Charging issues.

[kc5dlo]

Internal regulators electronics can start to fail and leak enough current internally to bootstrap the alternator into charging.
There are companies who make an internal regulator for GM or Delco Remy alternators where the replacement regulator is designed to leak enough to start the charging without a light circuit.
Perhaps your old original alternator was leaking enough current to kick itself on whereas the replacement one's regulator is not leaking current into the field winding.
I have created a charging system light using a clearance light from a trailer. If the old light and wiring is corroded or confusing take this route.
You just have to open up the clearance lamp and remove the ground connection to the mounting bolt and solder on a second wire to use in the new install.
Dave m7040

I was wondering if that might have been a possibility. I don't want to send the new alternator back if the problem is actually on my end. I did buy some bulbs and want to try to resurrect the warning light if I can this weekend. It does not take a lot of effort to swap the alternators again to see if it cures the problems. I will report back after the weekend with any progress.
I do appreciate all the comments and help!

Steve

 

[Winmac]

It's normal practice to drive the tachometer from the alternator on a Diesel engine, as there is no ignition system as in a gas engine.
The alternator is not the ideal solution but it's the cheapest.

 

[Industrial Toys]

I don't have "much" experience in this sort of thing, but every tach I have seen on a Diesel is either an older cable style or has a magnetic pickup counting flywheel teeth. How does the alternator style work?

Curious. Are they taking off some AC before internal diodes convert it to AC? This would be ingenius but would reuire a special alternator with this feature. I have replaced a few magnetic pickups and mechanical cables so this would be good news. An idea, that would actually save the end user money. How novel is that, nowadays?

 

[Winmac]

Yes, they tap directly into one phase of the ac circuit, it's quite easy to add the w terminal to most alternators that don't have it.

 

[Industrial Toys]

I have heard of a few cases of brand new or rebuilt alternators being defective. Poor QC. Probably has someones initials scribbled besides "checked" or "passed".

 

[Steave]

Can anyone explain why the tach connects to the alternator? I find this quit odd.

I never commented on this because I don't have a clue why it would connect electrically. Mechanical maybe?? I was waiting in hopes somebody ccould explain this.

 

[Steave]

My post #16 got posted a little late. I see somebody has enlightened us on this issue.

 

[Tractorboy88]

I used to service a LeeBoy Force Feed loader/Athey Loader which had a Cummins engine. Upon startup and a warm-up period, the engine would have to be revved to at least 1600 RPM for the alternator to begin working, but could then be brought back down to idle. It was fairly new and the manufacturer said everything was ok, that it was supposed to work like that. :confused3:

 

[Dave M7040]

Can anyone explain why the tach connects to the alternator? I find this quit odd.

Here is a long winded explanation of why this is done.
Unlike a gasoline engine with an ignition system which can provide a signal to a tachometer, older diesels can be a challenge to get a signal to interpret rpm's.
Using the alternator is a work around but with problems as the article I posted explains.
A tachometer is just a pulse counter and taking a signal from the alternator provides a pulse which, with some planning the tachometer can interpret to engine rpm's.
If you change alternator pulleys then you will be affecting the accuracy of the tachometer.
Dave M7040

Alternator Tachometer Signals

Introduction

Most alternators provide a signal that can be used to indicate how fast the alternator is turning. The signal is a half-wave rectified output which has an amplitude about one-half the DC output voltage.

Using a signal from the alternator as a reference to engine RPM is not without problems. The purpose of this application note is to clarify these issues.

Pulley Ratios

The alternator typically rotates faster than the engine because the engine has a larger pulley than the alternator. A rough idea of the ratio can be obtained by measuring the outside diameters of the two pulleys. However, the depth that the drive belt seats into each pulley must also be considered.

Number of Poles

The frequency of signals from the alternator depends on the number of magnetic poles in the alternator. Ample Power alternators have seven poles in the small frame units and six poles in the large frames. These produce seven and six signals per revolution.

Belt Slip

It's not uncommon to experience a small amount of belt slip even in well tensioned applications. Obviously, if slip gets too much, the belt will fail from overheating. Because of the possiblity of belt slippage, many people choose not to use alternator signals for RPM indication.

Signal Strength

Alternator tachometer signals are derived from the stator windings. The signal is thus dependent on the amount of energy being produced by the alternator. When batteries are being charged, signals are strong enough to produce good tach stability.

When multi-step regulators are used to charge batteries, the tach signal strength can vary according to the charge state. When the regulator switches from the absorption state to the float state, there may be complete loss of tachometer signal during the time that battery voltage decays. During this period most regulators shutdown completely, and the tach signal does likewise. Ample Power regulators step down from the absorption voltage in several steps, keeping the tach signal strength at a sufficient level to drive the tachometer.

Full Batteries

In the past, full batteries were more of a concept than a reality. With Ample Power regulators, batteries do get charged to a full state.

When the regulator finds that the battery is full, alternator field current is reduced as necessary to avoid overcharging the batteries. This often results in a tach signal which is too weak to trigger some tachometers. Erratic tachometer readings result, particularly at low RPM. One possible solution is to turn on some electrical loads, forcing the alternator to produce more output, and hence, more tachometer signal strength.

Tachometer Pickup

Because the alternator's prime function is to charge and maintain batteries, and because some regulators can actually provide a full charge, loss of tach signals is a given ...the regulator favors the battery. No one wants a boiling battery just so the tachometer reads properly.

Virtually all diesel engines have a port which will accept an RPM sensor. This mechanism produces a reliable tach signal without regard to battery state of charge. The RPM sensor does not suffer from belt slippage, and continues to operate even if the alternator has failed. We strongly recommend RPM pickups rather than using a signal from the alternator.

 

[Steave]

Here is a long winded explanation of why this is done.
Unlike a gasoline engine with an ignition system which can provide a signal to a tachometer, older diesels can be a challenge to get a signal to interpret rpm's.
Using the alternator is a work around but with problems as the article I posted explains.
A tachometer is just a pulse counter and taking a signal from the alternator provides a pulse which, with some planning the tachometer can interpret to engine rpm's.
If you change alternator pulleys then you will be affecting the accuracy of the tachometer.
Dave M7040



Tachometer Pickup

Because the alternator's prime function is to charge and maintain batteries, and because some regulators can actually provide a full charge, loss of tach signals is a given ...the regulator favors the battery. No one wants a boiling battery just so the tachometer reads properly.

Virtually all diesel engines have a port which will accept an RPM sensor. This mechanism produces a reliable tach signal without regard to battery state of charge. The RPM sensor does not suffer from belt slippage, and continues to operate even if the alternator has failed. We strongly recommend RPM pickups rather than using a signal from the alternator. [/B]

I guess that explains why this is not used often. I read where the old MGB cars had Tach's that used this set up. The OP said he would post back after the weekend and I am curious if the new alternator he bought is the same brand and style as the old one.

Thanks to this thread and information here I learned I know less about alternators than I thought I did.