To the electrically minded

Thinking about redoing the two-blub straight from generator test tonight, I rethought some of my earlier test results.

At idle, with one blub connected, I had 17 volts across. H4 blub is about 2.6 ohms if I figure correctly (haven't measured directly, using a online reference). That means the power output of my generator at idle is V^2/R or 17*17/2.6 = 110W. When I used two head lights, the effect voltage is halved to 1.3 ohms. I measured 11.7 volts, so the power output would be 11.7*11.7/1.3 = 105 W. So this says that at idle, my system is putting out about 105-110W.

I fully intend to redo both the 1 blub and 2 blub tests at 1,200, 2,100, 3,000, 3,900, and 4,800 rpm tonight. This should give good map of the power output of the generator across my normal operating rpms.

My only question is....I don't know what "normal" wattage for a kz750n-1 should be across these ranges. All the manual says is 17A at 10,000 rpm.

Well I'm waiting impatiently at work to do these tests, anyone have opinions on what "normal" power output on the generator would be?

another part of your test should be after the bike is fully warm, you can do this by running it with a fan in front of the motor for a period of time and then test it again while it is hot to see if you are geting a break down with heat

My question is this, if the magnets were weak, as BSKz650 said, "it would be a constant low voltage". I don't think it would fluctuate like that. The intermittent fluctuation seems like a ground or regulator. If either one is bad you could get the fluctuation and the low voltage.

Well, in the test, the regulator wasn't connected. I was taking the output from the stator to a separately built rectifier and feeding the rectified voltage to the lamps.

So I guess that leaves only grounding....

I blew that one, forgot that you had built one, my bad, so I would have to agree on the grounding

Most headlight wattage ratings I've seen are specified at 14v. That means at 55W, 14v, you get 3.9 amps. 55/14=3.9 That means the effective resistance is 3.6 ohms. The resistance of lamps vary with different voltages. I'm not sure where the 2.6 ohms rating comes from, but if it's an ohm meter reading, we can throw out that number. The resistance is much higher when the bulb is on versus when it's off.

It would be difficult to give actual wattage numbers when the bulbs are not at 14v, but at 17v we know one bulb uses more than 55W, but at 11.7v we know two bulbs are using less than 110 watts. That's why I threw out the 100w number as an approximation. If you get 14v on two 55w lamps, we know that you are getting at least 110 watts, but at what RPM?

After these tests, how about running the bike with the headlight fuse pulled and see if the same thing happens with the dropping idle etc.

You could have a defective battery which is temperature sensitive, or you could have a temperature sensitive regulator, but you are doing the right thing by isolating and load testing the alternator. That is step one.

Don't let the voltage go above 16v if you can help it.

the more I got thinking about this, since you have isolated the charging system the only thing left is thermal break down in the windings.
we used to trouble shoot wiring with a megger, may not be spelled right, but it would apply voltage to wires and you could find bad ones via going to ground under a load, wonder if there is a way to do that to the windings?

BSKZ650 wrote:

the more I got thinking about this, since you have isolated the charging system the only thing left is thermal break down in the windings.
we used to trouble shoot wiring with a megger, may not be spelled right, but it would apply voltage to wires and you could find bad ones via going to ground under a load, wonder if there is a way to do that to the windings?

This is a possibility, but if he can get 15v on two 55w lights at 3000 RPM, for a sustained period (he says problems happen after 5 to 10 minutes), then we know the alternator is not the problem. Verifying the alternator is good is really just the first step in the overall troubleshooting task.

However, don't rev the bike for 5-10 minutes, it will over heat if it's not moving. Do the test, then let it idle to come up to temp, then verify the voltage at 3000 RPM at several 5 minute intervals.

The battery should be charged before the test, and the bike should be run without lights to preserve battery power. I use an external power supply sometimes to keep the battery steady while it's running, but never while the bike's charging system is connected to the battery, obviously.

Identifying the exact problem is very time consuming which is why most people are satisfied with just replacing a bunch of parts until the problem goes away. I prefer this logical approach, even though it's not the fastest method.

Well last night I got home, just to be certain I wasn't current limiting the homemade rectifier, resoldered all the wires from stator with 18AWG wire. I then solder two headlight connectors to the output to make sure it was connecting well. Hooked it all up to the bike, clipped the voltmeter to the output leads and had notebook ready for fun.

2 55W blubs at

1,200 rpm - 13.7 V
2,000 rpm - 17 volts
2,100 rpms - blubs blew.

Ok, I think the generator is good!

I reran my solid wires from the stator to the rectifier and tried it out. With only the main fuse connected, and sense wire out, I was able to get slightly reved to go to 15 V. Connect sense wire, shunts to 14.5 V.

All but headlight running lamps drops it to about 14V. I couldn't test headlight as it was recently blown.

I'm going to get a new headlight tonight and try out basic running setup tonight.

My thinking is since I'm now running new wires from stator to regulator outside of bike, that perhaps my charging problem was spotty yellow wires from stator to regulator. If it was disconnecting or grounding intermittently, that would explain the low charging volts I was seeing.

BUT -- I am very VERY satisified to know that the generator is behaving well. That is no new rotor or stator needed (couple days thinking and tinkering saved about, oh, 250 dollars?) Arguably, the regulator could still be an issue, as well as bad harness wiring causing too much draw.

After I get it stitched back up, I'm going to run an ammeter on each of the 4 sub/non-main circuits and see what the running current draw is on each. From the diagram wattages, I should be able to tell a rough estimate of good/bad current draws on each circuit to focus attention on what harness parts might be bad.

Thanks everyone for helping me work this through and I'll post update when I can test normal running conditions again.

loudhvx wrote:

....

Don't let the voltage go above 16v if you can help it.

Oops, :ohmy: , I should have been more emphatic on that point.

Well, you can get cheap, halogen 55w bulbs at Home Depot if more test units are needed, but I think the alternator is ok. (I've never seen a rotor get weak or a stator go bad by itself).

It could still be the battery, reg/rec, or wiring. I think the next step is to verify the reg/rec (as you are already doing with the un-connected brown sense-wire). BUT MONITOR THE VOLTAGE AND DON"T LET IT GO OVER 16V this time
Just kidding, I'm sure you'll monitor it now.

If it turns out to be the reg/rec, I have a few spares and I'm near North and Pulaski.

Well, I think it is the regulator part. Here's what happened last night.

Feeling happy after putting the bike all back together that the generator was working, I decided I needed to get some spray paint. Anyone who lives in or near chicago knows that you can't buy it in the city, so I had to take a 25 mile ride to the nearest 24hour walmart. I thought this would be good test of the charging system.

After going about 10 miles, I hit some heavy construction and had lots of stop and go. As I went, the idle slowly dropped and the bike ran rougher -- my symptoms earlier of non-charging. I was able to run it find the rest of the trip at 5000 rpm in 5th. When I got to the walmart, I pulled the voltmeter out. At idle, battery getting 12.5V, at 4,000 rpm getting 12.85 -- not good.

Thankfully walmart supplies all the test supplies I'd need at 2 am. I was able to get 2 extra headlights and 2 sets of test clips for under $18!!

I first hooked it up with generator feeding reg/rect, brown sense disconnected, black and red feeding two parallel 55W blubs. At idle got 11.8V, by 2,000 rpm got 14 volts, by 3,000 inching over 15.1V. So clearly both the generator and the rectifier portions work.

However, when I connected the brown sense wire to the positive output side of the circuit, I got some weird behavior. At idle I still got 11.8V, by 1,800 about 13.5V. Then if I increased the rpms slightly, the blubs would start to oscillate in brightness and the voltage would go between 12.8 and 13.4 V very rapidly. If I increased RPMS more to say, just over 2,000, both blubs would dim significantly and the output voltage would drop to 10.2V and hold steady there. If i backed off the RPMS to around 1,800 I'd get the oscillation and dropped further it would stabilize back at 13.4 and then steadily decline with rpms back to idle. Very weird.

I assume this means my sensing/regulating ciruit is bad? First it shouldn't shunt until 14.5--15V, right? Also, as soon as it drops below 14.5 from shunting, it should stop, causing a rapid on/off shunting around 14.5V, yes?

I assume the regulator getting hot had something to do with seeing this behavior. Before I buy I replacement, just wanting to see what the consensus opinion of the weird test results were.

Post edited by: dnpurdy, at: 2007/05/31 10:24

I figured that it was the regulator, once they get hot they can do strange things.
got to give it to you, you tested the crap out of it rather than just replace some parts, me I prob would have put a regulator on it and then if it didnt fix it go to the next step