SLA battery charging

Discussion in 'The Projects Forum' started by Scubasteves, Dec 11, 2015.

  1. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    So here is the system: 4 12v 10Ah sla batteries in series to create a 48v battery powering 1000w motor on demand. I want to put another motor in that has a friction wheel that can be engaged on demand to recharge the 48v battery when engaged.

    Q1: will short (3sec-30sec) periods when the second recharge motor is engaged harm the 48v battery system?

    Q2: is a 48v dc motor the correct choice for the recharge motor?
    Q: Does charging the batteries as a 48v (paired from 1st use) unit harm them?

    Q3: if you were building this system, and you wanted the recharge motor, when engaged, to SLOW the system at the same approximate speed that brakes on a bicycle(traveling up to 30 mph on 26" wheels) would, what wattage would you recommend? Given that the wheel that makes contact is 2-3' in diameter.
     
  2. Lestraveled

    Well-Known Member

    May 19, 2014
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    Interesting....
    Could you provide a little more information. Is this a battery powered bicycle?
     
  3. Lestraveled

    Well-Known Member

    May 19, 2014
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    Questions that can be answered:
    Q1: No
    Q2: Need more info
    Q: No, but will need specific periodic maintenance
    Q3: Need more info
     
  4. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Yes it is for a bicycle.
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    The DC motor that drives the wheel can also generate voltage to recharge the batteries. This is very common. Why do you think you need a separate generator to recharge the batteries?

    Q3: Using the drive motor to assist in braking is also very common. In golf carts it is called "regeneration". No big deal.
     
  6. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    I am not certain the (aosom brand) cheap motor controller supports recharging. They don't advertise it.

    I also wanna use what I learn to make another similar system for a 12v battery that will be powering horn, blinkers, headlight, taillight speakers, etc. which brings me to another question:
    There are Two motors of equal quality, and same wattage moving(rather being pushed by) the same wheel/load. One is 48v, one is 12v. At full power roughly how many times greater is the torque of the 48v motor vs the 12v?
     
  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    First: Batteries
    Stacking four 12V batteries in series to get 48 Volts is OK, but there is an issue you have to deal with to keep these batteries from failing. In effect there are 24 cells that make up your 48 volt battery. They do not all charge or discharge at the same rate. So after a period of time the charge in each cell will begin to vary a lot from cell to cell. Once a month you will have to do an "equalization charge". You will need a charger for this. In effect, an equalization charge is a soft overcharge of the batteries in order to "reset" each battery to its max charge. If you do not do this equalization charge periodically the differences in each cell will continue to increase until one cell fails and then you are done.
     
  8. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Thanks for the tip. Any answer as for the voltage?
     
  9. Lestraveled

    Well-Known Member

    May 19, 2014
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    If the output wattage is the same, then the torque (load on the drive wheel) will be the same. Although, I think I may not fully understand your application.

    Talk on
     
  10. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Err wattage. My mistake haha
     
  11. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    No regen brakes on my controller.
    Am i right in thinking a stronger motor would provide more resistive force to cause the bicycle wheel to slow faster? And that any motor could be used as a generator?(provided no emf circuit)
    Also, wouldn't some charging device be necessary in between the recharge motor and the 48v battery to provide a proper charge and prevent the recharge/braking wheel from turning by itself/ using the battery's electricty?
     
  12. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Or is it maybe possible to rewire an emf like a one way valve to allow electricity into the battery but not out? And not need a charger because the voltages are the same?

    Edit: hmmm... an emf prolly wouldn't hold up under consistent pressure from the battery? As you can tell my knowledge on the subject is beginner
     
  13. Lestraveled

    Well-Known Member

    May 19, 2014
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    - A stronger motor has the potential to present more drag on the wheel. The load on the motor is generally equals the load on the wheel.
    - Yes, some kind of charge circuit would be required. Probably not a very complex one.

    You are doing great for a beginner.
     
  14. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    So if I use a 24v brushless dc motor(such as this: http://www.amazon.com/gp/aw/d/B00AU...=24v+motor&dpPl=1&dpID=418y85T-pPL&ref=plSrch )and this charger:
    http://m.newegg.com/Product/index?i...gclid=CPy4uLLs18kCFQVbfgodc-sMOQ&gclsrc=aw.ds

    Is that how to do it? A 3" wheel should spin no more than 3400 rpm if bike is going 30 mph

    And how do I orient the DC motor? So that that when engaged, it is pushed /spun backwards? Or so that it spins the same direction that it does when powered normally? It would geneterate power either direction, no? And how does that translate into how it is wired? Like normal?
    Is a brushed motor a better choice?
     
  15. Lestraveled

    Well-Known Member

    May 19, 2014
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    OK
    You don't want a brushless motor as a motor/generator. It will need to have magnets and brushes. Focus first on a good mounting method, then simply select the right polarity that charges the battery. A motor/generator will produce the same power regardless of the direction of rotation.
     
  16. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Thank you, sir!
    Would that charger device be appropriate?
     
  17. Lestraveled

    Well-Known Member

    May 19, 2014
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    The complexity of the charger would depend on a few things. If the generator was used to recover some energy while the bike is in use, and the generator was sized correctly, then a simple diode in series with the generator would be all that was needed. This would imply that you would use a smart charger when the bike in not in use. Is this close to what you had in mind?
     
  18. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    Yes. I just got my first two batteries in the mail. I intend to take very good care of them. The more I learn the more ways I find how to simplify it all; I will probably buy a new controller with rbs. and use a simple 48v to 12v to power the subsystems.
    I still would like to see an example of the two items, motor & diode. I'm am having trouble thinking of how to come up with the correct size for the generator. Then the diode will follow.

    I don't know where to start trying to figure how big the brushed DC generator motor needs to be. I just figured out that I need 110 N/s of braking power to come to a complete stop over 15 seconds. If I use a smaller motor but higher rpm, I could put a gearbox. I do want to know how to do this so I could potentially install rbs on any machine! :)

    I'm all fizzled out for today. I was reading some example of sizing a motor but I need to find some simpler ones
     
  19. Lestraveled

    Well-Known Member

    May 19, 2014
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    If you get a regenerative braking system you would not need an additional generator. It would be redundant.
     
  20. Scubasteves

    Thread Starter New Member

    Dec 11, 2015
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    I thought me saying that I still want to learn how to do this would elicit a useful answer. it might be applied to a non electrically driven system to generate power for those subsystems. Or any system where i want to convert kinetic energy to electrical.

    Pointing out redundancy is redundant.

    Any input, please?
     
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