electrical question

Hi all. I have a KZ750 which has been modified considerably, but has a stock
electrical system. I no longer have running lights, and now have dual front
headlights each with a single H3 55 watt halogen bulb in them. I want to
install 2 mini driving lamps, which each also have a H3 bulb in them. How
can I determine if my charging system can handle the extra load (other than
doing it and trying and frying it)?

 

The workshop manual will tell you how many watts (and indirectly, how
many amps) the alternator is rated for, at some rpm[1]. The problem is,
you don't really know exactly how many amps your bike consumes without
measuring it. Even worse, the amount of power available depends a lot
on the average rpms you maintain, which varies depending on whether you
are stuck in traffic, commuting, canyon carving, etc.

The only sure way to know if the alternator can support the additional
load is to experiment, by adding instrumentation (ammeter and voltmeter)
and a way to switch your additional loads into the system. If you are
not careful to measure the output of the alternator constantly to make
sure you are not overtaxing it, you might well fry it. Old bikes tend to
have trouble with bullet connectors losing their spring. When currents
increase, which overheats the connector, it further weakens the spring
contact, until it fails catastrophically.

My opinion is that you've already got enough light as it is, with two
55W H3 bulbs. You would be better off making sure that the beam pattern
of your existing lights is optimized.

 

Tom B

I don't know if this will help, but you can get a pretty good idea of what
your electrical system is drawing by connecting a multimeter between your
battery's positive post and the
red/positive cable. Measuring battery DISCHARGE: connect multimeter
positive
probe to battery positive post, and the negative multimeter probe to battery
cable.

With the engine not running, but your ignition turned ON, you can see what
all the lights and gauges are drawing. Hook in the "new" lights and do the
same measurements. Turn off others to check on their draw.

Now to get the electrical system draw including the engine's ignition
system, you
need to start the engine, but BE CAREFUL. To do these charge and draw tests
with the bike running, DO NOT connect the multimeter until AFTER you start
the engine, or the 20-30 amp starter motor draw from the battery will
probably trash your multimeter (set at 10 AMPS max.).

I removed the positive
cable from the battery and held it to the positive battery post and hit the
starter (wear gloves or hold the cable by the red insulator). I then
connected the multimeter with alligator clip probes to the cable and the
positive post and then removed the cable from the battery post. The current
was then flowing through the multimeter. As you roll the throttle, note the
amp draw at specific rpms. You're looking for the rpm-point where the draw
is zero. This is your break even point: the electrical system is neither
depleting the battery, and the battery is not being charged. It will
probably be somewhere in the 1500 rpm area (guessing) some minutes after the
bike is warmed up and the battery is fully recharged.

TIP: If you can, use a good quality digital multimeter that will display
positive and negative amps. I used a Radio Shack analog multimeter. An
analog meter cannot display a negative current draw without reversing the
probes. An analog multimeter can only "indicate", a negative amp reading as
the needle drifts to the left OFF the meter scale.

I hope this helps a bit. As in an earlier post to this thread, try to
connect
the extra lights run through an ON/OFF switch. When you get caught in slow,
or stop and go traffic, your rpms will be in the 1000 idle range which is
likely to be
below the break even point. Your battery will be discharging on a pretty
steady basis to keep the bike running and the lights/gauges lit. It will
take
some faster riding to recharge the battery. If the extra lights can be
turned off, your battery will last longer.

 

No. The engines, in general, [1] have to be spun faster because
permanent magnet alternators are typically mounted directly
to the crank while excited field alternators are gear or belt
driven to attain speeds *greater* than the crankshaft. To improve
output of the alternator, you have to increase the diameter of
the rotor, or increase the speed of the rotor. Harley uses a rotor
of around 6" diameter for their PM system, and it covers all of the
loads on my RK by 1500 rpm. In contrast, BMW airheads and some Guzzis
drive their Bosch EF systems directly off the crank. These BMWs are
notorious for their lack of output at anything less than highway
speeds. In some extreme cases, loafing along at 60 mph in high gear
would allow the battery to discharge with enough accessories and
"safety" upgrades. [2]

The Guzzis didn't didn't attain quite the same reputation as the
BMWs, as with their Italian electrical systems, the electrons really
had no place to go.

[1] You know about generalities.

[2] Extra lighting, heated clothing, the occasional radio.

Why not put transformers at each end of the stator-RR wiring to
reduce the current traveling through the wires?

It works for SoCal Edison.

???

I would take the stock headlight off the main wiring harness.
The mere use of a heavier wire would result in less resistance
than tapping the same feeble wires that power everything else on
the bike, regardless of whether or not the wire is bundled
with the main harness. You want the shortest and largest
wire practical between the headlight and the battery, with
only a relay for each filament and a fuse. Pick the relay
with the existing filament leads. You may find that you don't need
additional lighting.

Why not replace everything with 2 solder joints on each wire between
the stator and the RR. Emergency roadside repairs could be handled
with a pair of diagonal pliers and a few wire nuts.

So go down to your Kawasaki dealer and buy some new connector contacts.
Make an extended pigtail that can be soldered directly to the stator and
reassemble the connector shell with the new pigtail. If Harley-Davidson
can provide you with the resources to make this kind of modification,
I'm sure Kawasaki would only be too happy to do the same.

The "cheapy" fuse holders I got from Pep Boys are rubber, not plastic.

And they use the same style fuse as the rest of the bike (ATO),
which makes carrying spares more convenient.

 

A math equation should help here.
P=I*E
Power = Current * Voltage using simple algebra
Power/Voltage = Current

Therefore a 55W/12V = 4.58 Amps.
Look at your fuse in the circuit you are using and add up all the
current that will be passing through that fuse. Only load that fuse to
about 80% of it's capacity. Look at the size wire to the fuse and to
your light string and see if that size, gauge wire, will carry that much
load. You don't want to catch fire will riding down the road, or see
smoke ascending into the air as you try and impress your friends with
your additional lights.

Add up the total load of all the circuits and here again use an 80% rule.

Others have given you a detail of how to measure the amperage on your
bike so I wouldn't go into detail.

 

I really doubt this.

Much more likely they reckoned it was an improvement, and Japanese bikes
are not roadtested for anywhere near as many miles as their cars.

And even if they did detect an abnormal failure rate, they'd not have
the time nor the cash to completely redesign the electrics (launch date
impending), so they simply put it out "as is" and reckon that faults can
be picked up under warranty.

SOP, really.