Gauge Placement - ideas?

[Tinster]

Thanks Randal!

If I read this correctly, 100% of the alternator output
first passes thru the amp gauge and then to the car for use?

That seems like a lot of juice going into a tiny 2" gauge.
If the gauge blows up; the car will still run for a while off stored battery power?

Would it be less breakdown prone, if I ran a second 8 ga
wire from the alternator directly to the starter; as well
as the amp gauge circuit set-up you suggest?

d

 

[angelfj1]

If I read this correctly, 100% of the alternator output
first passes thru the amp gauge and then to the car for use?

<span style="font-style: italic">Dale: Unless you have a very early TR6, I believe you would (originally) have had a voltmeter and not an ammeter. In my TR250 and I believe the '69 TR6, there is an ammeter.
The original theory is that the battery is intended only as a source of stored energy to get the car started. In the early days, before practical alternators were developed, dc generators were used. Generators have two windings, a field winding which is stationary and rotor (armature) which rotates at engine speed. Since it is necessary to "collect" the electrical current from the armature which is rotating,the generator employs a set of brushes and a commutator. The brushes rub against the rorating commutator and are connected to wires which bring the current to the terminals of the generator where they are connected to the external system, including battery, regulator (control box) and electrical loads. The electrical principle of a dc generator results in voltage being produced which is directly proportional to rotational speed. So, the faster the engine turns, the more voltage is produced. The voltage of the generator is controlled by the number of windings in the armature. The current output varies widely from zero if the battery is perfectly charged and nothing is using any power up to the maximum rated output of the generator. The current output is controlled by the field voltage, but also by the speed at which the armature is spinning. This is important because a generator can only put out it's maximum rated current at or above some speed - at lower speeds the output drops off very quickly. This is why a generator-equipped car will not charge (or even maintain!) the battery at idle and this is one of the main reasons for the development of the alternator. Generators work fine when properly maintained, but few owners had the necessary maintenance done. This resulted in worn brushes, damaged commutator, dead batteries, and expensive repairs. These headaches all but disappeared when alternators were introduced in the late 1950's. The alternator operates on a different principle. First of all there are no brushes or commutator. This is a real bonus and desults in almost zero maintenance required. A rotating permanent magnet is used as the field and an ac voltage is produced in a 3-phase stator and rectified to dc in a diode bridge.</span>

That seems like a lot of juice going into a tiny 2" gauge.
If the gauge blows up; the car will still run for a while off stored battery power?

<span style="font-style: italic">Not to worry. These gauges are designed to carry their rated current. Most TR ammeters used in TR's are +/- 30 amps. But, the "average current is quite low, just a couple of amps. This is controlled by the regulator, which is either external to the alternator (TR250)or internal (TR6)</span>

Would it be less breakdown prone, if I ran a second 8 ga
wire from the alternator directly to the starter; as well
as the amp gauge circuit set-up you suggest?

<span style="font-weight: bold"><span style="font-style: italic">NO!!! Don't do that, unless you want to buy a new alternator. The starter requires a lot of current (here in the North, in cold weather up to 300 amps). The alternator is intended to maintain battery charge and run lights and normal accessories (30 - 40 amps) but is NOT intended to start the engine.</span> </span> We can discuss this off-line if you want.

 

[TR3driver]

If I read this correctly, 100% of the alternator output first passes thru the amp gauge and then to the car for use?

No, not quite. The alternator powers the car without the current passing through the ammeter. Only current going to/from the battery goes through the ammeter (except for the starter and a few other things).<div class="ubbcode-block"><div class="ubbcode-header">Quote:]That seems like a lot of juice going into a tiny 2" gauge.[/QUOTE]Not really. Inside the gauge is just a short length of fairly heavy gauge, solid copper wire. It can handle the current, no problem.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]If the gauge blows up; the car will still run for a while off stored battery power?[/QUOTE]Again, not really. If the ammeter fails, it will isolate the battery from the rest of the car. The car would run on the alternator, but only until the engine rpm drops far enough that the alternator will not supply the needed current.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Would it be less breakdown prone, if I ran a second 8 ga wire from the alternator directly to the starter; as well as the amp gauge circuit set-up you suggest?[/QUOTE]IMO, no. My 59 TR3A has covered several hundred of thousands of miles, mostly with a 60 amp Ford alternator, and still has it's original ammeter. I've never seen a Lucas ammeter fail from anything less than being pounded to bits with a rock (and I think even then it would have passed current).

Plus of course, adding the wire you propose would disable the ammeter (or at least make it read only a small fraction of the true current).

 

[TR3driver]

and this is one of the main reasons for the development of the alternator.

Sorry, Frank, I disagree. Alternators work on the exact same electromagnetic principles as DC generators; except they use diodes instead of a commutator to rectify the generated AC. They still have brushes, and rings for the brushes to contact (though they are called slip rings instead of commutators because the connection is constant). And their output is still a function of engine rpm, field current, number of turns, etc.

The main reason they work better at idle is a combination of smaller pulley and larger armature; both allowed because the simpler structure of the armature allows it to withstand the higher forces caused by high rpm and large diameter. The stock TR6 alternator still puts out almost nothing at idle.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]A rotating permanent magnet is used as the field[/QUOTE]Not a permanent magnet, but an electromagnet, just like the field of a DC generator. (At least for car alternators. Some low-output motorcycle and bicycle alternators do use permanent magnets.)
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Don't do that, unless you want to buy a new alternator.[/QUOTE]Here again, I disagree. It won't damage anything to wire the alternator directly to the starter solenoid, and in fact that IS the way Dan's kit is designed to be wired. Obviously (I hope !) the alternator is not turning fast enough to do anything while the engine is being cranked; but even if it was, it wouldn't damage it. But adding the jumper Dale proposed would prevent the ammeter from working properly, which kind of negates the point of hooking it up in the first place.

Dan's solution (as others have recommended) is to convert to a voltmeter. As I see it, there are pros and cons to either approach; it comes down to a matter of personal preference. I would (did) keep the original ammeter, but Dale can make his own decision. Either way will work adequately.

 

[RonMacPherson]

And then there is the "Delta" style alternator designed especially for vehicles that need maximum electrical output at low engine rpms like ambulances, fire trucks, etc...