Eric's Project #002

[albie]

glad you sorted out your issue....

sometimes somthing as simple as either shortening wires or running thicker wires usually solves alot of heating / voltage drops.

i had the same issue when I upgraded from 24 to 36v. The wires on the pack initially were to thin and heating up (just before the point where the plastic started to melt). A quick trip to the local electronics store (jaycar) resolved that by getting nice thick wires (and subsequently trimmed to a length required.

 

[Beagle123]

Yea, I never took it too seriously until I started working on these bilkes. But this has made me realize that if you we all should be using thicker wires. If 10 guage is getting warm at 50 amps, then perhaps then these numbers should be about rght:

12 guage = 20 amps
10 guage = 40 amps
8 guage = 60-70 amps

My bike goes to about 40 amp peaks, so I'm glad I used 10 guage wires!

 

[ort5]

Hi Eric,

Glad shortening the wire and adding the second strand helped. Your voltage drop now seems about right.

Happy riding!
Dave

 

[Beagle123]

Planning Upgrades

I've just finished upgrading my controller with new FETs and diodes, so now it pulls 50 amps @ 50 volts.

Right now I have a list of things to upgrade on my bike, then it will be done:

1) The back shocks don't flex at all. I've bought new shocks on ebay:
http://cgi.ebay.com/ebaymotors/ws/e...STRK:MEWN:IT&viewitem=&item=190190491832&rd=1

2) To add more shocks absorbsion, I purchased a suspension seat post:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=320208817002&ssPageName=STRK:MEWN:IT&ih=011

3) Currently I'm using the forks and disc brakes from a cheap wal-mart mountain bike for my front end. I'd like to replace it with a really nice set of forks with 5 inches of travel. And while I'm at it, I'd like to upgrade to 8 inch disc brakes (perhaps hydrolic). I don't know if hydrolic brakes are any better than mechanical. What do you guys think?

Here's what I'm looking at:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=250204502190&ssPageName=STRK:MEWA:IT&ih=015

http://cgi.ebay.com/NEW-2007-MARZOC...ryZ58085QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

4) I'd like to get a good torque arm. My axle is 13mm X 10mm. Does anyone know where i can find a torque arm (preferably flat)?

 

[deecanio]

Hi Beagle,

Can't help with the electrical side but sounds like you have that down anyway.
Can help with the brakes - the avid juicy's that your looking at are highly rated in dh mtb and i can tell you that the upgrade from 6" disks using cables to 9" disks using hydraulics is like going from v brakes to cable disk, MUCH improved!!!
i got some "hayes nines" last week and they are simply amazing brakes the price there looks good to me too!!!
i would say my bike must weight roughly 60lbs and i was finding that my old 6" cable brakes were ok but clearly not as good as they were at 30lbs!! the hydraulics are much more up to the task imo and you tend to get a better "feel" with them too - i can brake with one finger on them so would say yes, go for the hydraulics.
Forks - again the ones you are looking seem fine - marzocchi or roxshocks will be a great addition.
bike is coming on sweet there - looking forward to some vids when yur done!!!


cheers


D

 

[Beagle123]

Thanks dee:

I can't wait for videos too. I need to figure out how to strap a camera onto the bike.

I'll take your advice and get the hydrolic front brakes. I just have to get the cash together to buy everything.

 

[Johnbear]

My friend got this neat camera mount for Christmas - It was bought at a local bike store called bike doctor. It mounts to the handlebars and has a screw for mounting to the camera/ videocamera. It looks pretty cool, but I have not seen it in action yet.

 

[Beagle123]

New Shocks Installed, Trying to Make Charger Work

I just got these new shocks from ebay. They're much much better. They actually flex nicely unlike my other ones. Here are the latest pics of my bike as requested.

I'm using a lab power supply to charge my batteries, so I need to make an automatic cut-off switch to turn it off when the charge is complete. After making my first attempt using a current sensor, I realized that there was a simpler solution: use the voltage drop in the charging wires as the indicator to tell my device when to stop charging.

The circuit is pictured below.

Here's how it works: When the charger is charging the batts at 50 amps, the voltage at the charger is 4.2 volts, and the voltage at the ends of the charging wires is around 4.05v. So the difference is 0.15v. When the batteries start to get full and the current drops to 10 amps, the volatge at the charger is the same (constant voltage charging), but the voltage at the ends of the charging wires is about 4.18v. Voltage drop = 0.02v. So my device (hopefully) monitors the voltage drop and when it drops below 0.02v difference (meaning 10 amps of current), it will unplug the power supply (using a solid state relay).

But somehow its not working right. I think I blew the MOSFET. I connected the gate of the FET directly to the power supply, and perhaps it doesn't protect itself from overcurrent. Notice on my diagram, that when you push the button, the gate is directly connected to the power without any form of current limiting. Do I need to use a resistor to protect the gate of the FET?

What about powering the comparator chip? Can I connect that directly to the power supply, or does it need a resistor?

Thanks in advance

 

[fechter]

What's the power supply for the comparator? The gate should be happy as long as it never sees more than 12v. You do need a resistor coming off the output of the comparator since pushing the start button will be fighting the output. Amost anything will work, like 1K.

 

[Beagle123]

Hi Fetcher:

The power supply for the comparator is the charger/battery line which powers everything. I'm not using a voltage regulator or separate battery to power this unit. It runs directly from the scooter's batteries that are being charged. So there is an unlimited current available. That's why I wonder if I should put a resistor to the power pin on the chip to protect it.

Here is the latest diagram of the circuit.

It seems to be working now. Its running in the garage as I write this. Right now its charging at about 25 amps. I have the pot set so it should shut-off when it get so about 8 amps.

I moved the push button so that it would directly power the relay bypassing the chip. This button is included so I can temporarily hold the powe supply "on" while current starts to flow. Once there's enough current to hold it on, I can release the button, and it will stay on until current drops below 10 amps.

I added a resistor to the relay. I did this to be safe because I hear that the way that these solid state relays work is that they have a little LED inside them that projects light onto a material that then conducts, turing it on. If this LED is like normal LEDs, it will need a resistor to protect it from too much current. It may already have it built-in, but I don't know.

Also, I changed the resistors leading to the pot to be 3.3k resistiors. I need to be able to make a very precise voltage settting using this pot. The input from the charger side is exactly 4.18v. I need to set this pot to exactly 4.16v. If I were to just use the pot without resistors it would be nearly impossible to set it correctly because the range of the pot would be from 0v to 4.2v. By adding the resistors, the range becomes between 1.8v and 2.4v, so I can set it more exactly.

 

[Beagle123]

It Worked!

The charger shut-off when it reached 12 amps. Excellent.

Frank wanted to know a few things about my bike:

Gear Ratios:
80 tooth back sprocket
11 tooth front sprocket
20 inch wheel (big tires)

Top speed = 35 mph using NuVinci gear hub in highest gear.

Using the non-geared 1200 watt motor from Unite.
Acceleration = super strong in 1st gear, very strong in middle gear (no numbers yet)

 

[safe]

I haven't checked up on your bike for a long time. It looks like you've been doing some good work and I like your homemade charger idea... I might try something like that myself sometime. Your living in Los Angeles reminds me of how ridiculous life is here in the midwest in winter. You simply can't do anything here. (we are expecting more snow tomorrow)

The 1200 Watt Unite Motor is a really capable thing to start with. It's natural heat capability is really high so you can do a lot with it.

I'll be eager to see what kind of top speed you end up with. You might end up wanting to increase the front sprocket at some point.

Your motor with your configuration:

It looks like it could get pretty hot, but I've seen far more extreme heat profiles that this. Any time your average is about two to three times your "rated heat" you are usually doing pretty well. And I would guess that you will tend to use less than full throttle a lot of the time, so the leisurely riding style will help to keep the heat down.

 

[Beagle123]

My First Real Ride

I took the bike for a 10 mile ride today. I'm pulling 40+ amps at times. And, yes safe, you're right the motor was heating up. On a hot day it would have been really hot. I hit speeds of 30+ mph. Its hard to tell the top speed because its slower when its cold. I have a lot of wind resistance because I'm totally upright. Under the right conditions, I'm sure it will hit 35 mph.

My favorite part was how it handled the railroad tracks. I cruised over them without any jarring or shock. The 3 inch tires and shocks handled it really well. I can't wait to get a good set of front forks to complete the bike.

When I started I beleive the voltage was about 57.5v (4.1v/cell). After the ride, the batts were at 54v (3.85v/cell) I beleive that represents about a 50% charge. Since I started at 90% and went down to 50%, I'd estimate my bike could go 25 miles of hard riding or 30 miles of easy. I'm pretty happy with that. I still think I'm wasting a lot of energy at low RPMs. It would be nice to limit the current at slower speeds. All I have to do is twist the throttle a little and it shoots up to 30+ amps. Preserving that energy would be a good idea.

Hopefully Frank and I can come up with a controller solution.

 

[tailwind]

Congratulations Eric. Glad to hear that the maiden ride was such a success.

I am looking forward to the video.

Greg

 

[Malcolm]

Good to hear your hard work has paid off Beagle. Love those chunky wheels!

 

[Dee Jay]

Wow, nice work, Beagle! Human Beings are truly amazing (compared to a space lizard like me). IMO, your shocks looks much more solid than the first ones. I've been only skimming through this thread so I don't know if you're evolving towards the E-Motorcycle forum or are you DEVO and planning to grow some pedals to avoid imperial entanglements as I didn't see it in the plans.

J

 

[D-Man]

Well done Beagle. An amazing amount of work and mind boggling thread! Hope you have a nice big lock or maybe you might want to get a man eating pit bull to guard it against thieves.

 

[dirty_d]

your bike seems to do just about the same as mine since we have the same motor and about the same voltage mine is 48V SLA, my top speed is about 32mph with no pedaling. it would be nice to have one of those CVT hubs though . how many amps do you pull at top speed on level ground?

 

[Beagle123]

Thanks you guys. To answer your questions:

The Nuvinci hub really works well. The best thing about is that it is really strong. I have a 1200W motor directly pulling on a big 80 tooth sprocket (lots of torque) and it doesn't flinch. It seems much stronger than my gear hub (Shimano Nexus). I don't know the efficiency I'm getting but it seems fine.

I'm still not sure my exact top speed, but I'd guess about 32-35mph. Obviously I could go faster on a downslope.

Actually, I was thinking that electric motors don't need much gearing. I tend to put the shifter in the middle and just drive. If I'm in stop-and-go, I'll leave it in a slightly lower gear. However, I've come to the conclusion that the best solution for an ebike is having a 2 speed transmission. I have two different gear hubs and all that gearing is totally unnecessary. On my shimano, I switch between 2nd and 4th gear. I don't bother with any others. Optimally, I'd have one gear that maxes out at 20mph and another that maxes at about 32mph. That would be perfect.

 

[Beagle123]

I Made My Charger Cut-Off Switch, New Forks Are Here

I was up all last night working on the circuit board to make my cut-off switch. Fank has really been helping me learn electronics. I traced the circuit onto a copper board, then etched it. I secured everything into a box and it works great. All I have to do to charge my batteries is set my power supply to 4.27v and hook-up my bike. When the charging starts, the power supply delivers 50 amps of current to the batteries. As the charge continues, the battery voltage rises. And as the batteries become full, the current starts to drop. When the current drops to about 14 amps, my cut-off switch (pictured below) unplugs the power supply. This leaves my batteries charged perfectly at 4.15v. (I want them to be slightly undercharged to preserve them).

Eventhough 50 amps sounds like a lot of current, really it isn't. I have 14 sub-packs that are 18aH each. So eaach battery-pack is getting about 3.5 amps each. That only a 0.2C charge rate. Ideally, I'd use about a 150 amp charger.

I think completely charging my batteries would take about 6-7 hours.

My new Forks arrived. These are Mizrocchi, All Mountain forks. I learned that there are serious mountain bike people who make a science out of their shock absorbing forks. Many of these high end forks have 4 different adjustments on them. Some even have remote control (I shit you not.). These have about 5 1/2 inches of travel. This should be cool. Still waiting for my 8 inch hydrolic brakes.

 

[Beagle123]

Brakes Arrived, New Forks Installed

My 203mm (8 inch) Avid Juicy Brakes arrived, so I got everything installed today. The new suspension Forks rock. The first thing I did was run over a small curb and I didn't feel a thing. If I drive over a full 6 inch curb, it doesn't work as wll because the wheel hits it at an angle, but if you drive directly into anthing that's under 4 inches tall, it just absorbes everything. I drove off a big curb (perhaps 8 inches, and didn't feel anthiing in the front, but I felt some shock in the back. Overall, I'm really happy. The hydrolic brakes are a slight improvement over the mechanical 6 inch brakes I used before. I was happy with the old brakes, and if you want to save money, using mechanical disc brakes is fine in my opinion.

These forks altered the geometry of my bike because they raise the front end by 3.5 inches. I wanted this bike to look as small and inconspicuous as possible, but it keeps looking more and more like a motorcycle. ALso, now the kickstand doesn't work quite right.

My 2 year niece was visiting, and she pointed at it and said "motorcycle."

I had to correct her saying, "that's a little electric scooter that's under the 1000 watt legal limit."

Hi Frank: Yes, I did use expressPCB. I really like it. Thanks for the tip. I used the artwork to drill the holes by holding it down as I drilled. Then I connected the dots using the pen. Using double sided boards was an easy choice considering that that's what came with my RadioShack kit.

 

[Beagle123]

Bummer, Fried Cells

So I had my bike working perfectly. I rode it about 12 miles, and checked the batteries afterwards. They were great. They were all at about 3.9v (plus or minus 0.02). However there was one cell that was about 3.85 or so. I didn't think anything of it. But I also remembered that after charging this cell was 0.02v lower than the rest. That was more strange to me because they're all charged in parallel together.

Anyway, I rode it 24 miles tonight, and when I was coming home, my voltage meter was dropping quickly on the road home, and the bike started to lag. The voltage wasn't so bad at 49v (3.5v/cell) but somehow I was losing steam. When I got home, I tested all the cellls again. They were all perfect aat 3.73v/cell exactly right! Except the last one which was at 0.79v Oops. I guess its fried. If any of the cells were any good, I guess they aren't now.

Really, this is all a part of my charging plan. And the fact that I found those bad cells is by design. I'm charging all my cells in parallel so I get a perfectly balanced charge every time, so any bad cells should "stick out like a sore thumb." I will be glad to get these cells out of my bike and into the garbage. Also, these bad cells actually have worked to presserve the good ones. In my design, the bad cells will get pounded into the ground, but the healthy ones will stay safe because the bad ones are the bottleneck. Any extra resistance one pack takes just slows the current, protecting the good ones.

If the bad cell(s) were in a string of cells, the problem would be harder to diagnose. You'd have to test each cell to find the bad one.

I'm anxious to see how my bike performs with new cells.

I guess I'm going to do an autopsy later. I'll let y'all know if I find anything.

 

[fechter]

You might think about some kind of individual cell voltage monitoring during discharge (riding).

If one cell gets low, the overall pack voltage does not show much change, but you can fry the lowest cell.

 

[Miles]

Just noticed all the updates...

Well done, Beagle. Looking good.

 

[Beagle123]

Hi Fetcher and Miles:

Thanks for the input. I'm learning electronics now, so maybe I can make something to measure individual cell voltages. I was thinking of using a multiplexer to cycle through the cell voltages, and reporting the lowest etc.

Theories on why cells went bad:

1) I bought 12 Milwaukee v28s and they were all the same except for one. One had white cells and the voltage was 3.4v/cell. All the others were brown and were at 3.8. Perhaps bad cells?


I opened up the bike, and extracted the cells, and the bad ones were the white ones.

2) I realized that the problem cell was the first one connected to the controller/motor. The way my motor is configured, the positive battery terminal is connected directly to the motor (see pic). Does that mean that there's a bunch of voltage spikes and noise pounding the first cells? Also, I've heard that many defective deWalt packs have a bad first cell and the rest are fine. That's exactly what happened on my bike--first one bad, rest great. Perhaps I need a way to filter or shock-absorb the voltage? Maybe if I put a capacitor across the battery's terminals or a capacitor across the motor it would fix it?

Now I don't know what to think. It looks like the white cells were bad, but they were also the first ones! What's going on? I have more cells and capacitors.

Any theories?

Is adding caps a good idea?