I'll start at the beginning.
starter:S114-303A 1.2kW 12v
Since I got the boat about a year ago I've often had to hit the start button a couple of times before the starter would engage, but when it engaged it did so strongly and the engine
started reliably. When it didn't engage I could hear a "click" (I know know this is the solenoid engaging), but 0 engine turnover. When it worked there was a solid turnover and the engine would start w/o much trouble. No in-between.
A couple of times now I've tried to start the engine after a sail to return to dock
and I would just get the solenoid click and nothing else. I had an ancient "dumb" charging
system and the batteries came w/ the boat and I didn't know the history
. Being fairly new to things I suspected the batteries were weak and replaced the charger
and the batteries, but continued to have the same trouble (though I don't regret swapping them out anyway
After doing more research
I realized the symptoms were very much pointing at the starter/solenoid. Since I could hear the click of the solenoid every time it must not be engaging the starter reliably. I took out the starter/solenoid and had it rebuilt and put it back in. I held my breath and pressed the button and it started instantly!.... but I tried it a minute later and it was intermittent. I just got lucky on the first one (sometimes that happens).
I got out the multimeter and started measuring things. I have some background in electronics
, but not much on engines so I know enough about electricity to get myself into trouble, but not much about how the parts
I focused in on the inputs to the starter solenoid. I'll sum up what I think are the interesting measurements/experiments:
* If I use a screwdriver to short the low current
exciter input on the solenoid to the high current
input that comes from the battery
the starter engages 100% reliably.
* If I get the system in the state that the starter button is pressed, the solenoid has "clicked" but the starter isn't engaged I measure ~6v from the negative high current output of the solenoid and the low current exciter input of the solenoid. I measure 11v at the input to the ignition switch. This doesn't look good.
* If I turn all the batteries off at the DC panel and measure resistance between the input to the ignition switch and the exciter input to the solenoid I get ~.1ohm. Seems like it's not a loose/bad connection.
* If I disconnect the low current exciter and press the starter button I measure ~13v on the (disconnected) low current exciter input. (since there's no load I'm seeing the battery
directly which is being float charged. This tells me there's no short to ground since with no load I see the full voltage.)
* If I use the 10A current setting on my multimeter and measure the current going into the "low current" exciter input on the solenoid I see a brief reading of 16A on the meter and then the fuse blows. The wires involved aren't any bigger than 12AWG so this seems really suspicious. I'm having trouble finding out just how much current should be flowing into the exciter, but this seems like way too much to me.
My conclusions from that evidence:
The solenoid is drawing too much current into its exciter input which is dropping the voltage down causing a weak activation which keeps it from delivering enough power to the starter to engage it.
I don't know enough about how these parts
are supposed to work to know whose fault that is. I just had the starter rebuilt, so it seems odd that it would be at fault, but I don't see what else could cause it to draw so much current into its exciter input...
1. How much current should the starter exciter input draw?
2. If it's normal to draw >10A why are the wires sized as small as they are?
3. Is the >10A just inrush current? (I don't think so since the 6v reading at the exciter input stays for at least several seconds before I stop pressing the switch)
4. What could cause the starter to draw so much current through its exciter input? Anything other than the starter itself?
Thanks! This one is a bit of a head
scratcher for me...