xj voltage questions

[nightpilot]

I cleaned many connections as been suggested by the gurus and measured my xj at a max of 15.5 or so volts, I have some yellow 1156 bulb fog lights and it seems to drop around one volt when I turn them on. Is there a voltage or watt calculation that would tell me if a couple 55watt driving lights would still allow the battery to charge. does it take just over 12 volts to keep battery charging? Also, I measured the voltage at the aux power connections, does it matter where you measure it.

[TopCatGr58]

Hey NightPilot,

That 15.5 volts is a little over the rated amount it's supposed to generate. I would wonder if that was at IDLE or the 2500 rpm level? At idle even the XJ's brushed ALT which generates 26amps at max level may still not generate much over 12 at idle! Yes, you need more than 12 volts to push the electricitiy back into the battery against it's pressure.

Okay, the fog lights are probably ~27 watts, similar to the brake lights, or turn signals. Watts divided by volts gives you amps, so each bulb draws 2.25amps, or 4.5 amps for both. A pair of 55 watt driving lamps will draw a little over 9 amps.

I don't know/have any formula for determining how many volts you may loose with the increased amp draw, but remember, you want to measure it you want to do it with at least 2500 rpms. Measuring at the AUX terminal is probably adequate, but across the battery terminals would be the way to be sure just what charging voltage at the battery is still there with the increased light load! You have more charging capacity to play with on the XJ, but this is why we suggest going to LEDs for brake/run/turn lights to gain more spare amps for driving lights and such!
T.C.

[XJOK2PLAY]

Any Electrical GURU's know the formula?

You've asked an interesting question here...

Does anyone know the formula for figuring voltage drop in a 12 V. DC circuit?

I know the formula for determining VD in a 1/0 AC circuit is:

2 KIL 2xKxIxL
CSA CSA = (cross sectional area)

(For 3/0 AC, instead of 2, one must enter the square root of 3 wires = 1.732)

2= represents doubling the length of wire (1-Hot + 1-neutral.)
(I assume in 12V it would be 1 for the positive +, 1 for the ground -.)
K factor = resistance of circuit at given temps;
(wire insulation type factors here.)
I = represents inductive amps
L = represents length of the wire (one way only)
CSA = Cross sectional area of the wire guage used,
(which I get from a chart with the given wire guages in the NEC.)
In most cases, the resistance # (K) is 10.75

Does anyone know if this is the correct formula for 12 V. DC calculations as well?

If so, it could tell us what wire guage to use, as well as the overall voltage drop that can be expected.

I would suggest from experiences I've had w/ DC circuits that resitance is much greater, wire guages for heavier loads have to be larger, and the larger the wire guage and the shorter the overall length, the less VD there is in the circuit. Also, the reason relays are used in heavy circuit loads is usually to take the strain off of the switches, and may be necessary with driving lights to prevent premature failure of the switches...

Regardless, in ANY type circuit, (AC or DC) the most resistance occurs at the connections & switch contacts. There's more heat there, and more resistance there, which also means more voltage drop... so the fewer connection points the better.

Clear as muddy water? LOL
I would like to know if this formula applies, if someone knows.
Be cool to learn something new...

[nightpilot]

Hey TC
Thanks for the good info it really helps. Yes it was above the rpm where the alternator hits max output. The voltage does stabilize too at max so I guess i got lucky with this bike. The 15.5 volts is also running harley two filimant lights with red in rear as marker and turn signal. By the way, i put used stock older harley lights on this and the honda and they are good solid metal, cheap and good lenses.

The po took all the fuses out except main and I need to put fuses back in. TC i heard you had source of a fuse box, could you send me any info re that, here or on pm. For you mileage guys, like me, I get 38 on road and right at 40 on north carolina low throttle twisties. Am thinking about changing FD as this is my long distance cruiser but tech on it is beyond my ability at moment.

[DGXSER]

Hey Nightpilot,

I have installed the fuse box TC has available on two bikes and both went REALLY easy. Less than 40 minutes and looks and works great. There is a tech tip on it as well. Just PM TC and or Paypal him and he sends it right out.

As to the 750FD, if you do not over complicate it in your head like I did, it is a VERY simple and straight forward project. I spent more tiem dorkinaround with how to get the torque on the nut right and in the end it was just set it by feel and be done. I will say that after a few hundred miles, I do seem to notice the change in torque, as in it does not pull out form 1500 rpm in 5th gear to easily, but above 3k, I do not notice any difference and my milage has gone up.

[CatatonicBug]

For you mileage guys, like me, I get 38 on road and right at 40 on north carolina low throttle twisties.

How would it be?? I wish I could get my mileage that high. Even after a sync and colortune, I still get less than 30mpg. Someday, I'll figure it out...