# Dc-dc converter using laptop chargers



## the gas wizard (Apr 19, 2008)

hey everyone. i recently purchased 3 15volt 6amp toshiba laptop chargers. i connected the three input cables together. ie . all the neutral wires together and all the active wires together. and placed them onto the contactor side of the pack. then i put all the output wires together and made sure i had the polarity correct. ran them through a relay off the 12v ignition and a fuse and there you have it a 18amp 15v dc from 120v converter to keep your little auxilary battery charged! it will work on packs from around 96 volt dc upto 240dc! i'll going to post a youtube clip on it very soon but it is so simple. it took about 30mins to make it all neat and the chargers are $11.00 each including freight on ebay.com.au! so keep checking out my youtube site. its at 


http://www.youtube.com/user/lpgas1


i hope this helps some people. i think its an awesome way to go!

ev on my brothers!


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## PatricioIN (Jun 13, 2008)

that sounds like a great idea for EV's that have very few power accessories. Great video too... a good walk about and explanation of your EV. I actually need to do one sort of "summary" video of my conversion now that I see that...


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## order99 (Sep 8, 2008)

Hah, I gotta remember that trick! I was just going to use a big battery with an independent Charger(I seek to avoid needless complexity-and expense) but I like your idea MUCH better!


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## ice (Sep 8, 2008)

sounds good! I like to experiment things...


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## Greenflight (Sep 13, 2007)

Yeah, great idea... thanks for posting!


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## the gas wizard (Apr 19, 2008)

thanks guys! its been on the car now for 2 weeks and going stong! i'll post a video on you tube about it very soon! my page on you tube is i can run all of my accessories at once including head lights and the voltage is stable at 13.9v


http://www.youtube.com/user/lpgas1

have a look at my videos. i'll have more on there soon!


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## piotrsko (Dec 9, 2007)

not to be negative or anything, but have you ran it at more than 12 amps for any length of time? some of these things don't Siamese all that well and since it is unbalanced, one or more of the converters might cook under max load.

still not a bad idea however


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## the gas wizard (Apr 19, 2008)

yeah i have ran it with wipers and headlight and blower fan all on under normal driving and it works fine! i understand where your coming from though! maybe the toshiba got it right for the ev guy! haha


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## madderscience (Jun 28, 2008)

15V might be a little high for charging a 12V gel continuously but it is probably about right for a flooded one.

Based on my own experience playing with these things (computer power supplies and switching power supplies in general) There are significant differences in how well they behave when being run off of DC, and specifically low DC voltages (less than 120VDC). To get equal output to what they would get running off of 120VAC, you would need about 170VDC. This assumes that the internal AC to DC is a simple bridge rectifier and not a voltage doubler. 

Anyway, here is my experince: All such power supplies won't be able to put out maximum rated current running off of about 120VDC because their input side isn't running on full designed-for voltage. 

Some power supplies will just shut down harmlessly (but not very useful, of course) with much less than 120VDC. 

The one I am using to power the computer for my BMS works great down to about 80V, and will keep running (but not start) down to 50VDC. It is only good for 5A at 12VDC though, not good for a whole car DC-DC but perfect for its application. 

Beware though, one power supply I tried (an HP laptop power supply) actually started overheating when run off of TOO LOW of an input voltage. Some internal components started to burn up, though it was still functioning. I did not try to diagnose why it did this, I just threw it back in the junk bin and tried something else.

I guess long story short is experiment and make sure that the supply you are playing with will work under your worst-case scenario conditions. Also consider that most of these units are not ruggedized for humidity, vibration, etc.

Also, one thing that would be a good idea when paralleling a bunch of these things is to diode isolate them. That way if one is slightly higher or lower voltage than the others, they will not fight amongst themselves.  Since you have 15V to work with, losing a few tenths of a volt in the diode drop will harm nothing and may in fact make the setup ideal. You could also power different sections of the car off of completely independent supplies to isolate them that way, but the parallelism is good I suppose in that a single failure should not shut down the car.

Good Luck


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## ice (Sep 8, 2008)

again! nice work!


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