"jump" start batterys

Discussion in 'Electrical Systems' started by waikikin, Dec 5, 2007.

  1. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    I've been looking at some portable jump start units at the car shop, they come in sizes with batterys from 17AH to 35AH & have some "crank " rating as well, the application I'm thinking of is for my Sea Wind 24 sailing cat for mostly day sailing(hand start to outboard), occasional anchor light over night, intermitent use of internal lights & maybe running lights fot dusk returns to mooring & stereo. I guesstimate about 20Amp Hours per outing, the question is, are the batterys in these units suitable for this kind of use(I was thinking of getting 2, 1 for standby) & would it be possible to give back a little charge over a weekend with a say 10 Watt solar panel which kind of matches the output of the included mains charger. They look like a pretty convenient way to run the power on this type of use but have concerns that the batterys are more for pumping out lots of power in a short time, hope some one "knows whats inside" as the're priced quite cheap $40-120 & come with easy carry handle for take home charging. Regards from Jeff.
     
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    I guess the deciding question here is, what is the battery inside the fancy plastic box? In some cases it's a car cranking battery; in others, a deep cycle unit. For running no more than a few lights overnight, I don't see a big problem with even the cheap ones, although routinely draining them right to the bottom of their useful capacity is going to shorten the life a bit.
     
  3. Frosty

    Frosty Previous Member

    Just buy a good battery. Why pay for a plastic container.
    You'de get more for your money.
     
  4. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hello Regards from Jeff.

    Thase slave starters are really if you ask me just a money making scheme and not worth buying. It's a commercialized idea and you pay for what you get. If it breaks it's cheap enough so you won't bother to take it back after a month.

    The best you can do is to make your own. For 12V you will need one battery and for 24V two batteries. Forget the two small batteries in parallel scheme - they will run each other down.

    The battery size is usually a function of what you want to start with it. A 100Ah battery is good for most things. You will need to put it on a small trolley and hook a decent charger / monitor to it that will NOT OVERCHARGE. You will have to get a charger that will limit the charger output voltage.

    The charger circuit must be able to survive when the battery voltage drops as low as 6V... simply because if you run that battery flat that's about what the charger circuit is going to see (trust me !)

    You also need a THICK starter lead (16mm recommended) and DECENT clamps to slave start with silicon insulation (welding cables). Te-he... the wife had one of those dainty 8mm lead starter cables set... so if you slave start something nothing much happens, but the cables does get nice and warm ;)

    You have a choice of two types of batteries - LA (Lead Acid) like is used in cars and SLA (Sealed Lead Acid). LA batteries are cheaper, dirty if not kept clean, and doesn't tolerate standing around in a semi or uncharged state. If you use them even a little it's back to the wall plug. Charging voltage is 13.8V. While charging hydrogen is emitted and in a confined space pose an explosion risk if there is a spark or other source of ignition.

    SLA batteries is becomming fast more popular for many applications. Still somewhat more expensive but they are clean, charge up faster and tolerate abuse better. Charging must be voltage and current limited. You can turn them upside down and they will still work. Their charging voltage is 14.6V to 15V. First choice to use on any boat...

    All acid and lead batteries have a similar lifespan characteristic. To explain hypothetical... If you discharge them 90% you can re-charge (immediately) and use it say 100 times. If you discharge 50% the cycle increase to say 600 times 10% discharge only 10% abd you can re-charge 2000 times... you get the idea. The SLA batteries have better characteristics than the LA batteries.

    Do not short the terminals... not even by accident ! It's only in the movies that they short batteries to see if there are power...

    Topin makes a good SLA battery and Delco Remmies are good LA batteries.

    You cannot charge a SLA battery from the car lighter socket...Regards from Fanie
     
  5. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Sorry I overlooked the part for the seawind... if your need is 20Ah rather overrate it than underrate... the discharge will be far more on a small battery and will shorten life span. A good idea is always the solar panel which is expensive but maintenance free. Charging hours should be worked out for your part of the world. A little wind power generator is another option and works day and night... if there's wind of course.
     

  6. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Thanks for the great posts, I think I'll buy one & open it up to see what style of batterys in there & give it a go, maybe buy another if required, as the're cheaper than similar AH batterys theres not much to lose!, I"ll post what I find. All the best from Jeff.
     
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