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diode on starter contactor
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kenryan



Joined: 20 Oct 2009
Posts: 258

PostPosted: Wed Jan 17, 2018 3:58 pm    Post subject: diode on starter contactor Reply with quote

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?
Ken


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PostPosted: Wed Jan 17, 2018 4:10 pm    Post subject: diode on starter contactor Reply with quote

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.

On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken


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Joined: 28 Mar 2008
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PostPosted: Wed Jan 17, 2018 4:15 pm    Post subject: Re: diode on starter contactor Reply with quote

An arc suppression diode should be connected directly across a coil. It is best if the diode is located at the coil. If that is impractical for some reason, then the diode can be located farther away as long as it is still connected in parallel with the coil. The banded end of the diode must be connected to the positive coil terminal and the other end of the diode connects to the negative terminal of the coil. If the coil is internally connected to the case, then the diode should be connected to the case or any convenient ground, assuming that the case is grounded.

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kenryan



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PostPosted: Wed Jan 17, 2018 4:19 pm    Post subject: diode on starter contactor Reply with quote

Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.

On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.



On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken


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PostPosted: Wed Jan 17, 2018 4:34 pm    Post subject: diode on starter contactor Reply with quote

Think of the contactor's mounting screw as the ground terminal (it actually *is* the ground terminal). So the banded end of the diode is connected to the control terminal, and the unbanded end is connected to one of the mounting screws. Or as others have said, any convenient grounded terminal nearby. Note that you can solder or crimp a short length of wire to either/both leads on the diode, and solder or crimp ring terminals to the wire, if the diode's leads aren't long enough to reach where they need to go. Just slip some heat shrink tubing, or even wire insulation stripped off a bigger wire, over the exposed leads as needed to keep the 'hot' end isolated from ground.

On 1/17/2018 6:18 PM, Ken Ryan wrote:

Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.

On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.



On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken



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PostPosted: Wed Jan 17, 2018 4:36 pm    Post subject: diode on starter contactor Reply with quote

Use the mounting bolt then, with a ring terminal under the bolt head.

On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.

On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.



On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken


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kenryan



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PostPosted: Wed Jan 17, 2018 5:39 pm    Post subject: diode on starter contactor Reply with quote

Thanks everyone.

On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:

Use the mounting bolt then, with a ring terminal under the bolt head.

On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.

On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.



On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken


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PostPosted: Wed Jan 17, 2018 9:50 pm    Post subject: diode on starter contactor Reply with quote

I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.

Thanks
Bernie

Sent from my iPhone

On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Thanks everyone.

On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:

Use the mounting bolt then, with a ring terminal under the bolt head.

On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.

On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.

If you put it the wrong way round, don’t worry, it will just disappear.



On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?

Ken


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PostPosted: Wed Jan 17, 2018 11:00 pm    Post subject: diode on starter contactor Reply with quote

Bernie,
As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.
Bill

Quote:
On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com (arcticarrow(at)gmail.com)> wrote:
I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.
Thanks
Bernie Sent from my iPhone
On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Thanks everyone.

On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:

Use the mounting bolt then, with a ring terminal under the bolt head.
On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf. If you put it the wrong way round, don’t worry, it will just disappear. On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote: My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path? Ken ============= - Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List =========== FORUMS - eferrer" target="_blank">http://forums.matronics.com =========== WIKI - errer" target="_blank">http://wiki.matronics.com =========== b Site - -Matt Dralle, List Admin. rel="noreferrer" target="_blank">http://www.matronics.com/contribution ===========










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PostPosted: Wed Jan 17, 2018 11:27 pm    Post subject: diode on starter contactor Reply with quote

Bill,That refinement to the traditional circuit makes sense. Is there any particular diode?

Thanks,
Bernie
Quote:
On Jan 17, 2018, at 9:59 PM, Bill Bear <beartrax(at)mtaonline.net (beartrax(at)mtaonline.net)> wrote:
Bernie,
As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.
Bill

Quote:
On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com (arcticarrow(at)gmail.com)> wrote:
I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.
Thanks
Bernie Sent from my iPhone
On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Thanks everyone.

On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:

Use the mounting bolt then, with a ring terminal under the bolt head.
On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
Quote:
Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf. If you put it the wrong way round, don’t worry, it will just disappear. On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote: My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path? Ken ============= - Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List =========== FORUMS - eferrer" target="_blank">http://forums.matronics.com =========== WIKI - errer" target="_blank">http://wiki.matronics.com =========== b Site - -Matt Dralle, List Admin. rel="noreferrer" target="_blank">http://www.matronics.com/contribution ===========













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PostPosted: Thu Jan 18, 2018 5:43 am    Post subject: diode on starter contactor Reply with quote

Inductors (a solenoid coil is a good example of a large inductor) resist sudden changes in current flowing through them. When you energize the solenoid the current through the coil grows slowly to its maximum value. When you break the circuit with the switch you are forcing a sudden change in current, which causes a massive voltage spike. In the microseconds after the switch contact breaks the gap at the switch contacts is narrow enough, and the voltage rise at the inductor is big enough, to cause arcing and contact damage in the switch.

The diode allows the current in the coil to continue to flow after the switch contact is broken by completing the circuit from the ground terminal of the coil back to the now-disconnected other terminal. (A diagram should make this clearer). No sudden change in current means no sudden voltage rise and no possibility of arcing.

The energy to drive the continuing current flow through the coil after the battery power has been removed from the solenoid terminal comes from the energy stored in the magnetic field. As the field collapses the current drops to zero.

On Jan 18, 2018, at 1:59 AM, Bill Bear <beartrax(at)mtaonline.net> wrote:

Bernie,

As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.

Bill
Quote:
On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com> wrote:

I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.

Thanks
Bernie

Sent from my iPhone

On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com> wrote:

> Thanks everyone.
>
>
> On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com> wrote:
> Use the mounting bolt then, with a ring terminal under the bolt head.
>
> On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com> wrote:
>
>> Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
>>
>> On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>>
>>
>> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.
>>
>> If you put it the wrong way round, don’t worry, it will just disappear.
>>
>>
>>
>> On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>
>> My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?
>>
>> Ken
>>
>>
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>> -Matt Dralle, List Admin.
>> rel="noreferrer" target="_blank">http://www.matronics.com/contribution
>> ===========
>>
>>
>>
>>
>


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PostPosted: Thu Jan 18, 2018 7:38 am    Post subject: Re: diode on starter contactor Reply with quote

Here’s a really excellent video by a guy named Alan Wolke (an applications engineer at Tektronix) that explains back-EMF in inductive circuits and the function of snubber or flyback diodes.

https://www.youtube.com/watch?v=c6I7Ycbv8B8

As you watch this, keep in mind that Alan is using a small signal relay with a relatively tiny coil that operates on a few tens of milliamps. Then consider the typical starter solenoid: it should be obvious that the potential (pardon the pun) for large voltage spikes is amplified by the physical size of its coil and large current that it consumes in operation.

Eric


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PostPosted: Thu Jan 18, 2018 9:27 am    Post subject: diode on starter contactor Reply with quote

I really appreciate the discussion on the theory. Also found this issue discussed in Aero Connection. I have an old Bonanza that occasionally produces a chattering sound when the master/battery switch in turned on. Now I suspect it is the master solenoid contacts showing signs of failure. A new solenoid is in order but the diode protection seems in order also. A little research shows diodes available in many voltage, capacitance and temperature rating, anything from .07 to $300. What are the parameters of an appropriate diode to protect a 12 volt master or starter solenoid?

Bernie

Quote:
On Jan 18, 2018, at 4:41 AM, Alec Myers <alec(at)alecmyers.com> wrote:



Inductors (a solenoid coil is a good example of a large inductor) resist sudden changes in current flowing through them. When you energize the solenoid the current through the coil grows slowly to its maximum value. When you break the circuit with the switch you are forcing a sudden change in current, which causes a massive voltage spike. In the microseconds after the switch contact breaks the gap at the switch contacts is narrow enough, and the voltage rise at the inductor is big enough, to cause arcing and contact damage in the switch.

The diode allows the current in the coil to continue to flow after the switch contact is broken by completing the circuit from the ground terminal of the coil back to the now-disconnected other terminal. (A diagram should make this clearer). No sudden change in current means no sudden voltage rise and no possibility of arcing.

The energy to drive the continuing current flow through the coil after the battery power has been removed from the solenoid terminal comes from the energy stored in the magnetic field. As the field collapses the current drops to zero.

On Jan 18, 2018, at 1:59 AM, Bill Bear <beartrax(at)mtaonline.net> wrote:

Bernie,

As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.

Bill


> On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com> wrote:
>
> I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.
>
> Thanks
> Bernie
>
> Sent from my iPhone
>
> On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com> wrote:
>
>> Thanks everyone.
>>
>>
>> On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>> Use the mounting bolt then, with a ring terminal under the bolt head.
>>
>> On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>
>>> Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
>>>
>>> On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>>>
>>>
>>> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.
>>>
>>> If you put it the wrong way round, don’t worry, it will just disappear.
>>>
>>>
>>>
>>> On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>>
>>> My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?
>>>
>>> Ken
>>>
>>>
>>> =============
>>> -
>>> Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
>>> ===========
>>> FORUMS -
>>> eferrer" target="_blank">http://forums.matronics.com
>>> ===========
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>>> errer" target="_blank">http://wiki.matronics.com
>>> ===========
>>> b Site -
>>> -Matt Dralle, List Admin.
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>>> ===========
>>>
>>>
>>>
>>>
>>








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PostPosted: Thu Jan 18, 2018 9:50 am    Post subject: diode on starter contactor Reply with quote

A ten cent 1N4001 is just fine.

Voltage refers to a safe reverse voltage limit before avalanche breakdown: the coil diode is only reverse biased to 12V. A 1N4001 is rated to 50V.
Current rating: somewhat irrelevant, since there’s no sustained current load. A 1N4001 is good for up to 1A continuous, and 30A surge. Neither limit will be close to met in this application.
Capacitance: refers to the junction capacitance when reverse biased. Irrelevant in this application.
Physical package: anything big enough to solder easily will have enough thermal mass to absorb what little energy is stored in the coil magnetic field.

On Jan 18, 2018, at 12:26 PM, Bernie Willis <arcticarrow(at)gmail.com> wrote:



I really appreciate the discussion on the theory. Also found this issue discussed in Aero Connection. I have an old Bonanza that occasionally produces a chattering sound when the master/battery switch in turned on. Now I suspect it is the master solenoid contacts showing signs of failure. A new solenoid is in order but the diode protection seems in order also. A little research shows diodes available in many voltage, capacitance and temperature rating, anything from .07 to $300. What are the parameters of an appropriate diode to protect a 12 volt master or starter solenoid?

Bernie

Quote:
On Jan 18, 2018, at 4:41 AM, Alec Myers <alec(at)alecmyers.com> wrote:



Inductors (a solenoid coil is a good example of a large inductor) resist sudden changes in current flowing through them. When you energize the solenoid the current through the coil grows slowly to its maximum value. When you break the circuit with the switch you are forcing a sudden change in current, which causes a massive voltage spike. In the microseconds after the switch contact breaks the gap at the switch contacts is narrow enough, and the voltage rise at the inductor is big enough, to cause arcing and contact damage in the switch.

The diode allows the current in the coil to continue to flow after the switch contact is broken by completing the circuit from the ground terminal of the coil back to the now-disconnected other terminal. (A diagram should make this clearer). No sudden change in current means no sudden voltage rise and no possibility of arcing.

The energy to drive the continuing current flow through the coil after the battery power has been removed from the solenoid terminal comes from the energy stored in the magnetic field. As the field collapses the current drops to zero.

On Jan 18, 2018, at 1:59 AM, Bill Bear <beartrax(at)mtaonline.net> wrote:

Bernie,

As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.

Bill


> On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com> wrote:
>
> I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.
>
> Thanks
> Bernie
>
> Sent from my iPhone
>
> On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com> wrote:
>
>> Thanks everyone.
>>
>>
>> On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>> Use the mounting bolt then, with a ring terminal under the bolt head.
>>
>> On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>
>>> Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
>>>
>>> On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>>>
>>>
>>> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.
>>>
>>> If you put it the wrong way round, don’t worry, it will just disappear.
>>>
>>>
>>>
>>> On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>>
>>> My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?
>>>
>>> Ken
>>>
>>>
>>> =============
>>> -
>>> Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
>>> ===========
>>> FORUMS -
>>> eferrer" target="_blank">http://forums.matronics.com
>>> ===========
>>> WIKI -
>>> errer" target="_blank">http://wiki.matronics.com
>>> ===========
>>> b Site -
>>> -Matt Dralle, List Admin.
>>> rel="noreferrer" target="_blank">http://www.matronics.com/contribution
>>> ===========
>>>
>>>
>>>
>>>
>>








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PostPosted: Thu Jan 18, 2018 9:58 am    Post subject: diode on starter contactor Reply with quote

Alec,

That was a quick reply! Now I can proceed.

Thanks,
Bernie

Quote:
On Jan 18, 2018, at 8:49 AM, Alec Myers <alec(at)alecmyers.com> wrote:



A ten cent 1N4001 is just fine.

Voltage refers to a safe reverse voltage limit before avalanche breakdown: the coil diode is only reverse biased to 12V. A 1N4001 is rated to 50V.
Current rating: somewhat irrelevant, since there’s no sustained current load. A 1N4001 is good for up to 1A continuous, and 30A surge. Neither limit will be close to met in this application.
Capacitance: refers to the junction capacitance when reverse biased. Irrelevant in this application.
Physical package: anything big enough to solder easily will have enough thermal mass to absorb what little energy is stored in the coil magnetic field.





On Jan 18, 2018, at 12:26 PM, Bernie Willis <arcticarrow(at)gmail.com> wrote:



I really appreciate the discussion on the theory. Also found this issue discussed in Aero Connection. I have an old Bonanza that occasionally produces a chattering sound when the master/battery switch in turned on. Now I suspect it is the master solenoid contacts showing signs of failure. A new solenoid is in order but the diode protection seems in order also. A little research shows diodes available in many voltage, capacitance and temperature rating, anything from .07 to $300. What are the parameters of an appropriate diode to protect a 12 volt master or starter solenoid?

Bernie

> On Jan 18, 2018, at 4:41 AM, Alec Myers <alec(at)alecmyers.com> wrote:
>
>
>
> Inductors (a solenoid coil is a good example of a large inductor) resist sudden changes in current flowing through them. When you energize the solenoid the current through the coil grows slowly to its maximum value. When you break the circuit with the switch you are forcing a sudden change in current, which causes a massive voltage spike. In the microseconds after the switch contact breaks the gap at the switch contacts is narrow enough, and the voltage rise at the inductor is big enough, to cause arcing and contact damage in the switch.
>
> The diode allows the current in the coil to continue to flow after the switch contact is broken by completing the circuit from the ground terminal of the coil back to the now-disconnected other terminal. (A diagram should make this clearer). No sudden change in current means no sudden voltage rise and no possibility of arcing.
>
> The energy to drive the continuing current flow through the coil after the battery power has been removed from the solenoid terminal comes from the energy stored in the magnetic field. As the field collapses the current drops to zero.
>
> On Jan 18, 2018, at 1:59 AM, Bill Bear <beartrax(at)mtaonline.net> wrote:
>
> Bernie,
>
> As I understand it, when the solenoid is deenergized, a voltage surge peak passes through the circuit which ages the solenoid contacts. The diode prevents the passage of the surge current and lengthens the life of the solenoid contacts. The diode band end is connected to the positive side of the solenoid contractor and the other side of the diode is connected to ground at the solenoid.
>
> Bill
>
>
>> On Jan 17, 2018, at 20:49, Bernie <arcticarrow(at)gmail.com> wrote:
>>
>> I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.
>>
>> Thanks
>> Bernie
>>
>> Sent from my iPhone
>>
>> On Jan 17, 2018, at 4:38 PM, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>
>>> Thanks everyone.
>>>
>>>
>>> On Wed, Jan 17, 2018 at 3:35 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>>> Use the mounting bolt then, with a ring terminal under the bolt head.
>>>
>>> On Jan 17, 2018, at 19:18, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>>
>>>> Alec, like I said in my original post, there is no ground terminal. Ground is accomplished through the metal case.
>>>>
>>>> On Wed, Jan 17, 2018 at 3:10 PM, Alec Myers <alec(at)alecmyers.com> wrote:
>>>>
>>>>
>>>> Wire it across the coil, so from non ground terminal to ground terminal, so it’s reverse polarized when the coil is energized. Then when power is removed, the magnetic field collapses driving current through the diode and avoiding a large back emf.
>>>>
>>>> If you put it the wrong way round, don’t worry, it will just disappear.
>>>>
>>>>
>>>>
>>>> On Jan 17, 2018, at 18:56, Ken Ryan <keninalaska(at)gmail.com> wrote:
>>>>
>>>> My starter contactor's coil gets its ground through the contactor's metal case. Given that, does it make any sense to use a diode? If so, how would that diode be implemented and how would it remain effective when the case itself is the ground path?
>>>>
>>>> Ken
>>>>
>>>>
>>>> =============
>>>> -
>>>> Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
>>>> ===========
>>>> FORUMS -
>>>> eferrer" target="_blank">http://forums.matronics.com
>>>> ===========
>>>> WIKI -
>>>> errer" target="_blank">http://wiki.matronics.com
>>>> ===========
>>>> b Site -
>>>> -Matt Dralle, List Admin.
>>>> rel="noreferrer" target="_blank">http://www.matronics.com/contribution
>>>> ===========
>>>>
>>>>
>>>>
>>>>
>>>
>
>
>
>
>
>












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PostPosted: Thu Jan 18, 2018 10:09 am    Post subject: diode on starter contactor Reply with quote

At 11:49 PM 1/17/2018, you wrote:
Quote:
I’m trying to follow the diode and the starter sol. discussion. I missed the reason for the diode.

We've had several discussions on spike-suppression
diodes on relays and contactors over the years. One
of the first was prompted by a snafu over an
airworthiness directive against the ACS/Gerdes
off-left-right-on-start key switches. Seems
the inductive spike fire generated by relatively
high coil current of some starter contactors was
eating up the start contact in the key switch.

Here's one example of a OEM aircafter's response
to the AD.

https://goo.gl/1XvDtj

This was the CORRECT way to install the diode . . .
the AD also called for refurbishment of the
start switch contacts within the keyswitch.
Here's background on the physics for proper
placement of the diode.

https://goo.gl/WUS1Ya

The problem would get potentially worse when
lightweight starters started showing up.

Still more stress on the switch was a function of
a two-stage engagement scenario which impressed a much larger
engagement inrush current compared to legacy
starter contactors. Here's the background.

https://goo.gl/opeqsM

Later in the discussions, there was consternation
about how 'inadvised' configuration of spike
suppression would cause the contactor's points
to open more slowly and exacerbate contact wear.
The assertion was predicated on an article published
by Potter-Brumfield

https://goo.gl/iCrqch

The author asserts that a diode connected right
across the contactor/relay coil results in significantly
slower contact opening velocity. This prompted a
trip to the workbench to explore the physics:

https://goo.gl/KNTr8y

For our purposes, the diode was demonstrated to
effect a DELAY in contact first opening . . . but
once the contacts started to move, the AIR GAP
in the magnetic circuit had a much more profound
effect on opening velocity than did the slower
decay of current in the contactor coil.

The short answer is that adding a plain-jane diode
across the coil of any relay or contactor in
the airplane will not noticeably affect service
life of that device. The diode improves service
life of the SWITCH THAT CONTROLS THE CONTACTOR.
Further, contactor coils do not propagate spikes
onto the system looking for vulnerable solid
state electronics to fry.







Bob . . .


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PostPosted: Thu Jan 18, 2018 10:13 am    Post subject: diode on starter contactor Reply with quote

At 11:49 AM 1/18/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

A ten cent 1N4001 is just fine.

Voltage refers to a safe reverse voltage limit before avalanche breakdown: the coil diode is only reverse biased to 12V. A 1N4001 is rated to 50V.
Current rating: somewhat irrelevant, since there’s no sustained current load. A 1N4001 is good for up to 1A continuous, and 30A surge. Neither limit will be close to met in this application.

Absolutely correct. My personal favorites
are the 1N5400 series devices, NOT for their
electrical ratings but for mechanical
robustness. Example:

https://goo.gl/2CGXgf





Bob . . .


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PostPosted: Thu Jan 18, 2018 10:42 am    Post subject: diode on starter contactor Reply with quote

On 1/18/2018 12:13 PM, Robert L. Nuckolls, III wrote:

Quote:
At 11:49 AM 1/18/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com> (alec(at)alecmyers.com)

A ten cent 1N4001 is just fine.

Voltage refers to a safe reverse voltage limit before avalanche breakdown: the coil diode is only reverse biased to 12V. A 1N4001 is rated to 50V.
Current rating: somewhat irrelevant, since there’s no sustained current load. A 1N4001 is good for up to 1A continuous, and 30A surge. Neither limit will be close to met in this application.

Absolutely correct. My personal favorites
are the 1N5400 series devices, NOT for their
electrical ratings but for mechanical
robustness. Example:

https://goo.gl/2CGXgf





Bob . . .
And, while I haven't priced the 5400 series, the 4000 series prices used to be virtually identical from 4001 to 4007 (1KV rating). Not that you'd need it for this application, but when I repaired electrons for a living, we just stocked the 07s because they work for everything at that current rating.
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]


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PostPosted: Thu Jan 18, 2018 12:17 pm    Post subject: diode on starter contactor Reply with quote

>> when the solenoid is de-energized, a voltage surge peak passes
through the circuit which ages the solenoid contacts. The diode prevents
the passage of the surge current and lengthens the life of the solenoid
contacts.

For an abundance of clarity, the diode across the coil terminals does
NOT protect the solenoid's contacts. It protects instead the switch
contacts of whatever switch controls that solenoid coil: the starter
switch for the starter contactor; the master switch contacts for the
master contactor.

Paul


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PostPosted: Thu Jan 18, 2018 12:20 pm    Post subject: diode on starter contactor Reply with quote

Quote:
Quote:
Bob . . .
And, while I haven't priced the 5400 series, the 4000 series prices used to be virtually identical from 4001 to 4007 (1KV rating). Not that you'd need it for this application, but when I repaired electrons for a living, we just stocked the 07s because they work for everything at that current rating.

Astute observation.

I've not confirmed this with a real diode-maker
person but . . .

I was working at a nuclear fuels manufacturing
company in Apollo, PA where a colleague asserted
that variously rated diodes were all made on the
same line. They were screened for breakdown voltage
looking first for devices that would function as
1000 volt devices. When the order for 007 parts
was 'filled', the next screen was for the lower
voltage part with the lowest breakdown would
be marked 000.

Over the years, production variability went down
to the point where virtually all parts would make
the cut for 1kV parts. But rather than upset the
legacy apple-cart, they continued to market the
lower voltage part numbers . . . which were in
fact 1 kV devices.

Somewhere around here I've got a 2 kV power
supply. It would be interesting to see just how
far one can push the modern LV parts . . . but
that ain't happ'ng soon . . .


Bob . . .


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