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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