Need V and I limiter (AC)

S

subwar

Guest
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
 
Use a simple voltage regulator circuit on the feed to the light in
conjunction with a rectifier (the regulator wont work on AC)
subwar <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
On Mon, 08 Sep 2003 15:49:10 GMT, subwar <subwar2001@shaw.ca> wrote:

Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
The old Triumph motorcycles had a high power zener diode that was
across the alternator, when the voltage got to ~14 volts, the diode
conducted and dissipated the power as heat. Mine was bolted to the
air intake aluminum housing, some models had them in the slipstream
with their own heat sinks.

That may solve your problem if the alternator can stand the additional
loading. (and you can find a pair of high power zeners to use for AC)

The zener was rated at ~50 watts and the triumph had a lead acid
battery DC system.

A voltage dependant relay would be another simple solution. Relay
pulls in when the voltage is high and opens a set of contacts allowing
voltage to be limited by a resistor across the relay contacts.
Disadvantage would be hysteresis (pull in and drop out at slightly
different voltages). Hysteresis could be controlled by bending the
stop and/or contacts on the relay. It would take some fiddling to
make it work, and the relay would have to be protected from rain.

A resetable circuit breaker is a remote possibility - hard to find in
the exact size you'd need. There is a solid state (thermistor)
equivalent for a resetable breaker, but it has lots of hysteresis.

An all solid state regulator on a DC system would be more complicated
but work well and waste less power.


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I thought about this but I did see another circuit which looks
interesting. How about 2 12v zeners hooked in parallel with the
circuit so that when one side of the waveform went too high + it would
overcome the zener and flow to the other side thru the other zener as
it would act like a forward biased diode. Tell me what you think.

On Wed, 10 Sep 2003 10:17:14 +0000 (UTC), "Frontier"
<thefrontier@btclick.com> wrote:

Use a simple voltage regulator circuit on the feed to the light in
conjunction with a rectifier (the regulator wont work on AC)
subwar <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
How many Watts is the headlight? Or, how much current does it draw?
A 12 volt regulator with a bridge rectifier would work.

Jay

"subwar" <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
The light pulls 25w, it is a total separate system from the everything
else. Strange little thing.

On Thu, 11 Sep 2003 09:51:58 -0400, "happyhobit"
<happyhobit@wideopenwest.com> wrote:

How many Watts is the headlight? Or, how much current does it draw?
A 12 volt regulator with a bridge rectifier would work.

Jay

"subwar" <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
Hi Dan,

Your headlamp draws about 2 amps. Using a zener diode to waste the excess
current always seemed counter productive to me. But to be honest you will
lose 1.3 volts with the regulator solution. Here are some zener part #'s
1n3311-12 volt-50Watt, 1n2976-12 volt-10Watt. Don't know what they cost or
where you can get them.

Cost wise a rectifier/ regulator solution would cost about $5.00USD. You
could mount a bridge rectifier and a regulator on a piece of prototype board
or you could mount the components separately.

3 Amp 12 volt LDO regulator $ 1.55
6 amp 50 volt Bridge rectifier $ 1.80
Heatsink 12W 9C/W $ 1.36

Jay


"subwar" <subwar2001@shaw.ca> wrote in message
news:53j4mvgst4bf9c0lahgj168oms5imhur98@4ax.com...
The light pulls 25w, it is a total separate system from the everything
else. Strange little thing.

On Thu, 11 Sep 2003 09:51:58 -0400, "happyhobit"
happyhobit@wideopenwest.com> wrote:

How many Watts is the headlight? Or, how much current does it draw?
A 12 volt regulator with a bridge rectifier would work.

Jay

"subwar" <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
thanks for the ideas, maybe i'll try both as a head light costs $30 US
and is getting hard to find.

On Fri, 12 Sep 2003 21:26:54 -0400, "happyhobit"
<happyhobit@wideopenwest.com> wrote:

Hi Dan,

Your headlamp draws about 2 amps. Using a zener diode to waste the excess
current always seemed counter productive to me. But to be honest you will
lose 1.3 volts with the regulator solution. Here are some zener part #'s
1n3311-12 volt-50Watt, 1n2976-12 volt-10Watt. Don't know what they cost or
where you can get them.

Cost wise a rectifier/ regulator solution would cost about $5.00USD. You
could mount a bridge rectifier and a regulator on a piece of prototype board
or you could mount the components separately.

3 Amp 12 volt LDO regulator $ 1.55
6 amp 50 volt Bridge rectifier $ 1.80
Heatsink 12W 9C/W $ 1.36

Jay


"subwar" <subwar2001@shaw.ca> wrote in message
news:53j4mvgst4bf9c0lahgj168oms5imhur98@4ax.com...
The light pulls 25w, it is a total separate system from the everything
else. Strange little thing.

On Thu, 11 Sep 2003 09:51:58 -0400, "happyhobit"
happyhobit@wideopenwest.com> wrote:

How many Watts is the headlight? Or, how much current does it draw?
A 12 volt regulator with a bridge rectifier would work.

Jay

"subwar" <subwar2001@shaw.ca> wrote in message
news:i69plv0pilcriv2jr7gr2c3o0louia3bf3@4ax.com...
Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Thanks
Dan Sutherland
Click to expand...
 
On Mon, 08 Sep 2003 15:49:10 GMT, subwar <subwar2001@shaw.ca> wrote:

Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.
Click to expand...


Hi

Easy solution would be a 1 transistor current limiter circuit.

Regards, NT
 
Do you have a schematic?

cheers


On 19 Sep 2003 05:12:54 -0700, bigcat@meeow.co.uk (N. Thornton) wrote:

On Mon, 08 Sep 2003 15:49:10 GMT, subwar <subwar2001@shaw.ca> wrote:

Hi

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.



Hi

Easy solution would be a 1 transistor current limiter circuit.

Regards, NT
Click to expand...
 
subwar <subwar2001@shaw.ca> wrote in message news:<fe6nmv8cbk3bq1cg7mktntf75fcmabf55r@4ax.com>...

What I have is a small scooter that uses a alternator to supply the
head light. It is a direct line to the headlight for 12v AC. Of course
if I go down a steep hill the alternator will put out to much voltage
and burn out the low beam headlight. Any ideas on how to fix this
problem.

Easy solution would be a 1 transistor current limiter circuit.

Do you have a schematic?
Click to expand...

Hi. In my head yes, but not in ASCII, no. Correction: 2 transistor,
not 1.

Tr1 is a power tran, tr2 a signal tran.

The main pass transistor controls the +line, biased by an R from
supply + to its base. Tr 2 is attached with its collector to tr1 base,
emitter to supply -, and base to output -. There is, for 2A, a 0.3 ohm
R between Tr2 b and e.

Tr 2 stays biased off until i_out reaches 2A, when it starts to come
on.
Tr1 stays biased on until tr2 comes on. When tr2 comes on it robs base
driver from tr1 thus reducing i_out, keeping it to 2A.

You would probably need a bit of variability on the 0.3 ohm R to set
bri correctly.

This cct has one other advantage: because it runs the bulb on dc from
ac - rectifier - reservoir, the bulb reaches full bri at a lower
alternator speed than presently.

Regards, NT
 
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