Georges80: Question(s) about Fatman

George,

I was thinking about whether I could use the Fatman as an LED driver for
my car Dome. Your standard dome won't fit into my Honda Accord because
it uses U shaped clips instead of the end type clips in my Corolla.

Anyway, I was wondering: If I can rectify the 12.8V down to 3V or so and then use a Fatman to drive a Lux III, would it still be possible to somehow hook into the brightness rheostat so that when the lights are dimmed, the dome would dim as well. Would the 12+V input on the rheostat damage the Fatman module?

Any other issues I should think about, or need to know about?

Thanks.

George will be able to better answer this question..

But, I would just like to point out, that the Fatman is a boost circuit.
If you need to take your cars 12V down to 3V for the LED, you need a buck circuit.

Geoges Uflex and Nflex are buck circuits.
These also have multiple brightness levels, but are conrtolled by pressing and holding the power button, where as the Fatman can be dimmed with a Pot.

At jtice stated (thanks), Fatman is a boost (step up) driver. It would be totally defeat the purpose of having a switching supply if you first dropped the 12V down to 3V (lots of heat) and then tried to boost it back up for the LED.

Also, a current regulated switcher will try to keep constant current through the LED regardless of input voltage, so newer cars with the autodimming feature won't have that with a straight driver/LED setup. The LED/driver will work, it just won't dim.

The likelihood of been able to use the vehicle's dimming control (either automatic or via the rheostat on the dash) is zero with any of my drivers.

If you can't fit one of my buck converters into the light fixture somehow, then you're not totally out of luck. Some folk have just mounted my driver remotely (wrapped up into the headliner etc) and then fabricated a small mounting plate for the Luxeon to fit in the existing light fixture.

Then you have Darell (Mr EV) who has used my nFlex drivers in his EV with dimming control and autosleep (to turn off automatically if left on/door ajar etc). But, we all know about Darell... /ubbthreads/images/graemlins/crackup.gif

george.

[ QUOTE ]
georges80 said:
The likelihood of been able to use the vehicle's dimming control (either automatic or via the rheostat on the dash) is zero with any of my drivers.
george.

[/ QUOTE ]

I had a thought but it applies to the fatman since you can use a pot to adjust it.. using a dig. pot maybe you could control it.. of course you'd need to put a few lux' in series to get the voltage above 12V.

-awr

[ QUOTE ]
andrewwynn said:
[ QUOTE ]
georges80 said:
The likelihood of been able to use the vehicle's dimming control (either automatic or via the rheostat on the dash) is zero with any of my drivers.
george.

[/ QUOTE ]

I had a thought but it applies to the fatman since you can use a pot to adjust it.. using a dig. pot maybe you could control it.. of course you'd need to put a few lux' in series to get the voltage above 12V.

-awr

[/ QUOTE ]

Nope...

1) Fatman abs max Vin is 12V.
2) The pot is part of the electrical/control circuit of Fatman and cannot have power on it. A vehicle rheostat has some voltage across it - since it's basically a brute force dropping resistor. An external digital pot won't run on vehicle power and would need to be regulated - so more complexity.

I guess, since I've never wanted to dim my interior dome lighting, it's not been a consideration. My vehicle doesn't do the slow dim after the doors are closed so I don't miss that feature - not sure what it's good for anyway other than looking cute when you first buy it /ubbthreads/images/graemlins/grin.gif

I know that Darell on his EV used my nFlex driver and provided a switch to access it so if he want's to dim it or set it to a new level he can tailor each dome output. But, it won't dim via vehicle control.

Give it a few more years and all the mainstream vehicles will have interior LED lighting and then the features will be tied into an ECU...

george.

my thought of using the vehicle rheostat was this: use the voltage drop on that rheostat to have a control voltage.. run that over to the fatman, but use a dig. pot locally to actually control the fatman... i actually didn't even think of the Vin.. but you'd need a Vregulator to drop the voltage from the 14.4 max of the car... looks like it 'could be done' but a lotta work..

just like the idea of using a single driver to run multiple lights through the car... not really geared up for it since the wiring is parallel yet you want to run them series..

probably much more logical to put in an nFlex and a little wire back to a button.

-awr

I shudder to suggest the simplest solution, but a resistor is really all you need. It will allow the LED to dim like a light bulb would.

It will need to be a high wattage resistor, and plan on as many as 14.5 V coming from the vehicle. A cap or other filter might be worth considering, too.

Hey, how about 2 or more LM 317s in series. Set one so that it saturates at 12 V from the car. Once it falls below 12 V, the LM 317 no longer supplies the current (or voltage) needed to keep it burning brightly and it dims. The LM 317 is inefficient, but hey, it is in your car where power is cheap. Just another idea.