# 12V AC motorcycle regulator

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#### enduro250z

Joined Jul 6, 2010
69
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#### Suzukiman

Joined May 1, 2010
94
One thing to determine is whether the heatsink was completely isolated from any of the components as usually the heatsink will in some way be grounded to the motorcycle so it might as well be wired internally to ground if the schematic allows that.

TO3 transistors usually have a mica insulator between the metal case and the heatsink with white heat conducting paste. If the case is the collector then the case will only be grounded to the heatsink if the schematic requires a direct ground on the collector otherwise it would be isolated from the case.

Can you varify if any component terminates to the heatsink in any way? This will help confirm that the schematic is correct as per your module.
enduro250s
If you PM me your email address to me I will send you a writeup I did on the use of AC regulators on motorcycles. I have retrofitted these on many Honda XL250 and XL500 bikes to solve bulb blowing and weak headlamp issues as well as rewinding the ligtning coil.

****** Moderator's Note: These are public forums. All advice and help should be made in the forums for the benefit of all. Offfers of private help violate the spirit of the forums. *******

At the moment it seems as if yours is the simplest to construct, but will require quite a large footprint which is not always possible on some bikes. The OEM and aftermarket AC regulators are very small, some use the same heatsink as the rectfier bridge with all components inside, ground mounting through the center bolt and only one wire to tap into the AC between the lighting coil and the headlight. Those I have opened have only 3 components which were imposible to identify as the potting resin was too hard and the components were not marked.

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#### enduro250z

Joined Jul 6, 2010
69
For some reason i cant PM you. Can you try and send me one. If you cant send me a PM i will post an email address of mine i don mind making public. You can then email me there and then i will transfer you to my proper email address.

*****Moderator's note: We insist that help and advice be given publicly. Offers of private help are not in the spirit of these forums. *****

Well, no i cant see any component terminated to the heat sink.

The TO3 case was mounted with 2 secrews and in the screw holes were bushes so the screws cant be tounching the case.

The rectifier was mounted through its center stud. Its also has the wight paste under it but as the case is not part of the circuit this also was no electrically connected to the heatsink.

The onle wires comming out the unit were a black and red wire. These came from the AC terminals on the rectifier. Again not attached to the heat sink. The other terminals of the rectifier went to the zener diode and the transistor.

The other end of the zener joined in with the went to the other terminal on the transistor.

Now when i think about it, the diode and the + wire from the rectifer seem to be connected by the screw through the loop terminal and the threads conduct to the threads of the TO3 case as Solcar suggested. The heat sink is annoddized i beleive which wont conduct electricity.

The TO3 case i am now 90% sure is not electrically connected to the heatsink. The TO3 screws are isolated from the holes in the heat sink by plastic bushes and as the heatsink is annodized the mounting surface of the TO3 could no way be conducting to the heat sink.

The shim between TO3 and heatsink appears to be metallic. Is Mica metallic?

Yes i am familiar OEM honda XR/XL regulators.

I know a few guys who have de potted some motorbike CDI units and they tried the old chip and dig method but then i think one guy used a heat gun to melt/soften the resin.

Ive just spent a while searching the net and still cant really find anythign on a simple circuit diagram for a AC regulator.

I can find these aftermarket ones made by Tympanium USA, but some bike shops ask \$30 US for these. They are rated at 225 watts. These have been around since the 70's and i dont think have changed. They have been used on the winning Baja 1000 desert racing bikes over the years. Yes we could buy one of these but its not the same as satisfing your curiosity and making your own!

I am pretty sure mine in the black heat sink can be made smaller. You can use a smaller transistor and rectifier or maybe just 4 zeners arranged in a bridge? Im not sure how much work they do and if they need to be in a single component and mounted to the heat sink. I guess it depends on how much power you want to dump as to what rating of transistor you want use. I have seen 16amp bridge rectifiers that are less than half the size of the 35amp one in my unit and they still have a stud mount. I was reading on a website about transisitors and the TO3's seem to get praised for there robustness but they are a pain to mount.

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#### retched

Joined Dec 5, 2009
5,208
Why not post it here so everyone can read it?

As you can see, the longer you leave your thread open, and the more people that see it, eventually you will get the info you want.

Posting it here may help others know EXACTLY whats up.

#### enduro250z

Joined Jul 6, 2010
69
I had another look at my unit in on the black heat sink and i will say i am not 100% i have got the red and black wire (AC connections at the rectifier) the correct way around. As you can see those wires are no longer on the rectifier in the photo. I only went by my drawing i still had which i did 4 years ago when i first pulled this apart. I assume i did it right, but im not 100% sure and i can not remember. That would be the main part im iffy on and perhaps if the anode or cathode of the zener is connected to the transistor. My old drawing says anode connects to base of the transistor so i just assume i got it all right when i drew it many years ago.

#### Solcar

Joined Jun 8, 2007
21
Yeah, the trouble with a PMOS is the body diode.

It'll conduct in reverse and result in high power dissipation.
[eta]
Actually, there are several problems with using a P-ch MOSFET besides the body diode.

If Vgs drops lower than -20v, the MOSFET will be destroyed. Gate would have to be clamped to the source using a Zener or the like.

The MOSFET will have slow turn-on and turn-off times, leading to high power dissipation.

That's why I was fiddling around with the TRIAC. Actually, since the input is rectified in the toy I came up with, an SCR would be more appropriate. Just as long as the current through the gate could be boosted to say, 20mA or so, it would kick in until the current fell through 0. That's basically what I was trying to do; disable the SCR gate when the output was high enough.
I definitely forgot about the body diode.

Now that you said that, I did that and made a circuit not long ago that used a transistor to shunt current away from the SCR gate when the output voltage was high enough.

#### Solcar

Joined Jun 8, 2007
21
Hi Enduro250s, the case of an MJ802 transistor is the collector. Since the cathode of the zener diode connects to the collector in these types amplified zener diode circuits, the the zener can't have a nylon bushing insulating it from the case of the MJ802 in order for it to work.

The heat sink probably is best considered to be at ground potential because the anodizing might get scratched through or the threads of the mounting screws might contact the inside of the mounting holes. But, it is good practice to include a wire from the emitter of the transistor to ground also.

The devices from Jaycar that you linked to are not able to dissipate very much power. Even the MJ802 can only dissipate its fully rated 200 watts if the heat sink is big enough.

The MJ802 brings back memories of my wilder audio amplifier days because I had gotten from a yard sale a used Tiger amplifier kit that used that transistor.

#### Suzukiman

Joined May 1, 2010
94
Enduro250z I cannot PM you it says you have chosen not to receive PM's. You can activate it and I will try again.

Mica is like a transparent bit of plastic, but heat resistant and an insulator. It seems as if the intention of your circuit was to have the collector grounded to the heatsink which makes sense. Possibly a nut, screwhead or washer contacted the heatsink and TO3 case as the collecter must in some way have been wired and not left insulated from the circuit.

#### enduro250z

Joined Jul 6, 2010
69
Im in user control panel but cant seem to find where i can allow or disallow PM's

Well i think i have it set right??? I tryed to send suzukiman a PM but i cant, but if i try to send a PM to Solcar there is the option for that. Ok just send me it here <snip>

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#### enduro250z

Joined Jul 6, 2010
69
I checked again and i can see no way that collector on the transistor is electrically connected to the heat sink. The case mounting screws are isolated from the drilled holes in the heatsink by plastic bushes. I only had the one screw in the loop terminal remaining but i imagine that the other one had a fiber washer under the head of the screw aswell to provide extra security and not rely on the annodizing under the head to insulate the screw from the case. I am 99.9% sure the cathode and + from rectifier (joined in that loop terminal) make electrical contact to the collector via the screw through the loop terminal and then the screw makes contact to the threads in the TO3 case.

There appears to be a couple shims under the transistor. One looks like a silvery metal and i 'think' theres a thin plasticy film jn between the transistor and the metal like shim.

Now does that all make sense to you guys?

#### Norfindel

Joined Mar 6, 2008
326
The Zener + BJT circuit is probably something like this, but with a full-wave rectifier. This would be a minimal version:

The components i used are the ones that come with LTSpice. If making this circuit, every component should be chosen to meet the requirements.

Here's the circuit's output:

It will probably dim the lights too much, but you can always make the full-wave version.

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#### Suzukiman

Joined May 1, 2010
94
Im in user control panel but cant seem to find where i can allow or disallow PM's

Well i think i have it set right??? I tryed to send suzukiman a PM but i cant, but if i try to send a PM to Solcar there is the option for that. Ok just send me it here <snip>
Hi,
Go into "Control panel", Then "Edit Options" and you should find the box to check.
I have sent you an email with the document.

Mine is set to allow PM's, but maybe I am too new on the forum to qualify???

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#### enduro250z

Joined Jul 6, 2010
69

#### Suzukiman

Joined May 1, 2010
94
Enduro250z,
I have tidied the schematic of the working AC regulator up a bit. We just need someone to help confirm if this layout is 100% correct and will work. So far this is the lowest part count and easy to assemble method found.
Hopefully Solcar and Sgt Wookie or anyone else can help confirm if this configuration is correct.

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#### enduro250z

Joined Jul 6, 2010
69
Good stuff there. Yes i would also like to know if we have it 100% right but im fairly certain ive got it all right off my original unit.

In your case i reckon you dould downsize the components as you wont be needing to dump much more than 100 whats if your using these on stock XL/XR 250/500's etc, but for me i am interested in making some that can handle high power. I have found some TO-264 200 watt transistors which i think would be better than the TO-3 which is a bit of a hassle to mount idealy. On my old unit all they dis was silicone over the back side if it.

Since ive basically determined that none of the components are electrically connected to the heat sink, i would bolt it to the bike frame and get extra heat disipation through the bike frame and cooling air of the bike moving along if i dont mount it under the tank. Those universal ones with a stud mount hole in the middle supposedly handle 225 watts and they dont even have a finned heat sink. They just rely on the center bolt stud mounting and the bike frame.

Also since no components are connected to the heatsink, it wouldnt matter if the heatsink was electrically connected to the bike chassis.

I have spent ages and ages trying to find a heat sink the same as my old one but cant find one close to the same size which is 87 x 70 x 31mm and is much the same size as DC regulator rectifiers found on many road bikes.

it would be good if someone could run the circuit diagram above through a simulator if possible.

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#### Suzukiman

Joined May 1, 2010
94
Enduro250z what is the transistor you found? I am also looking around for an easily obtainable and cheaper one specifically not a TO3 type.

#### tom66

Joined May 9, 2009
2,595
If you assume the regulator is dropping at most 5 volts (that would be 15.5 volts a.c.) at 3 amps that is 15 watts power dissipation. Choose 20 watts, then you have the following results:

http://uk.farnell.com/jsp/search/browse.jsp?N=1004177+597237+373620&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=1004177+597237&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1004177%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D1004177

2SC6081 by Sanyo is readily available and cheap - about 68p. 20 watts, 50 volts Vce. It will need a good heatsink. It comes in a TO-220 case.

#### enduro250z

Joined Jul 6, 2010
69
There are heaps here www.jaycar.com MJ15003 in TO-264 case and rated at 250watts. Jaycar part number is ZT-2230 and its a NPN type.

Tom66, depending on what bike we have and the out put of the stator will depend on how much the regulator needs to handle. Im guessing suzukimans Hondas with unmodified stators are putting out around 60-80watts standard. That would mean if he wants to run with no lights during the day, he needs a regulator that can shunt 60-80 watts to the chassis.

For me im looking to make them handle some more power as my stators will be modified for highter output and i would like to run with no lights in the day so i would need a more powerfull transistor which is just a component change.

If you look at the photos on an earlier page you will see a small regulaor with a hole in the middle. These are in a die cast case 42 x 42 x 21 with no fins and these are capable of dumping 225 watts and largly rely on the bikes chassis as teh heat sink too and have no problems with that amount of power. These regualtors are mostly going to be mounted where they can get a bit of moving airflow too. So we dont need to have a heatsink the size of a shoe box like we would normally need if we were designing a audio amp of something like that.

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#### tom66

Joined May 9, 2009
2,595
I think you misunderstand. The regulator only dissipates power it needs to; it does not need to dissipate all the power the alternator can handle.

In general, power dissipation of a transistor is:
$$P_{dis} = V_{ce}(I_b + I_c)$$

$$I_b$$ is often only a few 10's of mA so it can ignored in this calculation, so more simply the power dissipation is such:
$$P_{dis} = V_{ce} {\times} I_c$$

So if the transistor is only dropping 5 volts and is passing 3 amps, 15 watts gets wasted as heat. Conservation of energy; the transistor has to either give the energy to the load, or waste it as heat.

Of course you wouldn't want to run a 15 watt transistor at 15 watts because that rating is for 25°C with some kind of magic liquid nitrogen cooling, which is why I would suggest a 20 watt or 30 watt transistor for the job.

If no significant load is connected, then the power dissipation is a few milliwatts due to base current. Milliwatts are usually not a concern.

I calculated the 3 amps from the original requirements of this circuit which was to power a 35W light bulb. Of course if you were powering say a 70W light bulb @ 12V, you would have ~6 amps, and approximately double power dissipation in the transistor, about 30W.

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