alternative alternaters

[Mahesh]

I will be working on the brake leds around Dec, have to sort the main car bits first.

Won't be buying any of the over counter stuff, it's either useless or overpriced. I can easily exceed the brightness levels of the existing brake lights, it's getting the right balance and longevity in a vehicle that matters more now, in other words quality product.

Once done, I will put a post with easy diy instructions.

[Jon Tilson]

Ok I cant find it but here goes...

Headlights are 55W on dip and 60 W on main if you use halogens. Pretty similar to old sealed beams...so maximum say
would be 240 W which at 12 V is 20 Amps....

Side lights are 6W x4 so 24 W so call that 2 Amps...

Brake lights are 25 W so x 2 = 50W or 4.5 Amps

Heater fan....3-4 amps. Wipers about the same.

HRW again call it 3 amps.

Ignition is 12V across 3 ohmes...so 4 Amps (being generous)

Overdrive solenoid holding coil should draw 2 IIRC.

So we have (main beam and brake lights and in o/d ...yeah right - pretty worst case then!)

20 + 2 + 4.5 + 4 + 3 + 3 + 4 + 2 = 42A at the very most for a running car. No ICE....

You can see why typically a 25A alternator is adequate. More typical would be a 60 mph cruise in the rain at night.
The airflow is adequate - no heater and you dont drive with the brakes on either...and on most motorways you
dont have main bean on...

That drops it to 10 (lights) + 2 (side) + 3 (ign) + 3 (wipers) +2 (o/d) = 20A....so in most cases you have 5A spare to charge
your battery....or a few less if you have the hrw on and heavy ICE....

Pretty close to Clive's estimates....

LED bulbs could save you about 6 amps? Ooops forgot the panel bulbs...another 2A max?

Jonners

[cliftyhanger]

I am currently (ha ha) pondering the Toledo. It has no hrw, a basic stereo (once I get it fitted) but will have to be std front lights plus a pair of spots. However for next years RBRR I may well add another set of lamps. After all there is a significant amount of night driving in remote areas on roads that are far from easy. So it will be drawing close on to the 40A that my little alternator supplies. Especially as it will rain and the heater could be needed too.
I have a couple of larger alternators, so I will see how I get on.
I will be relaying the headlights and the spots. In fact if I fit night breaker bulbs I may be ok with just one pair of ancillary lights. We will see. Need to finish the bodywork and tip the tin of paint over the car first.

[Edin Dundee]

.......

As an aside, if you're thinking, I've measured a discharged battery at much less than 10.5 v and it re-charged. That's because most ways of measuring it take current. And because the internal resistance in series with the voltage becomes huge in a discharged battery, the current into a multimeter or AVO creates a voltage across the internal resistance that is subtracted from the internal voltage you're trying to measure. If the internal resistance is big enough, much bigger than the internal resistance of the multimeter, you'll measure virtually zero. And as the internal resistance of the multimeter goes down when you switch to a lower voltage scale, the lower the scale, the more current the meter draws, and the lower the voltage you measure. It can be measured, of course, but it's a little complicated.

Graham

Sorry Graham I disagree. A dvm these days would have little effect on a battery when measuring the voltage, the last time I looked even an analogue meter had about 40,000 ohms per volt regardless of range and that was 35 years ago!

[GrahamFountain]

Sorry Graham I disagree. A dvm these days would have little effect on a battery when measuring the voltage, the last time I looked even an analogue meter had about 40,000 ohms per volt regardless of range and that was 35 years ago!

Industry standard was, for a very long time, 20 kOhm per volt of full scale reading. It's true that modern amplified meters can have much higher input resistance. But even they won't measure the internal voltage of a fully discharged, but still re-chargeable, battery, because they still have to draw some current, however small, to make the measurement. That's because they still use some of the power of the battery in the same way as a servo assisted brake still uses some of the power of your foot; and whatever the gain of the servo, it will need some foot pounds to make it work. And a fully discharged battery has, by definition, no power to supply. You could, however, measure the internal voltage at a number of higher states of charge, and extrapolate down to the zero charge value from those.

And you still have to apply a voltage that is greater than the internal voltage of the pile to get current into it. And it's that which matters to calculating the maximum change in charging current as a function of the change in the alternators maximum current capacity. As a result, if the alternators' internal voltages are the same 15 volts, and the voltage at which a battery starts to charge, even a little bit, can't be less than 10.5 volts, then the change in charging current can't ever, in otherwise equal situations, be more than 1/3rd ((15-10.5)/15ths) of the change in the maximum currents of the alternators. It's a pretty crude estimate of the maximum, but it puts the effect of the upgrade into perspective.

Graham