Need a better dc 12V/3.5A regulated out from ac 12V/35W alternator

[samuel.sam77]

Hi dear all


I want to construct a circuit dc12v/35w from ac 12v/35w bike alternator 120hz .
Application -install new 35w hid light.
input float voltage 7-16V ac 120hz
expected output 12v /35w

i tried with full bridge and lm2575 switching regulator . but its failure . input voltage too high so its burned.
any help

 

[ronsimpson]

lm2575 ....but its failure . input voltage too high so its burned.

It is a 40 volt part. It should not have burned because of high voltage.
It is a 1 Amp part and you want 3A. That is a problem.

Usually this part is used as a 'buck' so the output voltage is less than the input voltage. Example 16V in will output 12V. But it needs 2 volts drop to work. So Vin of 12V will output 10V. Vin=20-->Vout=12.

More information please. Schematic and photo will help.

 

[Nigel Goodwin]

I suspect he's trying to convert a direct lighting system - best option is to add a decent size battery and convert the lighting circuit to a charger.

 

[MikeMl]

Sam, where is the 120Hz in the circuit??? The alternator in the bike puts out a range of frequencies and voltages depending on engine speed...

Seems to me that you need to full-wave rectify the alternator to produce DC, use a huge electrolytic filter capacitor for filtering, and then either series-regulate, or shunt regulate to make ~14V DC.

 

[ronsimpson]

Seems to me that you need to full-wave rectify the alternator to produce DC, use a huge electrolytic filter capacitor for filtering, and then either series-regulate, or shunt regulate to make ~14V DC.

Mostly agree. but....
The generator voltage is 7 to 16V. Many types of regulators can not take 7V and make 12V. Some can.
Probably when the generator is making 7V it can not make the 35W required. Maybe 3 watts.

 

[Nigel Goodwin]

Mostly agree. but....
The generator voltage is 7 to 16V. Many types of regulators can not take 7V and make 12V. Some can.
Probably when the generator is making 7V it can not make the 35W required. Maybe 3 watts.

As I said before, you need a decent size 12V battery, and convert the lighting circuit to charge it.

It's NOT an easy exercise (I thought long and hard about it years ago - as the lights on my DT-400 were pretty feeble), most practical way would probably be to rewind the generator coils - and there are numerous examples of that on-line.

 

[MikeMl]

Mostly agree. but....
The generator voltage is 7 to 16V. Many types of regulators can not take 7V and make 12V. Some can.
Probably when the generator is making 7V it can not make the 35W required. Maybe 3 watts.

Most don't care what happens when the bike is at idle. Once the engine is turning up at speed, the alternator puts out too much; that's when the regulation is needed.

 

[Zerotolerance]

My solution would be buy a motorcycle rectifier/regulator, but then again idk if that would work, as my motorcycles stator puts out 89VAC then converts it to 14VDC through the rectifier/regulator

 

[samuel.sam77]

My solution would be buy a motorcycle rectifier/regulator, but then again idk if that would work, as my motorcycles stator puts out 89VAC then converts it to 14VDC through the rectifier/regulator

i agree but any simple circuit?

 

[samuel.sam77]

Most don't care what happens when the bike is at idle. Once the engine is turning up at speed, the alternator puts out too much; that's when the regulation is needed.

small doubt ac 12V /120hz voltage convert to dc what is the maximum output voltage in different rectifier topology(half wave,full wave, bridge rectifier)

 

[dr pepper]

Its probably a shunt regulator with a perm magnet dynamo.

I suspect the '2576 fried due to noise.

You could build a filter from chokes/caps, or do as allready advised fit a battery.

 

[samuel.sam77]

Its probably a shunt regulator with a perm magnet dynamo.

I suspect the '2576 fried due to noise.

You could build a filter from chokes/caps, or do as allready advised fit a battery.

its ok need a 13.5V/ 3A regulator circuit for battery charging circuit
for online use of load current 12v 35W

 

[dr pepper]

If its a permanent magnet dynamo the o/p can end up 100s of volts without enough load.