Alternator check

Historically, I always had trouble starting once temps got below about 40 degrees. Mostly, I felt it was because the starter didn't spin the motor fast enough.

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My experience as well.

Barron, where did you apply those additional ground cables?

Lew -

One bit of info on grounding:

http://robfrankham.co.uk/bike/earthing_article.htm

Snowbums' page:

http://bmwmotorcycletech.info/diodebds&grdgwires.htm

I bought a pre-made grounding harness from Motorrad Elektrik and installed it when I used his solid diode board mounts. I don't see it on his website, though.

Thanks Kurt, the first article makes a lot of sense, with the exception that I have no clue how "30 [and] 15 amp" wires relate to American Wire Gauge.

10 or 12ga?

"Amp"acity??

http://www.powerstream.com/Wire_Size.htm

Rob Frankham knows his way around these bikes from an electrical standpoint.

Update:

Someone on Boxerworks explain this of Rob's info:

"In general, 15 amp wire=14 gauge and 30 amp wire = 10 gauge. This varies A LOT with insulation types, conductor types and environmental conditions. The numbers I just threw out are for basic house wiring in conduit."

Also:

http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity#Load_Carrying_Capacities_or_Ampacities

Lmo1131 said:

Barron, where did you apply those additional ground cables?

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Lew, pretty much as described in the articles Kurt posted links to (above) from diode board mount back to common ground point at the coil mount and then back to negative terminal on the battery.

Saw your question on wire size and don't think it matters. 12 or 14 gauge seems ok. Main thing is that you are providing a nice path back, but I don't think you need a battery cable sized wire that takes a torch to solder connections to.

On a different note -- Take a look at your 3-cable bundle coming off the alternator if you still have the original one. Mine was totally corroded under the black connector plug (where you couldn't see it). Really easy to fabricate a new set of wires.

Barron

UPDATE.

All terminals cleaned (no corrosion found under the 3-cable bundle).

Additional AWG 12ga. ground cables run from diode board to battery (-) anode, and coil/frame ground.

Voltage regulator replaced (NAPA Echlin ECH-VR503 (equiv.: Borg-Warner R-588/Transpo IB301))

Voltage (measured across battery terminals):
@2500 rpm: 13.1
@4500 rpm: 13.9-14.0

Time for a ride... ... thanks for all the guidance!!!

Lmo1131 said:

Voltage (measured across battery terminals):
@2500 rpm: 13.1
@4500 rpm: 13.9-14.0

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Just out of curiosity, what is it at idle? I'm surprised it takes so many RPMs for you to get 14V, unless you have some loads drawing a lot of power.

For comparison purposes, I measure 14.0 V to 14.2 V from idle to anywhere up the RPM band.

I'll re-check that later this morning when I get back down to the shop.

FWIW, it's better than I had.

Alex, here's what I got this afternoon.

Indicated rpm per my /5 tach ... so who knows what the true rpm was.

@ 800-1000 rpm: 13.9

@ 2500 rpm: 14.1

@ 3000 rpm: 14.1

@ 4500 rpm: 14.1

The only difference between the condition of the bike, from yesterday until today, was that the battery was on a charger all night.

Lmo1131 said:

Alex, here's what I got this afternoon.

Indicated rpm per my /5 tach ... so who knows what the true rpm was.

@ 800-1000 rpm: 13.9

@ 2500 rpm: 14.1

@ 3000 rpm: 14.1

@ 4500 rpm: 14.1

The only difference between the condition of the bike, from yesterday until today, was that the battery was on a charger all night.

Click to expand...

Since Airheads use an electromagnetic rotor, alternator output in volts depends to a considerable degree on the starting battery voltage. I typically look for about a 3/4 volt maximum increase from battery standing voltage to alternator output voltage. Often I see .5v or .6 v increase.

The reason today's readings look better than yesterdays is that the battery was more fully charged.

You can't get satisfactory output readings with a poor battery in the system

Thanks for that info Paul.

I'm going to run what I've got for a while and see how it goes. The battery is a generic lead/acid. The PC680, mentioned by Barron, is a probable upgrade I will keep in mind.

Awwwww crap. That didn't last long...

Took a little 200 miler today; up to Big Sur and back; foggy at the start and cleared by 10, one of God's perfect riding days. Several starts and stops, with no problems. Got back to the shop and checked voltage just for the helluvit.

12.2V @ idle.

12.9V @ 3000.

It remains to be seen how the starter does in the morning. I suspect it will be it's same-o same-o reluctant self.

I give up, that's what I was getting with the 39 year old OEM regulator... .. . at least I'm only out $30.

Thoughts?

I think the $30 for the regulator was probably money well spent. It was time.

How old is the battery and who manufactured it?

Barron

Replacing the stock rotor with one providing more power is the only real solution. Based on articles about the /5 charging systems, the alternator (when new) puts out 180 watts. That amount of power is marginal. Add 35+ years of age considering corrosion and decomposition of winding insulation with mechanical wear and the alternator probably puts out less than 180 watts.

New rotor: http://www.euromotoelectrics.com/product-p/boalt-rotor642.htm

A new battery will also help but not fix the problem.

Edit: here is snowbum's page link for the alternator describing the /5 180 watt system: http://bmwmotorcycletech.info/trbleshootALT.htm It appears that altering the stator is needed to increase the output. So, just replacing the rotor may not be the solution.

There is no reason why a STOCK /5 with 180 watt system in proper working order will not start reliably at 40deg - something missing in this discussion.

Is the bike STOCK - headlight orig or 60watt max H4?

Are there other loads you have not mentioned?

Do not turn the light on till started

Does the bike have aftermarket electronic ignition - this is a cold weather nightmare since cranking draws voltage below trigger threshhold for some systems- if so use kick starter when cold

What other loads are there that are not stock?

If starting/runnig at 40deg use oil 10w40 or 15w40 - NOT XXw50

I have absolutely no trouble starting old /5s with small 10LA2 lead acid battery if the bike is properly tuned and making a 10 mile ride at 45mph or more with 55/60 watt H4 and 40watt electric vest on full.

Till you figure it out suggest you use the kick pedal before cold start

Ignition off - gas on - choke on - prime the bike by stroking through one compression per cyl to get fresh charge of fuel/air (save your battery making this effort)

Ignition on - kick or hit the starter should fire on first revolution
Kick is better since it leaves max voltage for ignition system

The original system is adequate - you really need to keep searching till you find what is wrong before just throwing a bunch of expensive aftermarket parts at this bike.

There should be no reason to need to keep a charger on the bike every night if the battery is good - this might be killing or has already killed the battery

There is no reason the bike (with points) should crank more than 2 or 3 revolutions before starting - not tuned properly if cranks more

"But there is still a slight hesitation when the starter engages (and has been since the bike was new); and the starter has never really shown any "authority" when turning over the engine."
=====================================
This is the case on one of my junkers known to have PO installed too small diameter wire for ground and feed to starter. I should fix it but usually just kick it.

Update

The original system is adequate - you really need to keep searching till you find what is wrong before just throwing a bunch of expensive aftermarket parts at this bike.

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Load-tested the battery yesterday: it had one weak cell (so much for "it's only six months old"). Replaced with generic lead/acid wet cell; charged for ~12 hours.

I made a extender cable for my digital multimeter, plugged it into the remote battery tender pig tail, tucked the meter under the map window on my tank bag and went for a ride:

voltage @ battery before start; 13.8
voltage @ 1000 13.9 - 14.1 (fluctuates)
voltage @ 2000 14.1
voltage @ 4000 14.16 (sustained highway speed; all lights off)
voltage @ 4000 13.85 (headlight on (60/55W H4; low beam))
when the head light is turned off voltage returns to 14.1+ almost instantaneously.

The bike started right up this morning after being left outside in the fog all night, off the battery tender. Turn signals cycle faster. Horn is louder.

I've never had instrumentation on this bike and have to say I like it. Now I'm thinking I'd like to permanently install that Datel digital voltmeter; $50 seems kind of steep but it is small, and waterproof...

So this would seem to mark the end of the quest for increased voltage. In the future I will suspect the battery when/if a voltage drop is observed.

Good to know - it was the battery. As a note, a battery hydrometer is always reliable to check the condition of a standard lead acid battery. I don't think most people own one - and one for a motorcycle battery is generally smaller than for a car battery so not as readily available in auto parts stores. Plus, they don't work for gel-cell or sealed lead acid batteries.

I bet the stock voltage regulator is still good.

glad its sorted out,
so another spare part for your collection ( the old regulator)

so another spare part for your collection ( the old regulator)

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Well that, and my multimeter.

Note to self: Next time, do not leave multimeter under tank bag map window, in direct sunlight, until the middle of the afternoon ...