Recently had a bunch of paint work done on my volvo TAMD-74P EDC engines. The alternators were removed as were several other components as part of the process. After reassembly, I'm getting battery alarms at the helm and I'm only seeing 12-12.5V when running without the battery charger on. The alternators have a terminal labeled "61" that should have 12v applied to it to energize the alternator. I've heard folks refer to it as an exciter wire. However, I do not see any meaningful voltage on this wire when the engine is on and running when measured between the 61 post and the negative on the starter. I've traced the wire and it runs to the black junction box on the engine and then up to the flybridge. After that I lose track because the wire seems to change color somewhere in the harness connections. Does anyone know where this wire would be connected? Some folks say it would be connected to the warning light panel, but somehow it's gotta have 12v on it. I'm trying to figure out where the disconnect is. I'm hoping theres just a blown fuse up there somewhere that I haven't found yet. The boat is a 2000 42' post SF. Any further troubleshooting suggestions would be appreciated. I'm in the Bahamas right now and would like to get this sorted before we cross back.
Does it charge when that exciter wire is jumped to the positive post? I did not realize the alternator was removed for painting. Is the case of the alternator making good (ground) contact with the block?
I tried connecting the positive alternator post to the “61” exciter post with a 14 ga alligator clips jumper and it flashed, insulation caught fire, and incinerated the jumper wire all in about 2 seconds. I’m not sure if the alligator clip grounded against the back of the alternator or what but it was…dramatic.
Ok here are some measurements from the port side, which does not have house loads. Battery charger off. 12.66V from positive to negative alternator post 12.6V from alternator positive to engine ground (bolt head) 13-13.1V from alternator positive to “61” 450mV (0.45v) from “61” to engine block bolt/ground so, it seems the “61” wire is at a 0.45V lower potential than the engine ground. I should note I also see that ~0.45v potential difference between engine ground and the 61 post when the engine is off/not running
Please post a pic of your alternator back. Point out what you think is the 61 wire. Late Monday night, have a note in to my VP tech just now. A pic may help. ,rc
sorry this took so long we were away from Internet for a while. I got the email and am studying it. Much appreciated
That pic is messed up. I believe the ground strap is on your post 61 connect and your brown (exciter?) is on the negative post.
I’m so embarrassed. From the angle I was looking I couldn’t see the “-“ and the “B” looked like a D. I pulled the wires off so I could see the labels better and you are indeed correct the exciter and negative wires were swapped ever since the guy painting the engine reinstalled it - and did both the same (wrong) way I’m gonna go hire someone to punch me in the face.
My greatest fear, the alt tried to bring up post 61 to 13.5 volt and fried&died in attempting so. So if it still does not work, get back to us.
Don't be so hard on yourself, I.ve done waaaaaay dumber things with waaaay worse outcomes. I could write a book.
Ok swapped the wires. Stbd side appears to be fixed - seeing 13.9V with the battery charger off. Port side no change. Still not seeing 12v at the exciter, even with the wires connected, and alternator sitting at 12.6v battery voltage with engine at 900 rpm. More troubleshooting to go there. If the alternator is indeed fried, I have a good spare on the boat. But I’d like to see 12V at that exciter wire - seems like I’d get that even if the alternator was bad, unless maybe there’s a ground internal to the alternator that is now fried? To be fair to myself, the ding dong who swapped the wires also installed the alternators upside down. So it looked more or less right, and I couldn’t read the labels.
Ran all day today and never saw above ~12.5v on the port engine. Battery alarm on the whole time. But great news that my stbd side is now running great - 14V all day! And that’s the side with my house loads so that’s the more important side.
Update - port alternator is fried as a chicken. I disconnected the 61/exciter wire and connected the alternator 61/D+ terminal directly to the + terminal of the start battery. Cranked the motor and ran it up to 1200 rpm. Never went above 12.5V. Came down and found the engine room smelling of electrical burning. Alternator was very hot and could see a bit of smoke with my flashlight. Before I shut down I measured 12.5v between my new “exciter” wire and the negative alternator terminal. I have a new alternator to install but I’m nervous about installing it without knowing the reason why the original exciter wire wasn’t working. Should I just go ahead and put the new one on? I don’t want to fry another $900 alternator
Yep, put the new one on. Ensure all is correct before turning the battery back on. The fried alt gave its life trying to make electricity higher than ground level. Send the dead alts to me when you return stateside. I have had some luck fixing these things. No telling what remains in my trusty miracle (Junk) boxes.
New alternator is on the port motor and I’m seeing 14.3V and 1000 rpm. So seems I have two healthy alternators again. Thanks for the help folks. I do possibly have a new problem emerging though, will start another thread for that.
