Amazing what a little air can do!

Well, the last few weeks have been super busy and we have a lot of blog posts to get uploaded once we have any actual Internet. Unfortunately WiFi is sparse and cellular sometimes works and sometimes does not. This post is being uploaded via satellite just so we can get something going.

While we were in Alaska and even a bit before I noticed that the alternator output fluctuates largely–outputting 100%, then 50%, then 100% again, etc. At the time I thought that it was normal, that the regulator reduces the power periodically as a way to help it monitor the charging progress. Over the last couple months however I came to realize that it can’t be normal, and in fact we have been getting very little charge into the batteries due to this constant fluctuation. I started monitoring the regulator’s display regularly to see if there was anything I could diagnose, and I tightened all the connections on the alternator finding the positive cable to be slightly loose.

The main thing I discovered through this close monitoring is that the alternator is running hot. Not just a bit hot, but HOT–over 100 degrees celsius. After just a little bit of motoring, the regulator indicated that the alternator temperature was 108C which is above the alarm limit of 107C set in the regulator. I check the belt tension (OK) and all of the settings (all OK) to no avail. I did find out that the temperature sensor was connected to the incorrect input on the regulator. We have a high output Balmar alternator and regulator setup, and our regulator supports two alternators, including temperature sensors for both. We have only one alternator and found that the temperature sensor for our one alternator was connected to the input for the second alternator rather than the first. I assume (though I have not confirmed) that the regulator will detune the alternator gradually based on it’s temperature, but that it wouldn’t be doing that for our alternator since the temperature data it is getting is intended for the second alternator that doesn’t exist. I corrected this when I checked the belt tension.

I shot an email to Balmar support about the issue and their reply indicated that the alternator is working too hard due to the size of our battery bank. Basically that when we increased the size of our battery bank, the alternator we have is no longer sized appropriately. They recommend that the alternator amperage to be at least 25% of the AH capacity of the bank. Since our battery bank is 600ah, the alternator should be at least 150amps, ours is only 100amps. Understanding that buying a $1500 alternator in Mexico is both challenging and expensive so Balmar also suggested that I find a way to get more air moving over the alternator while the engine is running.

Sitting on an anchor made it difficult to solve immediately but I did try setting the alternator to run at only 75% of it’s maximum. Unfortunately, as we motored the next day it didn’t seem to reduce the power output that much, nor did it reduce the temperature of the alternator, consistently hitting 107c still.

Luckily we finally made it to a city and I was able to pick up a 12v fan. I went with the 3″ version of the Rule 4″ In-line blower that already vents the engine compartment (which I replaced in October after realizing that it had not worked in the entire 3+ years we’ve had the boat). I mounted the 3″ fan on the side wall of the engine compartment blowing down directly onto the alternator. It is powered directly off of the alternator output connections but I added a relay to the circuit which is controlled by the power to the other fan. With this setup, the new fan only runs when the other fan is on, which is basically anytime the engine key is on.

With the new fan, I reconfigured the regulator for full output and monitored it while motoring several times. The alternator now stays under 100C, generally in the mid-80s celsius and the output power now stays at 80-90% amps without fluctuating to 50% any more. The last few times we’ve motored we have actually been able to fully charge the batteries, something that the engine has not been able to do for months.

I don’t really like the mounting, and I may try to put some sort of vibration isolating feet on it, since I can feel the fan vibration in the bulkhead outside the engine compartment, but in the meantime, one problem solved!


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