Sine Wave controller advice for new 20" fat bike

[IsaacLarsen]

Hi, I am looking to buy my first e-bike. My only experience with e-bikes is with the rental ones you find in big cities. They are pretty fun, but the motor noise annoyed me right away, especially at low speeds when it engages. Based on that I am thinking of swapping the controller immediately for a sine wave model.

The bike model I am leaning toward is the CMACEWHEEL RX20. It has a geared motor so there will still be the gear noise but I don't need it to be completely silent. Also changing the controller will increase power so that's also an extra benefit.

I'm hoping you guys could help me decide which one to buy. Bonus points if it offers a way to quickly change the max speed settings (I need to set it at 25 km/h to be road legal and change it to higher values when I want to be naughty). I found this cheap one on Aliexpress but I'm not sure it would fit inside the RX20's frame (the 30A model). I'm ok with mounting it outside the frame if the controller is so good that the hassle it's worth it.

Here are some relevant specs of the RX20:

• 48V 17.5Ah LG battery
• 750W geared brushless motor
• 48V 20A controller

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[amberwolf]

If you go with another LiShui, you can probably keep the display/etc you have and not have to rewire the bike. LS makes sinewave controllers too.

If you get the right model, it will also be compatible with the OSFW open source firmware projects here on ES / github / etc, which can give you other features not in the OEM fw if you find it lacking.

Note that using a controller with a higher current limit will put a higher load on the battery, causing more voltage sag and faster aging, and if the BMS in the battery isn't built to handle anything more than the original controller, you may have to change it to prevent shutdowns. (but if the BMS is sized to protect the cells like it should be, changing *that* for a higher current model may endanger the cells--you'd have to find specs for the actual cells you find in your pack (not whatever the seller/maker *says* are in there)).


Regarding the bike...the fat tires are going to eat up power, so unless you *need* fat tires for riding thru sand or other loose materials, I'd recommend something with more typical tires if you are already needing more power than it has available.

I don't know that specific frame, but it is very similar to the CEMoto frame of a 26" bike I've worked on for another ES member, and it's very "wiggly" at all the joins and pivots, which might be fixable by changing out the bushings/etc for better ones (or bearings), if you have that problem.



Before choosing anything, however...I recommend that you sit down and define the job the bike has to do for you (speed, acceleration, range, weight, etc), and what conditions it has to do that job under (terrain, winds, hills, road conditions, traffic, weather etc). Once you do that, you can take that information to calculators / simulators like those at ebikes.ca, and experiment with them to see how much power it will take to do what you want, and how big a battery to get the range you want at those power levels. It will also help you pick a bike that mechanically best does the job, too, so you don't have to change out or repair a bunch of stuff on it relatively quickly.

 

[IsaacLarsen]

Thanks for the detailed answer. I will be using the bike in my free time and I’m looking for maximum comfort. Mostly ride on the road with some light off-roading. I don’t expect to use it on huge inclines. That’s why a fat bike with front and rear suspension seems like a good choice to me. Riding a regular bike on Sampietrini is torture. The reason I’m considering changing the controller is also for improved comfort (less noise, smoother ride).

As I said, my only experience with ebikes is with the rental ones which should be limited to 250W as that’s the law limit in my country and they felt a bit underpowered to me but not too bad. Since the RX20 is a lot more powerful, it should be fine for me. However, I can see myself wanting more power in the future as I get more comfortable with the bike so going for a beefier controller straight away seems like the right move.

Those are the reasons why I’m leaning toward that model but if you have any suggestions I would be happy to hear them.

I can’t find anything about the specs of the battery. There are some replacements on aliexpress that claim 30A for the BMS, not sure if the original product is the same. I am inside an Italian telegram group of ebikes enthusiasts and most of them have the RX20 paired with this 35A square wave controller. Faster aging should be expected but I’m ok with that.

I looked into the Lishui open source firmware but it looks pretty involved and tbh I’m not sure why would I do that. It seems that the main advantage is the ability to add a torque sensor which I am not interested in doing. I’m not sure what I’m missing here. The most powerful Lishui controller I could find is 25A. I was hoping for 30/35A. If you have a particular model in mind, please let me know.

What do you think about this one? It has a speed limit feature that allows you to quickly limit the speed to 25km/h with a switch, which is exactly what I was looking for. It’s 45A but you can limit the current in the display settings and it supports higher voltages which leaves room for battery upgrades in the future. The problem is that it won’t fit inside the frame so I would have to mount it outside somehow.

 

[999zip999]

Here in United States there are a lot of e-bike sales as there are so many new e-bike stores that open up after covac and seems they imported so many more bikes than they need. There are a lot of sells I see the bike you're looking at has a $200 off.
Plus your controller says 10 amp constant and up to 20 amp first which is puny.
I have two 40 amp controllers one gives me 45 amps and 39 amps continuous. The other will pick up to 40 amps and settle down to closer to 30 amps. So that being said it's hard to rely on the printed numbers. When you're changing a controller it's not easy to find one that's plug and Play most times you'll have to cut off connectors and crimp or solder new connectors on to match your existing bike. And some connectors higo can be difficult to swap out. The guy that's been doing eBay for 13 years was trying to get a controller for a saunders he bought three different controllers trying to get plug and Play couldn't do it. After buying three Summers controllers he's still going to have to cut off the ends and match to the existing bike. Pain in the ass.
I just got a 3000 watt kit yesterday and I'm going to have to cut off the ends and redo the wires to conform to my battery and to match my other bike so I can swap out between the two. A pain. And reading about my display sw900 it might limit my 72v60 amp controllers amps.
It's tricky out there.

 

[IsaacLarsen]

You are used to way higher numbers in the US. In the EU 48v 10A is actually double the legal limit . I’m not necessarily looking for a plug-and-play solution, cutting wires is ok.

 

[E-HP]

I can’t find anything about the specs of the battery. There are some replacements on aliexpress that claim 30A for the BMS, not sure if the original product is the same. I am inside an Italian telegram group of ebikes enthusiasts and most of them have the RX20 paired with this 35A square wave controller. Faster aging should be expected but I’m ok with that.

Ask the guys on the forum if any have verified the cells used in the battery pack. If the LG cells are MJ1's (good), MJ1 cells are spec'd to provide 10A continuous current and store 3500mAh so that would be a 5P pack (5 parallel groups of 13 cells in series to get to 17.5Ah). . If so, the pack would be able to prove ample current capability (50A) for a 35A controller. On the other hand, LG also makes another 3500mAh cell that can only provide half of that current, so knowing what's in the pack let's you know how much you're hammering the pack and/or how long it will last. In any case, if you're OK with a shortened lifespan, then make sure the next pack is made of good cells. Note that although the pack may be able to provide up to 50A, the BMS may limit that to something more conservative.

 

[IsaacLarsen]

Ask the guys on the forum if any have verified the cells used in the battery pack. If the LG cells are MJ1's (good), MJ1 cells are spec'd to provide 10A continuous current and store 3500mAh so that would be a 5P pack (5 parallel groups of 13 cells in series to get to 17.5Ah). . If so, the pack would be able to prove ample current capability (50A) for a 35A controller. On the other hand, LG also makes another 3500mAh cell that can only provide half of that current, so knowing what's in the pack let's you know how much you're hammering the pack and/or how long it will last. In any case, if you're OK with a shortened lifespan, then make sure the next pack is made of good cells. Note that although the pack may be able to provide up to 50A, the BMS may limit that to something more conservative.

A guy in the group said that they use Chinese cells and not LG. I asked on cmacewheel.com and they said they use this:


3200mAh. That would be 16Ah, right? However, the guy said that they are resellers. Unfortunately, I couldn’t find a way to contact the producer.

I guess I’ll just have to check it myself when it arrives. The MH1 is 10A like the MJ1 so I should be good with a 30-35A controller if the BMS allows it.

 

[IsaacLarsen]

boys, I think I found the one: the sabvon SVMC7245. It should fit inside the frame with a few modifications. Sine wave with speed limit function, 3 speed function as well. What do you think? Could you also give me some feedback/suggestions on the bike model and battery?

 

[IsaacLarsen]

I'm also looking into the Flipsky 75100 but the setup process is a lot more involved. I also saw that some people can't get the calibration to work right and they end up with noisy motors.

 

[docw009]

I recall Amberwolf trying to help someone on the Cemoto bike. Wasn't it about adding a torque sensing BB? The suspension pivots were later reported to be loose by the owner in the EBR forum,

It was originally a 26" folding bike, and all they have done is adapt it to fit 20x4" rims/tires which are about 24" tall. Unless you have already bought it, I don't think it is a really good bike. It's been around for 7 years,

The folding frame makes it heavier than it needs to be. The hinge for folding weakens the structure, Not saying it's weak, but if you don't need a folding bike, don't buy one. In my opinion, it's not worth putting a higher power controller into that bike.

 

[IsaacLarsen]

I recall Amberwolf trying to help someone on the Cemoto bike. Wasn't it about adding a torque sensing BB? The suspension pivots were later reported to be loose by the owner in the EBR forum,

It was originally a 26" folding bike, and all they have done is adapt it to fit 20x4" rims/tires which are about 24" tall. Unless you have already bought it, I don't think it is a really good bike. It's been around for 7 years,

The folding frame makes it heavier than it needs to be. The hinge for folding weakens the structure, Not saying it's weak, but if you don't need a folding bike, don't buy one. In my opinion, it's not worth putting a higher power controller into that bike.

Thanks for the advice!

I think this is what you are referring to, right? That is pretty bad but the issue with that bike is related to the rear suspension and not with the folding mechanism from what I can tell. The bike I’m considering at the moment has a different rear suspension geometry. A user here that uses the same frame said it is “absurdly rigid”.

Initially, I was considering the Engwe engine pro which has a similar suspension to the Cemoto but then I saw that a lot of people have had issues with that design so I discarded that model.

I’m not seeing many complaints with the Cmacewheel RX20 though. This is all I could find (Mate X, similar frame design):

Could be a problem with that particular unit. Hard to tell.

I forgot to mention. I need to also buy an ebike for my girlfriend (probably the same model but I haven’t decided yet) and they both need to fit in my VW Golf. That’s why I am looking at folding bikes. I could probably fit a 20” non-folding bike if I remove the front wheel but it’s not as convenient and I would prefer not to buy a bike rack.

Yes, folding fat ebikes are heavier but when you have a motor doing the job for you and the range is good enough, does it really matter?

The folding mechanism could be a weak point but I’m not seeing many complaints about that either.

It might seem that I made my mind up and I’m justifying my choice but I’m not. I’m just trying to explain my thought process in detail. I’m doing a lot of research but, like I said, I have no experience with this. I am very open to suggestions.

 

[99t4]

I need to also buy an ebike for my girlfriend (probably the same model but I haven’t decided yet)...

The benefit to having two of the same model is that you can economize on the quantity and variety of spare parts you keep around. Possibly the same for tools also. And the knowledge you gain from tuning and troubleshooting one directly applies to the other.

 

[999zip999]

I don't know about Italy but here in Southern California we have many many e-bike stores. And there and they are pretty full of e-bikes you might look around that someone has an overstock and make an offer just because the price is printed on the tag it doesn't mean it's the price you have to pay.
Especially when you're buying two bikes and remember to buy a lock one for each bike and keep your eye on it the best you can. Even though the bikes might look the same they might not be from the same batch meaning they can have different batteries in different controllers even though they look the same on the outside. Just take a look at it and see how they match because I would think you would want both bikes your girlfriends and you to have the same components which is would be easier to find if something happened. Plus ask him how long they guarantee the bike ask him how long they guarantee the battery and the charger. Yes ask these questions before you buy and it's not bad to have a pen and notepad. People think you're serious when you take notes meaning it could be intimidating. Which would be good for you. Also in your little Pat have other bikes and prices that you've written down and go back and act like you're comparing make the guy sweat. Good luck.
Where in Italy do you do you live if you live in Italy

 

[IsaacLarsen]

I’m from northern Italy. I went to a couple of physical stores but their offerings were pretty bad. First of all, because of the legal limits, most of the bikes have a 250W motor. Also, most of the folding bikes are basically rebranded Chinese bikes just a lot more expensive and with a tiny motor. I mean how can you justify 1500€ for this bike? 36v 10ah battery, lol.

My best options are Chinese bikes from Aliexpress. This means I can forget about the warranty but I’m ok with that. Bikes are not that complicated; I should be able to fix or replace anything that breaks.