fault finding repair tips for a brushless capacitor compensated generator

Okay, I'm just going to show you a uh a

few basic fault finding tips to diagnose

um faults on a capacitor compensated

brushless alternator of the type

typically fit fitted to

Honda frame generators of the EC series.

So,

I've taken the back off of this one just

to so we can have a look at the back of

the alternator there. First thing to do

is just physically have a look around

all here. Uh you'll see there's bindings

in here. There's a couple showing there.

Quite often the this is done with um tie

wraps. But the thing is these bindings

can give you a clue as to what's going

on with the uh the alternator. So you

have a good look because if they're

broken in any way, it indicates that the

stator has got very hot at some point

expanded and snapped the bindings. So

that's pointing you towards a fully

stator. Um but before any of that,

before even taking the back off, what

you need to do first is start the

machine up, check you've got the right

speed. speed should be about 3,100 RPM

off load or if you're measuring via the

output about 52 hertz with no load. Then

if you're getting zero output from the

um from the sockets, the next thing to

do is just to give it a little rev, a

quick rev by just getting hold of the

throttle linkage. um and only needs a

blip because sometimes if it's if a

machine has lost residual magnetism in

the rotor that will just giving it a

quick rev will be enough to restore that

uh get the whole generating process

going again. Um if that doesn't uh you

you need to measure what output you're

actually getting from the uh from the

sockets. If uh if it's showing you

you're getting uh say 110 volts out of

the 220 volt socket, that can be a clue.

can be telling you've lost one one

winding on the stator as the state

usually has two 110 volt windings or it

could be telling you that you've got uh

contacts burnt out in your voltage

change over switch. Um the other thing

of course it could be telling you is

that you've got uh faulty diodes on the

rotor. That's there's the diodes on the

rotor I think sometimes called revolving

rectifiers. um if they're leaky, they'll

sometimes exhibit a symptom whereby the

voltage is very low off load and when

you put a load on it, the voltage will

pick up. So, there's a little clue

there. Uh the other clue that they

sometimes give you is that they're black

and blown to smitherines. So, it's

always worth looking for. Uh the only

real way to test them is to disconnect

one end and uh measure the resistance

across them. Should be high one way, low

the other way. Okay.

So you've uh you've run the machine,

you've given it a riv, done all of that.

Uh we'll come to look at this part which

is the capacitor. Now these capacitors

are quite large, capable of holding a a

fair bit of charge and thus giving you a

kick like a horse if you get your

fingers across them. So they need to be

discharged before you start playing with

them. I do it with a uh with an

insulated screwdriver across the

terminals. Uh, and I'm sure there's much

safer ways of doing it than proper ways

of doing it that you can probably look

up on um on Google to safely handle a

capacitor of this size. And then once

it's discharged, you want to measure the

capacitance across there with a meter

that will do it. And it'll have a value

written on the side. In this case, 16

microfarads. It looks like 16 followed

by U and a capital F. But that U is in

fact the Greek symbol for micro. 16

microfarads. So you would measure across

that and check that its value

corresponds to the value written on the

side. It's very common for these to

fail. They don't last forever and quite

commonly if they do fail they'll exhibit

some physical signs that there'll be

bulging, cracked, burnt, the caps will

be blown off. Um anything like that can

give you a clue as to what's going on.

When you come to replace one of those,

don't be tempted by a washing machine

for capacity off eBay. A starting

capacitor is just designed to get a

motor going for a few seconds. These

have to run for ages. So, you need the

proper capacitor to fit one of these,

otherwise it won't last very long.

Okay. Um, the next thing to check is the

windings themselves. So, we just

disconnect the main plug. They usually

have a plug coming off the stator, four

uh connections in it like that. Those

four connections are the ends of the two

110 volt windings. Uh you it's it could

be wired so that that's one winding

diagonally the other winding or this is

one winding and that's the other winding

kind of there's no convention about it.

If you fish about in there with a uh a

voltmeter set to resistance, you're

going to be expecting to find two pairs,

and they're both going to be the same

resistance in the region of an ohm or

half an ohm or something like that. And

once you've figured out which are the

two windings, there should be no

connectivity between them at all. Okay?

If any of those conditions aren't met,

then it's pointing you towards a fault

in the uh in the state of winding. Quite

often, these uh parts for these

alternators will be so expensive that

it's probably cheaper to just buy a

complete secondhand alternator and fit

it on than it is to change a part. Like

I say, typically a SP a stator on a on a

4 kilowatt

um alternator like this might cost you

£300. So um you know and you can usually

pick up a complete secondhand alternator

for say 150. So um it's worth thinking

about that. The other thing you need to

consider is that they don't usually fail

for nothing. There's usually a root

cause and the most common root cause

that causes them to fail is a dirty

carburetor on the engine. Dirty

carburetor leads to lower engine power.

When you put a load on the alternator,

it ends up slowing up the engine. You

slow the engine, you slow the fan that's

drive that's driving air through the

alternator, and that makes it overheat.

So, that's one thing to uh consider. The

other thing that will uh will cause them

to fail is if somebody's put a box over

them to cut down on the on the on the

noise, that will make them overheat.

Maybe somebody leave a coat on it. Maybe

it's got a mouse nest in there ex you

know um that's uh blocking off the air

flow. All sorts of things like that. But

basically there's no point just changing

a component in your alternator without

checking that your engine is capable of

delivering the power to drive that

alternator because low engine power

kills alternators. That's about I think

all I've got to tell you on for finding

a a simple capacitor compensated

brushless alternator.