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A brown-out alternative?
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user9253



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PostPosted: Sat Oct 13, 2018 10:44 am    Post subject: Re: A brown-out alternative? Reply with quote

No, the relay is not energized all of the time. There is no junction where the wires cross. The diode blocks current from the left and the open switch blocks current from the right side. The only way to energize the relay is by closing the switch. The relay drops out when the push button switch is released.

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zwakie



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PostPosted: Tue Nov 20, 2018 5:25 am    Post subject: Re: A brown-out alternative? Reply with quote

I like this approach very much for all the reasons Bob mentions in is opening post.

I would have expected a relay 'solution' could be even simpler than that: I would expect no more than what I have drawn up quickly as in attached schema.

I am however struggling to understand the way Bob has wired the S704, so please enlighten this not-so-electro-savvy-person: what is/are the fundamental difference(s) between Bob's schema and what I have come up with?

I suspect it has to do with the timing aspects mentioned, but don't see why 'my' lesser-component approach would not take care of those.


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PostPosted: Tue Nov 20, 2018 6:19 am    Post subject: A brown-out alternative? Reply with quote

At 07:25 AM 11/20/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "zwakie" <mz(at)cariama.nl>

I like this approach very much for all the reasons Bob mentions in is opening post.

I would have expected a relay 'solution' could be even simpler than that: I would expect no more than what I have drawn up quickly as in attached schema.

I am however struggling to understand the way Bob has wired the S704, so please enlighten this not-so-electro-savvy-person: what is/are the fundamental difference(s) between Bob's schema and what I have come up with?

I suspect it has to do with the timing aspects mentioned, but don't see why 'my' lesser-component approach would not take care of those.

Yes . . . timing. (1) You want the e-bus to be
'boosted' BEFORE the starter current begins
to flow and (2) remain boosted until AFTER
the starter current is interrupted. We're
talking tens of milliseconds here. The working
hypothesis: the S704 wired as shown will offer
a substantial drop-out delay (instigated by the
catch diode on the coil). Hence it provides the
necessary physics for condition (2).

I'll confirm this with an experiment on the
bench but I think the hypothesis is sound.



Bob . . .


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user9253



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PostPosted: Tue Nov 20, 2018 6:20 am    Post subject: Re: A brown-out alternative? Reply with quote

Marcel,
You are right about the timing. The purpose of the diode between the downstream side of the start switch
and the DC-DC converter is to conduct instantaneous power during the time that it takes the relay to close.
The purpose of the relay is to provide a delay opening the circuit to the DC-DC converter.
If you want to simplify the circuit, leave out both the diode and the relay and connect the DC-DC converter
in parallel with the starter contactor. As soon as the start button is pressed, the DC-DC converter will be energized.
The pilot is not going to let go of the start button until the engine starts. Once the engine has started,
even for a second, the battery voltage will be above 10 volts. Thus brownout protection will be no longer needed.
What do you have to lose by trying it? If it doesn't work, no harm is done. There will be brownout just like before experimenting.
I suggest that the E-Bus switch common pole be connected to the E-Bus so that either the DC-DC converter
or battery is selected, but both can not be connected together at the same time.


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PostPosted: Tue Nov 20, 2018 6:23 am    Post subject: A brown-out alternative? Reply with quote

At 07:25 AM 11/20/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "zwakie" <mz(at)cariama.nl>

I like this approach very much for all the reasons Bob mentions in is opening post.

I would have expected a relay 'solution' could be even simpler than that: I would expect no more than what I have drawn up quickly as in attached schema.

I am however struggling to understand the way Bob has wired the S704, so please enlighten this not-so-electro-savvy-person: what is/are the fundamental difference(s) between Bob's schema and what I have come up with?

I suspect it has to do with the timing aspects mentioned, but don't see why 'my' lesser-component approach would not take care of those.

Yes . . . timing. (1) You want the e-bus to be
'boosted' BEFORE the starter current begins
to flow and (2) remain boosted until AFTER
the starter current is interrupted. We're
talking tens of milliseconds here. The working
hypothesis: the S704 wired as shown will offer
a substantial drop-out delay (instigated by the
catch diode on the coil). Hence it provides the
necessary physics for condition (2).

Oops, hit the send too soon.

The diode around the S704 goes to condition (1).

The diode in series with the output from the
boost module goes to our lack of knowledge as
to how well the boost module tolerates
'back feeding' when not being used. It may
not be necessary but it doesn't hurt anything
either. The extra diode is already part of our
old friend, the diode bridge rectifier.

I'll confirm this with an experiment on the
bench but I think the hypothesis is sound.



Bob . . .


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user9253



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PostPosted: Tue Nov 20, 2018 6:33 am    Post subject: Re: A brown-out alternative? Reply with quote

Depending on the architecture of the DC-DC converter, a diode in series with its output may or may not be needed.
I assume that the converter changes supply voltage to AC, transforms it to a higher voltage, then rectifies
and filters the AC to change it back to a higher voltage DC. The rectifiers should block reverse current flow.
But assumptions can be wrong.


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zwakie



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PostPosted: Tue Nov 20, 2018 7:23 am    Post subject: Re: A brown-out alternative? Reply with quote

Thanks Bob and Joe, thanks for your (very) quick replies Wink, much appreciated!

So, let me rephrase to see if I understand the workings of Bob's schema correctly:

- the diode across the coil makes sure the relay opens tens of milliseconds later than opening up the start switch, hopefully the voltage on the battery by then has gone above brownout voltage (and you can replace this diode by a capacitor to increase the delay if so required);

- the other diode in the line providing instantaneous power to the DC/DC converter is there to make sure no electrons can reach the starter connector after the start switch has been opened.

Joe, thanks for pointing out my oversight of connecting the DC/DC to the E-Bus Switch common.

And for the two diodes: will any out of the 1N... series do?


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PostPosted: Tue Nov 20, 2018 7:31 am    Post subject: Re: A brown-out alternative? Reply with quote

Which would then be integrated in my schema as shown below.
Any flaws with that?


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PostPosted: Tue Nov 20, 2018 8:39 am    Post subject: Re: A brown-out alternative? Reply with quote

The main purpose of a diode across the relay coil is to short out induced voltage being generated by the
collapsing relay magnetic field. Without a diode or other voltage snubber, high voltage can arc across
the contacts of the controlling switch, eventually damaging it. I would not replace the diode with
a capacitor. Any arc suppression diode capable of conducting 1 amp or more will do.
The diode in series with the DC-DC converter should be rated at least 10 amps.
There is no need for two separate circuits and fuses.
Regardless of one or two circuits, the fuse(s) needs to be able to handle the DC-DC converter current.


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PostPosted: Tue Nov 20, 2018 9:39 am    Post subject: A brown-out alternative? Reply with quote

At 10:39 AM 11/20/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

The main purpose of a diode across the relay coil is to short out induced voltage being generated by the
collapsing relay magnetic field. Without a diode or other voltage snubber, high voltage can arc across
the contacts of the controlling switch, eventually damaging it.

Actually, a capacitor COULD be used to effect
drop-out delay per the t=rc constant of the
capacitor + coil resistance. But you would still
need a series diode to isolate the coil/capacitor
combo from the voltage source. A diode will do the same
thing per t=l/r but MAY prove to be too short.
The bench testing will deny/confirm the hypothesis.



Bob . . .


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zwakie



Joined: 03 Aug 2009
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PostPosted: Tue Nov 20, 2018 12:47 pm    Post subject: Re: A brown-out alternative? Reply with quote

user9253 wrote:
The main purpose of a diode across the relay coil is to short out induced voltage being generated by the collapsing relay magnetic field.
Sure, I did not mention that as that seems obvious to me, but good to add as a clarification. Thanks!

user9253 wrote:
Any arc suppression diode capable of conducting 1 amp or more will do.
Okay.

user9253 wrote:
The diode in series with the DC-DC converter should be rated at least 10 amps.
Yes, I can see why... (an even higher current rating might be required though, depending on used DC/DC converter type and battery voltage drop when starter engine spins up)

user9253 wrote:
There is no need for two separate circuits and fuses.
You are right, having thought about it a bit more I even think it is not a good idea to use two fuses as there is no way of knowing during preflight checking if one of the two fuses was blown, so you would not know that the circuit can only carry half the design current. Better to go with an XOR type of design...

user9253 wrote:
Regardless of one or two circuits, the fuse(s) needs to be able to handle the DC-DC converter current.
Sure enough (as do the wires Wink ).
Thanks again Joe for further explanations.


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PostPosted: Thu Nov 22, 2018 1:55 pm    Post subject: Re: A brown-out alternative? Reply with quote

One question as there's too many different types of diodes and I'm having trouble finding what I need: any suggestions for what type of diode is needed for the arc-suppression high-current rating line ? If you could provide one brand and item number to point me to the right type that would help me on my way big time.

Thanks!


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PostPosted: Thu Nov 22, 2018 2:48 pm    Post subject: Re: A brown-out alternative? Reply with quote

How about 1N5400
Mechanical strength of the wire leads is more important than other
characteristics. Arc suppression diodes are connected with the banded end
towards positive. The only time that they conduct is for a split second when a
coil is de-energized. Even a 1N4148 would probably work if they were not so
frail.


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PostPosted: Thu Nov 22, 2018 3:24 pm    Post subject: Re: A brown-out alternative? Reply with quote

Thanks Joe!

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PostPosted: Sat Nov 24, 2018 2:30 pm    Post subject: A brown-out alternative? Reply with quote

At 04:48 PM 11/22/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

How about 1N5400
Mechanical strength of the wire leads is more important than other characteristics. Arc suppression diodes are connected with the banded end towards positive. The only time that they conduct is for a split second when a coil is de-energized. Even a 1N4148 would probably work if they were not so frail.

In fact, ANY of the 1N54xx series is fine.
5400's may be harder to find than say,
a 1N5406.






Bob . . .


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PostPosted: Tue Dec 11, 2018 2:08 pm    Post subject: Re: A brown-out alternative? Reply with quote

I received the last bit today (DC/DC converter) and had some time to kill this evening, so I built the circuit and tested it successfully on the bench.

I used a Ripca 2152C for the relay and this little critter as the buck-boost converter: https://www.ebay.ca/itm/6-35V-to-1-35V-DC-DC-Buck-Boost-Charger-Power-Converter-Module-With-AluminumSG-/123523715069?oid=112837380675 , along with the diode(s) previously recommended.

It will be a little while before I reach the point with my panel upgrade to glass before I can confirm it really prevents a brownout. I will report back when the time comes (hopefully in 2-3 weeks from now).


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PostPosted: Wed Dec 12, 2018 4:32 pm    Post subject: A brown-out alternative? Reply with quote

At 04:08 PM 12/11/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "zwakie" <mz(at)cariama.nl>

I received the last bit today (DC/DC converter) and had some time to kill this evening, so I built the circuit and tested it successfully on the bench.

I used a Ripca 2152C for the relay and this little critter as the buck-boost converter: https://www.ebay.ca/itm/6-35V-to-1-35V-DC-DC-Buck-Boost-Charger-Power-Converter-Module-With-AluminumSG-/123523715069?oid=112837380675 , along with the diode(s) previously recommended.

It will be a little while before I reach the point with my panel upgrade to glass before I can confirm it really prevents a brownout. I will report back when the time comes (hopefully in 2-3 weeks from now).

Excellent!



Bob . . .


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PostPosted: Thu Jan 03, 2019 3:15 am    Post subject: Re: A brown-out alternative? Reply with quote

As promised: I have now tested my little circuit it in-situ on the plane, and I can confirm that I no longer have brownouts and cannot observe any ill effects.

I do not have the tools to do detailed measurements on the timing aspects, current back-flow and such, so I cannot report on that part. I do feel pretty confident that this design will meet my objectives though, time will tell...


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PostPosted: Thu Jan 03, 2019 7:08 am    Post subject: Re: A brown-out alternative? Reply with quote

Good work Marcel.

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PostPosted: Thu Jan 03, 2019 8:22 am    Post subject: A brown-out alternative? Reply with quote

At 05:15 AM 1/3/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "zwakie" <mz(at)cariama.nl>

As promised: I have now tested my little circuit it in-situ on the plane, and I can confirm that I no longer have brownouts and cannot observe any ill effects.

I do not have the tools to do detailed measurements on the timing aspects, current back-flow and such, so I cannot report on that part. I do feel pretty confident that this design will meet my objectives though, time will tell...

--------
Marcel Zwakenberg
Europa XS TG || 912ULS || PH-SBR


Thank you for advancing this idea and
sharing your findings!



Bob . . .


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