Marine application - 3 battery banks, 1 panel - how?

TenMileTenMile Solar Expert Posts: 62 ✭✭
Hey guys,

I'm wanting to add a small solar panel -- likely 80w to keep our battery system in the boat topped up. Beats having to pay for monthly shore power.

I'm currently considering the following battery setup:

Bank 1: Single Starting Battery

Bank 2: Single Deep Cycle - just for marine electronics (navigation, radio etc)

Bank 3: Pair of Trojan T105's for House Electrical - AC/DC lights and appliances

To charge these batteries today, I have the following sources:

1. Engine Alternator - 70A output
2. Xantrex 3-stage AC Charger (want to avoid using)
3. 80W panel with existing SunSaver-10 charge controller (currently not installed)

I don't want to have to combine any of these banks during charging given that they are all different battery types -- I think I'd extend their life if they are kept apart.

Is there a recommended design for keeping the 3 systems topped up?

Could I add a SunSaver Duo controller to this system and run individual feeds from the panel to each controller?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    Let me give you the short version: there's no point in adding the 80 Watt panel.
    Roughly speaking you've got about 400+/- Amp hours of battery (and mixed types too) against which 80 Watts is nothing. You might see 4 Amps of current from it on a 12 Volt system. Maybe 5 if everything is perfect.

    You could pick one, say the starter battery, and panel it with a small controller (in this case it would have to have an output suitable for recharging automotive batteries, not deep cycle ones). That way you could be sure of starting the engine and limping home if necessary. Likewise for the marine battery you could be sure of being able to call for help. As for the two Trojans ... 5 Amps would be insignificant.

    You might as well install a blocking diode on the panel and a three way switch so you can manually apply it to whichever battery. That coupled with three Volt meters to watch the level would be as good as anything.

    Sorry about the discouraging news. :blush:
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    So I understand that 80w isnt going to charge the system. My need here is really to maintain the batteries when im notnusing the boat. There are a couple of devices that draw a little pwoer off the house batteries, and rather than plug into shore power at $30 per mo, i am trying tonfigure out how to simply maintain.

    We would typically use the alternator to charge the system back up. I usually use an ACR to tie the batteries together while running. Was thinking the panelnwould top up and maintain. It often has a week or more between uses.

    What happens if i split the output from the panels between 2 controllers? Could i ger 2A to each battery?
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    What you could do (and I agree that 80 watts is hardly enough to keep any self discharge at bay) is use a Bluesky controller which has a second output line, such that when the first battery goes into absorb and there is excess PV it will start to charge a second, smaller battery. (There may be others that do that as well, I am just not familiar with any).

    The problem however, is that the 80 watt panel, if you put it on the largest battery will probably never get that battery to absorb, much less to float. 4-5 amps into a pair of T-105s is like spitting in the ocean. Conversely, I suppose, thinking out loud, put it on the smallest battery as the primary, and then send the excess to the larger. Personally, I would get a small dedicated PV for the starting battery, a 15 watt battery tender PV would keep it up over a week or two. I would then get a second for the Electronics, and then use the 80 watt for the house batteries, understanding that the 80 watts are just barely going to cover self discharge.

    Good luck, and keep in touch.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    One panel, three of these: http://www.solar-electric.com/sg-4.html
    Check that the battery doesn't "back feed" through them.

    Or better yet, three separate panels and three separate charge controllers.

    There really is no simple, inexpensive way of dividing up the output so that the two smaller batteries receive 1 Amp each and the larger 2 Amps (sort of ideal situation).

    How long the boat will be left unattended is also an issue, as even small charge going to a battery can cause problems over time - much like no charge over time.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?
    TenMile wrote: »
    Could I add a SunSaver Duo controller to this system and run individual feeds from the panel to each controller?

    Yes, but you have to put blocking diodes on the two charge controller inputs to keep them from backfeeding each other. This just came up on another thread and Slappy won the sharp cheddar by providing this link:

    http://www.morningstarcorp.com/en/support/library/ALL.APP.1_array_isolated_banks.01.EN.pdf
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    Okay, maybe I'm missing something here but seems to me an 80W panel should be *plenty* to maintain a pair of T105s!

    They are going to provide 220AH, lead-acid batts have about 2-10%/wk self-discharge. Let's go for worst-case, 22AH/wk = just over 3AH/day. 80W/12V=6.67A (ideal) heck, even if the panel only puts out 50% that's 3AH for each hour of sun. Unless the stored battery is WAY far north in winter there ought to be plenty of sun to keep the maintenance charge going each day. And unless the batteries are very old, hopefully they aren't losing 10%/week.

    I used my old Harbor Freight panels - that manage all of 20W on a good day - to maintain my truck's aging battery. (Had a company vehicle and drove the truck all of once a week - the battery was having trouble turning the engine over when I started this.) Even with the parasitic loads in my truck the SunKeeper charge controller dropped to float by midday easily, and kept the battery going a couple years longer than the previous two batteries lasted.

    Edit: Oops, minor math mistake. The 80W panel will be something like 17Vmp. So 80W/17V = 4.7A. 50% would be 2.35A. So now it'll take 1 1/2 hrs to replace the 3AH/day loss, plus more of course for inefficiencies. In the depths of winter, an 80W panel would be getting close to the edge but seems it should still be able to reliably keep a pair of T105s topped up. (Been a while since I've done any panel calcs, forgot about Vmp! :p )
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    Try this formula:

    80W @ 77% typical efficiency = 61.6W / 14.2 Volts charging = 4.3 Amps potential peak charge current.
    4.3 * 100 / 220 Amp hours = 1.9% charge rate. Pretty minimal.

    Now factor in the other two batteries he wants to maintain from the same panel. If they all want current at once, 80 Watts is going be pretty slim.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?
    TenMile wrote: »
    So I understand that 80w isnt going to charge the system. My need here is really to maintain the batteries when im notnusing the boat. There are a couple of devices that draw a little pwoer off the house batteries, and rather than plug into shore power at $30 per mo, i am trying tonfigure out how to simply maintain.

    We would typically use the alternator to charge the system back up. I usually use an ACR to tie the batteries together while running. Was thinking the panelnwould top up and maintain. It often has a week or more between uses.

    What happens if i split the output from the panels between 2 controllers? Could i ger 2A to each battery?

    to use an 80w pv to float charge 2 batteries it would be fine for, but not with loads on it as you talk of maintaining small loads and not just the batteries. it is no longer a float arrangement with loads present and those loads must be addressed. what happens while you get a string of cloudy days with the loads still on? if this happens a few times the batteries can be being maintained at a less than 100% soc and introduce sulfation to the batteries even if the small load requirements are being met.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Marine application - 3 battery banks, 1 panel - how?

    The typical draw off my batteries is generally pretty low. The largest draw is from a corrosion protection device called a Mercathode which is used to help protect the drive against electrolysis. It's typical draw is 200mA.

    I've decided against doing 3 battery systems, and will do 2 instead -- a starter battery, plus the house system that will consist of the 2 x T105s.

    Since I've got the stuff, I will set it up and give it a try and monitor its ability to keep the batteries topped up. Worst case, if it's not keeping on top of the charge, I can always plug back in.
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