Recently in Nickel (NiMH, NiCad) Category

Questions from Glenn about my Piaggio Boxer-EV:

1.After your initial problems with controller choice, have the motor and controller worked out OK for you? I'd be worried about motor cooling of something designed for air-over, prop slipstream. 

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.

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

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....

I have the Prius NiMH batteries installed and test drove it but the snowstorm of 2009 has put the dampers on harder testing. In any case, here's the new revised bill of materials (BOM) (dated 2009.12):

Base Unit	Piaggio Boxer (1971) - 50 cc 2-stroke internal combustion engine (removed)
Electric Motor	HXT 80-100-B 130Kv Brushless Outrunner from United Hobbies - link to new version of motor - Tachs: 5600 rpm @ 43.2v nominal (4500 rpm @ 36v; 6000 rpm @ 48v) - Max amps drawn: 100A @ 43V - Max watts drawn: ~ 4300 watts - Speed: 45 kph top speed (at current gearing)
Electronic Speed Controller	Castle Creations Phoenix HV-110 (link) - 110 amps @ 50 volts limit
Throttle	Magura 0-5K Potentiometer motorcycle twist grip throttle
Servo Tester (Pot to ESC)	Boman Industries Polar-Matic PC-50 (ebay)
Power Monitor	Cycle Analyst (link)
Batteries	Currently SLA: Prius Gen 2 NiMH - 6S2P packs (12 in total) - 43.2 volts nominal @ 13 Ah - 330 watt-hours (conservative) - Range: unknown
Power Connectors	- Anderson PowerPole 75A on main connections - link - Anderson PowerPole 30A on sub connections - link
Wiring	- 8 gauge stranded copper on main power lines and motor leads - 12 gauge stranded copper on sub power lines
Lighting	- Front lighting using high-power Luxeon LED - Rear lighting using high-power red LEDs
Low Voltage (12/5VDC) Converters	12VDC converter using National Semiconductor LM2576HVT-12-ND buck-converter for motor cooling fan, front lighting (via 5vdc) and rear lighting 12 volt to 5VDC converter using MC34063 Based Switching Regulator for front lighting Another 12VDC converter using National Semiconductor LM2576HVT-12-ND buck-converter for ESC controller cooling Quark Pro BEC 3A UBEC for servo tester / RC components
Things I burned out/destroyed	E-Sky EK2-0907 Servo Tester Doc Wattson power monitor ELF 100 ESC speed controller Castle Creations Phoenix HV-110 Right index finger on burnt out ESC Various burns and scrapes

I just won a bid for twelve Prius packs! They should hopefully be arriving later this week or early next.

Update: Batteries arrived and ready to be installed!

Each pack is a 7.2 volts 6.5 Ah prismatic NiMH battery with six cells. I'll be configuring them as 6S2P for 43.2 volts 13 Ah. I'm hoping that I can get at least 60% of the SOC from them (80% to 20% as on the Prius). That would be 43 volts, 7.8 Ah or 335 watt-hours.

This is perfect as I'm currently consuming 200 watts-hours each way with the heavy SLAs. The lighter NiMH packs should get my power consumption down even lower.

Type	Description	Wh	Weight
SLA	Tempest TR35-12 (rated 35Ah) -- 35 Ah @ 36 volts -- I don't get 35Ah, closer to 10 Ah due to Peukerts Specific Energy 35 Wh/kg nominal Specific Energy 10 Wh/kg derated	360 Wh	1 @ 11.8 kg 3 @ 35.4 kg (78 lb)
NiMH	Prius Gen II Battery (rated 6.5Ah) @ 1040 grams -- 13 Ah @ 43.2 volts -- derated 60% for a conservative Ah of 7.8 Ah Module Weight 1040 g Specific Power 1300 W/kg Specific Energy 46 Wh/kg nominal Specific Energy 27 Wh/kg derated	335 Wh	1 @ 1.04 kg 12 @ 12.48 kg (27.5 lb)

It looks like I'll be saving a good 20 kilograms or 50 pounds with only a slight loss in Watt-hours! I will have to bodge up a new battery carrier as the cells need to be kept under compression when being charged.

I just bought a used iMax B6AC charger (LiPo/Li-Ion/NiMH) to complement my previous Turnigy Accucel-8 charger. I had trouble finding the user manual but finally located it. I'm posting a copy here just in case anyone wants it:

• iMax B6AC Charger User Manual (pdf)

And here's a little comparison table that I drew up comparing the iMax with the Turnigy units:

	iMax B6AC	Accucel-6	Accucel-8
Max Power	50 watts	50 W	150 W
Max Current	5.0A	5.0A	7.0A
Max LiPo Cells	6	6	8
Max NiCD/NiMH Cells	15	15	27
Max Pb	20v	20v	36v
Power Input	100-240 VAC 11-18 VDC	10-18 VDC	10-18 VDC

My replacement ESC from Castle Creations (the Phoenix HV-110A) finally arrived today, along with a Castle Creations USB programmer for it. The Phoenix HV-110A is considerably beefier than the ELF controller that I burned out. I reprogrammed the Phoenix using the very nice USB programmer (notably: BRAKING off) and installed it onto my Piaggio.

If you have the right QuickTime codec installed, you can watch a very boring video of my biking revving up to speed.

Yes, that is indeed duct tape holding the motor wires and everything else together. My anderson powerpoles will arrive on Monday....

On the road, the moped ran just great, with a maximum speed of 20 kph (15 mph) as predicted by the voltage * kV (24V * 130 kV) of the motor. I also very quickly tripped the 30 amp fuse that was protecting the batteries. Luckily I had bought a whole pack of 30A fuses and had them in my pocket. I decided to go to a higher voltage as that would increase my top speed as well as lower the max amps drawn at the same speed.

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I wanted a bit more speed so I wired up the RC racing NiMH packs that I had gotten into a single pack: 9.6V 3800 mAH packs * 4 == 38.4V 3800 mAh megapack and plugged that into the system.

With 38.4V, my top speed increased to 30 kph (20 mph) and -- more importantly -- I could get to this top speed with popping the 30 amp battery fuse. However, if I tried to go up a steep hill, I would pop the fuse. I need to wire two 30 amps in parallel to get 60 amps -- or put in a 60 ~ 90 amp circuit breaker.

The ESC definitely got warm, in the high 30C range (90-120F). I think I will use active cooling for it. I have some CPU fans that I got at clearance that should do the trick. The motor barely broke a sweat, I do not think I will need to do much in the way of cooling it.

The moped was definitely a lot of fun zipping around the neighborhood with it.

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It got dark so testing was over for today. I spent the night rewiring the ESC into the test-box for my low-voltage systems and put a big CPU fan on all of it.

All in all, very very exciting. All that remains is to get some more NiMH packs and wire them in a 3P 4S configuration to get a 38.4 V 11.4 Ah pack. This should be enough to get me to work with a comfortable margin to spare.