Sunday, June 24, 2012

Controller / Alternator interaction SOLVED

Well, today I solved the funny ‘interaction’ issue between the TriStar MPPT controller and the mains alternator.  IDing the True Cause was made so simply once I dumped real-time data from the controller using a connected computer.  Most people who had commented back about this got it right, sort of. . . . Though  it was the controller going into Float Mode due to high charge voltage, what had bothered me was this reduced output would occur even when the batteries were down in charge (Vbat at say 14.3 while under heavy charging - receiving 195A from the mains alternator) –  I expected ALL sources to be in ‘bulk’ mode as we had not reached the terminal charge voltage of 14.6v (per Dyno-battery specifications for out house battery)

The issue was I had not wired up a remote Voltage Sense to the Morningstar controller – as that would require a not-so-simple pulling of yet-another-wire from the front of the boat to the back.   And even though I am using mcm373 cable for battery runs (mcm373 is two sizes larger then 4/0 wire);  195A from the mains alternator results in a almost 0.6v drop.   This was reflected back to the Morningstar causing it to see a higher assumed 'battery' voltage, cutting back back on delivered amps and even entering ‘float’ mode….

Example – while underway today I measured:
Vbat = 14.34v – per DMM (Link-10 shows 14.30v)
Valt  = 14.85v – Per DMM.
Aalt  =  195a  – Per clamp-on DMM.
Vmsc = 14.80v -  Per Morningstar internal reporting.

Morning Star had entered Float mode.

Without a remote sense wire the Morningstar can only see the voltage at the ‘common’ distribution point which starts with the actual battery voltage, and then includes the voltage drop over the mcm373 wire as a result of it carrying the heavy mains alternator current.  As opposed seeing only  the actual battery voltage.  (The mains alternator regulator was just fine, it already has a remote battery voltage sensing wire).

Lesions learned:
  1. Even if one uses BFA Wires (Big Fat A__) (mcm-373)- Lots of Amps still can cause a significant voltage drop.
  2. Don’t be a lazy bum, pull the remote sensing wire!!!

Oh well, guess will need to set aside a day to pull a cable.  Just need to decide how I can get it past the back of the washer without having to pull that out…

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