'94 CBR600 How to Build my own CDI Rectifier Circuit

 >From: "St. John Chen" SingCheong.DeleteThis@Netscape.net

 >I have a 1994 Honda CBR600F2. The CDI power rectifier break down 3 times for
the pass 2 years. I've giving up on Honda's CDI unit this time.

If the power rectifier you are talking about is actually the
rectifier regulator that charges the motorcycle's battery,
<a style='text-decoration: underline;' href="http://www.electrexusa.com/" target="_blank">http://www.electrexusa.com/</a> makes a less expensive replacement part which has
two SCR's instead of one...

But the fact that you are experiencing frequent failures of the same part
suggests to me that your real problem is
in the wiring harness of your motorcycle...

Production wiring harnesses have too many plugs and connectors that aren't
soldered. Heat builds up at each poor connection, burning up the power produced
by the alternator, making the connections hotter, and burning up the wire
harness eventually...

 > I want to design my own 3-phase power rectifier, and replace this unreliable
Honda rectifier.

That's easier said than done, and, if you make a mistake, you may wind up
buying a new alternator stator (ElectrexUSA makes a replacement stator, too) or
a new wire harness...

I once had an impoverished acquaintance who couldn't afford an original
equipment rectifier regulator for his Suzuki GS-1100G. I gave him a circuit
diagram, and he built his own RR, but he wound up frying the stator...

I looked at the Radio Shack online catalog and found that they can supply
3-phase full-wave rectifiers cheaply, but they don't give the specifications on
line, from what I can tell.

All you have in a 3-phase full-wave rectifier bridge is 6 diodes. The anodes of
the diodes are connected together and the cathodes are connected together. The
anodes are grounded to the case and the cathodes are the DC output...

The three alternator output wires are connected between pairs of diodes...

The output from the alternator, if it's a 3-phase wye-wound stator, would be
1.73 times the voltage from any phase to the neutral of the stator...

Since the neutral of the stator winding is probably buried away where you can't
get to it, if you measured with an AC voltmeter across any two disconnected
alternator output wires, you'd be reading 1.73 times phase voltage...

It would be around 140 to 200 volts...

So you would need 6 power diodes, with a reverse voltage rating of above 300 to
400 volts.

And, you would need an SCR that could shunt about 100 watts or more into the
heat sink when the phase voltage rose high enough to require the SCR to be
triggered...

The SCR would be connected to any of the three stator output wires...

In order to sense when to trigger the SCR, you need a
Zener diode rated at 14.5 to 15.0 volts DC connected to any of the three
outputs or to the rectifier regulator output, I have seen it done either way...

And, a pair of small resistors, a 100-ohm and a 1000-ohm resistor about 1/8th
or 1/4th watt are used to reduce the sensing current through the Zener to a
lower current required to trigger the SCR...<!-- ~MESSAGE_AFTER~ -->
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If it were Hondas problem all of that model of bike would have rectifier
problems...but they dont...so yours burning out is do to other reasons, such
as a short or overload in the rest of the wiring.
 >> Stay informed about: '94 CBR600 How to Build my own CDI Rectifier Circuit 

Thank you Phil Scott for your kind reply.

I've verified with a few biker friend, workshops, and internet. CBR has
problem with their CDI power rectifier.

It is unreasonable to have short circuit, because a short circuit may
cause at least 1 component malfunction, but there is none.

Overload is a more reasonable explaination. My instrument panel use
1.7W bulbs, which I can not find it in Malaysia's market. So, these
bulbs were replaced with 3W bulbs. Moreover, I replaced the headlight
bulb from 50W to 90W, because I always work late, and passing through a
dark valley everyday at late night.

However, this is became a requirement for my safety, and difficulty to
source for spare parts. Therefore, I prefer to design my own rectifier
to satisfy my need.

Just to share with bikers how much I have overload the rectifier in term
of Power (W) and Current (A). Below is the calculation.

Let's consider the extra power consumption due to the light bulbs.
There are 4 3W bulbs (3 * (3W - 1.7W) = 3.9W) and 1 90W headlight bulb
(90W - 50W = 40W), therefore the bulbs drawn extra 3.9W + 40W = 43.9 W
of power, which is 43.9 W / 14.2 V = 3.0915 to maximum of 43.9 W / 12 V
= 3.6583 A of current.

St. John Chen
Electronic/Computer Engineer

Phil Scott wrote:
 > If it were Hondas problem all of that model of bike would have rectifier
 > problems...but they dont...so yours burning out is do to other reasons, such
 > as a short or overload in the rest of the wiring.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: '94 CBR600 How to Build my own CDI Rectifier Circuit 

 >From: "St. John Chen" SingCheong RemoveThis @Netscape.net

 >Let's consider the extra power consumption due to the light bulbs. There are 4
3W bulbs (3 * (3W - 1.7W) = 3.9W) and 1 90W headlight bulb (90W - 50W = 40W),
therefore the bulbs drawn extra 3.9W + 40W = 43.9 W
of power, which is 43.9 W / 14.2 V = 3.0915 to maximum of 43.9 W / 12 V =
3.6583 A of current.

Typical lighting load of a motorcycle with a single 55/60
headlamp + instrument lights + turn signals + tail light + + brake light +
running lights is about 100 watts...

100 watts divided by 14.5 volts = 6.9 amps, so a 15 amp fuse would be adequate
for lighting loads with a safety factor of about 2...

A permanent magnet alternator produces current based upon the flux density of
the magnetic field, the rpm of the rotor, the impedance of the stator coil, and
the number of turns of copper wire in the stator windings...

A permanent magnet alternator doesn't know when to quit producing current, so
the rectifier regulator has at least one SCR to shunt excess current to the
heat sink of the rectifier regulator...

But, if the SCR or the Zener diode that triggers the SCR
burns out, you have no voltage regulation, the permanent magnet alternator will
just boil the battery dry...

The battery in a motorcycle with a permanent magnet alternator provides system
stability, absorbing a large percentage of the excess current from the
alternator...

But, if the battery is old or dehydrated, it can't do its job of absorbing
excess power...

And, don't forget I^2 * R losses in the wiring harness and connectors. Those
plastic connectors that connect your
alternator and rectifier regulator to the wiring harness will get hot and waste
a lot of power as heat...

Riders who get tired of melting the connectors usually just cut them off and
solder the wires directly together...<!-- ~MESSAGE_AFTER~ -->
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