warning, this another geeky post, so if you are not interested in boat electrons, skip this one!
For those of you who have been following along, and yea, we need to post more often to e blog, you may remember the power issues we had coming down the coast from Seattle. Basically rough a combination of some corrosion on the battery terminals and a voltage regulator that went wonky (and we are not sure if one caused the other or not), we ended up frying the old house bank on Piko. Albeit this was an expense I figured we wouldn’t we wouldn’t have until later, Tyne bank was 4 years old and I knew it was going to have to be replaced at some point. Not going into details, the regulator started outing out too much voltage and fried Tyne batteries. They were replaced by Deka 8c12 batteries in the same size in San Francisco before we headed south.
Piko uses(d) J185 sized floor sweeper batteries when I bought her and that us what we replaced the failed batteries with. These are an industrial style 12v battery similar in design to a ‘golf cart’ style battery, but in a 12v configuration. They are 190 Ah at a 20hr rate, so with two of them in parallel, we get just under 400 ah total, or about 200 of that usable using the 50% rule.
Feeding juice into the banks is an ample power 120a alternator now being driven by a balmar mc-614 regulator. We also have about 300 watts of solar, a Kyocera kd135 and a smaller 40 watt panel in parallel being fed into a Morningstar sun saver MPPT controller on each side of the boat. This combination will output about 12-15a into the batteries down here in the sun. That is just below what the ‘specs’ say, but is about right when you temperature compensate for the conditions down here. We usually get this output from about 10am to 4:30 pm every day over e winter.
The last part of the system, which is what I believe, led to the early demise of our new batteries is the canters link 20 monitor. This is a little box that should tell us all e stats of the batteries, it had a current shut so we can monitor voltage, amps, and amp hours used on the batteries. I has been on the boat for many years and has worked great in our pre-cruising lifestyle.
Sadly, we found out the amp hr gauge on this unit doesn’t work well at all if you have any sort of renewable energy on the boat. We had been using the gauge to determine when we had to run the engine to supplement the solar on the boat. Basically whenever we got to around 40-50% of the battery capacity used, we would run the engine and get the batteries back up to 80-85% where the solar could trickle them back to 100 over the afternoon. This gauge has some logic built into that resets the Ah meter back to zero after it senses a charge. This routine works great for people who use a shore charger and it works pretty well in this configuration. The solar not he boat, apparently, tricks the unit into thinking a complete charge had occurred when it had not. Basically whenever the current and voltage flowing into the batteries stayed at a certain level for a certain amount of time, which on a shore power is a good measurement that the batteries have been recharged, resets the counter to zero. What I didn’t realize is that this same condition happens almost every day when charging using solar when the sun goes down. This meant that we had slightly, but repeatedly at times been undercharging the batteries.
We had noticed that out banks voltage, which is another measure of its charge, though harder to use since the only time it is accurate is after letting the bank sit for some time with no energy going in or out, was too low. Sadly on a boat like ours, the batteries are NEVER at rest for any period of time, so you have to use your best judgment and see what devices are turned on at the time and make an educated guess as to what e voltage means. This is expressly why I bought the battery monitor, but I was lulled into a false sense of accuracy of it ah calculations. What this all means is we would check e batteries in the evening and see -4 ah which to us, meant we had used 4 Ah that evening after the sun when down. A morning, we might have been 100Ah down, though the meter reset when the solar had only put in 80Ah that day. So in reality, we were 24Ah down, not 4. Over time, this built up and hurt the batteries.
Batteries don’t like being disbarred too deeply. Car batteries, which are designed to crank e engine hard in cold weather, might only last a dozen or so z50% discharges. The deep cycle batteries we use on boats should last longer. I don’t have the specifics for the 8c12’s we have now, but they should last somewhere around 4-550 cycles to 50%. If only discharged them to 80% capacity, they might last over a thousand, and if brought them down to 25% only 100. Since these batteries are about 3 months old, they have about 100 cycles on them. Most were less than 50%, but there were a few days before thanksgiving that their voltages got down to 11.7 or so, which is pretty low. Now our voltages drop down to 12.1 after about 50Ah have been drawn, which is showing that our bank is only running at around 25% of its theoretical capacity.
Our solar controllers have a nice logging function on them, so not only can we see how much each string of panels is putting into the batteries over time, we can also see out voltages both highland low over time as well. This is where i saw the really low voltages the few days before thanksgiving. Sadly I was completely unaware that we we’re killing out batteries at the time since I was going off the link meters ah meter and though all was well.
We tried a single night in a marina a few days back in Ixtapa to try and run an equalization of the batteries. This is basically a controlled over charging of the batteries which could bring some life back into them. We did a full charge and let them stabilize, then used out outback charger to do the equalization with specs sent to us via Deka. This process makes the acid in the batteries boil, so you have to watch them very carefully when doing this.
Before doing this, I I’d check common things such as disconnecting the parallel batteries to make sure they individual voltages we the same, and checked GE specific gravity of each cell of each battery. The SG reading, albeit low even after compensating for temp, were all pretty much the same for all 12 cells, which mostly ruled out a short in one battery bringing the bank down. The connectors and batteries themselves were also clean and have been properly monitored and watered since install.
Sadly, the single equalization didn’t really seem to do anything and our batteries were not happy last night. We are going to spend some more money and try this a few more times in a marina before giving up hope in the batteries. We also might try using the PV on the boat to equalized each battery separately over the next few days since all the marinas where we are are wuitr expensive. Sadly, even with the mild abuse we gave them, they still should not be acting this bad in my mind, but getting warranty service on anything down in Mexico is basically next to impossible. Don’t get me started with the pain we have had with our new Asus laptop we bought before the trip!
If we do have to replace the batteries again, i think I am going to reconfigure the bank and use 6v batteries this time. The batteries we have now are not a common size and will be difficult to find down here, and next to next to impossible as we head further south. His would require us to rebuild the battery box to accommodate 4 smaller batteries compared to the 2 large ones we have now, but we should get slightly more capacity as well. If I can find t-145 sized batteries, we could get about 500Ah and theoretically a few more cycles out of the batteries before we run into this problem again. This is good for us because it give us more headroom before we get close to the 50% level and if we do, should get more cycles at that given level.
The reefer on the boat is the biggest consumer of energy. Down in zihuatanejo, where the water is over 80 degrees F in the winter and the air us even warmer, we are consuming about 80 Ah just keeping some meat frozen and the beer cold. I rebuilt the box itself with high efficiency insulation before we left, with that, these numbers seem in the ballpark. I can’ even image how much we would be drawing with the factory insulation! If we are sailing, we draw another 15-20 for the instruments and chart plotter, a few few Ah for lights and fans, maybe 10-15 for charging the laptops and iPods etc. We only run the water maker about once a week and it draws about 20-40Ah to fill up the tank depending on how low it was. That basically means that our 390 Ah of battery should be fine for our normal uses, but doesn’t give us a ton of headroom. Getting closer to 500 ah, which is a pretty large bank for a boat out size, would be really nice and would stop a few arguments between us if we both want to use our laptops at the same time if we are anchored in an area with free wifi.
Or we decide to give up on the freezer for the south pacific and only use it as a fridge. That would most likely drop or reefer budget by 25-35%. We are also thinking of getting an arch built for the boat to add another 1-2 large panels. As much as I hate e aesthetic of having a ton of crap on the back of the boat, adding another 135-200 watts of solar to the boat would also help a ton, and would give us something to make a little more shade in the cockpit than the boom tent that we currently use.
Here are some general numbers that talk about voltages at rest and how they relate to capacity and specific gravity:
Figure 1 - Battery State of Charge Charge Voltage Voltage Specific Level (12v) (6v) Gravity ------ ------- ------- -------- 100% 12.7 6.3 1.265 75% 12.4 6.2 1.225 50% 12.2 6.1 1.190 25% 12.0 6.0 1.155 0% 11.9 6.0 1.120