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Alternators - To Fuse or not to fuse - That IS the question

 
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kearney



Joined: 20 Sep 2008
Posts: 500

PostPosted: Sat Aug 12, 2017 8:41 am    Post subject: Alternators - To Fuse or not to fuse - That IS the question Reply with quote

Bib et Al

I have been reading with interest your monographs on fuses and circuit breakers. I had always thought that CBs were "modern" and fuses were "old school".

So this brings me to an alternator wiring question. Keep in mind this is based on the Z12 architecture with an electrically dependent engine - EFI/EI.

The questions is: why would I use a CB on the primary and backup alternator field circuits?

My rational for thing this is, if the alternator field circuit pops, something is wrong, likely with the alternator. With the Z12 architecture, the backup alternator should immediately come on line and keep me, the electro-goodies and the engine happy. Why would I ever want to push that breaker back in?.

If the backup alternator field CB then also pops, I would then think that something is very seriously amiss. Again, why would I ever want to reset that breaker.

In theory I would still have the battery to get me *somewhere* safely albeit with urgency.

Inquiring minds need to know.

Cheers

Les

PS: The above assumes that my post start checks confirms normal operation of both alternators.


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user9253



Joined: 28 Mar 2008
Posts: 1113
Location: Riley TWP Michigan

PostPosted: Sat Aug 12, 2017 2:11 pm    Post subject: Re: Alternators - To Fuse or not to fuse - That IS the quest Reply with quote

If you are using Z-12, neither of the alternator primary "B" leads have circuit breakers. One has an ANL fuse and the other has a fuse link. I believe that Bob now recommends fuses instead of fuse links. Regardless, I would use a 30 amp fuse for the smaller alternator "B" lead. The purpose of those fuses is to protect the battery and wires from a short circuit, NOT to protect the alternators. Alternators limit their own current. They are not capable of putting out much more than their rated current.
Some crowbar types of over voltage protection circuits have been known to nuisance trip the breaker or fuse. Thus circuit breakers may be used so that they can be reset in case they nuisance trip.
Some builders have elected to not install over voltage protection. In that case, fuses may be used. Most modern avionics are rated for 10 to 30 volts. Over voltage might not be as much of a concern as it once was. On the other hand, if an Earth-X battery is installed, it will disconnect itself from the electrical system if the voltage goes high. Without a battery to help limit the over voltage, even modern avionics are at risk of being damaged.
I spoke with an Earth-X representative at OSH. She recommended that the aircraft electrical system have over voltage protection to protect avionics. The Earth-X battery has its own built-in protection.


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kearney



Joined: 20 Sep 2008
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PostPosted: Sat Aug 12, 2017 2:47 pm    Post subject: Re: Alternators - To Fuse or not to fuse - That IS the quest Reply with quote

Hi Joe

Thanks for the response. However, the CBs I was referring to are located on the alternator FIELD circuits not the B Leads.

I understand about the ANL fuses on the B Leads and plan to comply with the Z12 architechure in that respect.

Also, to follow up on your comment on a nuisance trip, if a trip occurs, resetting a breaker to confirm that it was indeed a nuisance trip may be risky. If the problem is genuine, resetting the breaker may cause smoke to come out of wires.....

If this logic is correct, then why wouldn't it be *better* to simply use 5A fuses rather than CB's for the Z12.

Cheers

Les


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user9253



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PostPosted: Sat Aug 12, 2017 4:45 pm    Post subject: Re: Alternators - To Fuse or not to fuse - That IS the quest Reply with quote

Les,
Sorry I misread your post and mistakenly interpreted "primary" as the alternator stator winding.

The field current on some alternators can be as much as 5 amps when under heavy load. Perhaps a 7.5 amp fuse would be better for the main alternator field. 5 amps should be good for the smaller backup alternator field.

Eric Jones at Perihelion Design sells over voltage protection that opens the alternator field circuit without shorting it to ground. No blown fuses or popped circuit breakers.
http://www.periheliondesign.com/lovm.htm


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email(at)jaredyates.com
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PostPosted: Sat Aug 12, 2017 5:14 pm    Post subject: Alternators - To Fuse or not to fuse - That IS the question Reply with quote

I use the breaker in lieu of a switch for the alternator field, should I
want to manually disconnect it. If I was to use a fuse, I'd have to also
install a switch.
On August 12, 2017 18:55:03 "kearney" <kearney(at)shaw.ca> wrote:

Quote:


Hi Joe

Thanks for the response. However, the CBs I was referring to are located on
the alternator FIELD circuits not the B Leads.

I understand about the ANL fuses on the B Leads and plan to comply with the
Z12 architechure in that respect.

Also, to follow up on your comment on a nuisance trip, if a trip occurs,
resetting a breaker to confirm that it was indeed a nuisance trip may be
risky. If the problem is genuine, resetting the breaker may cause smoke to
come out of wires.....

If this logic is correct, then why wouldn't it be *better* to simply use 5A
fuses rather than CB's for the Z12.

Cheers

Les


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=471799#471799



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email(at)jaredyates.com
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PostPosted: Sun Aug 13, 2017 7:27 am    Post subject: Alternators - To Fuse or not to fuse - That IS the question Reply with quote

You tell by resetting the breaker, once.
On August 13, 2017 11:09:00 "kearney" <kearney(at)shaw.ca> wrote:

Quote:


Charlie

Your comment on the OV nuisance trip is interesting. How does one tell if
the OV was a temporary, non-threatening excursion or if it is the result of
something serious? Resetting the breaker seems risky.

Dave's comment about being able to isolate the field field when ship's
power is on without the engine makes sense. In that case I wounder if a
switch and a fuse would be better. Pulling breakers seems a bit kludgy.

Cheers

Les


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=471817#471817



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JOHN TIPTON



Joined: 17 Sep 2006
Posts: 225
Location: Torquay - England

PostPosted: Sun Aug 13, 2017 8:10 am    Post subject: Alternators - To Fuse or not to fuse - That IS the question Reply with quote

And if the breaker was compromised during the initial indication !!!

Sent from my iPad

----x--O--x----

Quote:
On 13 Aug 2017, at 04:24 pm, Jared Yates <email(at)jaredyates.com> wrote:



You tell by resetting the breaker, once.


> On August 13, 2017 11:09:00 "kearney" <kearney(at)shaw.ca> wrote:
>
>
>
> Charlie
>
> Your comment on the OV nuisance trip is interesting. How does one tell if the OV was a temporary, non-threatening excursion or if it is the result of something serious? Resetting the breaker seems risky.
>
> Dave's comment about being able to isolate the field field when ship's power is on without the engine makes sense. In that case I wounder if a switch and a fuse would be better. Pulling breakers seems a bit kludgy.
>
> Cheers
>
> Les
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=471817#471817
>
>
>
>
>
>
>
>
>







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