Jump to content

Nominations for Tractor of the Month
Garden Tractors and Parts on eBay



Photo
- - - - -

Briggs Dual Circuit Alternator


  • Please log in to reply
10 replies to this topic

#1 jonnycraftsman OFFLINE  

jonnycraftsman
  • New Member
  • Member No: 25593
  • 1 Thanks
  • 3 posts

Posted June 18, 2013 - 02:07 PM

I have an '85 Briggs horizontally opposed twin with the dual circuit alternator. These things put out just enough to charge the battery and power a couple lights.

 

I was looking at the wiring though and noticed that the DC is only half rectified with a diode. all I could find is that it should put out 3amps so I'm guessing that's really between 2 and 4 amps and between 12.5v and 15v. Working the numbers it looks like the AC supply must be around 27.6v accounting for a single resistor drop. So if you where to use a bridge rectifier couldn't you get 26.4v 2-4amp output?

 

Be nice to be able to run an electric PTO.

 



#2 boyscout862 ONLINE  

boyscout862
  • Senior Member
  • Member No: 8923
  • 9,803 Thanks
  • 7,544 posts
  • Location: N.E. Connecticut

Posted June 18, 2013 - 04:16 PM

Welcome to GTT. That is over my head so, wait for someone to give you the right answer. While waiting check out the Manuals and Photo Galleries. Good Luck, Rick


  • jonnycraftsman said thank you

#3 Arti OFFLINE  

Arti
  • Senior Member
  • Member No: 11282
  • 1,290 Thanks
  • 963 posts
  • Location: South West Wisconsin

Posted June 18, 2013 - 05:02 PM

I think that you would get 5 to 6 amps at 13.8 volts with a full wave rectifier.  I'm not sure if the field alternator windings would stand that for any length of time.


  • jonnycraftsman said thank you

#4 JDBrian OFFLINE  

JDBrian

    Super Moderator

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2507
  • 9,574 Thanks
  • 14,136 posts
  • Location: Hubley, Nova Scotia - Canada

Posted June 18, 2013 - 05:18 PM

You will likely get more current with the full wave circuit. It depends on the impedance of the windings and the load you put on it. It's likely designed to put out a certain current to the battery on the peaks of the AC rather than a certain voltage. I'm assuming it has no regulation other than the battery which acts as a current sink and prevents the voltage from rising. If you go to a full wave you will potentially get  more current but the peak voltage will be slightly lower due to 2 diode drops being in the circuit for each half cycle. You'd need to test this on a battery to see if it would work, but it will not function as it was designed. You could over charge the battery or over heat the windings of the stator. 


  • jonnycraftsman said thank you

#5 New.Canadian.DB.Owner OFFLINE  

New.Canadian.DB.Owner
  • Senior Member
  • Contributor
  • Member No: 10178
  • 2,224 Thanks
  • 1,451 posts
  • Location: Trenton, Ontario, Canada

Posted June 18, 2013 - 07:36 PM

You are all partly right.  The voltage (in a purely resistive load) would double.  The Vdc output from a 1/2 wave rectifier is Vp/pi or .318Vp, where Vp = the Peak to Peak voltage as measured on an oscilloscope.  For a full wave bridge rectifier it is 2Vp/pi or .637Vp.  In practices, the second diode drops about 1/2 Vdc.

 

That said, Power (an thus heat) increases with the square of the voltage.  In other words, when the voltage doubles, the power quadruples.  The coil will likely burn out.

 

That said, the rules are different for a battery, which is a capacitive & resistive load.  The voltage will build up in the battery and eventually hit almost Vp.  The time required to hit Vp will depend on the internal resistance of the battery.


Edited by New.Canadian.DB.Owner, June 18, 2013 - 07:36 PM.

  • jonnycraftsman said thank you

#6 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,319 Thanks
  • 28,636 posts
  • Location: N. W. PA

Posted June 18, 2013 - 09:12 PM

The full wave will take the RMS voltage of slightly higher, but no where near double in measured reality.
If the peak to peak is 30 VAC, the half would be 15 (every other peak) and the full would be 15, just twice as often.

Nuts and bolts, it should do more amps, maybe a volt or so measured higher.
As for the stator handling it all, that's unknown... Should, but ?
But here is the kicker: look at the circuit. On the stator, one end ties to chassis. For arguments sake, we will call it L2. The wire with the diode in it is L1.
On a full wave rectifier, you have L1 and L2 in, + and - DC out. But if you draw a line from L2 to -DC (because they are both chassis connections) what do you have? A messed up circuit, possibly even a voltage tripler due to the capacitance of the battery.

I don't think you would see a net gain in actuality. Possibly some real issues in longevity.

Attached Thumbnails

  • image.jpg

  • New.Canadian.DB.Owner and jonnycraftsman have said thanks

#7 New.Canadian.DB.Owner OFFLINE  

New.Canadian.DB.Owner
  • Senior Member
  • Contributor
  • Member No: 10178
  • 2,224 Thanks
  • 1,451 posts
  • Location: Trenton, Ontario, Canada

Posted June 18, 2013 - 10:09 PM

I agree with MH81 on his last point.  I hadn't considered the stator being frame grounded.  A full wave rectifier won't work in a system that is hard grounded on one end of the coil.  However, I stand by my math for a system where the coil has two non-grounded ends.


  • jonnycraftsman said thank you

#8 New.Canadian.DB.Owner OFFLINE  

New.Canadian.DB.Owner
  • Senior Member
  • Contributor
  • Member No: 10178
  • 2,224 Thanks
  • 1,451 posts
  • Location: Trenton, Ontario, Canada

Posted June 18, 2013 - 10:21 PM

You could just do this:

 

voltage doubler.png

 

But, that gives you +12vdc and -12vdc.  That's okay for charging a battery 24vdc with a floating ground that would run a winch or something, but not an electric PTO with a frame ground.


Edited by New.Canadian.DB.Owner, June 18, 2013 - 10:24 PM.

  • jonnycraftsman said thank you

#9 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,319 Thanks
  • 28,636 posts
  • Location: N. W. PA

Posted June 19, 2013 - 06:50 AM

You might be able to use the light circuit with a diode and gain another amp or so, assuming it has one.
It would be a separate wire that only drives the lights. Most I've seen were white, but I'm sure they could be other colors.
  • jonnycraftsman said thank you

#10 jonnycraftsman OFFLINE  

jonnycraftsman
  • New Member
  • Member No: 25593
  • 1 Thanks
  • 3 posts

Posted June 19, 2013 - 08:10 AM

Oh my god! I didn't think I was going to get so many responses! You guys are over my head but it sounds to me like there would be a considerable amount of testing involved to figure out all the variables and probably only a small gain if any.

 

MH81 your last post is something I'm considering. I do have the 14v light circuit so I was thinking of using that to power an auxiliary batt for a winch and forgetting the electric PTO. I'm pretty sure I'd only get an amp or two out of it though and I wonder if the coil would take it. I would still have to put the batt on a tender when I'm done I'm sure and the winch would probably only be good for lifting implements.

 

I'm seeing the logic if adding an alternator like others have. Seems like I could get all the power I wanted without a lot of engineering. Then I could use my winch for pulling as it might be handy for firewood duty.



#11 jonnycraftsman OFFLINE  

jonnycraftsman
  • New Member
  • Member No: 25593
  • 1 Thanks
  • 3 posts

Posted June 19, 2013 - 08:12 AM

Another nice thing with the external alternator is easy swap when it burns out.


  • MH81 said thank you




Top