Drawing enough current?

[Bobby Zero]

After doing some conversion on my own, I'm wondering why anyone would bother using a Star III with the MR Force FX. The Star III is designed to run on 1000 to 1400mA. The MR battery pack supplies a forward voltage of 3.9v average, but after the sound module, it's only supplying around 500mA. That's enough for a Star/O, but in my opinion, a waste of a Star III.

I notice, if you disable the sounds, the Star III will brighten considerably. Anyone else notice simialar results?

[MythranDir]

I have noticed the same power problem. When I hook up a Lux III to the MR board I barely get 250 mA (this was a Blue LED)!! Other people have resorted to wiring the LED directly to the battery through a relay, that is presumably turned on when the saber is activated. I have thought about replacing the 3 AA's with two 3.6V rechargeable Lithium Ion batteries, however I don't know if the MR board can handle the higher voltage (7.2 V instead of the 4.5 V provided by 3 AA's).



MythranDir

[Strydur]

well you guys got me curious and since I dont know how to use my multimeter worth a crap I did a little experiment.
../scripts/4aa.jpg
This is a amber led running off of 4aa with the proper resistor.
../scripts/3aa.jpg
This is the same setup running off 3aa in a MR with sound going.

Like I said I am not sure how to measure amperage but as far as I can see its running just fine off of 3aa with the sound playing.

Tim

[MythranDir]

Tim,

I have a few more thoughts about the issue of current and brightness.

First, the amber and red Luxeons operate at a forward voltage of ~2.95 V compared to the green and blue LED's that operate at a forward voltage of ~ 3.9 V. Empirically, I have found that I can get higher currents from 3 AA's for the red and amber LED's than I can for the blue, cyan, and green LED's. I was in the middle of documenting this more carefully when the fuse in my multi-meter blew out. Once I get it replaced I will try to complete these measurements.

Second, the eye responds to brightness 'logarithmically'. What this means is that if you increase the luminous output of the LED from say 10 lumens to 100 lumens, the eye will easily see this 10-fold increase in brightness; however, the eye will be much less sensitive to an increase in brightness from 100 - 200 lumens. This characteristic is what enables the eye to form an image of a scene even though the brightness of the various scene objects can vary by many orders of magnitude. This leads me to believe that doubling the LED current from say 250 mA to 500 mA might not be worth the effort, since to the eye the LED brightness may not be perceived to increase by a factor of 2. I have not checked this out myself, and the extent to which an increase in current increases its perceived brightness may depend on the LED color.

In any event, I plan on doing some experiments to check these things out more carefully.

MythranDir

[Strydur]

I will have to try it with one of the 1000mA led's. So far I have only tried the red and amber. That would make sense since the 1400mA ones require less voltage. You are correct that the eye can be decieved but what I was showing is that with 4aa and the proper resistor I am getting the proper mA out of the batteries and it looked exactly the same running with the 3aa and the sound going. But, like you said it might be totally different with the 1000mA led's.

Tim

[Strydur]

Well I finished my sons anakin just in time for halloween. I am still not having the same problem you guys had.

../scripts/blueled4aa.jpg
Blue led running at 1000mA off of 4aa.
../scripts/blueled3aa.jpg
Same led but running off of 3aa in the MR with sound going.

Tim

[MythranDir]

Tim,

It looks beautiful! I think I will do the same comparison you did (4 AA's with a resistor vs. 3 AA's using the MR board) and repeat my current measurements.



MythranDir

[Bobby Zero]

Well, actually, my point was that the Star/O and the Star III looked equally bright running off the MR board, as they're both drawing about 500mA or less. The only difference is that the Star III is twice as expensive, after buying the optics. So, why bother with the Star III?

[Strydur]

If I am running a red LED that has a forward voltage of 2.95 and I am using a 2.2ohm 5w resistor and 4AA then the LED is running at 1400mA not 500mA. If I then run the same led off of the 3aa inside of a MR hilt and it is just as bright then how can you say I am only getting 500mA out of an MR hilt? That just doesnt make any sense. Can you explain where my thinking is wrong since you keep stating that I am supposedly only getting 500mA out of the MR hilt?

Tim
The Custom Saber Shop

[Bobby Zero]

You really can't know for certain how much current your Luxeon is really drawing without testing it (under load) on a good multimeter. This is exactly what I've done, and I'm testing less than 500mA off the MR board when it's under load, using alkaline batteries.

Judging by our eyes is not terribly precise, as discussed earlier. You can't see the difference between the 4 cell and 3 cell configuration. I can't see the difference between a Star/o and a Star III when run off the MR board.

The low amps and lack of visible difference leads me to believe that there may be no point to using a Star III over a Star/o.

[Strydur]

Maybe we are talking about different versions of the MR, all I know is the 3w work just fine and look great. And if the mr is only supplying 500mA then evidently that is all that is needed to drive them to full brightness since they run just as bright as driving them off of 4aa at 1400mA. If you want to take pictures of your multimeter hooked up and testing it while running off the mr and again while running off of 4aa then I would love to see the results.

Tim
The Custom Saber Shop

[Strydur]

Ok I got my hands on a fluke meter and went a testing... Depending on how you tap into the mr power/sound module is what decides how much current you get.
../scripts/mrmod.jpg
Ok in this picture. If you hook you negative to pin1 and your positive to vdd you will only get about 500mA which is the way I have done it so far and seems to be plenty of current for the star III. From what I have read up to about half the rated current can be a visible difference but after half it is hardly noticeable. Ok, but if you want to get the full 1400mA then hook your positive to vdd and you negative to all the pins 1-6 and you will get pretty much exactly 1400mA. If you need 1000mA then use a 2.2ohm resistor in the circuit.

If any of you can confirm that this is the same for your modules please do so.

So I guess we where all right, sorta.. The mr board using the wiring I showed only gave you 500mA or less but if you do it this new way then you can get the 1400mA no problem.

Dont forget while testing you must take the LED out of the circuit and put your meter in place of it in order to properly calculate the mA going to the LED. Otherwise you are just measuring how much current is left over after the LED takes what it needs.

This is just the info I have learned and I of course could be totally wrong. So if you have other info or think I am figuring something wrong then please let me know so I can block you from posting..er I mean look into it.


Tim
The Custom Saber Shop

[Bobby Zero]

Sweet! Thanks for the info. I'll have to try that out.

[MythranDir]

Thanks for the info!! I will definitely give this a try.

MythranDir

[Strydur]

While this shows we have 1400mA of current it doesnt take into account that whole forward voltage calculation the led needs. I still dont fully understand how this all works. Someone get a rep from luxeon to explain it all before I rip my hair out[:(!]I need to look more into how that calculation works. If someone can shed more light on how this all works please do so.

Tim
The Custom Saber Shop

[MythranDir]

Tim, for a given desired current, the required value of resistance is obtained by dividing the voltage difference between the battery and diode by the desired current. For example, for a battery voltage of 4.5 V, and a diode forward-voltage of 3.9 volts, and a desired current of 1 Amp, the required resistance is (4.5 - 3.9)/ 1 = 0.6 Ohms. Some of the on-line resistance calculators round this up to a 'standard' value of resistance.

I tried hooking up the LED to the MR electronics as you suggested (hooking the negatives to pins 1-6) and was able to get more current, although for the blue LED I can still only get a maximum of ~ 500 mA. For the cyan and green I can easily get over 700 mA. However, I am not happy with the quality of my connections, and once I have solved this issue I will repeat these measurements. Thanks again for the info on the MR electronics.

MythranDir

[Strydur]

Do you measure the amperage while the led is connected?

Tim
The Custom Saber Shop

[MythranDir]

Tim,

You can measure the current when the LED is in the circuit. The multimeter is put into the circuit in series with the LED. In this way, you will be able to tell what the current actually is with the LED in place. When I do this with the blue LED using 3 AA's and no resistor, the best I can do is ~ 450 mA, using lithium ion batteries.

BTW, there is a huge difference in current depending on the type of battery. When I switch from the Energizer lithium ion batteries to Radio Shack alkaline batteries the best I can do is 350 mA.

I have also confirmed that when I use all the ground wires from the MR board I can get 450 mAmps through the blue LED, again without using a resistor. With red, green, or cyan LED's I can get upwards of 800 mA from the MR board. I think the issue with the blue LED is that it probably has a higher forward voltage than the other colors. This makes sense because blue photons are more energetic than the other colors.

Of course, 4 AA's can provide all the current you want for any color.

Thanks again for the info on the MR board. Connecting all the grounds has definitely increased the current.


MythranDir

[Strydur]

The thing I dont get is...If you measure the current using 4aa's and the resistor that the calculator says to use for 6v and a blue LED then you get the following measurements which dont make much sense.

../scripts/ledtesting1.jpg
no resistor..5770mA
../scripts/ledtesting2.jpg
with resistor..1663mA
../scripts/ledtesting3.jpg
with blue led and resistor..425mA

Which leads me to believe you cant accurately measure these fricking things!!!!


Tim
The Custom Saber Shop

[MythranDir]

I think your measurements are ok. If your question is why does the current go down to 450 mA when the LED is in the circuit, the reason is there is a ~ 3.9 V drop across the LED, which means the voltage drop across the resistor is only about 6 - 3.9 = 2.1 V. The current through the circuit is 2.1 V divided by the value of the resistor. Without the LED in the circuit, the entire battery voltage, 6 V, is dropped across the resistor, which means the current in the circuit will be 6 V divided by the value of the resistor. So, the current with the LED in the circuit will be at least 3 times smaller than when there is no LED in the circuit.

One weird thing I noticed is that when I first turn on the power (using the MR electronics) the current starts off pretty high and then drops and after a few minutes stabilizes at 350 mA. I think one problem is the AA batteries are not really intended to operate at these high current draws. I am thinking that as the battery discharges the battery resistance or voltage changes, thus changing the current delivered to the diode. I think that is why I observe higher and more stable currents when I use lithium ion batteries.

MythranDir

[MythranDir]

I found a way to get more current using the MR board. I use 2 Energizer 1.5 volt AA batteries, and one 3.6 V lithium battery. I found this battery at a speciality store, and it cost $10! This increases the voltage, and with this arrangement I can get over 600 mA of current. However, the current drops as a function of time. I have not yet determined what the 'floor' is, but I am still playing around with this configuration. Also, I am not sure how advisable it is to mix battery types. I could use 2 of these 3.6 V batteries I suppose.

Do you know if the MR board can handle 7.2 volts?

MythranDir

[MythranDir]

Ok, ignore what I said in my previous post. The new batteries I bought crapped out after 30 minutes of testing. Geez. I am about out of ideas. It seems the best configuration is 4 batteries, period. I seem to be able to get about 500 mA or so in this configuration. How I will implement this in a MR saber while keeping the same speaker arrangement is beyond me.

MythranDir

[Strydur]

Why go through the trouble though. I make and sell the MR conversions and they seem to run fine off 3aa..Ultra sells them and converts them and does the same thing. The fact is they look just fine, so who cares what the Ma is =) Besides if you are testing it and have 500mA while the LED is hooked up then you are getting the same mA you would be from using 4aa like I showed above.

Tim
The Custom Saber Shop

[MythranDir]

I agree with you!! It looks great no matter what the multimeter says. I am just going to accept what the MR board can deliver.

MythranDir

[falco13]

did anyone acctually answer the original question[?]

falco13

[Strydur]

Its was more of a statement than a question and it has been debated in all the posts between it and this one.

Tim
The Custom Saber Shop