# Leisure battery charging from engine?



## 90809 (May 1, 2005)

Dear all, 

A naive question maybe from a recent owner of a VW Autosleeper Clubman on a VW LT chassis. I'm not sure if my leisure battery is charging from the engine. It charges fine from a hook-up, but there is no indication (green light on the control panel) to show that it's charging when I'm driving. Should there be? As a photographer using a laptop on location, I'm frustrated at how quickly the battery runs down. I use an inverter, though it seems very inefficient to convert DC to AC and back again, but I've heard of no other way to do it. Any ideas on either of these matters would be most useful!

PhilipT


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## JockandRita (Jun 1, 2005)

Hi Phillip,

If you have a 12 volt meter, you could check the voltage across the terminals of the leisure battery, then, start the engine and check again to see if there is an increase in the voltage reading.

If there is a split charge relay in the system, you may not get a higher reading until the vehicle battery is charged and the relay switches over to the leisure battery.

I get a reading immediately the alternator is running.

Hope this helps,

Jock.


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## spykal (May 9, 2005)

Hi Phillip

AFAIK on your Autosleeper there will be no indication of the leisure battery charging when driving. if you wish to check that it is actually charging beg, buy or borrow a digital multimeter and check the voltage at the leisure battery when the engine is running ( fast idle will be OK).

The battery voltage at the leisure battery when the engine is not running should be around 12.6v and will jump up to the charging voltage ( 13.8v +) as soon as the altenator gets going. 

mike

P.S. you said "I use an inverter, though it seems very inefficient to convert DC to AC and back again, but I've heard of no other way to do it".... do what exactly? ... you never know there may be a better way ...but what exactly are you using the invertor for? if it is to power your laptop mains adaptor you may get a little better performace if you obtain a DC to DC adaptor for the laptop. The gain may only be small but could be enough to make a difference. The other suggestion I have is to carry another leisure battery just for powering the laptop.


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## 90809 (May 1, 2005)

Thanks folks, I'll check the charging with a multimeter. I've just found a DC to DC connector on the HP website http://www.shopping.hp.com/product/notebook/notebook_hp/batteries/1/accessories/ER691AA%23ABA, so maybe the problem is solved. My laptop uses 18.5 V dc at 4.75 A (not that means all that much to me, I'm afraid to say. However, I am a whizz at Photoshop...
Very grateful for your help,
PhilipT


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## DABurleigh (May 9, 2005)

Philip,

You might consider one of these:
http://www.action-replay.co.uk/Computing/laptop_power_adapter.htm

Though in your situation I'd probably go this route, I wouldn't expect the 30% gain claimed over an inverter. I would also look into the availability of bigger capacity batteries that fit my laptop, and get a second one. I use my laptop heavily for work, and while others faf around fighting over a seat near a power outlet, my 2 laptop batteries onboard give me a full working day without me contributing to trip hazards in conference rooms.

Dave


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## 90809 (May 1, 2005)

Thanks Dave. That adaptor looks much more affordable than the HP one. I'll also check out higher capacity laptop batteries. 
I've never actually run the leisure battery to a standstill. The inverter has a warning beeper which kicks in when the battery voltage drops. After 10 mins or so it starts this awful racket, ruining any concentration I have for the job!
Cheers,
Philip


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## DABurleigh (May 9, 2005)

Ah. Methinks you probably have a different problem. To what are you connecting the inverter? A 12V socket installed somewhere in the van by the manufacturer? These are notorious for having weedy wiring between socket and battery. Even at moderate currents the voltage drop on this resistive wire is enough to present the inverter and similar appliances with a voltage lower than its threshold operating voltage.

If so, either replace the wiring or install the inverter much closer to the batteries. Voltage drop at mains voltages, by comparison, is always ignorable.

Dave


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## spykal (May 9, 2005)

Hi Philip

One other source of quite a bit of extra power is your vehicle battery, many folk do like using any of the available energy in the vehicle battery in case they cannot start the engine when it is time to leave but I quite often use my vehicle battery as an extra source of power ... after all my vehicle battery is bigger than either of my 2 leisure batteries.

When I do use the van battery to power my laptop ( via a Kerio DC - DC adaptor) I protect it with a  >> Battery Protector << just to make sure that I will have power to start the engine in the morning. Interestingly in the three years or so that I have been doing this the protector has never ever cut off the power to the laptop, which maybe goes to show how much spare energy is available in there, so it a shame not to use some of it :wink:

Mike

P.S. and before you ask :roll: yes I have done a test with the battery protector to ensure that when it cuts off the supply from the van battery there is still enough energy to start the engine. Also in the spec of the protector it says _Automatically cuts power supply when the battery voltage is below 11.2V (±0.3V) _ ... I did worry that this was way too low but in use it seems to work just fine.. with the 11.2v setting and the load from my laptop it cuts off in good time and the battery is still ready and able to start the engine.


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## DJP (May 9, 2005)

> Ah. Methinks you probably have a different problem. To what are you connecting the inverter? A 12V socket installed somewhere in the van by the manufacturer? These are notorious for having weedy wiring between socket and battery. Even at moderate currents the voltage drop on this resistive wire is enough to present the inverter and similar appliances with a voltage lower than its threshold operating voltage.
> 
> If so, either replace the wiring or install the inverter much closer to the batteries. Voltage drop at mains voltages, by comparison, is always ignorable.


Definately the correct explanation IMO.
I've been there done that :wink:


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## sergeant (Jun 7, 2006)

Hi Phillip, Your computer says it takes 4.75a at 18.5v then if you use a dc converter from a nominal 12volts you in theory & round figures will consume at least 7amps per hour from your leisure battery which on your van will be an 85a one then theory!!!!!! says you will get 12 hours use, Steve


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## 92859 (May 1, 2005)

*lap top*

Greetings,

I got one of >>these<< today Phil, works a treat, adjustable output.


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## 90809 (May 1, 2005)

Thanks for all help and suggestions. Indeed I am drawing power from a 12v outlet yards away from the leisure battery. I'll fix up a socket directly from the battery. Still haven't checked the voltages - in my van I have to take the seats out, because the luxurious carpeting on the battery cover box won't pass through the hatch provided.
I thought I'd found a 12V 90W car adaptor at Maplins but it turns out that my HP laptop has an odd sized socket, as Maplins warned me it might.
So if I can find a DC adaptor, site a socket near to the battery and buy a spare laptop battery, I should have the problem sorted out! I'll let you know. Much obliged for the maths help - seven hours sounds a handy amount.
Cheers,
Philip


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## 90809 (May 1, 2005)

Misprint - twelve hours not seven! That's longer than I'm ever likely to need the computer, so that would be fantastic.
Philip


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## 90809 (May 1, 2005)

Hi all,

Just an update on this situation. I had my leisure battery tested - it is receiving a good charge from the engine and is well charged already. This in itself is a mystery, because the Zig control box registers it as uncharged (red light not green). So it seems as if the length of iffy cable theory is probably correct. I have connected a power outlet directly from the leisure battery, and it seems to do the trick - no annoying beeping or cutting out from the inverter any more, though I've only run my laptop for half an hour so far.
No joy so far on finding a DC to DC adaptor - there are plenty on the market but HP have changed the power socket size on its recent laptops and there is no third party adaptor plug that will fit. I'm waiting to hear from HP about this but it looks like I'm out of luck for the present.
Thanks again to all those who have helped on this most excellent website.

Philip


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## DABurleigh (May 9, 2005)

Philip,

What is your hp model; I don't think you've said so far?

Dave


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## 90809 (May 1, 2005)

Hi Dave,

My lapton is an HP Pavilion dv8395ea, bought in August last year. It has a nice fast processor and dual hard drives, ideal for the gigantic panoramic photographs I produce. Maybe it's a bit heavy on the juice though.

I guess it's only a matter of time before someone produces a plug that fits. I've sent a few emails to suppliers. Maplins says no go. Laptopbits suggest that a mains inverter is a more reliable supply - but they can't sell me one because that's what I use already. There doesn't seem to be an exact HP product either.

I did wonder vaguely about cutting the plug off an HP mains adaptor and sticking it on a third party DC adaptor, but it seems like a) a botch up, and b) a very expensive work around. But I think that siting the DC outlet socket close to the battery will be a big improvement, even with the inverter. It will have to do until a better product turns up.

Philip


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## DABurleigh (May 9, 2005)

Philip,

Doug of Action Replay (near me in Basingstoke) will be at Shepton next weekend if you are thinking of going. He will have his normal stand, including his DC-DC converter and plugs.

I wonder if you could post a picture of the plug and socket?

Dave


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## 90809 (May 1, 2005)

Hi Dave,

I haven't tried posting images to this site, so I hope the attached photo appears OK. The shaft of the plug is 9.5mm long and 4mm wide, and the hole in the middle is about 1.5mm diameter. These measurements can only be approximate as I need to get new glasses! 
I plan to be in the West Country soon so will try to call in at Shepton en route.

Cheers,

Philip


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## DABurleigh (May 9, 2005)

OK, I've pointed Doug to this. It looks a straightforward one to me. Take your laptop to Shepton! 

I wonder if tip A or T is close enough, if not it:
http://www.action-replay.co.uk/Computing/laptop_adapter_tips.htm

Dave


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## DABurleigh (May 9, 2005)

Philip,

Doug is almost certain it is a "T" one. He'll make sure he has them with him at Shepton. That's the Compaq one; it may or may not be a red herring that HP took over Compaq.

Dave


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