CEF50 Battery Range Extender: that juicebox strapped to your rig to decrease anxiety and extend your range aka fun?

[TCFlowClyde]

Just doing a CEF50 battery extender solo thread now that frame kits are shipping out. We've got a few CEF50 owners who not only dabble in E-mtb enthusiasm but have got some real pro background into programming and/electronics and possibly some battery pack builders.

That's not me but I did want to create a separate thread to tackle the issue for both M820 motor 36V and 43V setups on the CEF50 frame which currently has no prefabricated frame ports or dedicated battery interface for an extender.

So, what's the dilemma? Just match up the correct voltage and drill up a damn hole in the frame and then feed the connectors through the hole...right?

That's what I naively thought, but nope! It ain't that simple...of course not! @mike_kelly explains why in clear detail in another thread exactly why! Hence the logic of this thread. I'll try to copy over some of threads to set us off in a more rational direction.

So, this is the main dilemma.

The other two are the following:

1) the Bafang-made range extenders (250Wh?) for the 410Wh BT-F014 battery (43V) and 360Wh BT-F100 battery (36V) availability,

and

2) the very real possibility of buying a third-party bottle-cage-type extender from Amazon/AliExpress etc. Or just DIYing your own in a soft pack for a frame bag.

Here we go!

 

[TCFlowClyde]

Post in thread 'M820 Bafang - CEF50 frame (lightweight)' M820 Bafang - CEF50 frame (lightweight)

 

[gido]

Only need this and diy battery with matching voltage

20V-72V Dual Battery Connector for Increase the Capacity By Connecting Two Batteries in Parallel Equalization Module - AliExpress 44

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[TCFlowClyde]

Only need this and diy battery with matching voltage

20V-72V Dual Battery Connector for Increase the Capacity By Connecting Two Batteries in Parallel Equalization Module - AliExpress 44

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Shoot I messed up and meant voltage matching not amps...was editing a little late last night and erred---opps!🫣

But I'm hoping @mike_kelly agrees with your simple, yet elegant solution: that the parallel equalizer module of XT60 connector plugs is the quick answer and boom done! End of very short thread.

I'm betting @mike_kelly will weigh in soon here.

 

[mike_kelly]

Shoot I messed up and meant voltage matching not amps...was editing a little late last night and erred---opps!🫣

But I'm hoping @mike_kelly agrees with your simple, yet elegant solution: that the parallel equalizer module of XT60 connector plugs is the quick answer and boom done! End of very short thread.

I'm betting @mike_kelly will weigh in soon here.

That unit only has one electronic switch so it can only turn one battery on and off. But the last one I listed in the CEF50 thread has a swtich for each of the batteries. So if they discharge unevenly it can handle either battery being lower than the other.

 

[mike_kelly]

Since we are all waiting, and many of us would like to add a bottle battery, please indulge me to give a little lesson on lipo batteries for the few that may not have dealt with them DIY before.

First, a quick explanation of voltage and current. If we use water as an analogy, a barrel of water that is a foot in diameter but 50ft tall has a lot of voltage (the height) and low current or amperage the diameter. A spigot at the bottom of our barrel will let water out and it will be pushed out fast but the volume is low. So the voltage is the push and the opening diameter is the current or amperage. If we have a big flat barrel that is only ten feet tall but 5 feet in diameter it has the same amount of water but the spigot can be much bigger in the bottom of the 5-foot diameter barrel. So the water will come out more slowly but it might knock you over if you stood in front of it. So the big flat barrel has a lower voltage but a higher current but the same amount of water.
Basically, the Power in watts is equal to the Voltage x current measured in amps:
300 watts=10v x 30amps but also 300 watts=30v x 10amps.

Lithium Polymer and Lithium Ion batteries can be dangerous. They are made up of small cells of 3.6v that are packed in a vacuum. The reason is, Lithium will catch on fire if exposed to air. I know. I was opening a battery once to repair it and just nicked one of the vacuum bags with my exacto knife and filled the house with smoke in a minute.
I am a radio-control drone hobbyist and I have a metal shed in the backyard to house my batteries.
You have to treat Lipo batteries with care, especially the batteries we use in e-bikes because they have a lot of energy in them.
Because the basic Lipo cell is only 3.6 volts, they need to be joined together in series to create a larger voltage, more useful battery for an e-bike. When you connect cells in series, the minus of one battery connected to the plus of the next and so on in a daisy chain, the overall voltage is the sum of all the individual cells. If you tie all the minuses together and all the pluses together, that is called a parallel connection. In a parallel battery, the voltage stays the same and the current capacity adds. So ten 3.6v 2ahr cells in series make a 36v 2ahr battery. Ten 3.6v 2ahr cells in parallel make a 3.6v 20ahr battery. Note, that it is the same amount of power: 36x2=72whr and 3.6x20=72whr. Manufacturers use a combination of series and parallel connected cells to make our e-bike batteries.
Because batteries are not all the same, we have some risk when combining this spiderweb of cells together. The connections between the cells are designed to support a certain current capacity. The more current the bigger and heavier the connections must be between cells. That is why it is generally better to have higher voltage batteries. The watt-hours of a battery is the same for a 10v battery of 10ahrs=100whr as a 20v battery of 5ahr=100whr. Both will do the same work and move the bike the same amount. But the 20v battery will only need connections at each cell to support 5amps when the 10v battery will require larger heavier connections to support 10amps.

So the problem lies with the fact that not all the cells charge at the same exact rate and don't always store charge at the same level.
When you have two batteries (cells) connected in parallel, current will always flow from the higher voltage to the lower voltage. When we have the charger connected, it is a high voltage and the current flows into our cells and recharges them but the cells don't all capture the same amount of energy. So after the charger is removed, we can have every cell at a little different voltage and this is not good. The cells in parallel will tend to have current move from the cells with higher voltage to the cells with lower voltage. If you happen to have a bad cell with a very low voltage, a lot of current can flow all at once from a fully charged cell to the very low voltage cell. This current can be so high it melts the connection between the cells or produces a lot of heat that damages the vacuum and causes the package to burst and let air hit the lithium and then you have a fire

If this note is ok with you all, I will next write about how we prevent this problem by balancing the cells during charge. The end point is to explain that connecting an external bottle battery must be done correctly or we risk having the same problem as charging individual cells.

 

[mike_kelly]

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• Wednesday at 11:45 AM
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So the way manufacturers solve this problem is to charge a battery slowly. Every once in a while the charging is stopped and the battery is balanced. This allows the cells to equalize without there being a huge difference in voltage between fully charged cells and very low charged cells. This is done via an electonic circuit board called a Battery Management System. It allows the cells to be charged for a period and then balanced for a period. It watches to see if there are any anomalies in charging so it might detect a bad cell.

Lipos don't like to be discharged to zero. It usually destroys the battery. That is why the BMS will turn the battery off if you try and discharge the battery too low. It is a pain for us because we lose some of the capacity of the battery. There is no hard point of discharge that is accepted. It is a philosophical issue with engineers. So that is why some ebikes turn off sooner than others. It just depends on the choice of the engineer who designed it.

So you see that adding an external bottle battery is not a simple thing to do. What happens if you add a fully charged bottle and a nearly dead internal battery?

 

[mike_kelly]

As Patdam notes one way to protect the ebike is to have a module that acts like a super BMS to manage the internal and external batteries. One way a good extender module works is to watch the voltages of the battery and with an internal electronic switch it turns OFF the lower volt battery and connects only the higher voltage battery to the motor. As the motor uses energy from the higher voltage battery, it's voltage drops, sags. As it's voltage comes close to the voltage of the second battery the Extender module switches the second battery ON since they are now the same voltage. As they are both used if one drops faster than the other, once again it will switch off the lower voltage battery until the higher voltage battery until they both match again. This prevents the drastically different battery voltages from causing a rush of current from one battery to the next.
So with the Extender module described above both batteries plug into the Extender and the extender is plugged into the motor so the extender can control witch battery goes to the motor.

But we don't have a way of connecting the internal battery to an extender. It connects inside directly to the motor.
Now another problem is that when charging a battery the current flow from the charger to the battery is low, maybe 2 to 5 amps which requires small wires. But when the battery is being used to power the motor the current going out of the battery can be 60 amps or more which requires big wires.
So when you have a connection on the bike frame for a charger port is it designed only, with lower current wires, for charging at 2-5 amps or is it designed for charging or an external battery with full power wires?
So these are the reasons you can NOT connect batteries of different voltages like 48v and a 36v. It is also why it is best to connect two identical batteries, with the same voltage, amperage capacity and chemistry.
So here we have some of the issues we must discover. Luckily we get the bike frames disassembled so we will know how they are made and can possibly change something if we desire. Maybe there might be room inside the frame for a Extender module?
So you need to think about these things before you run out and buy an external bottle battery.

 

[mike_kelly]

I am still researching because most of the extender switches have a pretty big aluminum case to dump heat. I am also looking at Bottle Batteries that have a switch built in and allows it to switch between charging and outputting power. But the first question is how does the internal battery connect with the motor and the charge port? Is the charge port wire just barely big enough size to handle a 2-5 amp charging current? So adding a external battery would not work because the 60 amps the motor would draw would melt the wires? I am going to study the options but need to see how the CEF50 internal battery is connected and if the charge port is designed for an external battery with big enough wires and plug.
If there is enough room inside we can fix it to work our way and it would be really slick to have an internal extender switch so the internal battery connects to the switch and also the external port. But then we are subject to another point of failure if the cheap switch goes south and you have to take everything apart to fix it.
Might be better to replace the charge port with a bigger heaver duty four prong connector with the internal battery connecting to the charge port on two of the pins and then have an external extender and the output of the extender goes back in through the bigger four pin charge port to the motor. So essentially bring the internal battery connector outside to the external extender switch. we would also have to change the plug on the wall charger to match the new 4 prong.

There are other solutions too but we can't just hook up and external battery if the stock charging port has wires that are small and only designed to low amperage charge the internal battery and not made to handle the current of an external battery supplying the motor.

 

[mike_kelly]

This dual battery protector is nice because it has two electronic switches so it can turn off the internal or external battery which ever is lower voltage and they can offer a separate charge port.

https://www.aliexpress.us/item/3256804603627828.html?spm=a2g0o.productlist.main.29.3c7f59cdgVfikl&algo_pvid=75b190e8-bddc-428c-8595-8fbc9cc5759b&aem_p4p_detail=2023040618081718307555941285520002746740&algo_exp_id=75b190e8-bddc-428c-8595-8fbc9cc5759b-14&pdp_npi=3%40dis%21USD%2116.99%2116.14%21%21%21%21%21%40211bea0816808296978498427d06f0%2112000030496038373%21sea%21US%211615972092&curPageLogUid=9R736xwTmVLW&ad_pvid=2023040618081718307555941285520002746740_15&ad_pvid=2023040618081718307555941285520002746740_15




Parameter:
Maximum output current: 15A/20A/30A/40A/80A/100A/120A
Nominal Voltage: 20-72V, 20-100V
Plug Connector: XT60/ XT90/ QS8-S
14/12/10 AWG Silicone Wire
Wire length: 10cm

Size: 45x18.5x30mm, 45x18.5x49mm, 45x18.5x60mm, 45x18.5x71mm, 63x25x75mm

Woking Temperature: -20-60℃

Waterproof: yes
Application: Connect 2 Batteries in Parallel / Double Capacity, will discharge higher voltage battery and then once voltage same will discharge both batteries together
The two battery's voltage need to be almost same, and the battery's capacity can be different




Working Process:

1. MCU monitor voltage of both batteries in real time and send the voltage value by UART (Only if UART interface is available).

2. Automatic Battery working detecting. Switch to the battery and discharge it, if only one battery is connected with this module.

3. If the voltage of two batteries is not same, module will discharge battery with higher voltage firstly till two batteries voltage be same then will discharge both batteries together.

4. Two batteries will discharge together when two batteries voltage is same (Iout=Ia+Ib, Ia=Ib).

 

[TCFlowClyde]

Might be better to replace the charge port with a bigger heaver duty four prong connector with the internal battery connecting to the charge port on two of the pins and then have an external extender and the output of the extender goes back in through the bigger four pin charge port to the motor. So essentially bring the internal battery connector outside to the external extender switch. we would also have to change the plug on the wall charger to match the new 4 prong.

Ok, in a nutshell...we upgrade (with a beefier 4-prong wire harness) our charging port plug to allow for a ranger extender of same voltage to prevent voltage sag and uneven battery discharge? And bonus we won't be lighting one's a$$ on fire!?

Or did I oversimplify this?

 

[mike_kelly]

What it essentially does is move the battery plug out of the bike so you can plug it into one of the electronic switches to manage the two batteries, then the output of the electronic switch goes back in through the same connector to the motor.
Otherwise you have to hope there is room inside to house the electronic switch box and that it won't be too hot in there with the extra heat source of the switch.
Also if the switch ever dies then you have to drop the motor to get it out and replace it. If you extend the battey plug outside you can mount the electronic switch outside where it is easy to get to if it were to fail.

 

[TCFlowClyde]

Ok, in a nutshell...we upgrade (with a beefier 4-prong wire harness) our charging port plug to allow for a ranger extender of same voltage to prevent voltage sag and uneven battery discharge? And bonus we won't be lighting one's a$$ on fire!?

Or did I oversimplify this?
View attachment 111100

Also, Mike I'm gonna admit I probably would retain your breakdown better if Selma Hayek was serving as "nerd-whisperer" here to hold my attention...no offense... jus' say'n. Also, her purple dress made me reflect that now I don't have to sell off my cherished Hope E-cranks that fit the M820 anymore. See, I'm easy to distract with bling and buxomness...and beer.

 

[mike_kelly]

I don't drink beer I can see thru

 

[TCFlowClyde]

Damn Selma looks good! But so do those Hope cranks! Yeah, I hear yah on libation consumption. So, moderation in the finer microbrew beer. One stout is like dessert...plus knocks me out when solo car camping in the forest! Plus, just 1 post ride lighter brew in general to celebrate the adventure and fun with the E-mtb mental respite!

 

[TCFlowClyde]

What about the Rosenberger-style connector/charging port like the Forestal Siryon? It would be a big frame cutout...

Can we MacGuyver that?

 

[mike_kelly]

I never said anything about consumption
Things like Guiness Stout can be used for so much more than a beverage. It can be used as a horse liniment eetc.

From what Lanton says the motor connector is a XT30 which will only handle 30 amps so really heavy duty cables will not be required which is handy.

 

[TCFlowClyde]

I never said anything about consumption
Things like Guiness Stout can be used for so much more than a beverage. It can be used as a horse liniment eetc.

From what Lanton says the motor connector is a XT30 which will only handle 30 amps so really heavy duty cables will not be required which is handy.

Great even MacGyver was known to reject the light stuff...but we don't need him for this range extender project then....what about House MD?

 

[TCFlowClyde]

Bottomline...we'll have to wait for u to get your CEF50s and experiment on one of them?

 

[mike_kelly]

Just to test I ordered an ebike dual battery switch with a charge cable which seems like it would be convenient

.

 

[mike_kelly]

The one problem is not knowing how much room there is on the downtube for a bottle battery?

 

[TCFlowClyde]

There's kind of a dead space, a cavity just above the motor for harness and some more just below the charger port I'd bet. That DBBD is bigger than I like but it might be able to be stuffed in there?
So wait and see?

 

[TCFlowClyde]

The one problem is not knowing how much room there is on the downtube for a bottle battery?

Oh, you mean will the bottom clear the shock compression pathway? If so good point.

 

[TCFlowClyde]

Wholesale EU US stock 10S3P 36V 9ah downtube electric bike lithium battery for TSDZ2 Bafang BBS01 250w 350w 500W From m.alibaba.com

Wholesale EU US stock 10S3P 36V 9ah downtube electric bike lithium battery for TSDZ2 Bafang BBS01 250w 350w 500W from on m.alibaba.com

m.alibaba.com

 

[mike_kelly]

That mobile link does not work on my laptop but lots of bottle batteries of different lengths and like you said at what length do they hit the shock. I've found comparable prices on ebay with local stock, to AE.

 

[mike_kelly]

Just a few notes after getting my CEF50's. There is very little room on the downtube for a bottle battery. I ordered the smallest that I could find and they just fit. I wrote an article about making my DIY bottle extender.
With the cef50 there are a lot of batteries being used and many are different. So any info on DIY extenders for the cef50 may only be a solution for a particular battery.
For instance I have custom batteries made for me from Zhaosheng built in Bafang cases. But the genuine Bafang batteries are connected with canbus so the info on the battery status can be monitored by the computer display. Mine don't have that ability so they are simpler. A solution for a genuine Bafang canbus battery will be different. Just a caveat to the would be DIY buikder.

Also I ended up using simple ideal diodes to connect my external bottle batteries rather that multiple battery switches because my batteries have separate charge ports.