MR16 Parts Coop...is there an interest?

[budude]

The best thing about constant current sources is that you do not need to be concerned with the selection of current limiting resistors which can result in inaccurate/varying current levels depending on many factors (LED drop, heat, etc). The use of constant current chips keep the current at a particular level despite those changes. If you peruse around this and other forums, you'll find that resistor selections can be troublesome at times.

[occhristmas]

Ok...I am a bit dense as well.  Can someone explain specifically what modifications would need to be made to build the mr16 without the mosfets? 

I guess my confusion is that this is a coop interest board...then we ran into the issue of the mosfets not being in stock anywhere...and this is where i am fuzzy.  So, are we suggesting ways to build the controller not using the mosfets? 

My question is...are we still trying to put together a coop parts kit for the controller design as is, or modifying it into something that is maybe going to work or maybe not going to work?

Don't get me wrong, maybe going to work is definitely better than not being able to find all of the parts to complete the build. 

I just am not at the level of being able to intelligently discuss technical electrical terminology - all I know is to solder things where RJ tells us to!

[D56VillageNut]

Ok...I am a bit dense as well.  Can someone explain specifically what modifications would need to be made to build the mr16 without the mosfets?  

I guess my confusion is that this is a coop interest board...then we ran into the issue of the mosfets not being in stock anywhere...and this is where i am fuzzy.  So, are we suggesting ways to build the controller not using the mosfets?  

My question is...are we still trying to put together a coop parts kit for the controller design as is, or modifying it into something that is maybe going to work or maybe not going to work?

Don't get me wrong, maybe going to work is definitely better than not being able to find all of the parts to complete the build.  

I just am not at the level of being able to intelligently discuss technical electrical terminology - all I know is to solder things where RJ tells us to!

Check out the last part of Step 1 in the MR16 Manual posted in the wiki.  http://diylightanimation.com/wiki/index.php?title=Manual_MR16.  This will explain how the constant current portion of this controller can be set to a specific output (ie 100 mA) when not using the MOSFETs.  (Please note that as of now the pictures of the pc board in the manual are not of the latest version so you'd need to have one of the new version PCBs on hand to reference the markings on the board and the location of the components being mentioned.)

The MOSFETs essentially work like a relay in that they allow a large amount of current to be controlled by the low current "controller" portion of this board.  This was due to the MR16 being originally designed to power a 32 LED MR-16 bulb that ran on 12v and drew about .17 Amps each.  The controller with MOSFETs installed could handle up to 15 of these MR16 LED Bulbs on each channel.

The ability to leave off the MOSFETs and set the current output from the "constant current" portion of the board to a specific value (in mA) allows the MR16 board to run a single LED or small groups of LEDs on each channel.  A typical LED runs on about 15 - 20 mA of current.  As mentioned in an earlier post the control circuits on this board are good up to about 100 mA per channel which would mean that you should be able to run up to five (5) 20 mA LED loads on each channel of the board for example.

The MOSFETs can be added to the board to allow it to be used with current flows of 1 Amp or more per channel.  (The manual states 2.5 Amps max per channel and 35 Amps total for the entire MR16.)  
There is a specific resistor value (4.7K ohm according to the manual) that is used to set the correct "constant current output" when using the MOSFETs for high current loads.

In short you can build the MR16 as either a high current controller or a low current controller depending on your specific needs.

Hope this helps clear up some of the confusion.

Alan T

[RJ]

Ok...I am a bit dense as well.  Can someone explain specifically what modifications would need to be made to build the mr16 without the mosfets? 

I guess my confusion is that this is a coop interest board...then we ran into the issue of the mosfets not being in stock anywhere...and this is where i am fuzzy.  So, are we suggesting ways to build the controller not using the mosfets? 

My question is...are we still trying to put together a coop parts kit for the controller design as is, or modifying it into something that is maybe going to work or maybe not going to work?

Don't get me wrong, maybe going to work is definitely better than not being able to find all of the parts to complete the build. 

I just am not at the level of being able to intelligently discuss technical electrical terminology - all I know is to solder things where RJ tells us to!

In this case it is OK cause the MR16 was designed to be built both ways. It was original done for a member to run led's on his train as a constant current led driver controlled by DMX. Then as I was building it I found that people wanted a way to control the MR16 lights and thus would just need some mosfets to handle the addional load so I added them with the ability to leave them off and jumper. So it is both setups. The mosfets have sub's that will work since the called for ones are rated at 100 volts and 15 amps and the board is not designed for that much. So we have a subbed part for the mosfet with plenty in stock and all is good.

RJ

[ponddude]

Like RJ said he sent me what FETs could be subbed out.  I am going to get refresh the quotes and go ahead and start the COOP later on tonight.

Stay tuned......

[sittinguphigh]

Yes interested

[ponddude]

Just to let everyone know I started the COOP tonight.  It can be found here....

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[wbuehler]

Just to let everyone know I started the COOP tonight.  It can be found here....

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Awesome

Thanks for doing this

Bill

[budude]

The ability to leave off the MOSFETs and set the current output from the "constant current" portion of the board to a specific value (in mA) allows the MR16 board to run a single LED or small groups of LEDs on each channel.  A typical LED runs on about 15 - 20 mA of current.  As mentioned in an earlier post the control circuits on this board are good up to about 100 mA per channel which would mean that you should be able to run up to five (5) 20 mA LED loads on each channel of the board for example.

You have to be very careful there. A constant current source is generally meant to drive a single string of LEDs in series, not multiple strings in parallel. You essentially lose the whole purpose of CC because each string will have different electrical characteristics and you could have much more (or less) current going down one leg as opposed to another. This will result in uneven brightness and/or early failures. In addition, the failure of a leg could possibly lead to catastrophic failure of the remaining legs. This isn't so likely with five 20mA legs but still not optimum in either case.

[D56VillageNut]

The ability to leave off the MOSFETs and set the current output from the "constant current" portion of the board to a specific value (in mA) allows the MR16 board to run a single LED or small groups of LEDs on each channel.  A typical LED runs on about 15 - 20 mA of current.  As mentioned in an earlier post the control circuits on this board are good up to about 100 mA per channel which would mean that you should be able to run up to five (5) 20 mA LED loads on each channel of the board for example.

You have to be very careful there. A constant current source is generally meant to drive a single string of LEDs in series, not multiple strings in parallel. You essentially lose the whole purpose of CC because each string will have different electrical characteristics and you could have much more (or less) current going down one leg as opposed to another. This will result in uneven brightness and/or early failures. In addition, the failure of a leg could possibly lead to catastrophic failure of the remaining legs. This isn't so likely with five 20mA legs but still not optimum in either case.

I appreciate the feedback and understand what you are saying.  In response to the original question I was trying to help occhristmas understand the difference between high current configuration and low current configuration (ie why all the fuss about the MOSFETs ).  I would agree with not putting parallel loads on a constant current driver.  I should have made that clearer by stating "....five (5) 20 mA LEDs in series on each channel....".  Thanks for pointing that out.

Alan T

[budude]

Multiple 20mA LEDs in series require higher voltage but would still draw 20mA. However, I believe you can put an appropriate resistor to allow for a 20mA constant current source as well. The 100mA value is just the limit (as I understand it anyway). Anyway - just thought it was important to note about the parallel paths as it's easily overlooked.

[D56VillageNut]

Multiple 20mA LEDs in series require higher voltage but would still draw 20mA. However, I believe you can put an appropriate resistor to allow for a 20mA constant current source as well. The 100mA value is just the limit (as I understand it anyway). Anyway - just thought it was important to note about the parallel paths as it's easily overlooked.

I was looking at the datasheet and it seemed it would be OK.  The TLC5940 can put out up to 17 V per output depending on how its configured.