"Glenn Ashmore" wrote in message
...


Ed Price wrote:


So I looked at the Xantrex site, trying to get some idea of a
Zap-stop's performance. I couldn't find a circuit diagram for how the
Zap-stop is hooked up to the alternator. Xantrex says something
about connection across the rectifiers, but that isn't clear enough
for me. Also, Xantrex doesn't say anything about how fast the
Zap-stop begins to conduct when presented with a voltage excursion.

Does Xantrex have some hard data on their product, or do they just
expect you to trust them?

The Zap Stop connects between the alternator output and ground. It is
just a high voltage diode with a reverse breakdown voltage a bit higher
than the operating voltage of the alternator. When the voltage exceeds
this level the diode starts to conduct instantly shorting it to ground.

The alternator diodes are designed for high amperage at relatively low
voltages. The Zap Stop diode is designed for high voltages but will
only handle high amperage for the few milliseconds it takes for the
regulator to regain control. I don't think it could stand up to
something like a loose sense wire on a high amperage alternator where
the voltage and amp output stays high for any length of time.

--
Glenn Ashmore


If the Zap-stop is connected to the alternator output, then it is positioned
best to protect the alternator against transients originating in the rest of
the vehicle's electrical system. (The worst source might be a high-current
motor, like the AC blower fan.)

OTOH, earlier posts have said that the sudden removal of load causes a high
voltage transient in the alternator's windings. This means that the Zap-stop
protects the alternator diodes from a high voltage by requiring the diodes
to pass a massive current transient into the Zap-stop and to ground. That's
strange protection!

If you wanted to protect against an alternator winding over-voltage,
wouldn't you have to put the protection at the winding side of the
alternator diodes?

The last time I looked inside an alternator, it had three field windings
connected to a 6-diode full-wave bridge rectifier. Protecting the bridge
against voltage transients would require one Zap-stop type device across
each winding. An over-voltage event would then conduct through the Zap-stop
devices, and not through the alternator diodes.

Could all of this discussion have been based on a misconception of what
happens when a heavy load current (into an inductive load like a motor
winding). The potentially damaging transient is caused by the counter emf
from the load, and not from any "slow regulator" effect within the
alternator.

If the Zap-stop is mounted to the alternator output lug, then that's
apparently what the Zap-stop is configured to protect against.


Ed

I believe we may be looking at it wrong. Go back to the original
problem. When the high amperage going to the battery is interupted, the
voltage starts to rise. What the Zap Stop does is provide an alternate
path for the current so that the flow is not interupted. Yes, the coils
are still outputting through the rectifier but if we can detect the
start of this rise fast enough and redirect the rectifier output to
ground, the current flow never stops so the voltage never gets high
enough to damage the rectifier.

BTW, in the other thread you were asking about a schematic. Here it is:

+ --------|------ -

It is just a zenier diode (or maybe several in parallel) in a nice box
wired against the normal current flow. When the voltage rises above the
breakdown rating of the diode, it conducts. As usual with most
"marine" devices, it is 5% material and 95% marketing but it does the job.

Ed Price wrote:

If the Zap-stop is connected to the alternator output, then it is positioned
best to protect the alternator against transients originating in the rest of
the vehicle's electrical system. (The worst source might be a high-current
motor, like the AC blower fan.)

OTOH, earlier posts have said that the sudden removal of load causes a high
voltage transient in the alternator's windings. This means that the Zap-stop
protects the alternator diodes from a high voltage by requiring the diodes
to pass a massive current transient into the Zap-stop and to ground. That's
strange protection!

If you wanted to protect against an alternator winding over-voltage,
wouldn't you have to put the protection at the winding side of the
alternator diodes?

The last time I looked inside an alternator, it had three field windings
connected to a 6-diode full-wave bridge rectifier. Protecting the bridge
against voltage transients would require one Zap-stop type device across
each winding. An over-voltage event would then conduct through the Zap-stop
devices, and not through the alternator diodes.

Could all of this discussion have been based on a misconception of what
happens when a heavy load current (into an inductive load like a motor
winding). The potentially damaging transient is caused by the counter emf
from the load, and not from any "slow regulator" effect within the
alternator.

If the Zap-stop is mounted to the alternator output lug, then that's
apparently what the Zap-stop is configured to protect against.


Ed



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

OK, so the Zap-stop is wired across the output of the alternator, and it's
just a zener diode.

Now, how can a diode be damaged? One way is to exceed its reverse voltage
capability. Another way is to exceed its current capacity.

Put the Zap-stop as described, and apply the transient from the vehicle
side. Either a high-voltage positive or negative transient will result in
strong conduction through the zener. As long as the zener can sink it, the
voltage will be limited by the strong conduction.

But now, posit that the overvoltage transient is starting in the alternator
windings. The zap-stop, on the output side of the bridge, may go into strong
conduction. But that current will also have to flow through the bridge
diodes. So how does causing a massive current through the alternator diodes
provide protection?


Ed




"Glenn Ashmore" wrote in message
...
I believe we may be looking at it wrong. Go back to the original
problem. When the high amperage going to the battery is interupted, the
voltage starts to rise. What the Zap Stop does is provide an alternate
path for the current so that the flow is not interupted. Yes, the coils
are still outputting through the rectifier but if we can detect the
start of this rise fast enough and redirect the rectifier output to
ground, the current flow never stops so the voltage never gets high
enough to damage the rectifier.

BTW, in the other thread you were asking about a schematic. Here it is:

+ --------|------ -

It is just a zenier diode (or maybe several in parallel) in a nice box
wired against the normal current flow. When the voltage rises above the
breakdown rating of the diode, it conducts. As usual with most
"marine" devices, it is 5% material and 95% marketing but it does the job.

Ed Price wrote:

If the Zap-stop is connected to the alternator output, then it is
positioned
best to protect the alternator against transients originating in the
rest of
the vehicle's electrical system. (The worst source might be a
high-current
motor, like the AC blower fan.)

OTOH, earlier posts have said that the sudden removal of load causes a
high
voltage transient in the alternator's windings. This means that the
Zap-stop
protects the alternator diodes from a high voltage by requiring the
diodes
to pass a massive current transient into the Zap-stop and to ground.
That's
strange protection!

If you wanted to protect against an alternator winding over-voltage,
wouldn't you have to put the protection at the winding side of the
alternator diodes?

The last time I looked inside an alternator, it had three field windings
connected to a 6-diode full-wave bridge rectifier. Protecting the bridge
against voltage transients would require one Zap-stop type device across
each winding. An over-voltage event would then conduct through the
Zap-stop
devices, and not through the alternator diodes.

Could all of this discussion have been based on a misconception of what
happens when a heavy load current (into an inductive load like a motor
winding). The potentially damaging transient is caused by the counter
emf
from the load, and not from any "slow regulator" effect within the
alternator.

If the Zap-stop is mounted to the alternator output lug, then that's
apparently what the Zap-stop is configured to protect against.


Ed



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Ed Price wrote:

.... So how does causing a massive current through the alternator diodes
provide protection?

By limiting voltage. Diodes can tolerate massive current for short
(milli or microsecond) periods of time without damage from overheating,
but excess voltage spikes of the same duration may "zap" the crystal
matricies that make them work as diodes.

"Vito" wrote in message
...
Ed Price wrote:

.... So how does causing a massive current through the alternator diodes
provide protection?

By limiting voltage. Diodes can tolerate massive current for short
(milli or microsecond) periods of time without damage from overheating,
but excess voltage spikes of the same duration may "zap" the crystal
matricies that make them work as diodes.

In the long history of alternator existence, Xentrex has been the only one
to notice that alternators need a transient suppressor on their output
terminal?

Another poster contends that the alternator experiences several hundred
milliseconds of overvoltage before its regulation can adjust to a load
cut-off. A couple of hundred milliseconds dumping a hundred amps or so into
the short-circuit that the Zap-stop presents is bad news for alternator
diodes.

Please address my initial comment; why does Xentrex put the "protection" on
the wrong (my assertion) side of the alternator diodes?

Ed

"Glenn Ashmore" wrote in message
...
First of all, teh Zap Stop is not intended to protect anything from
external spikes. There are very few situations on a boat that will
cause a damaging spike back into the alternator other than a lightning
strike and in that case all bets are off.

The Zap Stop is only intended to protect the alternator from self
destructing from a load dump. It does nothing else. It does this by
clamping the voltage lower than the damaging point for the rectifier.
In a load dump the voltage spike is what fries the rectifier diodes not
the amperage.

And how do you "clamp" a voltage when a voltage source is trying to drive it
higher? As the Zap-stop does, by presenting a conductive path that has a
very low resistance. The current is limited only by the source's internal
resistance. I have no idea what the internal resistance of a large
alternator is, but I would guess maybe 0.01 ohms. The important point is
that you have to be able to sink a lot of current during the alternator's
field winding voltage excursion. Putting the protective device on the load
side of the alternator diodes is a solution that requires a heavy current
draw through the alternator diodes during a protective event.

For illustration, lets say we have a big honkin' 250 amp Balmar cranking
out full power 15 volts into the house bank (3,750 watts) when somebody
turns the master switch and the output voltage starts to rise. The
regulator is still supplying the same current to the field and the RPM
has not changed. As no additional energy is being supplied to the
alternator the total power output remains the same.

Absolutely bogus assumption about power output remaining constant.

I am assuming that your alternator has an electronic, not a mechanical,
regulation scheme. Are you claiming that the regulation can track load
variations during normal operation, but, if the load is suddenly shed, it
takes hundreds of milliseconds to react?!

Power is volts *
amps so as the voltage rises the amperage has to drop. For that 200-300
milliseconds that it takes for the regulator to adjust the field current
the zenier has to absorb that 3,750 watts of excess power. Diodes that
can handle this amount of power for that length of time are not hard to
find. Digikey sells them for about a buck apiece.

I checked my Digikey catalog, but can't find any "zenier" diodes. Perhaps
you could fix your spull chucker; your consistent use of the wrong spelling
is beginning to bug me, as real experts know the names of their tools. You
know, you pound nails with a hammer, and discussing nail technology is
disconcerting when the other guy keeps talking about his hummer.

But regardless of how much diodes cost, where you buy them, and whether they
will fail trying to carry x kiloamps for y milliseconds, the initial point I
asked was why it was good practice to put the protection on the load side of
the alternator diodes. Telling me that you can get away with it is not a
good answer.

Ed

Glenn Ashmore has accurately described the problem - load
dump. Depending on standard, load dump on 12 volts can be 60
volts or as high as 270 volts. Two standards are SAE J1455
and ISO 7637-1. As Glenn has accurately described, load dump
can be created by disconnecting a major load from alternator -
such as battery.

Another has too much experience without underlying theory.
His proof that something does not exist is that he
disconnected a battery and failure did not occur. Reasoning
equivalent to walking with only one leg which is why his
response is:
Absolutely bogus assumption about power output remaining constant. That leg called underlying theory is essential to understanding how things really work. Load dump means automotive type electronics must be designed beyond just the 12 volt power.

SGS Thompson defines load dump as:
- Peak voltage 80 to 100 volts
- Duration 300 to 400 milliseconds
- Series resistance 0.2 to 1 ohms"

Even laptop power supplies for mobile power cost more money
because load dump protection is required.

SG Thompson makes load dump protection circuits such as
LDP24 or RBO series. But they admit:
The protection at the alternator level is a quite new concept and
all the technical problems do not seem to be completely solved.

Yes, you were lucky in not damaging the alternator if
disconnecting when alternator was outputting power.

BOEING377 wrote:
Are zap stoppers really needed on alternators? These aftermkt devices claim to
portect alt. diodes against damage from transients. I can't imagine that
engineers at places like Motorola would design alternators that needed external
aftermarket devices to effectively protect them from transients. I have never
blown up an alternator from switching it in and out of a load, although people
say this is often fatal to the diodes. I have run alternators open circuit (no
load at all) with no problems. Was I just lucky?

Thanks. I gave up.

There are none so blind as those who will not see.

w_tom wrote:
Glenn Ashmore has accurately described the problem - load
dump. Depending on standard, load dump on 12 volts can be 60
volts or as high as 270 volts. Two standards are SAE J1455
and ISO 7637-1. As Glenn has accurately described, load dump
can be created by disconnecting a major load from alternator -
such as battery.

Another has too much experience without underlying theory.
His proof that something does not exist is that he
disconnected a battery and failure did not occur. Reasoning
equivalent to walking with only one leg which is why his
response is:

Absolutely bogus assumption about power output remaining constant. That leg called underlying theory is essential to understanding how things really work. Load dump means automotive type electronics must be designed beyond just the 12 volt power.


SGS Thompson defines load dump as:

- Peak voltage 80 to 100 volts
- Duration 300 to 400 milliseconds
- Series resistance 0.2 to 1 ohms"


Even laptop power supplies for mobile power cost more money
because load dump protection is required.

SG Thompson makes load dump protection circuits such as
LDP24 or RBO series. But they admit:

The protection at the alternator level is a quite new concept and
all the technical problems do not seem to be completely solved.


Yes, you were lucky in not damaging the alternator if
disconnecting when alternator was outputting power.

BOEING377 wrote:

Are zap stoppers really needed on alternators? These aftermkt devices claim to
portect alt. diodes against damage from transients. I can't imagine that
engineers at places like Motorola would design alternators that needed external
aftermarket devices to effectively protect them from transients. I have never
blown up an alternator from switching it in and out of a load, although people
say this is often fatal to the diodes. I have run alternators open circuit (no
load at all) with no problems. Was I just lucky?



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

because it is easy? or maybe you are trolling....

"Ed Price" wrote in message
news:Zp9Ra.613$Ye.496@fed1read02...

"Glenn Ashmore" wrote in message
...
First of all, teh Zap Stop is not intended to protect anything from
external spikes. There are very few situations on a boat that will
cause a damaging spike back into the alternator other than a lightning
strike and in that case all bets are off.

The Zap Stop is only intended to protect the alternator from self
destructing from a load dump. It does nothing else. It does this by
clamping the voltage lower than the damaging point for the rectifier.
In a load dump the voltage spike is what fries the rectifier diodes not
the amperage.

And how do you "clamp" a voltage when a voltage source is trying to drive
it
higher? As the Zap-stop does, by presenting a conductive path that has a
very low resistance. The current is limited only by the source's internal
resistance. I have no idea what the internal resistance of a large
alternator is, but I would guess maybe 0.01 ohms. The important point is
that you have to be able to sink a lot of current during the alternator's
field winding voltage excursion. Putting the protective device on the load
side of the alternator diodes is a solution that requires a heavy current
draw through the alternator diodes during a protective event.

For illustration, lets say we have a big honkin' 250 amp Balmar cranking
out full power 15 volts into the house bank (3,750 watts) when somebody
turns the master switch and the output voltage starts to rise. The
regulator is still supplying the same current to the field and the RPM
has not changed. As no additional energy is being supplied to the
alternator the total power output remains the same.

Absolutely bogus assumption about power output remaining constant.

I am assuming that your alternator has an electronic, not a mechanical,
regulation scheme. Are you claiming that the regulation can track load
variations during normal operation, but, if the load is suddenly shed, it
takes hundreds of milliseconds to react?!

Power is volts *
amps so as the voltage rises the amperage has to drop. For that 200-300
milliseconds that it takes for the regulator to adjust the field current
the zenier has to absorb that 3,750 watts of excess power. Diodes that
can handle this amount of power for that length of time are not hard to
find. Digikey sells them for about a buck apiece.

I checked my Digikey catalog, but can't find any "zenier" diodes. Perhaps
you could fix your spull chucker; your consistent use of the wrong
spelling
is beginning to bug me, as real experts know the names of their tools. You
know, you pound nails with a hammer, and discussing nail technology is
disconcerting when the other guy keeps talking about his hummer.

But regardless of how much diodes cost, where you buy them, and whether
they
will fail trying to carry x kiloamps for y milliseconds, the initial point
I
asked was why it was good practice to put the protection on the load side
of
the alternator diodes. Telling me that you can get away with it is not a
good answer.

Ed

"Glenn Ashmore" wrote in message
...
Thanks. I gave up.

There are none so blind as those who will not see.

w_tom wrote:
Glenn Ashmore has accurately described the problem - load
dump. Depending on standard, load dump on 12 volts can be 60
volts or as high as 270 volts. Two standards are SAE J1455
and ISO 7637-1. As Glenn has accurately described, load dump
can be created by disconnecting a major load from alternator -
such as battery.



Well, pardon me for asking you to address my question. In case you didn't
remember, since it always seems to slip your attention during your posts, I
wanted to know why the suppression is applied to the LOAD side of the
alternator diodes. Perhaps you two could stop slapping each others butts
long enough to try to answer that question.

True, there are none so ignorant as those who refuse to learn. Now that
we're even on stupid witticisms, can you try for a technical answer?

Ed