vehicle. On my 110 the standby load was less than 100mA. When the load is less than the self discharge rate of the battery itself you can work on Ampere hours and effectively neglect internal resistance, temperature etc. If you were to extend that discharge curve to the zero Amp point (ie self discharge) you would be somewhere in the order of weeks/months. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted August 10, 2017 Share Posted August 10, 2017 As above, anything I've 'winded' about is purely back of an envelope calculations and in no way are said to be accurate, more a demonstration that there is no problem here! Quote Link to comment Share on other sites More sharing options...
HoSS Posted August 11, 2017 Share Posted August 11, 2017 Agree. An overnight charge of a cellphone on a healthy battery should be no problem. But the more complete answer is the discharge curves, because the next question will always be - so how many cellphones can i charge The idea of comparing vehicle battery Ah and cellphone Ah and saying its ok is false though, as the charger continues to draw current even after the device is charged and is not 100% efficient. And if you leave that charger connected for a longer time it will discharge the battery. Hence the correct answer (and simplest to understand) is by the discharge curve and 'How much current can i draw for how long before the battery gets to x Volts, and wont start the vehicle?' Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted August 12, 2017 Share Posted August 12, 2017 There's a lot going on this thread, and some over-complication. But if I were doing any amount of camping, I'd go with a modified version of Miketomcat's solution of a voltage sensitive relay charging a second battery. This battery would feed fused, dedicated charging points. This eliminates, as far as practicable, user error, though you may want to trickle charge the second battery overnight before setting off on a camping trip, if you only drive your vehicle on short runs. Reading the OP's posts, it seems he might also be struggling with a parasitic draw somewhere, or possibly even a poor connection in the charging circuit. Youtube has a few videos on how to determine a parasitic draw using the voltage drop method. Start with that. Quote Link to comment Share on other sites More sharing options...
Davo Posted August 13, 2017 Share Posted August 13, 2017 "Cellphones"??? I thought they were mobiles over there? Anyway, this is an interesting thread so I can't help but ad my own opinion. I'd also recommend a second battery with whatever method of charging and isolating the OP would be happy with. It is for the usual spectre of Something Unexpected Going Wrong, as discovered by the OP, when having a second battery really helps. As well, once you have it set up, you realise how handy it will be. It's simple and straightforward and gives you a lot of extra options for that one time when you really need it. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 14, 2017 Share Posted August 14, 2017 When I had the FL my lazy solution for charging stuff and running the fridge was to buy a jump-start pack - they've got a 12v SLA battery that's more than up to charging cellphones etc., often have USB ports built-in, can be charged in-car or from the mains, are portable (you can bring it into a tent if needed), bonus points they can be gotten with built-in lights and compressors for tyres and of course can be used for their intended purpose of jump-starting things. Sure you won't run a big fridge from one for very long but for the original purpose of this post it could be a very convenient solution. The less lazy solution on the ambulance was a 2nd battery and a 12v/140A smart relay, easy. Quote Link to comment Share on other sites More sharing options...
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