In a message dated 1/9/98 5:01:56 PM Eastern Standard Time,
Matt.Kulka@hboc.com writes:
> Okay, I can visualize getting a cheap ammeter and connecting it between
> a battery post and cable to find out how much various things load my
> charging system. But you can't very well measure the draw of your
> coil's primary and secondary circuits (because the alternator never runs
> without that load.) As a point of curiousity, does anyone know how much
> juice it takes just to create the sparks?
>
> Also, what the heck is the formula for watts, voltage and amperes again?
> I haven't used it since high school.
Matt,
Let's start with the last part first:
1) Watts = Volts X Amps
2) Amps = Watts/Volts
3) Volts = Amps X Resistance
4) Amps = Volts/Resistance
Substituting 3 into 1, we have
5) Watts = Amps X Amps X Resistance
I wouldn't suggest that you try to measure the current drain. I would
recommend that you sit down with a pencil, a calculator, and your schematic,
and calculate the loads, using the formulas above. The wattage ratings for the
lights are readily available, but you might have to do a little guess work
with other things, such as the heater fan. Based on my own experience, I can
give you some rough approximations, though (very rough).
Heater fan - 5 amps or less
WS Wiper motor - 1.5 amps
WS Washer motor - 1 amp
Horns - 5 amps
Electric gauges - 0.1 amp each
Fuel pump - 3 amps (racing pumps might draw up to 15)
ignition coil (primary only - the secondary doesn't draw from the alternator)
- 4 amps or less
Radio - Depends on the volume, but a good average is to calculate the amps
based on the rated output wattage
Just the other day, on the Triumph list, a question was raised as to the
correct ratings for fuses. I calculated the loads on my TR6 on a fuse by fuse
basis, and I reprint it here. The results should be very similar for any of
the LBCs of the same era.
***********************************************************************
"RED" fuse - This fuse feeds all the tail, parking, marker, and dash lights,
and pulls less than 6 amps.
"PURPLE" fuse. - This fuse feeds the glovebox lamp, courtesy lamps, trunk
light, the horns, and the hi-beam flasher. With the exception of the horns and
the flasher, the load is less than 3 amps on this fuse. For a stock headlight,
flashing the hi-beams pulls about 9 amps, and the horns draw around 5 amps. If
you have quartz-halogen lights, the current will be more, but you really
should have them on a separate, un-fused, power source anyway (yes, I said
"un-fused" - that is not a typo!), and they should be relay operated. It is
very unlikely that you will have the doors, trunk, and the glovebox open while
blowing the horn and flashing the lights. Even if you should do this and blow
the fuse, the headlights, both hi and low beams, will still work, as they are
fed from another circuit. The flasher merely bypasses the headlight switch.
"GREEN" fuse - This one is a little harder to determine, as you will seldom
have all loads on at the same time, but the maximum load, with everything on,
is about 20 amps. This fuse supplies power to almost all of the loads that are
switched on with the key, the most notable exception being the ignition
circuit, which is fed directly from the key with no fuse.
**********************************************************
As you can see, you will have to consider the likely load combinations when
figuring the maximum draw, rather than just adding everything up. For example,
no need to include both the high beams and the low beams, unless you have
rewired your car so they can both be on at the same time. Also, no real need
to figure the horns, as they are only used momentarily, and the battery can
supply any over draw they might create for that short length of time with no
problem.
If anyone is interested, I would be glad to post my entire response to the
Triumph list here as well. It had to do with replacing the 35 amp Lucas fuses
with 35 amp fuses from the auto parts store (don't do it!).
Equation 5) should be looked at with interest. All wires have resistance.
Current through any wire produces wattage, or heat. From 5), you can see that
if you double the current, the wattage, or heat, is quadrupled! Interesting,
eh?
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition, slated for a V8 soon!
'68 MGBGT---organ donor for the '74
|