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B-lead protection

 
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aaaron(at)tvp.com.au
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PostPosted: Wed Jul 31, 2013 5:43 am    Post subject: B-lead protection Reply with quote

I'm finishing the wiring in my safari helicopter and need some advice re B-lead ANL or fuse. I'm using the skytec starter with built in solenoid with about 3 feet of number 2 wire going from the starter to the master contactor. I'm using a tractor style push-button starter switch and an externally regulated 40a alternator. Since I have no external starter contactor, do I need to run the B-lead from the alternator via a fuse to the master contactor or can I run it the much shorter length between the alternator and starter? If the former, I could mount the ANL holder on the firewall but I would have three fat wires (starter, B-lead and main bus) bolted to the master contactor. If I can just connect the alternator to the starter lead I can use an inline fuse holder. My questions are:
1. Where do I put the B-lead and fuse/ANL?
2. What size wire for the B-lead?
3. What size fuse/ANL?
4. Do I need to put a diode across the starter button and if so, which one and in what direction?
Thanks!
Allan


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nuckolls.bob(at)aeroelect
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PostPosted: Wed Jul 31, 2013 6:49 am    Post subject: B-lead protection Reply with quote

At 08:42 AM 7/31/2013, you wrote:
Quote:

I'm finishing the wiring in my safari helicopter and need some
advice re B-lead ANL or fuse. I'm using the skytec starter with
built in solenoid with about 3 feet of number 2 wire going from the
starter to the master contactor.

#2 is possibly overkill, #4 would certainly suffice
for your battery/starter wiring.

Quote:
Since I have no external starter contactor, do I need to run the B-lead
from the alternator via a fuse to the master contactor or can I run it
the much shorter length between the alternator and starter?

Take it to the starter.

Quote:
1. Where do I put the B-lead and fuse/ANL?

As close as practical to the starter but if
the fuse ends up in the middle of the wire run,
it's no big deal.

Quote:
2. What size wire for the B-lead?

8AWG is fine for 40A alternator.

Quote:
3. What size fuse/ANL?

I see Walmart is offering this fuse
in a 30A, which is plenty robust for
your alternator.

http://tinyurl.com/l6qbxsc

This is a miniature fuse for which you
can fabricate your own holder from a piece
of phenolic and some screws, nuts and washers
from the hardware store.

Quote:
4. Do I need to put a diode across the starter button
and if so, which one and in what direction?


Not ACROSS the button but from contactor side
of button to ground. Cathode connected to pushbutton,
anode to ground. Any of the 1N5400 series diodes
from Radio Shack are find. See:

http://tinyurl.com/l65nqnw

There was an AD issued against the ACS key-switch
some years back that put a diode across the switch . . .
completely ineffective.

http://tinyurl.com/l6qbxsc

Diode needs to wire across
the solenoid coil either at the switch as described
or on the contactor (probably not as convenient but
if you can put it there, that's good too.)

Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Wed Jul 31, 2013 12:11 pm    Post subject: B-lead protection Reply with quote

Quote:

2. What size wire for the B-lead?
3. What size fuse/ANL?


Here's a 40A MIDI style stocked by Digikey

http://tinyurl.com/mpudgxu

and a holder like this

[img]cid:7.1.0.9.0.20130731150249.020c51e0(at)aeroelectric.com.0[/img]

To mount it can be found here . . .

http://tinyurl.com/kcbyc79



Bob . . .


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donjohnston



Joined: 13 Dec 2009
Posts: 231

PostPosted: Thu Aug 01, 2013 5:26 am    Post subject: Re: B-lead protection Reply with quote

Quote:
Here's a 40A MIDI style stocked by Digikey

http://tinyurl.com/mpudgxu

and a holder like this

[img]cid:7.1.0.9.0.20130731150249.020c51e0(at)aeroelectric.com.0[/img]

To mount it can be found here . . .

http://tinyurl.com/kcbyc79


How do these compare with the ANLs that B&C sells? Other than being a LOT less money? Smile

Do they have a greater tolerance? Slower speed (of reaction)? Don't last in a harsh enviroment?


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nuckolls.bob(at)aeroelect
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PostPosted: Thu Aug 01, 2013 6:01 am    Post subject: B-lead protection Reply with quote

Quote:

How do these compare with the ANLs that B&C sells? Other than being
a LOT less money? Smile

Here's the data sheet on MIDI fuses

http://tinyurl.com/l985dtj

Here's the data on ANL . .

http://tinyurl.com/k7o3l3q
Quote:
Do they have a greater tolerance? Slower speed (of reaction)? Don't
last in a harsh enviroment?

The ANL has been around for about 80 years
and is still used in new design. Premier
was the last airplane we designed with a
majority DC power system in it. The distribution
panel contains a goodly number of the ANL style
limiters.

The MIDI's have roots in the automotive industries
where we have witnessed a continuous evolution of
designs. For example, cartridge glass fusses
got replaced by ATC plastics which in turn have
been superceded by the ATR micro fuses. All three
generations perform to their manufacturer's specs
and have been found suited to task in billions of
applications.

The ANL and MIDI are not drop-in replacements
for each other as you can deduce from their
performance curves. But the differences are
insignificant to our task. The advantage of
the more modern design is that they are made
in relatively large quantities on automated
machines for markets much larger than the
markets which nurtured the ANL devices.

Until recently (last 10 years or so) the
modern replacements for the ANL were not
as convenient to acquire. You could find
the fuses as after market service parts but
holders were more of an OEM item. But now
that Digikey has partnered with Bussmann
and Littlefuse to distribute them, procurement
is much easier.
Bob . . .


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