The GPSy EV Project

Acquisition: Garelli moped

2010-02-28T03:09:58Z

My latest acquisition is a beautiful old Garelli moped. I'm still ambivalent as to whether this will be EV converted. For now, here are some pics from the seller.

The seller called it a 1972 Garelli Bonanza, but I'm pretty sure it's a 1976 Garelli Eureka Flex instead. Here are some links to other Garelli Eurekas:

MopedArmy.org has the Clymer's repair manual for the Garelli on their website, but it's individual JPG files and I found it difficult to use so I collated them into a single PDF:

Antique find: Amprobe RS300

2010-02-18T06:48:37Z

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

Anderson Connector Meltdown

2010-02-16T03:28:25Z

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.

I think the electric winch I was using was consuming around 20-50 amps, but I'm not sure as I haven't put an ammeter on it.

Honda Gyro and electric trikes

2010-02-13T13:46:43Z

Me want a Honda Gyro Canopy. Perfect for commuting to work in harsh New England winters, along with your little puppy:

Unfortunately, very difficult to find in the USA and I'm not sure I want to go to the trouble of importing one from Japan just to convert it to EV.

Or maybe I can skip the whole EV conversion if I can find an elusive electric Daihatsu Hallo, whose "two 12V batteries, whose 75Ah capacity gave it a 30km range at a speed of 30km/h."

There's actually a Yahoo group for lovers of three wheel mopeds: http://autos.groups.yahoo.com/group/Ariel/

LM317 - a multipurpose voltage / current regulator

2010-02-11T01:36:40Z

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:

R2 = 192 * V - 240

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

Note 1: Although the schematic from the datasheet shows Vin > 28 V that's only if you want 25 volts out. In reality, as long as Vin + 2~3 volts > Vout, you should be good. So for a 5 volt output, Vin should be more than 7 volts.

Note 2: Note that the excess voltage is bled as waste heat since this is a linear regulator, so you shouldn't make Vin too high or the output current too much or you'll heat up the chip. If you want to really step-down voltage a lot, you should use a buck converter.

Note 3: The actual value of Iadj in the equation above is 100 μA which is 0.0001 amps. Thus in the equation above, including the Iadj factor would be 720 ohms * .0001 amps = 0.07 volts, resulting in a total of 5.07 volts or around a 1.4% higher voltage than expected.

9 watt LED light (bright bright bright!)

2010-01-31T22:55:14Z

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:

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 I have the LED clipped onto a pretty solid aluminium heatsink (with some heatsink paste of course) ready for testing. I'm powering it using a 3 lithium-ion cell battery (11.7 volts @ 1100 mAh nominal) using the aforementioned LM317 current regulating circuit.

The heatsink gets quite hot, around 60-70°C after about half an hour. When I mount this for real, I may need to use a bigger heatsink and/or think of active cooling (i.e., a fan).

We normally think of LEDs being "cool" light but that's because they are cool compared to incandescents. However, the efficiency of LEDs is only around 5-40%, which means that of the 9 watts getting pumped into this LED, around 60-95% is being expelled as heat. I don't think this is a totally bad LED but I still need a heatsink that can handle the worst case scenario of around 7 watts of heat.

This is a close-up shot of the current regulator (LM317) with the 1.8 ohm resistor mounted on a small PCB. The LM317 is being heatsinked but I found that it doesn't get nearly as hot as the LED.

With an input voltage of 12 volts, LM317 is dissipating around 1~2 volts @ 700 mA so that would be around 0.7 to 1.4 watts. Not too much.... I think...

With this setup, I measured a voltage drop of 9.38 volts across the LED.

My Minolta color meter tells me that the LED is 7800 Kelvins right at the start, which is quite a bluish hue. Oh well, that's what you get for a cheap LED! I don't know how many lumens (spec is 500) but it is certainly blindingly bright.

Spec color temperature is 6500 Kelvins according to DX. In reality, the LED seems to settle down a little bit as it warms up, but it seems to stop at 7500 Kelvins.

(Note to the nitpickers that the color temperature was tested then the display was "locked" on that value. So it's not showing my ceiling light temp!).

Even more: Note that this isn't even the brightest one on their website. They even have a brighter one, a massive 50 watt sucker with 1700 lumens for $60. The heatsinking for this must be intense!

And as noted on the comments below, there are single emitter LEDs such as the SSC P7 that give out 800 lumens @ 3.7 volts and so are brighter than this at just a bit more bucks.... :(

Additional fine print: I do make a small amount of points from an affiliate link to DealExtreme. But (I think) that it doesn't affect my review of their products.

Piaggio EV-Prius Batteries: Test Runs

2010-01-18T17:20:37Z

The weather was finally nice enough to commute to work this week on my Piaggio Boxer EV with Prius NiMH batteries.

Here's the data from my CycleAnalyst:

	Run #1 1.18 (To)	Run #2 1.18 (From)	Run #3 1.19 (To)	Run #5 1.20 (To)
Distance	5.2 km	4.85 km	4.21 km	4.19 km
Efficiency	45.1 Wh/km	39.2 Wh/km	42.2 Wh/km	47.6 Wh/km
Energy used	234.23 Wh	189.87 Wh	176.92 Wh	199.03 Wh
Charge Used	5.90 Ah	4.28 Ah	4.01 Ah	5.01 Ah
Max Amps	106 A	101 A	91 A	101 A
Average Speed	20.6 km/h	23.3 km/h	24.8 km/h	24.1 km/h
Max Speed	36.6 km/h	40.3 km/h	39.0 km/h	36.6 km/h
Starting voltage	---	49.9	50.2	47.2
Ending voltage	43.8v	45.9v	---	44.2v
Run time	15 min	12:30	10:10	10:24

My commute is slightly uphill on the way to work and downhill on the way back, which accounts for the difference in energy efficiency going to and from work.

The bike feels much lighter than with the SLAs and faster too (even with the gear reduction) so I have to say it's an unqualified success. I just hope I can get good life out of these batteries.

After Run #4, I was in a rush and so I put the charger on and went to a talk and then came back. About 3 hours had passed and the charger had over charged the batteries. It actually wedged the battery holder apart. So I'm worried now that my batteries will be weakened -- even though most of the bulging has subsided.

I reinforced the battery holder this morning and we'll see how it holds up.

Bought a cute folding bike from Italy

2010-01-16T15:51:17Z

I just bought a cute little folding bike. At first I thought it was a Brompton but a little more research shows that it's most probably an Italian bike, my best guess is the Amica built by the Carnielli bike company. I'm not positive since someone repainted the bike a horrendous orange.

Here are some Craigslist postings. They're expired but I'm hoping the sellers don't mind me keeping them here for posterity and to help people with price checks:

For sale is a vintage Amica by Carnielli folding bike Made in the 1960's by the Factory [Teodoro Carnielli] Located in Vittorio Veneto, Italy,

Bike weighs 35 lbs.
20" wheels
all original parts
3 speed, front and back breaks

►►►Vintage Italian Folding Bike - $225 (Fairfield, CT)

"Good condition. Has some light surface rust on chrome but it cleans up nicely. Rides great. I would suggest a brake adjustment. Note the white tires. A real classic. Easily folds up. Great Italian quality. Excellent compact option for commuters, campers, college campus, etc. "

-- this seller wanted $225 for this one!

VINTAGE AMICA 3 SPEED FOLDING BIKE - $140 (STATN ISLAND)

"AMICA 3 SPEED STRUMY ARCHER FOLDING BIKE MADE BY CARNIELLI IN ITALY DURING THE 1960ds.THE BIKE IS IN VERY GOOD CONDITION.

-- I didn't know that Amica made a three speed. That's an interesting piece of info. I wonder if it was a hub gear.

LED Voltmeter

2010-01-14T20:18:34Z

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

EV Warrior Drive Roller

2010-01-09T02:13:57Z

I'm working on a bicycle assist motor project. I thought about using a hub motor or chain drive but given the economy, I'm going with a friction drive. Friction drive is cheap, has few little moving parts to go wrong, and is cheap. I think I can make it using parts almost entirely found around the shop -- with the exception of the friction roller.

Now what I like about friction drive is if you use a roller with a one-way bearing and take advantage of some physics, the motor can release from the wheel entirely when freewheeling, so the bicycle remains entirely pedal-able on its own.

I decided to go with rollers from the defunct EV Warrior project. They're available on the surplus market, have one way bearings, and are nicely knurled. Other people are making their own friction rollers from BMX wheel hub extensions, but they don't have one-way bearings.

Here are some dimensions almost entirely for my own benefit.

Part	Inch	mm
Shaft OD	0.500"	12.70mm
Shaft ID	0.315" (a tad over 5/16")	8.00
Shaft Width	3.016"	76.61
Roller Width	2.375" 2 3/8"	60.35
Roller OD	1.275" ~1 1/4"	32.38
Key Notch Width	0.130"	3.32
Key Notch Depth	0.411"	10.4

Now, if I want to go 20 kph with motor assist, then how many RPM do I need. The math is easy since the bike wheel circumference is 1:1 with the road surface.

The roller OD is 32mm. That means ~~its circumference is 2*pi*r = ~200 mm or around 20 cm or 0.2 meters. To go 20 kilometers, it has to spin 100,000 times an hour or 1,667 times a minute.~~ Ummm... I do know the difference between radius and diameter, I think.....

Take 2: That means its circumference is pi*d = ~100 mm or around 10 cm or 0.1 meters. To go 20 kilometers per hour, it has to spin 200,000 times an hour or 3,333 times a minute.

I just hooked up the motor to a 16v power supply and measured its rpm with my optical tachometer as 6,000 rpm. That means that I'm really limited in my power source to 12 volts or maybe 24. In any case it's not good for my motor and I really should try to find one with a lower Kv but that would actually involve money which I am trying to avoid.

I just looked up the specs on my motor (MY-1016B) and it looks rated at 2900 rpm @ 24 volts @ 15 amps. So I must have either measured wrongly or maybe my jury rigged power supply was off spec or the no-load speed is quite high or the moon alignment was off with Venus. It's late so I will retry on a later date.

Motor:	Unite MY-1016
Voltage:	24VDC
Rated Speed:	2650-2900 RPM
Rated Current:	16.0-16.4A
Output:	300 watt

Update: With my math corrected and the real motor specs, it looks like I'm good to go. 24 volts should get me going to 20 kph and 36 volts should be good to 30 kph (or around 20 mph) which is plenty fast for New Haven streets.

Update 2010.02.22: Real world performance at 36 volts is around 20 kph at full assist. Working backwards, at 20 kph the motor is spinning at 3,300 rpm.

I'd really like to go 30 kph, but I don't think the current motor will get me there since that would require it to go at 5000 rpm. Even now, it's only a 24 volt motor and running it at 36 volts won't be good for it in the long run.

Of course I could go brushless, in which case this would be a good choice (over 1500 watts peak!): http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5204&Product_Name=TURNIGY_50-65D_270kv_Outrunner_(eq:_4030AXi)&aff=54444

Or: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7709&Product_Name=TGY_AerodriveXp_90_SK_Series_50-65_270Kv_/_2100W&aff=54444

LT1070-based 48V solar trickle charger

2010-01-02T01:18:37Z

On this cold New Year's Day, I've been thinking about the problem that NiMH batteries like to self-discharge. I'd love to trickle charge them with a low current but my current NiMH charger seems like 1) overkill; 2) liable to slip into the wrong charge mode and boil them dry; 3) too big of a hammer for this little nail.

So I thought of the 1.5 watt 12 volt solar chargers I had bought for my car back pre-Prius. These would be perfect except for the voltage. I think they are actually around 15 or 16 volts nominal, but my packs are 43.2 volts. So I need to boost the voltage....

Scrounging around the web, the best solution appears to be the LT1070 chip from Linear Technologies (www.linear.com). It requires minimal external components and comes with a through-hole TO-220 package for us non-SMD people.

So... how to design the right circuit..

This is my back of the napkin calculations using the design notes and should be taken with a huge grain of salt. Do not trust my calculations!

Vin = 14 volts
Vout = 48 volts

R1 = R2 * ( 48v / 1.244 - 1) = 46.606 k ohms
R2 = 1.24 k ohms

Duty Cycle = (48v - 14v) / 14v = 70.8%

L = (14V * ( 48V - 14V)) / (0.5 A * 40 kHz * 48 v)

L = 476 / 960,000

L = 495.8 uH

C1 = arbitrarily 100 uF with a low ESR
C2 = (48v * 1A) / (40kHz * (14V + 48V) * (0.33 Vpp))
C2 = 48 w / 818,400
C2 = 58 uF

Now although I started this as a trickle charger, the LT1070 series can handle up to 2.5 amps depending on the version, and so it could serve as the real charger.

Now a 200 watt solar panel would be pretty large (around 116 x 116 cm; 46 x 46 inches) and at current prices, around US$1000 -- so it isn't in my budget. But one can always dream!

p.s. This hilarious article is a must read before using the LT1070: http://ch.livejournal.com/608988.html

Favorite electronics mags

2010-01-01T21:17:30Z

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!

My partner would kill me if I didn't include her favorite zine: Country Living

And my favorite bathroom reading:Popular Science

Happy new year - and LED lighting

2010-01-01T18:36:01Z

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

This is also a good primer on LED lighting:

http://www.girr.org/girr/tips/tips7/white_led_tips.html

And (somewhat randomly) a rusty nail LED driver circuit: http://www.cappels.org/dproj/ledpage/leddrv.htm

Electric vehicle power and efficiency calculations

2009-12-28T14:29:17Z

In my search for info on calculating EV efficiency, came across this interesting article with java calculators: http://www.ecoworld.com/transportation/the-battery-powered-car.html

The articles mention that standard EV car efficiency is around 4.4 kilometers (2.7 miles) per kilowatt-hour.

My little scooter gets around 40 watt-hours per kilometer on SLA (I need to get new figures for the 43.2 volt NiMH packs). Flipping that around, that's 25 km per kWh. That's around 16 miles per kWh.

Another interesting article as to why the Chevy Volt isn't using A123 packs: http://www.technologyreview.com/blog/editors/22186/

And another javascript calculator that converts miles per kilowatt-hour to miles per gallon: http://car.pege.org/2008-fuel/kwh-mpg.htm

Charging my Prius packs

2009-12-22T16:39:40Z

Here's a great link to why you shouldn't charge your NiMH packs in parallel: http://tlb.org/nimhboom.html

More info will be posted here as to how I'm charging my packs....