24 Volt Inverter

Discussion in 'General Electronics Chat' started by TP201, Nov 15, 2014.

  1. TP201

    Thread Starter New Member

    Nov 15, 2014
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    Is it possible to attach an inverter directly to the output of an alternator or do you need batteries as an intermediate?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Since the alternator output is rectified AC you can drive a DC-AC inverter from it. You may need some low-pass filtering if the inverter is fussy as to its input quality.
     
  3. TP201

    Thread Starter New Member

    Nov 15, 2014
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    The inverter specification says Input voltage 24V - minimum21V maximum30V. Is that fussy? What do I use for low-pass filtering? The wiring specifies a 100A fuse from the power source. I am very new to this. I want to make sure I don't fry/damage the inverter in any way. Thank you for your reply
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    Most alternators are 3-phase, so by the time its rectified there isn't a huge amount of ripple - you could try about 4700uF and go on from there.

    Some of the last of the British motorcycles were marketed as trials bikes - with no battery. They just had a relatively modest electrolytic capacitor after the alternator/rectifier so the ignition coil could have a dwell time.
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    If its a vehicle altenator it will need some sort of battery, as they don't self excite like a generator.
     
  6. TP201

    Thread Starter New Member

    Nov 15, 2014
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    It is a self exciting 24 volt alternator with an internal voltage regulator for an excavator.

    Its run by a 3 hp briggs and stratton engine. I just got it running today and haven't tested its output yet but the alternator is rated at 40 amps.

    I have a 1500W inverter that I want to wire to the alternator to charge deep cycle batteries. I'm still putting the system together so I don't have all the numbers yet. I've been researching some and found that to charge a battery bank you need an amperage source that is 1/10th the amp hour capacity of the batteries.

    I posted to check to see if there was a chance to harm the inverter by wiring it directly to the alternator (with a fuse in between). Are inverters damaged if they are under powered?
     
  7. IamJatinah

    Member

    Oct 22, 2014
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    Hi All, I am a bit confused. Do I understand you are taking a 24v alternator, running that into an "Inverter"(115vac?) and then using the inverter to power a battery charger for deep cell batteries of what voltage? It sounds like you have a nice rectified 24(~28vdc) from the alternator output, you could then use as your bulk DC source voltage, thru a pass element to regulate charging rates for any battery of 24v or below.
     
  8. TP201

    Thread Starter New Member

    Nov 15, 2014
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    Yes that is the plan on current knowledge. They would be 12v batteries in series. I've been reading that charging batteries at a rate higher than 1/10 the amp hour capacity will shorten the life of the battery and that batteries need to be monitored so that a different amperage is applied at different times during the charging process. That is why I was thinking the battery charger would be the way to do it. I understand that charging the battery is going to take some time. I'm working on the fuel cost to see if this is practical.
     
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Sounds overly and unnecessarily complicated being it's industry standard to just use a alternator to directly charge batteries on 100's millions of machines and power systems world wide.

    As far as the battery life justification unless they are some super special type of batteries and not just a typical lead acid type the added cost and losses in system efficiency will never cost justify the multi step charging process.

    On top of that no you generally cant connect a off the shelf power inverter directly to an off the shelf alternator and have it work without a battery or at least a very large, 10's of Farad, capacitor bank in between. The alternators regulation system will never keep its output stable enough or be able to respond fast enough to be able to keep the power stable enough for the inverter to work properly.
     
  10. IamJatinah

    Member

    Oct 22, 2014
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    Well, TP201 does make a good point. Most Industrial 24v systems do a good job of regulating charges, but we all know there are good designs and not so good designs. Charging any battery too fast has implications, as in internal plates paste, heat and a few other things, and this can degrade the battery. Li is especially critical to charge rates, internal heats, and conductors, as well as force damage to it's outer package. Anyway, good luck with the charger, and for best results, look up the battery you would like to charge, and grab charge characteristics from that dataset/datasheet. Pass Element chargers are the simplest to make in my opinion, but I'm old, you kids out there today, have the edge over us dusty engineers ;o
    peace
     
  11. TP201

    Thread Starter New Member

    Nov 15, 2014
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    From what I have read about alternators is that they are used to top off the charge on a battery after the battery is discharged from starting the machine.
    The batteries I want to charge are sealed lead acid deep cycle batteries . I will be drawing the charge down to half the battery's capacity before recharging. From what I have read about charging this amount of draw down requires a different amperage to recharge, if I'm not mistaken an alternator is not designed for this type of recharging.
     
  12. TP201

    Thread Starter New Member

    Nov 15, 2014
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    I meant starting and recharging from any load the electrical system places on the batteries while running.

    How variable will the output of the alternator be even with an internal regulator that is intended to keep it at 24 volts?
     
  13. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Most are designed to try their best to hold about 28 - 29 volts up to their output amp amp limit and then work as constant current sources until the battery voltage gets high enough for the regulator to take over again, or the alternator burns up if it was not designed to handle extended high load conditions.

    This link will help you out a lot. http://www.solar-electric.com/deep-cycle-battery-faq.html#Battery Charging.

    Simply put not all deep cycle batteries share the same recommended charging rates. Some recommend no more than 1/10 their AH rating while others are good to 4X their AH ratings with most batteries falling anywhere in between.

    Ideally you need to go by what your specific brand and model of batteries manufactures specs say and then weigh out the cost Vs service life numbers to see whats most rational for your application and by rational I mean if spending three times what your battery costs on a charging system that only will at best net you 10 -20 % more life in ideal conditions really doesn't justify itself.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    Anything designed for simplicity could well have a permanent magnet alternator.
     
  15. TP201

    Thread Starter New Member

    Nov 15, 2014
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    Thanks for the link!
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    The permanent magnet alternators operate as current limited sources, the most common regulator is a row of thyristors that short out half-cycles of one polarity.

    Alternators with a field winding are designed to be constant voltage.

    Before alternators and electronic regulators, the voltage regulating coil had a bucking coil in series with the generator output, this meant that under conditions of heavy load the regulator actually increased the charging voltage - slightly more *NOT* constant current than just constant voltage.

    Incidentally - an unloaded permanent magnet alternator might possibly produce enough voltage to push lethal current at optimum RPM!
     
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