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Old 08-28-2017, 09:46 PM   #1 (permalink)
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Question ebike dilemma

So I have these solar panels and charge controller I was going to put on my van for an alt delete, but recently I came to my senses and realized that I don't drive the van enough (<3000 mi a year) to get much of a ROI out of any ecomods.

I am looking at getting an ebike for my commute because it is 2.5 mi each way with minor hills. I would like to use the panels to charge it (almost primarily), but the problem I am finding is that the charge controller only supports 12v, 24v, and 48v batteries. I already have a 12v LifePo4 pack that I can add cells to, but I can't find a decently priced 24v ebike kit. I am not very interested in going straight to 48v because of the cost of the cells + the BMS.

I have found plenty of well priced 36v systems ( like Ecky's) Is it safe to under-volt the motor, but have a 24v motor controller to control it? If I find its not powerful enough could I eventually upgrade to a 48v motor controller and battery and just over-volt the motor? I understand it could vary motor to motor, but for the most part is it safe?

I'm a college student that doesn't get paid much so the initial cost is pretty important. I'm thinking in the $500 total area. Suggestions are welcome.

Thanks, Matt

Links:
Solar panels, I have 2 100W
Charge controller Manual (Trakmax 30L)
Battery Cells

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Old 08-29-2017, 10:36 PM   #2 (permalink)
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For $500 in Indiana a good hybrid bike with accessories should fit the bill. I'm going to turn 64 next week and I commute 4 miles each way. A wind screen in the winter helps. Since photobucket is charging to share photos my e-mail for fairings and bike stuff is endlesstailwinds@gmail.com so I can share that way.

Aero mods to the van would be cost effective too.
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Old 08-29-2017, 11:47 PM   #3 (permalink)
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I love my ebike so far. Top speed is ~20mph which "brisk" on a bicycle. 14 amps @ 36v (~500w) accelerates strongly - most people who sit on it for the first time gasp and laugh when they pull the throttle. I don't yet know the range, but earlier tonight I put about 10 miles on a 13.2ah pack going up and down steep hills, and the charge level only just started to drop below full toward the end. On level terrain, you could probably charge it once a week with a similar battery.

I think you might be better off going with a 36v battery and using a DC-DC converter to get 36v from your panels. Reason being, voltage is what determines top speed. With the same motor I have, running 24v would give you a top speed of about 13mph with a full charge, and less as the battery voltage drops. More amps adds acceleration, but not top speed.

I like the twist throttle a lot better than the thumb throttle, and find the "LED display" kit to have much more responsive throttle than the "LCD display" kit, which is $40 more. The only advantage the LCD kit has is that it's programmable - not only do you get a speedometer and odometer, but you can increase the amps or limit top speed. I've run 20 amps through my motor a few times without issue, giving about 850w with a full charge. Probably not a good idea to stall one out with that current, but it seems fine for climbing hills around here.
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Old 08-30-2017, 03:20 AM   #4 (permalink)
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If you have any form of lithium on a BMS, it should control the charge for you and turn off the current as soon as any one cell hits max voltage. Meaning you don't need a charge controller.

If you're not going lithium, you could use 3 separate solar panels with 3 separate, small 12v solar charge controllers -- one going to each battery. But it will be up to YOU to make sure they stay balanced. (by letting them all charge up fully via solar now and then would be the easy way)
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Old 08-30-2017, 08:21 AM   #5 (permalink)
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Quote:
I commute 4 miles each way. A wind screen in the winter helps.
4 miles is quite the trek for me. I hardly could do 3 miles on a pedal bike, and I'm 19 years old. I'm not comitted yet, but I don't think I am going to ride in the winter.

Quote:
I think you might be better off going with a 36v battery and using a DC-DC converter to get 36v from your panels. Reason being, voltage is what determines top speed. With the same motor I have, running 24v would give you a top speed of about 13mph with a full charge, and less as the battery voltage drops. More amps adds acceleration, but not top speed.
The controller auto detects the battery voltage and sets it accordingly. I don't know how that would react to the converter.

Quote:
If you have any form of lithium on a BMS, it should control the charge for you and turn off the current as soon as any one cell hits max voltage. Meaning you don't need a charge controller.
Wouldn't the voltage have to be somewhat regulated? Reason I ask is because solar panels are constant current and the voltage changes as the sun changes, which is what the point of the controller is. Or atleast that is what it says in the manual for the controller.

Now that I think about it there is a load connection that supplies up to 10A. I could just get the BMS set for 12v charging and plug it in there, kind of bypassing the charge function, so no worry about 36v charging. Does that sound plausible?

I think if I go for 36v I'll just change cells and not use the 12v pack I have. It would be cheaper using a pack like what Ecky used, than to have to buy individual parts and put together myself. It would also have excessive power (36V 20Ah pack would be the result). How do you charge your ebike Ecky? I don't see a charger on the build list you posted, only a plug.

Thanks, Matt
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Old 08-30-2017, 08:44 AM   #6 (permalink)
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Regarding top speed, A motor's max RPM (at least in this setting) is a function of how it's wound and the voltage you supply. A controller can limit it below this, but you can't keep the same top speed with a lower voltage by changing the controller. Amps x volts gives you your torque / acceleration, while volts and RPM are directly correlated. I just had a custom 20" wheel built for my trike, and I needed to have a custom motor wound for it to get higher RPM at the same volts. Rather than ~240RPM, I had it wound for 400RPM to maintain approximately (slightly higher) top speed with the smaller diameter wheel. The downside to this is that you get less torque with a higher RPM - basically like gearing in a transmission, except it's baked into the motor itself.

For charging, I bought this 36v 2amp power supply:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Snipped the ends, replaced it with butt-ends and made a butt-end to XT60 adapter.

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Old 08-30-2017, 11:06 AM   #7 (permalink)
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After thought on my part, it is way cheaper to buy a battery than it is to build my own based on my 12v pack. It will cost almost as much to go to a prebuilt 48v unit as to go custom.

Does this seem like a good combination? The battery has a wall charger, so if I am not going to get enough of a charge from the solar I can plug in.

Battery, 48v 12AH,
BMS included

Conversion kit,
48v 1000W
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Old 08-30-2017, 01:58 PM   #8 (permalink)
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The item description says that battery is too small for a 1000w setup, so you'll either need a bigger battery or a lower power motor kit/ability to turn down the power output of the 1000w kit. Be careful buying batteries on ebay. I would head over to the Endless Sphere forums or other ebike forum and see if there are any sellers that sell quality batteries.

You might be better off selling your solar stuff than trying to charge with it. That 48v 12Ah battery would cost less than 10 cents to charge almost anywhere in the US.

Do you already have a bike? You could see if pedal power can work for you. It sucks getting started, but after a week or two your butt will get used to the saddle and you'll stop feeling like you're going to die from the effort.
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Old 08-30-2017, 05:27 PM   #9 (permalink)
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Vskid3: I know I am an impulse buyer, so I need to wait before buying. I do have a bike already. I agree with you about trying to pedal power it. I used to ride all the time before I had my license, now I don't ride at all.
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Old 08-31-2017, 01:31 AM   #10 (permalink)
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My son got suckered into buying a 1000w ebike with an undersized battery pack. He thought it had a wiring problem cause it shuts down every time you hit the throttle hard. Turned out the BMS shuts down the pack from over current. He never got it running. Get a 500 watt kit or a bigger battery. How much do you want to pedal or do you want to pedal at all? Those direct drive motors don't coast well so you need to be under power all the time. Not a big deal as long as you know. 500 watts is plenty if you don't mind pedaling a little.
If you still want to go cheap and stick with 24 volts, look for a used Schwinn IZip or Currie EZip. It's low tech and not as good as BLDC in many ways but sometimes you can find a really good deal. You can move the parts to another bike if you want. I re-geared mine and I'm quite happy with it. It doesn't have much torque off the line but it will cruise at 20-22 mph. I like to pedal all the time anyway and it is great for a pedal assist. I get some assistance up to 25 mph on 24 volts and there is no motor drag when the power is off. Something to think about.

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