Building a Battery Charger with Car Alternator

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Discussion Overview

The discussion revolves around the feasibility of building a battery charger using a 3/4 hp 240-volt AC motor to drive a 55-amp car alternator. Participants explore the efficiency, practicality, and potential issues related to this setup for charging caravan batteries.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the viability of using a motor and alternator combination to charge batteries, expressing concerns about the adequacy of the setup.
  • Another participant argues that the proposed method is inefficient, highlighting the energy conversion process from AC to DC and suggesting the need for additional load on the alternator.
  • A different viewpoint suggests that despite inefficiencies, using the existing motor and alternator could still be a practical solution.
  • Some participants discuss the limitations of the alternator's output, noting that the 3/4 horsepower motor may not provide the full 55 amps due to power conversion losses.
  • There is a discussion about the phases of electrical power, with some participants clarifying misconceptions about the number of phases in residential power systems.

Areas of Agreement / Disagreement

Participants express differing opinions on the efficiency and practicality of the proposed battery charger setup. While some acknowledge the inefficiencies, others argue that it could still be a viable option given the available components. The discussion on electrical phases also reveals a lack of consensus on terminology and understanding.

Contextual Notes

Participants mention the need for calculations regarding the rotational speed of the alternator and the potential for bypassing moving parts, indicating that further engineering considerations are necessary. There are also references to previous discussions about residential electrical phases, suggesting a broader context of confusion in this area.

rolly
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hi
i wish to build a battery charger using a 3/4hp240voltac motor driving a 55amp car alternator will this work has anyone done this before and will my caravan batteries be oka i have a gen set to drive the electric motor all these questions i hope to be reveled rolly
 
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Punctuation is your friend.

If I understand your problem correctly, you have a 240vac electric motor with which you wish to drive an alternator to produce a 13.6vdc output in order to charge the batteries for your van?

This would be a waste of energy, to begin with... you are using two phase 240vac wall power to turn a motor which turns a generator that makes a three phase ac voltage which is then rectified into a dc voltage to charge your batteries.

http://members.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm is a decent explanation on the internal workings of an alternator along with ways to use one for other than its intended purpose. I would say that you might want to add some load other than the batteries to the alternator, and you will also need to calculate the correct rotational speed for the alternator.
 
Last edited by a moderator:
As Dngrsone pointed out this is a rather inefficient way to go.

In addition you will not be able to get full rated output (55 Amps) from the alternator as 3/4 horsepower works out to about 40 amps at 13.8v.
 
It's not that bad of a way to go. I've done it. If you already have the motor and alternator why not? Efficiency isn't always that big of a deal.
 
True, a motor generator is almost the only way to go in some applications, like changing the frequency of a primary power source (going from, say 60Hz to 400Hz). I was just pointing out the inefficiency in this case.

With a little engineering homework, he might be able to bypass the moving parts and just run the AC straight through the regulator-section... that's a little beyond my knowledge and scope at the moment.
 
BTW Dngrsone, he is not using 2 phase.
 
Oh? He not American, then? I didn't know if those 50Hz/240vac systems over there were one or two phase.
 
There is no such thing as 2-phase. Not in the sense you are thinking of it anyway.
 
I'm thinking my house is powered with phases A and C from the neighborhood network... two phases of the three available from the sub-station.
 
  • #10
Dngrsone said:
I'm thinking my house is powered with phases A and C from the neighborhood network... two phases of the three available from the sub-station.
Residential electrical power and confusion about the number of phases has been discussed in several threads recently so I won’t get into it again (search for "phase").

FYI the typical home in the USA receives single-phase 240vac. The 120vac is derived from the 240vac.


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