Hi

Referring to SgtWookie's design for Motorcycle Rectifier-Regulator (Post #5) at

http://forum.allaboutcircuits.com/threads/12v-ac-motorcycle-regulator.39419/

1) I would like to request SgtWookie to please explain the use of the inductor L1. That circuit simulates the exactly same without the inductor.

2) I simplified it as per attached. I got perfect regulated voltage 14.4V; the mosfet remained super cool however, only D3 got hot. Doubting the condition of D3, I replaced with a fresh one but same result. I would like to have some valuable comments, why it is getting hot and what should be done to control heat dissipation.

Thanks in advance.

 

If one diode in a bridge is getting hot then it usually means the opposite diode has failed short. In this case, with D3 overheating, that would be D1. This assumes everything is wired as per diagram. The 1N5408 is rated for 3A which is OK for 2.5A output, but the MOSFET regulates the output by drawing extra current through the bridge so the diodes have to be able to cope with the maximum generator output.

Not SgtWookie, but the inductor is probably there to help smooth out the switching spikes to keep them out of the control circuit. That circuit uses the MOSFET as a switch - it is either fully on or fully off - that keeps the power in the MOSFET to a minimum. Your circuit uses the MOSFET in a linear fashion so the power dissipation will be higher.

 

Thanks for the input, AlbertHall.

After replacing D1, I shall get back to you on Monday.
Regarding mosfet, frankly I was also expecting the heat dissipation but, it is super cool!

 

It might get hotter when the bridge is working properly.

 

I suspect the anode of D3 should not be grounded in the real world (only in the Spice simulation).

Edit: Ignore. I was squinting at a small screen and misread the schematic .

 

I suspect the anode of D3 should not be grounded in the real world (only in the Spice simulation).

If not then D3 would be of no use and the bridge would be incomplete, ultimately the rectification would be half-wave instead of full-wave.

 

Post a picture of the actual pcb circuit you built, you may have something wrong...

 

It might get hotter when the bridge is working properly.

The D3 is in perfect health however, I replaced with a new one.
No change, exactly same results.

 

 

After replacing D1, I shall get back to you on Monday.

The D3 is in perfect health however, I replaced with a new one.
No change, exactly same results.

But did you replace D1?

 

You have the Generator and Negative rail shorted out, Bottom picture, bottom two tracks with a small copper link.

 

But did you replace D1?

I am sorry for the typing mistake, I meant D1.
Yes I replaced D1.

 

You have the Generator and Negative rail shorted out, Bottom picture, bottom two tracks with a small copper link.

No, that small portion of the Negative Rail is disconnected.

 

I am sorry for the typing mistake, I meant D1.
Yes I replaced D1.

And D3 still gets hot?

 

The problem is when this is wired to the bike?
Then check that neither generator wire is shorted to chassis.

 

The problem is when this is wired to the bike?
Then check that neither generator wire is shorted to chassis.

I tested the circuit on two other bikes and got the same result.
D3 ===> Extremely Hot
D1 ===> Fairly Warm
Mosfet ===> Cool
Regulated Output ===> 14.4 - 14.6V

 

I tested the circuit on two other bikes and got the same result.

Did the original circuit use a bridge rectifier? If not, one end of the winding may be grounded and that would account for the hot diode.
With the board disconnected check across each of the four diodes for a short and also check that the generator winding has no connection to the bike chassis.

Then, just to make me happy, remove the diagonal link which has one end between D1 and D2. It doesn't (or at least shouldn't) connect anything and it it worries me.

 

Did the original circuit use a bridge rectifier? If not, one end of the winding may be grounded and that would account for the hot diode.
With the board disconnected check across each of the four diodes for a short and also check that the generator winding has no connection to the bike chassis.

Then, just to make me happy, remove the diagonal link which has one end between D1 and D2. It doesn't (or at least shouldn't) connect anything and it it worries me.

Which original circuit are you talking about? I'd referred to Sgt.Wookie's circuit which had 4 diodes.
I had already checked each diode for shortage, all are fine.
The generator winding has no connection to the bike chassis.

The diagonal link which you are referring was actually used to provide a convenient connection to the harness connector when it was soldered directly to the veroboard. Later I removed the connector and reattached via wires so the diagonal link is confusing you, though I had clearly indicated that the link is separated from the negative rail................2nd picture, 4th track from the bottom. But still, as you said, I should make you happy.

The circuit's behavior is the same with that link removed.

 

Which original circuit are you talking about?

The one the bike was originally fitted with.

But now I give up - I have no idea why the diode is overheating.

 

Can you tell us the exact make/model of your bike's generator?
Have you checked with a meter, when the generator coil is in place, that there is no leakage current through the bike chassis (e.g. due to insulation damage)?