Another Ammeter bypass question

[69moredoor]

since it’s raining I’m lining up the next project. Read a ton of posts and a ton of different ways to do it. So correct me if I’m wrong. I’m looking for the easiest simple way. So.....
I have some welding cable (6gauge) that I’ll use for the bypass. Make the cable and run from alternator to large post of starter
Cut ammeter wires at bulkhead (under hood side) and connect.
Already have a voltmeter installed
Is that it? What am I missing ?

 

[65 Dartman]

Cut ammeter wires at bulkhead (under hood side) and connect.

I might be mistaken on this but if the wires are done this way, you will have no power to the fuse block, ignition switch or headlight switch.

 

[Mattax]

What am I missing ?

Everything.
Seriously. Don't do this.
Leave it alone unless there is a good reason.
If the power feeds through the bulkhead connector have been overloaded or you're afraid of that possibility, then any or all of these will reduce the loads through those connectors:
a - run parallel wires through a firewall grommet to the ammeter studs
b. - put a terminal stud in the engine compartment and wire through the firewall like the later cars with 60/65 amp alternators.
c. install a headlight relay circuit. A plug and play version (like Crackedback makes) or permanent doesn't matter. Draw power direct from the alternator stud

 

[69moredoor]

Ok thanks for helping me avoid a cluster f. I saw in a post where crackedback said to just run the large wire from alternator to starter lug and do nothing with bulkhead if it’s not fried. Mine isn’t so just do that? I also plan on doing the headlight relay

 

[Mattax]

That might have been a specific situation. When batteries are moved to the trunk or electric fuel pumps and fans are installed the circuitry is usually reworked.

This is factory main circuit for most years.
One power feed comes from the alternator.
Another power feed comes from the battery.
There is a big splice where they join. It's the primary power distribution point.

You can see what would happen if you cut the two feeds and connected them together in the engine compartment.

When we turn on the dome light, or headlights with the key off, power flows from the battery to the main splice and then on to the circuit that leads back to ground.
When the engine is running, the same thing but power flows from the alternator.
This because current flows from the highest voltage power source.

One method of reducing the current through the bulkhead connector is to run parallel wire(s).
A relatively easy way to add a parallel wire is attach it at the ammeter stud.
Current will then take the shortest or easiest path.

Lets say the battery is really low needs recharging, and the car is being driven with the lights on, wipers on.
Current flow will follow the easiest and shortest paths. Assuming the bulkhead connector is OK, just the current for recharging the battery will take the new parallel wire. That's still OK.

 

[Mattax]

Putting the headlights on a relay will reduce the current flowing through the bulkhead connectors (to B1) approximately 9 amps. That's pretty significant. Not only is that going into the passenger compartment, but also back out through bulkheads on small (18 awg) wires.

Running a higher rated alternator can result in higher charging rates if the battery is run down.
This is the main circuit from the '73 Dodge FSM for a dart with the high output alternator.
Its not clear to me whether the alternator output wire through the bulkhead connector was retained, but it would work either way.

I've not seen this in real life or even photos of a real one but would certainly like to.

PS. If you don't want an ammeter, the alternator output and battery feed can both be connected together on one of the ammeter studs. Everything still gets power and a fusible link still protects everything (except the starter) from a short. You just won't know if the battery is charging.

 

[Dave NEO]

as far as eliminating the ammeter, can you show that in a diagram or explain easiest way to do that? am wondering if you cannot get at ammeter itself maybe you can get to the correct wires somehow.

 

[Mattax]

See post #3.

 

[Dave NEO]

I have done c. - trying to understand a. and b. - I want to completely bypass the ammeter and just go alt to stater relay - is that a reasonable solution? I would use a fusible link in that wire - BTW I did try this once and got flickering everything at idle which I did not expect...

 

[Mattax]

What is the problem you want a solution to?
If you don't want to use the ammeter, then just connect the wire terminals together.
If you've added electrical equipment - a winch, EFI, anything that draws a lot of current or draws down the battery, then a different wiring strategy should be figured out.

Keep in mind that power always comes from the source with the highest voltage.
The battery's effective voltage is always 12.8 V or less.
The alternator's output voltage is controlled to be around 14.0 Volts.
Basically there is a power feed from each to the main splice.
Current flows from the battery to the main splice when the alternator voltage is less than the battery's. (typically when engine not running)
Current flows from the alternator to the main splice when it is producing enough energy to supply the demand. (typically everything when the engine is running)
Each of these power sources gets a relatively direct wire feed to the main splice. Generally this is a pretty good strategy.
Some mid 70s A-bodies split the alternator feed before going through the firewall in various way. And 67 and maybe some other years split off the horn power.
My point is you're asking about changing the wiring strategy when all it seems you want to do is not use the ammeter. The way not to use the ammeter is connect the wires together (if the ring terminal connections are in good condition, just put them together). Its very important to have a good durable connection.

 

[69_340_GTS]

I have done c. - trying to understand a. and b. - I want to completely bypass the ammeter and just go alt to stater relay - is that a reasonable solution? I would use a fusible link in that wire - BTW I did try this once and got flickering everything at idle which I did not expect...

Yes you can do that. I have, and it works fine. But you'll have no reading on the ammeter.

 

[Dave NEO]

ok thnks. I just came in from cleaning up the old VR and testing this again - I am getting voltmeter needle pegged (scale goes to 16V) connected to BAT stud on alternator - and just the low battery 12V reading at the positive side of battery telling me it is not getting a charging current - any ideas on why alternator is showing such a high output and yet no charging current getting to battery? I am hesitant to attach wire from alternator BAT stud direct to the starter relay with high output like that...though I guess the fusible link in there should protect starter relay and starter..will a bad VR let the alternator put out excessive voltage?

 

[69_340_GTS]

Many alternators put out 16V when charging the battery.

 

[Mattax]

ok thnks. I just came in from cleaning up the old VR and testing this again - I am getting voltmeter needle pegged (scale goes to 16V) connected to BAT stud on alternator - and just the low battery 12V reading at the positive side of battery telling me it is not getting a charging current - any ideas on why alternator is showing such a high output and yet no charging current getting to battery? I am hesitant to attach wire from alternator BAT stud direct to the starter relay with high output like that...though I guess the fusible link in there should protect starter relay and starter..will a bad VR let the alternator put out excessive voltage?

Prob should start a new thread since its not related to the OP's.
I'm going to assume the car still has stock wiring as of now.
In which case there are two things to figure out.
1. What voltage is the Voltage Regulator seeing?
2. Why isn't the battery seeing the same voltage at the alternator is producing?

For (1) measure the voltage at or as close to the regulator's blue wire.
With that and knowing the year of the car, we can start to figure out (2). Its likely the same reason, like a fault in the alternator feed such as 7milesout found
Ammeter pegged...
But it may be more, as he also found.

As far as the volts at the battery go. They do not tell us if the battery is charging. Volts at the battery tell us potential for the battery to be charged or cooked.
Anything between 12.8 and 15 Volts at the battery positive should let it charge if needed. With higher voltage available, the faster it will charge. Too high (over 15 or so) and it will probaby start to boil off the acid.
The ammeter will show if it is charging, and if so, how much current its drawing.

For example, this little charger shows Voltage applied and current flowing.
This battery at 75% charge is pulling 3.5 amps when supplied at 13.4 Volts

Later on when its fully charged, it sucks zero amps. Voltage hasn't changed.

 

[Dave NEO]

ok great info - let me digest - I will also charge the battery so starting out with a fully charges battery . thanks

 

[Mattax]

ok great info - let me digest - I will also charge the battery so starting out with a fully charges battery . thanks

Sounds good. Start a new thread when you're ready. Copy or quote from here as needed.
When you do, post the year.
Maybe this will help visualize the circuit even if your car is not a 60s. (mid 70s can differ the most from this scheme but the concept is similar)

When current is flowing, voltage should be the same all along the flow path until there is resistance.
So if the alternator output is at 16 Volts above ground, its probably because the regulator is seeing a much lower voltage.
When the regulator sees low voltage, it attempts to maximize the alternator output.

 

[Dave NEO]

'68 barracuda - that diagram helps though - will go with new thread