My electric bikes & projects

[California98Civic]

Another cool thread. I just replace my bike charger. But first I investigated. The insides were mostly greek to me. I want to learn though. I'd also love to learn how to safetly adjust voltage. I have a 12s lithium battery. Most of the cheaper chargers are about 1.5 volts below what I need because they are for 10s lithium.

[Stubby79]

Originally Posted by California98Civic

Another cool thread. I just replace my bike charger. But first I investigated. The insides were mostly greek to me. I want to learn though. I'd also love to learn how to safetly adjust voltage. I have a 12s lithium battery. Most of the cheaper chargers are about 1.5 volts below what I need because they are for 10s lithium.

Look for a mini "pot" (potentiometer, in other words a variable resistor), usually near the output wires. Turn it one way or the other with a small screwdriver. Look like this, though maybe only 1/4" or smaller across:



You might "cook" the charger like I did, mind you, as you can probably expect a lithium battery to suck down the amps faster than a cheap lead-acid charger will want to put out. Might not too. Should be OK with one meant for lithium.

You can probably get away with one made for slightly higher voltage, seeing as your BMS should determine when it's time to cut off the power. (Err...do this at your own risk, mind you!)

Never mind on most of that; found your thread again!

[Stubby79]

My luck...not only has it been too cold to ride, it dang well snowed!

It never snows here. Ok, rarely. We get a couple of inches once or twice a year. Usually by this late in February, it's 10 above or more and all the trees are in full bloom.

If this is what mother nature is going to do when I get an eco-friendly ride, maybe I need to go dance naked around a tire fire to offset it!

[Stubby79]

Oh, hey...it looks like I never continued my story from the first post. Ha! Only took a couple of years to notice.

About to and a half years back, I bought another fixer-upper ebike. Bit better quality than the ones I originally had. Bigger batteries, more power. As she was when I picked her up:



Dead batteries, flat rear tire, plus a year or more weathering to undo, which meant taking apart all the switches and cleaning the contacts as well as cleaning and removing rust. She's been a faithful ride ever since.



And here's trouble brewing:



This is the "bike" I was referring to "still riding around" in earlier posts. It ran well with my LiFePO4 pack for a while, but I lost another cell or two, and it got shelved, as I was out of replacements. Expensive learning experience! I've recently(if 3 months ago is recent) built it a brick of healthy used lithium batteries. For now I'm still using their original BMSs and charging each of the 5 packs off its own charger, as I trust their BMSs.

Brick:



Plenty of room where the big old 20ah SLA's were: (Still room for one more of the packs it's built from)



I also "upgraded" the controller. Somewhat unnecessarily. I was trying to give the "bike" regen braking. Turns out that "EBS" (electronic assist braking) is not the same as regen braking. In fact, I have no idea what it is because it doesn't seem to make a difference.

I did get more power out of it - it's a 40 amp controller vs maybe 27...? - so it has a lot more gusto. The controller is also rated up to 64v...which is good, since the nominal voltage of my pack is 55 and the full-charge voltage is 63. (which is what the capacitors inside it are rated for, so no going higher yet).

I still need to test the actual capacity of said brick, but expect to have 1.25kwh based on the tests already done on some of the cells. Maybe that will be a project for tomorrow...

[Grant-53]

Regenerative braking is when the motor is used as a generator to charge the battery. Dynamic braking is when the armature terminals are connected so the motion creates a current and magnetic field that works against the magnetic field from the field coils. It does not lock the wheel.

[Stubby79]

Originally Posted by Grant-53

Regenerative braking is when the motor is used as a generator to charge the battery. Dynamic braking is when the armature terminals are connected so the motion creates a current and magnetic field that works against the magnetic field from the field coils. It does not lock the wheel.

And EBS is neither!

[Stubby79]

Continuing my current obsession with lithium-ion batteries, I wanted to know more specifically what kind of capacity I would get out of my "bricks" in my electric scooter "bike"...

Finding a test load was a bit of an annoyance. At least one with any significant current draw. I started with an inverter to run something on AC, but the low voltage shut-off on it kicked in half way through. So I boosted the output, but that was a PITA and flaky. I needed something simple and reliable. And I had a box full of incandescent 12v bulbs from switching over a few cars to LEDs, so this was my setup:



I remembered making something similar as a kid for much smaller bulbs. Nothing to it but a 1x4 with 5/8" holes and two pieces of aluminum foil:



Good for burning off 10 amps! (and doesn't care if the voltage drops, either)

So far, I've been getting a good 21AH out of each of the smaller bricks that makes the bigger brick:



That's actual, usable amp-hours, under load and going through the BMS for both charging cut-off and low-voltage discharge cut-off. Cells settled around 4.15v after charging (a touch low), and low voltage cutoff was a hair below 3v.

Temperature makes a fair bit of difference too, according to the data sheet for the cells. And its fairly chill in my work shop.

I'm fairly pleased with the results. 21ah under a decent load totally blows away lead-acid, and the battery weighs 1/3rd as much.

[Stubby79]

Do I want more lithium batteries?

No, nevermind...that's a given!

Do I need more? That's the real question.

I haven't even settled on what to do with some of the ones I have!

[Stubby79]

Took the hybrid for a real ride today. (It was decently above freezing at last)



18km!

Ok, that might not sound like much compared to people who are used to it, but it's probably twice what I could do without assistance. And I probably would have ruptured something trying!

Batteries were at 28.3v (I used 2 bars, so about 25%) and 27.1v (it had 2 bars left at one point).

Don't know how accurate that LED display is, since when I turned it off or switched to the other battery, it showed full or almost full again. The same battery that was showing only 2 before was showing only 2 used when I got home...

But rough estimate based on voltage...the first used about 15% and the second used 50% of capacity(those numbers could be out to lunch since I am looking at a generic voltage vs capacity chart). 65% of 9ah, 152 watt-hours, ~8.5 wh/km.



I won't know without using my AH meter to check how much it take to recharge the batteries (too late, this round), but that should be in ball park range. That's right around 1/3rd what my all-electric powered electric scooter/bike runs at.

The real point though is that I got an hour of decent exercise without killing myself, and felt productive doing so. This should make for a pleasant pass-time in the spring and summer!

PS: I just realized that's farther than I "commute" to work!

PPS: Theoretical range of 55km between both batteries.

[Stubby79]

Stiff an sore!

Everywhere but my legs!?