# Understanding Volts and Amps and things?

Discussion in 'The Beginner' started by Tecnikal, Oct 22, 2013.

1. ### Tecnikal

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I've had a little search through these forums and done a google search with not much luck.

Can anyone point me to a thread or webpage that explains to the complete novice about the readings that come up on the little computer pad in motorhomes.

You can click on the car sign or the motorhome sign and then click on the Battery voltage or battery current button. (V and A)
Things like:
What should Battery voltage read when full? Can you use the leisure battery till it says zero and then charge it up?
What is A and Ah or d after the number?
I've been told you have to watch these numbers and keep them at certain levels to stop you tripping out the park etc.

Those are just a few things, but basically I need to get the the whole volt and amp thing explained to me before we go off on our first motorhome trip and I blown the darn thing up.

Preferably explained in words of one syllable lol.

It all seems so daunting at first.

Any help is appreciated.

Thanks.
Brian.

2. ### TheBig1FunsterLife Member

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try reading this thread. although concerning solar panels, it includes explanations of how the batteries work
http://www.motorhomefun.co.uk/motorhome-chat/71780-solar-panel-how-does-work.html#post839690

in essence its all quite simple though. a full battery will read between 13.5 and 13.8 volts if the charger is connected. you only use about half the potential power in the battery before recharging 11v is about as low as it should go as 9v and below will damage the battery

a 110a/h battery is able to give in theory 110amps for 1hr or 55amps for 2hrs etc. in reality though expect a 110a/h battery to be good for 55a/h useage.
so if your tv takes 8amps expect 6hrs continuous usage without recharging. Most modern tvs take less than 8amp though

a well set up van with LED lights and normal use of pumps and a couple of hours tv you should get a weekends use from your battery. if you use sites with electric hookup, then this is irrelevant as the battery will continue to charge as its used. those hardcore campers that prefer to be offgrid for weeks on end use solar panels and generators to recharge the batteries

oh, and the state of the battery will not effect the site electrics at the bollard

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3. ### motorhomeloverBanned

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14.5volts when charging 13 volts wen full
Never leave a leisure battery at lower volts with out charging as it will damage the battery

Amps are not as easy to work out.
The old saying. A little knowledge is dangerous springs to mind
So don't get involved in that side. Leave it to an auto electrician

Simples :thumb:

4. ### SuperMikeFunster

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A 12v battery, measures 12.6v fully charged, when it has been off the charger for at least 2 hours. 12.3v is as far as you should take it down, about 50%. At 12v it is flat and at 11v you have killed it big time.

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5. ### TechnoFunsterLife Member

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As Big1 said 11 volts ON load is time to turn it off

Last edited: Oct 23, 2013
6. ### estcres

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Hi Brian,

V = Volts

A = Amperes (Amps)

Ah = Ampere Hours

d = discharge.

If you can imagine pushing something along a surface it will create a resistance and you will need a "force" to push that thing along. That is what a Volt does. In technical terms:-

"A volt is the pressure required to push 1 Amp of Current through 1 Ohm of Resistance"

An Amp is the unit of current and is used to work out you wattage. Ie:

Amps x Volts = Wattage ( 10A x 12V = 120W)

Watts/Volts = Amps (120W/12V = 10Amps)

So if you have a Battery with a capacity of 110Amps, you divide that by the Amps of the item, In this case 10Amps and that will tell you how long that item should last using a fully charged Battery:-

110A/10A = 11Ah (Amp Hours)

d = discharge and this indicates that your batteries are discharging that number of Volts or Amps.

Dividing your Battery Amps or Volts by the figure displayed will give you an indication of how long your battery will work

A Fully charged Battery should be somewhere around 13.2 Volts and a discharged Battery is usually around 12 Volts.

If you take a battery reading straight away after charging you will get a much higher Voltage reading, it is recommended that you wait about 20 minutes after charging to get an accurate reading of you Battery.

I hope this helps a bit, but, I expect you are more confused that at the start.

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7. ### WisselFunster

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A 12v battery fully charged should read about 12.7v, as others have said this is when the battery has been off charge for at least 3 hours.

A battery being charged from the vehicle alternator should read around 13.7v while the engine is on and then trickle down to 12.7v over a few hours if fully charged.

If your using a Smart Charger (sterling battery to battery, sterling alternator to battery, CTEK D250S, multi-stage mains charger etc) then the battery will show a reading of up to 14.7v. Again after a few hours of not being charged it will read about 12.7v when fully charged.

If your battery is reading 12.2v after a few hours with no charging then the battery is about 50% full. This is about as low as most batteries like to be dis-charged without damaging them (some traction batteries can go much lower).

If it's reading below say 12v the battery is dead, will definitely need charging and may need replacing (most garages can test the battery very quickly and free of charge).

If you are using a standard split-charge system in your van this can only charge a battery to around 85%. Using an example of a 100Ah battery being charged from a basic split charge system this would mean the battery would only charge to around 85Ah and at 50Ah it would need charging. Effectively, this means the 100Ah battery has 35Ah of usable power.

A smart-charger can charge the battery to 100% so using the same example as above means you have 50Ah of usable power.

I did so much research on this subject before installing my electrical system it was getting ridiculous

Last edited: Oct 23, 2013
8. ### magicsurfbusFunster

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If you're into your volts and stuff, try buying a couple of lighter socket voltmeters, and sticking one in your dashboard socket and one in an available socket in your habitation area. You can watch the voltages rising and falling at various stages of your journey to your heart's content.

Typically the engine alternator or campsite hookup charger will put around 14.2v through my batteries, and will adjust for fridge, headlamps, heater etc. The solar panel (with its charge controller) on a sunny day will maintain the leisure battery at around 13.6v, then when the sun goes down the leisure battery settles to around 12.8v. If we put the telly and satellite tuner on we sometimes see the leisure battery drop below 12v but it pops back up again as soon as we switch the gadgets off.

Whilst I take the point about discharging damaging batteries it doesn't necessarily wreck them altogether. My engine battery accidentally discharged to an almost unreadably low voltage this winter, but after recharging it's still doing the business, supporting all the demands I can throw at it, and is starting the vehicle first time every time. Discharging is however best avoided, and having one of the ciggie lighter voltmeters above provides an early warning of any problems.

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9. ### PhilandMenaFunster

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10. ### Tecnikal

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Thanks

Thanks for all your hlep guys.

there seems to be a few differences of opinion there but I think I got the idea. My leisure battery reads 12.9 when full. I drove it for four hours and charged it for 2 so assumed that was enough to fully charge a battery.

I assumed that half power would be 6.5 but clearly it doesn't work that way. Some of you say that I can run it to 11 and others say 11 would be dead and run it to 12.3. I guess I'll get the hang of it.

I can't guarantee the battery is brilliant anyway, I beleive it hadn't been used for many months before being sold to me. If they are not too expensive it might be worth me getting a new one. This one has been in the motorhome for 14 years as far as I know in my 1999 model.

11. ### estcres

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If that is the original battery it's done very well.

12. ### Tecnikal

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I dont know if it is the orginal. Was looking at Leisure batteries online and I guess the thing to do is to get the 110a instead of the 80a. If I've got this right it means it will last longer ... ummm or does it mean I can run more things off it. Actually probably both. oh gawd! I've confused myself again. lol.

13. ### PhilandMenaFunster

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In short, do not let your battery discharge more than 20%.

14. ### Tecnikal

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Thank you

Have read the article posted. Great article. I think I have a better understanding now. I've just got to get my head around it. Thanks for all your help everyone.:thumb:

15. ### Wildman

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Power refers to amps not volts i.e. a 100 amp/hour battery is at 50% discharge when 50amps have been used.

understanding the relationship between amps, volts, watts is not something you can grasp in 5 mins, if you find yourself down this way or at any meet I attend I'd be happy to talk you through it.

16. ### mike9jr

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Seriously........? Not let them drop below 20%.....
I'm gonna use all my payload on batteries!!!!!!!

I may have to look at solar..............