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

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