Laptop Powered E-Bike

Still have all the parts, still no new progress. I did though, decide to run the 12V stuff off the main battery instead of a separate one. Adding up the Watts for all the little devices really didn't give a big number. Plus, wiring and charging will just be simpler that way.
 
My e-bike battery has been sitting on a shelf for 3 years, but I took it down today to put it on a tester. The cells are still balanced, and it's sitting at about 33% charge. It was only at 50% when I put it together.

I got it off the shelf because I hope to finish building the box for it soon. Maybe I'll actually finish this project someday, LOL.
 
The battery box is now built.
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I've also done the wiring needed for balance charging, series monitoring, and even a temperature senser.

I guess the next thing is to secure it to the bike frame and start hooking things up!
 
Pretty sure the open motor sprocket and chain is a major safety hazard. You'll want to put on some covers, so that clothing cannot get caught and sucked in.
Also, the 3 bolts going through the battery... The whole box is going to get bumped and shaken countless times. Are you absolutely sure that they're not going to eat through the plastic battery holder over time, and short the cells?

Does the starter motor really need cooling fans? I'd have thought the massive cooling fins would be enough.
 
Well, it's a prototype, so who knows what will happen until it happens. For example, I actually got the bike ready for it's first test ride yesterday, and the PWM regulator I bought keeps cutting out. I think I may need one that can handle higher amps. Didn't see that coming. I need to get my meters hooked up to be sure.

The battery is also supported by the bottom and sides of the box, and held in place by nylon spacers. So hopefully there won't be an issue there. The starter motor still generates a fair amount of heat despite my modifications. It was never intended for continuous use. The fans use a tiny amount of power compared to the motor, so they really shouldn't affect the range at all. I don't think the drive chain is close enough to worry about cloths. The pedal chain is closer, and I've never had a problem with it.
 
ajw22 said:
Also, the 3 bolts going through the battery... The whole box is going to get bumped and shaken countless times. Are you absolutely sure that they're not going to eat through the plastic battery holder over time, and short the cells?
Click to expand...
My thought as well, it sounded like a not great idea. Even if the threads are insulated, they could easily vibrate through their insulation against cells. Bikes are bumpy.
 
I had that thought as well. Once I disconnect the controller from the battery, whatever it is resets. The controller has an LED that remains lit after power cuts out. That has led me to think it might be the controller. But I have to get my meters out and see what's going on. If it's the BMS, then I think there would be no voltage on the output while it's tripped.

In either case, I've done some searching and found both a BMS and controller capable of more amps. I just have to be careful not to overtax the battery.
 
Was the controller LED fully lit, or did it seem a bit dim?
It would make sense for the BMS to still let through a miniscule current through, even after the over-current / short-circuit sensor was tripped. Without getting into details, it's the obvious mechanism to detect that the "faulty" load has been removed, and thus the tripped BMS should be reset.
 
I got my meters hooked up today. It's definitely the BMS. It lets a couple volts through to the controller, but that's it.

I also measured the current. At the time the BMS tripped, I saw 73A. I built the battery for 60A, thinking I wouldn't need that much. 70A is about as much as it can safely give. Looks like I'll need a second battery, either in series to increase the volts, or in parallel to increase the amps. The controller is only rated for 60A. I guess I've got some more designing to do.
 
If you have 73A at 30V, that's over 2kW. Quick googling indicates that's enough power to get to 60kmh / 40mph. Have you measured how fast the wheel was turning? Maybe it's already waaay faster than you can safely use.

Perhaps the starter motor is just a bad choice?
"The efficiency of most starter motors is around 60%"

Starter Motors and Circuits (Automobile)

15.3. Starter Motors and Circuits 15.3.1. Starting System Circuits The starter circuit is very simple in comparison with most other circuits on the modern vehicle. The voltage drop in the main supply wires is the problem with the system which […]
what-when-how.com what-when-how.com
 
Yeah, it's probably a bad choice. But so few people have even tried it, I'm really curious if I can make it work. With me on the bike, it was barely moving. I know that motors draw a lot of amps when they're stalled, or nearly stalled. I think that's part of my problem.

Maybe I need something to keep the amps from going over 60. Something that doesn't just cut off like the BMS does. The only way I know of to do that would be a boost converter with a constant current adjuster. It would have to be pretty chunky though, to be able to handle 60A. The volts would drop in order to limit the current, but that's better than having to stop the bike and reset the BMS.

Assuming I could find a booster that big, I could put 30V, 60A in (1800W). My controller can do up to 50V, so that would mean 36A out. Minus inefficiencies. Then if the current draw were getting too high, I'd just lose torque for a bit instead of the whole thing just switching off.
 
Well, I couldn't find a booster that could handle 60A, so I bought 2 that can do 40A, and I plan to use them in parallel. I've been told that to do that, a resistor must be placed after each one, or all the current will go through one and not the other. I don't really understand that, but it has something to do with how the regulation works I guess. Supposedly, a small amount of resistance after each board will keep them in balance.

I also had to learn to calculate the heat loss of each resistor in Watts, so I can buy some that will handle the heat. For some reason, I'm having a hard time wrapping my brain around that one too. But I think I got it. It's the Voltage drop across the resistor (not the total Voltage of the circuit) times the current.

So with each booster/resistor supplying half the current, that would be 50V, 30A, and the recommended resistance (as far as I can tell) is 0.1Ohms. 30A x 0.1Ohms = 3V, and 3V x 30A = 90W of heat for each resistor. It also means that my 50V output will be dropped to 47V, but at 30A, that's still 1400W to the motor. I suppose I could push it a bit and draw the full 40A from each booster. But this heavy usage should only happen for a short time, I hope.

I don't know if this will work, but the idea is that with the maximum Volts and Amps set on the boosters, if the load is too heavy for the motor, The high current draw will cause the boosters to drop the Voltage, which I hope will keep the BMS from tripping. Or it will just fry the booster boards. Or maybe the BMS will trip anyway.

If it doesn't work, I may try buck regulators instead. Now that I've ordered the boost regulators, it occurs to me that they will only drop the Voltage down to that of the battery. Whereas buckers could drop the Voltage all the way to 0V. I'll try the boosters first anyway, because I'd rather boost the Voltage and keep the current down if I can. But we'll see what happens...

It's no wonder that people skip all this and just buy a conversion kit! But I'm enjoying the challenge, and learning a lot more than I would if I were just using plug and play parts. :)
 
rebelrider.mike said:
or all the current will go through one and not the other
Click to expand...
The boost converter measures the voltage on the output side. If it's below the set threshold, it lets through a pulse/boost of current to get the output voltage above the threshold.
If you have 2 converters in parallel, unless the 2 units have _exactly_ the same thresholds (practically impossible), inevitably one will more or less consistently trip the threshold before the other and raise the output voltage above the threshold of the other unit, resulting in one unit doing most/all of the work.

The resistors divide the one common output voltage into 3 different voltage areas: The 2x outputs of the boost converters, and 1x the motor.
Suppose the converter#1 threshold is set to 50.0V, and converter #2 to 49.8V.
The motor of course sees the lowest voltage (say 49.5V). Converter#1 that just finished boosting is going to have the highest voltage (say 50.1V). The other converter#2 is going to have an intermediate voltage (say 49.8V). As the motor draws all voltages lower by 0.1V, now converter#2 is going to hit its threshold and start to boost. Followed soon after by #1 again, etc.

rebelrider.mike said:
recommended resistance (as far as I can tell) is 0.1Ohms
Click to expand...
I've never actually tried this. But theoretically, you only need to ensure a sufficient voltage difference in the 3 areas, just enough to cover for not being able to set _exactly_ the same thresholds. My guess would be that it'll be in the 0.1V ~ 0.3V region. So a 0.003Ohm/3W ~ 0.01Ohm/9W type resistor should be enough.
Note though, that a 3W resistor will get super hot when driven at a constant 3W. Best to go at least 2x higher.

One issue is that at lower loads, the voltage differences are going to be reduced, too. So you might need a higher resistance to ensure a 50:50 load split during intermediate load situations. At much lower loads the issue becomes irrelevant, as one converter is plenty to handle the entire load anyway.

Also, cabling will add useful resistance, too. So if you have some distance between the converters and load, it might make sense to use 2 separate cables to the load.


Again, I never actually tried any of this.
 
I just got a new multimeter with the ability to measure DC Amps via a clamp instead of having to use an in-line device. I'm very curious to see this load imbalance phenomenon actually happening. I think I'll start without resistors (and a lower current draw) to see what happens and then add the resistors. Maybe I'll have to buy a few different kinds until I get a setup that works.

I can see why one booster allowing slightly more current than the other if the Voltage is slightly lower. I don't understand how one booster would end up delivering almost all the current. But then, there's a lot of things I don't understand, and I've melted a few things unintentionally... Anyway, if I can get away with lower Ohm resistors, that would be great. All these extra components are stealing power away from my inefficient motor, LOL.

Also messed up my math earlier. Starting with the battery limit of 33.6V, 60A, that's 2016W. So boosting to 50V I'd have a maximum of only 40.32A. I could almost get away with a single booster. But at its lowest, the battery will be at 20V. Keeping the current limited to 60A out of the battery, I'll only have 1200W to work with. At 50V, that's only 24A. I'm starting to think that I really should be using a buck converter instead...

While all this tinkering with numbers and learning new concepts is fun, I can't help but think that there's got to be an easier way to limit current without breaking the circuit.
 
Well, I've been doing more thinking...
Money isn't as tight now as it was when I started this project. Maybe I'll get a front wheel hub motor. I could use one of my Voltage boosters for that one, and the other for the starter motor. Run them both on 48V. Totally eliminates the need for load sharing resistors. It would also remove the issue of the starter motor stalling out and tripping the BMS. So about 25A for the hub motor, and 35A for the starter motor.

Of course, getting a proper hub motor kit would mean I don't actually need the starter motor anymore. But I'd still like to tinker with it. I'm sure I could make it work eventually.
 
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