REFLECTOR: Using the starter supply(+) wire as a charge wire

[Dave Philipsen]

Just an idea...you could still install an ammeter that only shows how 
much the alternator is charging into the system. It wouldn't ever show a 
negative indication (that is, how much the battery is being drained) but 
it could be helpful in indicating that your alternator is working. I 
think you could do that by installing the shunt between the alternator 
output and the starter/battery wire.

Or, you could even have your ammeter show both charge and discharge if 
you feel comfortable with allowing starter current to flow through the 
shunt. The ammeter shunt that came with my EFIS is a pretty hefty chunk 
of metal and I would imagine it could handle the brief, high current 
surge while the engine is starting. There would be a slight voltage drop 
there...possibly no more than if you had the normal firewall starter 
contactor though. You could do that by installing the shunt between the 
positive post of the battery and everything else. Another variation on 
this would be to actually use your firewall starter contactor as a 
"short" across the shunt only while the engine is starting thus 
temporarily lessening the voltage drop across the shunt and providing 
more power to the starter.

Just thinking aloud here...others may have comments on why they don't 
think this is a good idea but I don't see anything terribly wrong with it.




Terry Miles wrote:
>
> Hi all,
>
> I thought the sanding would never end, now I can’t seem to get out of 
> the electrical design stage and actually start wiring this thing. Here 
> is a topic I want to run by the group to see if anyone has any 
> experience with this.
>
> I have a Grand Rapids EFIS and engine monitor system. The EFIS gives 
> digital voltage readout of the V that it is sensing in its own input 
> power line. Additionally there are 3 available power inputs so I will 
> have a 2^nd and even a 3^rd Voltage taps elsewhere (like a hot batt 
> bus) if I want it at the expense of using up my user defined auxiliary 
> inputs. I mention this because if I go this route, I will _not_ 
> install an ammeter. I can’t easily wire in an ammeter now if I have my 
> #2 starter supply wire as a charging wire too.
>
> I talked w/ Skytec starters today. On their web site they talk about 
> an alternative wiring scheme that eliminates the normal firewall 
> starter contactor which is required on certified span cans. I can wire 
> my starter button directly to the coil/contactor that is bolted to the 
> Skytec starter instead doing the conventional route of contactor in 
> the nose that then ports juice to the Skytec contactor and its starter 
> motor.
>
> Other facts: The control to alternator output is a manual on/off 
> switch on the overhead. I will wire in a 60a current limiter between 
> the B-lead and the starter lug as described below.
>
> I will wire the B lead of the alternator over to the now dead Skytec 
> input lug and use it like a terminal to the #2 starter (+) wire in the 
> utility duct and will now carry juice back to master relay and from 
> there to normal bus distribution. .
>
> This is not a new idea. Nuckols mentions it in chapter 7 is his book 
> on how to home builts. The Skytec tech support guy saw nothing wrong 
> with it, as long as I made sure to cut the jumper wire that now exists 
> between that input lug and a (+) jumper to their contactor coil.
>
> Am I missing anything? Is anybody running this way?
>
> Thanks,
>
> Terry
>
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-- 
Dave Philipsen
Velocity STD-FG
N83DP