77 KZ650 typical current draw before start?

Hello all!

I bought a 77 KZ650 last weekend (see pic), and have been working on some electrical issues while I wait for the title.
The bike is mostly stock except for dyna s ignition and 3 ohm dyna coils. I have new plugs, wires, and 5 ohm coils on order.

With the key turned on (ignition), and the engine switch off I measure about 2 amps.
With the key turned on (ignition), and the engine switch on I measure about 4 amps.

Does that current draw sound reasonable?
The 2 amp draw with engine switch off seemed high, and since I've found some of the POs "interesting" wiring choices, I'm not always sure what to trust.

Is the head light always on? The Dyna and 3 ohm coils should draw more than that.
Steve

No, the headlight is off and controlled by the right hand light switch.

If nothing is on, there shouldn't be any draw.
Steve

I should add that the primaries measure about 3.1 ohms (3.5 minus lead resistance) and the battery is low due to the PO wiring an LED indicator resistor which was keeping the flasher on all the time. He wired it in parallel with the flasher to ground.

One coil's secondary measured 12-15k. The other measured 150k, and then 1G after more testing.
That's why I'm replacing the coils, and figured new wires and plugs would be nice.

I'll charge the battery and recheck the current draw.

I'll check the key off current draw, but I believe it is 0.

That's why "PO's suck."
Steve

The 77 KZ650 has a field coil (identified by the three screws in the triangle shape on the alternator cover) which will be on anytime the key is "on". When the motor is not turning, the field coil will be at full draw. That is normal for that model, but not a great regulator design. You can probably find the resistance of the field coil in the manual somewhere. Expect it to go higher as the field coil heats up, which means current will go down as it heats up.

When you turn the ignition on, then the Dyna S draws current through one or both coils. 4 amps seems low, but maybe the amp meter is not that accurate, and/or you have some losses in the wiring. As with the field coil, the resistance will go up as it heats up, so the longer you have the switch on, the lower the current will get. Do not leave the key and ign on for long. You can cook the Dyna S, or the coils, and same goes for the field coil.

Interesting...Isn't a field coil better than a permanent magnet rotor? nice idea to directly modulate the current output to the demand, rather than charging all the time, to shunt and dump the excess.

Tyrell Corp wrote: Interesting...Isn't a field coil better than a permanent magnet rotor? nice idea to directly modulate the current output to the demand, rather than charging all the time, to shunt and dump the excess.

Yes, way more efficient for crankshaft power, and it allows you to use a more powerful alternator since it won't be so wasteful. This allows you to have a much wider range of varying loads (like on a car). The one KZ650 I tested would get nearly 14v at idle. (And stay at just over 14 at higher RPMs.)

I think the permanent-magnet 650 alternators that followed, in 78 and 79, were made with just enough power to run the bike, so the regulator wouldn't have to dump as much extra power, and the crank would use minimal power for generating electricity, but they may have cut it too close. They didn't really leave enough extra capacity in case someone added lights or a more consuming ignition (like the Dyna S). They corrected that in late 79 or 80 by converting to 3-phase.

The problem with the 77 system is that they didn't take full advantage of the efficiency. They didn't go the one extra step of running a dedicated output from the rectifier to power the field. I call this extra output the "aux" output. Had they done this, and added one extra resistor, they would have greatly reduced the current the battery would use in times when the bike was switched on while the crank was not turning. This would also reduce heat in the field coil during those times, and would also free-up more current for the starter during electric-start.

That extra resistor limits the current usage from the battery. Only a tiny bit is needed to get the alternator to start generating some output. Once the alternator is starting to create output, the majority of field-coil power comes from the alternator itself via the dedicated "aux" output.

You've probably seen this type of setup on some other brands of bikes back in the 1970's.



I think, in the end, though, the system was too expensive and complex, so they went with the permanent magnet system, which is better suited for sportier bikes, since they won't be used for Saharan expeditions.

That's very interesting. Have you tried implementing that mod?
I assume it requires a different rectifier.

I have a feeling my current readings are low because of battery drain.
I'll make a measurement with a charged battery and new coils when the parts come in.
I ordered from Z1 yesterday, but it looks like my parts haven't shipped yet.

Yes, i used that design on a couple Yamahas... YR5 and RD350.