1984 r65, engine surging and battery dying

[montmil]

Another way to check the rotor is with an ohm meter.

With the brushes off the slip rings, touch the meter probes to both slip rings. Your 1984 model should show a value of 3.4 ohms with a margin of 10% +/- either side.

An ohm meter can also check the stator in situ. No need to drag out your oscilloscope.

Monte

[clonmore1]

Okay, here is where I show my lack of experience

What is surging? I've seen this relating to later oilheads (R1150 etc), but not on here before, I may know it as another term but would appreciate being pointed in the right direction!

Thanks

[wirewrkr]

It's charging fine at 13.5 volts.
Go ride it.

[Barry]

What is surging?  

Weak mixture surging is uneven power delivery, feels like it won't pull properly until you roll the throttle off and on again.

[clonmore1]

Thanks Barry,

I understand now!

[tvrla]

It's charging fine at 13.5 volts.
Go ride it.

Except for the fact his battery is going dead.

So there is something the matter. At this point I suspect the battery.

Surging is a lean condition that produces a 'hunting' for the right RPM, and a feeling of weakness. In the oilheads it's caused by the fuel mapping running it lean, plus possibly ignition timing problems as well. The timing got messed with to pass EPA. You don't hear about surging much with the airheads since they were jetted rich - or at least rich enough - and as the needle and needle jet wears, they get richer.

Monte - an ohm meter is still a static test. These things often test good at rest, but when spinning, fail. This is due to the wiring being flung around and into a position where it shorts. The Oscilloscope will show the different phases while the alternator is in motion - so is a much better test.

But who has an oscilloscope and knows how to use one? Not me! It's just easier to swap with a known good rotor. These things are, after all, the most common failure item in the charging system.

[clonmore1]

"Surging is a lean condition that produces a 'hunting' for the right RPM, and a feeling of weakness".

Hi wirespokes, that's an expression I would understand very well, with Barry's explanation and this it makes sense.

Is it a problem with BMW's or all makes? I remember it being a problem with carb based cars in the 70's prior to fuel injection becoming the norm, so I assume the same would be for carb based bikes?

[Barry]

Not sure where you are up to with the charging issue but given everything else proven good I wouldn't be overly happy with a max. of  13.5 volts. You'd just about get by without supplementary charging if the bike was only ever used for long runs.

Ideally you want 14 volts or a bit more.  An adjustable regulator will let you set the voltage to suit the the bikes use. I have mine set at the realistic maximum safe limit of 14.4 volts as I do a regular short commute as well as some longer runs.

[tvrla]

Is it a problem with BMW's or all makes?

A symptom of lean running is surging. Doesn't matter how the fuel is delivered - it's not getting enough.

Barry - the current is more important than the voltage. The bike will run just fine on 13.5V - my R90 ran that way for years. And it's true, 14.4 is better, and the regulator could be changed or adjusted to accomplish that, but it won't cure the problem in this case.

There is a rule of thumb with these bikes which goes: it takes 15 minutes running at 3500RPM or above to recharge after starting the engine. It is possible this bike hasn't been run enough between starts and the battery is running down.

But I really am suspicious of the battery.

[Barry]

Barry - the current is more important than the voltage. The bike will run just fine on 13.5V - my R90 ran that way for years. And it's true, 14.4 is better, and the regulator could be changed or adjusted to accomplish that, but it won't cure the problem in this case.  

Yes I agree. My own car is not much above 13.5 volts but it's not an issue as it's rarely used for short journeys. I wasn't suggesting it would cure the problem which is why I qualified it first by saying "given everything else proven good"  

When everything else is proven good if the output is still 13.5 volts that suggests to me an adjustment or new voltage regulator is advisable particularly if the bike is to be used for short runs.

I agree with your comments about running time needed to re-charge a battery after a start. Many people imagine that alternators charge a battery vastly faster than a decent automatic bench type battery charger.  They do not except in circumstances when the battery is substantially discharged and then the high charge rate it is not a good idea for the health of the battery. The battery charge rate depends on the internal resistance of the battery and the voltage difference between the battery and the charging system. It's simple ohms law. In other words if a battery is severely discharged it should ideally be charged first. Expecting the alternator to do it means you will need to drive for hours. I suspect that many people who use a vehicle infrequently and then only for short journeys never fully charge the battery which results in a shorter battery life. Having the correct output of 14 volts or a little more from the regulator at least gives short journey users a fighting chance of keeping the battery charged.

[Bob_Roller]

I seen this mentioned before about some of the OEM voltage regulators .

I have a regulator with a small adjustment screw on the bottom.

Has anybody adjusted this, if so, what was the result, an increase in voltage output across the whole rpm range, or just high rpm voltage output ?

Or is this one of those things that's best left undisturbed ?

[Barry]

I have a regulator with a small adjustment screw on the bottom.

Has anybody adjusted this, if so, what was the result, an increase in voltage output across the whole rpm range, or just high rpm voltage output ?

Bob, I haven't adjusted your type of regulator but I have adjusted the earlier mechanical type. I imagine the electronic type would be the same. The adjustment will raise the maximum output voltage by delaying the cut off point of current to the field windings (rotor). It's a mark/space thing where the current is constantly being switched at high frequency with the on/off or mark/space ratio changing the average current delivered to the field winding.  So it raises the maximum voltage but also seems to have an effect across the whole range in that it also will lower the rpm at which the gen light extinguishes. In other words you get charging commencing a little earlier. I'm confident that's the case with the mechanical type but I might need to think about how the electronic regulators work.

It's worth noting that the standard alternator is really a 20 amp output at 14 volts which gives 280W. If for example the voltage regulator is set at 13.5 volts then what you have is a 270W alternator and if set at 14.5 volts you get 290W. Marginal perhaps and of little consequence because the current doesn't change but true.

[tvrla]

Be careful adjusting the regulator because its output changes with temp. I don't recall at the moment which way it goes, but think it rises when hot. So it's wise to set it when hot.

Some things don't do will with higher voltages than 14.5 - halogen lights for one. Life span goes down quickly with over-voltage. Electronics can be sensitive also.

[Barry]

Be careful adjusting the regulator because its output changes with temp. I don't recall at the moment which way it goes, but think it rises when hot. So it's wise to set it when hot.
 

The voltage is designed to fall when hot to match the falling internal resistance of the battery and therefore it's charge requirements.  So it's usually recommended to adjust the regulator cold. I've never done it on the bike but I have driven my car around with an accurate voltmeter hooked up and the fall off in voltage as the regulator gets warm is quite noticeable. Certainly several tenths of a volt. If a regulator tested at 13.5 volts hot it would be very much nearer 14 volts cold. My guess 13.8 volts.

When ever I have quoted voltage regulator settings they have always been with the regulator cold at say 20 Deg C. The temperature gradient effect is even enough to cause some confusion if we are in markedly different climates.

[tvrla]

Thanks Barry! Goes to show how often I've adjusted mine.