wiring up my hot rod and i have an ammeter question. i am going to run a wire from the battery + terminal to one side of the ammeter and from the other side of the ammeter to the battery terminal of the ignition switch. i am going to run a lead from the battery terminal of the ignition switch to the unswithed side of the fusebox and a wire from the igntion terminal of the ignition switch to the keyed side of the fusebox. assuming everything is off will the ammeter drain the battery. i am using an external regulated delco alternator with the hot lug of the alternator hooked to the hot lug on the starter through a fusible link.
No, the ammeter will not drain the battery when hooked up like you state. The ammeter is straight through and acts just like a piece of wire. However, when hooked in this manner, it won't indicate charging current. It will only show a discharge and never move to the charge side of the meter. The ammeter needs to be in the circuit between the battery and all other circuits on the car with the exception of the starter. If you remove the alternator output wire from the starter and connect it to the bat terminal on the ignition switch the ammeter will work correctly.
The alternator output AND the battery power to the ignition switch need to be hooked on one side of the ammeter, the other side goes back to either the battery or battery terminal on the starter solenoid. The latter is preferred as there is less exposure to corrosion. Come off the battery terminal at the switch for unswitched fuse panel power. A voltmeter is a better choice with an alternator system.
The garbage preferably... If you feel you just have to install one, put it in the wire from the gauge to the ignition switch, at the meter end of the wire.
Just tried that if you hook the alternator output and one side of the ammeter to the battery terminal on the switch and the other terminal of the ammeter to the starter the ammeter does not read the load. At least the way I am trying it am I doing something wrong?
All charge and discharge needs to flow through the Ammeter [except the main starter feed] The ammeter is generally limited to 35a [over that is "Chernobyl"] but you can run an alternator safely by making a Diode Shunt using a Vishay 150a diode .[or a pair] This shunt is connected parallel direct from the Alternator to the battery. The principles behind a "diode" is they have a fixed voltage "forward drop" required to open them. [approx 1.13 v] 90% of the time the alternator is just maintaining the battery and running accessories so the diode remains closed. The ammeter has a progressive voltage drop, so current will take the path of least resistance through the ammeter [so it's scale will remain unaltered] When the ammeter is pegged out at maximum value the voltage drop across the ammeter exceeds the voltage drop of the diode , so the shunt starts flowing the excess current [there is actually a point of equilibrium where both are flowing] Another plus is if the ammeter totally fails the electrical system flows all charge/discharge via the shunt [it won't leave you stranded on the side of the road] On my friends Chevy pickup we mounted 2 x diodes [back to back and parallel] so it flowed both directions. This was mounted to a plastic board and hidden inside an old regulator box 90% of the time the ammeter is only showing low values [and all current is flowing via the ammeter] but we have had it pegged out to maximum a few times with the battery being used to jump start others , but it always recovers back to normal https://nz.rs-online.com/web/p/schottky-diodes-rectifiers/3952594 The alternative is disconnect the ammeter and simply charge direct to the battery. BUT the addition of a simple diode allows the instrument to function normally without chopping up an oem dashboard.
What load? If the only wires you have at the ignition switch bat terminal are the alternator output and the ammeter, it should work. Power from the battery comes to the starter terminal and then through the ammeter to the ignition switch. That's the correct way to wire it.
Apparently, yes. All current besides the direct from battery to starter must go through the meter, or it's not going to be read.
That comes about because the battery cable stud on the Delco starter is a convenient point to connect the heavier cable from the alternator than going to the battery in many cases. Then you get to a Ford with the solenoid on the inner fender or firewall and that "Hooked the starter" doesn't hold water. This diagram is busy and you have to decide what is relevant but it shows how an ammeter is normally wired up and how a volt meter is hooked up. You have to be able to mentally separate things and see what is relevant to what you want to do though. The big problem and really the only actual problem with an ammeter is that most vehicles including a lot of hot rods and customs have accessories in them that just flat demand more current than what an ammeter is up to handling. No power anything and no sounds system life is good, high draw but temporary run items like power windows or seat can be run with relays that draw their power directly from the battery rather than through the ammeter and igniton switch. We ran into that in the 70's and early 80's when we started running Halogen lights and adding sound systems with amps.
The problem with the above schematic is the way the ignition switch power feed is connected [it only shows charge through the ammeter and not discharge] If the ignition feed wire is moved [as below] it will read both ways and the ammeter shows charge/discharge to the battery. If there are accessories that draw a lot of current from the alternator ,it doesn't flow back through the ammeter to the battery as long as the Alt can keep up [if the alt can't keep up, it shows discharge at the ammeter] edit: A 2-way diode shunt is added in purple [2-way provides a safety net if the ammeter has a total break in the circuit and is basically a wire connected direct from the alt to the battery]
Amp meters were used for generators that put out 30 amps 50 years ago, today's alternators put out 3 times that. Use a voltmeter to simplify the wiring headaches and save the the amp meter for diagnosing charging problems if they occur.
On your schematic the ammeter will show charging any time the engine is running. It won't reflect the load of the accessories. If you turn the key off and turn on the headlights, the ammeter will not show a discharge. As you turn on accessories the meter will show more and more charge. The idea of an ammeter is to see the current flow to the battery.
The ammeter does not display the 'load'. What it's supposed to show is the charging current with the motor running or a discharge current if there's issues with the charging system or the motor isn't running. If everything is working the way it should and the battery is charged, this will typically be about 1 to 3 amps to the plus side of the meter. A pretty small meter deflection. Right after starting or charging a low battery it can show more until the battery is charged. The meter will 'blip' when turning on a load like the headlights but quickly drop back as the regulator adjusts. The 'corrected' drawing @Kerrynzl posted is correct (well, except for that useless fuse). Here's a factory drawing showing the same thing... The alternator output and ignition switch and/or unswitched fuse panel power go to one side of the ammeter, the battery to the other side. It MUST be connected that way for the ammeter to function correctly, this will be true no matter what brand/type alternator you use. If with the ignition off and turning on a load like the lights, the meter reads to the positive side, reverse the connections at the meter.
I'm using a voltmeter instead of an ammeter in a '77 Ford system. How do I wire the voltmeter, and where do the wires go from the regulator post S, A+ and I?
If you're not using an idiot light, use the above ammeter diagram and just delete the ammeter. The voltmeter just needs a 12V switched source, pick that up in the most convenient place.
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