Adaptor for leisure battery

Dee Dee

Free Member
Sep 27, 2014
5
0
houston
MH
none
Exp
3
I just ordered leisure battery 100 Amps and a charge relay for my van. It's not a campervan, mostly work based van. I need the second battery for laptop mostly. Now, what adapter to use to connect the laptop to the battery? Apparently classical inverters are not very efficient as the current has to be transformed twice, from 12V to 220v and back to the laptop input standard. But little do I know. I never tried it before. Another option would be to convert from 12v straight to laptop via a dc to dc converter Is this a better option? I can charge my laptop from the cigar socket so thinking as well about just buying a simplified adaptop for a fiver that will simply take the current from the leads of leisure battery, and to which I can connect my laptop charger. What the best option would be here? Thanks
 

pappajohn

LIFE MEMBER
Aug 26, 2007
35,874
23,653
YO11 2BD
MH
Homeless
Exp
Since 2005
If you can currently (no pun intended) charge the lappy via a fag lighter socket then thats all you need connected to your new battery.

But......using the lappy while charging it will extend the charge time dramatically.
 
OP
D

Dee Dee

Free Member
Sep 27, 2014
5
0
houston
MH
none
Exp
3
My bad, I don't have a laptop cig charger. I have one mini usb for my tablet. The tablet can charge, but don't know about laptop.
 
OP
D

Dee Dee

Free Member
Sep 27, 2014
5
0
houston
MH
none
Exp
3
yep they are cheap allrighty. I will need to connect it to leisure battery. I can get a cig socket with jumper cables for a few pounds, if that's the most efficient option, or a more sophisticated dc to dc converter. How long do you think the laptop will run on this before depleting the leisure battery? How long does it takes to recharge it back again from alternator with the engine running? It's a standard laptop 15 inch with the input of 3 something Amps or so it says on the tin.
 

Badknee

LIFE MEMBER
Aug 25, 2014
5,302
33,966
notloB
MH
Hobby 750 tag.
Exp
Full timing for five years and loving it!
The clue is in the name, 100 amp hour. I would imagine there is no such thing as a DC to DC converter but a good idea would be an inline fuse between the battery and the puter.
 

scotjimland

Free Member
Jul 25, 2007
32,020
29,504
.
MH
.
Exp
.
yep they are cheap allrighty. I will need to connect it to leisure battery. I can get a cig socket with jumper cables for a few pounds, if that's the most efficient option, or a more sophisticated dc to dc converter. How long do you think the laptop will run on this before depleting the leisure battery? How long does it takes to recharge it back again from alternator with the engine running? It's a standard laptop 15 inch with the input of 3 something Amps or so it says on the tin.
3amps is the current when powered from the mains.. not when supplied by a 12v battery ..let me explain..

when calculating the time the battery will last you need to consider the power .. in watts .. check the laptop label.

for example.. an 80 watt laptop powered by a 12v battery uses 80/12 = 6.66 Amps.. call it 7amps

You battery is lets say 85 ah .. with a useful capacity of 45 ah (you don't want to discharge below 50% )
divide 45/7 = 5 hours.

Recharging time from the alternator is difficult to calculate, too many variables.. has to be checked with an amp meter while charging.. but roughly the same time as it took to discharge..

Back to your question.. John and Brian both provided the solution.. an in-car 12v laptop adapter , you can remove the cigarette lighter plug and fit crocodile clips, preferably insulated ones, and if required a longer lead.. and clip onto the battery posts

you may have to screw a self tapping screw into the battery post to get a place for the croc clip to attach .. or use a full size quick release battery clamps

if you do this remember to fit a fuse near the battery end of the cable..

quick release battery clamp
 
Last edited:
OP
D

Dee Dee

Free Member
Sep 27, 2014
5
0
houston
MH
none
Exp
3
thanks guys, I'll do just that, the clamps look alright. A bit disappointing how much power it can transfer in a session. I think 80 Watts or as it is case of my laptop 90W is the max power a laptop will use with the cpu going at full blast all the time, which hardly ever happens. I hoped to get at least 12 hours from 100 Amp battery.
 

pappajohn

LIFE MEMBER
Aug 26, 2007
35,874
23,653
YO11 2BD
MH
Homeless
Exp
Since 2005
3amps is the current when powered from the mains.. not when supplied by a 12v battery ..let me explain..
I hope it isnt 3amps at mains voltage Jim.......thats 690watts.

It will be 3amps from the chargers 19 volt output which is just 57 watts
 

scotjimland

Free Member
Jul 25, 2007
32,020
29,504
.
MH
.
Exp
.
I hope it isnt 3amps at mains voltage Jim.......thats 690watts.

It will be 3amps from the chargers 19 volt output which is just 57 watts
indeed John.. my mistake..

however in my explanation I did say to calculate the amps when supplied from the 12v battery had to be made using the wattage on the label of the laptop.. and not what was on the mains power adapter
 

Minxy Girl

LIFE MEMBER
Aug 22, 2007
18,525
18,178
E Yorks
MH
Globecar Campscout
Exp
Since 1996
thanks guys, I'll do just that, the clamps look alright. A bit disappointing how much power it can transfer in a session. I think 80 Watts or as it is case of my laptop 90W is the max power a laptop will use with the cpu going at full blast all the time, which hardly ever happens. I hoped to get at least 12 hours from 100 Amp battery.
Perhaps another option would be to look at getting a second battery for your laptop to supplement it's power range that way? You could then recharge them both at home and this could give you an extra couple or so hours, so maybe 4 hours in total for the laptop batteries - although this will depend on the efficiency of the laptop itself! Using 2 laptop batteries and your leisure battery, you won't get 12 hours but you might get near 10 if used carefully (ie by tweaking your power usage, lowering screen brightness etc). As for recharging your leisure battery itself it on the run, how long is a bit of string! It will depend on how much draw you are making for other things, like lights, wipers, radio etc, how far you travel. The only way to keep it charges would be to plug it in to the mains overnight at home.
 
SMC Motorhomes Newark
RoadPro
Johns Cross
Safeguard Motorhome Insurance
Rhino Installs
Friendly professional service from qualified technicians
Free Club Stickers
Dave Newell Leisure Vehicle Services
Top