Checking Total Output Current

[IanDMacDonald]

So, I'm getting pretty serious about attending two rallies this year. I at-least have Geezer's R/R on my bike. I know the system does not leave much room to add stuff. I already have Cree LED driving lights on the front tapped into my lighting circuit. I want to buy and add a GPS to my bike. I'm worried adding too much more will burn my bike's alternator up.

So, how do I go about measuring the total current output of the bike? Amp clamp? Amp clamp on each circuit coming off the fuse box?

[crazy steve]

Do you want to measure the output, or the current being used? If you want actual use, measure at each individual circuit then add them up. I'd also do the measuring at your 'running rpm' as the higher voltage will increase current used. While only 'continuous' loads will count for this, checking with the 'intermittent' loads (horn, turn signals, brake lights) will tell you if you might exceed the total available from the charging system. You don't want to see more than about 16 amps in continuous loads as that's 80% of total rated capacity; running most electrical components above that number for more than brief periods is very hard on them.

Also note that any marginal connections with voltage drop through them adds to the current draw; that's a reason why good solid connections are important....

[3Phase]

Ian,

Total current output is an interesting problem, how interesting to do you want to make it? Checking each individual circuit would be a fun (for certain values of fun) project just so you have some idea of what each circuit normally requires.

Assuming the charging system is working correctly, the only place you can measure total DC output from the alternator is somewhere along that short stretch of Red wire from the Regulator/Rectifier to the main wiring harness connector or after the harness connector but before it gets spliced to the Main 30A Red wire to the battery and the ignition switch.

If you want total current supplied to the bike from the battery and the alternator, measure somewhere along the Red wire after the 30A Main fuse.

An inline DC ammeter would work best but they're expensive and you'd have to modify the wiring. A clamp-on ammeter would work but wouldn't be as accurate.

You could use a clamp-on ammeter to measure the AC on each of the three alternator wires down at the alternator/harness connector behind the fuse panel, then add them to get the total current supplied by the alternator before some of it gets turned into heat by the wiring, the Tachometer and the Regulator/Rectifier.

For 1978 and 1979 models you would also have to measure the AC on the Yellow wire from the alternator to the Headlight relay.

1980 and later models don't use the Yellow alternator wire, they tap into one of the White wires and dissipate some AC through the Headlight relay diode and the Headlight relay.

.

[IanDMacDonald]

Hmm. Interesting. I know for a fact that using my LED lights snd heated vest at the same time resulted in taxing the charging system.

[3Phase]

Ian ... you sort of left out the part about the heated vest but you should be alright with the LED driving lights.

You can run a heated vest for limited periods of time but it'll tax the electrical system. You'd need to use one with a good temperature controller that varies the duty cycle to control the temperature and not a cheap controller that's just a stonkin' variable resistor.

An XS11 is at heart a 1/4 mile bike with keen consumer features that varied by year/model but it's not a cage or a snowmobile so you'll have trouble powering the heated windshield, wipers, and controlling the snowplow with the stock electrical system too, not just a heated vest.

FWIW I used to live in the mountains and rode until the snow got deep enough to high center the bike and it ceased moving forward under its own power. That told me it was time to stop riding and tear down the bike for the annual deep cleaning and maintenance; never owned or used a heated vest but I may have to try one someday.

.

[crazy steve]

...You could use a clamp-on ammeter to measure the AC on each of the three alternator wires down at the alternator/harness connector behind the fuse panel, then add them to get the total current supplied by the alternator before some of it gets turned into heat by the wiring, the Tachometer and the Regulator/Rectifier...

Actually, to measure this way you would read any one of the wires (as long as the windings are good each will read the same) then multiply that by 1.73 (the square root of 3) to find the total output (because it's 3 phase... pun intended ).

It's not that hard to calculate total load. Other than the ignition, all the 'continuous' loads are rated in watts (lights) so simply add all the watts together and divide by 12 for amps. The ignition can be roughly figured by assuming that it uses under 80% of the fuse size (10 amps) so that is under 8 amps, probably near 7 amps or about 95 watts. Add in the rating of any additional accessories (converting to either watts or amps so you're using the same value, although using watts will be more accurate) and there's your load.

The XS alternator is rated at 20 amps/290 watts at 14.5V @ 5000 rpm. It will produce somewhat less at lower speeds; reduce voltage by 1 volt, now you're down to 270 watts.

[IanDMacDonald]

I left-out the heated vest, as it will not be used in the Summer, and at the same time as other accessories. I know that vest pulls quite a bit of current. No way could the bike handle the whole heated outfit.

I cannot imagine the GPS pulls anything close to what the vest does. I should be okay.

[3Phase]

Ian, the GPS should be fine with the LED lights unless you're using it with a 36" display or something else equally bizarre.

Actually, to measure this way you would read any one of the wires (as long as the windings are good each will read the same) then multiply that by 1.73 (the square root of 3) to find the total output (because it's 3 phase... pun intended ).

Yebbut it's not that simple, Steve, you can't measure just one leg because the three legs aren't equally loaded:
1978/'79 (Ian's bike) uses one leg for the Tachometer.
1980/'81 uses one leg for the Tachometer and another leg for the Headlight relay.

I don't remember how the XJ11 loads the alternator ahead of the Regulator/Rectifier but it's different; not sure it's better but it is different.

.

[crazy steve]

Yebbut it's not that simple, Steve, you can't measure just one leg because the three legs aren't equally loaded:
1978/'79 (Ian's bike) uses one leg for the Tachometer.
1980/'81 uses one leg for the Tachometer and another leg for the Headlight relay.

I don't remember how the XJ11 loads the alternator ahead of the Regulator/Rectifier but it's different; not sure it's better but it is different.

.

The tach uses the alternator for a signal, not power so the load is probably in milliamps. Same for the headlight relay... you can ignore those loads.

The only difference with the XJ is it lacks the headlight relay, instead using a set of NC contacts in the 'start' button to disconnect the headlight when the button is pushed.

[3Phase]

The tach uses the alternator for a signal, not power so the load is probably in milliamps. Same for the headlight relay... you can ignore those loads.

Ignore loads? Now you're not doing science, you're doing science fiction. That's why I told Ian it would be interesting.

You can't discount the Tach current because it's not always just a few milliamps through all of those 1970s discrete components, especially as RPMs go up.

The Headlight relay in my '80G burned up three 1N4007 diodes. Those are 1A forward current/30A (for 1 cycle), 1000V peak inverse voltage diodes and Columbo ate them until I gave up and just bypassed the stupid relay. The current on the Yellow wire to 1978/'79 relay in Ian's bike is highly unlikely to use less current than the White wire for a 1980+ relay.

So, that's at least one ampere and sometimes more than one ampere right off the top of the alternator current before it even gets to the Regulator/Rectifier.

The only difference with the XJ is it lacks the headlight relay, instead using a set of NC contacts in the 'start' button to disconnect the headlight when the button is pushed.

<sigh>Yes, I remember the Headlight Start Button bypass. I'll have to look at the XJ schematics again but I think there were a few more sneaky loads and they are all distinctly non-zero unless you're totting up I(imaginary total) instead of the real I(total).

.

[natemoen]

Easy way, put in am ammeter and make sure it doesn't drop into the negative.

[DiverRay]

<sigh>Yes, I remember the Headlight Start Button bypass. I'll have to look at the XJ schematics again but I think there were a few more sneaky loads and they are all distinctly non-zero unless you're totting up I(imaginary total) instead of the real I(total).

Don't forget, the XJ has a REAL alternator with BRUSHES. I think it also puts out more amps... Not a part of this story.
Move along, nothing to see here......

[crazy steve]

...The Headlight relay in my '80G burned up three 1N4007 diodes. Those are 1A forward current/30A (for 1 cycle), 1000V peak inverse voltage diodes and Columbo ate them until I gave up and just bypassed the stupid relay. The current on the Yellow wire to 1978/'79 relay in Ian's bike is highly unlikely to use less current than the White wire for a 1980+ relay....

Well, if you're running the system with defective components, sure it'll use more power... .

The coil in that relay was probably partly shorted which is why it killed diodes. On the '78/79 bikes, this relay power is pulled off the yellow wire which is in the 'neutral' (center point) of the 'wye' winding, so whatever power it uses will show up equally on any of the white wires; no need to measure it separately.

As to the tach, I suspect that if you disconnect (one at a time) the white signal wire and then the brown power wire, you'll be hard-pressed to measure any difference in voltage or current elsewhere...

[3Phase]

De! Def! <splutters> Defective! Wye I aught to Delta....

I think what killed 'em was that they were perfectly good diodes in generic 1N4000 series plastic bodies that couldn't handle the heat like the stock diodes Yamaha used with ceramic bodies. I thought about adding some thermal paste and a heat sink to a plastic diode to keep it cool, then I thought about not worrying about it and got rid of the diode and the relay.

The '78/'79 relay run off of the Yellow wire wye tie is set up as a reactive load, not a resistive load and there's nary a diode in sight of that circuit but it's a big son of a gun so it's pulling more current at 6V, 1/2-phase voltage, than the '80-style 12V, full-phase voltage relay. I think you'd have to measure the current with and without the 6V relay plugged in to get a reliable reading for I(total).

The power consumed by the Tachometer pulling the trigger signal from the White wire is not going to be much but! people are dropping in relatively expensive LEDs to get rid of instrument lamps that use much less than 1/4A so it's not trivial.


Ray, both alternators are, "real alternators!"
The XJ's is slightly more efficient and can generate more amperes than the XS' because it uses brushes instead of a magnetic coupling for the Field winding. Magnetically-coupled alternators don't wear out their air gap and burn stuff up even after more than thirty years so which is better: a few more reliable amps or years of service? Anyway, the part of the alternator being measured for current output -- the Stator -- is similar on both machines.

.

[MaximPhil]

I always enjoy electrical posts when 3Phase and Crazy Steve get going.
Of course I do not understand any of it but they are always funny

Ian I have a simple volt meter on mine and with it I have been able to avoid draining the battery while running aux lights. GPS uses very little.
2 x 55 watt aux lights could not be left on for more than about 20 minutes at 5000 rpm I changed to 35watts a side and it sustains them at highway rpm. but not in town.
My own quest for clean connections and 12+ volts to the headlight continues.
Phil