REFLECTOR: How to protect the battery bus

[Hiroo Umeno]

Thanks for all of you for your input.  I think I have a plan on how to proceed from here.

My current setup is that the battery's positive terminal connects to the master solenoid through the shunt and then the starter contactor connects to the master solenoid.

My short term plan is to change the order so that the master solenoid comes first, then the path forks in such a way that the starter contactor is connected directly to the master solenoid bypassing the shunt and the rest of the aircraft bus still is connected to the shunt so that I can get a reading on charge / discharge indication on my UMA ammeter.

My long-term plan is to replace the shunt with the non-contact current sensor that will be connected to the annunciator box Version 2 I am developing that will give textual display of system status through VFD.

Hiroo

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Douglas Holub
Sent: Saturday, February 17, 2007 8:44 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: How to protect the battery bus

I meant to say that I'll use a 200 amp fusible link at the 24 volt battery. I've got a hall effect sensor for measuring current. I don't think you can count on a shunt to blow very quickly (if at all) during an over current situation.

I'm a KISS believer, and if I don't need a component I don't put it in. The more parts you have, the more things can go wrong. But I figure that the starter is practically always used when the plane is on the ground, so if the fuse blows for whatever reason while I'm trying to start the engine, at least I'll already be on the ground.

Doug Holub
Top Door, FG w/ electric nose lift
----- Original Message -----
From: Douglas Holub<mailto:doug.holub at tx.rr.com>
To: Velocity Aircraft Owners and Builders list<mailto:reflector at tvbf.org>
Sent: Saturday, February 17, 2007 1:18 AM
Subject: Re: REFLECTOR: How to protect the battery bus

I'm planning on putting a 200 amp shunt right at the battery + terminal (24 volt system.) I've been reading that the big wire going from the battery to the starter isn't protected in certified aircraft, and there's not much metal in our airplanes to which it could possibly short, but I just feel better knowing that it would be virtually impossible for the battery to ever be able to discharge itself to ground (maybe after a crash?), which could easily get something hot enough to catch fire.

Doug Holub

----- Original Message -----
From: Keith Hallsten<mailto:KeithHallsten at quiknet.com>
To: 'Velocity Aircraft Owners and Builders list'<mailto:reflector at tvbf.org>
Sent: Friday, February 16, 2007 9:40 PM
Subject: Re: REFLECTOR: How to protect the battery bus

Hiroo,

Why is there a shunt in the starting circuit?  Starting will take several HUNDRED amps, and there's no need to measure them.  A shunt that will work at that range won't have much precision for normal electrical system currents.  What are you really trying to measure?  If you put a shunt in the alternator "B" lead you will measure what current the alternator is producing, which seems useful to me.

Keith Hallsten


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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Hiroo Umeno
Sent: Friday, February 16, 2007 11:56 AM
To: reflector at tvbf.org
Subject: REFLECTOR: How to protect the battery bus

Last weekend, I cranked the fickle Franklin one too many times.

(Yes, I am still trying to find out why it simply will not run...  Long story.)

On the third cranking, the voltage on the battery must have dropped sufficiently that the starter motor stopped turning the prop.  I probably left my thumb on the starter button a tad longer than I should have.

The shunt blew and the whole electrical system went (except the backup battery system that ran the instruments (glad to know THAT works well).

That got me thinking.  Shouldn't there be a CB or something protecting the starter line?  I've heard that the starter line is the only line that should NOT have a CB on.  Yet I've managed to fry the shunt.

Any thoughts?

Hiroo
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