Ok, regulated is better, but how about resistored?

Orion

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Understandable and given that a regulated light is better. But is a light with a resistor so undesirable? When money is an issue, more volts than necessary and a resistor to can't be all that bad, can it?

Say two CR123 cells, a 3 watt LED, and a 2.8 ohm resistor?
 

gadget_lover

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Re: Ok, regulated is better, but how about resisto

Given a choice between having no light and having one with a resistor...

The choice is rather obvious.

Resistors are not bad, per se, unless you have badly mismatched your battery pack and LED. If you are dropping more than 1/4 the voltage you really have the wrong setup. I.E a 12 volt battery running a single 3 watt luxeon. The resistor is going to burn about 3 times the power that the luxeon would use.

Daniel
 

xpitxbullx

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Re: Ok, regulated is better, but how about resisto

Here is a question along the same lines. If I wanted to run 11V but my battery pack is 15V and the ballast requires 1amp. Could I add, lets say, a 4ohm resistor to compensate for the extra voltage?
 

Lynx_Arc

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Re: Ok, regulated is better, but how about resisto

4ohms at 4 watts would do it but as the voltage drops from 15v so will your overall circuit voltage to your ballast follow proportionately and when the voltage of the batteries sag to 11volts your resistor would drop it considerably below that.
 

chrisse242

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Re: Ok, regulated is better, but how about resisto

[ QUOTE ]
Orion said:
Understandable and given that a regulated light is better. But is a light with a resistor so undesirable? When money is an issue, more volts than necessary and a resistor to can't be all that bad, can it?

Say two CR123 cells, a 3 watt LED, and a 2.8 ohm resistor?

[/ QUOTE ]

My first mod was like this, and I still use it from time to time. I used a 3.3 Ohm 2 Watt resistor for a cheap "Walther tactical Flashlight". Turns a useless twenty dollar light into something usefull, and lacking a converter there are less parts that can fail. If you already have a light and want a cheap mod for it, or you're new to modding, just do it.

Chrisse
 

xpitxbullx

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Re: Ok, regulated is better, but how about resisto

With the resistor (waiting for a regulator) the light will then be able to use my rechargeable cr123 batteries. I'll measure the voltage after every 5 minutes to determine how long the batteries can be used before removing the resistor. I was thinging of putting a resistor inbetween 2 metal discs with non-conductive epoxy to bond the discs into a 2 or 3mm sandwich. I'll just throw it in behind the batteries and remove it when the voltage decreases enough in the batteries. I was also thinking of a way to leave the resistor sandwich in and make a slide switch of some kind to bypass the resistor. That way I dont have to remove it and place it in my pocket when the voltage starts to sag.

Either that or keep buying boxes of surefire 123's. Hmmmm...
 

KevinL

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Re: Ok, regulated is better, but how about resisto

One of the things I thought of is a "high beam/low beam" switching system using resistors. My plan called for two switches with resistors of different values, in parallel. Let's say one of them has 1 ohm, the other one has 2.2 ohm.

Both switches off - light is off
2.2 ohm switch on - light is on, low beam (more resistance)
1.0 ohm switch on - light is on, high beam
Both switches on - light is on, maximum power.

Opening both paths will give you 0.6875 ohms of resistance as parallel paths decrease resistance. With two switches you get three light levels. Resistor values are given as samples only, you'll need to do a lot more calculations yourself for your specific applications!

IMHO, resistored, regulated, or direct drive - it really depends on the problem you are trying to solve. All have their merits and failings (there's no perfect solution or we'd have universally agreed upon that already), and the important thing is that you are comfortable with the choice you are making. It is, after all, your light /ubbthreads/images/graemlins/smile.gif

The OA4D Cookbook Mag is a resistored design and still one of my favorites, even though I have some very interesting regulated ones around here.
 

HarryN

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Re: Ok, regulated is better, but how about resisto

I have been down both paths with this with $ spent on each method, so here is MHO and what I am doing for my upcoming small light.

I personally like the 2x123 format, good power capacity, flat voltage curves over a broad demand, small, etc. These also have the real advantage of being able to drive a light under adverse weather conditions.

In my particular light, I am using a 223 battery (breaking the rules, of course), but this is a 2x123 setup prebuilt in series, with both terminals on the same end - this was a particular advantage for my setup.

As far as regulated vs resistored - In order for most of the regulated setups to work in a buck (down convert) mode, the electronics need Vin at least 1 V above Vf. If you have a Lux III with a Vf of 3.5V, add a protection diode (0.3V), you are fast approaching 4 volts.

If you then look at the energizer curves, and try to draw 500ma + from them, the voltage delivered will rapidly sink to only 0.5 V or less of headroom. This is getting pretty tight. A cold battery might not do it.

For my light, partially due to space constraints, I used a 2 ohm, 1206 size resistor for high, 10 ohm for medium, and 200 ohm for low. Since there is already 0.5 - 1 ohm due to springs, contacts, etc, this puts the actualy current (at least in theory) around 750ma, 300ma, and 30ma respectively.

My worst case condition for power dissipation is somewhere around 1 amp (at the very start of the cell life), so 1amp x 2 ohm = 2 watts in the resistor, and 3 watts in the Luxeon III. This ratio actually improves within 1 minute as the voltage stabilizes closer to 5.3 volts (at least on the charts)

The real problem I had with the design was that all of the small resistors I found were only 1/4 watt or less. I ended up, much to my dismay, having to have a batch of custom resistors made up for the ohm range I wanted. The price per resistor was not that bad (a few $), but the min order was 250 for each resistance, so it added up.

I now have a lot of these resistors either already or almost due. I do not need all of them, so if anyone else needs some 1206 size 2, 10, 25, 30 ohm, 50 watt (yes, that is a fifty watt) resistors, PM me.

I probably will put them up in the shoppe so I don t have to deal with logistics.

I think that if you have a 2x123 format, and unless you get regulator electronics that can handle both buck and boost, resistor is not that bad.

Pulling more than an amp out of a 123 IMHO is not ideal.

HarryN
 

NewBie

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Re: Ok, regulated is better, but how about resisto

[ QUOTE ]
HarryN said:
As far as regulated vs resistored - In order for most of the regulated setups to work in a buck (down convert) mode, the electronics need Vin at least 1 V above Vf. If you have a Lux III with a Vf of 3.5V, add a protection diode (0.3V), you are fast approaching 4 volts.


[/ QUOTE ]

It depends alot on the chip utilized. Many will allow you to get very very close to Vin on a buck, it is not uncommon to be able to operate within 0.18V. As far as the protection diode, you can toss that too, if you put features in the light to prevent the battery from making contact if inserted backwards. With some chips, they have an integrated oscillator and charge pump for the top MOSFET which allows them to go to 100% duty cycle so you can turn the top MOSFET on 100%, and if you utilize 0.020 or 0.010 ohm MOSFETs, with a 0.0046 DCR inductor, you are only looking at the total drop as a result of 0.025 to 0.015 ohms (or a voltage drop of only 0.0175 Volts to 0.011 Volts (or 0.0175 to 0.011 Volts headroom, and when the battery drops to below VF the battery is directly connected to the cell for all intense purposes....

To give a person an idea of what that low of a resistance is like, many flashlight bodies and switches have a higher resistance than that.

The 2 x 123 makes the cell efficiency increase alot too. Losses inside are I^2*R
 
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