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?

"BOEING377" wrote in message
...
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?


The fault conditions of a vehicle electrical system are very well known.
Good engineering practice dictates that the item you design should withstand
all normal operating conditions, plus those conditions generated by a single
fault, or even multiple faults. How long your device survives, and how many
multiple fault conditions it will tolerate, is controlled by economics.

Running the engine while the battery lead is disconnected is certainly a
single-fault (and reasonably likely to occur) condition. I know I have done
this rather often, and I have never had any associated failures. OTOH, it
has always been done with GM autos with internal regulator alternators. So,
however they do it, the GM engineers have designed-in a control over that
single-fault condition.

Notice that I said a "control" and not a "tolerance". In the "no battery"
single-fault condition, the alternator will supply the vehicle electric
power load. If the loss of the battery allows for the alternator to create a
vastly over-voltage condition, then protection would have to be designed
into every electrical load device. It's a lot easier to just control the
alternator output voltage.

From my experience, the alternator is one of the most reliable parts of your
car. Almost everything wears out or needs service before the alternator. If
your alternator fails, I think you must be exceptionally unlucky, or very
creative in producing a really unusual fault condition.


Ed

For what they cost, they're good insurance. At least, if you think somebody
will turn the battery switch off while the engine is running.

--


Keith
__
Why is it that if you tell someone there are 6.3 trillion stars in the
universe they will believe it,
but if you tell them that your teak has wet varnish they have to touch it?
"BOEING377" wrote in message
...
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?

What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

"""""For what they cost, they're good insurance. At least, if you think
somebody
will turn the battery switch off while the engine is running.""""""""""
S/V Express 30 "Ringmaster"
Trains are a winter sport

SAIL LOCO wrote:
What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

I didn't read it that way.

HE said "running the engine while the battery is disconnected."

I am talking about disconecting the battery while the engine is running.

BIG difference.

--
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

If he's "running the engine while the battery is disconnected," but he
didn't disconnect while it was running, I'm wondering how he got it started.

"Glenn Ashmore" wrote in message
...


SAIL LOCO wrote:
What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

I didn't read it that way.

HE said "running the engine while the battery is disconnected."

I am talking about disconecting the battery while the engine is running.

BIG difference.

--
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

You can disconnect the battery while the engine is running and cause
no damage to the alternator, provided the alternator is not putting
out much current. (battery fully charged, no accessories drawing
current)

If the alternator is supplying much current then you will probably zap
the diodes in it.

The voltage regulator monitors the alternators output voltage and
changes the field voltage on the alternator to control the output.

The problem is, being that a magnetic field is involved it does not
change instantly. There is a time lag for the field to collapse and
reduce the alternators output.

When the load is suddenly disconnected from the alternator, when there
is a substantial load on it, there is a large voltage generated in the
alternators windings from the collapsing winding magnetic field. (the
magnetic field collapses because there is no more load on it) That is
connected to the diodes.

The voltage regulator sees the large voltage spike and tells the field
winding to shut down the field current but it is too late as there is
no way to stop the magnetic field in the alternator windings from
collapsing. The regulator can stop the field from building up before
the alternator output current goes up but once it is there, the
magnetic field has to first collapse to stop further output.

When the alternator is putting out a large current the alternators
windings have a high magnetic field in them. Disconnecting the
alternators load causes the magnetic fields to suddenly collapse and
generate a large voltage with nothing to limit the voltage. (no
battery to absorb it)

Note: A changing magnetic field is what generates voltage in the
windings. This happened normally when the alternator is supplying
power as wanted. The uncontrolled change is what causes the damage.

Regards
Gary


On Sun, 13 Jul 2003 02:17:15 GMT, "johnh" wrote:

If he's "running the engine while the battery is disconnected," but he
didn't disconnect while it was running, I'm wondering how he got it started.

"Glenn Ashmore" wrote in message
...


SAIL LOCO wrote:
What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

I didn't read it that way.

HE said "running the engine while the battery is disconnected."

I am talking about disconecting the battery while the engine is running.

BIG difference.

--
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

Jumpre cables :-) Actually it takes a second or two to get the
alternator up to full current. The main thing is that once the
regulator starts putting out a significant current and the circuit is
broken, the regulator can't drop the field current fast enough to
protect the diodes.

With a starter battery, the alternator is usually only topping off the
battery for what was needed to start the engine which only takes a few
minutes. After that the load is just the other devices on the system
and disconnecting the battery makes little difference. An alternator
recharging a house battery bank could be putting out many amps for an
hour or more. This is one of the major differences between a normal
automotive alternator and a true "marine" (read EMT, utility or
industrial) alternator. In comparison an automotive alternator has it
real easy.

Also, the voltage is directly related to the number of flux lines broken
by the coil wires. When the field current stops the magnetic field
collapses and then the number of flux lines broken is the combination of
the coil rotation and the collapsing field. The result can be a spike.

johnh wrote:
If he's "running the engine while the battery is disconnected," but he
didn't disconnect while it was running, I'm wondering how he got it started.

"Glenn Ashmore" wrote in message
...


SAIL LOCO wrote:

What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

I didn't read it that way.

HE said "running the engine while the battery is disconnected."

I am talking about disconecting the battery while the engine is running.

BIG difference.

--
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







--
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 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

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

Since we are on the topic does anyone know for sure if the ZapStop can be used
with the Hitachi alternators with the built in regulators found on most Yanmar
engines? Thanks.
S/V Express 30 "Ringmaster"
Trains are a winter sport