12v to 24v

Discussion in 'General Electronics Chat' started by Tobias, Nov 18, 2011.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
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    I have a 12v alternator in the system right now and need to run a 24v system for four brush-type motors.The motors are rated for 24v, I need to double my speed. I have found this device in the link below that will do the trick and let me keep the 12v alternator. That is I understand what this deal does correctly. The only problem is I need it in a couple of days and they are in Australia. I had 10amp fuses inline with the motors and never blew the fuse. So I only need 5amps at 24v. Any ideas how I can step up the voltage to 24 using two 12v batteries and keep the 12v alternator?

    http://redarc.com.au/products-and-se...ger-12v-to-24v
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Are the four 24v brush-type motors the only thing the alternator is powering?

    Any chance of adding a 2nd alternator?
     
  3. Tobias

    Thread Starter Active Member

    May 19, 2008
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    The four motors are the only thing the alternator is powering. A second alternator is the second route I am looking into at the moment.

     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    OK then, why not just modify the regulator so that it outputs ~27.6v instead of 13.8v?

    You might do that by using something in the feedback path from the output of the alternator to the input of the regulator. Tell the regulator a "little white lie". You might accomplish that with an opamp driving a power transistor.

    I'm not sure how much current the field takes (actually, the rotor in an alternator) in order to generate the output; but it'll certainly vary over the RPM range; much more @ idle then at speed.

    The regulator will probably need at least 11v or so to supply current to the field. Then you might scale the rest of the output something like 15v in = 11.5v to the regulator, etc. and finally 27.6v is 13.8v at the regulator. It's just a rough idea.

    What is your application?
     
  5. Tobias

    Thread Starter Active Member

    May 19, 2008
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    I screwed up in answering your question. The existing alternator is powering alot of other things on the tractor. This is going on a farming application. The motors are turning metering plates for fertilizer. After testing and realizing a few things in the math for the metering plates we realized we needed to have almost double the rpm on the electric motors.

     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    if you're considering adding a 2nd alternator, why not just get a 24V alternator?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Well, there goes that alternator mod idea.

    That Aussie site's products are for battery chargers, not for constant output like you're wanting.

    have a look here:
    http://www.powerstream.com/dc12-24-doubler.htm

    One of these would be much better:
    http://www.powerstream.com/dc1-extreme-12-24-15A.htm

    On something that gets heavy-duty use under sometimes really lousy conditions, you need something that's weatherproof and a good bit over the required capacity. If you bought the minimum supply, you may wind up overloading it just trying to turn the motors on. Even with a 360W 15A supply, I'd suggest staging the motor turn-on so they don't try to start all at once.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    You may be able to get a military surplus alternator. A typical alternator from a reasonably recent military vehicle puts out ~65A @ ~27.6v.

    [eta]
    Also, many buses have 24v electrical systems. If there's a truck/bus junkyard near you, you might have a look.
     
  9. Tobias

    Thread Starter Active Member

    May 19, 2008
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    I am hoping to not to fabricate up a PTO drive for a second alternator but I might be heading that route. Thank you for your input.
     
  10. SgtWookie

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    Jul 17, 2007
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  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Oh yeah, I missed the deadline part; With that time crunch I would hit up the junkyard for a 24V alternator, preferably the military high output type SGT suggested, or if not a big truck alternator might do it.
     
  12. JMW

    Member

    Nov 21, 2011
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    Many marine applications (not USMC) use 24VDC. There are alternators available as well as 12 to 24 volt inverters.
    Interesting site.
    Just found it as a link from somewhere else.

    Regards,

    Jim W
     
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