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> 12v Ac To 12v Dc 5a Converter, need help building a converter
BLinindoll
Posted: December 05, 2010 11:59 pm
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Hey guys. I'm new to the forum and have a question. I am a snowmobiler from New York and there is a lot of discussion on a forum I am a member of about how to get HID headlights to work with our sleds that produce 12v AC. HID's use DC.

I am not an expert in electronics by any means, but I can research the hell out of something and usually build what I need to in order to get the job done.

If you haven't figured it out by now, we're all trying to figure out how to build a converter/rectifier to convert 12v AC to 12v DC. I've found some info on how to do this, but the only problem is HID's use about 5 amps to start and then drop to about 3 amps to run.

Any ideas about a circuit design?

Thanks in advance!
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VenomBallistics
Posted: December 06, 2010 12:51 am
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I cant see how it can run AC without killing your ignition electronics.
Im not aware of a bulb that is intolerant of AC
these things not withstanding ... you want to research "bridge rectifier"
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Nothing40
Posted: December 06, 2010 02:37 am
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Rectified and filtered 12Vac will make approx 16Vdc. A bit high for some/most automotive electronics,but some will tolerate it just fine. Whether or not your HID's will tolerate a higher than average voltage is another question,only one way to find out.


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CWB
Posted: December 06, 2010 03:33 am
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the other side of this is fluctuating voltage .
did you ever notice how dim some of those headlights get when idling ?
i would rectify the ac , run it through a regulator , charge a battery and then run the hid .


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VenomBallistics
Posted: December 06, 2010 04:37 am
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QUOTE (Nothing40 @ December 06, 2010 02:37 am)
Rectified and filtered 12Vac will make approx 16Vdc. A bit high for some/most automotive electronics,but some will tolerate it just fine. Whether or not your HID's will tolerate a higher than average voltage is another question,only one way to find out.

its closer than that ... most automotive voltages actually measure high in the 14 - 15 range ... that being the case .. whats a couple volts.
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MikeGyver
Posted: December 06, 2010 05:15 am
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Need more info...
How is the sled making 12vac? does it have a traditional alternator? does it have a regulator? or is it a coil in the flywheel that is powered by a magneto's magnet?
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BLinindoll
Posted: December 06, 2010 03:12 pm
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Thanks for all the quick replies!

The sled makes unregulated ac for most of the electronics like the halogen headlights and the hand warmers. it does have a 12v acc outlet which is DC. I might be able to use that circuit to power the HID's as long as it can withstand the amperage draw of 6 amps on startup. the ballasts go down to about 3.5 amps while running once they warm up.

if i have to rectify the unregulated ac side, the higher voltage is not a big deal. i am purchasing fully digital ballasts which supposedly can handle a pretty wide range of voltages. im just hoping at idle it will create enough voltage to keep the lights on. if not i guess i'd have to run it to a battery

if i go the rectifying route, would i need any type of capacitor in there somewhere? is so, how many farad?
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BLinindoll
Posted: December 06, 2010 03:13 pm
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QUOTE
  Need more info...
How is the sled making 12vac? does it have a traditional alternator? does it have a regulator? or is it a coil in the flywheel that is powered by a magneto's magnet?



it makes ac using the magneto... no alternator

This post has been edited by BLinindoll on December 06, 2010 03:15 pm
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tekwiz
Posted: December 06, 2010 10:20 pm
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Most ACC outlets should be capable of 5A. Check the service manual for your sled to make sure, or contact the dealer for your brand. No filter capacitor should be needed, but if one is, than you will need something ~10,000f @ 35V. Or add a small SLA battery, which will also prevent dimming while idling. A 12V, 7AH alarm battery would be ideal.
I know that snowmobile engine alternators used to be around 10-15A total capacity back in the 80s, but the newer models are likely higher.


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CWB
Posted: December 07, 2010 03:50 am
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"The sled makes unregulated ac for most of the electronics like the halogen headlights and the hand warmers ."

just as a point of clarification and the possibility of keeping *something* down the road from becoming a silicon to carbon converter ...
halogen headlights and handwarmers are not really classified as "electronics" ... these are purely resistive devices and "do not care" if they have AC or DC applied to them .
of course this applies to other filament lamps and similar devices (eg : cigarette lighter) as well .


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tekwiz
Posted: December 07, 2010 06:40 pm
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If you equip your ballast with a bridge rectifier, it will then run from AC or DC of either polarity. A 10 amp unit should be used & must be mounted on a small heat sink. For a snowmobile, a few square inches of .062" (1.5mm) aluminum plate is more than enough for this.


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BLinindoll
Posted: December 08, 2010 12:35 am
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QUOTE (tekwiz @ December 07, 2010 12:40 pm)
If you equip your ballast with a bridge rectifier, it will then run from AC or DC of either polarity. A 10 amp unit should be used & must be mounted on a small heat sink. For a snowmobile, a few square inches of .062" (1.5mm) aluminum plate is more than enough for this.

would it be ok to use one 25A bridge rectifier on each ballast? i know its overkill but i like the spade terminals on the higher amp ones. i feel like the thinner wires on the smaller amperage one might break with the vibrations over time.
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VenomBallistics
Posted: December 08, 2010 01:34 am
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absolutely ... 25A is that bridge rectifiers red-line ... theirs nothing wrong with pushing a device to 20% its capacity and everything wrong with pushing it at 120%
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tekwiz
Posted: December 08, 2010 08:50 pm
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Yep. You are right about the vibrations, too. A bit of RTV silicone seal goes a long way towards vibration stabilizing wiring, too. Never use solid wire in an automotive application...always stranded. The finer the strands, the better.


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For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

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