Recently in Electronics / Controllers Category

I had hooked up one of my larger SLA batteries to a winch to move some logs around. I thought that the 30 amp PowerPole connectors on the battery leads were maybe a bit undersized for the winch, but was lazy and went with them anyway.

I originally thought one of the PowerPoles wasn't properly seated and it melted down. That's perhaps one of the problems with the small PowerPoles, there isn't a clean "click" confirmation of seating.

Closer examination of one of the melted PowerPoles showed however that the tongue that grips the connector had arcing on it; obviously it had shorted and overheated, causing a melting of the connector. Very strange.

Closer examination of the crimped connector showed that the connector itself was bent upwards. What I now think happened was that the main body of the plug was bent and not seated in the plastic case, and this caused the mating connector's plug to wedge itself between the tongue and the plug (instead of on top of the plug), causing sparking and overheating.

Well, my favorite discrete component of the week has to be the lowly LM317 voltage/current regulator. As one of my previous posts showed, I'm using it to current regulate some high power LEDs and I also use it as a voltage regulator.

Here's the quick and easy way to wire up an LM317 as a voltage regulator:

where the values of R2 and R1 are calculated as follows to give Vout:

R2 is usually set to 240 ohms and you can ignore Iadj to a point. Rearranging the equation gives you:

So if you want a 5 volt output, then R2 = 720 ohm (and R1 = 240 ohm). The TO-220 form factor of the LM317 that I'm using can provide up to 1.5 amps of output current and can be paralleled if I need more.

Late update: or you can just use an online calculator: http://www.jlab.org/~hansknec/index.html

DealExtreme is one of my favorite online stores. It's a distributor of inexpensive electronic gadgets based in China. I'm always finding something new there. The latest treasure is this little-but-very-bright bare LED:

DealExtreme lists it as a 10 watt LED (SKU 5876). Unbelievably it's just under $12 with shipping included!

Looking at the die shows that it is 9 discrete high-powered white LEDs in a single package. DealExtreme is bad about specs, but the comments in the DX forum seem to suggest that 700 mA at 12 volts is a reasonable spec for this LED. This would yield 8.4 watts.

(I'm wondering though if it isn't 3 x 350 mA @ 3.5 serial LEDs in a 3 parallel strings, which would be 1050 mA @ 10.5 volts. But for now, I'll run it at 700 mA).

DealExtreme lists it as 500-600 lumens @ 6500K color temperature.

As with most LEDs, you need a good current regulated driver circuit since you can't just run these things off a resistor. I decided that the easiest and simplest driver would be one based off the amazingly versatile LM317 chip.

As before, these sites have good javascript based circuit diagrams for calculating LED driver circuitry:

• http://diyaudioprojects.com/Technical/Voltage-Regulator
• http://www.reuk.co.uk/LM317-Current-Calculator.htm

Plugging my values (700 mA) into them yielded the need for a 1.8 ohm resistor with my LM317. Here's the schematic that I designed around those figures (courtesy of ExpressPCH):

Bodged together and plugged into a li-ion pack from my model helicopter and voila, an amazing amount of light. I'm thinking of using it on the headlight of my Piaggio (which currently uses a 3-watt LED) or to replace the bulb on my old 15-watt Niterider headlight, which has seen happier days.

(More photos and photometric testing after the jump)

Here are some of the magazines that I've been reading recently in my quest to beef up my robotics / electronics skills (disclaimer: Amazon referral codes embedded):

• Nuts & Volts -- one of my favorites as it has projects from beginning to advanced
• SERVO Magazine -- very useful nuts and bolts robot construction

• Robot -- more glossy and less informative than Servo

• MAKE: Technology on Your Time - fun projects but often not enough detail. expensive
  

Amazon is also offering $5 off eligible subscriptions until Jan 31st, so now is a good time to bite!

Happy new year! A new decade!

I've been playing with LEDs for my EV and robotics projects. It doesn't seem to make sense to use incandescent bulbs in an EV build -- it'd ruin the whole concept of going green.

LEDs are tricky to deal with though, especially the high-output "star" type LEDs that are emerging. Rather than voltage regulation, you have to regulate the amount of current that goes through them. This isn't fixed, because as an LED heats up, its resistance goes down (unlike an incandescent filament whose resistance goes up as it heats up, thus self-regulating). If it gets too hot, it goes into thermal runaway and you soon have what ledophiles call a Dark Emitting Diode (DED) -- dead, get it?.

So, you need some form of a current regulating system. For small 3mm or 5mm LEDs, people just use a fixed resistor since the current demand is rather small, around 20 ma. This limits the maximum current that can go through -- but it also limits the max brightness because you have to put in a safety factor and you can't easily adjust for fluctuating voltage.

Here's a good javascript calculator for series/parallel LED resistors:

http://led.linear1.org/led.wiz

The problem with 5mm LEDs is that the clear plastic casing limits the amount of heat that the LED can output (and yes, LEDs do produce waste heat, although not as much as incandescent lights). Heat control is one of the main factors affecting the output of LEDs and the reason why manufacturers went to the star configuration, which allows you to directly back the LED with a heatsink -- which lets the LED current jump from 20 mA to 350 mA with a concomitant light output.

Now, if you want to use a high output Luxeon or Cree star, you also have to current regulate as mentioned before. The typical white high-output LED takes 350 ma with a forward voltage drop of 3.5 volts. With a light output of 120 lumens, this is good enough for a moped, scooter or bicycle headlight.

Cree even has a high-power star that consists of four of their 120 lumen LEDs mounted on a single die. This produces 480 lumens, although you'll need to regulate four x 350 ma. There are other stars that bundle 2 x 120 or 3 x 120 lumen LEDs. More than enough to blind you -- or for a car or motorbike headlamp.

For high power LEDs, the LM317 seems a good choice for current regulating at a low cost. Here's a good javascript calculator for that:

http://diyaudioprojects.com/Technical/Voltage-Regulator/

and some more info on why current regulation is necessary:

http://users.telenet.be/davshomepage/current-source.htm

When I was first starting out with the Piaggio conversion, I was monitoring my power consumption using a Doc Wattson / Watt's Up. Good for checking on amp-hours used, voltage, etc.

A few weeks into the conversion, I dropped my bike chain on the Doc Wattson and broke the LCD glass. Very annoying -- they should provide a lexan cover on things like this that will get banged around.

I asked the manufacturer if they did repairs and they didn't. I asked them for the spec on the LCD and they said it wasn't divulge-able. They did give me a discount on my second one and I threw the old one in my "crash" bin.

Well, fast forward a few months more and I've been working with STAMPS and PICs and know a bit more about LCD screens -- especially how most 16x2 displays are driven using the same HD44780 IC chip.

Time to open the Doc Wattson up and see what's in it.

More after the jump

This is the post-flameout, rebuilt Piaggio Boxer EV. I changed the battery carrier from a top-mount system to saddle bags. This lowers the center of gravity and makes it easier to handle. I'm going to replace the seat with something more classic looking.

I welded the saddlebag carriers myself from steel tubing with my MIG welder.

The Electronic Speed Controller (ESC) is sitting on top. It's the replacement HV-110 that I received from Castle Creations with additional capacitors soldered in parallel on the input lines.

It's sitting in a Lexan enclosure that I bodged together. Unlike the old metal enclosure with a single temperature controlled fan, the new enclosure uses two fixed speed fans that pull the air across the ESC and the voltage converters (sitting below). They also are assisted by draft air when the vehicle is at speed.

This photo was taken a few minutes after a short run, the temp of the caps is 34 centigrade which is nominal. Anything less than 60 centigrade I think will be ok. The caps are rated at 85C.

Although the angle of the photo above makes it look like the ESC could short out on the voltage converters, it's actually held a centimeter or so above and everything is well insulated.

As I mentioned in a comment, I've been playing with microcontrollers these days. I started out with a BASIC Stamp2 system which was great and very educational, but quickly ran into its limitations -- the main one being financial, each STAMP is around $40-50 which limits its applicability.

But the advantage of the STAMP is that it's very easy to program (in BASIC!) and that it has the ability to pulse PWM to control RC servos, which makes it ideal for EV projects.

On my explorations for a cheaper microcontroller, I came across the open source Arduino which was fantastic except that it was still expensive ($20 / chip for the cheapest) and the programming environment was more fidgety that I liked.

The solution appears to be PICAXE. The cheapest one is $3 / chip (wow!) and it can do full time PWM as well as has a A/D converter right in the chip. And its fully scalable as well. The BASIC programming language seems very similar to the STAMP and runs on Macs, Linux, and MS.

$3/chip for the 8M means that I'll be able to place them everywhere! Cheap is good!

Extremly cool. Must watch. The one problem I currently see in it is that cell-phone cameras are often fixed focus and can't go to infinity properly, which would disrupt the Bokode. But as cell phone cameras improve, the Bokode applicability should also improve.

My little Piaggio-EV is back up and running. I made the following mods:

• My replacement HV-110 is now installed in an external plexiglass box with (much) better airflow and forced as well as passive air cooling. The forced cooling is on full all the time rather than the temperature variable fan that I used to have.
• Extra caps (470 uF x 6) soldered in parallel with input leads
• (Slightly) beefier wiring used -- 8 gauge rather than 12 ga
• 75 amp Andersen PowerPoles used instead of 30A
• Wiring shortened a bit
• Thermometer probe directly on caps to monitor heat

So far, it seemed ok. After my ride to work this morning, the caps heated up a bit -- from 17°C ambient at the beginning to 37°C ambient at the end of the 5 kilometer ride. I'm working on getting even more cooling in there.

6 amps used. 30 watts/kilometer average energy expenditure.