Add a Cree HeadLight to your 48V system

[hardym]

Here's a way to add cheap, but powerful head and tail light to your 36 or 48 volt system for under $50.

Start with this Cree light package from ebay for $30. This is a Super bright light that has more than enuf power for night rides. It Includes a small battery pack that you will not need. http://www.ebay.com/itm/261129243438?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649





Add in this DC-DC converter $4.99 + shipping. http://www.ebay.com/itm/300810925667?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649




Any variant DC-DC converter is fine, but make sure you get the LM2596HV (HV= High voltage). One with a built-in cooling fins may be better

Adjust the Dc-DC converter down to about 3.2 volts. This seems to reduce the overall power consumption of the converter when used with the light. I've encased the DC-DC converter in shrinkwrap.

I have a switch on my controller, and the inrush current on the DC-DC blew out the switch. So, I soldered a T0-220 N-FET to the neg input lead of the DC-DC converter, and use the controller's 5V supply to the Gate of the mosfet. This allows the 5V line to turn on the Dc-Dc converter. I included a 10K resistor between the Gate and Gnd to help the MOSFET turn off.



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For the tail light, I manually soldered all the leds in parallel (bypassing the built in control circuit) and then to a 100 ohm resistor in series to the DC-DC converter output. The Tail light is on whenever the controller is on, which is nice.
Mark.

 

[NeilP]

For the more 'electronically challenged ' among us..can you give a little schematic of the wiring of the TO 220 package FET to power on the dc-dc convertor

I have been looking at powering one of those tail lights too, but decided to go with a LM338 and power the rear lamp with 3 volt as per original..so the flash modes etc still work.

The headlamp I used came from e-bay complete with a up to 90volt supply - down to 12 volt convertor.

 

[amberwolf]

http://www.ti.com/product/lm2596#technicaldocuments
has an interesting design generator applet on it

spec sheet
http://www.ti.com/litv/pdf/snvs124b
A Low Cost/Parts-Count DC/DC Converter w/Multiple Outputs (Rev. A)
http://www.ti.com/litv/pdf/snva003a

 

[alfantastic]

Is there room inside the light unit to fit the DC-DC converter?

 

[NeilP]

I have not taken one of those apart, but from the ones I have stripped down, I doubt it

 

[wannesd]

I know absolutely nothing about electronics (which is about to be perfectly obvious):

Why can't we just solder a resistor inline with a lead to the pack, to get the voltage we need for the lamp?

 

[alfantastic]

I know absolutely nothing about electronics (which is about to be perfectly obvious):

Why can't we just solder a resistor inline with a lead to the pack, to get the voltage we need for the lamp?

I'm no expert either, but I should imagine the DC-DC convertor is far more efficient than running a resistor inline to reduce the voltage.

 

[onlineaddy]

The headlamp I used came from e-bay complete with a up to 90volt supply - down to 12 volt convertor.

Would you share with us which light that is? Thanks.

 

[amberwolf]

Why can't we just solder a resistor inline with a lead to the pack, to get the voltage we need for the lamp?

That would limit the current to a certain maximum, but even that would change as the voltage of the pack dropped over time.

Same thing for voltage--as the current drops, the voltage across the resistor would drop. But depending on the resistance of the lamp, it mightn't be proportional--some lamps change resistance dpeendign on the current flowing thru them (or rather, the temperature of the filament), so that makes it more complicated.

Plus if you have to drop a lot of voltage across the resistor, and you need to pull a fair bit of currnet thru it, it will get very hot, and need to be large and have a large heatsink, or even a fan. Same thing with linear regulators (like the lm317).

 

[hardym]

Thanks, i posted a schematic of the MOSFET switch on the DC-DC converter in the first post, and a picture of the MOSFET soldered and screwed onto the DC-DC converter.

I haven't opened the Cree light, but the DC-DC coverter is larger than the light, so I dont suspect it would fit in side. My installation has the Dc-DC converter tied underneath the controller. As you can see in the picutre, it's only about an inch wide.

WRT Resistor vs. DC-DC converter: Yes, it's much more efficient to use a DC-DC converter rather than a resistive load, espeically when the voltage difference is great. With a DC-DC converter with good effiency the power in equals the power out. With a resisive load, the current in equals the current out and all the delta V is lost in heat.

The CREE draws about 300 ma at 4V, or about 1.2W. With the DC-DC converter, the draw is only 40 ma at 48V or 1.9 W. If you used a resistive load, the resistor would consume 48-4=40V * 300ma = 12W. (Not what you want on an E-bike.)

Mark.

 

[sn0wchyld]

I know absolutely nothing about electronics (which is about to be perfectly obvious):

Why can't we just solder a resistor inline with a lead to the pack, to get the voltage we need for the lamp?

I'm no expert either, but I should imagine the DC-DC convertor is far more efficient than running a resistor inline to reduce the voltage.

in simple terms yes. running a ~5v 10w light off a 50v pack means you'll have 2A flowing through the resistor, at ~40-45 volts. that's ~90W, so you're ~75% efficient LED light just went down to about 7% - and you've got 90W of heat to dissipate. a DC-DC converter would be in the region of 80% efficient (vs 0% for the resistor)..........
edit
just realised DM answered better than mine anyway.

 

[wannesd]

Allright, that makes sense.

What would I need to power this as a headlight?
http://www.ebay.com/itm/170957833798?item=170957833798&pt=Motors_Car_Truck_Parts_Accessories&cmd=ViewItem&hash=item27cde18646&vxp=mtr

I have a DC-DC from lyen, but it's 3A max I think.
I run 14S lipo

 

[potatorage]

I have one of those LM2596 and they get very hot at 3A. I don't how long you can expect them to last when run continuously at 3A.

 

[hardym]

The Cree Light and tail light togher draw about 40 ma input and 300 ma Output. Yes, the DC-DC will get warm but not hot. Suggest getting one of the heat-sinked version of the LM2596HV (e.g., link below). You will still be able to heat-shrink this package wiht a 1" tube.

http://www.ebay.com/itm/4-5-60V-to-1-30V-LM2596HV-DC-DC-Voltage-Regulator-Power-/230756983303?pt=LH_DefaultDomain_0&hash=item35ba302207