Batteries not charging off the alternator

[jaysweet]

Well, I'm docked at the Cambridge Yacht Club. Solo docking at an unfamiliar T-head in a cross wind. It wasn't pretty, but nothing got hurt except a boat hook that didn't stay out of the way. Plugged in to shore power, and thankfully, the batteries are charging. So if my theory about not charging all day Saturday and Sunday (14 hours * 2 amps = 28 AH = 12% of my house bank used), even though we had shore power Saturday night, is correct, then I must have done something stupid like flipping on the wrong breaker on the AC panel. They are outlets, microwave, battery charger, and water heater. I know we used the outlets, so... whatever.

Anyway, after overnighting here, I've got 2 days to get back to Rock Creek (in the mouth of the Patapsco), with an anchor out overnight. But I'll start out fully charged, so this will work out.

 

[Hayden Watson]

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In the past, I noticed it does this when the key is turned to "off" on the panel, but that's not the problem. Then only wild card here is that I did just bypass the red and white starting circuit wires. Hard to see how that relates, but...

...

I am not sure what you meant by this statement. It could be that you inadvertently disconnected the alternator from +12v which would not let it bet energized. There is a small wire that must send 12v in order for the alternator to make power. It is not sufficient for it to be only connected to the battery on the big power lug that the charge it sent through.

 

[jaysweet]

Where does the cable from the starter go? Directly to the start battery or to the 1-2-Both Switch? Where does the cable from the alternator go? Directly to the Battery or to the Starter? or to the 1-2-Both switch?

The smaller wires are probably not carrying the charging current, unless they are the same size as the wire coming off the alternator. The red wire you disconnected and left disconnected, where is the other end? On the alternator maybe?

I'm pretty sure the huge red cable to the starter B+ goes to the 1-2-both switch. It has to, since it's dead when that switch is set to "off". The smaller red wire that I disconnected (and presumably bypassed) _should_ be the one that goes to the engine panel. If I got this wrong, then I've disconnected something that presumably had a purpose in life. I taped up the (hopefully disconnected) ends of the red and white behind the engine panel so they can't do anything nefarious. I could take the panel off and see if the red I taped up is still hot. If so, then I unhooked the wrong wire.

The small red that I left connected at the starter B+ goes somewhere mysterious. It's very hard to trace without untaping and unzip-tying lots of wires that run behind the starter. I should do this, but probably won't until I get home.

In any case, I think I have to put my further diagnostics on pause until maybe the weekend. I have to get the boat back home, and have a couple of days of medical stuff to deal with.

Again: thanks for your help, all!

 

[jaysweet]

I am not sure what you meant by this statement. It could be that you inadvertently disconnected the alternator from +12v which would not let it bet energized. There is a small wire that must send 12v in order for the alternator to make power. It is not sufficient for it to be only connected to the battery on the big power lug that the charge it sent through.

By "I did just bypass the red and white starting circuit wires", I meant that I just completed the fix for the notorious Yanmar starting problem, and I did it by running new 10 gauge wire from the starter to the engine panel. See this other posting: Yanmar electrical problem. .

Your statement that "There is a small wire that must send 12v in order for the alternator to make power." sounds like exactly what I was fishing for. If I left that small wire disconnected instead of the one I intended to disconnect (the one that supplies power to the engine panel), that might explain why I'm not charging.

This sounds like one of the few things I could do out here in the field that might lead to a fix. Just reconnect that small wire at the starter B+ lug. If it is, as you say, something to do with the failure to charge, it might fix it. If it is just the 12V power supply to the panel, it will put 12V on that wire behind the engine panel that is no longer hooked up to anything (but which I did tape over pretty securely with electrical tape). Probably no harm done in the short run.

Anyway: thanks for the input, and I hope you're right!

 

[jaysweet]

So I hooked up the small red (to the starter B+ lug) that I had thought was the panel 12V supply (which I bypassed). Turned off shore power. The Balmar was showing negative 5 amps, which means power was leaving the battery bank (probably to the fridge and a charging iPad). Started the engine: the Balmar showed plus 25 amps, which means the battery bank was charging off the engine. Problem solved! Thanks, Hayden! And thanks to the rest of you who commented.

I agree with Dave Lochner that it doesn't seem reasonable that this small red wire could be carrying the full current to charge the batteries, and indeed, that power should be coming from the alternator. But somehow, this small wire does seem to control the charging. I'll have a go at the wiring diagram and dig into this later. For the moment, the problem's solved, via a particularly easy fix.

When I get home, I'll take the _other_ small red and do a continuity check between the end near the starter and the end (now taped up) behind the engine panel. Then I can just leave it disconnected, knowing that it's just a spare, bypassed wire.

 

[Davidasailor26]

I’m not completely clear on what was connected where, but it sounds like you had accidentally disconnected the field excitation wire, and now you’ve reconnected it. The excitation wire is the one that brings current into the electromagnets in the alternator to start generating the charging current.

The excitation wire should be switched, usually by the key. If you’ve jumped it in a way that it’s on all the time it’ll be an extra parasitic draw on the battery when the engine’s not running, and it could overheat the field wires.

 

[jssailem]

Not sure whether you found the engine manual.

Yanmar 2GM20F Manuals

Yanmar 2GM20F Pdf User Manuals. View online or download Yanmar 2GM20F User Manual

www.manualslib.com

You'll find the electrical connections and an alternator output-voltage test in the manual.
Not all wires are meant to connect to the +B terminal.

each terminal has a distinct function, the alternator relies on all three working in perfect coordination:
·The field terminal energizes the rotor.
·The B+ terminal delivers generated power to the battery.
·The sense terminal feeds voltage information back to the regulator.

You're getting power to the battery. It would be wise to be sure what else is happening.

Here is another popular site with info on your alternator connections.

Alternators & Voltage Sensing - Marine How To

Regulator Sensing Voltage at Alternator End The topic of wiring a high performance alternator regulator, and doing it correctly, comes up a lot. One of the most confusing and often misunderstood areas, that can bite into your charge performance, is incorrect voltage sense wiring. This short...

marinehowto.com

 

[jaysweet]

I’m not completely clear on what was connected where, but it sounds like you had accidentally disconnected the field excitation wire, and now you’ve reconnected it. The excitation wire is the one that brings current into the electromagnets in the alternator to start generating the charging current.

The excitation wire should be switched, usually by the key. If you’ve jumped it in a way that it’s on all the time it’ll be an extra parasitic draw on the battery when the engine’s not running, and it could overheat the field wires.

With the reservation that I don't know much of anything about what "the field excitation wire" means, I suspect you've got it right. I think that's exactly what happened. But since I'm not completely ignorant wrt electronics (although the discerning reader may well have their doubts), I do plan on reading up on how the alternator charging circuit works after I get back from this trip. Nothing like personal experience to motivate you to learn something about how your boat/engine works.

Re. your last paragraph: I hooked up a wire that I had unhooked earlier. So it's hard to see how I could have introduced some unforeseen new variable into the equation. I unhooked the wrong wire, and I've hooked it back up again. Should be ok.

 

[colemj]

I’m not completely clear on what was connected where, but it sounds like you had accidentally disconnected the field excitation wire, and now you’ve reconnected it. The excitation wire is the one that brings current into the electromagnets in the alternator to start generating the charging current.

The excitation wire should be switched, usually by the key. If you’ve jumped it in a way that it’s on all the time it’ll be an extra parasitic draw on the battery when the engine’s not running, and it could overheat the field wires.

This. It explains everything you experienced, as well as how the circuit should not be wired.

You will have one or two small wires connected to the back of the alternator. These are part of the excitation circuit, and usually go back to the switch panel, where they are powered when you turn on the switch.

It sounds like somehow you bypassed this circuit. It should not be wired directly to 12V.

The circuit usually works through the charging warning light. When you turn on the key, 12V is supplied to the alternator excitation terminal through the charging warning light (and the light goes on). When the alternator starts, it provides 12V on the excitation terminal, which turns the warning light off. It is now self-excited and the field controlled by the internal regulator until the key switch is turned off again.

Was/is your charging warning light turning on and off like described before and after the changes you made?

Mark

 

[jssailem]

Was/is your charging warning light turning on and off like described before and after the changes you made?

Based on what the OP described I’ll bet a beer it is not. The reason I shared the links to his Manual. Too many what ifs. Not knowing how the circuit is connected opens the door to dangerous situations.