Charger ratings. Max bank size?

Discussion in 'OnBoard Electronics & Controls' started by DennisRB, Nov 15, 2012.

  1. DennisRB
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    DennisRB Senior Member

  2. Frosty

    Frosty Previous Member

    No where near big enough.

    Twice the size at least.

    500 needs 50 amp= 10% minimum.
     
  3. CDK
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    CDK retired engineer

    No, the charger has current limiting so it will not overload on a 500 Ah bank. But the cycle steps will be much longer than the microprocessor anticipates, resulting in "bad battery" warnings and possibly automatic shutdown.
     
  4. DennisRB
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    DennisRB Senior Member

    That makes sense CDK. However I assumed the super expensive (but low power) ctek I had used previously on another boat would also just limit current to prevent overheating while I ran a fridge, with the worst case being the batteries would slowly run down. But it overheated and died before the voltage got below 12.7

    Frosty if you need a 50A min charger. Why do cruisers get away with solar and wind that might supply 10-20A max? My loads would be not more that 5-10A usually and maybe 20 for a an hour or 2 if I watch a movie. Of course thinks like the toaster draw 100A but only for 10 minutes. I would expect the battery bank to absorb this then be topped up again by the charger.

    Either way I think I will just get my Heart EMS 1800 system going with a step down transformer (imported US boat in Australia). It will do 65 amps.
     
  5. michael pierzga
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    michael pierzga Senior Member

    On the practical side if you plug in and start charging with a 25 amp and at the same time the background load...light, nav gear, refer is 25 amp then your battery receives nothing.

    Its not only battery bank size its total load you anticipate.

    As for windmills and solar...that gear only works for liveaboards. If you use the boat you will have to charge batteries via gen, shorepower or engine
     
  6. DennisRB
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    DennisRB Senior Member

    That is obvious Michael. Which is why I said my average load is only about 5 amps. Which should give 20 excess to keep the battery charged.



    I have been living on my boat for almost a year while sailing from the USA to Australia. I have never lived on it when connected to shore power though. So I know how much power I use very well. I have an inadequate solar array and no wind. I need to run the 12V gen for about 2 hours a day. I obviously do not want to run this once I get to my slip.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Sure, me too. Ive been living on boats for 40 years. Sitting in the nav station now.

    A major advantage of a " small " battery charger is that it draws less AC and wont blow the shore power breaker in small ports around the world and small permits you to be more versitle when using your generator. .I would go small charger .

    I use two small battery chargers. More expensive but has benifits like redundancy. Ive gone thru 4 chargers on this boat in the past 18 years. Normally heat damage. A small computor type van to add air when charging is a good idea.

    My consumption when sailing is about 600 amp hr per day at 24v, when anchored the comsuption drops to 250.

    The big consumer is always refrigeration.

    Sailing implies 2 or three anchor pulls per day plus full navigation and autopilot.

    A valauble addition is a battery monitoring system like Magnetronic . Allows you to understand your daily power use and monitor the charging or your bank
     
  8. Frosty

    Frosty Previous Member


    Thats called contradicting yourself.

    Do you eat cheese before you go to sleep. I always used to get salmanela poisoning off Pealle when I was in Torremolinos. You know what rice in a bowl with rotten mussels and crabs arse It makes you dream crazy stuff man.......

    A charger converts,-- it uses no more than it needs to convert --like an invertor A large one does not use more as on standby its uses nothing but waste inherent in the design flaws of the machine.
     
  9. DennisRB
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    DennisRB Senior Member

    I ended up going to a local store (Supercheap) and found multi stage 20A charger (300ah max bank size) for $160 on special, so we just bought it (Calibre 20A). Even if I don't end up using it on the boat permanently it will be good for at home.

    Things which I think wont work are the automatic charge cycles. The bank is too big plus there is normally at least a 10-15 amp house load while we are on board. My E meter did register that it fully charged the battery but it obviously took a while since the excess amps left to charge are pretty low.

    The stages in order are:

    Soft start. This is a pulsed start stage which apparently reduces gassing. It passes this stage.

    Bulk. It seems to get past this stage. The parameters for bulk are not described.

    Absorption. I have not tested it for days yet but it does not seem to pass this stage. Voltage is supposed to get to 14.7V but it does not have the power to get voltage as high as that withe the fridge loads etc. The battery is fully charged though. I even boosted it with the generator to be sure, but it still does not appear to be able to pass this stage. Maybe once I get back to Brisbane and move off the boat and turn the appliances off it might get past.

    Analysis. A crude stage where charging is stopped and if the voltage falls below 12.4V during a one minute timed period the faulty battery light comes on. I guess if it did get to this stage and someone turned the blender or microwave on during the one minute it might trigger the faulty battery indication.

    Boost. Voltage regulated 15.5V at max of 5A. When current gets below 3A it will move to the next stage (float). I guess having 15.5V applied when you are using 12V appliances is not a good idea anyway :p There is just no way that 5A will raise voltage as high as this with a 500AH bank and some appliances going. I don't think this stage is suitable for use on a cruising boat while loads are connected. I think even when I turn all the appliances off the charger will not have the power to pass this stage. There is also an overcharge protection function but the operation is not described. I assume it does not let the batteries sit at 15.5V for too long.

    Float. This will deliver a 60-80hz pulse at 13.7V. This would be a good stage, but because it will never pass the other stages I guess it will never be active.

    Overall its has no trouble keeping our batteries full with fridge, freezer, laptops and watching a few movies. So it does the job. It also has a few other good features like an automatic fan. If it overheats it will not shut off. It reduce power to max of 15A. I think its in this mode most of the time as its getting a pretty good workout and its mounted inside my lazarett. Its has short circuit and reverse polarity protection. It does not put out any power until its connected to a battery. There is a swich to select AGM/Gel where all the voltages I mentioned are lower.

    I think for $160 its decent.
     
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  10. michael pierzga
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    michael pierzga Senior Member

    Does it have a sensor on the barrery to prevent the battery bank from overheating .?

    Cooked batteries is a common problem
     
  11. DennisRB
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    DennisRB Senior Member

    No it doesn't. But I doubt its going to overheat the batteries. Its just too small compared to the bank size. It does have ambient temp compensation though so it automatically reduces voltage and current when air temps are not. I guess this will help somewhat.
     
  12. michael pierzga
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    michael pierzga Senior Member

    All the marine battery chargers that I familiar with have a voltage sense input, plus battery temp input.

    The battery bank temp sensor calibrates the output of the charger as well as preventing runaway charging.



    The following table shows the voltage applied to a wet battery for any given temperature. Low voltage for a hot battery, high voltage for a cold battery

    Temperature F/C Absorption Voltage
    122/50 13.80
    104/40 13.98
    86/30 14.19
    77/25 14.34
    68/20 14.49
    50/10 14.82
    32/0 15.24
    14/(-10) 15.90
    (-4)/(-20) 17.82


    In the end if you only have a small batt bank then just throw them out when they prematurely age. If its a prematurely aged big bank, 10 grand down the drain
     
  13. CDK
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    CDK retired engineer

    Your assessment is correct Dennis, the charger does not walk through the stages; it does that only when the load is switched off. And be happy that it doesn't, because 15.5 V is life threatening for non-electronic 12 V equipment.

    You could set the switch for gel batteries and see what happens then. The charger should reduce the absorption stage to just over 14 V and skip the boost stage because gassing in a gel battery causes irreversible damage.

    When I bought a motor home a few years ago it came with a gel type house battery that died within a month. It was replaced under warranty, but the new one also rapidly deteriorated. Only when the 3rd battery was installed, the dealer discovered this little slider switch covered by an umbrella of wires and set it in the correct position.
     

  14. DennisRB
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    DennisRB Senior Member

    I have set the switch to GEL for the reason you say. Not that it would matter as it it will never get to "boost" anyway. Its nice being able to run all my gear without worrying about having to run the gen. My importation red tape is over now. Our yacht is now fully imported and we will leave Bundaberg tomorrow for Fraser island. :)
     
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