depletion mode............

what exactly are you looking for in the specs to see if it's depletion mode......

Here's the MOSFET I mention before:

http://rocky.digikey.com/WebLib/Infineo ... Rev1.2.pdf

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Vgsth, V(oltage)g(ate to)s(ource)th(reshold). This is the voltage at which the MOSFET starts to turn on at. Depletion or enhancement mode, for an NFET, as one increases the voltage as measured from source to gate, it will eventually turn on. A depeletion mode transistor has a negative voltage; an ehancement mode transistor has a positive Vgsth.

This transistor, as seen on page two, has a threshold voltage of 1.2 to 2V. This is the point that the transistor starts to turn on at--don't expect it to carry 50A at only 2V Vgs.

You're obviously quite a bit more electronically skilled than I am, so let me pose this challenge to you:

Each of your headlamps has two filaments, a low and a high beam. Design your headlamp controller such that it has a mode in which each headlamp's high and low beam filaments are operated in series (yes, I mean series) with each other. Can you do it?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yes, but timing is critical when you just want to go to high or low so you don't have a short (at least the way I'm thinking about it)..........

You'll have the 2 filaments running at about 1/2 voltage (they're not identically rated, so they'll be slightly different) so they shouldn't overheat the bulb.

Will there be enough heat for the halogen cycle?

This sounds like a DRL solution though.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

It would indeed be important to avoid short circuits. I have a diagram and control module for doing this with electromechanical relays, but I'm curious if you can come up with a cleaner solution.,
The bulb won't overheat. The high-beam filament will dimly glow as it acts as a ballast resistor for the lower-wattage low-beam filament.
Yes.
It is. It's optically a pretty good one, makes a reasonably good-performing DRL and keeps the bulbs cleaner (halogen cycle) than simply reducing power to the low or high beam filaments. It's not an economical solution from the perspective of power consumption, though. Headlamp-based DRLs never are.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

How many relays?

There could be a combo relay/FET solution or a total FET solution


let me ponder............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Correct me if I'm wrong, but the neg lead is common to the two filaments, right? So wire up the common wire to a relay such that it is grounded for regular lights, and floats for DRL duty.

At the moment I'm thinking 3 relays; one for DRL, one for low beam, the other for high beam. The DRL relay is wired, using diodes, such that it turns off if either the low or high beams are active; DPDT relay. In the unactive state, high beam goes to 12V, and low beam to GND. In the active state, the DRL relay connects nothing.

The low and high beam relays are DPDT also; but when they go active, they provide both GND and 12V to the filament of choice. In any case, the stock wiring is used only to control the relays. In the unactive state, these relays connect nothing.

Maybe tomorrow it'll dawn on me a much better method.

I came up with a couple of 3 relay solutions......

My last 3 relay solution can have 2 of the relays replaced with an NFET.

Relay 1 SPDT:
Power in
NC contact to Low lug
NO contact to High lug

Relay 2 SPST or NFET
Ground lug

Relay 3 SPST or NFET
High lug


Low Beam:
Relay 1 remains off (power is connected to low lug already)
Turn relay 2 on (or NFET on) grounding low circuit

High Beam:
Turn relay 1 on (connect power to high lug)
Turn relay 2 on (or NFET on) grounding high circuit

DRL:
Relay 1 remains off
Turn relay 3 on (or NFET on) grounding high lug. Circuit is low lug thru low filament, then high filament, then ground.


I think the 1 relay 2 NFET is the cleaner solution (total FET is possible, but gets dirtier (the dual-throw aspect of the relay is useful))

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I feel like a dog thats just been told a joke. (its way over my head)

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Excuse me, does this smell like chloroform to you?

I thought I knew more about MOSFETS before this started.......

But it actually made me dig some more and I understand N-channel enhanced MOSFETS now (well better)...............


(you need a high-side driver when a NFET is used on the high-side (before the load))

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I came up with a way to have DRL, dim low beams, and bright high and low beams with 3 SPDT relays.............

(If anyone really wants to know, I'll post the info )


Also for fun, I hooked up the high and low filaments in series. Amp draw was about 3.3 (compared to 4.5 for high only), and the output was yellowish and low.

Does the low output actually do anything for you in DRL mode? (and how about a motorcycle, where you might want more output? )


And BTW, motorcycle wiring is really crappy and convoluted.
I measured 14.25 volts at the battery and 12 volts across the headlight..............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

1) If we delete the needless "dim low beams" mode, does that simplify the circuit any?

2) Does your DRL mode run the low + high in series?
Yes please!
Definitely! The minimum effective intensity for a DRL in most conditions is about 350 candela. Glare becomes a problem somewhere around 3,000 candela. With the low+high in series, and a line voltage of 13v, the low beam filament is going to see in the neighbourhood of 9.5 to 10.5v (do you agree with my calculations?), meaning oncoming traffic sees between about 600 and 2000 candela on a large lighted surface area at most every observation angle, which is a highly effective intensity range without a glare problem (glare problems exist if the driver uses DRL mode at night or in dusk/twilight).
Who says you want more output?

Similar and worse drops are common in car headlamp wiring, both old and new.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Same amount of relays (although instead of 3 SPDT, it can be 2 SPDT and 1 SPST) and almost identical wiring. Without the dim low beams there's less wiring. The dim low beams was because on a motorcycle I have only 1 headlight and wanted to preserve the life and only go brighter if I need to
Yes
I have no idea how you did the calculations, and it didn't seem right to me, so I used my spare bulb and old bulb (burn't out low) in series and got the following just running off a battery (no charger or alternator)

low filament 6.8v
high filament 5.15v

Only 11.95 volts because of all the jumper wires, and no charging.....

But the proportion should be the same with higher voltages.


I don't know, you're the expert


I've only hand drawn the wiring, so get your paper and pencil ready.

Relay terminal ids:

86 control input
85 control output
30 power in
87a normally closed contact
87 normally open contact

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

3 relays

Relay 1 (low)
Relay 2 (high)
Relay 3 (DRL)


Relay 1 wiring:

terminals
30 high filament
87 positive source
87a ground
86 existing high filament wire
85 relay 3 30 terminal and thru diode to relay 3 terminal 85


Relay 2 wiring:

30 low filament
87 positive source
87a ground
86 existing low filament wire
85 relay 3 30 terminal and thru diode to relay 3 terminal 85


Relay 3 wiring:

30 lamp ground relay 1 & 2 85 terminals
87 not hooked up
87a ground
86 power source
85 grounding switch to turn on DRL


Normal operation:

Whatever beam is on activates the relay for that beam (terminal 85 grounds thru relay 3)

DRL operation:

Relay 3 disconnects ground. Relay for high or low beam (whichever is on) grounds thru DRL switch turning that relay on. Power then passes thru that filament and out the other filaments relay (which is grounded)


Design considerations: This was designed for a motorcycle which always has a headlight on. DRL is an override mode which is manually turned on or off. So instead of high or low beam you would have high,low or DRL.


If you want low dim, make following changes

relay 1:
87a existing headlight high

relay 1 & 2:
85 relay 3 30 terminal only

relay 3
87 existing headlight low

you can figure out the current paths..............


I'll give some more thought to an auto setup........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The automotive solution has the above as a starting point.

The variations are in the control, if auto already has DRL, if you're adding DRL, and if you want to turn DRL off............


What solution are you looking for?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes