REFLECTOR: How to protect the battery bus

Brian Michalk michalk at awpi.com
Sat Feb 17 09:47:32 CST 2007


If one is dead set against the hall effect sensor:

If one absolutely wants to measure current in this wire, use the wire 
itself as the shunt.  It has a resistance, that's why you get a voltage 
drop.

Don't like the sensing capability?  Install a smaller gauge wire.  It 
will be lighter and cheaper and more reliable than the equivalent 
shunt.  Don't like the voltage drop?  Why the #%R^% are you using the shunt?

Sid Knox wrote:
> Hiro, I am in Keith's camp here... I have never before heard of a shunt in 
> the hugh current starter circuit.  I can think of not one valid reason for a 
> shunt in this line.  Some of the posters have mentioned protection from 
> shorts... but that is not what a shunt is for.  It is no suprise the engine 
> cranks slow using a shunt with enough resistance to fry itself on two or 
> three hundred Amps.
>
> You say "The shunt drives the ammeter."  IMHO it makes no sence to attempt 
> to measure starter current with anything other than a Hall Effect, clamp-on 
> meter and that is only for diagnostics and has little utility as a cockpit 
> display.
>
> Sid Knox
> Oklahoma
>
> Velocity  173 RG  N199RS
> Starduster  N666SK
> KR2         N24TC
> W7QJQ
>
>
>   
>> From: "Hiroo Umeno" <humeno at microsoft.com>
>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>> Sent: Friday, February 16, 2007 4:35 PM
>> Subject: Re: REFLECTOR: How to protect the battery bus
>>     
>
>
>   
>> The shunt drives the ammeter.  In my case, even under the best of 
>> circumstances, the first
>> rotation after the starter engages is painfully slow.  It usually takes 
>> about 2 seconds for the
>> starter to get past the first compression stroke of the Franklin engine, 
>> then after that, it cranks fine.
>>     
>
>   
>> Last time, I held my finger on a bit too long hoping that the weakened 
>> battery can
>> still overcome the compression stroke ending up in a blown shunt.
>>     
>
>   
>> Hiroo
>>     
>
>
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