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Is there anyone out there who has constructed a successful AC motor-generator battery charger?

+1 vote
Is there anyone out there who has constructed a successful AC motor-generator battery charger?

More specifically, an AC motor driving an automotive alternator.

Or knows of someone who has done so?  Even a simple "YES" is useful information.

Or can direct me to a web page?

Or fill me in on ANY observations? belt or direct drive? shiv (gear) ratio?  current? RPM?

Or, has had a bad experience attempting such?

I have doubts and any response (or lack thereof) will help me confirm or dispell my suspicions.

Thank you.
asked Dec 12, 2013 by j-keith (12,800 points)

Most cars manage with just a flexible rubber belt!

I run solar power at 4 locations with wind back-up at 3 of them.

I have found, repeatedly, that there are two problem areas: 1. Battery type - automotive useless, I usually go for individual cells (used on long-term storage OR fork-lift trucks); (2) Charging regulator circuit. Sometimes it is a good thing to discharge batteries say down to 20/30% (using a resistive heater element as a load) then re-charge.

4 Answers

+1 vote

have done this for experiment in the 1980ties.

Mostly, I wanted to test how the alternator behaves if driven by a wind turbine.

(have also built a generator bicycle with a car alternator).

Then I found out that many guys in the USA have used alternators, driven by powerful motors at high speed (ca 3-5kW power and alternator speed ca 10000rpm) as arc welder generators. In this case the built-in voltage controller has to be taken out and replaced by something controlling for ca 40V of idling voltage and limiting the current if necessary. I guess that the internet is still full of these alternator welding generators.

The efficiency of the alternator is below 50% at 12V and when misused as a weld generator, even far lower.

In 1981 a friend of mine and I built a test stand for alternators to measure the efficiency in original and rewound state. We wrote a small book on rewinding the alternators for windpower. Still available (german language).

If interested, i can write down the experience with the alternators, or if you have a special project can give support. Also hints for rewinding the armature for different voltage/speed relations
answered Dec 12, 2013 by joribo (2,340 points)

Thank you for the interesting and useful information, joribo and daklak.  This increases my knowledge base.  This further proves my point that virtually nobody has created a successful electric motor driven alternator for battery charging applications.  One bit of interesting info is that gross overpowering of alternators seems to be a solution.

...do you have a special reason why to use a rotating system? A simple transformer and rectifier will do with better efficiency and cheaper.
But there is a special rotating inverter, in german they call it Einankerumformer probably "single armature rotating converter" which is basically a motor and generator in the same machine. There you can put AC in and DC out or vice versa. We had this in the university, is rare, efficiency can be around 60-70%

Someone else wants to do it this way and has already had a false start.  This should be a workable method, but I agree that it is perhaps a poor way to go.  Good learning experience however.
Old plating shops use large rotary converters to generate DC--old technology, but runs wonderfully silent compared to the depressing buzz of static converters...

Just let me pick your brain a little--Do automotive alternators have active current limiting?  Certainly old units that use external voltage regulators do not, but how about those with integral regulators?

The ones which are typically in use now (ca 10-20 years ago manufactured) use a simple P-controller made of discrete elements, cast in epoxy, united with the brush holder. I have a book on alternators and can mail you a schematic. As it is a P-controller it has a natural deviation. And the alternator has its internal resistance. Now, when loading the whole alternator, the voltage drops, the controller gives more excitation, but overall a certain voltage drop happens at the alternator output.. This limits the current to ca 55-60A for the usual types when, for example, connecting a battery of 9V (deep discharged). If short-circuited, the whole thing has a foldback characteristic. That is because also the excitation voltage collapses. So it is short-circuit proof.
To my best knowledge there is no active current limiter function in the exciation controller, it is indirectly present. (might have been added in newest versions, not fully sure)

OK, Good info!  By P-controller, do you mean proportional as in PID terminology?

yes, I meant P = proportional.  The excitation controllers which I have seen so far used purely P and no integral =I and no derivative =D.
 In 1975 I built one myself for my motorcycle. I can mail you some more infos about alternators, best is privately because most readers will not be so much interested in the details, I guess.
0 votes

Hi Jim,

### More specifically, an AC motor driving an automotive alternator.

Yes, I did and except for a very specific issue, my set up is running well. I hope you remember my case.

The specific issue has nothing to do with the running the alternator by the AC motor or charging the batteries by the alternator but of a different nature.

answered Dec 15, 2013 by psb1967 (230 points)
edited Dec 15, 2013 by psb1967
0 votes

Hi Jim,

Wish to share with you a new development in my project. The problem of my AC motor coming to halt, connected via a V-Belt with a Car Alternator to charge the battery when routed thru' the Charge Controller, HAS BEEN SOLVED.

I used your original 12 Volt External Charger Control and also another one made by a local friend of mine for testing. Once clearly understood the problem was caused by the alternator not either by the relays or by the AC motor, I set out to identify the particular action that makes the alternator to stop.

Day before yesterday finally I managed to do that and then hooked first your Charger Control, it worked well and followed by that the one constructed by my friend. Both worked very well without causing the alternator to stop or making the Ac motor come to halt. I tested the circuits with 12 Volt 30 Amps and 12 Volts 65 Amps Alternators run by 1.5HP and 0.5 HP Ac motors and 100 AH and 55 AH batteries.

As soon as I take a video I will send you the link.



answered Dec 21, 2013 by psb1967 (230 points)
0 votes

I have seen many of them look under the hood of your car.  If you do not have the proper regulator you will be llike most it will not work properly, generator or alternator.  Be sure you have enough torque and RPM.  A small motor will only give you a small amount of power.

Discharging your batteries that much is going to cause them to sulphate and loose capacity.
answered Feb 25, 2016 by gilshultzhome-com (17,730 points)

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