fuse the rectifier

[petersbc]

my tach lead grounded in the control and overload the charge section of the stator burning it out. So 200 unnecessary dollars later im looking at fusing all leads, the two inputs to yhe rectifier, the tach, and the charge lead. Since this is a 9 amp stator my thought is 10 amp on all leads and a 2 amp on the tach. Tjis is a 78 johnson 140 with electric tilt/trim.

Any issues with doing this?

 

[TrueNorthist]

A fuse won't really protect the rectifier as the damage will be done before the fuse blows. One can also use looming or shrink-wrap etc to ensure nothing can short like that which is what I would do for that circuit. To be honest, I am not sure what effect a fuse may have on the rectifier inputs. Most fuses introduce resistance to the circuit and that might cause issues? Don't really know.

 

[petersbc]

Not sure i get "the damage is already done" the charge circuits are designed to put out 9 amps and im quite sure it runs at 9 amps quite often. Its the dead short im trying to guard against.

Your point with the loom etc. is well taken but there are many opportunities for shorts on an aluminum hulled boat as well as a rectifier that fails out on the lake can cook a stator getting back to the dock and no amount of loom will protect from that.

 

[TrueNorthist]

A diode will fry in just a few milliseconds. AC fuses (input side) come in many varieties of fast or slow trip times, otherwise you will have endless false-tripping and/or burned diodes. I know fused rectifier inputs are common but I just do not know what the rules are.

 

[TrueNorthist]

Yikes, the forum has suffered a cerebral embolism.

According to my Seloc, a 140hp might have as high as a 35 amp charge system (and a rectifier/regulator) but it looks like you are pretty sure what you have? The only info I can find on input side fuses is for larger rectifiers, but the instructions say to use a fuse or breaker rated to 175% of the full load current. I would think the rules are the same here.

 

[gm280]

There are also circuits that can cut the output in milliseconds as well and protect the rectifiers. It is just how far do you want to go with protection? You can make a protection circuit that is totally adjustable and set it at 9.1 amp if you like... JMHO

 

[TrueNorthist]

Ah, there you go. gm280 has the inside dope. But like I said, I would probably just ensure there is lots of protection on the wiring itself instead of adding more expensive components that may or may not like a marine environment.

 

[Chris1956]

First of all, what charging system do you have? Next question, what are you trying to protect? You want to protect the stator, right? So fuse the stator wire on a stator/rectifier system, where it leaves the flywheel on it's way to the tach. If that fuse blows, no harm will come to the stator or tach. The same goes for the yellow/grey wire from a voltage regulator to the tach.

Also, Rectifiers will limit the voltage that flows thru them without damage. However, if the rectifier becomes disconnected from the battery by a fuse or other means, the rectifier will blow. Fusing from the stator to the rectifier is OK, but there is usually no need to do that, as the components are close to each other, and unless the stator shorts to ground, the rectifier will blow first.

 

[nphilbro]

I did the same thing on my 175 Ocean Pro with 35A stator. I've also briefly lost a ground wire while bouncing 7-10ft swells, had another burn up from overheating. $1000 bucks of bad design. I finally built my own with replaceable rectifier from Fry's. It's not perfect but just charges a steady 13.8V. A better solution might be the mosfet style R/R you can find on a topic I started last November.