Another Makita BML185 18v Mod...

I am new here, so bear with me...

I've been following http://www.candlepowerforums.com/vb...-your-help-with-18v-worklight-led-replacement! and his light looks great. I now want to build my own.

I have a few questions on things I am not sure about. I have purchased:
http://www.vantecusa.com/en/product/view_detail/96
http://pcb-components.de/index.php?...category_id=6&option=com_virtuemart&Itemid=64
http://pcb-components.de/index.php?...category_id=8&option=com_virtuemart&Itemid=64
5xCree XM-L U2 Star Base

Is there any point in using all 5 LEDs or should I just you 4 LEDs. Also, do you think my heatsink will be able to cool led's efficiently? How many? And what AWG wire do I need to purchase? I am sure I will have more questions as this is my first light build. This is all I can think of at the moment.

Isnt anyone willing to help?

Thanks everyone for the help. It was greatly appreciated.

ksears91 said:

Isnt anyone willing to help?

Click to expand...

ksears91 said:

Thanks everyone for the help. It was greatly appreciated.

Click to expand...

Willingness may not the problem here, other members may not be familiar with the products you linked and don't feel qualified to comment - Norm

Well thanks for the reply. I will just have to research more and try to figure it out. I will post results when I am finished. Thanks.

Can't comment on the driver or dimmer because i don't speak German; the voltage range looks like it is appropriate though.
The fan dimensions (88mm) seems larger than the interior dimension (70mm) listed in your linked build thread. Also, have you figured out what resistor to use between the 12volt fan and battery pack?
I'd estimate that using 5 leds won't leave much voltage overhead for the driver.
For a heatsink of that type to work, the light's plastic casing has to be modified to allow cool air in (intake) and hot air out (exhaust). That was the problem that is still being solved in your linked build thread; have you come up with a solution?

Sent from my DROID RAZR using Tapatalk

darkknightlight said:

Can't comment on the driver or dimmer because i don't speak German; the voltage range looks like it is appropriate though.
The fan dimensions (88mm) seems larger than the interior dimension (70mm) listed in your linked build thread. Also, have you figured out what resistor to use between the 12volt fan and battery pack?
I'd estimate that using 5 leds won't leave much voltage overhead for the driver.
For a heatsink of that type to work, the light's plastic casing has to be modified to allow cool air in (intake) and hot air out (exhaust). That was the problem that is still being solved in your linked build thread; have you come up with a solution?

Sent from my DROID RAZR using Tapatalk

Click to expand...

The 2 tabs on the heatsink can be ground down to provide the needed dimensions. I will be using a 12v regulator to power the 12v fan. I am not sure what you mean by "overhead for the driver." I have not come up with a permanent solution for the cooling. I will see how how the temps are outside the casing and modify the casing as much as I have to to reach same temperature. I do not have to run the LEDs on high 100% of the time. I was thinking of using a "KSD 9700 90ºC BiMetal Switch" on the heatsink and have it kill the light if the temp is too high. I am not sure how or if this will work. Any input?

And thanks for the response.

I'm glad to help (what little help I may be able to provide); I'm no expert. Since I'm on a computer, I was able to view the english versions of the spec sheets for your driver. It is buck-based, which means that the driver steps down the voltage of the battery pack to the voltage of the led bank. So in order for the driver to operate, the battery voltage has to be higher than the led voltage; that's what I meant about driver overhead. For the sake of argument, lets say that the average Vf of an xm-l at 2.8 amps is 3.5. 4 xmls x 3.5= 14 volts; that leaves 4 volts of overhead for the driver to operate from. However, 5 xmls have a combined voltage of 17.5; this leaves .5 (nominal) volts for the driver to operate from. Since under load the voltage of a battery drops, your battery pack will likely be unable to run 5 xmls for any significant period of time. I think in your particular build, 4 leds is your best bet.

Given that your driver does not appear to have its own temperature sensor, adding a separate one that acts as a failsafe is a good idea.

Now lets move on to the heat issue. In the other Makita build thread, it was eventually stated (by the light builder I think) that if he were to do the mod again, he would not use a heatsink meant for a GPU. While the copper is great, as is the fan, there is only so much it can do on its own to cool the leds. Another person even commented on "separating" the interior of the light body into two partitions; one with cool air and one with the warm air from the heatsink. I would love to be wrong about this, but I would wager that partitioning or sectioning the light would do very little to cool anything down. I believe the reason that a GPU cooler works so well in a computer is that it is not alone. Yes, the copper pulls heat away from the processor, and the fan helps move heat away from the copper in the form of hot air...but where does the air go? Even with the vents in a computer case, without any other active fans, the hot air pulled away from the GPU will mostly just stay where it is, and eventually the components will cook themselves. A standard desktop computer will have I believe four fans in addition to its GPU and CPU fans. Two case fans, one acting as intake and one as exhaust, and two fans in the PSU (again one acting as intake and one as exhaust). Those extra four fans are what move the hot air out of the case and cool air in.

So getting back to your build, I think even if you swiss cheese the plastic head of the flashlight, you will still have some temperature problems. However, if you were able to mount two small fans on either side of the light to act as intake and exhaust, you would probably be able to push enough air over your GPU heatsink to keep it cool-ish.

Again, I'm not an expert, so please take what I say with a grain of salt. I'd also shoot the original builder a PM and see if any improvements have been made to his light to keep it running cooler.

ksears91 said:

The 2 tabs on the heatsink can be ground down to provide the needed dimensions. I will be using a 12v regulator to power the 12v fan. I am not sure what you mean by "overhead for the driver." I have not come up with a permanent solution for the cooling. I will see how how the temps are outside the casing and modify the casing as much as I have to to reach same temperature. I do not have to run the LEDs on high 100% of the time. I was thinking of using a "KSD 9700 90ºC BiMetal Switch" on the heatsink and have it kill the light if the temp is too high. I am not sure how or if this will work. Any input?

And thanks for the response.

Click to expand...

darkknightlight said:

I'm glad to help (what little help I may be able to provide); I'm no expert. Since I'm on a computer, I was able to view the english versions of the spec sheets for your driver. It is buck-based, which means that the driver steps down the voltage of the battery pack to the voltage of the led bank. So in order for the driver to operate, the battery voltage has to be higher than the led voltage; that's what I meant about driver overhead. For the sake of argument, lets say that the average Vf of an xm-l at 2.8 amps is 3.5. 4 xmls x 3.5= 14 volts; that leaves 4 volts of overhead for the driver to operate from. However, 5 xmls have a combined voltage of 17.5; this leaves .5 (nominal) volts for the driver to operate from. Since under load the voltage of a battery drops, your battery pack will likely be unable to run 5 xmls for any significant period of time. I think in your particular build, 4 leds is your best bet.

Given that your driver does not appear to have its own temperature sensor, adding a separate one that acts as a failsafe is a good idea.

Now lets move on to the heat issue. In the other Makita build thread, it was eventually stated (by the light builder I think) that if he were to do the mod again, he would not use a heatsink meant for a GPU. While the copper is great, as is the fan, there is only so much it can do on its own to cool the leds. Another person even commented on "separating" the interior of the light body into two partitions; one with cool air and one with the warm air from the heatsink. I would love to be wrong about this, but I would wager that partitioning or sectioning the light would do very little to cool anything down. I believe the reason that a GPU cooler works so well in a computer is that it is not alone. Yes, the copper pulls heat away from the processor, and the fan helps move heat away from the copper in the form of hot air...but where does the air go? Even with the vents in a computer case, without any other active fans, the hot air pulled away from the GPU will mostly just stay where it is, and eventually the components will cook themselves. A standard desktop computer will have I believe four fans in addition to its GPU and CPU fans. Two case fans, one acting as intake and one as exhaust, and two fans in the PSU (again one acting as intake and one as exhaust). Those extra four fans are what move the hot air out of the case and cool air in.

So getting back to your build, I think even if you swiss cheese the plastic head of the flashlight, you will still have some temperature problems. However, if you were able to mount two small fans on either side of the light to act as intake and exhaust, you would probably be able to push enough air over your GPU heatsink to keep it cool-ish.

Again, I'm not an expert, so please take what I say with a grain of salt. I'd also shoot the original builder a PM and see if any improvements have been made to his light to keep it running cooler.

Click to expand...

I think the battery actually measures closer to 20v. I also already glued the LEDs (5) to the heatsink . I figured I would just run it at 50% if it got to hot. Also, will the sensor I provided work? I was planning on using a separation plate like mentioned. There is really no room in there for a 2nd fan. There is actually really no room in there for a fan+heatsink unless it is like a GPU setup. I don't have anything to check temps. Thermometer will be here shortly.

Yes, I believe the battery comes off the charger at about 21 volts. The nominal voltage of the pack, 18 volts, is where it spends the majority of its discharge curve. So right off the charger, yes it should be able to light up all 5 leds. Plus the driver says that it is up to %97 efficient, so it may run for a while driving 5 leds. I don't know about the sensor off hand, I'll google it tomorrow. It was really late at night when I read the other Makita thread; what is trying to be accomplished by adding in a separation plate? All I remember was the mention of keeping the cool air separate from the hot air...

ksears91 said:

I think the battery actually measures closer to 20v. I also already glued the LEDs (5) to the heatsink . I figured I would just run it at 50% if it got to hot. Also, will the sensor I provided work? I was planning on using a separation plate like mentioned. There is really no room in there for a 2nd fan. There is actually really no room in there for a fan+heatsink unless it is like a GPU setup. I don't have anything to check temps. Thermometer will be here shortly.

Click to expand...

darkknightlight said:

Yes, I believe the battery comes off the charger at about 21 volts. The nominal voltage of the pack, 18 volts, is where it spends the majority of its discharge curve. So right off the charger, yes it should be able to light up all 5 leds. Plus the driver says that it is up to %97 efficient, so it may run for a while driving 5 leds. I don't know about the sensor off hand, I'll google it tomorrow. It was really late at night when I read the other Makita thread; what is trying to be accomplished by adding in a separation plate? All I remember was the mention of keeping the cool air separate from the hot air...

Click to expand...

Basically he did not want the hot air recycling in the chamber. The separator would provide fresh air for the intake. Also, will it hurt anything if I run 5 LEDs on that drive at 18v?

That's right, thank you for the reminder. That may actually end up doing more than i thought it would.

Will it hurt anything on the driver? Not that i can see. Per the specs it can drive up to seven leds with a max input voltage of 28. Just know that with five leds, when the driver shuts off the battery won't actually be fully discharged.

Sent from my DROID RAZR using Tapatalk

darkknightlight said:

That's right, thank you for the reminder. That may actually end up doing more than i thought it would.

Will it hurt anything on the driver? Not that i can see. Per the specs it can drive up to seven leds with a max input voltage of 28. Just know that with five leds, when the driver shuts off the battery won't actually be fully discharged.

Sent from my DROID RAZR using Tapatalk

Click to expand...

What if I only run they at 50% brightness? (i also bought the uDim) does that drop the voltage or only current?

That will drop the current that is sent to the led. It will also decrease the voltage drop of the battery; less current draw means less voltage drop.

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I think most of my questions are answered now. All I can do now is test temps and put the thing together.

Only other real questions I have are:

Will that bi-metal switch work for me?

The uDim draws current even at 0% brightness. Anyway I could build a circuit using a MOSFET, capacitor, and resistor. Basically When I press the momentary on button, it will charge the capacitor. The resistor will slowly drain the capacitor (maybe over 20min) and this will cause the MOSFET to go back into an off state, cutting the circuit off. Not sure if this will work. Any feedback??

ksears91 said:

I think most of my questions are answered now. All I can do now is test temps and put the thing together.

Only other real questions I have are:

Will that bi-metal switch work for me?

The uDim draws current even at 0% brightness. Anyway I could build a circuit using a MOSFET, capacitor, and resistor. Basically When I press the momentary on button, it will charge the capacitor. The resistor will slowly drain the capacitor (maybe over 20min) and this will cause the MOSFET to go back into an off state, cutting the circuit off. Not sure if this will work. Any feedback??

Click to expand...

Anyone??

If you use the stock switch to turn on/off the MOSFET and run the LEDs at low power (350mA/per) you will still have more light than stock without heat issues and avoid the real problem with that light which is bulb life. At low current the battery will stay in regulation far longer as well. It's a plastic light, not titanium.

rufusbduck said:

If you use the stock switch to turn on/off the MOSFET and run the LEDs at low power (350mA/per) you will still have more light than stock without heat issues and avoid the real problem with that light which is bulb life. At low current the battery will stay in regulation far longer as well. It's a plastic light, not titanium.

Click to expand...

I have had the lights running outside the housing and the heatsink never gets hot to touch, at least after 10 min. My IR gun says the temp is under 70c, but I do not know how accurate that is. And I am not really sure what you are talking about with the MOSFET. Why would you need the mosfet with the stock switch? Can the switch not handle the load?