Recently in Test Equipment Category

An anonymous poster criticized my use of LM317 chips as current regulators for high-power LEDs. While I think they are great for 350 mA single LEDs, they are clearly inappropriate for the 12 watt LED that I was playing with.

My LED was taking around 800 mA @ 12 volts. A little searching around reveals that a good alternative is the AP8803 which is a LED buck driver which can handle 1 amps @ 8-30 volts. The nice thing (aside from its 92% efficiency) is that you can set up a dimmer circuit on it using minimal parts -- or PWM control from a microcontroller.

A recent find in an estate sale was this old Amprobe analog amp-volt-ohm meter. I believe it's an Amprobe RS300 but not entirely sure, since the RS300 apparently isn't supposed to have an ohmmeter on it.

My one has:

• Amps: 0-6; 15; 40; 100; 300
  
• Volts: 0-150; 300; 600
  
• Ohms 0-1K ohm
  

PDF manual: Amprobe-RS7A.pdf

This isn't entirely useful as most of my circuits aren't AC, the voltage range is too high, and it's missing the attachment for the ohmmeter which isn't switchable range and not that useful either.

But it is bakelite and looks nice! :P

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)

Found a great article that describes how to make a LED voltmeter using a chip designed specifically for that, the LM3914. http://www.evconvert.com/article/led-bargraph-battery-monitor

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

The ELF 100 ESC (electronic speed controller) arrived today and I installed it in my Piaggio Boxer. The install was a cinch and everything seemed to be going very smoothly.

I did some test runs with the rear wheel elevated using my 24V SLA batteries. Here is my data table:

Dial	Motor	Rear Spindle	Tire / Speed	Amp Draw
0-1	0 rpm	0 rpm	0 rpm	0.03A
2	411	162	14 rpm / 1 mph	-
3	1180	335	31 rpm / 2.5 mph	-
4	1801	1495	120 rpm / 10 mph	6.6A
5	2390	1950	156 rpm / 13 mph	8.2A
6	2850	2330	185 rpm / 15 mph	9.4A
7	3327	2720	217 rpm / 18 mph	10.16

I ended the no-load test at dial position 7 on the servo tester as I didn't have a secure way of securing the moped on the center stand and if it came off the center stand during the test, the kinetic energy would rocket it off my back deck.

I tried some partial loads and the amps consumed quickly jumped to 30A as the ESC tried to maintain motor speed.

The motor sounded very good and heated up only a very small amount (to 38 centigrade). So everything looked good for a road test. I took it to my front yard and dialed the servo up to 4.

The moped took off and I dialed it to 5 and went down my street at about 15-20 mph. At the end of the street, there is a slight down incline and in order to come to a stop, I dialed the servo back to 0.

The rear wheel skidded to a halt and the ESC beeped menacingly at me then shut up. I tried to dial speed back up again and nothing happened.

I tried resetting the system and it didn't work. That's when I noticed the ESC was getting VERY HOT. I now have a blister on my index finger. I yanked my main system power and pushed the unit back home. I'm just glad it chose to blow near my house and not 5 miles out!

I let the ESC cool down and then plugged it back in again. It quickly started heating up again, drawing 10 A off the battery (240 watts) and not making any sounds (it normally will "sing" to you to let you know it's OK).

Although I didn't see where it went, I have the feeling that I let the magic smoke out of my $30 ebay special ESC. I've since yanked it off the bike and will likely go and buy a "real" ESC (like a Phoenix HV100).

Until then, I'll try to conduct an autopsy on my ESC. I've got the protective shrink wrap off and the chip that seems to be the one getting super hot is marked 78M05 and it has three leads coming off of it. I'm hoping that if I post some good autopsy pix, maybe Fechter on E-S can help me diagnose it.

In any case, the moral of the story is that the HXT outrunner will work, but it really really really needs a good ESC. And you should make sure your ESC settings are correct before taking it for a test drive. In the back of my mind, I'm wondering if the ESC was set to brake at throttle 0, which would have been disastrous.

p.s. A quick google reveals that a 78M05 is a voltage regulator chip. Makes sense that that would what blew. My guess is that when the ESC told the motor to brake, the motor said "sure, here's A GAZILLIO AMPS in back current to ya!" and that blew out a chip on the ESC.

The servo tester that I ordered last week arrived by mail today. Still no sign of the ESC from Hong Kong so I can't wire everything up, but it's a start.

I go the E-Sky EK2-0907 servo tester from Hobby Lobby. With shipping, it was $13.69 although you can get it for a few less dollars if you shop around. I just wanted a basic model and it fit the bill. Most of the units that I see on ebay are identical to this.

You really can't get much simpler. It has inputs for battery power (5-6V) and two server outputs. There were no instructions enclosed but except for wiring it up wrongly, I can't see what the instructions would've said.

On an RC model, you would hook the servo motors to the servo tester to make sure that they were operating correctly (i.e., moving through their full range) in order to diagnose whether your servos were sticking or your RC receiver wasn't sending the right signals.

I'll be using it as my throttle control. I'll be plugging the motor ESC (electronic speed control) into the servo teste. The ESC looks like a servo to the unit and so if you dial in 0, the motor should be at a low RPM or stop; and 10 would be full speed.

I took the servo tester apart and it looks like the main knob is a standard 5K potentiometer. That means that once my testing is finished, I can replace it with a Magura 5K pot throttle that is standard for many e-motorcycles. For now, I'll leave it be.

The main controller chip is most likely something like a 555 timer chip. Basically a servo tester sends out 10-20msec pulses every 60 msec and the servo throw depends on the length of the pulse (10 msec for minimal throw; 20 for max). This is an efficient design and one that's very resistant to RF noise and signal loss. Which means I can make the controller wire pretty long (and unshielded) without too many problems.

The other thing that arrived was a Venon Smart Temp. I was about to buy a cheap BBQ or auto indoor/outdoor thermometer so that I could monitor my engine temperature when I noticed the Venom was just a few dollars more. The neat thing about it is that it will also monitor my BEC/servo voltage too. And if the motor temp exceeds a pre-programmed limit, it can limit the throttle to a pre-programmed limit. So I can set it, for example, that if the motor gets over 60C, then the max throttle is reduced to 60% to protect the motor.

Hopefully my ESC will come tomorrow or Wednesday. My house is filling up with parts that I can't use! I should also be working on the motor mount as well as get some of the servo wiring and BEC placement done in preparation. I could also use some more Dean's connectors....

Well, the postal carrier came and left without leaving me an ESC + servo tester, so I still can't install the HXT outrunner. But, she did leave me a little package from Hong Kong that contained the laser photo tachomoter that I ordered from ebay. I'm still amazed at just how cheap Chinese manufacturers are pumping things out. A laser tach would have cost me over a $100 just a few years ago, now I can buy one for $23 w/ shipping from Hong Kong. Incredible.

The quality of the unit is quite good. The laser beam is nice and coherent with minimal spread. The unit is sensitive enough that I could do my motor readings using some duct tape rather than expensive retroreflective tape (that they kindly include a small sample of with the unit).

This will be lots of fun.

Anyway, I went ahead and did some motor speed readings on my Boxer to check out my gear ratios. This is with the back wheel raised on the center stand (no load test):

Motor spindle speed / front hub speed: 3272 rpm
Rear spindle speed / flywheel speed: 2091 rpm
Wheel speed: 168.8 rpm (14 mph)

Motor amp draw was 5 amps, so close to no load. From this, I can see that my motor to wheel ratio with the 1.5" front sprocket is 19:1 rather than the 39:1 calculated by using the gear ratios (I think there is another gear inside the flywheel that I didn't consider). When the motor is at full speed, the wheel is going at 14 mph.

Anyway, I'm glad I got the tach since it's telling me the real motor:wheel ratio rather than the calculated one, which was always a bit iffy since I had a centrifugal clutch and could never test the entire system.

For $23, the laser photo tach is definitely a good buy and it'll be even more useful when I get the HXT mounted and have a variety of volts and amps combinations to play with with the new controller.

---

After zapping the moped with the tach a couple of times, I decided to take it out for another spin. Seems like the battery is coming up to speed after a couple of charge/discharge cycles as I was able to get 5.0 Ah out of it today.

Trip distance: 5.3 km (3.3 miles)
Moving time: 26 minutes
Moving average: 12.2 kph (7.5 mph)
Max speed: 18.3 kph (11.1 mph)

Total energy: 5.0 Ah
Total Energy: 0.11 KWh
Peak amps: 22.14 A
Min voltage: 21.05 V

km / kWh: 48 km / kWh (30 miles per kWh)

I have some NiMHs on order, I can't wait until they arrive too! Running on two 7 Ah SLAs stinks!