Added lights, more power?

[newmaac]

I am thinking about adding more lighting capacity to my
1980 Special, in the form of a halagen headlight and/or driving lights mounted to the case savers.
What is necessary to make certain that I have enough power to do this without causing other electrical problems?
I seem to remember a post a few years ago regarding changing relays?
Is there already enough power being generated?
TIA,
Mike

[sixtysix]

Sorry but the XS has about 8 amps of capacity available after the normal stuff, and that is only at higher RPMS (above 2500). Switching your driving lights through a relay does not 'add' any power, it only allows the switch to pick up the relay instead of powering the lights directly, it also allows you to switch it with the ignition power or another source of your choice.

I tried to put on 55W driving lights and found that they drew too much power. Here is a post that I pieced together on the other list when somebody asked about power output on an XS:

Depends on who you listen to....

Greg LaPook posted this a while back:

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I have measured the output of the alternator with a new voltage regulator installed. The results are:

1000rpm = 5.6 amps
1500 = 11.7
2000 = 17.8
2500 = 20.4
3000 = 22.2
4000 = 23.9
5000 = 24.8
6000 = 28.8

My bike is a 1980G standard and the specifications state that the alternator should put out 20 amps which is obviously a conservative rating.

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Multiple the current by 12 to get wattage figures. Remember you have a 55/60 watt head light, several 15 - 25 watt tail/turn lights, brake light, resistance in connectors, and base line power needed to run the ignition system. At low RPMs you are likely not putting out enough electrical power to overcome the drain of the accessory lights. (A pair of 55 watt riding lights takes up almost 10 amps of power.)

Later Yamaha bikes went to a brush-type alternator design. (My 82 XJ and '83 XS 400 both have this type.) This design has a higher output, 80 to 100 watts more on the XJ over the XS if I remember correctly. (It is one of the reasons the XJ engine has different cases on the engine's right side.)

Result is that accessory lights should probably be turned off if you are spending much time below 3000 RPM, such as idling at stop lights or commuting around town. No way of increasing the output that I know of. You could try running heavier gauge wire to the accessories to cut down on line resistance and switch the lights through a relay, cutting out the switch resistance.

Jerry Feilds
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A formula I learned was take the number of Watts you are running, divide them by 12volts, and that gets you the amps you are drawing. Now, they have stated that the XS produces 20 amps, well, you first have your main headlight stock at 55watts, then 2 tail lights 8watts each,license plate 4watts x 2; so far 79watts ~6.5amps draw...not to mention how many amps to run the engine system..lets say 3 amps gestimate for total of 9-10 amps.....now add 2 more halogen driving lights at 55watts each, 110w/12v =~9 more amps, plus the extra drain when you hit the brake lights at another 55watts/4amps, and turn signals/pair also at 55watts/4amps, plus turn signal indicator at 3.4watts,neutral light indicator at 3.4 watts,gauges lights at 3.4 watts x 4=13.6 watts:total extra is total ~10 amps ......so you can see how much stress you're putting on the electrical system!!
I found a pair of Non-Halogen driving lights...only 35watts per bulb, that I mounted on mine, and I don't use them very often, rarely drive at night, and only turn them on in the day when I want to be seen for special traffic situations.
Safe driving....T.C. 81SH Godzilla

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Numbers from the microfiche for a '79 XS:

A.C. generator output is 14.5 volts at 20 amps max measured at 5,000 RPM. 290 watts available, theoretically.

For the '82 XJ:
A.C. generator output is 14 volts at 26 amps max measured at 5,000 RPM. 364 watts to work with.

If you are running a 60 watt headlight, 3 running lights at 25 watts each, stop light at another 25 watts, you are up to 160 watts without accounting for power needed for ignition system and optional relays. Call the total 200 watts with turn signals working. Doesn't give you a lot to work with, 90 watts, and if you are running 2 each 55 watt aux lights, you are pushing the limit and probably discharging the battery at low speeds.

FWIW, many people have reported that the actual output is higher than the book figures. However, old and corroded connectors can eat up some of the power due to resistance, so the 290 watt figure is probably a good ballpark number. If you do go with the optional lights, use them at highway speeds only to avoid discharging the battery.

FWIW2: The XJ uses a different charging system; it has brushes where the XS version does not. That is one of the reasons the right engine cover on the XJ looks different than the XS, and why some accessories, such as engine guards, are not a bolt-on swap between the XS and XJ.

Jerry Fields

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And finally from me:
Yesterday I went on a ride with about a hundred harleys and maybe 20 or so bikes of other manufacturer. It was a poker run and bike blessing run. At the second stop my bike would not start, it acted as if the battery was dead. I was pissed that I had to push start my Yamaha in front of all those Harleys (I think only 2 saw me). I have a new maint. free battery and I managed to finsh the run by shutting off my aux. lights and only driving in 4th to keep the revs up. It started OK the next three stops.

When i got home I put the battery charger on and the battery was very low (was drawing 15 Amps , then I put it on 2 amp charge). The battery charged up great overnight. In the morning I checked the battery voltage (12.8) and started the bike. Voltage remained at 12.5 -12.8 and went up to a max of 14.5 at about 4000 RPM. This seems pretty normal to me. Then I turned on my aux lights.....I could not get above 12.8 even at 4000RPM. There was no wattage listed on the package for the bulbs so I assumed they were low. I checked them and they were drawing a max of 8.25 amps at 4000RPM, with the voltage at 12.8 across the battery. This works out to about 52 W per bulb. I put these lights on last fall and did not notice any problem until yesterday. I left them on once or twice and hooked up a relay to drive them, so they would not come on until the key was on, I also put in a switch to shut them off by cutting the ground to the relay, (all of this the day before yesterday).

Now how much extra juice does an XS have (mine is an 80G) ? I am not running any other aux equipment. I thought somebody said it was like 20 Amps. What wattage bulbs can I run and not effect the charging circuit? Do I have some other problem, like weak stator (or is that even possible)? Or something else gone bad? Did my relay mod cause some problem that I am not thinking of?<<

Then after several replies, which had a variety of answers...........


>>Thanks to all who replied to my charging problem. Here is the update. Today I replaced the regulator/rectifier unit and the problem was still exactly the same. So I replaced the stator and coil unit, and the problem was still the same. The resistance readings were OK, but I figured I'd give it a try. I cleaned all connections and did not find any corroded ones. So here is my take on the problem: Two extra 50W lights are just too much for an XS to handle.

I set my throttle lock at 2000 RPM like the book said and after a few seconds the voltage did build up to 14.25V, book says 14.5 +/- .3V, (does get to 14.5 before 3000RPM) so I guess it is within spec. Bike acted exactly the same with both stator/field coil units and both regulator/rectifier units. With the (aux) lights on I could not get more than 12.8 volt across the battery.

So what I have done, is found a set of 35W lights and mounted them in place of the 55W ones. I have yet to do a check out of the system with them on.

Gary Granger