Spare 110 amp battery in car split charge question

[foggydave]

Hi
If we go away for a long period I carry a spare 110 amp leisure battery. (The wife watches a lot of television)
I charge it through a Durite relay so that the battery is isolated until the alternater pumps out 13v +. When connected the battery constantly charges at 14.5V and does not diminish as the battery charges up.
The question is. Does a normal car battery charge system constantly charge at 14.5 volts whilst the car is being driven or does the charge go down as the battery tops up?
Will it harm my leisure battery if it is constantly charged at 14v + or will the battery take only what it needs?

 

[Sproket]

Either your relay is faulty or your Alternator is over charging for it to be at 14.5v all of the time... the battery charge is replenished after starting unless something else is drawing power, the Alternator will slow the charge rate down, but depending on the condition and age of your 110 battery that might not be telling the relay that it's full so it is always demanding power.

Has the 110 amp battery been checked ?
If you disconnect it & leave it for a week or two how much is the volt's dropping. ?
How are you checking your voltage ?

If you put one of these in your car you will see what the battery voltage is with out lifting the bonnet, you will see it fluctuate as the demand for power increases... it would be quite easy to make a cable up so that using the same gadget you could monitor the battery in the boot ....

 

[WoodlandsCamper]

What does this mean in the given link?

"When engine running (do not drive),"

 

[foggydave]

Hi Sproket

Thats a handy little gizmo. As you say a bit of diy and a handy little volt meter. Thanks for the link
As I understand it my Durite voltage sensitive relay just opens when the alternator output reaches a certain voltage and then stays open until I switch the engine off.
I check the voltage using a standard Clarks work shop voltmeter with the meter prongs inside a 2 pin plug which is attatched to the battery terminals
The car battery is new and the leisure battery is 2 years old and holds its charge ok. If as you say the alternator should reduce the charge I wonder if having 2 batteries on the system confuses it somewhat.

 

[Sproket]

What does this mean in the given link?

"When engine running (do not drive),"

I ain't got a clue.... maybe for an extra 50p they don't set on fire :lol:

After recently changing both the Alternator & battery on my truck, mine is just sat plugged into the cigarette lighter monitoring the voltage for me and if you watch the read out you can tell when the heater plugs are fully warm before starting, cheap an chearful and it works....

 

[Sproket]

Hi Sproket

Thats a handy little gizmo. As you say a bit of diy and a handy little volt meter. Thanks for the link
As I understand it my Durite voltage sensitive relay just opens when the alternator output reaches a certain voltage and then stays open until I switch the engine off.
I check the voltage using a standard Clarks work shop voltmeter with the meter prongs inside a 2 pin plug which is attatched to the battery terminals
The car battery is new and the leisure battery is 2 years old and holds its charge ok. If as you say the alternator should reduce the charge I wonder if having 2 batteries on the system confuses it somewhat.

What should be happening is that when you are driving around and you get to the traffic lights and the engine is ticking over as the output voltage drops the relay should close until the voltage gets high enough for it to open & start to charge again...

For less than a fiver for two ... I would make a lead up and try it ...

 

[foggydave]

Hi
The relay works properly and cuts out at low revs and in at 13+ volts. My problem is that there is a constant charge of 14+ volts and I need to know if this is correct.
I have ordered a voltage meter so will see do some checking.

 

[Spurtle]

I have always been lead to believe that a lead acid battery should not be charged at more than 2.4 volts per cell, or 14.4 volts for a 12 volt battery.

If a battery charger does it the 'textbook' way (well at least as I was taught it should ) it will charge at somewhere towards its maximum current rate and the volts per cell will increase , until they reach 2.4 - this only happens at approx 70-80% of full charge.

At this point, it should enter a constant voltage phase , holding at no more than 2.4 v per cell and the current will gradually reduce as the battery approaches 100% charge. The current at that point will have dropped to about 2% of its 20hour rating ( for a battery with 90 ah 20r rating, that would work out at 1.8 amps)

Ideally, as full charge is reached , voltage will be reduced to about 13.4 and the current to less than 1 amp.
This will keep the battery fully charged , without risk of boiling .

These figures are affected by temperature.

Tto check whether a charger , or any charging system, is doing what is says on the box , you would need an ammeter in addition to your voltmeter.

So 14.5volts is borderline for overcharging your battery but you need to determine whether the current is reducing as full charge is reached, to tell whether your charging system is working correctly.