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Battery Charging and Load layout


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so I've decided to rebuild the entire electrical system while I wait for the painter to come right. This is a sketch I came up with last night - its rough and certainly not a complete wiring diagram at this stage but I thought I might as well through it out for constructive critism anyway!

 

I haven't worked out the loads yet but thought I'd go for the following mostly around best bang for buck at this stage.

DVSR - BEP mini switch w- DVSR

Start Bat - 30-50Ah (o/b is a honda bf20 with a 12V alt rectified and regulated)

House bat - ~100 Ah

Solar Panel 5--100 Ah

MPPT controller ~20A

 

Loads are pretty light really - the highest being the fridge (tropicool 3000 - only run on economy as a "day cooler),  LED nav and cabin lights, charging for ipad, phone, batt powered speakers, and autohelm which I'll really only use when I need to leave the helm occainsonally.

 

Anyway flame away!

20160121120638.pdf

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I'd question how well a DVSR would work in this scenario.  The O/B alternator would be the only source to charge the start battery and the start battery is quite small relative to the house.

 

Take this scenario

 

Full start battery, depleted house battery - no OB running:  The VSR will bridge the two batteries as the start has reached the VSR threshold.  The two batteries will try an equalise meaning that current is going to flow from the start to the house thereby draining the start battery.  The VSR will release the bridged connection once the disconnect voltage threshold is reached leaving a slightly charged house and more depleted start battery. Unless the OB is restarted the start battery will stay depleted.  The house battery will continue to be charged by the solar.

 

You may also find that the alternator on the OB will be overloaded when the two batteries are initially bridged as it will be trying to charge the house.  Unless the alternator is rated for continuous use you may also experience premature failure.

 

Personally I would leave the OB alt to charge the start only and use the solar only to charge the house.  You may need to charge the house battery from 230V prior to going out but a 100W solar panel is going to provide a reasonable charge in anything but poor light conditions.  The 100W semi-flexiable panel that Matt put me onto was still putting out power in what I would consider low light conditions.  I have had no need to run the diesel to charge the house battery at all so far this summer (I do have a compressor driven fridge/freezer tho so need to run the motor for this).

 

My 2c worth.

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Most ALT's on outboards are 8A output, unless you have a big outboard with dedicated ALT, and assuming you wouldn't, then 8A is the max you are going to get. That's going to be a fair number of hrs of running the outboard to charge a flat House bank.
A 100W Solar panel is going to give ruffly the same charge current and as the ALT, but at least that runs silently for as long as the sun shines decently on the panel.
A VSR is a good thing to have if you have House and Start banks connected together. When the Start Bank starts to drop, the VSR switches out the Start Batt so that it is saved for engine starting. Personally I prefer to keep both banks separate, and divide the charge via a charge splitter, but I realise that for small boats, having the power of both for a short time can be helpful.

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I would suggest 100A/hrs sn't enough for a house system.

I've tried that and despite 240W Solars/MPPT etc we, ( or more accuratelily THEY) managed to bleed it dry and kill the battery. Don't just consider the daily loads think about the drain that happens overnight/all the time when there are no solars going on - kids watching DVDs, instruments, fridge going 24/7, toilet pumps, galley pumps, stereo (loud setting), anchoring lights as per the other thread, the casual iPhone on the charger overnight, cabin lights left on 'cos the kids know ON but not OFF etc etc. All of a sudden there's no ergs left and the beers in the fridge are getting warm.

Our electrical development programme used to be 1 x 110A, this was changed to two of them and still had an issue so have now gone to a bank of 2 x 195A which means over any 24 hour period we will never lose more than 5% capacity....and still manage frozen margaritas !!

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sh*t 400Ah - 100kg worth give or take! But I take your point.  I think though that we'll be starting out with a pretty minimal load demand and work our way up to all the "ncessitied" of life on a caravan.  I might up the house  and the solar on the strength of both Bill and Ken's comments - which ups the MPPT as well I guess.

 

Ken - where do you position 100W of solar - I'm thinking it needs to go away when under sail.

 

Ferrari - my read of the maerial for the BEP switch bank with VSR suggests that you describe shouldn't happen in that when the O/B is stopped the relay should open to disconned the start bat from the house bat.  However I hadn't actually thought about draining the start bat as a consequence of the VSR closing.  If that happens then I guess it contiuously opens and closes as the upper and lower thresholds are reached.  Will think about that some more - I did see a sktch on an RV site with two separate VSR's which I think might have dealy with that.

 

Wheels the o/b alt is voltage regulated and 12A so a bit better than where you are coming from but I do take your point.  I do think we'll be doing a bit of motoring in the first year or two as the kids get used to the attitude of the boat which is part of the reason why I'd like to have them connected but maybe you're right and I should just keep them separate given the disparity.

 

Thanks again guys

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Perhaps instead of getting more heavy batteries and another solar panel, you could get a small petrol inverter generator and a battery charger. That way if the Sun has not been out to play, you can top up with the genset. Plus if you time it right, say every evening when the kids watch a movie, you could flick on the fridge and let it cool down again while in the genny. A lot lighter than a battery and they are very quite. Just hang it over the back of the transom when running. I know someone that used to do that and it worked well for them.

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thanks wheels - I recall a discussion on gensets here last year?

 

As we roll into a beautiful weekend I'm also reminded of keeping "fridge to fridge" commute time so a bare minimum.  I can be on my boat within 10mins of leaving the house which is pretty good but wasted if the contents of the fridge are not cold.  Do people keep their fridge running on their moorings using solar and perhaps a timer? In the summer I intend being on board 2-3 times a week with any luck (perhaps only once in the winter months but wouldn't bother with the fridge) so can keep a regular eye out it sorta does make me a little nervous.

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We have been having similar discussions about our boat. Here are a few points that I think are worth looking into

 

  • The best quick charge solution that I have found is the outback battery charger, basically a 55a alternator connected to a small 4 stroke motor. https://www.macfarlanegenerators.com.au/products/c113/Outback-Battery-Chargers
  • It is easier/cheaper to minimise consumption than to provide more power. As you have done, have LED lights on all regularly used lights, especially the anchor light. How much do u really need that fridge?
  • Also dont forget that discharging a FLA battery below 50% shortens its life, and below 30% damages it irreparably. Also it is difficult to get a battery back above 80% unless on overnight charge. This means that you effectively have 1/2 of a batteries rated capacity as usable. We have 115aH and only run the basics (no fridge or autopilot). I think you might need more batteries.
  • Most battery chargers will lose their warranty if run by generator (was told not to do it by the boys @ burnsco)
  • The output of an alternator on an outboard is lower at idle than its rated output. you might get 5a out of it if idling to charge (and only from 30-80% charge.
  • Simplicity is good. We have a one two both switch for our batteries with the outboard connected to the switch and the solar panel connected to the house battery. This means that we can charge either battery by outboard. Connecting two dissimilar batteries together, even by VSR seems like trouble to me. I think that you would have more than enough CCA if you bought 2 115A house batteries and dropped the start battery. Your batteries would probably last longer as well.

I hope that helps!

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I have 2 50w panels, they are lashed down or just sitting on deck, often on top of the upturned dinghy, or lashed to front beam. I really want to swap to flexible panels in a year or two when I hope to be able to cruis emote again. If rough or big sail, they sit on quarter berth,..

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Just a note - some of the newer VSRs use mosfets to switch, and contain reverse current blocking diodes. These units only ever pass current in one direction, so it's not possible for them to discharge your start battery, for example.

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  • The best quick charge solution that I have found is the outback battery charger, basically a 55a alternator connected to a small 4 stroke motor. https://www.macfarla...attery-Chargers

     

    An interesting looking unit.

    The only problem with a non controlled ALT is that as the charge comes up on the battery, the input current drops away from the ALT and becomes less efficient. A charge controller allows the max possible charge current to be applied to the batteries till they are fully charged. A little Inverter Genset driving a 3 step Battery charger works very well, because as the current to the battery drops away, the load on the genny does also and the genny lowers it's revs and saves fuel and noise.

     

  • Most battery chargers will lose their warranty if run by generator (was told not to do it by the boys @ burnsco)

     

    That should not be the case, although read the warranty card and if that is stated, don't by it, go find a decent charger.

    • Also dont forget that discharging a FLA battery below 50% shortens its life, and below 30% damages it irreparably. Also it is difficult to get a battery back above 80% unless on overnight charge. This means that you effectively have 1/2 of a batteries rated capacity as usable. We have 115aH and only run the basics (no fridge or autopilot). I think you might need more batteries.

       

      This is true for any type of Lead Acid Battery, not just FLA.

             

      I am being a little nit picky here. You are kind of correct, but just to make it more accurate.

      As soon as you start to discharge a battery, the process of Sulphation begins and the ability for a battery to accept a 100% charge again ever so slowly diminishes. The deeper you discharge, the greater that little bit that is not recharged ever again.

      The 50% mark is a rule of thumb. It is determined by the sum of above.

      For ease of explanation, I will give simple numbers to illustrate.

      Battery costs $100

      Lets say that you only ever discharge the battery by 10%. You may get 20yrs of life from the batter. But it's rather useless if you spent all that money and yet never use it. You could save yourself $50 bucks and get a battery half the size, for half the price and weight.

      Lets say that you take the battery down to 50% discharge, no more and then fully recharge again. You may have a life of 10yrs from your battery. So the Battery comes at a cost of $10/yr

      Let say you discharge to 30% left each time before recharge. You may now only get 5yrs from the battery. That is costing you $20 dollars per year. 

      So the rule of thumb was that at 50%, you get the best value for money versus current available over time.

       

      • Connecting two dissimilar batteries together, even by VSR seems like trouble to me. I think that you would have more than enough CCA if you bought 2 115A house batteries and dropped the start battery. Your batteries would probably last longer as well.

         

        You are correct here if you don't have a charge splitter and if you don;t have a VSR. It is important to have both House and Start being the same age, type and size of battery, or unequal charging can take place and cause premature failure due to overcharging of one and under charging of the other. With the use of a VSR, the batteries are disconnected (as you know) at a set voltage, so that unbalanced charge does not occur. But the down side is that they battery switched out never ever gets to be fully charged above the 75 to 80% mark and that lack of charge comes at a cost to it's life. It is one reason why Car batteries have a ruff 5 to 7yr life. The ALT never gets the battery above 13.8V and this comes at a cost to it's life. To fully recharge, the battery must be supplied with a voltage of 14.4 to 14.8 Volts.

        Having a separate start batt enables the safety of being able to start the engine should you accidentally discharge the House too far.

         

         

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Agree it's easier to minimise consumption. On that point, figure how much you need in the fridge and whether you need to freeze or just keep cool and size accordingly.

 

Don't get one of those thermoelectric coolers that also warms - they absolutely kill the battery. What you need is compressor fridge, like Waeco/Dometic or Engel. Looking at specs of the Waeco CFX 35 it says

 

0.32 Ah/h at +20 °C ambient temperature, 0.60 Ah/h at +32 °C ambient temperature, both at +5 °C interior temperature

 

 

So that's something like 8 - 16 Ah in a 24hr period - which should be easily replenished by a 80-100W solar panel on a normal day. Yeah, a panel that size is big, but I had no problem mounting it on a rail (for cruising I took the top pushpit lifeline off and fitted a tube in its place, on which I had some of the starport mounts for the panel) on the transom of my 930.

 

Get a portable fridge, that way you can get the temperature down at home then take it to the boat cold already. For longer trips I would freeze my meat packs at home so they slowly defrost in the fridge, which also reduces the load on the battery. Buy your meat vacuum packed so they won't leak and also it'll last longer.

 

Also, don't turn the fridge off at night or whatever - all that's doing is allowing the interior to warm up, so when you turn it back on it has to go hard to cool down again. The designers designed it to be on full time so just leave it running and it'll use less juice overall.

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On the Waeco type fridge, as it empties but you still want to keep the remaining beer, I mean food, cold; just cut some polystyrene blocks up into different shapes and fill the fridge up. Fridge works a lot more efficiently cooling these than air - which also escapes every time you open it.

I've tested it and I believe it does work. Bit of a pain but the blocks are light, and it does teach certain other less energy conscious people on the boat to conserve power.

When finished cruising, clean fridge, store poly blocks in fridge.

 

And plus 1 on keeping the fridge on all the time, don't turn it off at night.

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just thinking about this a bit more before heading off to the pub.  If some are suggesting that I should have a lot more bat capacity - say +200Ah - why would I even bother with a start battery.  It's only a 20hp motor that can be pull started with ease if necessary.  Surely I just have one bank of bats - or two 100Ah bats that I allow to be utlilsed by the "house".  CCA won't really be a problem I don't think - the smallest 12V battery you can buy is all that is required.

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A starting battery is seperate so that in the event of a flat house battery you can still start. CCA is not an issue for most house banks, but not what they are for. Personally I have 3 banks. Start, House, Radio banks.

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