Identifying / upgrading craigslist ebike

[Jenming]

Hi people,

I picked up an ebike on craigslist and am having fun with it, but want to see if I can make it a little better. I'm hoping to go 20+ mph for about 20 miles on a charge.

This is what I've been able to figure out so far.

It has an Aotema front hub motor. I didn't get anywhere googleing the serial number, but it has 3 wires coming out of it. From what I can tell from elsewhere on this forum, that should be a brushless motor without hall sensors and be .. fine? Not really worth upgrading for an entry level ebike.

It has a controller with no external markings with 3 wires connected to the battery and another bunch of wires that I assume would go to hall sensors if they existed. Anyway to figure out what kind of controller I have? It has some screws and I could take it apart.

It has 3 lead acid batteries in series for 36V, 9ah. I don't think I am actually getting 9 ah out of them though. It goes about 2 or 3 miles and then power drops rapidly. This was done at 32 F, so maybe it gets a little more in normal weather.

It seems to me that replacing the battery and leaving everything else alone should get me to my 20 mph / 20 mile range.

Would it be as simple as replacing the SLV with something like this:
https://bmsbattery.com/ebike-battery/165-36v-15ah-li-ion-shrink-tube-ebike-battery-pack-ecitypower-battery.html

Or can I bump the voltage up just a bit (44v) and put two of these in series? There seems to be a lot of love for LiPO.
https://hobbyking.com/en_us/turnigy-high-capacity-battery-12000mah-6s-12c-drone-lipo-pack-xt90.html

If I go with LIPO, I can't seem to figure out if I need a BMS? Or do I just get one of the balancing chargers Hobby Kings sells?

Thanks for your help.

 

[Chalo]

If your battery doesn't have a BMS, then you are the BMS. I personally have better things to do than frequently measure my cell voltages, but to each his own.

The BMS Battery pack you linked has a pretty low continuous current rating-- too low for a Wilderness Energy BL36 system like I suspect yours is. At least some of those kits came with 50A controllers, if I remember correctly.

Hobby King lipo packs of appropriate size will have plenty of current capacity-- along with short cycle life, inconsistent quality, lack of physical protection, and risk of fire.

 

[amberwolf]

It has an Aotema front hub motor. I didn't get anywhere googleing the serial number, but it has 3 wires coming out of it. From what I can tell from elsewhere on this forum, that should be a brushless motor without hall sensors and be .. fine?

It's probably a sensorless brushless motor, if all three wires are the same thickness. There' are some threads on the Aotema setups if you poke around.

It has a controller with no external markings with 3 wires connected to the battery

With an SLA battery, 3 wires to it is unusual, unless it has both a thick and a thin positive battery wire, and a thick negative. (then the thin one is actually a "keyswitch / ignition" wire). Where specifically do each of the three wires go?

and another bunch of wires that I assume would go to hall sensors if they existed. Anyway to figure out what kind of controller I have?

Could be anything; there's literally hundreds of thousands, and almost none of them have any documentation anywhere, including on sites like this. Only a very few have ever been documented or figured out; many are similar to each other, but not identical.

If you really need to know about the controller itself, opening it may tell you some things; depends on what you want to know.

It has 3 lead acid batteries in series for 36V, 9ah. I don't think I am actually getting 9 ah out of them though. It goes about 2 or 3 miles and then power drops rapidly. This was done at 32 F, so maybe it gets a little more in normal weather.

Tha'ts pretty normal for any SLA. You don't usually get more than half of the capacity it's labelled at, even brand new, as it's not rated for that capacity at a current more than 1/20th of the "a" part of that. (meaning, a 9Ah is only rated 9Ah when drawing 1/20 * 9A from it, under ideal conditions in a lab).

It seems to me that replacing the battery and leaving everything else alone should get me to my 20 mph / 20 mile range.

As long as you are getting 20MPH out of it now, then yes.

20MPH typically takes around 20wh/mile or so, so for 20 mile range you'd need at least 400wh. For a 36v pack that's about 11Ah; for a 48v pack that's more than 8Ah (don't know if your controller can handle any more than 42v full charge of a 36v pack, some can, some can't). Personally I recommend adding at least 20-25% to those, so you have extra range to account for headwinds, detours, and pack degradation over time. Plus, the smaller a pack is, the harder it's being pushed, which affects it's lifespan.

Would it be as simple as replacing the SLV with something like this:
https://bmsbattery.com/ebike-battery/165-36v-15ah-li-ion-shrink-tube-ebike-battery-pack-ecitypower-battery.html

At a guess, would probably work, if it can supply enough current...but you may want to look around the forum at the various BMSBattery threads, as not everyone has had good luck with that company actually sending the item that was ordered (mostly with motors).

But before you pick a battery, it would be helpful to know how much current the system draws at max, and just riding at cruising speed. At the moment, you don't know what it is because the controller has no markings, though if you have (or get) a wattmeter you can find out how much current is drawn under load using your SLA, which gives you an idea of how much current the new battery has to supply at max.

If I go with LIPO, I can't seem to figure out if I need a BMS? Or do I just get one of the balancing chargers Hobby Kings sells?

If you have no experience with RC LiPo, I recommend you read around the various RC LiPo for noobs threads like those by Neptronix, so you don't have problems (some of which can result in serious fires), before you go that route. It has it's uses, but it's QC is notoriously inconsistent and even when you use it within it's limitations sometimes things go spectacularly bad. (they have, rarely, been known to burst into flames just sitting there, without having even been used yet).

 

[dogman dan]

Its definitely the aotema 36v-48v kit. The motor can handle a lot, so upping the power is definitely possible with another sensorless controller.

But there is an easy way, just pair what you have, with a decent 36v or 48v lithium battery. 48v will get you 25 mph plus, close to 30 actually, when the battery is at its fullest. Really, except for the connectors, particularly the one to the battery, those kits are not bad at all. I ran one almost 10,000 miles of commuting.

Make the battery 10 ah at minimum, and ideally 15 ah. You will get one mile per ah of 36v, with a reserve, and if you don't go max speed, even more from a 48v 15 ah. That is the 22 amps controller typical with the kits, and a 15 ah like the one you linked to will do fine without being too big to carry easy. Your cruising current will be about 15 amps. If you want to get a battery that is easy to carry, but can handle a bit more current, look at 36v 20 ah packs. Same size and weight, but more cells in each cell group when its in 36v configuration. So each individual cell has less load, at 15 amps of load. But again, 48v 15 ah will do. 48v 20 ah, now you get into harder to carry on a bike. Bulky, and heavy, for rear racks.


Your battery will have either a different connector, or just bare wires, so just replace your battery to controller connector when you get a new battery. When you do, be very careful to make a note of which wire is actually the positive from the battery. On those kits, the wires from battery to controller may not be red is positive. It's likely to be reversed. On the battery side of that plug, red is +. On the controller side, it may be the black wire. Mix those up and connect, and you will fry the controller.

 

[Jenming]

Thank you all. Those were very helpful responses.

I'm going to go ahead and replace the lead-acids with hopefully a 48v / 15 ahr pack. Should have some fun with it this summer

 

[dogman dan]

Oh yeah, you gonna have some fun. Rear hubs are better for off road riding, but with practice, you can still go some gravel paths or dirt roads with that bike. And it will be surprisingly nice on pavement. Hit that throttle mid corner, and it pulls you out of it fast. 8)