# Converting AC to DC

#### #12

Joined Nov 30, 2010
18,190
Huh? You think made up numbers used to show how to use the equations are actual recommendations for the project?
I didn't read your post slowly enough to pick up the idea that you were intentionally using a parameter so very far from being practical.

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#### Brownout

Joined Jan 10, 2012
2,390
Your generator is probably two magnets (one N and one S) embedded in the flywheel and a pickup coil, giving you a positive and a negative pulse each revolution. At 3500 RPM, this would give you a frequency of ~58 Hz. The capacitor banks needed to smooth this 2.5 amp output whould be huge, so I would just skip the caps. You probably will only notice the flicker at low RPMs anyway.
That's exactly what I was thinking in post #8. Like my outboard motor, an extra coil near the flywheel, using the same magnets as the magneto, to generate battery charging power.

#### wayneh

Joined Sep 9, 2010
16,288
Any explanation for the 20V??
It's what you would expect from rectifying 15VAC combined with voltage drop across two diodes in the bridge. There's nothing unexpected.

#### iONic

Joined Nov 16, 2007
1,650
1) Apparently some of you haven't read what I wrote last!
The Bridge used is rated: 800V, I=8A, Ifms200A
2) 37.5W Incandescent bulbs do not illuminate squat
I also already have a replacement LED array
http://www.amazon.com/gp/product/B00IDSIBLG?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00
It's a kick-ass, bright light, hopefully I won't get "snow-blind" using it!

One of the two lights was used for my mobility scooter, the second for the snow blower.
I am measuring the voltage with the blower on with no forward drive or drive gearing, and no blower on. Idle is it's full power, engaging anything may slow the motor down if at all.

The alternator is a half-circle DC output. Don't know much more about that.

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#### SLK001

Joined Nov 29, 2011
1,543
1) Apparently some of you haven't read what I wrote last!
The Bridge used is rated for 8A and 200V, 800V

The alternator is a half-circle DC output. Don't know much more about that.
What is a "half-circle DC output"?

#### iONic

Joined Nov 16, 2007
1,650
It's what you would expect from rectifying 15VAC combined with voltage drop across two diodes in the bridge. There's nothing unexpected.
That's if it really is AC... +/- Xv, or is it really just the positive pulse wave without the negative portion based on the design of the alternator??

Beginning to think that this is what I am passing through my bridge rectifier..

#### BR-549

Joined Sep 22, 2013
4,938
Being you said the bulb was very dim,....I would check the flywheel and pickup assembly. Check the clearance to spec and make sure its free of crud. Look for an adjustment. If you don’t want to disassemble....see if you can get the long spout of contact solvent cleaner on target while engine running. Douche it out good.

I still recommend the replacement bulb I suggested($8), before any mods.....just to see if it is close to the brightness you expect. It will help determine if you output is really what you think it is. Thread Starter #### iONic Joined Nov 16, 2007 1,650 Being you said the bulb was very dim,....I would check the flywheel and pickup assembly. Check the clearance to spec and make sure its free of crud. Look for an adjustment. If you don’t want to disassemble....see if you can get the long spout of contact solvent cleaner on target while engine running. Douche it out good. I still recommend the replacement bulb I suggested($8), before any mods.....just to see if it is close to the brightness you expect.

It will help determine if you output is really what you think it is.
The light has always been dull, it's a 37.5W Yellow Incandescent. I wanted brighter and whiter.

#### BR-549

Joined Sep 22, 2013
4,938
If you can verify the bulb voltage while lit, it will tell us the power available. Before any solution can be considered, we must know that parameter.

Everyone is assuming that your supply can supply the wattage of the bulb.

A proper voltage measurement will verify this.

Is it the proper spec bulb? Has it been replaced?

#### wayneh

Joined Sep 9, 2010
16,288
That's if it really is AC... +/- Xv, or is it really just the positive pulse wave without the negative portion based on the design of the alternator??

Beginning to think that this is what I am passing through my bridge rectifier..
That would give the same voltage after the rectifier+cap, under low load. Either way, the rectifier+cap acts as a peak detector unless there is a load to draw the voltage down a lot during the "off" times.

But, a problem comes from what your meter reports in this scenario. An expensive "true rms" meter wouldn't report 15VAC, but something lower. I'm not sure how a cheap meter comes up with a value. Does it measure the peak and assume a sine wave? That would be consistent with what you are speculating.

#### Techno Tronix

Joined Jan 10, 2015
139
The rectification can be use here but it will only flow in one direction.

#### iONic

Joined Nov 16, 2007
1,650
At this point I am too far into the retrofit to test the voltage with the original 37.5W bulb. The meter I used was a FLUKE 35 (used to use it at work on Mfg equipment at IBM)

#### shortbus

Joined Sep 30, 2009
7,470
Most of the flywheel alternators have a half wave rectifier built in to them. For making DC to charge the battery.

#### BR-549

Joined Sep 22, 2013
4,938
Install small battery? I like it.

#### iONic

Joined Nov 16, 2007
1,650
Most of the flywheel alternators have a half wave rectifier built in to them. For making DC to charge the battery.
Thanks Shortbus. Sounds about right for my mower. The snow blower, on the other hand, has no battery, nor does it need one.

#### BR-549

Joined Sep 22, 2013
4,938
Could I see a picture of your snow blower? I saw some truck and train size ones when I was young, but I’ve never been close to a handheld one. And I don’t want too! No more snow for me.