Will this work as a DC/DC step down converter?

[Andrew]

I've got a couple of cheap Cree LED torches and want to hard wire them to a battery pack. Will the voltage step down converter below do the job?  Or have I missed something?

http://www.ebay.co.uk/itm/130627119497?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Andrew

[Bikemad]

Andrew,

The biggest problem with that particular converter is the very low maximum output current that would be available.

Output current: Maximum output current = 3 / (input voltage - output voltage)

If you're using a 48V pack to supply around 4V for the torch, it would give the following:
Maximum output current = 3 / (54 - 4) or 3 / 50 = 0.06Amp or 60mA

My 5Watt Cree torch draws just over 1 Amp (1054mA) on the brightest setting when powered by a fully charged lithium cell (4.2V). This is over 18 times greater than that converter is supposed to produce, according to their details.

I really think a different converter will need to be used. Although this 4.5-60V LM2596HV DC Voltage Regulator Power Converter is more expensive, it should at least be able to power a couple of 5Watt Cree torches connected in parallel.

Alan
 

[Andrew]

Hi Alan, Happy New Year!

Funnily enough I have saved a number of possibilities on ebay including your suggestion.  The reason that I ask is because I have a converter that I've used already with success but this time with  a new one  I put a direct current of 54v into to the 63v converter and changed the voltage output to 4.2v which was measured by my turnigy watt meter. 
It now seems that the voltage converter is dead, there were sparks when connecting to the step down converter. Have I been unlucky? or was it something to do with my lack of understanding?
all I did was directly connect my 54v battery to the step down converter to a watt meter with the potentiometer set to 4.2 v

the other thing that worries me is  I made a + and - connection of poles on my pack which created a spectacular spark and also melted posts/poles of the an anderson connector . will this effect the battery pack? I hope not.  the battery still shows the correct voltage although I have not used the pack yet.  What are the consequences of battery pole connection?

[Bikemad]

And a Happy New Year to you too.

Is it possible that you may have inadvertently reversed the polarity of the input wires, or possibly allowed the output wires to touch against each other? As this would almost certainly produce sparks and also result in instant failure of the converter.

As far as the battery pack is concerned, it is unlikely to have sustained any cell damage, unless it had been directly shorted out much longer than just the split second which produced the big spark and burned the connectors.

I did a similar thing with one of my LiPo packs when I reconfigured the power leads of two paralleled packs to form two series packs, while the balance leads were still connected in parallel through the balance board I use for parallel charging! 
Fortunately the end of the power connector melted before I was able to push it in far enough to make a good connection, otherwise the balance leads would have certainly melted and could have caused the pack to explode into flames.

Alan
 

[Andrew]

Well I never knew you were a Lipo user   Living life lon the edge ay?

my li-ion packs have a fuse built in, and obviously this did blow when the pack poles touched so this I hope also protected the cells.

As you say I probably did reverse the input input wires(on more than one occasion dooh!    I will buy a new converter via ebay and change the way I connected everything together to test it.

Thanks very much for the words of wisdom and for giving more instruction.

I'm sure I will have more questions to come as usual.

Andrew

[DirtyGinge]

Never a dull moment eh ?, wait till you see the spark on an 84V system

Hows the sensorless coming along ?

[Andrew]

Everything is ready to go on the new build, though I'm waiting on a new frame bag for the batt pack. The other frame bag is now back on my mini motor bike. I've put the mini monster controller on the bike but the wheel is running rough, I tested combos of phase, but I think maybe the halls are a different way around on the monster to the GM motor? 

To be honest I've been expecting a LYEN phase/hall tester to arrive over the past few days to make the job easier, I could do it the old fashioned way by going through 36 variations but I've paid good money for a lazy solution . I've been holding out but the US postal service has kept me waiting       

I'm afraid it's a bit of a poor show, and I got a bit deflated when I couldn't get my chinese torches working. I hard wired them both, drilled into the torches and soldered and then my dc/dc converter packed in

As you say, never a dull moment.

Anyways, have you dug out your Pie yet (hint hint)

[DirtyGinge]

well I found it in the shed lol....

Ill plan to do it this sunday, ill let you know how I get on , how long do you want the wire ?

[Andrew]

40 inches from the exit hole should be plenty? hope that's ok.

[Leslie]

No.

Linear converters only burn off volts in heat, and only have a 45v difference from input to output. You can use them up to hundreds of volts but only allow a 45 V-drop over the regulator.

If you have a cree lamp that draws 800ma @ 3.75v 3 watt torch and use a 36v pack youre talking about a 39v drop over the regulator at 800ma.  This equals 31 watts. You will burn much more power then you get to the torches. I do believe you can do it but not with that heat sink.  You'll need a heat sink and fan to keep the regulator temperature in spec.

A 48v pack, this reg will failz.  On any pack this regulator will fail to power a led torch.  I used to series torches to take away the v drop off the regulator, but this introduces new issues.

=====================================================================

You need a switching regulator that converts the high volts and low current >into< low volts and high current.


Monkey Magic put me onto these.  They are idiot proof and totally isolated from input to output they has a safety mechanism that kicks in if you muck up the fine adjustment.  They wont output over 3.7v @ adj <<< I think.

http://www.ebay.com.au/itm/DC-to-DC-Converter-VKA60MS03-1-48V-3-3V-12A-out-Nice-/370102917617?pt=LH_DefaultDomain_0&hash=item562bda59f1




Can take up to 72v, they are tiny in size too.  I got mine to output 3.5v and is perfect for leds.  With a 48v system and heat sink glue this to a good hunk of aluminium you can easily output 10 amps @ 3.5v. 

It draws about .100ma from my pack to power a 1amp lighting system.  Leaving this on over night or the next wont kill your pack.  I could run my lights for 150 hours with this regulator.

However, with a linear regulator, you have to provide the current the light draws.   And @ 1A the linear reg will flatten flat in 12 hours.

Imagine a 35 watt led light system on your bike.    a 35 watt led ststem would draw approx one amp from a 48v pack.

This light system I ran off this converter was 16 watts.



The big light in the middle fell sacrafice to kids touching little fingers, they picked the lens off.  But still the two 3 watt torches is plenty enough.  Almost as good as ar lighs.