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Converting to all DC?

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Trying to get my head around these electrical systems. I've been riding dirt bikes since I was a kid and never had to learn, but now have a dual sport and WANT to.

 My bike (14' Beta 520RS) has both AC and DC output. Converting over to LED lighting and wondering if I'm already rectifying to DC for LED headlight, can I just make the entire stator output DC to the battery and power all the lights off DC? I have heard about "floating the ground" but unsure what this means. Is 1 side of the AC grounded? 

 Also would like to know WHY they split into both AC and DC. If they are rectifying/regulating already, why not just make it all DC in the first place?

Teach a man to fish please....

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Subscribing, because although I have an applied electronics engineering degree from 30 years ago, I don't know why engineers would want both current types on a bike.

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Reading a little more, it seems there's more output available as AC, of which incandescent bulbs dont care if AC/DC. 

Plus the weight and complications of more components on the bike. 

This I understand...for a dirt bike. Once you put a battery and starter you need DC, so why not just use one stator output and a good reg/rec and be done?

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I'll take a guess but keep in mind I am not an electrical engineer.  Rectifying/regulating AC to DC there is going to be a loss in efficiency, so the most efficient system would be to only rectify/regulate what absolutely needs DC power (charging battery to run starter motor).  Another advantage of isolating the starter/battery system from the rest of the electrical system is there is less chance of a dead battery keeping the bike from starting.  Just my guess though...

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Posted (edited)

An alternator (stator + rotor) produces AC voltage by design, thus the name, and is much more efficient than a DC dynamo generator in terms out power output vs. size, weight, and energy required to produce a similar voltage and current.  AC voltage lends itself well to ignition firing under varying engine RPM and works fine with most incandescent lighting.  Unfortunately, there's no practical method to store AC voltage to operate an electric starter motor.  So DC voltage was introduced for this via AC voltage and regulator to charge a 12 VDC battery and operate a 12 VDC starter motor circuit.  Recent advances in bike components and accessories such as ECU, electronic CDI controller, electronic oil injection, LED lighting, USB power for phones and GPS etc. have increased the interest and demand for clean stable DC power.

"Floating ground" is a method for isolating stator AC circuit ground from rectified DC circuit ground, else a short would occur in the rectifier diodes as AC phase shifts between positive and negative sine waves. 

Trail Tech makes this aftermarket 100W high output DC-only kit for those interested in converting their bikes to all-DC power.

Edited by wwguy
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Thanks for the explanation gents I appreciate it

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 So I spent a lot of time going over my wiring diagram (with colored pencils and bugged eyes. Here is a cleaner version). The ONLY things that seem to run on AC are the parking light, high beam indicator lamp and the headlight. I see no other AC, unless some of the wiring to the ECU directly is AC.

 The bike also seems to be DC grounded to the frame. There are no points on the diagram showing the AC grounded to the frame, other than through the load (headlight). The headlight wiring is grounded to the frame on one side and is fed AC from the other. Does this indicate that the AC ground is "floated" from the factory?

 I bought a generic ebay LED headlight bulb, a full wave rectifier with heatsink, and a 4700uF capacitor. I'm going to wire that in on the AC wire feeding the headlight switch so it will output DC to both high and low beams. The only AC return I can see is at the rectifier, and I assume this is a good spot to grab the other lead.

Does this make sense? Uploaded diagrams for reference.

2014 RS wire diagram.JPG

2014 Beta 520RS wiring diagram- AC highlited 1.jpg

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The diagrams are missing something. A link between ac- and dc-. Electricity flows in a loop, and the loop is not obvious in the diagram.

 Test it with a bridge rectifier, if it looks like you are only useing 2 of the 4 diodes, you will need to float the ac. Think it's a center tap on the stator.

Why, AC, cuz 2 diodes is a 1.4v/14.4v drop. That's about 10% lost in efficiency. Luckily, led are about 1000% more efficient than incandescent. 

Iv run leds on the AC with out a bridge or caps and it worked with my leds, but I didnt like the flicker. Especially since its half wave.

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Thanks. How would I know if only using half of the rectifier? More flicker? The AC ground/negative/return (unsure of the correct term here) is what's throwing me. AC is fed to the light, but the DC ground completes that circuit, so the AC and DC share a common ground? I thought this was bad.

The DC is definitely frame grounded. I need to spend some time tracing the actual wires. The LED lamp runs bright on the stock AC but flickers at low RPM. I'm sure it will die in short order if not fed DC.

 Thanks all for your assistance!

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There must be an internal ground in the generator or the rectifier, other wise there is no complete AC circuit through the lights. The lights do provide a resistive path for the AC.

If the alternator connector is easy to get to just read the two alternator leads to ground, and then you'll know.

 

 

 

 

 

 

 

 

ac

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