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  1. #1
    TimeBandit's Avatar
    Join Date
    Jun 2016
    Tampa Bay

    MOSFET Regulator/Rectifier upgrade - FX HO

    Regulator MOSFET upgrade :

    (OEM Reg – 2005 FX HO)

    I'm calling this an "upgrade" because it is an improvement over OEM design. OEM on these crafts, and many others, use the popular SCR-based shunt regulators, and while they are robust and work, they are not the most efficient choice these days, especially for those of us running lithium packs. The MOSFET Regs are just hands-down a better shunt regulator. Here’s why:

    Improved Voltage Regulation - MOSFET-based regs having both a more stable and relatively higher charging voltage than OEM, usually 14 – 14.4v. SCR regs can swing up and down, dip into the low 13s, especially at idle. While not so much an issue for recharging typical lead acid batteries, it might be those of us that are running lithium packs instead. As opposed to the 12.8v of acid batteries, these lithium batteries hover around 13.6v fully charged, so an SCR reg can have issues putting amps back into them. With the MOSFET regulation well above the lithium’s threshold, it's not hard to do the math.

    Cooler running - The OEM reg runs pretty darn HOT - it’s why it’s got those heat fins. SCR-based regs normally run hot – it’s normal. The components that do the actual shunting (SCRs) are still slightly resistive, even in their conductive (shorted) state. This translates into heat energy. Depending on RPMs, this can add up to as much as 50 watts being absorbed by the regulator alone, and we all know added heat stresses can promote failures. The MOSFET regs have better conductive characteristics, thus run way cooler by comparison. Their ability to better shunt the stator’s voltage potentials more fully, disables the stator’s ability to output power more effectively during states of power excess. All-in-all, it just does it better.

    How to identify a MOSFET Reg :

    Your choice, you can still go OEM (they do make MOSFETs too), or buy an aftermarket brand. Shinendigen is the primary Reg manufacturer in the OEM market, and a good 99% thumb-rule is the that MOSFET type Regs begin with “FH”, while the lesser SCR Regs begin with “SH”. Both the FH & SH regs are widely used in the motorcycle industry, so they are not hard to find. For example, the FH020AA and the FH012AA are good choices among many. These are very popular and are rated to regulate up to 40-50amps - plenty. There are many aftermarket clones of these two Regs as well, just make sure “MOSFET” is specifically stated. Some aftermarket MOSFETs are dubbed “Heavy Duty” - read the print.

    Caution on aftermarket MOSFETs: If you want to maintain the original engineered way your craft regulates power, stick with the shunt-type Regs. There are so-called “series” Regs on the market (i.e. Compufire), but this type of regulator drastically deviates from the OEM specifications, including industry’s proven power regulation methodology for Permanent Magnet Alternators (aka PMAs - our stator/rotor).

    Doing the mod :

    (FH020AA Aftermarket)

    I went with a decent FH020AA clone. The problem is that the connector is not the same. I’m not a fan of hard-wiring a Reg, so I decided to get a whole kit which comes with new connectors. Cutting a perfectly good connector is a bit unnerving, but done right, the new connectors will look and be just as good as factory.

    (Connector swap required)

    As you can see, the FH020AA has two separate connectors; one for the AC and one for the DC side. Putting the new connector on was pretty trivial. I only suggest you take your time, test-fit the order of the connector seals, pins, etc . . . I crimped & soldered the wires to the pins for added measure. Looking at the OEM plug on my FX, we have 5 wires (black, red, & 3 green). The greens are the stator wires. They are all AC, so it does not matter as to the pin-order in the connector. However, the black & red (Reg DC output) very MUCH matters! So observe the instructions that come with the Reg to insure the polarity is correct.

    Installation went clean. The new Reg bolts right up to the OEM location, so no issues there.

    Although this upgrade focused on my 2005 FX HO, the same would apply to other craft having 3 stator wires and an "SH" Reg. Obvious give my craft is 10+ years old I have no reservations with hacking-off an oem connector - your mileage may vary.


    For those that want to know more about shunting -vs- series regs - read below :



    Regulator controversy – shunt -vs- series :

    A few last words here in-closing . . . there is a lot of Internet mis-information regarding shunt regulators -vs- series regulators, claiming wasted power, etc... I happen to be in the camp that shunt-regulation is in-fact the most optimal means in controlling the Power output of permanent magnet alternators (PMAs). Unlike the automotive systems, which have variable (electric) excitation fields, our rotor/flywheel has a constant excitation field, aka rare-earth magnets. This makes these generators constant-current natured. The key concept is that Power (aka electrical work) is a degree of current & voltage potentials. Both must be present, yet the two inversely effect each other. Having either just one OR the other means no Power is conveyed. Ohms-Law, in that Power is Volts times Amps. Zero multiplied by any number, will always be ZERO. It really is that basic. So in regards to regulating Power output of PMAs, it works like this :
    Once the Reg detects a Power surplus is present, it shunts (shorts) stator coil. Without any electrical resistance, 100% current is permitted to circulate inside the coil as it passes through the magnetic field. Full current flow means voltage is inversely sent to 0 volts, preventing any voltage potential from building-up. The coil’s cannot convey Power in this state. This technique effectively “disables” the stator’s ability to make Power for as long as the shunt is present. Yes, full current is indeed circulating between the stator & the Reg - but because it is virtually a perfect short (especially with MOSFETs), and because we are talking induction principles, there can be no Power transmitted from the generator. Much miss-information proclaims shunting is not efficient, thus egregiously wastes Power, heat, and fuel. While (like in all systems) there are some benign inefficiencies in both the stator, wiring, and the regulator components, shunting does not consume or throw Power away. It is in-fact still the most optimal way to disable (aka regulate) the Power production of these PMA devices.
    Last edited by TimeBandit; 08-12-2016 at 09:29 PM. Reason: fat fingers

  2. #2

    Join Date
    Jan 2016
    Lots of letters there.... did it work, does it charge, how many hours have you had trouble free?

  3. #3
    TimeBandit's Avatar
    Join Date
    Jun 2016
    Tampa Bay

    Thanks for asking (I think).
    Of course it works. No reason it wouldn't - as I've been doing this on my motorcycles for years (swapping the scr's for mosfets).

    Pic above is at idle, which is pretty impressive considering my custom volt-meter is registering a stable 14.3volts at the battery. Remember, I'm now running lithium iron packs, so the system settles to 13.6-ish at complete off/rest. All-afternoon running & my reg is not hot at all to the touch.

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