Help with battery for tablet charging

[Blitz]

hi all
Been doing some research into tablet/phone charging whilst camping but not getting very far.
I know they don’t drain a battery too much but. I will be camping with 6 kids plus 2 or three adults. All with tablets that will require charging every day (kids that’s what they do)
Though about just taking a leisure battery and charging it before we go. However read if you drain this by more than say 30 percent I’m gonna kill it. Something I didn’t realise.
Advise and options please because I don’t have a clue on this stuff. Also not wanting really expensive options. I don’t think loads of mobile power banks is the way to go and at £20 a pop that will add up too.

 

[Phil_G]

A typical phone battery is a single lithium cell of around 1 amp hour. For the purposes of a simple example, a single cell voltage is very approximately 4v. Most chargers these days are switch-mode, so assuming this is the case, charging a 4v cell from a 12v supply will only draw a third of the actual charge current from the 12v source, therefore a full 1Ah phone charge will take only one-third of an amp hour from your 12v leisure battery.
If yours are linear chargers then the drain is the same as the phone charge current so the loads are 3x more than switchers. Linears are very inefficient when dropping significant voltages (8v in this case). Bear in mind that if your campsite is remote, a phone will ramp up its power (even if unused) and so its battery wont last as long as it would in a good-coverage area.Scale this up, fully charging ten x 1Ah phones from completely flat will draw 3.3 amp hours. A large tablet might have a bigger cell, say 3Ah, but even ten of these will only take 10Ah assuming all ten tablets are completely flat. You can make it an exact science if you wish, its only maths, but with only partially flat devices and a mix of smaller and larger cells, I'd guesstimate a week should be quite doable
Cheers
Phil

 

[Blitz]

Thank for the extensive reply. If I work on the worst case of 10ah per day then that would be 7oah out of the battery for a week. Is that ok for a leisure battery to loose without damaging its life span ? Obs depending on its size in the first place.

 

[Phil_G]

If you want to cover the worst possible case, you'd need something to support your leisure battery - solar or an occasional run out (assuming you have a split charge arrangement). 70Ah is rather a lot to take from even a 180Ah battery if you're not putting anything back. A 110 might not even give 70 and an 85 almost certainly wont. I'd work it out on typical usage rather than worst case
On second thoughts, I'd take bikes, cricket bats & hiking boots rather than phones and tablets!

 

[Blitz]

Oh yes I would love to shove those tablets where the sun doesn’t shine.
Thanks for your help.

 

[Tourershine]

On second thoughts, I'd take bikes, cricket bats & hiking boots rather than phones and tablets!

On third thoughts, i'd leave the kids at home with a giant box of Cheerios, a few gallons of milk, and 6 chargers plugged into the mains.
Knowing how focused my kids are on their devices, I doubt they'd even notice you've gone away and come back.

 

[Blitz]

Don’t joke about it my 17 year old wouldn’t unless I nicked his PS4

 

[Tourershine]

Oh yes I would love to shove those tablets where the sun doesn’t shine.

Another 5 years of technological breakthroughs, and that might be how we all charge our mobiles whist out and about....

 

[DaveyB]

On third thoughts, i'd leave the kids at home with a giant box of Cheerios, a few gallons of milk, and 6 chargers plugged into the mains.
Knowing how focused my kids are on their devices, I doubt they'd even notice you've gone away and come back.

Milk???? Now you clearly are not down wiv d kids. Surely you know it’s Redbull, Monster, Rockstar et al.

 

[Tourershine]

Milk???? Now you clearly are not down wiv d kids. Surely you know it’s Redbull, Monster, Rockstar et al.

Clearly I'm not. I only know of Redbull from the Soapbox races (which are brilliant by the way, and we should be represented with a T6 kart in the 2018 races)
As for the other chocolate bars you've mentioned, I have never heard of them. I'm a Marathon bar guy,

 

[DaveyB]

Clearly I'm not. I only know of Redbull from the Soapbox races (which are brilliant by the way, and we should be represented with a T6 kart in the 2018 races)
As for the other chocolate bars you've mentioned, I have never heard of them. I'm a Marathon bar guy,

Now that would be awesome, a t6 forum inspired soapbox for Redbull Soapbox Race London.

 

[Tourershine]

The seed is sewn....

 

[Tourershine]

Sewn, sowed, sow? Where's Polzy to correct me.

 

[Pauly]

Funny you guys should mention that as i was in discussion with the boss about a T6 soap box last year for London, we actually put an entry in but left it too late and only had a couple of weeks to get sorted and it didnt work out, unfortunately 2018 is in LA

 

[DaveyB]

Funny you guys should mention that as i was in discussion with the boss about a T6 soap box last year for London, we actually put an entry in but left it too late and only had a couple of weeks to get sorted and it didnt work out, unfortunately 2018 is in LA

Why is that an “unfortunately” you do realise that ladies go roller blading in bikini’s along the beach roads in LA don’t you.

 

[Tourershine]

Yeah, but it's too far for me to drive, and my wheels would get sea salt on them.

 

[Blitz]

Oh just a quick back to battery's question sorry. How long does it take to charge a battery say 30% whilst running the engine. I've really no idea

 

[Phil_G]

Oh just a quick back to battery's question sorry.

Its almost impossible to say, there are so many dependencies. You really need some sort of metering, power panels are very cheap to buy now, this will tell you exactly how many Ah have been transferred into the leisure battery. Doesnt need to be complicated, a simple model aircraft power meter would easily plug inline with your VSR and cost very little. Hobbyking or Ebay, this kind of thing: Digital LCD Watt Meter Battery Balance DC RC 60V/100A Volt Ammeter Amp Analyzer | eBay. These are generic devices, loads of them about, they show you the battery voltage, current going in, and accumulated amp hours. The display cycles through the various readings. Its just a suggestion but for under a tenner they're very handy as a general tool if you play with batteries a bit.
Cheers
Phil

 

[Blitz]

Thanks Phil that covers another question I had too. Top Lad

 

[Phil_G]

Here's another, seven quid, delivered!
100a 60v DC RC Helicopter Airplane Battery Power Analyzer Watt Meter Balancer BG | eBay
Worth mentioning that these things have an 'in' (source) and an 'out' (load) so if you wanted to measure discharge rather than charge,
you'd need to swap the in & out.
For measuring a charge, your leisure battery is the load. For measuring discharge, your leisure battery is the source.
Getting the 'in'and 'out' the wrong way around doesnt do any harm at all, it just doesnt read current if its the wrong way around.
I have a similar one on my electric pushbike, so I know I've enough juice to get home. Seemples !
Cheers
Phil