12vdc to 15vdc car charger for laptop

[lozza47]

Hi all whiz's,
Have got a 12vdc cigarette lighter fitting for my laptop, but the laptop needs 15vdc, SO !!!! how can get 15vdc out of the cigarette lighter ?????????????? what do i need ?????????????
Regards lozza

 

[MikeMl]

My Dell laptop came with a charger that works from 12 to 24VDc, or 100 to 250V Ac.

 

[crutschow]

You would need a boost type switching regulator.

 

[ronsimpson]

Hi all whiz's,
Have got a 12vdc cigarette lighter fitting for my laptop, but the laptop needs 15vdc, SO !!!! how can get 15vdc out of the cigarette lighter ?????????????? what do i need ?????????????
Regards lozza

Car voltage can be all over the place. When the car is off 12V. Leave the lights on for a while and you will get 10V. With the car is on maybe 14 volts. (14.5??? 15V???)

If you feel lucky, try it and see if the laptop's battery charges.

 

[MikeMl]

Car voltage can be all over the place. When the car is off 12V. Leave the lights on for a while and you will get 10V. With the car is on maybe 14 volts. (14.5??? 15V???)...

Ron, it is not that bad. With engine running, voltage will be 13.8 to 14.5V. Parked, the voltage will be 12V to ~13.2V. During starter cranking (when all loads should be disconnected) the voltage may sag as low as 10V.

If the voltage ever to reach 15V, the car's voltage regulator is hosed...

The OP needs an "automotive" charger, specific to his lap top. If I was too cheap to buy the one that is made by the maker of lozza's laptop, I would be haunting the local thrift shops. They frequently have old (pre-windows) laptops complete with carrying cases and power-supplies for a few bucks. **broken link removed** has hundreds of Chinese aftermarket chargers...

 

[ronsimpson]

In my truck the cigarette lighter does not disconnect during cranking. The voltage has high ripple at 8x the cranking RPMs. (V8) I agree a well maintained battery is 13.8 to14.5V. I have seen the peak voltage get very high on old, high resistance, batteries as they die.

I also don't know how the laptop is built. Is it possible for current to flow out of the computer and back into the car during cranking or if the lights get left on?

I agree, go get the real charger!

 

[kinarfi]

If you're interested in building your own, say so, and I'll see if I can find the schematic for the one I made for my 18.5 V 3.5 A HP Lap Top.

 

[bigal_scorpio]

If you're interested in building your own, say so, and I'll see if I can find the schematic for the one I made for my 18.5 V 3.5 A HP Lap Top.

Hi Mate,

As it happens I am interested in your supply so if you could post I would be happy to have a look.

Al

 

[MrAl]

Hello to OP and later joiners,


If you want to charge a laptop battery from the car cigar lighter and the battery is 15 volts, then yes you need to boost it from a nominal 12v to 15v.

But there's one more thing. Because the battery is probably Li-ion that means you have to be very careful about how you charge it. If it is NiMH that is a little more forgiving.

And yes the issue with the car voltage is that it can be anywhere from about 8v to 15v or if not trying to start the engine maybe about 11v up to 15v. So you need a boost circuit that can work from say 10v to 16v and put out the required current for the battery, and also a battery charging circuit that matches the chemistry of the laptop battery.

So the requirements are:
1. Boost circuit that can take 10v to 16v input and put out the required max voltage and at least the min required current, and
2. Charging circuit that matches the laptop battery chemistry, and
3. Fuses.

 

[kinarfi]

Hi Mate,

As it happens I am interested in your supply so if you could post I would be happy to have a look.

Al

I'll get some photos today and redraw the schematic, I must have lost it some where along the line.
Kinarfi

 

[gerty]

The cop cars around here had the best luck using a 400w inverter and the original 120v charger.
They had all kinds of rebooting issues everytime they started the car, or turned the siren on. I wasn't involved with working on it, just heard the stories from the officers.

 

[lozza47]

sounds good to me knarfi, thanks heaps, go find it, will wait till i get a message from you, good luck and cheers pal.

 

[kinarfi]

**broken link removed**
This is the first of several photos, I mounted the LT1270A and the diode to the heat sink and then super glued the pot to the LT1270A and the 1uf cap to the pot, as well as the inductor to the heat sink. I have had a few failures with super gluing, but where it failed was on larger, heavier jobs. The small circuit board was salvaged from something else that I don't remember and is a fan speed controller which reduces the speed of the fan until the heat sink heats up, haven't really used the power supply yet as the laptop I built it for cratered and was replaced with another HP but I haven't found a plug for for it yet, so if anyone knows where to get just a plug for an HP, let me know. Let me know if you have questions, always glad to help.
Kinarfi

 

[lozza47]

Hi kinarfi,
UM !!!! and again UM !!!!!!!!!!! thanks heaps for the reply, but UM !!!!!!!!!!!!!!!! heavens above ????????????????? i gotta take a back seat here, maybe even move to the back of the class, i just an absolute electronics idiot, i can almost get the in and outs of the diagram (i think) but how in hell am i going to build that ?????? LMAO i think i've bitten off more than i can chew here. i think i should apologise for wasting your time, ???? i got no hope here. LMAO. You guys are right up with all the tech, but you are talking an idiot here LMAO, i gotta thank you guys heaps but i am lost in "outta space " and way out of my comfort zone here. LMAO

 

[bigal_scorpio]

Hi kinarfi,

That looks good to me and I will build one shortly, though its not for a laptop but for another project that just requires more voltage than the car has.

If you show a close up of the HP end I will send you one, I should have one as I repair laptops on a regular basis and the ends are one of the first things that get broken.

Thanks, Al

 

[kinarfi]

Hi kinarfi,

That looks good to me and I will build one shortly, though its not for a laptop but for another project that just requires more voltage than the car has.

If you show a close up of the HP end I will send you one, I should have one as I repair laptops on a regular basis and the ends are one of the first things that get broken.

Thanks, Al

When you order parts, get the isolated tab schottky diode, then you don't need to put the insulator under it and both T220s can mount to the same heat sink.
Here's a list a list of parts that I used:
LT1270A switcher from Texas Instrument - mine was a sample - http://www.linear.com/
33 uH Inductor from Wurth Electronics - again, a sample - https://www.electro-tech-online.com/custompdfs/2012/09/7443633300.pdf
Schottky Diode - I would recommend the insulated tab http://www.digikey.com/product-detail/en/MBRF1045-E3/45/MBRF1045-E3/45GI-ND/2153374
1000uf 35V electrolytic cap
1K ohm resistor
1 uf capacitor
aluminum heat sink or a suitable piece of aluminum
10K pot - I recommend a 25 turn trim pot - http://www.digikey.com/product-detail/en/3296W-1-103LF/3296W-103LF-ND/1088045
optional - small fan - http://www.digikey.com/product-detail/en/MC25101V2-000U-A99/259-1570-ND/2757808

here's some photos of my plug and socket:http://community.webshots.com/album/583273461NouhCR disclaimer, my wife took the photos If you have them, I'll PM you my address
Thanks
Kinarfi

 

[Boncuk]

I'm surprised there seems to be a big problem about a break of charge voltage for a few seconds.

Starting an engine should not be a matter of hours, but of seconds.

I'd just suggest to use a low cycle lead-acid-battery for the laptop.

The battery should be used if the no-load-voltage is at about 12.5V. If you're afraid your laptop battery will discharge too fast while connected to the starter motor, just disconnect it from the board circuit and leave it connected to the laptop.

If it was fully charged at that time it should serve as proposed for the time it is meant to be.

Boncuk

 

[bigal_scorpio]

Hi kinarfi,

Sorry its been a while, had some bad family stuff going on mate.

Does you charger have a small pin in the centre of the plug? Can't quite tell from the Pics. If so then there is a problem or may be?

The ones with the small pin are 3 pole connectors and though you can usually power the lappy with a replacement plug (which are ALL 2 pole only) the charge circuit does not work as the lappy knows that the PSU is not an original. Though the manufacturers will tell you that the 3rd pin is to make sure that the supply is good enough I am a bit suspicious that they just do it to sell their own parts. I am a sceptic! HP and Dell have both done this at times.

There are a few sites that show you how to jury rig the new PSU so that the lappy sees it as an original but the fix does not always work, but I never saw one damaged by trying it.

I will have one of the plugs to send you but if it is the 3 pole one the replacement would only have 2 poles and the centre pin is not connected but it is possible to add a wire by drilling the plug from behind. I will go into it if yours is 3 pole.

Also I would need you to measure the outer metal sleeve as there are 2 sizes.

EDIT, I may even have a complete lead salvaged from a broken PSU.

Let me know, Al

 

[kinarfi]

wow, if you have the complete lead, that would be awesome, Yes I have the small pin in the center. **broken link removed** the laptop is HP 2000, if you can't get the info you need of the new photos, let me know and I'll break out the calipers.
Thank,
Kinarfi

 

[bigal_scorpio]

Hi mate,

I have a complete lead like that!

PM me your address and I will post it to you.

Al