Adapting Gauge cluster ammeter for higher output alternator (1 Viewer)

[JohnJL]

Hi all,
I have seen the threads for Dakota Digital dashes, and for a few folks who gutted a voltage meter and placed that in the stock ammeter location. I am building a wiring harness from scratch so can do what I want. I am trying to keep the stock aesthetics and keeping the stock cluster, but I want a safer ammeter wiring (not full current to the dash) and to re-calibrate the ammeter gauge to handle a ~130 amp alternator. I have a bunch of electrics and electronics on the truck and a double-battery system so need more load capacity and reliability.

I'd like to use a later Toyota alternator, I see a few threads with some that may fit as well as the 130 amp Jag/Denso and FJ60 Bosch 80 amp units. I can make my own brackets.

I have never wired in a shunt before, is this wiring diagram accurate? I circled in orange the wiring from the alternator + to a shunt which is bridged by the ammeter in the dash. The current from the shunt then flows to the main battery switch and fuse panel.

A few questions...

1. Is this wiring correct?
2. How do I size the right shunt?
3. Can I use resistors or something in the current feed to the ammeter to adjust its sensitivity to =/- 130 amps?
4. Other ideas for making the Ammeter work without tampering with its mechanics?

Thanks!

 

[JohnJL]

I am using Blue Sea fuse and battery charging pieces, they offer this in 50 amp, 100 amp and 200 amp...could I use a 200amp version (if my alt is 130 amp) along with some resistor (that didnt create a ton of heat) to recalibrate the sweep of the 30 amp stock gauge? I would re-label it 150 amp each direction if I could fool the gauge into safely covering the higher possible output of the alternator?

Thanks!

Analog Meter Shunt 200A - Blue Sea Systems

 

[JohnJL]

Also if I understand how an ammeter works, it is essentially sensing the polarity of the field on the circuit? So a question for those who have a better understanding than I, when the ammeter is "pegged" the magnet is simply in the full position possible, but thats not actually harming the gauge? I can understand not wanting to actually put 120 or even 50 amps through the dash area and gauge, but if a shunt is installed so that the ammeter is sensing the current but only a very small actual draw. Would that eliminate the danger of that wiring carrying so much current, and if the ammeter is "pegged" then the needle is simply in the maximum position but its not dealing with large current/voltage so not in danger of harming the ammeter?

Is that right?

 

[Pin_Head]

All coil/needle/spring meters sense power in watts (volts times amps). Since the voltage is relatively constant in an automobile, the meter can be calibrated to read the approximate current flow in amps.

For a charging system it is useful to know whether the current is flowing in to the battery (charging) or out of the battery (discharging) or if the battery if fully charged and all the power is supplied by the alternator (the meter reads zero when the system is in this happy space).

Since meters that would read high current levels would be expensive, all automotive amp meters use a shunt that is either built into the meter or is located remotely in an external location.

Just because you have an alternator rated at 130 amps doesn’t mean that the amp meter needs to read this much current. It only needs to not burn up. The amount of time your alternator will be putting out the full 130 amps is low. The battery will charge quickly and then the output will drop. Even a 130 amp meter will read zero the vast majority of the time because the battery is charged and the alternator is working.

To double the range of a 50-0-50 amp meter to read 100-0-100, you would cut the resistance of the shunt by half. The shunt would be something like .001 ohm, so this is something you will need to calculate by the length and diameter of the wire rather than putting a meter on it. You would need to know the resistance of the meter coil and the current at 14V that makes it swing full scale to calculate the required shunt resistance.

 

[Pin_Head]

One more consideration:

With a 130 or 200 amp full scale meter, you may never notice when your alternator stops working because the amount of current that the cruiser uses may only be 10 to 15 amps, which would be 10% of the fuel scale deflection. Even with the headlights on, it may only be 30 amps. You would be better off with an idiot light when the voltage drops below 12.5 volta or a volt meter.

 

[JohnJL]

Thanks for the replies, I think I am narrowing in on understanding now. I have a separate volt meter, and yes I agree with the batteries in at least reasonable charge the alternator will not be putting out huge amps except in rare circumstances. I would like to keep an eye on the flow with the stock ammeter, do you have a view whether it matters to the well-being of the stock ammeter if, with a shunt of say 200 amps to handle winching at night with lights, if is a problem of the ammeter? That is to say even if it gets "pegged" beyond 30 amps, it would still be accurate right around the "0" point? Its that crossover between charging and discharging that I find it most important to monitor...

Thanks!

 

[Pin_Head]

30-0-30 seems about right in a FJ40. I never saw my meter pegged in either direction, but it would deflect about 20-25 amps. You know it is working because you can see the needle flicker when the turn signals are on.

 

[bikersmurf]

I’d not run the winch through an ammeter. There’s a reason winches are wired in with O gauge wire... and not practical to wire your ammeter in with it. A shunt like that will help, but I’d still wire it direct to the battery.

I’ve got a rig with a similar shut... I believe it’s likely a 200 or 250 amp one. I’ve seen the alternator put out 150+ amps. It was setup with a voltmeter also which is useful for seeing smaller variations. With such a small needle swing, +/- 150A wouldn’t be very useful. Mine covers more than 300 degrees vs a landcruiser which moves more like 90 degrees.

 

[JohnJL]

I’d not run the winch through an ammeter. There’s a reason winches are wired in with O gauge wire... and not practical to wire your ammeter in with it. A shunt like that will help, but I’d still wire it direct to the battery.

I’ve got a rig with a similar shut... I believe it’s likely a 200 or 250 amp one. I’ve seen the alternator put out 150+ amps. It was setup with a voltmeter also which is useful for seeing smaller variations. With such a small needle swing, +/- 150A wouldn’t be very useful. Mine covers more than 300 degrees vs a landcruiser which moves more like 90 degrees.

The way I have it in the diagram I dont think thw winch will be drawing any more current through the ammeter that is would at idle. Please say if I am wrong. THe winch would be connected directly to batters #2 B+.

 

[bikersmurf]

I'm not seeing where the winch is wired in the diagram.

to Bat 2+ (direct to the battery) and you'll be set. I did have a master kill solenoid for safety since the winch since it wasn't a fused line.

 

[JohnJL]

There is no winch in this diagram, my question is about if the ammeter woulf be damaged if it got more than the stock 30 amps in a shunt installation where actual amps could be much higher occasonally.

 

[Pin_Head]

I don’t know of any way to predict the outcome. You have to just try it and find out. Wire the alternator output directly to the battery through the meter and then apply full battery voltage to the slip ring brushes and see what happens. I Kind of doubt that it is going to be 130A. If the meter starts to smoke, pull the plug.

 

[JohnJL]

Well this didnt work. The alternator isnt charging when the motor is running. I *currently* have a new 60 amp externally-regulated alternator. I took a stab at wiring in a shunt and sending the alternator + directly to the battery. I think I have too many things going on at once, so I am going to simplify and check basic function and charging before getting fancy again. I dont like sending full Alternator charging current through the ammeter in the gauge but I will revert back to "stock" in the interests of diagnosing what is going on.

My externally regulated alternator has different markings on it than in the 1974 wiring diagram...will post some pics and the Haynes diagram marked up soon.

 

[1969FJ]

I am surprised you used blue sea and did not realize the answer is there.

Sizing a Shunt to a DC Ammeter - Blue Sea Systems

 

[JohnJL]

I am surprised you used blue sea and did not realize the answer is there.

Sizing a Shunt to a DC Ammeter - Blue Sea Systems

Thats the page I used to order the shunt I chose. The issue I think I created through is that I may have some of the alternator wiring wrong...a post up shortly...

Thanks for the reply!

 

[JohnJL]

I will start a different thread here since a few things have changed from my original question...thanks all!

 

[pb4ugo]

You're now charging the battery with the wire going from the alt directly to the battery and are no longer charging it thru the wire going thru the ammeter. Hooked up this way makes the ammeter use less. You would want a voltmeter or a idiot light.

 

[1911]

You're now charging the battery with the wire going from the alt directly to the battery and are no longer charging it thru the wire going thru the ammeter. Hooked up this way makes the ammeter use less. You would want a voltmeter or a idiot light.

That's what I did; replaced my ammeter with a voltmeter.

 

[pb4ugo]

That's what I did; replaced my ammeter with a voltmeter.

Me to. I run a internal regulated GM alt with the big wire run to the batt. and an idiot light. I didn't like all the charging going thru ammeter and wiring harness. I've run across several burnt up harnesses in the past where the wire going thru the ammeter was melted and burnt the wires next to it. If your interested in this you can look at M.A.D. electrical website for more info.