Alternator needs battery power to generate power?

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7th June 2016, 04:29 PM
dom14

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Alternator needs battery power to generate power?

Hi Guys,

I've been wondering(again). :)

I'm onto a little garage project of combining an old mower motor with an alternator to make a simple generator.

It is that i'm bit confused with the idea in the heading of this thread.

1)Do I need to connect a 12V battery to the alternator exciter(or field wire/trigger wire) OR

2)Can I simply join the field/trigger wire to the B+ and that should do the job?!!

3)How do I use the sense wire? Do I need to join that to the B+ as well(when there's no load present)?

Thanx in advance for any advice/tips/explanations.
7th June 2016, 04:38 PM
LostBenji

A small battery to provide exciter power to get the field energised, after running and producing power then it could be run standalone but regulation will be shit. Use a battery on it (just a little mower battery is fine) and run the sense wire to the Battery + terminal. Ground or chassis to the - terminal.
7th June 2016, 04:45 PM
Yendor

Whats the generator going to be used for?
7th June 2016, 05:05 PM
dom14

Quote:

Originally Posted by LostBenji

A small battery to provide exciter power to get the field energised, after running and producing power then it could be run standalone but regulation will be shit. Use a battery on it (just a little mower battery is fine) and run the sense wire to the Battery + terminal. Ground or chassis to the - terminal.

Thanx mate. If I understood you correctly, without the battery, it won't be possible to excite the field coil, and
battery is also necessary for the ongoing voltage regulation as well?

It's not possible to use the alternator as generator(12V or so) without a battery?

Thanx
7th June 2016, 05:08 PM
dom14

Quote:

Originally Posted by Yendor

Whats the generator going to be used for?

I'm thinking to run 12V appliances or combined with an inverter to run mains appliances, and of course on rare occasions to charge a battery as well.

I imagined it might do lot better than my measly little generator? :)
7th June 2016, 05:43 PM
Yendor

If your going to run accessories you will need to fit a battery, so you might as well make it a decent size one.

The alternator might self excite but you will need to find the sweet spot in the RPM. This could be a bit hit and miss so I would recommend connecting up the exciter/warning light circuit. You can just connect this to positive (no warning light) but I would use a warning light. If you do just connect it to positive it will still need to be via a switch or it will flatten the battery when the alternator is not running.

Just connect the sense wire to the B+ terminal on the back of the alternator.
7th June 2016, 06:06 PM
mudnut

An old style twelve volt generator will have more chance of "self excitation", but a battery would still be needed to give proper voltage regulation as well.
7th June 2016, 06:24 PM
dom14

Quote:

Originally Posted by Yendor

If your going to run accessories you will need to fit a battery, so you might as well make it a decent size one.

The alternator might self excite but you will need to find the sweet spot in the RPM. This could be a bit hit and miss so I would recommend connecting up the exciter/warning light circuit. You can just connect this to positive (no warning light) but I would use a warning light. If you do just connect it to positive it will still need to be via a switch or it will flatten the battery when the alternator is not running.

Just connect the sense wire to the B+ terminal on the back of the alternator.

Thanx mate..but..

Alternator stator winding need the field winding(magnet) to generate electricity out of the stator winding.
Then without a battery to initially turn the field winding into a magnet it apparently won't work?
But, once the stator winding started generating electricity, it can feedback to the field winding and feed each other?

So, it it essential to have a battery connected to the field winding, at least for a fraction of a second to generate electricity out of the stator winding?

Does it work in theory?! I mean like chicken or the egg first sort of situation(which obviously I don't have to understand, but would love to :) ).
Is possible by wiring up an alternator to self excite by connecting the trigger wire to B+?!!
If I understood you correctly above, it's possible, provided I work out the proper RPM spot for that by experimenting?

I understand that without a battery, alternator B+ output voltage won't be smooth(battery function as a capacitor to smooth the alternator's pulsed DC output?).
So, if I'm to use an inverter, it would be a good idea to make alternator's output is smooth by connecting a battery to B+?!!
And that would also apply to many 12V appliances as well.

The only issue with using a decent size battery in the unit is that it would make it heavy. But, of course, the battery doesn't need
to be attached/fitted to the generator.
7th June 2016, 06:30 PM
mudnut

You could use a small pony alternator that uses permanent magnets to give an initial start up. I have tried running alternators on a bench test, but I had to flash start the field.
7th June 2016, 06:32 PM
dom14

Quote:

Originally Posted by mudnut

An old style twelve volt generator will have more chance of "self excitation", but a battery would still be needed to give proper voltage regulation as well.

Yes, I think you answered my question on the previous post by the above answer.

It's pretty obvious I need a battery connected to make the generator a useful thing for 12V appliances or mains appliances via an inverter, as you explained.

My physics head can't get around the process of "self excitation". :D

If the stator winding can't generate electricity without the field winding's rotating magnet, where on earth does the stator winding
generate the initial electricity to power up the field winding??!!

I can't get my head around that!!!

What comes first, chicken or the egg? :D
7th June 2016, 06:37 PM
Yendor

Quote:

Originally Posted by dom14

Thanx mate..but..

Alternator stator winding need the field winding(magnet) to generate electricity out of the stator winding.
Then without a battery to initially turn the field winding into a magnet it apparently won't work?
But, once the stator winding started generating electricity, it can feedback to the field winding and feed each other?

So, it it essential to have a battery connected to the field winding, at least for a fraction of a second to generate electricity out of the stator winding?

Does it work in theory?! I mean like chicken or the egg first sort of situation(which obviously I don't have to understand, but would love to :) ).
Is possible by wiring up an alternator to self excite by connecting the trigger wire to B+?!!
If I understood you correctly above, it's possible, provided I work out the proper RPM spot for that by experimenting?

Are you talking without a battery fitted?. Without a battery fitted I would doubt an alternator will start charging.

Quote:

Originally Posted by dom14

I understand that without a battery, alternator B+ output voltage won't be smooth(battery function as a capacitor to smooth the alternator's pulsed DC output?).
So, if I'm to use an inverter, it would be a good idea to make alternator's output is smooth by connecting a battery to B+?!!
And that would also apply to many 12V appliances as well.

The only issue with using a decent size battery in the unit is that it would make it heavy. But, of course, the battery doesn't need
to be attached/fitted to the generator.

Without a battery fitted the regulator will have a hard time controlling the voltage. Depending on the load of accessories voltage could rise up to 19 volts
7th June 2016, 06:37 PM
dom14

Quote:

Originally Posted by mudnut

You could use a small pony alternator that uses permanent magnets to give an initial start up. I have tried running alternators on a bench test, but I had to flash start the field.

Ok, cool.
If i understood you correctly, it's possible to "self excite" an alternator in theory and practical,

but I still need to give the initial "flash" to the field coil via a battery(unless the field coil is a permanent magnet setup)!?
7th June 2016, 06:42 PM
dom14

Quote:

Originally Posted by Yendor

Are you talking without a battery fitted?. Without a battery fitted I would doubt an alternator will start charging.

Yes, without battery fitted modern alternator won't be able to generate any power. Am I right?
At least we need a battery connected to the field coil for a fraction of a second to generate any power via the stator coil?

Quote:

Without a battery fitted the regulator will have a hard time controlling the voltage. Depending on the load of accessories voltage could rise up to 19 volts

Yes, I understand. You explained that pretty well in previous post.
7th June 2016, 06:49 PM
dom14

Thanx mate.

I think I understand it now.

Battery is needed for at least three purposes

1)To "flash" the field coil initially, so the stator coil can generate electricity.

2)To smooth out the pulsed DC output from alternator B+ as it would in a conventional bridge rectifier equipped AC/DC conversion circuit with a capacitor.(battery = capacitor in this case).

3)Regulator would need the battery to regulate the output voltage of the B+

Am I right?
7th June 2016, 07:13 PM
Yendor

Quote:

Originally Posted by dom14

Yes, without battery fitted modern alternator won't be able to generate any power. Am I right?
At least we need a battery connected to the field coil for a fraction of a second to generate any power via the stator coil?

Without a battery positive connected to the B+ terminal of the alternator and the negative connected to the housing of the alternator it's very unlikely to start charging.

It is possible with the battery connect as above and the warning light circuit (or trigger/field as per the diagram you posted) not connected for the alternator to start charging. But you would need to find the sweet spot in the RPM.
7th June 2016, 07:14 PM
Yendor

Quote:

Originally Posted by dom14

Thanx mate.

I think I understand it now.

Battery is needed for at least three purposes

1)To "flash" the field coil initially, so the stator coil can generate electricity.

2)To smooth out the pulsed DC output from alternator B+ as it would in a conventional bridge rectifier equipped AC/DC conversion circuit with a capacitor.(battery = capacitor in this case).

3)Regulator would need the battery to regulate the output voltage of the B+

Am I right?

Yeah I can live with that.
7th June 2016, 07:42 PM
dom14

Quote:

Originally Posted by Yendor

Without a battery positive connected to the B+ terminal of the alternator and the negative connected to the housing of the alternator it's very unlikely to start charging.

It is possible with the battery connect as above and the warning light circuit (or trigger/field as per the diagram you posted) not connected for the alternator to start charging. But you would need to find the sweet spot in the RPM.

Yes, if I learnt it correctly from your posts, the wiring of my proposed home made generator has to be almost like the wiring in the wiring diagram to make it useful, including having a battery.

So, "self excitation" of modern alternators is NOT possible without the initial "flash" of electricity into the trigger/field/exciter wire.
After that, self excitation can continue, provided I get the correct RPM right for that.
7th June 2016, 08:33 PM
Yendor

Quote:

Originally Posted by dom14

Yes, if I learnt it correctly from your posts, the wiring of my proposed home made generator has to be almost like the wiring in the wiring diagram to make it useful, including having a battery.

Yes except just wire the sense wire to the B+ on the back of the alternator.

Quote:

Originally Posted by dom14

So, "self excitation" of modern alternators is NOT possible without the initial "flash" of electricity into the trigger/field/exciter wire.
After that, self excitation can continue, provided I get the correct RPM right for that.

There's no guarantee that without the warning light circuit connected that the alternator will start charging every time. But normally you can find a spot in a certain rev range and it will.
7th June 2016, 10:18 PM
GeeYou8

Maybe the project needs to be changed to a petrol powered battery charger?
My 2 cents worth is that there will always be some residual magnetism in the rotor for self excitation, you could add a couple of little button magnets to the rotor, would affect your regulation a bit. Still need a battery to smooth things out.
Graham
7th June 2016, 10:30 PM
dom14

Quote:

Originally Posted by GeeYou8

Maybe the project needs to be changed to a petrol powered battery charger?
My 2 cents worth is that there will always be some residual magnetism in the rotor for self excitation, you could add a couple of little button magnets to the rotor, would affect your regulation a bit. Still need a battery to smooth things out.
Graham

Hey Graham,
Thanx for the tip mate.
Actually this was a little garage project I started last year, then abandoned for some reason.
I think the potential noise put me off.
Now, I realize it's not that hard to come up with a good backyard muffler to reduce the noise.
Cheers
Dom
7th June 2016, 10:30 PM
dom14

Quote:

Originally Posted by Yendor

Yes except just wire the sense wire to the B+ on the back of the alternator.

There's no guarantee that without the warning light circuit connected that the alternator will start charging every time. But normally you can find a spot in a certain rev range and it will.

Thanx mate. I will keep you informed on my progress. Cheers