Zap Stop - Fact or Fiction ?

[hpeer]

So, I just ordered a hundred of these buggers from DigiKey for $14.35 plus tax $0.86 and shipping.

I'll still need to connect the wires, but I think I can handle that.

[Maine Sail]

Originally Posted by perchance

The simplest solution is to install make before break battery switches to eliminate the chance of inadvertently switching under load.

Or direct wire your alt to the battery bank then you can't accidentally disconnect the load. Most all batt switches for many, many years have been make before break but OFF is OFF, no make, and many a boater has accidentally turned the switch through OFF when really wanting to go to BOTH or #2 thus frying the alt.

As has been stated the ignition switch is not the issue it is the battery switch and passing through OFF and disconnecting the load from a running alt that is the diode eater..

[GordMay]

Originally Posted by Maine Sail

Or direct wire your alt to the battery bank then you can't accidentally disconnect the load...

... As has been stated the ignition switch is not the issue it is the battery switch and passing through OFF and disconnecting the load from a running alt that is the diode eater..

The best battery switches also have an AFD, Alternator Field Disconnect (aux. sw.).

See ➥ http://bluesea.com/viewresource/91

And ➥ http://www.cruisersforum.com/forums/...ect-21444.html

[Maine Sail]

Originally Posted by GordMay

The best battery switches also have an AFD, Alternator Field Disconnect (aux. sw.).

See ➥ Alternator Field Disconnect - Resources - Blue Sea Systems

And ➥ http://www.cruisersforum.com/forums/...ect-21444.html

Absolutely! The Guest switch on my own boat has one but I don't use it because I direct wire. The problem becomes that many switches do not have an AFD and to change out a switch requires new holes and perhaps even a different mounting location on some boats, especially if the switch is fit into the switch panel.

If you have an AFD that is a great option but many switches just don't have it...

[hpeer]

Well the joke is on me.

My 100 diodes came in, packaged in a strip/reel for mass production soldering. Their size is somewhere between a skinny deer tick and fat flea.

Now, where was that post on the $25 zap stop?

[senormechanico]

Originally Posted by Maine Sail

Or direct wire your alt to the battery bank then you can't accidentally disconnect the load. Most all batt switches for many, many years have been make before break but OFF is OFF, no make, and many a boater has accidentally turned the switch through OFF when really wanting to go to BOTH or #2 thus frying the alt.

As has been stated the ignition switch is not the issue it is the battery switch and passing through OFF and disconnecting the load from a running alt that is the diode eater..

What happens when the alternator diodes short for some other reason?
You can't disconnect the short circuit without some heroic measures if you even HAVE that option before the boat burns.

I'll stick with at least a switch.

[Therapy]

Originally Posted by senormechanico

What happens when the alternator diodes short for some other reason?

.

I don't know the pluses and minuses of some of the details but diodes short? I never heard of that. I figured they just opened.

[senormechanico]

The usual failure of most diodes I've seen (admittedly in electronics) has been shorting due to either over current, or over voltage.

At anchor and loving my boat's wireless Wi Fi setup,

[Therapy]

Originally Posted by senormechanico

The usual failure of most diodes I've seen (admittedly in electronics) has been shorting due to either over current, or over voltage.

At anchor and loving my boat's wireless Wi Fi setup,

I didn't know that.

The last alternator I "blew up" I thought they opened. Maybe not.

Thanks.

[GordMay]

Originally Posted by senormechanico

The usual failure of most diodes I've seen (admittedly in electronics) has been shorting due to either over current, or over voltage...

Failure Modes ➥ Troubleshooting Chapter Three. Failure Modes.

Rates diode failure “shorted” as a high probability, and “open” as a low probability failure mode.

Agreeing, Mil Handbook 338* lists 3 modes of failure for diodes and the likelyhood of each:
Short Circuit -- 75%
Intermittent -- 18%
Open circuit -- 6%

* ➥ http://www.barringer1.com/mil_files/MIL-HDBK-338.pdf

[lucseawalker]

I will order some of these diodes to make replacement zap-stop on my alternators. How do I determine which side of the diode go to the 20amp fuse then the positive and which side to the negative? Tnx for the pointer

[atoll]

Originally Posted by lucseawalker

I will order some of these diodes to make replacement zap-stop on my alternators. How do I determine which side of the diode go to the 20amp fuse then the positive and which side to the negative? Tnx for the pointer

touch one end to a +pos and with a (multimeter in series set on voltage) touch the -neg,the diode will only register voltage in one direction.

[sartorst]

When a battery is in a low state of charge or worse dead and the alternator is charging near max output and the battery is removed from the circuit the instant the disconnect occurs the regulator sees voltage going down and ramps up the voltage ! NOW the voltage is high and nothing to absorb it (battery) the diodes can not handle this much back flow so POW blown diodes , most diodes or burned to an open circuit but can be damaged and are no longer a( check valve )and allow electrical flow to ground which will drain battery

[senormechanico]

Most diodes will have a polarity marking. If there's a band around one end, that's the cathode or + end.
Connect + to + and - to -.
It will not conduct anything until the breakdown (protection) voltage is reached.

sartorst,
Your scenario is correct, and when the diode(s) short with no fuse or breaker protection, something's gonna burn.
It will probably be the alternator output lead wire.

[Stu Jackson]

Some good answers so far, but the most important thing is

It All Depends On How It Is Wired

If your alternator output goes to the C post of your 1-2-B switch, or to any other disconnect to the ALTERNATOR OUTPUT (AO), then a zap stop is a good idea. The concept of "make before break" switches is, in my mind, ludicrous, because one shouldn't be moving the damn switch position when the alternator is running, EVER! Tell your borther-in-law to NEVER touch the switch!

However, a zap stop is a one time use only device, and, unless you check it regularly, you'll never know from just looking at it (assuming you can behind the alternator) whether it is fine or not.

The better approach is to get the AO OFF the switch entirely, and run it, fused, to your house bank, and get an echo charger to charge your start bank.

You can then turn your switch off even when the alternator is running! Really.

The ignition switch only turns off the regulator, internal or external doesn't matter.

Then you don't even need a zap stop.

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com