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High charge current on startup

Peter Costick

Well Known Member
Hi

I have noticed in recent months that on start up my charge current reads high, for example 25 amps. The ammeter is configured to measure charge into the system, that is if the engine is not running it reads zero.

As I sit there warming the engine the charge declines over say 5 minutes to a normal amount, say around 11 amps. If I switch power loads such as AP servos, landing lights and such on and off the reading responds accordingly.
When I check the current draw for devices listed on the VPX, and switch them on and off, there is nothing suggesting a large draw for any item.

I suspect then this could be an alternator or battery related issue. The battery is an Odyssey pc680 which is about 4 years old and still spins the engine over very well when starting. The alternator is a 60 amp Plane Power unit and certainly seems to keep the battery charged.

I have had the cowls off and looked for any loose connections or tell tale signs but so far I have seen nothing.

So my question to those in the know is ....what do you think this could be?

Thanks

Peter
 
Sounds normal to me. Your voltage regulator is responding to the voltage drop caused by the engine start, and therefore replenishing the battery to a full charge. Once that is achieved, then your ammeter should indicate the actual equipment draw.
 
This sounds correct

Remember that the VP-X is only accounting for devices that have their current run through them. If you ammeter is measuring alternator output (it sounds like it is) then the difference between the ammeter current and the VP-X reported current is the amount of current going into your battery.

One way to solve this mystery is to put Amploc KEY100 hall effect sensors in and wire them to whatever EFIS you're using. You can have one go from alternator to the battery, and battery to VPX. You can then see the whole picture in one place.

But I don't see anything wrong with what you've posted. Your alternator is charging your battery after a big discharge event of starting your engine.
 
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