How do i wire my second hand alternator to charge a car battery direct?
Answers:
Hmm, ok well as you have already sussed, the chassis is negative - and needs to go to the neg of the battery.
The other wire is positive and CAN be connected directly the battery however it may make sense to get a regulator if possible (scrapyard) otherwise when the battery is full, the voltage is likely to rise higher than you wish - which will result in electolye loss from the battery and possible damage to whatever load the battery is connected to.
As you may already know, if ever the battery goes VERY flat, you will need to briefly apply power to the alternator before it can generate power - this is because it NEEDS a little power to energise the electromagnet.
Your meter can go over the pos + neg to measure voltage OR in series in the current setting to measure current - WANRING you may not wish to do this unless the battery is almost fully charged AND you have a regualtor - otherwise current flow could be high enough to damage the meeter unless it has a fused current range (10A smetimes fused, 20A meters often unFUSED)
To get the unit working, you will often find a car engine needs to rev at around 800rpm - which I am guessing equals around 1800-2500 rpm on the alterator (due to pulley ratios).
An alternator going around at a few hundred rpm isn't going to do much I fear.
What kind of alternator is it. GM, Ford etc.
Master tech
Put the positive wire to the positive battery terminal. Connect the negative battery terminal to the body of the alternator. A bit of solder might help here.
First point: does your ALTERNATOR produce DC or AC? Is it a generator taken from a car or truck - if so, then probably yes. Check this by looking for the commutator. If it doesn't have one, it is probably an alternator producing AC. In this case you will need a rectifier ("bridge" type) to convert AC to DC. These are standard and easily available from electronic shops.
When you have sorted that out, you will want to connect the + from the generator (or + from the rectifier attached to the alternator) to the + of the battery to charge, and likewise a wire connecting the - to the - of the battery. The body of the alternator/generator should be attached to an earth conductor (a wire leading to a pipe buried in the ground) but this is a safety issue, nothing to do with charging the battery.
The special advantage of having a rectifier is that it will prevent the battery from discharging through the generator if the generator is turning too slow to provide a voltage high enough to oppose the battery's voltage.
Your multimeter, set to VOLTS should be connected across the + and - wires.
If you want to e-mail me with a phone number if uk I can give you as much help as you need have you calculated if the wheel is powerfull enough to drive the alternator and have you got the gear ratio right. Ive already done this. Merrydeedee@ yahoo.co.uk
First you need an alternator with rectifier and regulator built in, in the UK this means virtually any Rover, Ford ,Vauxhall alternator, these will also be negative earth. This will be an excited field alternator (some motorbikes are permanent magnet).
The main output connector connects to positive, the body connects to negative.
Now the difficult bit .
The IND connection, this goes to + ve through a 5 amp bulb, which glows when the alternator is not turning fast enough to charge and provides current to the field coils to initiate charging, hence at low rpm the alternator consumes power instead of produces it, on a car this rpm is below tick over but is about 2000 alternator rpm. the "Ignition" switch isolates this circuit when the car is at rest.
Your problem is car alternators run faster than the engine by perhaps 3 times, so you are looking at 3000 rpm to produce power and the alternator will be producing up to 750 watts, and absorbing 3 times that, is that 2 horse power, is 1000w = 1 hp can't remember.
How fast is your water, our village water wheel does about 15 rpm
or 1 rev = 4 sec, so we would need 200 to 1 gearing to spin the alternator.. I do not think your project is feasible. In any case you need a mechanical governor to switch off the battery feed when rpm drops, you know balls out type a la traction engine.
Redesign around a permanent magnet alternator, with rectifier and Zener Diode like a 1970s British Motorbike, use the bearings from the car alternato but fit the Rotor and coils from ideally a big Lucas alternator such as Mk3 Norton Commando and connect up rectifier positive to battery positive and hag a 12 volt Zener with heat sink across the battery to prevent overcharging.
This set up will charge when the wheel spins starting at 1000 shaft RPM as they run at engine speed and will not take current when not charging.
Not such an easy armchair project but it does stand a chance of working.
We all need low rpm 12/24/48 or even 300 volt alternators but because Environmentalists are largely con men and women who do not actually believe in alternative energy, out to make a fast buck no one makes any.
The large terminals are the positive feeds the small terminal is the output you should take you reading from that , not forgetting that alternators have to have a positive feed and earthed as you say from the body , although there are some with an earth terminal it is userly marked with the negative sign. I might add water is not a good sorce of motive power for an alternator, first it is very slow speed second if it gets inside you will lose a lot of your output to shorting
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