power inverter 12vDC to 240vAC

Discussion in 'OnBoard Electronics & Controls' started by sebski, Jul 17, 2008.

  1. sebski
    Joined: Nov 2007
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    sebski New Member

    Hello,
    Could you guys advice me what will be the best way to install inverter on boat?

    I am planning to have separate battery for inverter (dont want to connect to current instalation).

    How can I ground inverter? I mean ,where to attached wire from inverter earth connection? to the water?

    Thanks,

    Sebastian
     
  2. Landlubber
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    Landlubber Senior Member

    It is best to have a ground plate installed in the bottom of the boat for a decent ground. Use one of the radio type plates like Dyna.

    The chassis of the Inverter is connected to this. What sort of boat are we talking about here, big or small? The total AC wiring is dpendant on how it is set up, more details are needed.
     
  3. CDK
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    CDK retired engineer

    Unless you intend to take the battery home after use, you'll connect the negative pole to that of the other batteries and the + to an alternator or diode bridge so it will be charged. The negative wiring includes the engine block and propulsion, so that is a good grounding point. On a sailing boat, the ballast in the keel is also part of the ground wiring.

    Keep battery and inverter close together, since 1 Amp drawn from the 240V side means 20 Amps from the 12V side.
     
  4. Fanie
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    Fanie Fanie

    I agree with CDK - just connect the neg to the rest of your system's negative. The pos can be free or floating but has to be connected to a source for charging.

    ALso confirm what CDK mention about efficiency... you need a LOT of 12V Amps for very little mains power, really not worth it. Since most apps work off a lower voltage in any way it may well be worth it to look for the lower voltage counterpart. We got a bit comfortable in our ways... just plugging things in from mains.

    You have to overrate the inverter's capability... if you need 1000W you have to install at least a 1500W. A good condition 60AH battery will run about 3 hours supplying at 20A, then needs proper charging for about 8 or more hours. A not so well charged battery will not give much.

    Some things can only work off mains - microwave oven is one

    Almost all other appliences can work off 12V. PC works off 12V, 5v, 3v3, -5V and -12V. LCD monitors work off 9V or 12V although they have power supplies built in. Fridges have very efficient 12V motors in nowadays, saw some that draws 2.7A from 12V which is not bad take into account it doesn't run all the time.

    Disaster strikes when the wife moves into the boat. That 2000W hairdryer is a big no-no for inverters :D Get the 12V version instead... and put a timer on it. Seems they enjoy the heat and blows for an hour plus... or it feels that way :D

    If the wife needs to run the big dryer it may be worth it to have a small 10A power generator just for that. She carries it onto the boat by herself of course :D

    Gas is a relief. In the old days before mains power was everywhere you used to get many gas appliences, even irons. My mother-in-law (280 years old) has a whole variation of gas things they used to use. It may well be possible to make heat with a small gas flame and blow it with a 12V fan for the hair drying saga. Gas is good for water heating systems.
     
  5. masalai
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    masalai masalai

    Thanks Fanie, but I am STILL not allowed to give you points..... WTF?
     
  6. Fanie
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    Fanie Fanie

    What's with you and the points :confused:

    I'll give you my bank acc number instead :D
     
  7. Landlubber
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    Landlubber Senior Member

    Fanie,

    "A good condition 60AH battery will run about 3 hours supplying at 20A"

    no it wont......
     
  8. masalai
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    masalai masalai

    So, what is the answer? please?....
     
  9. Landlubber
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    Landlubber Senior Member

    Mas,

    To start with, you should never take a lead acid battery (conventional wet flooded, gel or AGM) beyond 50% capacity if you want longevity (recycles and capacity residual). The deeper the battery is cycled the lesser the battery life, it goes from about 6000 cycles to less than 2000 cycles from 10% discharge to 90% discharge...quite a dramatic loss of life that can be avoided simply but not recycling so deep, and spending more money on decent recharging systems.

    As the voltage of a battery drops, the current increases trying to maintain the wattage of the unit being driven. A fully charged battery sits at about 12.7 to 12.8 volts, it is considered dead flat at 11.7. At 12.2 volts the wet battery is half charged, and going downhill rapidly if consumption at the same rate continues.

    Unfortunately batteries are basically never fully charged (another story), and regularly only have about 80-90% of their capacity charge when considered full, so the problem is amplified even more. Now if we take the power down to about 50% then we only use about 30% of the batteries capacity before we are at the 50% residual......in other words, we only get about 30% of the batteries expected or stated capacity before it is considered to be at stop use area.

    So if you want to be able to draw 20 amps continuously from a battery, and still remain above the 50% limit, you will need a bigger capacity battery9bank). cruising yachts often run to the 50 to 80% discharge capacity, not good, but it is because they have not done their homework correctly, or have been advised wrongly about batteries. Half the problem is of course the battery charging system, it simply is rarely ever good enough for the job at hand.

    We should not pull more than about 25% of the capacity of the battery if we expect it to live a long life, hence we see we need 4x the actual demand of the battery as being the storage capacity of the bank. And only have one house bank, make it a decent one and the overall battery capacity will naturally be doubled, thus the discharge rate is lessened as a $ of total capacity....thus keeping reserves above the 50% rate.

    I could go on forever with this, it is one point I regularly see done wrong on cruising boats particularly.
     
  10. Landlubber
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    Landlubber Senior Member

    One more point here that pisses me off, those small centrifugal plastic bilge pumps are rated at 13.7 volts, not at 12.7.

    they are rated with the engine running, crap. The 1000 litre pumps then can olny do that at engine running voltages on a level surface....ever see one installed on a level surface, so now we have the 1000 pump trying to pump uphill (head of pump) so that it can spill its discharge down again, at a much lower voltage than rated at, through skinng pipes and some people even put in check valves further restricting the discharge rate. You would be luck to ever get 50% stated capacity with the boat on the pick.

    just be aware of this......
     
  11. Fanie
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    Fanie Fanie

    Yes it would :D But it would be totally depleted, and it also depends on the type of battery you use. LA won't, SLA will... I have run my two 105AH SLA's down a couple of times... they supply untill there's nothing more and then retire to the lounge for a charge, so to speak :D

    But you are correct, the less of a battery's capacity you discharge before charging it again the longer it will last. SLA life expectancy is about as follows but don't hold me to specifics... I'm forgetting things ok - this also varies from manufacturer to manufacturer.

    1 - 100% discharge - up to 200 cycles
    2 - 50% discharge - up to 700 cycles
    3 - 20% discharge - up tp 2000 cycles
    4 - 10% discharge - up to 5000 cycles

    So you get the idea. Using as little as possible power and charge it back as soon as possible. LA won't get past the first point, it will be buggered long before that.

    Also, I wasn't suggesting that for that kind of capacity you should use a 60AH battery... it was merely to indicate the max amount of power you are supposed to get from that size battery.

    The AH rating is supposed to be the amps you can draw for the time Amp x Hour. A 100 AH battery is supposed to be able to supply 10 A for 10 hours to make up for the 100Ah.

    Now there's something else about these batteries. The higher current you draw the quicker it will get depleted... not making the AH rating. Below a certain current drawn you can exceed the AH rating of that battery. Running a 20A inverter load from the 60AH battery you probably won't make 3 hours. However, running a 1A light off it you may well get 65 to 80 hours off it.

    On the torches we make drawing 4.5A off a 7AH battery we get about an hour's light from it, while someone tested the small neons drawing 800mA gives power for up to 10 hours from it. Needless to say the battery is depleted in both cases and is not how it should be used unless in an emergency... which btw is why we don't have a low voltage cutoff, if the **** strikes you want light.

    The different type batteries needs to be charged in the correct way to achieve fully charged states. A SLA cannot be charged from an alternator.
    Two problems - the initial charge current would exceed the max allowed charge specified for the SLA battery and will damage the plates. The second problem is alternators are made for charging 13.8 - 14V... SLA needs charged with at least 14.6 - 14.8V (some manuf say 15V).

    So charging a SLA battery you need to current limit and voltage limit the charger. SLA batteries also likes to be pulse charged. They also charge up faster and at lower currents than their LA counterparts.

    LA batteries loves supplying high currents for short periods, they are designed for that, ie starting that V8 drawing 150A on a cold morning... and you can hear the fan belt screech after it started as the alternator is pumping a nice rectified 3-phase 60A+ back into the battery. They are made to be charged at high currents.

    Both LA and SLA's run themself down when in storage, LA being the worst... they have limited shelf life and need recharge often, ie once a month at least. SLA last somewhat longer, need a recharge very 3 months or so. This is because LA has a higher internal leakage than SLA.
     
  12. Fanie
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    Fanie Fanie

    The problem with these pumps are they are pathetic designed. They have really designed these more like a gimic that anything else. The problem is mostly the motor. It uses brushes that are usually copper plates that is spring loaded to the armature to make contact. The resultant sparks on it works like a spark eroder, eroding the flimsy copper 'brushes' away very quickly. Thumb suck they work for about 5 hours to 30 hours :mad:

    The correct type of motor it should have is a brushless dc motor and a better designed vein area. Bilge pumps should be low pressure high volume pumps, instead they are a bad compromise. between an auto window washer motor and a borehole pump :rolleyes:
     
  13. Fanie
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    Fanie Fanie

    There are some new batteries currently being developed that can charge back to a full charge state in approx 90 seconds (1 1/2 minute !) have no memory and can be left uncharged (flat) for long periods of time without any damage. They are also not sensitive to their discharge rate and up charge rate where gas and temperature generated is usually a problem. The current setback on them is the price tag.
     
  14. Fanie
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    Fanie Fanie

    Found it... these should give you an idea.

    At least I didn't lie about everything :D Seems the shelf life is temperature dependant... but they indicate around 6 months

    One last thing... these batteries shouldn't be left standing on a cement floor. They lose their natural temperature and they lose their charge capability. A battery left on cement for a week is usually ready for the scrap heap.
     

    Attached Files:


  15. Landlubber
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    Landlubber Senior Member

    OK Fanie, i understand what you are saying...maybe mistook your original comment a bit...have fun
     
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