Update on the Power Saga

Well, it looks like we are getting down to the bottom of what is going on with the electrical system on Piko, and gladly, it is not as bad as I had feared.

Thanks to all of you who have wrote in with suggestions, and also to Larry from Panta Rhei who is my resident EE (Electrical Engineer)  whom which I have spent some time going back and forth on how to track down the issue and what we need to go forward.

Firstly, our batteries are getting better.  We have been doing boat based equalization for the last few days, using the engine to charge the batteries then the PV array to equalize them through the day..

A few things to note:  You need an accurate volt meter to really get into this.  We have two permenantly installed meters using different systems on the boat.  Our primary is the Xantrex Link 20.  The second one is the Mate on our Outback inverter/charger.  I take all my detailed readings with my old Fluke 75 VMM I bought back when I was in EE school myself.  Things I have noticed just pertaining to reading the bank voltage:  The Outback Mate always seems to report .1 volt low, so I have had to up calibrate it so it matches my fluke.  The Xantrex read accurate during discharge, but is abou .15 volts high during charge.  They are all reading from slightly different places in the electrical system, so a very small amount of voltage loss is expected, but we had been using the Link meter as our quick check since it is easier to look at than the Xantrex, and it was ALWAYS reading .1 low.  That doesn’t seem like a lot,but .1 V is almost 15% difference in charge going by voltages.

You then also have to see what is going on with the system.  We already knew this, but it does make it difficult to get good reading of SOC from voltage since the regular numbers are only accurate on a battery that has rested for about a day.  I am mean to my batteries and they are always in play, either being drawn down or charged up.  You also have to know how much current you are pulling related to your overall capacity to make the numbers work.

SOC vs Voltage during discharge

I also have started taking regular specific gravity readings of all the cells in the bank.  This really is the only accurate way to see the health of your batteries, but it requires you to take the caps off and measure the weight of the sulfuric acid in the batteries with a special glass meter.  You can then relate that to numbers from your battery manufacturer, compensate it for our batteries temp and get good reading.

Here is the little excel spreadsheet I created to get some good numbers…

Battery Health using chemistry only

Sadly, I didn’t write down any of the specific gravity numbers from when our bank was really unhappy,but I do know the the highest numbers I was seeing at that point were in the 60% range, and that was after a charge.  Reverse engineering the SOC, assuming the SG to voltage, it looks like our bank is about 90% happy now.   You will notice that cell 1 on battery A is lower than the other values, but not drastically so.  The other 11 cells are all pretty much in the same ballpark which is what you would expect and want in a healthy battery bank.

My toughts in general are that we could use a sligtly bigger bank on the boat.  Our daily consumption down here is in the range of 150Ah.  That incudes the fridge, lights, computers, part of the watermaker etc.  That is also with me being the energy Nazi as I am now known.  Since we have 390 Ah, and you basically never want to go below 50% SOC, we have 195 AH to use each day.  We are pretty darn close to that number and always feel like we are watching ourselves.  So, since I don’t think we need to replace these batteries right now (we still have 2 months in mexico to re-evaluate before we head to more remote places) I think we will probably increase our capacity by 100-200 Ah when we do replace them.  This would allow us to cycle them even less, which makes them last longer and I can tone down always trying to not use anything that uses a watt.  The second conclusion is that while our solar, which is to large Kyocera KD135’s and two smaller 40 watt panels are just not enough to be completely of the grid.  We seem to average about 100 Ah from them into the batteries each day, which just keeps up with us on a low energy use day, but falls behind if we want to watch a movie or use power tools etc.  Since the two large panels we have are mounted like wings off the rear life lines (converted to stainless steel tube in that area) we don’t really have space for more without building a structure.  So that means we are most likely in the market for an arch.

I REALLY dislike cruiser butt as they call it.  The Pretorien has nice lines, and I have been against the aesthetics of a arch or Bimini, but I think I might have to break down.  If we built an arch, we could either add two more KD135s to the boat, or possibly one large 220 watt panel in the middle with the smaller 135s on the outside.  That should nearly double our charging capacity either way.  Sadly the arch itself is more expensive than the panel(s) and w need to find a good fabricator in mexico to build it.  Also, none of them are where we are, so we need to head north and see if that is even a possibility.

Anyway, we are good for now, breakfast is almost ready and the seahawks are playing this afternoon, so I guess that means this is all for now…

Categories: Geeky and Techy, Mexico, S/V Piko, Upgraded Systems | 2 Comments

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2 thoughts on “Update on the Power Saga

  1. gordon sims

    good report, lauren, esp that the batts are showing signs of not having given the ghost yet! conservancy is always a positive in these equations….

    another thing that sticks in my mind as not ideal about PIKO’s batt setup in the lack of any airspace adjacent to the batts and poor ventilation of the compartment, which is bound to affect performance/efficiency. the downside of this arrangement is exacerbated in warmer climes. i’m tossing out a thought: especially if you do go with larger bank, redesign compartment to allow for air flow (which=cooling) around batts, and considering that there is only the one hole to eng space, consider openings that either naturally create convective action, or possible solar powerd fan that pushes air clean air into compartment combined with a vent, preferably to atmosphere, for exhaust gases. i recognize that it’s a very tight space, further limited by being, for all practical purposes, in the qrtr cabin, but with a creative mind like yours, i bet there’s more than one solution. one would need to be mindful that lead-acid batt gases are corrosive (epsecailly to sensitive electrical components), not to mention not friendly to accomodation spaces, so the exhaust venting would be carefully considerd as to discharge locale.

    if you don’t end up going with larger bank, i’m a proponent that you would find some way to airate and better ventilate the existing compartment.

    do i take it you’ll be watching the hawks?! i’m picturing that in me mind’s eye right now! well, i better go myself ’cause kickoff is in just a few minutes!


    • Lauren Buchholz

      Yea, i am aware the ventilation’s pretty poor back there and the batteries probably get warmer than they need, but there isn’t much i can do with the current batteries. Whew do repla the bank and move to 6v ones, I think there may be enough space to add a small gap wi a fan venting somewhere, but eve right now, the batteries are only about 10 degree over cabin anyway, which is swill quite warm and only getting warmer…

      And yes, i am watching the game right now in santiago with a bunch of other cruisers… At least the beer is cheaper down here than in the states, because the game sure wasn’t worth it!

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