# Alternate Rectifier/Regulator for a Rotax 503 DUCATI

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#### Tuneturkey

##### Well-Known Member
HBA Supporter
The ROTAX user manual and installation manual don't say much about the chatacteristics of the output voltage for instr's, battery charging, lights other then that it is an a/c voltage that increases with RPM.
Does anyone know what the a/c voltage out of the generator is thru the operating RPM range of the engine, say 2500 to 6000 RPM.
Has anyone done a DIY full wave rectifier with a std adjustable (0-35VDC) dc regulator and doesn't mind sharing a schematic?
Thanks,
Tuneturkey

#### Armilite

##### Well-Known Member
Not an Electronics Person, but I got to Ask, WHY, you want to change something that isn't broken, hasn't been a problem in 40 years, with lot's of Cheap parts from Rotax, Skidoo, Seadoo to pick from.

503UL
Ducati Double CDI
Generator Performace 155 W DC
rpm 6000 1/min
Voltage 13.5 V

A Single Ignition SEADOO 580 Sator $34, same as 277, 377, 447, 503 uses. I like Seadoo parts account they have better connectors. #### Tuneturkey ##### Well-Known Member HBA Supporter Not an Electronics Person, but I got to Ask, WHY, you want to change something that isn't broken, hasn't been a problem in 40 years, with lot's of Cheap parts from Rotax, Skidoo, Seadoo to pick from. 503UL Ducati Double CDI Generator Performace 155 W DC rpm 6000 1/min Voltage 13.5 V https://www.rotax-owner.com/en/support-topmenu/technical-information/rotax-engine-specifications/3-503-specifications/file A Single Ignition SEADOO 580 Sator$34, same as 277, 377, 447, 503 uses.

I like Seadoo parts account they have better connectors.View attachment 91120 View attachment 91121 View attachment 91122
Because I am an Electronics person, and its my prerogative to ask!

#### Jerry Lytle

##### Well-Known Member
Well, that certainly elicits further comment.

#### Derswede

##### Well-Known Member
"Ah do not think that means what you think..."

Believe you need a fixed output supply. 12 and 24v are your typical outputs. An LM317 and a fistful of components will get you fixed output. Google "LM317 12v 24v output supply schematics" and you will find several schematics which will give either fixed outputs or variable. I use the LM78XX series in the TO-3 case. With a good heatsink, and some heavy filtering on the input DC, I have driven those to 150% max ratings. Got to keep them cool, a good heatsink and airflow are mandatory for 85% to over rated current modes. I have melted a few as well. Let the stock regulators handle the battery charge/ignition circuits, tap off the AC to power your supply. Reliable and avoids a short circuit from taking out your electronics or shutting down the engine.

#### dino

##### Well-Known Member
HBA Supporter
I think putting the output on an oscilliscope will help. The old 532 coils had AC spikes up to 140V if a recall. Maybe one of those 22000uF capacitors that Rotax suggests would help tame these before the DIY regulator.

#### Derswede

##### Well-Known Member
Dino, you are quite correct. I use several HV high cap capacitors on a similar circuit (motorcycle), as the transits can cause problems. Most of my applications are noise sensitive (Radio comms), so my filtering will go beyond the standard. Your comment brings up another thought, in that you will need to spec the parts for higher voltages than one may assume when looking at nominal voltage outputs. If you google "Over voltage transient protection", there are some good ideas out there. Remember, "tune for minimum smoke!"

Derswede

#### proppastie

##### Well-Known Member
Log Member
Reliable and avoids a short circuit from taking out your electronics or shutting down the engine.
so for us "not electronics guys"....this isolates the ignition and the electronics.....what's left

#### Derswede

##### Well-Known Member
Proppastie, not sure what the original poster’s desire was, but I use a system to charge a separate system for a radio application. Noise is a killer for such systems. That is my use. If a spike comes thru and wipes out your electronics from a direct connect, the isolation of a separate system will prevent such things. If you were to look at a DC bus, you will see quite a few spikes, etc on a typical system. A couple of good caps across a DC bus will help such things. A separate system like I mentioned will increase isolation by a considerable amount. So, it depends on what you need. Personally, a couple of good caps should do for a majority of installations. My system is overkill except in special cases.

Derswede