| Recommended alternator charging voltage [message #358580] |
Sun, 13 September 2020 21:03  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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Senior Member |
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So, on the way (still in the driveway) to take to coach in for transmission problems, the GEN light is on. Get out the voltmeter and I have near zero volts at the input to the isolator. So I start the Onan and let the combiner do its job feeding power to the engine. I tell the shop to replace the alternator, but I'll keep the old one to repair and keep as a spare.
So when the coach is fixed and ready to roll, I picked up the coach and head back home. Its raining so I pull ON the headlights and flip ON the electric wipers. I see from the corner of my eye an orange light coming ON in the DigiPanel. Focusing on it, its the battery voltage flipping from Orange/Green to Orange only with the intermittent wipers. So I know my battery voltage is less than optimum.
Back home I check the voltage at the input of the isolator = 13.3 and output = 12.6V. So I check the output of the alternator is 14.5V. More tests show the alternator output is pretty much constant at about 14.5V even though the voltage sense is only 12.6-12.8V.
I repaired my old alternator (bad diode trio) and also replace the regulator with the same as is in it, a Transpro D101HD 14.8v. So I swap the old alternator back in. Now I get 15.6v at the isolator input and 14.8V at the isolator output. I checked the output of the alternator and its 16.5V, so I have about 0.8V IR loss in the alternator wire. I turn the headlights ON and it jumps to a loss of 1.2V. Checking the resistance per foot of #10 wire, that works out to about 100Amps, which I know cannot be right. So I decide to replace the alternator output wire. I used the old wire as a fish and found 2 junctions in the old wire. The new wire shows a loss of 0.2V which works out to 25Amp from the alternator which makes more sense.
I opened the new alternator and found it had a D689 regulator. A quick Google shows it to be a 14.5V one-wire regulator. The sense wire connection is a DUMMY! So be aware these things look the same, but what is inside may not be right. Even with the new wire... 14.5V - 0.8V (under load isolator loss measured 0.85V) - 0.2V (wiring loss) = 13.5V which is not enough to fully charge unless on a long trip.
SO, my question is... the D101HD regulator in my old alternator is 14.8V, so with voltage feedback it will try to keep the voltage at the battery at 14.8V approx. I think this is a bit high, but is the same regulator that was in it since 2008. I'm wondering if it should be maybe 14.3V. Or do the new regulators ramp the voltage down over time?
What say yea?
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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