Protecting the Alternator Regulator from Incorrect Shutdown

[MarkSF]

This weekend we blew the alternator regulator for the second time, after shutting the engine down in the wrong order. You stop the engine in my boat by pushing the throttle against a spring. What you don't do is turn the key off first, as the leaves the alternator without load. I did it the first time, and would not make the same mistake again, but my crew did it this time because I had not explained to him the correct order. It is very natural, unless you know otherwise, to turn off that key.

So given how easy it is to make this mistake, is there a way to protect the alternator regulator?

[AnchorageGuy]

Mark, Move the key switch to a place that is not easy access, like maybe inside the cabin. It won't eliminate it but will help. Also there is a Zap-stop that can be attached to the alternator that will sacrifice itself instead of your regulator, or do you mean you blew out the diode? Chuck

[Bash]

Originally Posted by Waterwayguy

Mark, Move the key switch to a place that is not easy access, like maybe inside the cabin. It won't eliminate it but will help. Also there is a Zap-stop that can be attached to the alternator that will sacrifice itself instead of your regulator, or do you mean you blew out the diode? Chuck

I'm not crazy about the suggestion quoted above. There have been a couple of times, over the years, where I've had to start the engine up in a hurry, and it was good not to have to go down below in order to do so. Having the key close to the helm can be a good idea.

[Maine Sail]

I am having a tough time figuring out how they wired it so the key disconnected the load or batteries from the alternator. Most keys can be turned on and off without issue as they are simply the excite voltage and will simply turn off the regulator but not disconnect the load. Having a hot regulator and suddenly disconnecting the "load" (batteries) is what normally causes the spike that blows out the diodes. Seems it is wired funky if the key disconnects the load but should be a very easy fix if that is what it is doing.

Zap Stops generally only work once. The second time they need it the owners usually have no clue it even blew so they fry the diodes yet again. The Balmar TSP has a replaceable fuse but again you'd need to know it was blown in order to replace the fuse so it can protect the alt the next time around..

The most simplistic fix is to simply fix what the key does to the alt or run the alt output directly to the house bank.

Can you give us a wiring schematic?

[MarkSF]

Thanks, I will try to check that the alternator output goes directly to the battery selector.

[btrayfors]

Originally Posted by MarkSF

Thanks, I will try to check that the alternator output goes directly to the battery selector.

Oops.....Mark, that could be the problem.

As Maine indicated, turning off the ignition switch normally doesn't hurt anything, providing it's properly wired.

However, turning off the battery selector switch while the engine is running, even for an instant, can blow the diodes in the alternator. While many battery switches are of the make-before-break type, IMHO it's really playing Russian Roulette to move the switch with the engine running.

In any event, alternator output should be wired directly to the batteries (not to the selector switch), with an appropriate fuse located near the batteries. Best practice these days is to wire all onboard charging sources -- wind, solar, alternator, battery charger, generator, etc. -- directly to the house batteries. Then, use a small voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge to maintain the start battery. With this setup, there's absolutely no need to switch anything....it's all automatic.

Bill

[MarkSF]

Well I did just check the wiring diagram for the Universal 5424, which shows that the alternator output should go to the ammeter, then back to the starter + connection which is connected to the battery (or battery selector in this case.). It should not be via the ignition switch.

[btrayfors]

Originally Posted by MarkSF

Well I did just check the wiring diagram for the Universal 5424, which shows that the alternator output should go to the ammeter, then back to the starter + connection which is connected to the battery (or battery selector in this case.). It should not be via the ignition switch.

Mark,

Yes, that is how many older boats are wired.

In the light of present standards, recommendations, and electrical practices however, there are at least four things "wrong" with that setup.

1. Going thru the selector switch sets up the possibility of damage to the alternator, as described in an earlier post;

2. There is no fuse protection between the alternator and the battery and, indeed, none between the starter and the battery. While ABYC standards do not require such protection, as Nigel Calder says...there is no good reason NOT to provide such protection on the smaller yachts. The danger is the potential for a short circuit which could cause a fire;

3. Boats were set up this way with the idea that the alternator would basically connect to the start battery and, if desired, could be "switched" to charge another battery (e.g., the house battery). Problem is, boat's these days are power hungry and tend to have larger and larger house battery banks. These require a lot of charging, whereas the start battery requires very little charging. As a consequence, alternators when connected only to the start battery -- either directly or via a selector switch -- just loaf along after a few minutes, since it typically takes less than 1 amp hour of power to start a small diesel. That energy is replaced in just a few minutes, leaving the alternator idling most of the time.

4. If the alternator is switched to a large house bank -- most especially an AGM house bank -- the charging requirements tend to overload the alternator to the point where it can easily burn up unless de-rated or regulated via an external smart regulator and/or remote temperature sensors. Most stock alternators on small diesels are simply too small for the house banks they are intended to charge these days.

That's why, as stated in an earlier post, the best practice these days is to:

1. connect all onboard charging sources to the house batteries, using appropriate fusing near the batteries;

2. use a smart regulator capable of protecting the alternator so it doesn't burn out, and set it according to the size of the alternator and the size and type of house battery bank to be charged; and

3. keep the start battery topped off using a voltage follower device as mentioned above or an automatic charging relay (ACR).

That's the ideal. You may not want to re-vamp your system now, but it's something to think about for the future.

Meanwhile, to protect your alternator:

(1) don't use AGM house batteries; and
(2) don't move that selector switch while the engine is running.

Bill

[senormechanico]

I don't know exactly what the part number of a Zap Stop really is, as it's inside heat shrink, but I DO know it's nothing more than a Zener Diode rated around 18 volts.
Alternator diodes are usually rated about 25 volts if I'm not mistaken.

Digikey or Mouser Electronics would be an excellent place to find one cheaply.
I'd go for one rated for the full alternator output, something like 100 amps transient rating at 18 volts.
That would cover anything the alternator could possibly generate.

BTW. my Zap Stop is still good and it's older than the boat.
It's mounted right on the back side of the alternator.

[GordMay]

Originally Posted by senormechanico

I don't know exactly what the part number of a Zap Stop really is ...

At one time, the Zap-Stop was a:
Motorola #MR2535L Zener diode
➥ http://www.onsemi.com/pub_link/Collateral/MR2535L-D.PDF

[svHyLyte]

I have a very large placard next to the ignition/start key "Push Engine Stop Button Before Turning-Off Ignition". I have an equally large placard next to the Engine Stop Button, "Push and Hold 'Till Engine Stops". Engraved red plastic placards with white lettering from a Trophy shop. It has worked for us.

[goboatingnow]

I have a very large placard next to the ignition/start key "Push Engine Stop Button Before Turning-Off Ignition". I have an equally large placard next to the Engine Stop Button, "Push and Hold 'Till Engine Stops". Engraved red plastic placards with white lettering from a Trophy shop. It has worked for us

This is a bit of a marine "old wives tale", There should be no electrical reason why shutting off the "ignition", before stoping the engine, has any electrical effect. other then de-powering the panel and de-energising the alternator "excite". sometime rule was needed as the power to the stop solonoid was passed through the ignition switch, which is bad practice.

Dave

Dave

[zeehag]

dang you have an expensive learning curve and you have driven waaay too many cars.
i like my engine kill swiTch--is a pull KNOB--the key is right next to it. is NOT a car. GOOOD LUCK.

[MarkSF]

Originally Posted by goboatingnow

This is a bit of a marine "old wives tale", There should be no electrical reason why shutting off the "ignition", before stoping the engine, has any electrical effect. other then de-powering the panel and de-energising the alternator "excite". sometime rule was needed as the power to the stop solonoid was passed through the ignition switch, which is bad practice.

Dave

Dave

So it was pure coincidence that the alternator stopped working the moment this was done?

[Maine Sail]

Originally Posted by MarkSF

So it was pure coincidence that the alternator stopped working the moment this was done?

It may not be a coincidence but really depends upon how it is actually wired.

I have come across incorrectly wired ammeters where someone moved the wire when replacing the ammeter and moved it so it could be interrupted by the key. Lots of red wires back there and easy confusion for someone who did not mark things when they removed them.

This was not how the factory wired it but how a mechanic or DIY did it when they were in there. There should not be any possible way for your key to break the load if the system is wired correctly.

BTW you'd be well served to yank that ammeter and replace it with a volt meter. That charging circuit wiring has been a source of many charging issues over the years and most of these engines/panels have been upgrade at this point. Simply take a jumper from the alt output over to the starter post. This removes about 15+/- feet of small gauge wire before your alt output gets back to your batteries. The alternative is to go direct to the house bank with a fuse close to the battery..

Simply put if you turned off your key and if fried the diodes your charging circuit wiring is very poorly wired. Key switches are not meant to have 45+ amps running through them, which it sounds as if yours does, somehow..