# How many Amps?



## AL8 (Feb 16, 2009)

Could someone tell me roughly, when on EHU, what the amps (AH) being put into the leisure battery will be?

I'm sure it's going to vary from manufacturer to manufacturer, but is it likely to be 1 or 2AH or nearer to 10AH?

I'm wondering because I want some idea of how long on EHU it will take to recharge, say half my amps = 110.

Clearly if I get 2A from the charger it will take 55 hours, or if 10A it will take 11hours.

My fear is that it's going to be more of a trickle charger, maybe not even 2 amp!

Which explains why some people fit a 2nd charger?

Or have I missed something?

As ever, thanks in advance for sharing your knowledge.


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## gaspode (May 9, 2005)

The amps delivered by any charger will vary depending on the state of charge of the battery. If the battery is well discharged I would expect any modern built-in charger to deliver at least 15amps (many will deliver considerably more) at switch-on, lowering to a trickle charge as the battery approaches full charge.


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## olley (May 1, 2005)

Hi Peter it will depend on the size of your charger, the size and the discharge state of your battery. Roughly speaking if your charger is a modern 3/4 stage it won't pump more into the battery than 20-25% of the batteries ah, assuming its in a fairly discharged state, and this will rapidly fall of as as the battery voltage rises.

An older single stage charger won't even pump that much in, as they are usually set at around 13.8volts, while the 3/4 stage can go to around 14.5volts for a time.

Olley


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## JeanLuc (Jan 13, 2007)

It depends on the output from your onboard charger. I guess most of them give a charging current of around 15 - 20 amps. So, a 110 Ah battery, discharged to 50% will take at least 4-5 hours to recharge. (The time will depend on the charging regime - i.e. how the stages are controlled.) In the later stages, the current usually falls to quite a low level.

My charger puts out 18 amps max charging current and I reckon to leave it on overnight, or preferably 24 hours to recharge 2 x 110 Ah batteries.

Philip


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## AL8 (Feb 16, 2009)

Many thanks for your answers – nice and consistent as well 

I doubt that I have a truely modern ‘modern multi-stage charger’ as standard fitment on a ‘03, but I will take some photos asap & post them for a more concise question. 

I’m guessing and I know that’s a bad thing to do, but, I think I have a 13.8V charger (as I’ve never read any more than that on a voltmeter, neither on the panel nor my own voltmeter directly from the battery) when on EHU or when I think the batteries should be ‘hot’.

And having seen ‘cheaper’, ‘older’ chargers I don’t seem have a box big enough to be able to pump out many amps, hence the original question. I know the modern 10+A chargers are very small.

But we will see.

I’ve got a fair understanding of the whole system, but it’s pinning down the specifics of my MH that I feel I need to do.

Just for your info: The reason for the question is that I recently upgraded from 1 dead x 85A battery to 2 x 110A batteries, I’m confident in the install, but I don’t seem to be getting to charge the batteries fully on a EHU overnight and recently we have not been in a position to remain on EHU (at storage or on site) for more than about 14 hours. Hence wondering about the ‘power’ of my charger; had the answers come back as ‘..almost all MH’s have a trickle charge system putting in about 3A…’ the mystery would be solved.

I’m fairly confident that I will find that I have an in-balance between usage & charging time – an in-balance the ‘wrong’ way of course 
Whether that in-balance is due to: 
1. Good ‘low power’ charger but lack of EHU time.
2. Faulty ‘high power’ charger complicated by lack of EHU time.
3. Good ‘high power’ charger with enough EHU time, but some other problem.
remains to be seen.


Again thanks for your answers, the batteries are ‘on test’ at the mo, hopefully that will eliminate them from the equation.

Watch this space.


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## gromett (May 9, 2005)

I had to look into this some time ago due to my 880AH battery bank 8O 

Batteries can usually safely be charged at 20% of their capacity max. But after they reach around 80% this reduces in stages (if using a multistage charger)

My charger was a 120Amp jobby but would only every put at most 85amps in. I tried to never let it get below 60% and from 70% it would take 4 hours to charge to 100%

The new van will only have 440AH battery bank so will be looking for a new 50amp charger. As a full timer/wild camper it is important to me to keep the batteries as fully charged as possible so a good charger is important. I will be going down the victron route again if possible.,

Cheers
Karl


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## Vennwood (Feb 4, 2007)

I did a similar thing to Karl. I have around 700Ah and the onboard charger only put out 18amps so I fitted 2 Sterling Pro Digital 4 stage chargers to boost and shorten the recharge time.

Of course if you fit a decent solar panel then, in summer at least, it will recharge your batteries during the day.

Others on here have gone for either Efoy fuel cells or the EG Self Energy LPG chargers.

The secret is not to let your batteries get low and either of the above will start to recharge automatically. The solar panels are great during summer but not so good in the winter. But if you go the solar route then do get as large a panel as you can afford and have room for.


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## grizzlyj (Oct 14, 2008)

The Ctek charger I've just bought says 115Ah 16 hours, 225Ah 32 hours to recharge 80%. (XS 7000 12v 8 stage). So one overnight EHU may not be enough to fill them right up?

Would I also be right in saying it depends what else you are using from the hookup? If 10amps are available but the heating/hair dryer etc etc is also on how do those amps get spread around? So the charger may not be getting a full monty anyway?


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## Vennwood (Feb 4, 2007)

grizzlyj said:


> The Ctek charger I've just bought says 115Ah 16 hours, 225Ah 32 hours to recharge 80%. (XS 7000 12v 8 stage). So one overnight EHU may not be enough to fill them right up?
> 
> Would I also be right in saying it depends what else you are using from the hookup? If 10amps are available but the heating/hair dryer etc etc is also on how do those amps get spread around? So the charger may not be getting a full monty anyway?


That's not quite how it works as I understand things. Each appliance will take what it needs until you ask for more than it can deliver. So in the case of a 10amp supply, your appliances would work fully until you added an appliance that took you over the 10 amps. At that point the circuit would trip and you would loose the power to everything. Something many of us have experienced in the past, particularly in France at some Municipal sites. So your charger would be getting its full monty up until the time you added say an electric kettle and that took you over the top


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## sallytrafic (Jan 17, 2006)

Vennwood said:


> grizzlyj said:
> 
> 
> > The Ctek charger I've just bought says 115Ah 16 hours, 225Ah 32 hours to recharge 80%. (XS 7000 12v 8 stage). So one overnight EHU may not be enough to fill them right up?
> ...


That's exactly right! I had toyed with several replies but couldn't come up with one without the pedant in me worrying about how to do it without at least paying lip service to Thevenin's and Norton's Theorems


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## AL8 (Feb 16, 2009)

grizzlyj said:


> The Ctek charger I've just bought says 115Ah 16 hours, 225Ah 32 hours to recharge 80%. (XS 7000 12v 8 stage). So one overnight EHU may not be enough to fill them right up?


I fear I have nothing as grand as a Ctek charger (although I think it might be climbing the shopping list :wink: ) sorting out my battery charging requirements (I WILL get that picture - I promise) and as the batteries seem to have got a good bill of health, with the comment that they needed a GOOD charge. My crude assumption that my time on EHU is lacking have possibly been confirmed (or at least strongly strengthen) by the figures quoted by grizzly.



grizzlyj said:


> Would I also be right in saying it depends what else you are using from the hookup? If 10amps are available but the heating/hair dryer etc etc is also on how do those amps get spread around? So the charger may not be getting a full monty anyway?


And of course, as I think I understand it, you need to be talking about Amp at the same voltage ie. 10A @ 240V has little to do with 10A @ 12v. eg. The charger may well be putting into the battery 15A @ 12V but only drawing (say) 1.5A from the 240V. Thus as the others have said the the 1.5A is added to the heater, kettle etc etc until (in this example) 10A @ 240V is reach & then the trip goes.

When on EHU I'm always concerned about the Amps, especially when often I find 6A (or less) is available. I use the formula of Watts/Volts= Amps.. therefore a kettle rated at 2KW is 2000w/200v=10amps, or something of 600w/200v=3A. Or 4Amps gives you about 800Watts to use at any one time, 6A = 1200W (1.2KW), 10A = 2000W (2KW) etc etc, Before I get shot down, I use 200 because it's very easy for the maths & gives me a little saftey margin - on many of the sites I've used once that trip goes there is no going back until ticket-boy comes along with the EHU keys


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## grizzlyj (Oct 14, 2008)

sallytrafic said:


> That's exactly right! I had toyed with several replies but couldn't come up with one without the pendant in worrying about how to do it without at least paying lip service to Thevenin's and Norton's Theorems


Since Thevenin's and Norton's Theorems are two equally valid methods of reducing a complex network down to something simpler to analyze, and Crystal Healing is an alternative medicine technique that employs stones and crystals as healing tools, I don't see the link? Is this a way of "charging" more for electrical work on campers, fix the problem from both a karma soothing and wiring based way?

Or are you refering to another form of pendant? 

The above T&N description is a google quote, I'd never heard of it till your post


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## gromett (May 9, 2005)

Grizzly you beat me too it. I was at a loss as to what network theory had to do with this. You don't really need to go beyond ohms law to work this out. Don't even need to consider Xc, Xl or Pf as straight forward resistive loads using ohms law covers the requirements quite adequately.

Karl


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## nicholsong (May 26, 2009)

As a Pedant with a Penchant for Pendants, I have been laughing my earrings off at the last few posts.

NOW can we get back to the topic.

I am sure Ohm's Law will suffice, maybe with a twist of Fleming's Left Hand Rule?

Geoff


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## sallytrafic (Jan 17, 2006)

grizzlyj said:


> sallytrafic said:
> 
> 
> > That's exactly right! I had toyed with several replies but couldn't come up with one without the pendant in worrying about how to do it without at least paying lip service to Thevenin's and Norton's Theorems
> ...


Well for pedants (and pendants  ) although the simple truth is that each device will attempt to pull from the EHU what current it normally does until the combination trips the supply there are more things afoot.

What determines how much current flows in a device? Well the impedance of that device and the applied voltage. No equipment is purely resistive, the voltage will change because of volt drop and won't be exactly the same throughout the installation so the net result of that is the current in the circuit will be complicated (and complex). I only mentioned T and N as that would be a step in identifying how exactly the current would divide under all circumstances. I could have mentioned Kirchoff as well as Wattless current, complex numbers etc etc etc. all of which would have had some bearing on how the current is portioned out.

However as I said the excellent explanation from Vennwood would have been my explanation had I been able to keep all those thoughts of exactitude out of my head


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## GMNTI (Oct 11, 2009)

*Charger Testing*

An iteresting study of motorhome charger performance can be found here :-

http://www.adeptscience.co.uk/autodownload.php?uid=411288&did=10757


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## AL8 (Feb 16, 2009)

AL8 said:


> ......I will take some photos asap.....Watch this space.


At last 

God knows why Elddis cut the label, obviously to hide the makers mark, but I dont really understand why.

So from the images I think it's an old style, non-multi-stage 13.8V charger, with a max DC Output of 166W or 12A @ 13.8V.

Am I correct?

Is there anything else that you can tell me from the pictures - other than I'm a rubbish photographer :roll:


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## sallytrafic (Jan 17, 2006)

Yes its a fairly solid single stage charger I have often seen their like in older motorhomes. At 13.8V you shouldn't get gassing unless the battery temperature is very high. It will take the batteries a long time to be fully charged as the charge current will taper off at the end.


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## Mick757 (Nov 16, 2009)

Whilst not wanting to hijack this topic, i couldnt see the point in starting another on a very much related theme; its apparent that extra units are fitted by some, so can i ask what others do to facilitate carrying multiple batteries?

My single 110 amp is in its box, which is virtualy sealed from the hab., and accessed from the outside. I know shoving extra batteries somewhere like under the seats isnt the done thing, so whats the answer to provide additional siting for an extra battery(s)? Cradles under the chassis?

Thanks - Mick


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## AL8 (Feb 16, 2009)

sallytrafic said:


> Yes its a fairly solid single stage charger I have often seen their like in older motorhomes. At 13.8V you shouldn't get gassing unless the battery temperature is very high. It will take the batteries a long time to be fully charged as the charge current will taper off at the end.


Sorry for the long delay... work got in the way :roll: 
So, if i wanted to introduce a more modern charger (say CTEK) this is the unit I'd be replacing? Would it be a fairly straight forward task?


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## eddievanbitz (May 1, 2005)

sallytrafic said:


> Well for pedants (and pendants  ) although the simple truth is that each device will attempt to pull from the EHU what current it normally does until the combination trips the supply there are more things afoot.
> 
> What determines how much current flows in a device? Well the impedance of that device and the applied voltage. No equipment is purely resistive, the voltage will change because of volt drop and won't be exactly the same throughout the installation so the net result of that is the current in the circuit will be complicated (and complex). I only mentioned T and N as that would be a step in identifying how exactly the current would divide under all circumstances. I could have mentioned Kirchoff as well as Wattless current, complex numbers etc etc etc. all of which would have had some bearing on how the current is portioned out.


LOL and you didn't even merge them and quote Millman's Theorem revisited to explain the link between the two :lol: But as you say Vennwood is spot on in his explanation

What a great site!

Eddie


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