# Battery charger

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

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 [Broken] 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.

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NoTime
Homework Helper
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.

Averagesupernova
Gold Member
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.

Averagesupernova
Gold Member
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.

Averagesupernova
Gold Member
There is no such thing as 2-phase. Not in the sense you are thinking of it anyway.

:grumpy: 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.

GENIERE
Dngrsone said:
:grumpy: 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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