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Old 06-14-2011, 08:17 PM   #1
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Default DC Power Supply Question

So I bought a passport 6s lipo dc charger not realizing it required a seperate power supply. So while digging through my boxes of old computer parts, I discovered I had an old laptop power supply that puts out 19v at 7.9 amps. Do y'all think this will work? The charger states to use 11-14 volts so I haven't wired it up yet, as I don't want to fry my charger. I put my volt meter on it, and only got 3 volts, but I don't know it has some sort of load sensor that regulates it.

Thanks!
Clayton
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Old 06-14-2011, 09:13 PM   #2
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I am not a fan of the conversions like this...

Do yourself, your local fire department, and your homeowners insurance a favor and buy a true power supply for your charger. You will thank yourself later for lack of headaches "hacked" power supplies often provide people.

Later EddieO
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Old 06-15-2011, 05:59 AM   #3
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Use a standard automotive battery charger as a supply for the hobby charger.
I have a really old one that handles 20amps continous.
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Old 06-16-2011, 03:08 AM   #4
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Quote:
Originally Posted by Charlie-III View Post
Use a standard automotive battery charger as a supply for the hobby charger.
I have a really old one that handles 20amps continous.
Check with the Manufacturer of the Charger before doing this. I believe many chargers specifically state NOT to use a 'battery charger' to power the unit.

Luke.
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Old 06-16-2011, 04:42 AM   #5
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I have used converted power supplies for DC chargers from Desktop computers but never a laptop supply. Not the volts is your biggest concern as is the amperage. You pull high current might heat up that power supply and who knows what could happen. Id get the right power supply for that charger.
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Old 06-16-2011, 04:59 AM   #6
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Originally Posted by lukethedork View Post
Check with the Manufacturer of the Charger before doing this. I believe many chargers specifically state NOT to use a 'battery charger' to power the unit.

Luke.
I believe the Passport charger has leads to be used direct to a car battery (like the Venom Pro Charger), so what's the difference between a car battery & a car battery charger??

I would be hesitant to use a car battery charger into a DC supply port on some equipment though.
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Old 06-16-2011, 07:02 AM   #7
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I use a converted power supply out of a computer and it has worked perfect for 4 or 5 years now.

Modding a PC Power Supply into a 12 Volt Supply for your DC charger


I wouldn't use an automotive battery charger to power my r/c batt chargers.
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Old 06-16-2011, 07:12 AM   #8
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Quote:
Originally Posted by Rok Krawl View Post
I have used converted power supplies for DC chargers from Desktop computers but never a laptop supply. Not the volts is your biggest concern as is the amperage. You pull high current might heat up that power supply and who knows what could happen. Id get the right power supply for that charger.

The laptop power supply outputs 19 volts at 7 amps. The power supply that horizon sells is rated at 12 volts and 10 amps so I am not really worried about the amperage for this power supply. I just need to wire in a voltage regulator to limit it to 12 volts.
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Old 06-16-2011, 08:09 AM   #9
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Quote:
Originally Posted by Charlie-III View Post
I believe the Passport charger has leads to be used direct to a car battery (like the Venom Pro Charger), so what's the difference between a car battery & a car battery charger??

I would be hesitant to use a car battery charger into a DC supply port on some equipment though.
A 12 volt car battery is pure DC..

12 V car battery chargers are made to do just that, charge lead acid car batteries.. These battery chargers generally do not have any filter capacitors across the output like good quality power supplies do, just a rectifier to convert the AC output of the transformer to DC.. This means that the 12 DC output has quite a bit of AC ripple imposed on it, and this ripple can affect the operation of the RC battery charger..

Cheers

Last edited by StumpyRC; 06-16-2011 at 09:30 AM.
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Old 06-16-2011, 09:53 AM   #10
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Quote:
Originally Posted by du4x4 View Post
So I bought a passport 6s lipo dc charger not realizing it required a seperate power supply. So while digging through my boxes of old computer parts, I discovered I had an old laptop power supply that puts out 19v at 7.9 amps. Do y'all think this will work? The charger states to use 11-14 volts so I haven't wired it up yet, as I don't want to fry my charger. I put my volt meter on it, and only got 3 volts, but I don't know it has some sort of load sensor that regulates it.

Thanks!
Clayton
It can work, but unless you have have electrical experience, I would not recommend this as your first project. The safest bet is to just get a 12V PS.
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Old 06-16-2011, 09:59 AM   #11
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When I was a kid, it was common to see people either using these or a 12 volt battery to power chargers, sometimes both. Legit power supplies like a Rivergate (sold under a different name then) were big bucks even for the small ones. A 12 volt battery charger could be bought for $20 or less at most Auto-parts stores....

While they worked, you are 100% correct about them being VERY dirty power. They would often cause numerous false peaks on our chargers, so constant monitoring was a must....from a safety standpoint, they are pretty safe......just gotta keep the leads from touching!

Surely better than a hacked PC power supply or a chopped up cord from a laptop.

Later EddieO

Quote:
Originally Posted by StumpyRC View Post
A 12 volt car battery is pure DC..

12 V car battery chargers are made to do just that, charge lead acid car batteries.. These battery chargers generally do not have any filter capacitors across the output like good quality power supplies do, just a rectifier to convert the AC output of the transformer to DC.. This means that the 12 DC output has quite a bit of AC ripple imposed on it, and this ripple can affect the operation of the RC battery charger..

Cheers
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Old 06-16-2011, 10:10 AM   #12
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Does the PC power supply really have these variations in output as well?

I would assume that something used to power pc components would be suitable to do the same for Rc. I really want to mod this one I have as I can use it for more then just my Rc stuf as it has variable outputs.
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Old 06-16-2011, 10:16 AM   #13
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Depends on the PC powersupply..........the cheap ones are just that, cheap. People always like to blame windows for the blue screen of death, but many times its a crappy power supply that causes the lock up. (have 3 brother in laws, a father in law and 3 sister inlaws who have all worked or still work at intel....you learn stuff like this!)...

I tried the PC powersupply mod once........and never again. I am an expert solderer and know electronics well enough to do some cool stuff......and it was a huge headache. One of the biggest problem is there are so many different variations of them out there, half the time the damn instructions don't work......cut the blue wire! I only have green and yellow....wtf?

Same yerself the headache.......buy a real power supply. If you need adjustable voltage, I am sure Heyok could make you a voltage adjustment device for cheap

Later EddieO
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Old 06-16-2011, 10:28 AM   #14
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Quote:
Originally Posted by Charlie-III View Post
Use a standard automotive battery charger as a supply for the hobby charger.
I have a really old one that handles 20amps continous.

This only works properly if you use a lead acid battery as a filter and buffer. The lead acid charger puts out extremely dirty, barely regulated power. With a big enough battery at the leads it smooths things out and it works well.


If you are up for some work to save money, a PC power supply works very well. Some people prefer to spend money instead of time. I use a rack mount supply for most of my 12v power. A Meanwell would be the best quality, but there are plenty of cheap ebay knockoffs out there too. like so... http://cgi.ebay.com/DC-12V-10A-Unive...#ht_1633wt_905

Last edited by JohnRobHolmes; 06-16-2011 at 10:31 AM.
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Old 06-16-2011, 12:11 PM   #15
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RCBro the PC power supply outputs are clean. They work great. I found that it was easy to follow the instruction on the sticky. If you find one that has a real on/off switch on the back that makes it even easier.(the wires may be different on these, and most do not need the resistor) I cut and desoldered all the unneeded wires, and now have a 5v and 12v output @ 350watt, I think there is also a 3.3v output if needed.

Last edited by 92LILREDYJ; 06-16-2011 at 12:17 PM.
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Old 06-16-2011, 03:50 PM   #16
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Using a PC Power Supply Unit is a great idea BUT,
consider using a used SERVER power supply as most of them does NOT require any type of modding. (Hot swappable psu).

In my case, I am using a used IBM 235 660Watt server power supply which absolutely does not require any sort of mod. 12v rail provides upto 37A. Even at full load voltage does not drop below 12v aswell.

Here is picture of pin out on backside.
I wired up two 12v+ground and using servo wire attached with a switch to power up the PSU.
Best of all, I picked up this PSU from local used computer shop for only $25. and it's more than quiet enough to not even bother me.
Shop also had a HP server 1300W PSU with 12v rated for 75A on 100/120VAC for same price but it was bit louder for my liking.



Last edited by xxgg; 06-16-2011 at 04:04 PM.
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