Low rpm battery charging using car alternator

Thread Starter

allaidept

Joined Mar 5, 2017
17
Hello,
I need to charge a Pb battery using no more than 1Ah using a car alternator mounted on an fitness bicycle.
It is hard to achieve 1000 rpm pedaling .
What do you propose to change in system? I do not need lots of charging Amps, I need just low rpm.
Thanks.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
I can achieve just about 700 rpm with that pulley. Tried a small one, 40 mm diameter, but is very hard to rotate the alternator.
I need an alternator modification, not a mechanical one.
Thanks.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
Yes, i need only 1Ah load, no more. Can i modify somehow the excitation voltage? Tried with a 6 ohm resistor in series with excitation coil, but I have no load at all.
 

MaxHeadRoom

Joined Jul 18, 2013
22,325
If the alternator has a built in regulator, changing the excitation is not going to work, it is set by the regulator.
You would have to fit a custom regulator to increase the voltage.
Max.
 

wayneh

Joined Sep 9, 2010
16,765
I need to charge a Pb battery using no more than 1Ah using a car alternator mounted on an fitness bicycle.
Which do you need more, to charge the battery or use the alternator? I ask because it's the wrong tool for the job. The windmill guys rewind alternators with higher gauge (thinner) wire so that the voltage is higher (and current lower) for a given rpm. But that's a lot of work just to charge a small battery.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
Which do you need more, to charge the battery or use the alternator? I ask because it's the wrong tool for the job. The windmill guys rewind alternators with higher gauge (thinner) wire so that the voltage is higher (and current lower) for a given rpm. But that's a lot of work just to charge a small battery.
Thanks for info. I need to charge a 35Ah 12V battery. I do not need high charge curent. I need standard auto battery charging voltage, 14 V at about 500 rpm. It is just a hobby to keep me motivated doing sport indoor.
 

wayneh

Joined Sep 9, 2010
16,765
Thanks for info. I need to charge a 35Ah 12V battery. I do not need high charge curent. I need standard auto battery charging voltage, 14 V at about 500 rpm. It is just a hobby to keep me motivated doing sport indoor.
The old lighting dynamos that sucked power off a tire were designed to put out about 6W. You can feel that drag but it’s not huge. I think anything more than about 20W would be unpleasant, like uphill and into the wind. So you need a design that will put out 1.5A or so at 14V.

An automotive alternator is overkill but they’re essentially free if you don’t mind taking the time to rewind it for lower rpm.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
The old lighting dynamos that sucked power off a tire were designed to put out about 6W. You can feel that drag but it’s not huge. I think anything more than about 20W would be unpleasant, like uphill and into the wind. So you need a design that will put out 1.5A or so at 14V.

An automotive alternator is overkill but they’re essentially free if you don’t mind taking the time to rewind it for lower rpm.
Thanks, fine idea with an old dynamo.
I already have the alternator, I saw a video on yt, a 6 ohm resistor in series with excitation coil reduced the human power necessary, but I do not understand how, I tried and no load at all.
 

crutschow

Joined Mar 14, 2008
26,329
a 6 ohm resistor in series with excitation coil reduced the human power necessary, but I do not understand how, I tried and no load at all.
Then reduce the resistance until you get the load you want.
That resistor reduces the rotor excitation current, lowering the magnetic field, which thus reduces the output voltage/current.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
Then reduce the resistance until you get the load you want.
That resistor reduces the rotor excitation current, lowering the magnetic field, which thus reduces the output voltage/current.
Thanks. But are you sure I'll get low current and not low voltage? Will be too simple.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
You'll get a slightly lower voltage which will generate a lower current.
You don't get one without the other.
Hello again.
I think that voltage will not drop because of controller, it must keep the voltage above 14 V, right?
Only the current will drop.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
Ok people,
It was my fault, wrong pins.
Soooo... It's WORKING!
6 ohms resistor do about 0.8 Ampers in excitation, this means less work and STILL GENERATING ENERGY and charging about 0.5 Amps at 600 rpm.
Thanks all for info.
SOLVED.
 

Thread Starter

allaidept

Joined Mar 5, 2017
17
If the alternator has a built in regulator, changing the excitation is not going to work, it is set by the regulator.
You would have to fit a custom regulator to increase the voltage.
Max.
NEWS. Surprise. My alternator does NOT have a built in regulator. So I must reconsider all my work. I will test your information using a regulator and send feedback. Thank you.
 
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