Charging ancillaries

[Anderzander]

Would anyone explain the calculations I need to do to see what I could leave plugged into a permanent live 12v feed, before I reach a point of not being able to start?

I'm just thinking of leaving phones or an iPad charging in the Land Rover 

My 90 has the standard battery and I'm tainted by the experience of having run it down a couple of times so it didn't have enough left to crank the starter over.

That was mainly traced to a faulty Parrot head unit, where it looked like it was switched off- but the GPS and blue tooth was still working away in the background. Couple that with leaving my side lights on seemed to flatten the batter quite quickly.

So, if anyone would take the time to help me make sure I don't end up not being able to start it miles from home ... I'd really appreciate it. ?

[rtbarton]

It's all to do with ampere hours, you'd have to factor in temperature, condition of the battery as well.

The only calculation I'd do to make sure I wasn't left stranded would be to deduct the cost of a split charge system and 2nd battery from my bank balance and see if I could afford one and if so fit it and charge my devices off that.

When I rewired my Landrover I ran the hazards and sidelights off the 2nd battery, so if I had to park up or leave the vehicle at night the "starting" battery wouldn't get flattened.

[Snagger]

There are far too many variables.  How discharged are the tablet or phone?  how many days between starting the engine, and how long is it run for?  What other electrical systems are running on the vehicle while it is unused, in addition to the clock, stereo memory, alarm, etc.  Then there is the starting reliability of your engine.

If you're worried, then you don't need to spend a great deal on a reserve battery system, much less than a typical dual battery setup.  You just need a small capacity battery, 30Ahr will do, a key type isolator and the wiring to fit it in parallel to the main battery with the isolator operable from the cab (only has to be in the cab to ensure that you periodically connect it to charge the battery up and disconnect it at the end of every drive - if you have it under the bonnet, you won't bother disconnecting it.  A fully charged 30AHr battery should be quite capable of starting the engine even in cold conditions if the main battery is dead, though you'd benefit from having an isolator on that battery too so that when starting from the reserve, it isn't also pouring into the dead battery.

[Arjan]

Yes... Impossible to answer with this info.

We have 2 batteries in the LR's and this kind of stuff runs off the 2nd battery

 

[rtbarton]

33 minutes ago, Snagger said:

...

If you're worried, then you don't need to spend a great deal on a reserve battery system, much less than a typical dual battery setup.  You just need a small capacity battery, 30Ahr will do, a key type isolator and the wiring to fit it in parallel to the main battery with the isolator operable from the cab (only has to be in the cab to ensure that you periodically connect it to charge the battery up and disconnect it at the end of every drive - if you have it under the bonnet, you won't bother disconnecting it.  A fully charged 30AHr battery should be quite capable of starting the engine even in cold conditions if the main battery is dead, though you'd benefit from having an isolator on that battery too so that when starting from the reserve, it isn't also pouring into the dead battery.

Inevitably you will forget to open the isolator when you start the engine and this will fry the wiring between the two batteries.  The only safe way to do this is to use a split charge system..

If you have the old-school alternator then a relay connected to the alternator warning light will do the trick, if you have a modern setup where the alternator is controlled from the engine computer then a DC-DC or voltage sensing charger is called for.

EDIT - reference to blocking diode removed - this would still discharge the main battery.

EDIT EDIT - you could fit a blocking diode if you fed it from a "live with ignition" source, just make sure it can supply the current safely.

Edited August 7, 2017 by rtbarton

[Snagger]

Rubbish.  If you have normal, decent sized cable between the batteries in parallel, you won't fry anything.  The only risk is running the engine and alternator with no battery connected, wit the potential to damage the alternator, but you're not going to get it started without a battery connected.  What do you think happens on a jump start?

There is a place for expensive split charge systems, and that is generally the shelf of the Gucci camping shop.  Those sorts of split chargers are not needed to run a reserve battery - even most campers only need a heavy duty relay controlled by the alternator output to charge a second battery.  Expensive split chargers and battery managers are only needed for complex systems with fridges, heaters, water pumps and other relatively continuous, high demand items.

[rtbarton]

The starting current will be taken from both batteries, so you'd need starter cable between them.

What do you think happens on a jump start? - You use jump leads.

need a heavy duty relay controlled by the alternator output to charge a second battery - Which is exactly what I said, although a standard automotive relay works fine.  In my experience.

 

[Snagger]

If you have two 12v batteries connected in parallel, then you will only get 12v at the vehicle circuits regardless of which battery is connected, or if both of them are, even with both fully charged, so you can't fry anything..   Using standard battery cable between the batteries is what I said in my first comment, along with an isolator to disconnect the reserve battery once charged or on engine shut down.  Why you think jump leads behave any differently to the above is beyond me.

However, a standard relay, which is rated at 30A, is not sufficient for starting the engine.

A typical split charge system as sold by 4x4 suppliers is much more expensive than required for this task, and frankly, less reliable than the simple isolator.

[SteveG]

Plenty of us have run dual batteries with no split charging for winching without any issues. 

The only recommendation is to use two identical batteries, and preferably bought new from the same batch. If winching use, 35mm2 or bigger cable to wire the batteries in parallel. 

Cheers, Steve 

[miketomcat]

I happily leave my phone to charge on a single battery over night with no issues in the morning. I've also charge my phone several times in this manner when camping. But as said the best is to run a split charge and second battery of some sort.

I fitted a second battery with a voltage sensitive relay (from a heated rear window set up) between the two battery's so it drops out when the engines off but opens when the alternator starts charging.

This is what I did for the fridge in the 110 while the wife's away on holiday with the kids.

Mike

[rtbarton]

7 minutes ago, Snagger said:

 

Sorry Snagger you're not making sense

If you have two 12v batteries connected in parallel, then you will only get 12v at the vehicle circuits regardless of which battery is connected, or if both of them are, - True, but

so you can't fry anything - The starting current will be drawn from both batteries, you'll fry the interconnecting cable unless it is starter-type cable

Using standard battery cable between the batteries is what I said in my first comment - You didn't mention any type of cable in your first comment.

If you have normal, decent sized cable between the batteries in parallel, you won't fry anything - ( Your 2nd comment)  What is "decent sized cable?"  If you mean starter grade cable then I've already agreed with you.

However, a standard relay, which is rated at 30A, is not sufficient for starting the engine. - Nobody's suggesting it is - it's fine for the sort of setup the OP wants, assuming an old-school alternator, like I said.  Use a relay with 30 amp cable you get automatic operation of the circuit, you don't need to spend money on starter cable and you can put a normal blade type fuse at each end for added safety.

along with an isolator to disconnect the reserve battery once charged or on engine shut down. -  A system that relies on the driver to disconnect the batteries isn't as good as one that does the job automatically.

Why you think jump leads behave any differently to the above is beyond me. - Using starter cable will emulate permanently wired in jump leads, but why would you want to for this application?  

Just now, SteveG said:

Plenty of us have run dual batteries with no split charging for winching without any issues. 

The only recommendation is to use two identical batteries, and preferably bought new from the same batch. If winching use, 35mm2 or bigger cable to wire the batteries in parallel. 

Cheers, Steve 

Absolutely, I've done the same with a Perkins 4236, but let's get our feet back on the ground and bear in mind what the OP's application is.  He wants to charge electronic devices without any risk of discharging his battery, we're agreed the best method would be a separate 12v battery charged from the main battery when the engine's running.  There are several ways of doing this, the OP can please himself which he chooses.

 

[GW8IZR]

I don't agree the best way is the complexity and cost of two batteries at all.. not to charge a phone up.

For the required load I think I'd put a timer relay on an auxiliary circuit and have it go off after a couple of hours.

[Snagger]

rhbarton, it was quite clear from the context of my post that I was saying to wire in the second battery with battery cable, not dash wiring.  You are now trying to split hairs because you have been caught out spouting rubbish about having to use a full on split charge system and there being a risk of "frying" components when there is no such risk.

Is is also utter rubbish to claim that a system that needs driver selection rather than automated connection is inferior.  It may be slightly less convenient, but it will be cheaper and more reliable.  Which is best depends very much on the user an application.

A 30A system is not going to be sufficient for starting the engine, so your relay and blade fuse isn't going to do anything useful.n  My understanding, possibly flawed, of what the OP wants to do is to be able to leave items in the car, charging with the ignition off for extended periods.  My suggestion is a reserve battery, quite likely second hand to keep costs down, and relatively small, just to restart the engine once if the main battery is discharged by the various appliances running off it.  How does a 30a relay help in that situation?

As for the system emulating permanently connected jump leads, that's exactly the point.  You think it'd be better too have a second battery but need to use jump leads every time you want to connect it for charging or starting?

If you want a twin battery system, then there are expensive ways, cheap ways, simple ways and complicated ways of doing it.  I am putting forth the simplest and cheapest, given that the OP's requirements are pretty straight forward.

[rtbarton]

Nowhere  did the OP say he wanted to use the 2nd battery to help with starting.

The relay isolates the two batteries when the engine isn't running, so the main battery is left fully charged if the 2nd one discharges.

[Bowie69]

To be honest, if you want to charge a phone, which only really takes a couple of hours tops, with newer models, a phone battery is around 3AH, your LR battery is around 72AH.

If your vehicle battery is charged and in good condition, and your phone dead flat, then even allowing for 50% efficiency (unlikely this low) you are taking less than 10% of the capacity.

If you leave your sidelights on, that is 4x5W bulbs = 20W = 1.75A, which means your battery will be totally dead in less than 40 hours, however a battery at maybe 50% may not be enough to start your engine.... so call it 20 hours, 15 hours to be safe? Basically, don't leave them on

If you want to run things like hazards, sidelights, a cigar lighter socket, inverter, chargers etc, then yes, a simple 30A relay with fuse between the batteries would be fine. You just need to wire the accessories, and the hazard/sidelights circuits to the second battery, so will take some modification. 

So, 30A relay and a decent inline fuse holder, and a new feed from the second battery to wherever you are running the accessories, and you are done. Reckon could do the lot for £15, plus the cost of the battery

The 30A relay in this form, when switched from the alternator or oil pressure switch will only pass current when the engine is running, and lead acid types take around 20-25A max, so perfectly safe.

A big chunky isolator is quite a cost, and something to forget, so in the above situation not a viable alternative to an automated relay.

[Snagger]

16 minutes ago, GW8IZR said:

I don't agree the best way is the complexity and cost of two batteries at all.. not to charge a phone up.

For the required load I think I'd put a timer relay on an auxiliary circuit and have it go off after a couple of hours.

That's another viable and cheap alternative.

I wouldn't say a second battery with an isolator is remotely complex, though, and possibly easier to rig than a timer relay.  It does give a hand backup for bad weather or frequent short journeys, but it may not suit some people, and here is no guarantee that a timed charger circuit will leave enough battery power for engine starting if the battery was already heavily discharged.  The second battery is a handy backup for a bad alternator, a dying main battery and a bad starting engine, not just for charging phones.  but, I agree it may be overkill for a lot of people.

[Snagger]

8 minutes ago, rtbarton said:

Nowhere  did the OP say he wanted to use the 2nd battery to help with starting.

The relay isolates the two batteries when the engine isn't running, so the main battery is left fully charged if the 2nd one discharges.

You're right, but there was concern over multiple drains flattening the battery on some previous occasions and the possibility of it occurring again, not just due to charging PEDs but also through faulty units like stereos taking excess drain.  So, apart from a reserve battery, what other option is there if you want to leave electronics powered up?

[GW8IZR]

Complicated to buy, wire, find space for, maintain all to charge a phone and an ipad?

The load required is tiny in reality and Its  possible, and  I'm guessing here, the starting battery isn't actually getting fully charged due to the usage of the vehicle which for most of us here is 'occasional use' but thats conjecture.

I reckon the bottom line is that if the OP had a good starting battery that was getting fully charged it would have ample capacity for his needs including charging the phones when needed ;-)

 

[reb78]

32 minutes ago, Bowie69 said:

To be honest, if you want to charge a phone, which only really takes a couple of hours tops, with newer models, a phone battery is around 3AH, your LR battery is around 72AH.

If your vehicle battery is charged and in good condition, and your phone dead flat, then even allowing for 50% efficiency (unlikely this low) you are taking less than 10% of the capacity.

If you leave your sidelights on, that is 4x5W bulbs = 20W = 1.75A, which means your battery will be totally dead in less than 40 hours, however a battery at maybe 50% may not be enough to start your engine.... so call it 20 hours, 15 hours to be safe? Basically, don't leave them on

If you want to run things like hazards, sidelights, a cigar lighter socket, inverter, chargers etc, then yes, a simple 30A relay with fuse between the batteries would be fine. You just need to wire the accessories, and the hazard/sidelights circuits to the second battery, so will take some modification. 

So, 30A relay and a decent inline fuse holder, and a new feed from the second battery to wherever you are running the accessories, and you are done. Reckon could do the lot for £15, plus the cost of the battery

The 30A relay in this form, when switched from the alternator or oil pressure switch will only pass current when the engine is running, and lead acid types take around 20-25A max, so perfectly safe.

A big chunky isolator is quite a cost, and something to forget, so in the above situation not a viable alternative to an automated relay.

I imagine that this is what Anderzander actually wanted from this thread.

[rtbarton]

15 minutes ago, Snagger said:

You're right, but there was concern over multiple drains flattening the battery on some previous occasions and the possibility of it occurring again, not just due to charging PEDs but also through faulty units like stereos taking excess drain.  So, apart from a reserve battery, what other option is there if you want to leave electronics powered up?

from my first post (paraphrasing):

... to make sure I wasn't left stranded would be to ... fit [2nd battery & split charger] ... and charge my devices off that.  ie fit a reserve battery.

I also mentioned that sidelights &c could be wired to run off the 2nd battery, thus leaving the main battery fully charged for starting.  Wiring another battery in parallel with the main battery would drain both batteries, it would only extend the time before you end up with flat batteries, not eliminate the problem.

If that's what the OP wants to do it's up to him.

Another way round the OP's situation would be to have a 2nd full-sized battery (connected via a split charger/blocking diode) or one of these jump start devices so if you do drain the main battery you can jump start the vehicle.  This way you wouldn't have to rewire the sidelights &c so you could leave them on if you wanted to.

[rtbarton]

46 minutes ago, Bowie69 said:

...

The 30A relay in this form, when switched from the alternator or oil pressure switch will only pass current when the engine is running, and lead acid types take around 20-25A max, so perfectly safe.

...

Using the oil pressure switch not advised, working oil pressure can be achieved on a difficult start before the engine starts.  Plus the fact the oil pressure switch opens when the engine is running complicates things slightly.

[Bowie69]

5 minutes ago, rtbarton said:

Using the oil pressure switch not advised, working oil pressure can be achieved on a difficult start before the engine starts.  Plus the fact the oil pressure switch opens when the engine is running complicates things slightly.

That's a fair point well, and politely made

My parents camper was wired like that from the conversion, many moons ago... I suspect people were worried about frying the alternator when it has the vacuum pump in the back of it as well

[rtbarton]

Going OT, in the good old days you could get reverse oil pressure switches which closed on high pressure.  These controlled a field coil relay which powered up the alternator field coil once the engine was running, this meant you couldn't fry the alternator if the engine stopped and you didn't switch the ignition off.  It's always better to have fail-safe systems rather than rely on the driver! 

[rtbarton]

Another point in favour of using a split charge system and keeping the 2nd battery away from the starting circuit is that you can use a leisure battery as the 2nd battery.  These are designed for the job, but don't like heavy starting currents whereas a conventional battery can provide the high cranking current to start the engine.

[Mo Murphy]

Stephen old chap,

If you leave your lights on for long enough they will flatten any battery.

 

Charging a phone or ipad overnight will not flatten your starter battery. If it does then you need a new battery.

 

If you are really worried, the best way to avoid compromising your starting ability is to leave home with the phone fully charged and should it require charging then do so whilst the engine is running.

 

HTH

Mo