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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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 Posted: Wed Jun 13, 2018 7:15 am Post subject: STARTER VOLTAGE SPIKE |
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Below is a quote from VansAirforce post #24 by Cumulo
http://www.vansairforce.com/community/showthread.php?t=160519
| Quote: |
Re:big bang
The diode bridge inside the average alternator is robust enough to snub and dissipate the starter energy provided the alternator "A" lead is intact and on line across the bus.
From my perspective Nuckolls is a new guy. He didn't start monkeying with this stuff 'till Cessna had begun using alternators, so he is not well placed to be the last word on this subject.
Let me describe the sequence involving a starter that has the potential to damage electronic stuff:
1. The Master is turned on, connecting the battery to the bus.
2. The starter button is pushed, energizing the starter solenoid
3. The starter solenoid connects the starter to the bus.
4. several hundred amps flow to the starter and the starter begins to spin the engine.
5. Battery is low, so starter slows and and stalls.
6. the stalled starter with a hundreds of amps demand pulls the bus voltage down to a few volts.
7. Master solenoid drops out , disconnecting battery from bus.
8. the very strong magnetic field of the starter collapses (the starer now is just a massive inductor of copper and iron)
9. A very high energy spike WILL BE produced if there is nothing to snub and dissipate it.
The above is not the normal start sequence. Normally, the STARTER solenoid releases first,turning the starter off and the starter energy is dissipated on the solenoid copper contacts.
BTW, proof by authority is not a good way to argue, but I DO have an A&P, accessories, radio, instrument repairman certs, had a repair station for a decade and stick wise most everything but an ATP. And way back when I worked for a living I was an Electrical Engineer doing mostly military and computer design stuff.
Nuckolls has done some really good stuff and I tip my hat to him, but I can demo blowing a small diode out with a starter spike any old time.
I think that having to start a dark airplane is too restrictive, too old timey. Protection should be standard so strobes, radios, EFIS, EMS audio amps can be on with no fear of damage from any cause. Stay tuned. |
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Joe Gores |
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ceengland7(at)gmail.com
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| Posted: Wed Jun 13, 2018 8:05 am Post subject: STARTER VOLTAGE SPIKE |
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On 6/13/2018 10:15 AM, user9253 wrote:
| Quote: |
Below is a quote from VansAirforce post #24 by Cumulo
http://www.vansairforce.com/community/showthread.php?t=160519
> Re:big bang
> The diode bridge inside the average alternator is robust enough to snub and dissipate the starter energy provided the alternator "A" lead is intact and on line across the bus.
> From my perspective Nuckolls is a new guy. He didn't start monkeying with this stuff 'till Cessna had begun using alternators, so he is not well placed to be the last word on this subject.
>
> Let me describe the sequence involving a starter that has the potential to damage electronic stuff:
> 1. The Master is turned on, connecting the battery to the bus.
> 2. The starter button is pushed, energizing the starter solenoid
> 3. The starter solenoid connects the starter to the bus.
> 4. several hundred amps flow to the starter and the starter begins to spin the engine.
> 5. Battery is low, so starter slows and and stalls.
> 6. the stalled starter with a hundreds of amps demand pulls the bus voltage down to a few volts.
> 7. Master solenoid drops out , disconnecting battery from bus.
> 8. the very strong magnetic field of the starter collapses (the starer now is just a massive inductor of copper and iron)
> 9. A very high energy spike WILL BE produced if there is nothing to snub and dissipate it.
>
> The above is not the normal start sequence. Normally, the STARTER solenoid releases first,turning the starter off and the starter energy is dissipated on the solenoid copper contacts.
>
> BTW, proof by authority is not a good way to argue, but I DO have an A&P, accessories, radio, instrument repairman certs, had a repair station for a decade and stick wise most everything but an ATP. And way back when I worked for a living I was an Electrical Engineer doing mostly military and computer design stuff.
>
> Nuckolls has done some really good stuff and I tip my hat to him, but I can demo blowing a small diode out with a starter spike any old time.
>
> I think that having to start a dark airplane is too restrictive, too old timey. Protection should be standard so strobes, radios, EFIS, EMS audio amps can be on with no fear of damage from any cause. Stay tuned.
--------
Joe Gores
Yeah, I replied to it, as well. Hilarious.
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jun 13, 2018 8:13 am Post subject: STARTER VOLTAGE SPIKE |
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At 10:15 AM 6/13/2018, you wrote:
This is a myth that has been propagated for
decades and has no foundation in physics.
Recall that the bench demonstrations for dissipating
the magnetic field collapse in a battery contactor
showed that the energy resulting from the spike
was dissipated in an arc that forms between the
spreading contacts of the controlling device, i.e.
the switch. The energy did NOT propagate onto the
bus in any significant way.
The same thing happens with starters except the
device taking the abuse is the starter contactor.
Yeah, there's some fire between the opening
contacts but that energy has to jump the RESISTANCE
of the arc and then boost the bus voltage against
the surge mitigating effects of battery(s) and
a host of capacitors built into the electrowhizzies.
Not once in 50 years of pondering the vagaries of
electrical system gremlins on vehicles have I
seen a measured/demonstrated risk to electrowhizzies
from a release energy stored on the starter's
inductance.
WAaayyy back when, we thought that 'starter
spikes' were killing the transistors in the newly
minted solid state features of radios at Cessna.
It turned out that depressed bus voltage during
cranking due to soggy battery was killing the
radios . . . NOT starter spikes.
That REAL threat to EARLY solid state designs
has been fertilized into any number of ol' pilot's
tales that are without foundation.
Bob . . .
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