After becoming becalmed a number of miles from home port I discovered to my dismay that both batteries were no longer capable of starting the engine. The battery 'test' meter on my electrical panel had given up the ghost before I bought the the boat, but I had never bothered to replace it. Big Mistake ! On eventually getting home after a lot of drifting, plus a tow until some wind was found, I set about trying to figure out all the things that contributed to the problem. One easy remedy was to be more careful with leaving the battery switch on the 'both' position to much.
The next was to replace the test meter on the panel, I installed a Xantrex link lite.
The first thing the link lite informed me of, within minutes of installing it, was that there was very little charging being done by the alternator. I had recharged the batteries, in the meantime, so did not expect to see much current flowing into the battery, however, two things concerned me. The battery voltage with the engine running (at any rpm) was only 12.8 V and if I switched any additional load such as deck lights on (5A), the current reversed polarity indicating the battery was discharging rather than the alternator taking on the extra load, and stayed reversed,but slowly decreasing to about -1A..
My engine is a Volvo MD7 with an SEV Marchal 35 amp alternator. A pretty standard set up I think. I've removed the regulator from the alternator and brought it home to check out. On applying a dc voltage across terminals marked D31 (red) and D- (black) I find that the voltage on the field winding terminal DF (green) drops when the D31 terminal reaches (low and behold) 12.8 V. I think its supposed to switch at 13.8 to 14V depending on load, or close to it.
So the alternator is not particularly effective with so low a float voltage, and I suspect the regulator trip voltage is creeping down as the unit deteriorates slowly, leading to a greater chance of a problem when the operator stupidly leaves the mast head light on for five hours during the day. for example.
Anyway I pass my regulator findings on in case anyone else is on the slippery slope of a slowly deteriorating voltage regulator or can shed additional light on the issue.
Hopefully with a new regulator, the link lite, and a more disciplined approach to battery usage, (and probably the addition of a 20W solar panel sometime in the future) I'll not have to endure the ignominy of being towed in for a while.
A slow discharge !
Moderator: Jim Walsh
Although the logic may be sound, I believe you really need to monitor the current into the field, through the slip rings.
Although conceptually the voltage starting to drop is and indicator the actual excitation current could still be significant. I think this can be demonstrated if you think about the charge level after moderate discharge, the system does not respond with full charging current. I recently had an alternator issue with my Universal M18 and diagnosed the regulator by injecting a current into the slip rings via a power reastat.
IF you ultimately need an alternator, I have some recommendations I shopped around for best price
Although conceptually the voltage starting to drop is and indicator the actual excitation current could still be significant. I think this can be demonstrated if you think about the charge level after moderate discharge, the system does not respond with full charging current. I recently had an alternator issue with my Universal M18 and diagnosed the regulator by injecting a current into the slip rings via a power reastat.
IF you ultimately need an alternator, I have some recommendations I shopped around for best price
John M.
Smart Charger?
Balmar makes a great smart charger that just might help.
Take a look at their site and you just might get the answer
you need.
I have the 2020 Volvo and use a 60 amp Balmar with a smart
charger, and it works great.
On my old MD7A there was also a smart charger that was installed
by the previous owner. After approximately five years of use it
finally gave up the ghost, but it also worked great until it died.
Ken Cave
CD 28 Dragon Tale
La Conner, WA
Take a look at their site and you just might get the answer
you need.
I have the 2020 Volvo and use a 60 amp Balmar with a smart
charger, and it works great.
On my old MD7A there was also a smart charger that was installed
by the previous owner. After approximately five years of use it
finally gave up the ghost, but it also worked great until it died.
Ken Cave
CD 28 Dragon Tale
La Conner, WA
Voltage regulator was intermittent
Thanks for the suggestions. Just to close out this thread I tried finding a replacement regulator for the SEV alternator but they are no longer available except maybe e-bay. I bought a Balmar single stage regulator, the BRS 12T. Its about their most basic model. My batteries are wet cell and I don't run the engine long enough to warrant a complex charging profile, so basic is fine for me. It wires in very easily in place of the old regulator. I did not have a stator output on the alternator, so I left that wire off the regulator , the MD7a has a separate sender for the tacho any way.
Started her up and got a solid 14.2V on the batteries, with different loads switched in, e.g. deck lights, drawing 5A, even at idle speed still got 14.2V. The set voltage is adjustable on this unit so I may lower it a bit. The old reg was cutting in at 12.9 and could not support any additional load current. I'll keep an eye on it, but I think the problem is solved, for now at least.
Started her up and got a solid 14.2V on the batteries, with different loads switched in, e.g. deck lights, drawing 5A, even at idle speed still got 14.2V. The set voltage is adjustable on this unit so I may lower it a bit. The old reg was cutting in at 12.9 and could not support any additional load current. I'll keep an eye on it, but I think the problem is solved, for now at least.