120 volt to 12 volt power supply - Team Camaro Tech
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  #1  
Old Mar 1st, 06, 10:09 AM
sneakey pete sneakey pete is offline
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Question 120 volt to 12 volt power supply

Hello folks, I'm looking to your vast knowledge base to give me ideas. I am currently using a heavy duty winch (off of a power utility digger truck) for my boat winch. I have a big deep cycle battery for a power source, with a automatic battery charger hooked up to keep it topped up. This seems to last me about 3 seasons and then the battery looses it's oomph and runs the winch a little too hot. I would like to find or build a power supply unit to convert 120volts ac to 12 - 18 volts dc with approx 80 - 120 amps. The reason I want to keep the 12 volt winch is just in case of power outages then I can simply boost the unit to bring the boat in. I've been thinking of looking for an old welding machine but was wondering if you folks have any ideas on something else out there that is easy to salvage/convert that is under our noses that I'm just not thinking of? Or any other ideas on how to get 12 to 18 volts dc with apporx 80 to 120 amps?
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  #2  
Old Mar 1st, 06, 10:37 AM
12run 12run is offline
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Default Re: 120 volt to 12 volt power supply

I don't think a 12 volt supply with that much output amperage is going to be cheap to buy or build. A welder with DC output might work, but the only specs I could find were voltage at maximum amperage which were 25 volts at 125 amps. The voltage output might be lower at a lower amperage setting, but I can't say for sure. I did find high amperage 12 volt supplies, but I'm not sure you want to spend this much.
http://www.batterystuff.com/battery-...2-volt/21amps/
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  #3  
Old Mar 1st, 06, 10:38 AM
Silver69Camaro Silver69Camaro is offline
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Matt Jones
 
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Default Re: 120 volt to 12 volt power supply

Boy, that would be a pretty big transformer! A 2kW converter would be hard to find for a reasonable price, I would think.

Maybe convert a 200A welder (you'd need to big one for the duty cycle). Ugh, I don't even want to think about it. I'd stay with the deep cycles!

The only other thing I can think of is get yourself s 150-200A alternator, then drive it by a 3HP AC motor. The problem is that alternators can't put out max current for very long, so you'd need a safety factor.
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Old Mar 1st, 06, 11:19 AM
sneakey pete sneakey pete is offline
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Default Re: 120 volt to 12 volt power supply

Thanks for the quick responses, actually in my haste I forgot to mention I have access to 220V in the boat house so a welder isn't out of the question, just I forgot about the duty cycle thing, so could be a problem seeing the winch runs for about five to six minutes at a time. Maybe 4 times a day tops.
Never thought of a alt ran off of a electric motor, hhmmm. Wonder how much power it would take to spin it at 2200 rpm or so to get out the power i'd need.
I wonder how I would make out with two batteries with my auto charger, shouldn't be as big of a voltage drop. Now I won't be able to sleep thinking about this one. Thanks folks and if any more ideas come to mind let er rip. Thanks again !!!
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Old Mar 1st, 06, 12:12 PM
Everett#2390's Avatar
Everett#2390 Everett#2390 is offline
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Default Re: 120 volt to 12 volt power supply

Quote:
Originally Posted by sneakey pete
This seems to last me about 3 seasons and then the battery looses it's oomph and runs the winch a little too hot.
It reads normal service to me. With the amount of load being placed onto the battery, I'm surprised you're getting 3 years of service.

You are placing a heavy load onto the battery by using the winch. This creates a large amount of chemical reaction within the battery. Then you are trickle charging it back to its normal charge.

So now you want to make a better mouse trap. As stated, you can buy a constant voltage constant current power supply. We just bough here at work, 0-200 volts DC with 0-50 amp current output. This means regardless of voltage output, it will maintain up to a max of 50 amps, whether its at 10 VDC or 200 VDC. This power supply weighs over 200 lbs. and requires 220 VAC 3 phase power to operate and we paid $3800 USD for it. You'll need a special transformer to convert the boat house 220 VAC 1 phase to 220 VAC 3 phase.

So what you'll saying, "More Power!" not impossible but alittle hard to get there.

I believe its going to take alittle more than a 3 hp motor to generate a constant "starter motor" current. You're going to need to run welding cable, 4/0 AWG, to remove any current losses for this low of voltage and amount of current.

What I would do is to replace the handle of a manual hand crank winch with a gearbox reduced electric motor, or better yet, get a 220 VAC electric motor driven winch, and drive it with the boathouse 220 VAC power. now you're talking.
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Old Mar 1st, 06, 12:56 PM
Silver69Camaro Silver69Camaro is offline
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Default Re: 120 volt to 12 volt power supply

3HP was just a knee jerk reaction. 120A at 18vDC is 2160 watts, and each HP is 746 watts (assuming 100% efficiency, actually 90-95%).

Ok, to concerve duty cycle, multiply your max current draw times 2, so:

120A*2 = 240A
Assume 95% efficiency from alternator: 240A * 1.05 = 252A

Now, that gives us 4500W at 18vDC. So,
4500W/746 (W/HP) = 6.1HP

Assume 90% efficiency of electric motor = 6.1HP*1.10 = 6.7HP

Now, belt drives can be 85-95% efficient depending on pitch, RPM, etc. Let's assume 90:
6.7HP * 1.1 = 7.4HP.

So there you have it, you should have a 7.4HP motor to drive a BIG alternator. The big problems is efficiencies, because you're loosing 25% of the input energy. If you do a direct drive with a flex coupling, that would cut out the belt drive loss.

Everett has a good idea. Reduce the speed of a 220V motor with a worm gear system for big time reduction, and run that to a properly sized manual drive setup.
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Old Mar 1st, 06, 01:14 PM
sneakey pete sneakey pete is offline
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Default Re: 120 volt to 12 volt power supply

So by the sounds of it I'm hooped. It's either regular maint of battery changes or else change system over to a ac motor with a speed reducer/worm drive unit, which I have considered. As you can see I was trying to get the best of both worlds. The unit I have now has so much power I hate to loose it as it does an awsome job of moving huge boulders brought in by the ice from time to time. Perhaps I can still utilize the 12 volt system for work and just set up a ac system for the boat track/dolly. Thanks again for your input, always very much appreciated.
- Cheers
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