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Philip's Ravings

MOSFET regulator/rectifier on a Honda CB1000R Predator

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The regulator/rectifier terminated itself on my bike (Honda CB1000R Predator). It also damaged the battery so that it was unable to hold a charge. It's the second bike I have owned that this has happened to.

I went down to the local Honda parts dealer. I don't know why, but I assumed since they were such a common part they would be readily available in the country. I was really hoping to get the bike going again, so when I was told that it would takes 2 weeks and it would come in from Japan I decided to look at other options.

I've used Econohonda in Hamilton quite a few times in the past. So I sent them an email. Malcolm came back offering me an "upgraded" regulator/rectifier and it also cost less. The bit I was more interested in was the fact it was in the country and available the next day. So I ordered it.

The new regulator/rectifier was a MOSFET unit. Not knowing much about regulator/rectifiers this didn't mean much to me. So I did a quick Google and found most bikes come with an inefficient diode based regulator/recifier based on technology from the 1960's. There are several replacement options but a popular option was using a MOSFET based unit. Basically these are transistor based, have a substantially longer lifetime than diode based units, provide a far more stable voltage output, and if they do fail they don't trend to terminate batteries. I saw some talk about them being kinder on the stator, but the reasoning behind this doesn't add up to me. So I discount this "advantage".

The longer lifetime and being kinder to the battery were two big pluses for me. The problem with the regulator/rectifier failing and killing the battery is that it never seems to happen in a convenient place (like home). For me it happens when I take the bike somewhere and then it leaves me stranded.

The new MOSFET unit look similar to the old unit, but had the mounting holes maybe 5mm closer together than the OEM unit. So I used a file and "slotted" the existing holes so it could mount in the same place.

Now the more painful bit. The connectors were completely different. Malcolm supplied a kit with new connectors using spade fittings. So I took the plunge and cut the old fittings off, crimped and soldered on the new spade connectors. I decided to solder them as well because a lot of current can flow through these wires, and I wanted to minimize any losses. I want my charging system to be as good as it can be.

Now the test. At idle I was now getting 14.1VDC at the battery terminals. At 5,000 RPM I also got 14.1VDC at the battery terminals. Impressive! Completely flat and regulated output regardless of RPM. This also means if I do commuting at "low" RPM the battery will still get a nice slow charge. And that is the other bit I like. At 14.1VDC it will always be a nice slow charge. This is going to be real good for the battery lifetime.

After this experience I will never fit the older technology diode based regulator/rectifier to another bike again. These MOSFET units are just so much better.
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  1. The Reibz's Avatar
    Informative writeup Phil. Glad you got it sorted