(caution: The following is a technical blog which may be of very little interest to you if you aren't fix-it minded. I'll return to my regular fluff pieces tomorrow.)
Okay, I've got a problem and I just KNOW there's someone out there with the answer at their fingertips. Ever since I was in the Navy I've been doing electrical work and I think I'm reasonably good at it. I even basically taught myself how Programmable Logic Controllers work way back in 1985. So, I think I have an edge over the average joe trying to take care of his electrical issues. At least that's what I used to think. But I'm stymied. Here's my problem:
I have two battery banks. One is the house bank and serves all the electrical needs on the boat except for starting the engine. The other bank is the starting battery and it's only job is to start the engine. The house bank is made up of 4 Trojan T-105 6VDC golf cart batteries connected in series-parallel so that I essentially have 2 large 12 VDC batteries. This bank has a total of around 250 usable amp-hours available for running the lights, autopilot, bilge pump, refrigerator, watermaker, stereo, 2-way radios, fans, inverter for charging the computer and cell phones, etc. The starting bank is one 12 VDC battery with a humongous amount of cold cranking amps but not a bunch of reserve power.
The batteries are separated in use by a selector switch which, when ON, sends starting juice only to the starter and house juice only to the distribution panel. When the switch is in COMBINE, the two banks are connected together. This is in case the starter battery gets run down and the house bank is needed to start the engine.
To keep these batteries charged they are connected to the alternator when the engine is running, the 160 watt solar array all the time, and the Xantrex charger when we're connected to shore power or the Honda generator. The Xantrex charger can charge up to 3 banks individually. I can program it for the type and size of the batteries it's dealing with and each bank can have its own charging regimen.
When charging with the solar cells or the alternator, the batteries are combined through a Blue Seas Automatic Charging Relay (ACR). The downside of this set-up is that both banks are charged the same way even though they have different requirements. Also, the ACR can interfere with the "smart" features of the Xantrex charger which is why Blue Seas issued a technical paper suggesting the ACR be disconnected when a smart charger is in use. I've been following this advice for some time.
So what's my problem?
Well, the problem is that I cannot keep the starting battery charged. I'm not really sure when the problem started but it was before I bought the new starting battery. I was having the same problem with the pair of group 27s I used to use for starting. I figured back then that it was just because the batteries were so old, so I replaced them with a new battery.
Here's what happens when I'm charging with the smart charger: The charger checks the batteries and applies charging voltage according to the state of discharge. If the battery is really low, it starts with a BULK charge where the battery is receiving high current. At some predetermined point, the charger changes to the ABSORPTION mode where the voltage remains constant but the current declines. Finally, when the battery is fully charged, the charger enters a FLOAT stage where the charger continues to deliver a lower level of voltage to maintain the battery in the fully charged state.
Well, this is all fine and good on the house bank which works just like it's supposed to. But the starting battery is another matter. Even though the Link 20 battery status meter shows a -36.5 amp-hour deficit, the voltage on the battery is up around 13.65 VDC so the charger thinks it's just fine and applies a FLOAT charge. But, as soon as I push the starter button on the engine control panel, it's clear that the battery is NOT fine as it can't even crank the engine over once. And, as if that wasn't enough, even with the charger connected, by morning the amp-hour deficit will be -37.1 Ah. Obviously there is something using battery juice even when the engine isn't being started, but that isn't even the issue. The charger should have absolutely no trouble keeping up with this miniscule draw but ti doesn't. It just lets the battery keep draining.
And it gets even weirder. Okay, maybe the Xantrex smart charger isn't so smart, but what about the simple alternator, or the solar panels? We can motor for 24 hours with the alternator merrily running along and when we get where we're going, you think the battery will crank the engine? NO! How about the house batteries? Oh they're just fat and happy and showing a 0 Ah deficit. Which is good, don't get me wrong, but I wish the starting battery would be so cooperative.
Last week, while we were at anchor, I fired up the generator and turned on the Xantrex so I could "equalize" the starting battery. Equalizing is when you force a fairly high voltage (around 16.5 VDC) through the battery to dissolve the sulfates off the lead plates. This is a way of revitalizing a battery that has been chronically undercharged or is just getting old. Every hour or so you take a specific gravity reading to check the state of charge. When all the cells are reading correctly, the battery is charged and you can stop equalizing. This looked promising at first. The voltage to the battery was high and the amp-hour deficit started to fall. After about 3 hours, all the cells were reading good. My hydrometer isn't good enough to get an accurate specific gravity reading, but they were all in the middle of the green zone. The Ah deficit was still -26.4 or something but I decided I'd run the generator long enough.
Next day I tried starting the engine and got the anemic Rrr-Rrrr... of a nearly dead battery for all my efforts.
So, I can't seem to charge my starting battery. The only time I've had any luck was when I disconnected the leads from the battery and connected a standard 6A automotive starter to it for a few hours. The next day the battery was able to start the engine. Reluctantly, but it started. I'm trying that again tonight and watching the Ah deficit to see if it returns to 0. It's not a regimen I want to follow but it may provide another clue.
Oh, and before you suggest it: the Xantrex requires the battery to have a minimum Ah rating of 60. My starting battery is rated at 90 Ah if I remember right.
So c'mon folks, help a poor sailor out. I'm hoping there's an old battery hand out there that'll write in and tell me some not-so-obvious mistake I made that could be easily remedied. Right now I'm flat out stumped. And I don't like it one little bit.
Okay, I just checked the Link 20. With the automotive charger connected to the starting battery, with the positive lead from the battery disconnected (except the one to the Link 20), after less than a half hour of charging, the battery status is now (supposedly) fully charged with an Ah surplus of 0.1 Ah. That doesn't make any sense at all to me. The game is afoot, Watson. Just to add fuel to the fire, I just now reconnected the main positive lead, the one that goes to the starter, back up to the battery and left the automotive charger on. We'll see what that does. Just for the record, the Link 20 shows me that the automotive charger is charging at 16.15 VDC on "High" (6 amps). I switched it to "Low" (2 amps) which stared out at 15.30 volts bit quickly dropped to 15.10 and was looking like it was going to just keep slowly dropping. Switched back to high and it's maintaining between 16.10 and 16.15 volts.
Help me if you can, I'm feeling down.