The Stovebolt Site Forums The Shop Area The Electrical Bay Wiring in the circuit breaker and shunt?

My 57 3600 is nearly ready to drive!

All I have to complete now are a couple of electrical items.

I bought a 100A circuit breaker as recommended on this forum.
But where do I wire it?
Between the battery and ignition, or between the alternator and amp meter?
Somewhere else?

I also obtained the components to build a "Shunt" to protect my amp gauge.
I believe this goes between the alternator and the amp gauge.
Or is it between the amp gauge and load?

If I run Halogen lights, fog lights, and an electric fan should I bypass the amp gauge for some of the heavy loads?

I also have a 30A thermal circuit breaker, should I wire this into my electric fan circuit separately from the 100A main breaker?

I can tune Webers, rebuild almost anything, run machine tools, etc., but electrical is my weak spot.

All help appreciated.

I re-read the description of the shunt.

"The solution I decided on was to fit an array of high power shunt resistors wired in parallel with the Amp Meter, these have the effect allowing maximum current flow, but also of limiting the current that flows through the actual Amp Meter movement itself. This is because the current flow is split between the Amp Meter and the shunt resistor array in both charge and discharge situations."

So I think "In Parallel" means that it is wired across the amp terminals, sharing them with the rest of the wiring?

Correct!
The shunt bypasses part of the current around the ammeter. Since the older meters were designed to be used with low-current output charging systems, all they really serve to indicate with an alternator-equipped system is whether the charging system is working, not the actual output. In the days of 25 amp full-current generators, putting the whole charge current through the meter was not an issue. Of course, back then, the highest current draw accessory was a cigarette lighter!
Jerry

Why do you need an external shunt? The stock ammeter has a built-in shunt. If you look at the wiring diagram for your truck you'll see that the ammeter does NOT measure the current output of your generator (or alternator). The loads are all paralleled off prior to the meter and the starting circuit bypasses it altogether. The only current the ammeter measures is the amount of discharge current flowing from the battery at any given time, or the amount of charging current flowing into the battery. The highest reading you'll ever see is if you crank your battery almost dead, in which case you either need a tune-up or a better battery. The only other way to see excessive current through the ammeter is to turn on every accessory you have (motor off), but why would you do that?

I have no idea why you would want a 100A main breaker on a truck. I worked at the telephone office right there in Gardnerville and the whole exchange that fed Topaz, Stateline, and Coleville too ran off a 400A breaker!

It was suggested in earlier thread that a 100A circuit breaker could be used to protect my wiring in case of a bad short since I insist on retaining the Amp gauge.

NAPA had it in stock, so it appears they sell a fair number of them.

The shunt will keep the Amp needle from being pinned when I run halogen lights, heater, and wipers at the same time.
I have a new battery and alternator, even with a full battery charge the Amp gauge will peg if I rev the engine at all.

I went ahead and wired the electric fan main power directly to the battery, connected through a 30A thermal breaker as suggested by Painless Wiring.
The fan relay power is still wired to the ignition.
A fan thermostat switch to the relay prevents the fan running when it is not needed.

Again, you can be running 100 amps worth of accessories but your ammeter will be showing only an amp or two of charge into your charged battery.

There's something wrong here. Assuming you have your rig wired like it came from the factory the amp guage should barely wiggle when you rev the engine when the battery is charged. Are you using the original wiring or is it an aftermarket wiring harness? I suspect the ammeter is wired into the circuit in the wrong place. There's no way you should see that kind of current flow into your fully charged battery!!!

Your fan sounds like it's wired correctly.

I guess if you want to run a 100A breaker you can but I shudder to think what might happen if it tripped some night while you were coming down Kingsbury grade!

like waldo says, if you're pegging your ammeter under any condition other than an absolutely dead battery there's something wired way wrong.... the power tapping connections for accessories should come off the same terminal that the alternator is connected to, the other side of the meter goes to the battery [via the starter connection usually], the meter should only be showing the current going to the battery NOT the current being used system wide

a 100 amp breaker anywhere will only serve to cut power after the fire is underway, there isn't anything you're using that should draw anywhere near 100 amps, and each circuit should be fused as required by it's draw .... I suppose if you put it on the output of the alternator it would save things in the unlikely event the alternator decided to put out way more than called for

Bill

Will compare vehicle to house wiring
100 amp breaker could be good idea comparable to 200 A main in house panel.
It would protect main fuse bus
THEN each load is fused on fuse bus.

CURRENT SENSING to ensure battery is charging for the most part.

Comes in two flavors where meter is cut into the wiring and carries current (it has a shunt inside it)
SHUNT type shunt is a dropping resistor such that meter reads a smalllvoltabe proportional to the current ie 100 amp to 50 mV.


from battery to a wye. you are sensing current in theis lead. At wy point one leg of wye to alternator / genterator andd ontehr leg to fuse panel. This darn thing I am tired of fooling wththe idiotid graphics
Dan Bentelr













xxxx

Hmmm, seized/shorted alternator and resulting fire, maybe that was the thread I saw which suggested the 100A breaker?
I seem to recall the same fellow had more than one alternator fail in a disastrous fashion.
Perhaps related to U.S. brands not actually being U.S. made?

Too many forums to keep track of all the threads!

I clearly remember reading a convincing discussion which suggested the 100A breaker as a safety.
I just need to remember the details of it's installation.

I think that once you power the fan directly from the battery through a relay, your amp meter becomes irrelevant. For instance, if your fan was drawing 10 amps and your alternator was supplying 5 amps of that, it would read as charging and your battery would be discharging. You would never know this until the battery went dead.

If your worried about a bad short or a fire mabe the best thing to do is a fusable link on the alt.and one on the battery input from the ampmeter looks better and would give you better protection.I wired my truck #10 wire from alt. to ampmeter from the same post on ampmeter to fuse block with 6 cir. and from ampmeter other post to starter conection so the only thing my ampmeter see's is the current charging the battery. Any one time fuse such as a fusable link will give you better and faster protection than a circuit breaker.Circuit breakers are mech.and are more prone to fail,thats why fuses are being used on more electical eq.

Pete

There are some good points here, and a few absolutely ridiculous assumptions mixed in. Equating a 12 Volt DC wiring system to a 120/240 volt AC house wiring setup is comparing apples and oranges. It's not uncommon for a 12 volt starter to draw 300 amps or more- - - - -that's why 12 volt battery cables are at least 4 gauge.

So far as the safety of a source circuit for a fuse block or other accessories, do what the manufacturers do, and wire in a fusible link to several circuits. They come in various gauges and current capacities, and the circuit protection can be tailored to the load. The only circuit where an automatic-resetting breaker would be appropriate would be headlights. Even with a serious short, the lights need to flash on occasionally for safety.

A high-output alternator can supply 100 amps or more to the battery immediately after starting, so pegging a 25-amp ammeter is not only possible, it's very likely, even if the accessories are wired to the downstream side of the meter. Shunt the heavy charge current enough to keep from damaging the meter, if you want to keep the dash looking original.
Jerry

With all due respect to Jerry, for I appreciate all the wise advice he gives on this forum I beg to differ on this one.

Let's say 'frinstance that the ol' girl doesn't want to start on a particularly cold morning. You crank and crank but she finally roars to life. Now, what should you see on the ammeter?

My contention is if it says 100, run like H@!! 'cause it's about to turn into a fireworks show. As I understand the regulator, be it external or internal, the initial charge voltage will rise to about 2 volts above the sensed battery voltage, and as the battery charges will continue to rise until it's limited at about 14.2V. As far as I know, the maximum safe charge rate of a lead-acid battery is 10 amps or so.

If anyone has actually witnessed a 100 amp charge current (into the battery) please enlighten this ol' guy, I'm still learning!

I teach electrical systems every day, and I see it every time I do a high-load battery test followed by a max output alternator test. For the first 5 to 10 seconds of an alternator output test, whatever max capacity the stator can produce will go right into the battery. It's not uncommon to see 120 amps or more at less than 14 volts after doing a loads test.

To do an alternator max test, load-test the battery to half its cold cranking amp rating for 15 seconds at least twice. This will break down the surface charge of the battery and let it receive a high charge rate for a few seconds. Turn on the high beam headlights, the wipers, the heater blower, and any other accessory available for a couple of minutes. Start the engine, and immediately rev it up to 2,500 RPM or so. Observe the ammeter on the charging system tester. The full capacity of the alternator stator will be applied to the battery. On one we installed on an '06 Chevy Tahoe just before Christmas, the output was 140 amps for about 15 seconds. The voltage did not rise above 14 volts during that time. After about 30 seconds, the amperage dropped to 45 amps, and the voltage went up to 14.2. 10 minutes of running time later, the amperage was just under 15, and the voltage was 14.8.
Jerry

Edit: After a heavy cranking session on a cold morning, the battery will take the full alternator output- - - -whether it's 55 amps, or 150 amps. As the terminal voltage rises, the current will drop dramatically, but for a few seconds, the only restriction to current flow will be the resistance of the alternator stator, because the battery is acting almost like a dead short. If it can deliver 300 amps to the starter, it can also accept a 300-amp charge rate, at least for a few seconds. DC current will flow either way at the same rate.
Jerry

OK, some excellent discussion here!

After reading some of this discussion I decided to fire up the truck again and note the result.

I have carefully rewired the alternator with new connections, just as it has been wired and driven for several years.
This is currently an external regulator GM alternator.
This may not be the best conversion.

I now have some concern that the regulator may not be functioning properly.

At fast idle the Amp gauge shows a charge, just past half-way to the full mark, with a light flutter.
If the RPM is increased the Amp gauge flutters hard, between midway to max charge.

My analog volt meter reads 13.75V at idle, pegs at 16V off idle.
I need to find my digital meter to read the full charge rate.

I am going to charge the battery again to ensure it has a full charge and repeat this test with the digital meter.
I may have to pull the dash cluster again to confirm how the loads are connected to the Amp gauge.

What I read here is that the only load is to the battery, with all other draws taken from the ignition switch.
I have to note, that does not sound like what I observed when I took the gauge cluster out to repair the wiring.

In any case I think I will limit my alternator to no more than about 70A rated, and will probably put the circuit breaker between the alternator and Amp gauge.

The good news is that the electric fan and choke both work very well.
Only one wire left for brake lights to work!

wiring for your setup .... yes you have a bad regulator - and maybe a bad battery as well

an externally regulated alt has been working fine on my 58 for years with no circuit breaker or shunt

Bill

That's exactly why I put a shunt across the ammeter on my '50 pickup. When I bought my truck at a show at the Hershey fall show several years ago, the truck was fitted with a 10SI alternator and the gauge was pegged on the charge side. A quick check with a clamp on meter showed that the alternator was pushing out 60A for a few moments immediately after starting if the motor had cranked for any length of time. The alternator still does this, but with the shunt in place, the needle kicks over, but doesn't peg. There's some more detail here -scroll down the page once you've clicked the link.

Stuart.

16 volts is WAAAY too much! It sounds like you've got a shorted regulator that's delivering full field current and letting the stator voltage increase without limit. That situation will boil the battery dry and damage other parts if it's not corrected soon.
Jerry

The battery is new, less than an hour in service.
I will check the wiring and look into the voltage regulator this evening.

O.K., I'm convinced. If you're running an alt. that can put out more than your amp guage reads, you should install a shunt.

Thanks Jerry

Sounds like you've zeroed in on your problem Richard, good luck and let's get this thing cruizin' the beautiful Carson Valley soon!!

I have often thought about the problem of high amp alternators on old amp gauges. Stuart's Shunt set up is a great idea for giving you more current capacity but retaining the look and function of your original gauge. Hotrod is right 16v is uncontroled charging, The regulator's base for 10DN delco's must allways be grounded, If there not for even a few seconds for a test or "temp" It may damage the regulator micro circut, asuming you don't have a mechanical type.
I will use that system when I finaly break down and convert to 12v... which I hate to do because I like brag about how good my 6v system still works LOL.

Terminal No. 3 of the regulator appears to have been overheated at some time.
The wire block is slightly melted too.

I will have a new one on Thursday, then I can make another run at this.

Well, NUTS!

I put on a new connector harness and new regulator.
Verified that the regulator is wired correctly.

Charge voltage measured at the battery came down to a more normal 15V as read on an analog meter.

But the amp gauge still bounces, and now my fuel gauge bounces too!

I've lost my light for the day, back at this tomorrow.

OK, I've finally got this sorted out!
I've got my basic system all wired up, everything is now working except the fuel gauge, I will tackle that another day.
I have not put in the shunt yet, but I will.

I put the big breaker between the battery and the main harness.
I used a relay for the electric fan power and accessory fuse block.
Unless the key is on, NO accessories are powered up.

Yes, you "can" use the original Amp gauge without a shunt, provided that the battery is in excellent condition and well charged.

My Amp gauge has survived several sessions of starting the truck, messing around trying to get lights working, etc.
If the charge gets even a little low, the Amp gauge WILL momentarily pin, on start-up.
No damage so far.

I am going to add the Shunt before I begin to really use the truck.
I've added an electric fan, electric choke, and will be adding halogen headlamps and fog lights.
The truck also has an electric dump bed, so there are plenty of items to easily draw the battery down.

My final decision that if anyone wants to retain the original Amp gauge, a shunt IS necessary to limit gauge travel and prevent a bent or stuck needle.