M.O.S.F.E.T FH020AA Universal Motorcycle Rectifier/Regulator

I've created this Webpage/Blog as a lot of the links I found to do this job were dead :(

Regulator Fault:

Voltage across the battery @ idle should be between 14v and 14.5v DC(20v DC setting on Multimeter).Higher and there's a fault and battery can be swollen,tight to get out of battery box.

Rectifier fault:

Not as easy to know.Usually lower voltages than above across the battery and battery discharging/vehicle harder to start.R/R should be tested as per the manual.

In either case it's best to replace the Battery as it can't now be trusted.

Old Style R/R units can run as hot as 90 Deg C(194 F).MOSFET units typically run between 40-60 Deg C(104-140 F).Adding a cooling fan can increase the life of either unit.

If your present Rectifier/Regulator is old or has failed it may be a good time to.,"Upgrade" to a  M.O.S.F.E.T(Metal Oxide Field Effect Transistor) based unit as their price has dropped over the years.The one I have fitted is a cheap copy but does the job.You can use these on Virtually any 3-phase Stator Motorcycle Charging system.They are not,"Bike Specific".

They are superior to the old Stock R/R as they use less current to work(typically 100mA(0.1amp).Run cooler,are more efficient at the current conversion and regulation of the voltages so can even extend the life of your battery.Also most,like the one I have used,contain a,"Thermal Cut-out" which switches the unit off if ever it did get warm to protect itself and the charging system and then switches back on.In reality you would never even know it's done this and it may never even get used but it's added protection the old Types don't have.

Quick job

1:Remove all of the connectors between the Stator and the R/R and replace with suitable 25amp + wires direct to the /RR.

2:Remove all of the connectors between the Wiring Harness and the R/R in the Regulator side of the system and replace with suitable 20 amp wire.

I can't give credit to the original poster of this image as there was no name around :(

Some units come with a Red dot where the positive marker is and a Green dot where the Negative/Ground marker is.All these units AFAIK use the same convention for polarity of the Regulator side of the units e.g the Positive wire/pin is always nearest the Stator Pins.This is very important.The Stator wires can go to any pin as they are AC and have no polarity.The Regulator side MUST be wired CORRECTLY!

Quick Charging system 101

The Stator/Alternator/3 Phase system

Inside the engine a permanent magnet spins inside a set of coils wired as to make 3 coils(even if it looks like there's 9 or 6).This creates magnetic fields that form and collapse and are created again over and over and this in turn generates AC current and Voltage in the coils.Automotive devices need DC Current./Voltages to work on the Lights/Ignition etc so this Current has to be converted to DC hence the Rectifier part of the R/R.The amount of current and Voltage sent to the system/Battery has to be controlled and this is done by the Regulator part of the R/R.


I'll make the point now.It is Paramount to the success of any electrical soldering of joints that you treat EVERY one as if it were THE most important one on the machine.NEVER take second best or a,"It'll be OK" attitude.If you don't make EVERY soldered joint TOTALLY electrically secure it will come back and bite you in the Bum<grin> :O

If you need help or want some extra tips with your soldering technique there's plenty of help on YouTube and when soldering"Patience is a Virtue that pays dividends".

Wire Splicing/Soldering On YouTube

Safety Warning!

It's very easy to burn yourself with a Soldering Iron so be careful ALL the time!!

The job.

1:Choose where you are going to fit the new R/R.On my Suzuki SV650 it cannot use the original position/bracket on the right hand side under the rear fairing as the MOSFET R/R is too big and the rear fairing won't fit over it.By research I found it can be fitted in the same position but on the other side of the frame that has no R/R bracket so will still be under the Rear fairing.

   Wherever you choose make sure it's not near any engine heat or can get road crud/rain etc thrown onto it.Although MOSFET R/Rs run cooler they still need "Air-Cooling"and an additional fan helps big time especially in Hot Climates.It's better to fit an R/R somewhere where it can get air passing over it whilst riding and if possible out of the line-of-sight of Road Debris/Moisture.

2:Once you have decided above measure the wire/s you will need to take the 3 Stator wires and the two DC Positive/Negative wires to it including any re-routing you may have to do.

Tips:Always cut your wires a little longer than needed just in case you have to move them until you are happy.They can always be trimmed before you solder to the R/R.

You can and should secure your new cable routing using Tie-Wraps or similar so no movement or chaffing can happen but don't pull them too tight!

                                    Hard Wiring option and why I choose it.

I have qualifications in Electronic servicing so in-line Electrical connectors on Automotive vehicles are a,"Pet Hate" of mine.Anyone who designs a circuit wants as few POCB(Points Of Corrosion Breakdown) in the Circuit.On my Suzuki SV650 and in their infinite wisdom Suzuki not only had the usual one 3 wire Heavy Duty Block connector in-line but TWO!!!.If you add up the male and female contact points and add them to the ones at the R/R this is a total of 15 points that can corrode.

They are used for ease and speed of production on assembly lines and in some cases they do make Fault Diagnostics easier but on a simple circuit like an Automotive Charging circuit it's much better to get rid of them IMHO.

Why don't I like it?

Well every one of those points,if and when they corrode if not regularly serviced,will increase the resistance in the Circuit.This not only robs current from the circuit but makes other parts of the system have to work harder and reduces their life-span including the R/R.

 However that's not this worst of it.Each one of those points by corrosion/resistance increase over time can start to heat up.This can and has led to the melting of the connectors and the shorting of the Stator wires and a blown good Stator!

I posted the above so you know why I chose how to Solder my MOSFET and Charging circuit the way I have.It's,"Dealer's Choice".

I removed the Block connectors in the Stator line and also the 2 pin one in the Regulator line.

3:.Solder the correct minimum 25 amp(2.0mm/14g) heavy duty wire to the 3 wires from the Stator.I paint the soldered joints(remembering to make sure they are absolutely solid/good) with some,"Clear Nail Varnish".3 coats.Why Clear Nail Varnish?Well it's a great insulation lacquer and cheap from ASDA/Walmart :)

When it's dry a move my,"Heat Shrink" sleeve into position over the joint/s and shrink it with a Cigarette lighter or similar.Then I tape the joint with PVC Electrical insulation tape.

I did this to ALL three Stator wires individually and then secured then all together with PVC Insulation tape.By doing this there is little or no chance of them shorting to each other or moisture getting into them so as to prevent corrosion.

4:Repeat the process with the Regulator wires and use minimum 1.5mm/16g 20 amp wire.


Stator wires now go in one line,no connectors except the spade connectors to the R/R.

Regulator wires now go the harness in one line,no connectors except the spade connectors to the R/R.

Note:When some people do this Upgrade/Mod they choose to wire the two Regulator wires directly to the battery.Again this is,"Dealer's Choice" I just couldn't be bothered to hack my wiring loom.Might change my mind as some later date.

Tools/Stuff list.

Soldering Iron.I use a quality 25w Antex brand,Some might think this is low powered but it' delivers heat better than some cheaper higher wattage ones.
Antex 25w Soldering Iron

In the US even this one will do the job, Amazon US Cheap Soldering Iron.

Mulitcore solder,

PVC insulating tape.

4.8 mm Heat shrink tubing

(You may need some 3.8mm as well for the smaller wires.You can buy packs off Ebay/Amazon with various widths).

Clear Nail Varnish(ASDA/Walmart) used to insulate soldered joints before Heat-Shrink sleeve application.

Pliers(I use the cutter inside the pliers to square off the ends of the wires that I have,"Tinned" with solder before making the joints).

Cigarette lighter(Used to Shrink Heat Shrink and also to melt end of the wire insulation to bare them by pulling the softened plastic covering off with my nails if you don't have a,"Wire Stripper".

Carb/Brake cleaner(I use it to spray the bared ends of the wire before soldering to degrease the wires after twisting the stands together prior to soldering).


You can get it in the US off Amazon now :)

Spray a small amount of ACF50 on all the pins and spade connectors with it once all fitted and before you push them on.Will hold corrosion back for around 2 years.I use it on EVERY connector and Bulb holder on my machines..Can be used on Radiator pipes to stop decay and all fasteners/bolts etc.Best,"Liquid Maintenance" ever invented for Motorcyclists.

As stated MOSFET R/Rs run cooler,use less current,are overheat protected and more efficient than Standard R/Rs.

Only downside of ,"Hard Wiring" is that if and when you need to change the Stator you will have to desolder/chop the wring.This is no biggy to me for the benefits of not having extra CPOB(Corrosion Points Of Breakdown) in the circuit and a superior current path.

If you need help you can contact me at   PuttingOutFires*gmx.co.uk just change the Asterisk for an @ sign.

Page 2:More Pictures to Help Here


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