Hey all of you electrical types out there, is there any way I can convert 12 vdc to 48 vdc? I’ve got this cool piece of equipment that runs at 48vdc that I want to run off of my car’s electrical system. Any help would be appreciated.
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- Did you get a train horn? (-One I saw once ran off 48 volts) heh heh,
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- Did you get a train horn? (-One I saw once ran off 48 volts) heh heh,
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- What you want is an inverter. I couldn’t Google any 12vdc->48vdc’s right off, but I did find a few 12vdc->24vdc. You may be able to run two of these with outputs in parallel. -Or maybe not, be sure to ask before you buy anything. - MC
What you want is a DC to DC convertor. I took a quick look in the newark catalog, ( http://www.newark.com ) and found a bunch, but none that take 12 V and convert to 48 V. Plenty convert 48 V to 12 and I found one that coverted 20 to 48.
What you may have to do is get an auto inverter that converts the 12 V to 110 AC and then an AC power supply that will convert the 110 into 48 V.
How much current do you need?
You could also get 4 12 V Lead Acid gel batteries, use diodes and a switch to hook them up in parallel to the car system for charging and in series for operating the widget.
DANGER! DANGER WILL ROBINSON!
Running two volage sources in parallel results in the same voltage. You can run batteries in series to add voltages but I don’t think this should be attempted with active devices like inverters.
Oops, good point KeithB, I only need .07 amps. I should have mentioned that in the OP.
The widget in question is a rotating light and (very loud)horn. What would happen if I just ran 12vdc to it? Would it still work, but weaker? Perhaps I’ll try that tonight.
Since we’re on the subject, how does a DC/DC convertor work? Does it invert the input voltage, use a transformer to boost/lower the voltage, then convert back to DC? Or is there some other type of circuitry involved that I’m not aware of?
I think it does invert raise and rectify but I am not sure. your best shot it to go to 110 ac then you can go down to 48 w/o and trouble.
August:
4 Watts (.07 A @ 48 V) should be doable, but I cannot find units that convert 12 V to 48 V, I checked Lambda and Kepko, two of the larger power supply mfg’s.
At 12 V, the motor probably won’t turn on.
One thought I had is that some of these high power Car audio amps may have a DC to DC converter, and you may be able to pull 48 V off of that. What are you using to run it now? If you are running it off 110 V, than you may be able to run to Radio Shack (ptui!) and by an inverter.
If you are electronically inclined you may be able to use one of the DC - DC converter IC’s to roll your own. If this is an option, let me know and I will root around to find some suitable chips.
frogstein:
Yes, some do have a power oscillator that drives an AC signal into a transformer which then rectifies and filters it, but most use a variation of the switching regulator topology that uses builds up a current in a coil that generates the voltage required. Most operate in the 200 kHz to 500 kHz range, so the inductors can be pretty small.
Padeye:
To amplify your point, I do not believe that any of the super-efficient DC-DC convertors can be connected is series to bost the voltage since the system ground at the input is connected to the low voltage side of the output. If the unit uses a transformer than the input and output may be DC isolated and can be connected in series.
I did find this:
http://www.mouser.com/catalog/cat_606/320.pdf
look at the lower right of the page number 618-obq23wc1224. If your unit will work at 30 V, you can run from the -15 V to the +15 V and isolate the 0 V line. Note that the blurb mentions that the isolation voltage is 500 V. This strongly implies, contrary to Padeye’s warning, that you can buy two of the +/- 12 V units and hook all the outputs up in series to get 48 V. Though you might want to ask the question of ETA - USA though.
Hope this helps!
>> I only need .07 amps. The widget in question is a rotating light and (very loud)horn
First, let me doubt this. 70 mA @ 48V is less than 3.5 watt which is not enogh for a rotating light and loud horn no matter how you cut it. Please double check this before you go any further.
On the subject of power supplies and converters I am quite knowledgeable as I have designed and maintained quite a few in my time. I am familiar with both linear and switching types.
I am not about to write a dissertation which would be too braod and most of it useless but this is not a difficult problem to solve. If you want to email me I’ll try to help.
I happen to make use of both kinds. I used to use a 12vdc to 24vdc converter. It took the 14.4 volt battery ( nominally a 12 volt system…) and sent it into a filtering box. That box basically then presented it “back into the system” as "another"12 volts dc. It was then matched with the original 12 vdc, and voila. 24 Vdc. Can’t tell me it doesn’t work that way, my $ 1850.00 converter is sitting on the shelf in the garage, having been rendered useless by…
Going the OTHER way. Now, I have a 24vdc supply for the system. Since most of the system- monitor, follow focus, video transmitters, accesory ports- are made for 12vdc, I needed a way to step down carefully. I had an inverter chip installed. Problem LAST week was, when I used it for the first time, it got WICKED hot because I was drawing over 5 amps continuously. That’s another solution. Point is, you can indeed go both ways. Going 12 to 24 volts sucks up the amp hours available. Double the voltage, halve the amps. Going 24 to 12 doubles the amp-hours available of course, but is rough on the system heat wise- sometimes. If I run it without using the light, then the inverter chip will perform beautifully.
How you can get 48 vdc from a single 12vdc source? I am in agreement with the poster who doesn’t believe it only draws point 7 amps. Maybe it draws SEVEN AMPS, but not .7 . My dual lamp emergency light, with NO siren, draws enough that when I turn it on and the car’s not running, the lamps turn slower and with a dimmed delivery of illumination. Does it have to run off of the car? And, for how long at any given time?
And, something to worry about but not related to dc voltage, do you have any legal right to be running a lights and siren combination in your car??
Let us know how you solve the problem. I’d be wary of involving my car’s supply of 12 vdc in any scheme to flip it over to 48 vdc. Just don’t call us for bail money 
Cartooniverse
Those dc/ac inverters you can buy that plug into the cigarette lighters? If they’re well protected, you could start with one of those. IF that thing really does draw only .7 amps ( and, again I doubt this too, along with my esteemed voltage vicar sailor), you can deliver 110 vac. THEN, wire up a converter or buy one off the shelf that delivers 48 vdc. Me, I have my doubts.
Sorry for the added posting, just wanted to throw that in to the mix.
Clarification: a power supply or converter has an input and one or more outputs. The outputs can be “floating” or they can have the same ground reference. If they are floating, then the outputs of two or more power converters can be connected in series (although it is still not a good idea). If they are not floating then they cannot be connected in series.
.07 amps does sound way too low, as some others have noted. However, I’ll take it as written.
The desired device is known as a boost converter. Might be possible to find commercially. If a hobbyist were to roll his own, look in the National Semiconductor datasheets (power devices) for the LM257X series.
DC to DC converters are pretty straightforward devices which you can get commercially or build your own if you know something about electronics.
For 12 V input and 24 V output or under (like you often see for laptops) they often use a very simple circuit which works in a similar manner to an hydraulic ram pump: an inductor is shorted to ground by a switching device. After it has built in some energy, the switching device opens and the inductor charges a capacitor through a diode. Pretty simple but it is not efficient for higher voltages and the output is not floating.
For higher voltages and floating outputs you just have a small transformer and the 12V input is switched by transistors or whatever. This is how 12V-DC to 110V-AC work. They first convert the 12V DC to about 150V-DC at high frequency, to keep the transformer small, then they switch the 150 V again to make it AC.
Hey, Man !! You’ve touched upon a possible solution to the O.P., no? If that’s how those cute little 12vdc/ 110vac car converters work, then why can’t our esteemed Doper August West get inside one of those boxes, and find the moment when the 150 vdc is being supplied to the magical drop of goo that converts it to 110vac, and make use of the 150 vdc?? He/She can then step down that high voltage to 48 volts? No?
<------ not ashamed to show ignorance of this part of the process. Is that even possible??
Yes, that would be doable. The ratio is set by the ratio of turns on a small feerite transformer. If you take out about 2/3 of the turns and leave only 1/3 it should work… except it is easier said than done and it may be easier to build your own transformer… and the rest of the circuit as well.
No one seems to make this animal and there’s probably a reason. Given the likely power requirements of such a device and the risk to your car’s electrical system if you make even a small mistake in designing or installing a 12V-48V conversion device, you might be better off simply installing a 48V DC UPS battery (expensive) in the trunk or running four 12V car or motorcycle batteries (less expensive) in series with a harness you can attach and detach so you can charge them separately. If you’ve just got to to use the horn and light in your car this might be the easiest, safest and cheapest solution to satisfy your signaling needs.
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- Well nuts. I meant to say “run the outputs in series”, . Padeye is correct: most ordinary invertors/transformers are not meant to be stacked, but if you can get two cheap 12->24 convertors or one very expensive 12->48 convertor, I’d try the two cheap ones first, myself (-considering the small amount of power involved here-).
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- Get yerself some electronics hobby magazines to find suppliers-- you can find surplus outlets that sell pieces of most everything for pennies on the dollar and since 48 is a multiple of 12, I’d bet there’s already small invertors out there made to do it and they’re cheap enough that you won’t care about melting down up a couple. You just have to take the time to look around. Just run them off a fuse and put 'em in a metal+grounded cabinet. - MC
MC as I mentioned, connecting them in series is generally not a good idea even if it were possible (and it often isn’t) for safety and protection reasons. I would not recommend it unless you know exactly what you are doing and what risks you are assuming.
To me it seems quite easier to find the correct outputvoltage… at any rate we have not heard from the OP again… maybe he lost interest or maybe he was electrocuted with his first experiment…