Motor & Battery: 12V 3.5A/hr Support 120V 4.7A Motor?

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Discussion Overview

The discussion revolves around the compatibility of a 12V 3.5Ah battery with a 120V 4.7A motor, exploring the necessary specifications for battery support and the type of electric motor involved. It includes considerations of voltage conversion, battery capacity, and the nature of electric motors, touching on both theoretical and practical aspects.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that a 12V 3.5Ah battery cannot support a 120V 4.7A motor without voltage conversion.
  • One participant suggests using a transformer for voltage conversion and recommends a 120V battery with at least 5Ah capacity for better backup.
  • Another participant calculates that the current draw at 12V would be 47A, indicating that the battery would deplete in less than 4.5 minutes, though this might depend on the intended use.
  • Some participants argue that a 3.5Ah battery is not designed to handle such high currents, using analogies to illustrate the limitations of battery capacity.
  • There is a mention of jump-start batteries potentially handling high currents for short durations, although 3.5Ah is considered small for such applications.
  • Participants discuss the capability of sealed lead-acid and NiCd batteries to deliver high currents, albeit for limited timeframes.
  • There is a debate about whether electric motors are typically DC or AC, with some asserting that most large motors are synchronous AC, while others mention that small domestic motors are often non-synchronous AC.
  • One participant questions the operation of AC motors, particularly regarding polarity and the use of permanent magnets.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the compatibility of the battery with the motor, as multiple competing views are presented regarding battery specifications and motor types. The discussion on the nature of electric motors also reveals differing opinions on whether they are predominantly DC or AC.

Contextual Notes

Participants express various assumptions about battery performance under load and the operational characteristics of different types of motors. The discussion includes references to specific battery types and their capabilities, but does not resolve the implications of these characteristics on the original question.

snaz_86
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1) will a 12v 3.5amp/hour battery support a 120v - 4.7 amp motor? if not kind of battery specifications will.

2) Is an electric motor a DC or AC.

help is much needed,thank you.
 
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No. It wont. But by voltage conversion, inbetween by transformer, you can.
better to go for 120V battery with 5 Amp/hr so that atleast for 1 hour u ll get backup supply.
 
Even with a voltage converter, 4.7 amps at 120V would convert to 47 amp at 12V (ignoring the inefficiency in the converter). The 3.5 amp-hour battery would go flat in less than 60*3.5/47 = 4.5 minutes.

Of course that might not be a problem, depending on what you want to do.
 
It won't even make it 4.5 minutes. A 3.5 amphour battery is simply not designed to handle 47 amperes ever. Think of it like this: I can hold a given weight at arms length for a given amount of time. I can hold a twice that weight at arms length for a shorter amount of time. But it is unlikely that I can ever hold 1000 pounds at arms length no matter how short of a time. I'm simply not built to handle it.
 
It might - a jump-start battery can handle quite a bit for a few seconds. 3.5Ah would be unusually small for one of those though. For example, this one is 9Ah: http://hitches4less.stores.yahoo.net/stcoeljustsy.html

Whether or not that would be useful depends on what the OP is trying to do...
 
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You can get sealed lead-acid batteries down to 12V 1.3AH. They would certainly bang out 50 amps or more, but not for long.

Probably even a 12V NiCd pack would manage 50A if you short circuited it (but don't try that at home!)
 
The battery probably won't hold not for any backup time u need like 10 of those batteries to have decent backup.
An electric motor is usually DC driven cause from the way it works, if u put AC current on it, it will move back and forth thus staying in the same place and we don't want that to happen do we ?!
 
Actually, most big commercial/industrial motors are syncronous ac. The oscilating induction field drives the motor in sync with it.
 
r u sure about that? i mean i know that the engine operates by varying its polarity on 1 side, and keeping it the same on the other. would be difficult to do that using AC, unless you r using a permanent magnet system ? what do u think?
 
  • #11
russ_watters said:
Actually, most big commercial/industrial motors are syncronous ac. The oscilating induction field drives the motor in sync with it.

And most small motors in mains powered domestic electrical equipment (fans, vacuum cleaners, etc) are (non synchronous) AC.
 

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