Another battery question. (1 Viewer)

[irnbru]

After just purchasing 2 new leisure batteries I am trying to get a better understanding of how they operate in the hope they will last a few years. So far I have learned that 2 batteries in parallel shows up like 1 big battery so can someone explain

1.How the 2 batteries discharge. Do they do so at the same rate or does one run to half empty 1st?
2. Does the system stop producing battery power when the batteries reach maximum discharge limit or is it up to me to monitor the level on 1 or 2 of the batteries each time we use them? If I have to monitor at what level on the meter would be the lowest to use, sorry if im confusing you.

 

[pappajohn]

as both batteries appear as a single large battery they discharge as one battery.

The batteries will discharge to a dead state eventually (0v) and will not recover when charged.

Its up to you to monitor the discharge and act accordingly...ie: recharge when at a max of 50% discharged.
50% equates to approximately 12.2v

 

[irnbru]

Thanks for the reply but this is confusing me more now. When the banner batteries were put in two days ago the meter reading was 12 point something so after 50 percent they should still read 12. Something?

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[maz]

Thanks for the reply but this is confusing me more now. When the banner batteries were put in two days ago the meter reading was 12 point something so after 50 percent they should still read 12. Something?

That 'point something' is the important bit. 12.7v = ~fully charged, 12.3v = ~50% charged.

 

[pappajohn]

no....fully charged, but not on charge, they will show 12.6v to 12.7v.

As the batteries are used the voltage drops to a point they cannot provide enough volts to power the appliance, whatever that may be.

Akin to filling water glasses from a jug...each glass takes a little more from the jug until eventually the jug is empty and you drank the water in the glasses.

A 12v light bulb will still work at 11v but will be extremely dim compered to running at 12v or more

 

[irnbru]

Aaah think im getting it now. :thumb:

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[UK Pete]

Also batteries have a limited amount of charge disharge cycles, so not letting them run down to as low as 50% helps them last longer as i understand it
pete

 

[Tootles]

There is a 'rule' that batteries coupled together either series, or series parallel, should be all of the same size and amp-age capacity.
Never found it matters personally, however............

 

[irnbru]

Wha can I get for point 4.?is it equal to so many amps?

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[pappajohn]

Wha can I get for point 4.?[HI]is it equal to so many amps[/HI]?

very loosely, yes.

110ah battery at full charge (12.6v/12.7v will have 110amps stored.

12.4v is around 25% discharged so capacity is around 77amps

12.2v is around 50% discharged so 55amps capacity....for our purpose technically flat.

Once a battery gets below 50% discharged it starts to oxidise the lead plates and this causes the charging process to work so much harder to recharge....over time it becomes impossible for the charge current to pass into the battery due to the amount of oxide on the plates.

If charged straight away, or as soon as practicable, from 50% the oxide is easily broken down and the battery accepts a charge.

 

[irnbru]

So if i use 50 percent how many amps do i have to play with. Sorry but dont understand the last answer.

Ps I have 2 batteries together.

 

[pappajohn]

So if i use 50 percent how many amps do i have to play with. Sorry but dont understand the last answer.

from fully charged you have 55amps to play with from a 110ah battery.

After using those 55amps (50% of fully charged battery) you need to recharge the battery or risk damaging it.

I know the battery holds 110amps but thats how it works unfortunately.

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[UK Pete]

If you use 50% of your battery power you have taken it to its limit so you really dont have anything to play with if you want to keep the battery in good health, although technically you will half the amp power stated on the battery but as mentioned you will be doing the battery harm
pete

 

[irnbru]

So whats the point in having 2 batteries linked together? Does that give me 110 or even 100 to play with?
Thanks for your patience while i continue to get my head around this.

 

[Tootles]

Supposedly, a 'leisure' battery can re-coup more of it's am-page capacity then a traction battery, (from total discharge), however, (unless things have changed since this happened to me), charging over ten amps can buckle the plates, causing the battery to be useless within a short time, (12 months with me).
This might be different now????????

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[pappajohn]

So whats the point in having 2 batteries linked together? Does that give me 110 or even 100 to play with?
Thanks for your patience while i continue to get my head around this.

correct.....2 batteries joined pos terminal to pos terminal and neg to neg will give you 110amps to play with and will still be 12v.

I have 4 x 110ah so have 220amps to play with between charges

 

[maz]

Try thinking of it as a balancing act - what you take out against what you put in - and aim to keep the battery voltage (off load) at around 12.7 or 12.6 v. Yes, you can let it drop lower than that on occasions but when it gets to 12.4v, that's when I'm rummaging in the locker for the generator.

 

[peterc10]

So whats the point in having 2 batteries linked together? Does that give me 110 or even 100 to play with?
Thanks for your patience while i continue to get my head around this.

If you link two 110Ahr batteries together in parallel then you have 220Ah total. 50% of that means that you have 110Ahr to use up before you recharge, rather than 55Ahr if you only had one battery. Ahr is short of amp hours, i.e. amps used multiplied by the number of hours you are using it.

Amps x Volts = Watts. So for every watt of power you use in a 12v system you use one twelfth of an amp per hour of use. So check the wattage of each appliances and bulb, divide it by 12 and then multiply it by the hours you will use it. Do that for each appliance and then add them all up to give you the Ahrs you are using.

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[irnbru]

I think I must be getting short changed here. Our batteries were fully charged yesterday morning, now reading 12.3
We have only had tv on about 4 hrs. Been charging mobiles and tablets, not used much light either. Heating been running approx 3 hrs. For 2 batteries I was expecting much more.

 

[maz]

I think I must be getting short changed here. Our batteries were fully charged yesterday morning, [HI]now reading 12.3[/HI]
We have only had tv on about 4 hrs. Been charging mobiles and tablets, not used much light either. Heating been running approx 3 hrs. For 2 batteries I was expecting much more.

Is that with the above loads still running tho'? See what voltage the battery recovers to after they have been switched off for a short while.

 

[pappajohn]

I think I must be getting short changed here. Our batteries were fully charged yesterday morning, now reading 12.3
We have only had tv on about 4 hrs. Been charging mobiles and tablets, not used much light either. [HI]Heating been running approx 3 hrs.[/HI] For 2 batteries I was expecting much more.

if thats blown air heating then it kills batteries.

The fan in the heater can take up to 10amps per hour so theres 30amps gone already.

LCD Tv at 20 watts is another 1.5amps per hour so another 6 amps gone.

Phone chargers...negligible.

Lights. If they are standard halogen filiment then around 1.75amps per hour each light.

So your battery consumption so far is about normal.

As Maz said, once everything is turned off the voltage will rise slightly...this is normal.
A car battery can be fulluy charged but when you crank the engine the battery volts can be as low as 9 or 10 volts...but soon come back to 12.6v once you stop cranking..

Juggling battery useage against battery capacity is a fine line and is something which comes with experience.....it is a limited power source and needs to be used frugally if you want a decent amount of time from them.

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[irnbru]

Ive gone back to MH and unplugged chargers. Will check the reading in a few hrs when we return to MH. Checked tv it says 40w.

You are all most helpful, THANK YOU

 

[maz]

if thats blown air heating then it kills batteries.

The fan in the heater can take up to 10amps per hour so theres 30amps gone already.

I think that 10A figure must be only when the fan's doing 'vertical take-off' which it doesn't do for long. Once it settles down to normal speed it draws only just over 1A. (Truma Combi 4E/6E anyway).

 

[peterc10]

if thats blown air heating then it kills batteries.

The fan in the heater can take up to 10amps per hour so theres 30amps gone already.

.

Not sure where your figures come from. I have a Truma combi 6E. The handbook says its short term maximum for 12v electrics is 5.6A, which is when it first fires up to start and you can hear the fan running quite loudly. The average power is listed as 1.3A. I have checked whilst the heating is running and their figures are, if anything, higher than I was seeing.

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[maz]

Will check the reading in a few hrs when we return to MH.

So what was the off load reading? Don't keep us in suspense!

 

[pappajohn]

I think that 10A figure must be only when the fan's doing 'vertical take-off' which it doesn't do for long. Once it settles down to normal speed it draws only just over 1A. (Truma Combi 4E/6E anyway).

Not sure where your figures come from. I have a Truma combi 6E. The handbook says its short term maximum for 12v electrics is 5.6A, which is when it first fires up to start and you can hear the fan running quite loudly. The average power is listed as 1.3A. I have checked whilst the heating is running and their figures are, if anything, higher than I was seeing.

my apologies.....was thinking RV at the time....the rv fan is a constant speed/constant flow and is thermostatically controlled....either running or off with nowt in between.

 

[irnbru]

Sorry for the delay in replying. Reading read 12.37 and now im home they mustve charged, now read 12.73 so next time I go away I willkeep a note of what Im using.

Does a 300w inverter use all the 36amps or only if you use all that load worth. I was using it for mobile and tablet charging?
Thanks

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[peterc10]

I was using it for mobile and tablet charging?
Thanks

Don't do that, you are introducing two lots of load losses. One when the inverter changes it to 240V and another when your phones charger converts it back to 5V or whatever it uses. Just buy a 12v charger - plenty of USB about.

 

[maz]

Sorry for the delay in replying. Reading read 12.37 and now im home they mustve charged, now read 12.73 so next time I go away I willkeep a note of what Im using.

Does a 300w inverter use all the 36amps or only if you use all that load worth. I was using it for mobile and tablet charging?
Thanks

So the battery had dropped quite a bit. As you say, it's a good idea to keep a note of what you're consuming until you get used to it.

The inverter will draw from the battery to feed only what load you're running. However as Peter says, there is an inherent loss through the inverter (allow 10% loss as a rough figure) and it's not the best way to charge other batteries.

 

[JJ]

I suspect that guages used in motorhomes to display volts etc are not always very accurate.

Ok to use to get a rough idea but not to use as gospel truth.


JJ :Cool: