Blue Sea ACR Wiring Question

[DaveInDenver]

I tested the Exciter Circuit this morning. Its the blue wire from the Alternator that is connected to the dash charge indicator light. I've been told this circuit should have 12v when ignition is on or the alternator won't excite a charge. I checked this circuit both at the Distribution block end and at the Alternator end. 1.57v and 1.86v. When I ground the blue wire circuit to the alternator housing I get 12.79v. That tells me something in that circuit is preventing sufficient voltage to reach the alternator to excite a charge.

What are you measuring when you say 1.57V, 1.86V and 12.79V? Is that the voltage of the D+ terminal?

 

[Tiktaalik]

Correct. The D+ Terminal.

 

[Tiktaalik]

Here my plan.

I am going to temporarily remove the harness wire that connects to the D+ Alternator exciter wire in the distribution box and run a wire directly from the battery. The dash charge indicator won’t work but I’ll know for sure if the alternator works at that time. My question is, should this new wire be fused? If the alternator charges properly when it’s getting the full 12v on its exciter input then I have confirmed that the problem lies in harness circuit that connects to the the D+ terminal in the distribution box.

Part two of my question relates to the new dual battery set up. On one hand I’d like to keep the wiring as stock as possible and include the distribution box set up and dash charge indicator light in the wiring to the starter battery. On the other hand I recognize that it’s a 34 year old truck and some previous owners have done their job to make the stock wiring more unreliable.

What would you do? Include stock distribution panel to keep it to stock wiring diagram or bypass and re-wire?

 

[luthj]

If the factory parts are in good condition, just run them to the battery like they were previously.

You can always work up an LED and ballast resistor and mount it on your dash somewhere as an indicator light. Typically you need at least 100mA to initiate the charging in the alternator, which is enough to illuminate a small lamp or LED.

A compact volt meter would also work fine.

Note that you want the alternators D+ connected to an ignition switched source, otherwise the alternator will drain the battery when the engine is stopped.

 

[DaveInDenver]

You should measure a voltage close to 0V at D+ when the regulator is first coming up before the engine is spinning and the alternator fully regulating. That would mean current is flowing through the field from the battery through the indicator.

Once the engine is running and the alternator is spinning and excited it should be generating current internally. At that point D+ should be the same or higher than B+ and no current flows from the battery through the lamp.

Maybe the amount of current being supplied through the lamp circuit is too low to bootstrap your alternator.

 

[Tiktaalik]

Thank you! Very helpful. I do have a dual battery gauge that I plan to install.

The only reason I hesitate to include the stock distribution block is that previous owners have made some very poor modifications and additions to it and I worry that it will be (or perhaps already is) causing problems. I am a novice when it comes to auto electrickery but at least I am detail oriented and to a proper job. I have been pulling a lot of orphaned wires from the system since I bought the truck. A previous owner had a veggie oil system installed and left fuel pumps and harnesses behind when the systems was removed.

If the factory parts are in good condition, just run them to the battery like they were previously.

You can always work up an LED and ballast resistor and mount it on your dash somewhere as an indicator light. Typically you need at least 100mA to initiate the charging in the alternator, which is enough to illuminate a small lamp or LED.

A compact volt meter would also work fine.

Note that you want the alternators D+ connected to an ignition switched source, otherwise the alternator will drain the battery when the engine is stopped.

 

[luthj]

If you current system is suspect, document it well. Then consider a blue seas or other universal fuse/relay/distribution block. Whether its worth it or not depends on the complexity of the wiring, available space etc.

A higher output alternator may require more current on D+ to start charging. Each alternator design may have different numbers of windings in the secondary coils. If you have a high resistance (poor connection) anywhere in the D+ circuit (light, cluster, or to the battery), then that may be the cause of the issue.

 

[DaveInDenver]

I'd also consider putting back on the original voltage regulator that the alternator was tested and supplied with. Removing the adjustable one you put in after the fact to eliminate another variable. If the regulator isn't set or working right it might not bootstrap or switch to a steady PWM once the alternator is running.

 

[Tiktaalik]

I supplied 12v directly to the D+ terminal and barely got any detectable voltage. Does that mean it’s a ground issue or is it faulty alternator or regulator? Could the regulator prevent it from grounding properly? I tested the alt casing before and it appears grounded. I’m getting close to taking it in to a shop.

 

[luthj]

A faulty regulator will prevent charging.

You got "barely detectable voltage" where? Between which two points?

 

[Tiktaalik]

I will give that a go but my alternator guy kept the original one so I will need go retrieve it.

I'd also consider putting back on the original voltage regulator that the alternator was tested and supplied with. Removing the adjustable one you put in after the fact to eliminate another variable. If the regulator isn't set or working right it might not bootstrap or switch to a steady PWM once the alternator is running.

 

[Tiktaalik]

I bought three new adjustable regulators that my alternator guy set to 14.7v. When it wasn’t charging I replace the new adjustable with one of my other new adjustable ones. Still not charging. I will retrieve the non adjustable regulator that the alternator came with and test that one.

I removed the dash charge light wire from the distribution block and replaced it with a wire coming straight from the battery’s + terminal. The D+ terminal isn’t getting the necessary voltage it needs so I thought I’d bypass the dash charge light circuit and run a wire directly from the battery to excite the alternator so it can start charging. The problem is, even with a direct supply of 12v from the battery the D+ terminal is only getting 0.1-0.2v.

I measured between the + post on the battery and the wire that I connected to the distribution block post which in turn is connected to the D+ terminal. Then I attached that wire to the + post on the battery and started the car. Still not charging when you rev the engine.

A faulty regulator will prevent charging.

You got "barely detectable voltage" where? Between which two points?

 

[DaveInDenver]

I'm curious like @luthj what you mean "barely detectable voltage". With the D+ jumped to B+ the alternator should try to produce as much current as its capable. If it's not then the field winding or regulator are suspect.

 

[luthj]

You do have a good engine to battery ground strap right? Its not corroded or loose?

 

[Tiktaalik]

Oh! I didn’t connect D+ to B+. I just connected D+ straight to the battery via the distribution block. I can try jumping D+ to B+ when I get home from work this afternoon.

I'm curious like @luthj what you mean "barely detectable voltage". With the D+ jumped to B+ the alternator should try to produce as much current as its capable but worse case is you should still measure battery voltage. If it's not then the field winding or regulator are suspect.