In the circuit posted by Alec-t......

Would the circuit still work as outlined with a .47uf cap ?

 

Alec put a lot of effort into that elegant design and the TS was really happy with the result. The problem with the MC is making it small.
But IP65/IP67 cases are available http://www.twinner.com.tw/files/gainta/G1XXMF SERIES.pdf has a 64 x 58 x 35 mm enclosure which still could be too big.



A search for "Debe atom" should reveal some interesting construction techniques for building a solid state ignition module. No PCB was required. He starts with some Aluminum "C" channel. That technique might work for you. That design could be "potted" with some electrical grade silicone. The electrical grade doesn't have acetic acid in it which will corrode parts. Three unsupported sides. If you want to form the sides get some Teflon or bondable Teflon (usually about 0.005" thick with an etched surface that can be epoxied) They can be removed after the silicone sets.

Here https://www.rshughes.com/p/Loctite-...nd-Paste-300-Ml-Cartridge-40088/079340_40088/ is an expensive version.

This https://www.rshughes.com/search.html?q=locktite+si5011 should work too. It's a milky white when dry.

Found this on ebay.....
Aluminum Circuit Box. 45x45x19mm

 

The IP rating of what I suggested was IP65 or IP67. See https://en.wikipedia.org/wiki/IP_Code

 

The IP rating of what I suggested was IP65 or IP67. See https://en.wikipedia.org/wiki/IP_Code

Help me out here.....why do I need to worry about IP ratings?
(I simply don't know)

I can't use just any enclosure that will suffice?

 

IP5x
Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment.
Why?
Dirt roads. Pollen.

IPx5
Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.

Why?
Washing the bike with a hose.

So, >IP55

You don't need an enclosure if you pot it. The motorcycle environment is harsher than the interior of a car or even under the hood, So, the IP rating is a classification system. Note that there may be a NEMA equlivelent enclosure type.

Your worst enemy is probably salt spray depending on where you live, Salt used to de-ice roads could cause corrosion.

There is also a PCB conformal coating that you can spray on too. See https://en.wikipedia.org/wiki/Conformal_coating


Check your "conversations".

 

Would the circuit still work as outlined with a .47uf cap ?

Yes.

 

Excellent !

Thanks again sir !

 

IP5x
Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment.
Why?
Dirt roads. Pollen.

IPx5
Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.Why?Washing the bike with a hose.
So, >IP55

You don't need an enclosure if you pot it. The motorcycle environment is harsher than the interior of a car or even under the hood, So, the IP rating is a classification system. Note that there may be a NEMA equlivelent enclosure type.

Your worst enemy is probably salt spray depending on where you live, Salt used to de-ice roads could cause corrosion.

There is also a PCB conformal coating that you can spray on too. See https://en.wikipedia.org/wiki/Conformal_coating

Check your "conversations".

ok. Thanks
I intend to pot the circuit. Just not sure yet how to handle the heatsinking of the MOSFETS when I do.
The potting material will probably be thermally conductive but electrically insulating so maybe I'll just pot everything right up to the point where the MOSFET contacts the heatsink.

 

Am I understanding the MOSFET connections and capacitor orientation?
(The image has been corrected and re-uploaded)

 

Am I understanding the MOSFET connections and capacitor orientation?

You have the drain and source names incorrect on the bottom MOSFET.
The symbol orientation is correct.

 

The two FET sources connect together. The two FET drains connect to the cap. The capacitor should be non-polarised, so can be connected either way round.

 

Here is the (hopefully) final schematic I will use. 2 things.....

1). Alec-t, do you or does anyone see any issues with this schematic?
2). If I was making a PCB for this, which trace segments might need to be wider for carrying more current?
3). If I put this in an aluminum box with the MOSFETS heatsinks attached to the aluminum box, would the aluminum box become electrically active (for example, would the box need to be protected from touching the motorcycle's frame?

 

1) No.
2) Personally I wouldn't use a pcb, but if you do, it's the yellow bits that carry heavy current:

3) Not if you use the recommended insulating kits for mounting the FETs.

 

anyone see any issues with this schematic?

Did you intentionally change from NMOSFETs to PMOSFETs?

 

Good catch, Crutschow!

 

I read they were "better" ? Does that change the functionality ?

Is the circuit as designed good to go?

Or are N channel Mosfets a requirement?

 

I read they were "better" ? Does that change the functionality ?

And where did you read that?
What was the context?
What does "better" mean?

P-MOSFETs can be better for some applications, like a high-side switch in the positive rail, but not particularly for this application.

No, it does not change the functionality.

Or are N channel Mosfets a requirement?

They are not a requirement, but N-MOSFETS are generally cheaper for the same current carrying capacity and on-resistance compared to a P-MOSFET.

 

TBH,
This electrical jargon is not my specialty. But those last bolded lines sounded impressive.

1. The n-channel device has following problems in the device processing. Most of the mobile contaminants are positively charged. Since NMOS operates with the gate positively based with respect to the substrate, these ions collect along the oxide-silicon interface. This charge causes a shift in VTh. Also, there is fixed positive charge at the Si-SiO2 interface resulting from various steps of the manufacturing process. This also shifts the threshold voltage. Both these charges have tendency to make the device normally on. These two charges exist in PMOS device too, but the positive ions are pulled to the AI-S1O2 interlace by the negative bias applied to gate. There, they cannot affect the device threshold severely.
2. Another problem with NMOS device occurs during the oxidation of silicon which takes place at the Si-SiO2 interface. No real abrupt change occurs between silicon and Si02; rather there is a transition zone. This transition zone contains positively charged Silicon atoms which increase the absolute magnitude of the threshold voltage for a p-channel device and decrease the absolute magnitude of the threshold voltage for an n-channel device. This means it is difficult to make an n-channel device that is off at zero gate voltage. This is why it is more difficult to make an n-channel device than a p-channel device.

• PMOS technology is highly controllable.
• It is a low cost process.
• It has good yield and high noise immunity.
  
  http://www.circuitstoday.com/pmos-vs-nmos

 

This means it is difficult to make an n-channel device that is off at zero gate voltage.

Depends upon how you define "off".
It's not a significant problem in any practical N-MOSFET I'm aware of.
For example here's the leakage of aN IRF3205 N-MOSFET from its data sheet.
That amount of leakage will not be a problem in most high current switching applications, which this 80A device is designed for.



And here's the leakage for a two small, 200mA, N-MOSFETs, the 2N7000/2.



Again, that's not likely to be a problem in most low current switching applications.

 

The shunt type regulator circuit that you showed replaces the high current zener diode that used to be on some motorcycles. To use polite terms, the whole concept was REALLY DUMB!! The cheap and reliable replacement that allowed charging the battery and not burning out the lights when the biker reved the engine and the zener diode failed was to put in a rectifier and a series regulator circuit. A power-tab three-terminal voltage regulator with two 15 amp, 100 volt, PNP transistors "wrapped around" it and a decent heat sink and the regulator will last forever if built well. Total parts cost of about $10, so it was cheaper as well.
For a six volt circuit with a six volt battery and lights, you will need to use a six volt power-tab regulator IC.
Having a series voltage regulator does demand changing the wiring harness a bit but the benefit is easily worth the effort.