# Charging leisure battery from the Engine.



## bestyman (Jul 21, 2013)

I have the usual set up of an engine battery and a leisure (well 2 actually) that are charged from the alternator when the engine is running.

I have read of the issue that when the engine battery is full the alternator sees no need to output a high charge. But why does the alternator not see the 2 batteries as one anyhow? 

I have read about a Sterling battery to battery charger that overcomes this problem, but I think I may have a simpler solution. 

Why not drive around with the vehicle headlights on, heater fan in full, things  plugged into the engine cigarette  lighter socket and fridge on 12 v. Surely the alternator would sense that it needs to output some power and thus charge both engine and leisure batteries? Would this work?


Ok that's my first question, but I have another idea too. What would happen if I plugged a small invertor into the cigarette lighter socket from engine battery and plugged a 240v car battery charger into this which was connected to the leisure batteries? The leisure batteries would in effect be getting charged twice at the same time. Would the 2 charging sources conflict?

Or would this work. Simply forget about the split charge relay and connect the batteries simply in parallel so both are seen as one and charged in no time by the alternator. When you park up flick a switch and isolate the starter battery.


Thoughts please.


----------



## Bigpeetee (Jul 21, 2013)

What you're forgetting is that there is a resistance inherent in the cabling between the two batteries, so that as the leisure battery draws current to charge, there is a voltage drop along the cable so the voltage reaching the leisure batt is always less than the starter batt.

If you beef up the cables and fit a high current relay then you improve the charging as the two batts will be seen more as one. Not perfect but a good start. You might find that this alone is sufficient for your needs.

It depends on your use, do you drive each day away or stay at one location for a few days.

Have you reduced your power consumption to a minimum?

Do you have a solar panel.

In my circumstance, improved cables and a solar panel give my batts sufficient charge.

A battery to battery unit such as Sterling, acts as in inverter and provides the leisure batts with the optimum charging conditions, however you would still need the higher current cables to supply the power, so trying that approach first is preferable.

I wouldn't try to combine an inverter/charger system together with the alternator system.


----------



## mojojo (Jul 21, 2013)

Hi, we are just starting out with a ldv convoy conversion. We haven't yet got the lesiure batt connected to the alternator. Would the inverter connected to a charger to the lesiure battery work as a temporary fix? We went out last weekend and the batt did not even last the night!


----------



## bestyman (Jul 22, 2013)

Thanks Pete,
I don't have a problem with flat batteries, just returned from 5 nights with a drive after night 3 and still returned 2/3 full. 
I'm just sometimes too curious and like to know how things work.


Mojojo,
From my tenting days I used to charge the spare leisure battery from the cars cig lighter. Look on ebay or Amazon for " cigarette lighter jump start" then you will also need a cigarette lighter to crocodile clip adapter. This set up worked well for many years.
Your solution would work but make sure that the inverter can provide enough power for the charger and only use when engine running.


----------



## LT Man (Jul 22, 2013)

I must be lucky or something.

I have got two leisure bats. connected in parallel , one 110 amp and one 85 amp. These are not a good mix if you look at some posts on here but could only fit small one under drivers seat and the 110 in passenger side.

They are charged off a basic split charge relay set up and a second circuit running my 12v supply to fridge and a acc. socket with a 12v cool box plugged in for the drinks. 

This system has never seen my bats less than full all the time and the wires to them are not that big(would guess 10amp ).

The only thing  that I do is drive every two days but am convinced that they would last at least 4-5 days min

LT Man


----------



## Teutone (Jul 23, 2013)

mojojo said:


> Hi, we are just starting out with a ldv convoy conversion. We haven't yet got the lesiure batt connected to the alternator. Would the inverter connected to a charger to the lesiure battery work as a temporary fix? We went out last weekend and the batt did not even last the night!



You need to work out how much power you consume and then size your battery to allow for this.
But first minimise your power consumption with LED lights etc.


----------



## cornishlad (Jul 28, 2013)

OP:_I have the usual set up of an engine battery and a leisure (well 2 actually) that are charged from the alternator when the engine is running._
You have a split charge relay installed ?

_I have read of the issue that when the engine battery is full the alternator sees no need to output a high charge. But why does the alternator not see the 2 batteries as one anyhow?_
It does. Normally the engine battery is fully charged and the LB is not. I've yet to read a an explanation of how the alternator controller deals with this situation but it does pretty well. Majority of motor homes are equipped this way and, provided your split charge relay is working properly and the wiring is of adequate gauge  you should have no problem.

_I have read about a Sterling battery to battery charger that overcomes this problem,_ 
If you can afford the Sterling B2B system you LB may get charged a little more fully than with the basic ubiquitous split charge relay.

_but I think I may have a simpler solution. Why not drive around with the vehicle headlights on, heater fan in full, things plugged into the engine cigarette lighter socket and fridge on 12 v. Surely the alternator would sense that it needs to output some power and thus charge both engine and leisure batteries? Would this work?_
Absolutely not !! The alternator will  get called on for all those unnecessary amps and quite possibly there will be less available for battery charging.

_Ok that's my first question, but I have another idea too. What would happen if I plugged a small invertor into the cigarette lighter socket from engine battery and plugged a 240v car battery charger into this which was connected to the leisure batteries? The leisure batteries would in effect be getting charged twice at the same time. Would the 2 charging sources conflict?_
Yes - and as the VB and the LB are connected together when the engine is running so you'd be trying to charge the LB from itself.:rolleyes2:

_Or would this work. Simply forget about the split charge relay and connect the batteries simply in parallel so both are seen as one and charged in no time by the alternator. When you park up flick a switch and isolate the starter battery._
That's doing manually precisely what the split charge relay should be doing. Arte sure your split charge system is working at all ?


----------

