48V 20AH e-bike 2nd Battery

[bob58o]

Is there any reason I can’t use this battery as a replacement without any extra electronics?

It was only $218, which is fairly inexpensive for its capacity. From the manufacturer it’s $590.

The original battery has a on/off key built it and uses C14 style plugs (I think they are called C14).

Trying to double up the range of my e-bike. It’s a 48V 750 watt (possible 1000 watt listed as 750). It came with a 48V 20AH battery. It tops out about 24mph and probably has a range of ~35 miles without pedaling. I’ve never drained it all the way out of fear of having to use power of my own legs.

The charging is slow at 2 amps. So I guess it would take 10 hours to fully recharge.

I purchased a second battery. I don’t plan on running them in parallel, just swapping one for the other to be used while first one charges. I tried to look for cables/pigtails with 10 awg.


Airuxuan 48V Battery 48V Ebike Battery 20Ah Electric Bike Battery 48V Lithium Battery with 2A Charger, T-Plug, XT60 Connector and BMS for 250-1000W Electric Bicycles Motor/Ebike Kit https://a.co/d/f6nFYHK

 

[bob58o]

 

[ezcome-ezgo]

I see no reason, but I am technologically (not literally) blind.

 

[Rat]

The key fit into that battery box is there for no more reason than to prevent parasitic drain when not in use, and to prevent accidental engagement without a rider.

As far as playing nice, Ah ratings don't affect any part of compatibility beyond battery size and weight.
A 20ah battery is going to be dynamically the same as having two 10ah in series no matter what the matching base voltage is (but smaller than 2 physically).

There is absolutely no reason you can't wire in a toggle to do the same thing if you're talking about direct swapping the battery without employment of the fancy case. As for needing extra electronics specifically? Absolutely none required.

 

[bob58o]

The key fit into that battery box is there for no more reason than to prevent parasitic drain when not in use, and to prevent accidental engagement without a rider.

As far as playing nice, Ah ratings don't affect any part of compatibility beyond battery size and weight.
A 20ah battery is going to be dynamically the same as having two 10ah in series no matter what the matching base voltage is (but smaller than 2 physically).

There is absolutely no reason you can't wire in a toggle to do the same thing if you're talking about direct swapping the battery without employment of the fancy case. As for needing extra electronics specifically? Absolutely none required.

Thank you. I don’t need a switch. I think I can just unplug the battery when not in use. I did get a case/bag claiming to be fireproof. I’m not sure what causes battery fires, but I suspect AliExpress batteries being resold might be at risk.

I guess the real questions come when I run my batteries in parallel to try to power an inverter.
48V 40AH.

 

[Rat]

Thank you. I don’t need a switch. I think I can just unplug the battery when not in use. I did get a case/bag claiming to be fireproof.

Anything to hold the battery but you'll eventually regret that choice after having to fiddle with the connector before and after every ride... then theres the wear and tear that will eventually make the connector not fit so good (the only variable is how long that will take)

I’m not sure what causes battery fires, but I suspect AliExpress batteries being resold might be at risk.

Primarily faulty wiring in cheap motors but that only leads back to the actual primary cause which is short circuit to ground.

As the #1 culprit, it doesn't matter if it's a pinched wire, failed solder joint or a somhow reversed plug in the system... when positive meets negative there are almost always sparks, and there is absolutely always heat, then comes the magic smoke and flames, although that is typical an electrical fire of the wiring not the battery itself... not that the battery won't join it.

Secondary to that is faulty chargers and overcharging with an unregulated box
(old school units like mine are not regulated and charge in one of 3 selected modes 6v-6A, 12v-2A, or 12v-12A) which can push more voltage and amperes into a battery than its actual "standby voltage". If this happens it tends to bloat the case and scorch the battery so that it never holds a charge again and you can typically smell the sulferic smell (oddly enough even from Lithium batteries) but this can and will cause a battery fire eventually if not addressed.

I guess the real questions come when I run my batteries in parallel to try to power an inverter.
48V 40AH.

Parallel increases your storage capacity not standby voltage so for all intents and purposes it only makes 2 or more batteries become one solitary battery

Serial wiring is where thing get hot, this increases the standby voltage by how ever many base units are used, but not the Ah runtime at all.

Then there is Paralell Series which effectively increases voltage an Ah but can only be done in balanced pairs where you'd have say 2 pair in series (4 batteries) that are also connected at one end in parallel. Assuming 12v 10Ah each, that would give you a 24v 20Ah unit. Stacking parallel series gets more complex as you increase the individual cell count.

 

[bob58o]

Sure I understand series and parallel.
For example, enough 3.7V batteries in series to get to 48 Volts.
13 in series.

Then enough of those 48V strings connected in parallel to get to 20AH capacity.

Since the battery is a 13s 6p (13 in series, 6 in parallel), guess that means they claim these 18650’s have a capacity of ~ 3300mAH.
I’m not sure if that is about right.

I’m concerned about connecting two different 13s6p in parallel to get me a 13s12p.
Not sure how charging or discharging might be problematic if trying to use these to power an inverter. Do I need some type of voltage/charge balancer?

Both batteries claim to have built in BMS. I’m not sure what they do. Both come with 2amp chargers. When my current battery is done, the charging light switches from red to green. Not sure if the battery or the charger controls the overcharge protection feature.

 

[bob58o]

As far as fiddling with the connector, I already do this. I park the bike then bring the battery inside to charge. The key is a hassle. It also locks the battery in place and I struggle with the locking mechanism every time. Jiggle, push, pull out a bit, swear, kick, pray,…

 

[Rat]

Sure I understand series and parallel.
For example, enough 3.7V batteries in series to get to 48 Volts.
13 in series.

Then enough of those 48V strings connected in parallel to get to 20AH capacity.

Since the battery is a 13s 6p (13 in series, 6 in parallel), guess that means they claim these 18650’s have a capacity of ~ 3300mAH.
I’m not sure if that is about right.

On average yes that is on point although they average between 3000-3500

I’m concerned about connecting two different 13s6p in parallel to get me a 13s12p.
Not sure how charging or discharging might be problematic if trying to use these to power an inverter. Do I need some type of voltage/charge balancer?

No all the same rules still apply as long as you connect at the correct points and polarity. Parallel-series connected to another Parallel-series for a target V/Ah is common regardless if it's in series or parallel. The one constant is how the Voltage and AH is totaled at the terminal... the larger the AH the longer it will take to deplete and likewise recharge...at some level stepping up the charging rate would be required

Both batteries claim to have built in BMS. I’m not sure what they do. Both come with 2amp chargers. When my current battery is done, the charging light switches from red to green. Not sure if the battery or the charger controls the overcharge protection feature.

The charger by means of a microcircuit probably a diode setup where when it reaches peak capacity, it opens the circuit so that it's not charging not discarging. The fly in that soup it required the ACV to detect the drop so if a power outage occurs that circuit end up closing and discharging the battery.

It's not cost effective manufacturing for batteries to have an overcharge protection circuit, although they do exsist and tend to be more for things like emergency lights since they exsist hardwired to a 120AC source with the same basic protective circuit but instead of discharging the battery that same circuit redirects to the flood lights via diodes

 

[busted_blocks]

It would be rare for a cheap battery to actually have 3500mAh cells, they are expensive. Much more likely 2500mAh-3000mAh unless they advertise what cells are in there. Sanyo has a 3500mAh 18650 as does LG (MJ1). Most Chinese no name battery pack capacities are exaggerated as it's very hard to test for the average consumer.

Most BMS's will have overcharge protection. They monitor each cell voltage and when a single cell is over 4.2 or 4.25 it shuts off. Some have shared power and charge ports some have separate. The image you showed has both, which implies, but doesn't guarantee, separate mosfets for charge/discharge protection. I attached a picture of a cheap Chinese BMS, similar to what would be in that battery. On the right in the Chinese you can see 4.25 +/-, this is where is says overvoltage protection. I'm not saying it's perfect but it at least offers some protection.

Another note on cell failure. 18650's or pouches can fail internally, this sets off a exothermal reaction that is uncontrolled. In 18650's it builds up pressure and there is a pressure release. If you're lucky, the cell vents and doesn't cascade. Far from a guarantee. I've had an 18650 fail as a short after years of use. Then all the cells in the same circuit discharge through that cell and things get very hot. Pouches have no such venting, they just basically catch fire and it spreads to all other cells. I had a drone crash and watched it all burn to a mess.

I have a lot of battery stories but it's a bit off topic.... I included one pic of the clamp hitting the BMS during one battery build.

On the original topic, I agree, that battery looks fine for your setup. If the voltage and output power rating match you're good to go.

 

[busted_blocks]

I had an old pack similar to the amazon ad you showed, and tore it open to show you. Cheap Chinese cells, not branded so very unlikely they could be over 3000mAh.

You can see the cells are welded together, covered in 1mm FR4 sheets and then blue heat shrink. The end of the pack has a BMS with wires that go to each set of parallel cells. These monitor for over voltage or under voltage. The 6 black chips are MOSFets, or switches if you like, to cut off the charge or discharge in event of failure. Super cheap but they have this feature.

I Just noticed when zooming in on the picture, what feature this doesn't have is cell balancing. The transistors and resistors for that feature aren't populated on the PCB. Everything for a price. This means over time you lose capacity not only from wear on the cells but because the highest and lowest voltage cells become farther and farther apart in voltage. The BMS will cut off charging when the first set of cells hits 4.2, and cut off discharge when the first set of parallel cells hits 2.5V. Due to differences in cells this tends to get worse over time leading to a part of the capacity you can't use.

 

[bob58o]

They claim the BMS does a lot.

This review seems to be from somebody who knows more about batteries than me.

“Worked fine on an otherwise stock razor mx650 with original brushed motor, but once I replaced the stock motor controller the shortcomings became apparent. One strip of 6 cells has all its current going through a single nickel strip, of which these strips are usually rated for a 7A max current over it. This strip that takes up the load is bent over one side of the battery, creating a weak point of higher resistance. Needless to say, upon upgrading the motor controller, the strip burnt through right where it was bent over ... before the BMS wanted to limit the battery, or fuses blew. This little strip of nickel basically functioned as a very smelly fuse. Luckily I was watching it and no fire resulted, just some burned plastic and tape... my cells are all still good and I can fix it, but this is some poor battery design work. Suggest another brand if you can manage it. The BMS seems decent enough, rated 30A continuous, probably 60 amp max draw. Fairly certain the 650 stock motor wasn't trying to draw more than 60A from the battery at the time it melted. If it was, then the 650w rated motor from the razor was trying to draw 3000w or more from the battery... unlikely. If my calculations are correct, 60A/13 should be max 4.6A running through that particular strip. Maybe the BMS failed to limit at 60A or, in my non expert opinion, the bend in the strip just affects the resistance that much that it burned up with that amount of current going through it ...hard to tell. There was also one cell in the middle of the pack that was different than all the rest suggesting this was probably a "remanufactured" battery. So I'm going to fix this, probably get a better BMS installed and get a current meter on the battery and see what the motor and controller are actually trying to draw, and will update if I find out more”

 

[busted_blocks]

The current the strip can take depends on it's thickness. Typically .1,.15 or .2mm. It's a limiting factor in the design. the different color cell doesn't mean remanufactured, just different batches of cells. You can see in the battery I opened the different colors. Small battery factories are not that careful and don't necessarily care a lot, need a few more cells, go grab them for over there... Motors can draw a ton during acceleration which can certainly draw more than 60A but this amount is limited by the motor controller. To what? depends on the bike. If you bike has good acceleration off the line, it's drawing a good amount of current. Might want to consider a better battery. Interesting the poster says brushed motor, usually they are brushless. He also says everything was fine UNTIL he replaced the motor controller, thus likely having it set to something unlimited for battery current. On my bike and other projects, we set the max current in the controller to the max current of the battery. If yours controller is stock it's probably fine. Note probably comes with no warranties

I suspect most cheap batteries are built the same way. Exactly enough to give the stated specs and not 1A more. Remember on the cheap one I opened they even removed a few resistors and transistors to save money. Maybe including pick and place fees, saved $0.10. It's amazing how much they cut costs. It's a shame on Amazon you have no way to offer the extra $20 to the factory that can turn something so so into something decent. I've talked to one battery guy about how they re-laser the model numbers on the mosfets to show they are good quality but still get to install the cheap ones.

 

[busted_blocks]

View attachment 144832

Just a comparison how I did the connections on the last group of cells on 2 of my bike batteries.

 

[Rat]

Interesting the poster says brushed motor, usually they are brushless. He also says everything was fine UNTIL he replaced the motor controller, thus likely having it set to something unlimited for battery current.

RAZOR uses brushed motors in everything they make. Why? Because brushed motors deliver more torque on demand while brushless motors gotta wind up before they get there. Even then their torque is nothing compared to a brushed motor.

In the word of Ebikes I've noticed that hub motors tend to always be brushless with a planetary reduction, or brushless and gearless. Center drive tends to always be brushed and have a gear reduction.

Odds are the OE controller was very limited to the safe side, very likely to the point of being a handicap... not uncommon practice to prevent system ignition.

 

[bob58o]

Except for the battery everything would remain stock. The only alteration would be inside the LCD display controls. There is a “max velocity” setting. It was limited to ~15 mph until I changed this setting. Now it goes about 25mph.

 

[busted_blocks]

RAZOR uses brushed motors in everything they make. Why? Because brushed motors deliver more torque on demand while brushless motors gotta wind up before they get there. Even then their torque is nothing compared to a brushed motor.

In the word of Ebikes I've noticed that hub motors tend to always be brushless with a planetary reduction, or brushless and gearless. Center drive tends to always be brushed and have a gear reduction.

Odds are the OE controller was very limited to the safe side, very likely to the point of being a handicap... not uncommon practice to prevent system ignition.

Never heard brushed motors have more torque. Since brushless are more efficient, I would think you could drive them with more current at stall for max torque. However all my EV/ebike experience is with brushless motors. Brushed should be electrically easier to control as you don't have to time pulses (ideally sinusoidal) to each motor phase, I think the brushes provide that function. It's hard to generalize what type of motors ebikes have. Price might have a lot to do with it. Surron are mid-drive with brushless motors but pretty high power too.

Your for sure are correct the Razor has a brushed motor. Where I am, brushed motors for ebikes are uncommon, I'm not sure I've seen one in person. Most use the small hub motors with internal gears. Mid-drive of any kind are pretty rare to see too.

 

[busted_blocks]

Except for the battery everything would remain stock. The only alteration would be inside the LCD display controls. There is a “max velocity” setting. It was limited to ~15 mph until I changed this setting. Now it goes about 25mph.

I don't think the top speed setting will spike your current. It's acceleration that would be the issue.

 

[bob58o]

The acceleration isn’t going to pin you back, but if I’m on pedal assist lv 5 and I’m trying to slowly maneuver a series of sharp turns I need to be careful with my feet. I had a bit of an accident when I was still figuring it out.
When not expecting it, there is a noticeable jerk.

 

[busted_blocks]

The acceleration isn’t going to pin you back, but if I’m on pedal assist lv 5 and I’m trying to slowly maneuver a series of sharp turns I need to be careful with my feet. I had a bit of an accident when I was still figuring it out.
When not expecting it, there is a noticeable jerk.

It's a tough one. I'd have said 100% go for it without the review showing the very limited power connection at the terminal. I checked some other similar ads and they all have a good percentage of bad reviews. Seems hit or miss with Amazon batteries. That metal strip, depending on thickness is only rated 10A continuous or even 7A which is only about 500W continuous safely. It's probably OK, marginally for your application. For all we know they fixed that issue already. Can't say for sure...