Location of diodes in the Alternator Restart system?

[Rick Erwin]

Originally Posted by wslade2

Ammeter should be hooked in “series”. one probe of the meter hooked to one end of wire and other probe hooked to the other end. Just think of it like cutting the wire and putting the meter in the line, like two leads of a light socket. If you’re able to select, start high on the amperage and work down. I don’t buy very expensive meters and most of those have a 10 amp capacity. It’ll say on the meter. They usually use a fuse and if apply too much current they’ll blow the fuse and end reading zero. If zero reading, check fuse in meter in case it’s blown. You should get some kind of reading. If not back to testing every connection and solder joint

wslade2, thank you again. That is how I thought the multi-meter should be hooked up to read amperage. That's how I thought I'd done it successfully in the past, and YouTube verified that. What I didn't check is the fuse in the multi-meter. Perhaps I can get to that tomorrow, as I'd still like to know.

Well, today I had some level of success. After doing three different iterations of an under-load test at each junction in the restart system, (for some unknown reason), the system started showing voltage at the field terminals. I don't know why, which is frustrating, because the problem could return anytime.

The decisive test will be to run the engines and perform the Alternator Restart Test to see if the 1.75-ish volts at each alternator are enough to excite the fields and restore power to a cold electrical system.

Rick

[wslade2]

With wiring issues, sometimes you just have to keep going over it. A little detail can be the problem.

[Rick Erwin]

Today there was a measure of success.

We ran the engines and performed a pseudo test of the Alternator Restart system. It worked!

The entire system has not been reinstalled yet from the testing, so I just used dry cell batteries to excite the rear alternator and it fired off with 1.5v. Once the rear alternator restarted, the front came up as well. The next step is to reinstall the system and do another test. Since testing has shown I will have 1.75-ish volts at each alternator's field terminal when the system is installed, I'm hoping I'll be good to go.

I did see it would NOT restart with ANY load on the system though. Since an alternator's field has about a 3.5 amp load, I think it would be advisable to only try to restart one alternator, then turn on the other alternator.

There will be more testing to follow.

[Rick Erwin]

So, I have:

• Changed from the original two D-Cell batteries to the currently specified four C-Cell batteries,
• Replaced the Alternator Restart switch,
• Replaced the resistor,
• Replaced the two diodes,
• Reinstalled, and tested the system.

I now have 2.2 volts on the field terminals of the voltage regulator's Molex connectors.

Either alternator will now consistently restart when:
1. The electrical system is unloaded, "and"
2. Only one alternator switch is turned on.

My experience has yielded the Alternator Restart system will not restart both alternators at the same time, nor will it restart if there is anything but the most minimal load on the bus when the restart system is activated. I was able to restart an alternator, with one led taxi light switch turned on, but with nothing additional.

Both the "Alternator Restart Test" checklist, as well as the "Total Loss of Electrical Power" checklist, indicate the electrical load should be reduced, and specify both alternator switches should be turned ON when trying to restore power. So, if you really must use this system, contemplate turning only one alternator ON, as you follow the checklist.

Once one alternator is restarted, and power is being resupplied to the General Bus, there will be power to the remaining alternator's field terminal, so when the remaining alternator's switch is turned on, it will come online also.

Has anyone been able to restart more than one alternator at a time, and/or restart with any kind of a load on the electrical system?

Can anyone explain what the purpose of the resistor is in the line from the dry-cell batteries to the Alternator Restart switch? It sure seems counter-productive as it lowers the voltage at the field terminals of the voltage regulator's Molex connectors.

Rick

[mshac]

Rick, as I study the system, it makes no sense to me why the resistor is in the circuit. If its voltage that makes the alternator restart, and more voltage is better (at least up to the alternator's rated voltage), why would we want to reduce the voltage in the circuit with a resistor???

It would be like putting a resistor in a circuit with a light bulb - the light bulb would be dimmer due to lower voltage.

A resistor may be used to prevent voltage spikes, but again, in a DC circuit with small batteries like this one, I just don't see the need.

You could simply put an alligator clip test lead on either side of the resistor to bypass it, and then test your voltage at the field when pressing the restart button. You should see an increase.

If you do this test, please let us know your findings.

[wslade2]

Here’s some interesting reading:

http://www.electronicsplanet.ch/en/e...-in-series.php

In short, don’t bypass the resistor, it protects the diode

[Rick Erwin]

wslade2,

Thank you for posting the article.

Jumping around the resistor was one of my options if I couldn't get the system to work, but thankfully it now works as designed. It's actually a pretty cool system. Hopefully, it will never be needed.

Rick