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Thread: cranking issue solved?

  1. #41
    Low Bitrate nrls2000's Avatar
    Join Date
    Oct 2004
    Quote Originally Posted by Dracos
    yea, but what has been designed does what you said without that switch. it just does it all automatically.

    Farad caps are dangerous and should be treated as such. they only provide a couple of miliseconds shot of power for something like a bass hit. it wont work for the time it takes to start.

    And yes - cranking = turning your engine over to start.
    Caps are not dangerous and can(if large enough and coupled with resistance) sustain for multiple seconds. A 20v 1 farad cap can discharge in milliseconds but if a full discharge load is not present it will only discharge what is needed until it is empty. The size needed to sustain 6 to 15 amps for 3 seconds would be too large(and costly) to be practical. An Isolator also protects each battery from a failure from the other. If using a small battery (5ah) than a simple diode is all that is really needed. However if you are using two large batteries of the same size an Isolator is necessary.

  2. #42
    Variable Bitrate Dracos's Avatar
    Join Date
    Sep 2004
    United Kingdom
    Quote Originally Posted by nrls2000
    However if you are using two large batteries of the same size an Isolator is necessary.
    And that is the principle I was working on - 2 normal car batteries (a standard one for starting + a Deep Cell one for the ICE/PC)

  3. #43
    Nic is offline
    FLAC Nic's Avatar
    Join Date
    Oct 2003
    Melbourne, Australia
    ok all of the stuff in this thread has been spoken about over and over again...

    Problems with caps... in order to have it work you need a bloody big cap, there have been various discussions on this in theory if you have a big enough cap and a decent electrical system it should be able to smooth the voltage (you need the diode in there too so the motor dosent pull the current) i havent heard about anyone being able to get this working and for the price its not worth it when you can get a cheap seeled lead acid battery.

    Problems with diodes.. yes they work but they generate heat, this could be lots of heat depending on what diode you get, this is why i switched to a relay. The diode will also introduce a voltage drop which means the backup battery may not be charging, or charging much, depending on this drop. IMO if you are running 2 reasonably sized batterys a battery isolator is a good option, both batterys will get the same voltage so the alternator current will be shared more evenly, they are manufactured to be able to cope with decent currents and keep the voltage drop minimal.

    On another note large caps can be very dangerous if they are misused (think shorting the terminals with a screw driver, or throwing them against a brick wall)

    ok ive finished
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