Noob alert.... Potentiometer with ROP and DD-P7?

Can I use a variable resistance potentiometer instead of a switch in my ROP-low, to variably dim the output?
Can I do the same in a DD-P7?

Sorry if this has been discussed before. Someone was asking me about the feasibility at a recent meet and I drew a blank.

Not sure if I fully understand- but Peak LED Soulutions uses a Potentiometer with their adjustable Law Enforcement Series- the Night Patrol and First Responder- some of those models have the Seoul P7 in them......

kramer5150 said:

Can I use a variable resistance potentiometer instead of a switch in my ROP-low, to variably dim the output?
Can I do the same in a DD-P7?

Sorry if this has been discussed before. Someone was asking me about the feasibility at a recent meet and I drew a blank.

Click to expand...

Yes you can. How well it would work, what potentiometer you would want to get, etc. I don't know about though.

Somebody correct me if I'm wrong, but I don't see any reason at all why you couldn't... it just might not be very feasible.

Resistors are used all the time to throttle current and reduce output (malkoff switch ring for one). Why couldn't I place a variable resistance pot (high quality) in line with the PR lamp or DD-P7... it would be like a dimmer knob to regulate (for lack of a better term) current flow to the lamp.

I would need to mod the stock mag switch to house the pot, and keep the PR lamp tower but that doesn't seem nearly as difficult as some of the other mods I have read about.

Surely someone on CPF has tried it.... and it must have failed or more builders would be doing it.:thinking: Seems like a very nuts & bolts mechanical way to get longer running, lower output out of a D mag.

kramer5150 said:

Resistors are used all the time to throttle current and reduce output (malkoff switch ring for one). Why couldn't I place a variable resistance pot (high quality) in line with the PR lamp or DD-P7... it would be like a dimmer knob to regulate (for lack of a better term) current flow to the lamp.

I would need to mod the stock mag switch to house the pot, and keep the PR lamp tower but that doesn't seem nearly as difficult as some of the other mods I have read about.

Surely someone on CPF has tried it.... and it must have failed or more builders would be doing it.:thinking: Seems like a very nuts & bolts mechanical way to get longer running, lower output out of a D mag.

Click to expand...

Like I said, I don't see why it wouldn't work. The trick, especially when dealing with higher currents, would be to find a potentiometer with an appropriate range of resistance. Also, if this replaces the stock switch, then you would have some retrofitting concerns.

With some resistance (reducing) mods made to the Mag and a potentiometer with appropriate resistance, this could be great. The P7 would be more likely to be a success, in my opinion. The ROP would proably get quite yellow as you dimmed it.

You can do this, but most potentiometers can't handle the current. and typically have too high a resistance to be useful in serious lights. For the ROP, consider that you have a roughly 7.2V supply, and the ROP bulb is in the neighborhood of 1.5 ohms (yes, it's non-linear, but I'm looking for a quick approximation...), so when you're running half-voltage (= 1/4 power, more or less), your pot must also be 1.5 ohm, and drop 3.6V, so 2.4A * 3.6V = 8.6W. (Also, note that you have an efficiency of only 50% -- so if you're trying to stretch runtime, this might not be a good way...) So you'll need a pot going from 0 to no more than 10 ohms, and rated for 10A dissipation -- which exist, I'm sure, but are not common, and will probably be a little on the large side.

For the P7, the computations are a bit rougher, since all the (useful) current variation occurs in the top 25% or so of the voltage scale, but similar resistances should be useful. It will have less dissipation, though, which is good for efficiency.


In either case, the better solution is to use the potentiometer as a control signal for a variable-current (P7) or PWM (ROP or P7) driver. (Of course you could use variable-current drivers with incans, but there's less than no point.) Simplest way would be a serious MOSFET with the pot as a voltage divider driving the gate, but now the MOSFET has to dump the 10W instead, and you still lose efficiency.

Better yet is a circuit using the FET in switching mode (PWM), since the FET uses no power when fully off, and almost no power when fully on. Should be a pretty basic 555 project, if that route suits you.

Alright.

Are you planning on just replacing the switch with a Pot, and hoping the Pot will get the job done ? Or are you going to build an actual driver circuit ?

You can't just run a straight pot. A typical pot is rated for about a 1/2watt at best. Maybe 1 watt if you get a larger one. You'll fry it instantly.

Someone mentioned the word throttle ? The Pot is pretty much like a gas pedal, and the pedal itself does not control the engines power. The pedal activates and operates the carburetor which regulates the flow of fuel to the engine, in turn controlling its power.

You need a Carburetor for this to work. LED lights generally tend to have a Driver Circuit running them. So some tech decided to control the driver with a Pot instead of the click programmed output levels. Still the pot is just telling the driver what to do.

You'd need a variable voltage regulator to this. It's a special kind of transistor that can take the current and does all the work, and the pot controls it. Its actually a VERY simple circuit. Problem is, for me, the only regulator I can name off hand is the LM317, and its only good for about 1.5 amps. So, if could run a ROP Low bulb, but not the ROP high bulb.

You'd need to find one with about a 5amp rating. This unit might get rather large. Also they generate heat, they need to be heatsinked. If you rigged an LM317 with a ROP low, you'd have to bolt it to the body of the mag (assuming you're modding a mag) for proper heat sinking, or it would overheat. Your light would also double as a hand warmer.

A 5amp Regulator controlling a ROP High bulb might need more sinking then just the mag body. So now this mod is getting rather large. Top it off, Regulators are inefficiant, the power you are restricting get burned up in the heat they produce. So you have less light yes, but you battery runtime is no better, if not less.

The way around this is to use a PWM type regulator, tho highly efficiant this is a complicated digital design.
At this point, if you actually want a variable output light, your best bet is just to grab up one of AW's Incan Drivers, which is a ready made drop in PWM regulator, and use a Bi-Pin bulb instead.

I have one of his Incan drivers, I love it.