'75 Charging Numbers

[YamadudeXS650C]

I've had my '75 for 5 years now and it has always been a bit quirky in the charging domain, compared to my '76, '83 and '82 which give me consistent numbers on the voltmeter.

The '75 is running and starting well, but the numbers concern me a bit. I'm interested in others' opinions.

Background:
The regulator is a VR-115 (replaced last year) It is rated to regulate from 13.8 to 14.8v.
Rectifier is a modern cheap Chinese "Centry" 35 AMP 3 PHASE unit, wired it myself (correctly).
I've inspected/cleaned all the wiring connections.
New BigCrank 220cca battery this month which I fully charged.
Modern fuse block.
Slap test is OK
Brushes are good.
Rotor: 5.3 , No shorts.
No voltage drop at the brown wire going to the reg.
Probing the back of the stator connector (3 white wires) at idle, I get 12.3v on all 3 of the combinations.

I just installed an onboard voltmeter and the new battery. All my XS's got a BigCrank this year.
Voltmeter is wired directly to the battery and switched (mini toggle)

On the first long test ride sunday, I was initially getting 14.4v on the meter at speed, but by the end of the test it was only 14.1. At idle it is 13.5.
On the second long test ride yesterday I got only 14.0v, and by the end of the long run the number was 13.9.

It seems to be charging well; after sitting for 22 hours, the resting voltage is 13.1 this morning. However, maybe (?) it is overcharging, as my other bikes all are at 12.9 after resting overnight.

 

[Jim]

Could it be your new voltmeter is off slightly?

 

[YamadudeXS650C]

Could it be your new voltmeter is off slightly?

That did occur to me yesterday, Jim.
When the weather clears (maybe today), I'm going to hotwire another new voltmeter (same item) temporarily and see what I get.
I just hooked up my best multimeter and got a resting voltage on the '75 battery of 13.03 I guess that isn't too far off from 12.9, but I've never seen a 13 volt reading after the floating charge has dissipated.

 

[YamadudeXS650C]

I also have a spare early rotor which tests at 5.4, so I'm thinking of switching that one in at some point.

 

[Paul Sutton]

Usually the regulator will have a stated set point voltage. This could be anywhere from 13.8V to 15V, but usually about 14.2V to 14.5V. When operating, the voltage should show within approximately +/-0.2 volts of the set point due to temperature compensation: Cold conditions require a slightly higher charge voltage and hot conditions need a slightly lower voltage. When riding you should see a stable voltage e.g. 14.1 - 14.3V all the time if the set point is 14.2V. Big swings in the voltage from say 13.8 - 14.2V are often due to the rpms being low or the current drain too high.

I do not believe you are overcharging because the voltage observed is too low. Over charging occurs when the voltage gets up in the 14.8 - 15V or higher range. Over charging is not about charging but refers to a high voltage causing the water in the battery's electrolyte to be split into hydrogen and oxygen. This loss in water leads to battery damage due to the resulting increase in acid concentration.

You may find that the voltages stabilise after a few rides as the electronics go through a few heating cycles. There is nothing wrong with seeing 13.1V after a good charging, especially when the battery is new. The difference in 12.9V and 13.1V represents a very very slight difference in overall charge capacity and flicking the lights on for a few seconds will quickly use up the capacity and drop the voltage to about 12.6V which is the usual indicator of a good battery.

I hope this helps.

 

[5twins]

My VR115 reduces it's charging output a little after riding some and replenishing the battery as well. I think it's normal for that regulator.

 

[YamadudeXS650C]

Usually the regulator will have a stated set point voltage.

Thanks Paul,
It would be nice to know what the set point voltage is for the VR-115. I searched and couldn't find it.

 

[YamadudeXS650C]

My VR115 reduces it's charging output a little after riding some and replenishing the battery as well. I think it's normal for that regulator.

I have a VR-115 in my '76 as well. I've only done a rather short ride with this onboard voltmeter with the '76 (hotwired and taped to the handlebars), so I'll be interested to see what the voltage fluxuations are when I mount it permanently and take a longer ride.

 

[5twins]

I also noticed the slightly higher output in colder weather. Nice to hear it's normal.

 

[YamadudeXS650C]

The weather is still drizzly and the roads very damp, so I did some driveway testing and short runs up and down the road in front of the house just now.

Hooked up my best multimeter in tandem with the onboard voltmeter, the latter which I have mounted on 3 of the XS's at this point;

because it is directly wired to the battery, it is quite responsive. My testing shows that it is consistent with the multimeter, reading just a hair (0.08) higher,
therefore the voltmeter reliability is not an issue.

I did 4 tests in the driveway, and one on the road, cooling the bike in-between.
At first the readings were erratic. On the second test, for example, I got 14.4v at all rpms, which is concerning.
In the third I saw 14.0 idle, 14.4 above 3K. I've seen this before.

In the last 2 tests, the readings stabilized somewhat. I was getting about 13.0v at idle and 14.0v at 3K and above.
Occasionally, upon decel, I would get 14.3v and 14.4v momentarily.

However, 13.0v (idle) and 14.0v (above 3k) are the most typical of my readings. In fact, with the previous battery (actually a good one) and previous regulator (a VR-115 equivalent) last year, these were typical readings.

I'm going to do more testing in the coming days, but I do have this question in my mind about the typical 14.0v charging reading I'm getting: The manual say it should be 14.5 - 15 (my other three XS's are well within that range). In the real world, I've been reading over the years at this forum that the minimum reading is 14.1, and anything less wouldn't keep the battery adequately charged.
Is this correct?
.
.

 

[joebgd]

Are the BigCrank batteries led acid or gel? I might like one due to I do hit bad traffic on occasion. Can u post a link. I have a 1980 the best battery I've tried so far is the yuasa led acid.
Plus one on the voltage dropping when hot.

 

[Jan_P]

As I have understood it there is a current into the battery ( Charging ) or out of the battery (Discharging )
I also believe that the electrical characteristics is somewhat temperature dependent.
If the battery has say 13 V and the alternator gives 13.1 V DC the battery gets charged ..
If the alternator gives 12.9 the battery drains
And as in the case of a open circuit rotor No charging the bike takes what it needs from the battery until it is so weak
that the spark dies.
i have had charging Voltages 12.7 ish ( stator defect ) being able to ride without light to 15.2 range
( defect stock regulator ) where the Boyer started misfire and dying on one cylinder unknown if it was the box or Coil
with a better regulator it ran again. I suspect the extra 2 V and say 10 A gives a surplus heating 20 W that on warm days
caused problems. Cant say for sure.
There is also the charging current . I used a Car charger in the beginning that had a Ampere meter that Showed the current that was little higher starting but fell down when charging was done
Nowadays on MC batteries the charging current is kept down
I have never measured any charging current but Brit bikes had them meters.

So to sum it up
13.4 and upwards charges the battery
15 and up can cause problems in electronics not there from the beginning
fex Pamco ignition sits in a hot place as well as coils I did read a little about batteries in Warm Climate as Mr Mailman
Arizona Heat is not good for them
So my personal view right or wrong is that
The manual say it should be 14.5 - 15
Was aimed at stock setup that can have the battery charged but at the expense of shorter life on electronics and rotor windings
13 .4 V I feel would be optimum .. Keeping the battery charged and not heating circuits and battery.
Unless the starter is used frequently for long periods consuming power
I have a Bosch regulator at 14.1 --14.4 But feel lower would also work Kick start only.
If I recall right I am below 13 at startup and idle I have my meter across the battery .
It jumps to above 14 and then I don't look so closely if it is 14.4 or 14.1 have an analogue meter with a switch

 

[YamadudeXS650C]

Are the BigCrank batteries led acid or gel? I might like one due to I do hit bad traffic on occasion. Can u post a link. I have a 1980 the best battery I've tried so far is the yuasa led acid.
Plus one on the voltage dropping when hot.

See the "USA-Made Big Crank™ ETX15L Battery" at BatteryMart.com

 

[Jim]

I'm going to do more testing in the coming days, but I do have this question in my mind about the typical 14.0v charging reading I'm getting: The manual say it should be 14.5 - 15 (my other three XS's are well within that range). In the real world, I've been reading over the years at this forum that the minimum reading is 14.1, and anything less wouldn't keep the battery adequately charged.
Is this correct?
.
.

I wouldn't be concerned Jeff. Just in round numbers, let's say a fully charged battery is 13v. As long as your voltmeter shows a value above that, there's current being fed to the battery. Now, if you were reading 14v and switching the headlight on (and hi beam too) caused that number to drop below 13v, now you're drawing current from the battery to cover the load.

And that's one reason an ammeter is useful to have. It's only function is telling you how much and which way is the current going.

This statement in your first comment confirms the battery is being charged adequately...
"It seems to be charging well; after sitting for 22 hours, the resting voltage is 13.1 this morning. However, maybe (?) it is overcharging, as my other bikes all are at 12.9 after resting overnight."
You've got a meter on it now so you can monitor it. My suggestion... ride and be happy.

 

[YamadudeXS650C]

As long as your voltmeter shows a value above that, there's current being fed to the battery.

Thanks Jim, I get it.

I'm one of those people who pursues an explanation for all variations from the norm. It drives my primary care doctor nuts; she once blurted out, "Why, why do you want an explanation for EVERTHING?!?"

And then there's my '83 and '82 which give me very predictable, consistent and strong voltmeter readings, which are reassuring. I love to watch the meter on those bikes.

I'm looking forward to soon permanently wiring the '76 for the same meter. Given that it has a similar VR, I'll be looking to see what fluxuations it produces (assuming it is the VR that is the source of the variation).

Considering disconnecting the one on the '75
.
.

 

[Mailman]

I have VR-115 regulators on both of my bikes and I also have the same voltage meters that you have , mounted on both of my bikes, however they pick up power through the wiring harness, so the voltage shows about a half a volt drop at the meter.
Anyways, I have noticed that the charging voltage cycles up and down when I’m riding, much like you’ve described. When I first start out it always charges 14+ volts, then it’ll quickly drop down to high 12’s to low 13’s.
I actually feel reassured to see the charging system cycling like that according to demand!

 

[5twins]

For the first few years I had my 650, I didn't monitor or check charging output. I had no voltmeter mounted. It was only after reading about all the charging problems here that I started checking it. I found I wasn't putting out very good charging voltage, only in the high 13's max. But, I had never experienced battery problems, never had the battery go dead or anything. I "fixed" it anyway, by adjusting the original regulator I was still using, to put out low 14's max. So, to answer your question about whether 14.1 volts is adequate, I'd say yes.

Today, I have the VR115 and a voltmeter installed. I watch and monitor the charging output closely on both my 650s. I get a nice steady 14.2 or 14.3 volts right after starting (a few tenths higher in colder weather) on the '78 with the VR115, and that drops down to around 14 or the high 13's after riding a few miles and replenishing the battery charge. The voltmeter on this bike saved my bacon when the rotor started failing a couple years ago. The charging output got very erratic, bouncing up and down (but mostly down).

 

[YamadudeXS650C]

The voltmeter on this bike saved my bacon when the rotor started failing a couple years ago. The charging output got very erratic, bouncing up and down (but mostly down).

Thanks for sharing.
My concern regarding my low 14v readings is now dissipating, but I'm going to keep a close eye on the meter for any more erratic numbers like I saw yesterday.

 

[YamadudeXS650C]

I've had the opportunity to take 4 more extended runs, and thus get a clearer sense of the regularity of the voltmeter read-outs.
I'm getting 14.3 initially, and after a hard run of 25 minutes or more, the numbers come down 4 tenths to 13.9

However, on the hunch/hypothesis that the heating up of the alternator is reducing the charging efficiency,
today I removed the alternator cover,

and took a 3.5 hour, 60 mph run the length of Rt 26 with my neighbor (on his '66 Shovelhead).

I encountered a drop of only two volts tenths rather than four, so I am fairly confident that the heat-up of the alternator accounts for about half of the voltage drop.

I'll be reinstalling the cover, but with the added knowledge of that which is going on with the running voltage decline.
.
.

 

[Mailman]

I encountered a drop of only two volts, rather than four, so I am fairly confident that the heat-up of the alternator accounts for about half of the voltage drop.

I'll be reinstalling the cover, but with the added knowledge of that which is going on with the running voltage decline.
.

That’s interesting, I have seen this pop up from time to time. I remember reading several times on this forum, attempts to bring down the operating temperature of the stator by adding ventilation to the cover. I will admit I have thought of doing something similar myself. Here in the desert, the heat is intense and I never have to ride in the rain.
Here’s XSJohns,

Retired Gentleman’s,

and my favorite Robs, avatar. @willis