Too late maybe?
THe question about the alternator starting has been answered.
How much trolling vs running were you doing? Hours?
What is your trolling rpm?
What kind of loads are you running? How many amps do the loads draw.?
Fridge, stereo, lighting, freezer, and so on.
What I am leading up to is your alternators may have been working BUT and this is a BIG BUT, if the rpm is too low the alternator can only produce a small fraction of the RATED capacity., maybe as little as 5 – 10%.
A voltmeter as shown would have warned you something is amiss.
THis means the batteries may be taking the brunt of the load so they discharge.
You are not the only person to run into this. DO NOT assume that a 100Amp alternator produces 100A at all rpm. Most alternator only produce close to the rated capacity when they are turning at over 2/3 of their rated rpm.
That rated rpm is not the engines’ rpm. If the engines are rated for 3000 rpm MAX and the alternator is rated at 10,000 RPM , which is common then there is 3.3:1 ratio. If the engine is operated, trolling, at just above idle say 800 rpm then the alternator will be turning at 3.3 x or about 2400 rpm.
Way to low for the alternator to produce any where near its rated output.
If you don’t believe me look up almost any alternator mfgrs. output graphs
of amps out[put vs alternator rpm.
There are alternators that are wound to produce far more current at low rpm than the typical alternator supplied on most boats. You will find them with companies supplying EMT vehicles. Ambulances, fire trucks and so on as they often need to run a bunch of stuff with the engines just off idle.
Test your alternator at what ever engine rpm you operate at checking for amps output. If you don’t have a clamp on ammeter capable of reading DC amps then borrow one or borrow the buddy that does have one for a few minutes. But you need to know what the loading draws are vs the alternators output at what ever engine rpm you operate at.
*************I will add, quote********
I understand that #2 connects to the battery and #1 connects to the ignition in one of the pictures on this site it says use it if you want the alternator to turn on faster. Can someone elaborate on this? Like what are we talking about time or at a higher rpm?**********8
#1 – to overcome the low residual magnetism problem. THis connection strengthens the magnetic field almost instantly so the alternator will start charging almost immediately.
#2 – If I remember correctly and actually I don’t, I just realized, so I will almost bow out on #2. I THINK, THINK, it may be an external voltage sensing terminal. Many alt. have this now so rather that sensing the battery voltage at the alt., they now sense at the battery which can often be somewhat lower. Now the alternator knows to raise the output voltage to compensate. THe result is a faster and more complete recharge.
Got away from being lazy and looked it up. Yes, it is.
#3 – is for a tachometer drive signal.
However if the engine is basically idling there is no way that will make much difference.
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