thaeber
Well-known member
This looks like a bad idea imho, placing significant weight at the worst place available on the frame in regards of weight distribution / center of gravity. 2kg wobbling around on the toptube..
CEF50 External battery build
- Thread starter mike_kelly
- Start date
- Thread starter
- #32
The main weight would be below in it the frame. This is extender not main battery and it is small.
thaeber
Well-known member
360 Wh at 36 Volt would mean 10S2P 20 x 21700 cells configuration. 1.4 kg batteries, plus Nickel, plus BMS, plus wiring and bag. Appr. 2kg. I wouldn’t like to have that on my toptube. But that’s only me
- Thread starter
- #34
Suppose it depends how often your wheels leave the ground and how high 
thaeber
Well-known member
500ml…
You see the emoji there?
It was obviously a joke...
Myalteregohamish
Active member
That's a really good point and since I own that exact one and having put over 1000 miles on it, I can attest that you don't notice it. That said it's a good bit lighter. However, since you are building a battery you can get it to match weight wise.
There are many holes in the frame where the wire can be removed. The manufacturer thought of us. The bag is secured at the bottom with a plate and bolts. I've never liked the hidden battery solution.Well, they are definately not invisible...
View attachment 132464
View attachment 132465
I am wondering where he got the wire into the frame... I recall him saying, he built the batteries himself.
The canyon has a removable battery and it's very good.
temon10
Well-known member
Just an idea....
540Wh inside plus 360Wh extender on Tantan E67 frame. Very slow project
540Wh inside plus 360Wh extender on Tantan E67 frame. Very slow project
How much does an empty frame weigh? Should this frame have a removable battery?Just an idea....
540Wh inside plus 360Wh extender on Tantan E67 frame. Very slow project
View attachment 132697 View attachment 132699
View attachment 132700 View attachment 132698
temon10
Well-known member
about 2,8kg. nope this frame is the same with LCE930 using non removable battery.
temon10
Well-known member
it's slow project, will update when finish.
So planning a range extender for my LCE930. Is there any reason this would not work?
Charging connectors could be different but need to be 4pin minimum and handle 20A. Easier would be to use the battery balancer, but then I would need a second port to connect the range extender.
- Thread starter
- #47
Looks good to me.
- Thread starter
- #49
You have to stop each battery from discharging into the other.
Isn’t possible ti have the extender discharging into the main battery directly ?
Myalteregohamish
Active member
The ideal diodes make sure the back flow of power doesn’t take place into from the lower capacity battery. Assuming they’re both at 100%. Then you just converge them with a Y connector. So the gauge on the display. Initially comes down from 100% to around 70ish percent which is when both batteries seem to start discharging and then discharge slows down all the way to the bottom.
- Thread starter
- #52
That is quite dangerous. If you rode say 20 miles on your main battery and then added a fresh external battery during the ride there is a good chance you could destroy your bike. The internal battery will be discharged because you used it up, and the voltage will be low. The external battery is fully charged so the voltage is high. Current flows from a higher voltage source to a lower voltage source. If the difference between the lower voltage and higher voltage is a lot, then the current will be high. This high current may be higher than the battery is designed for, the "C" rating. (the size of the internal wires etc) Then it is a good chance that the wires will overheat then damage the batteries. Hence flames and melted plastic.
That is why you need two ideal diodes to prevent the two current sources from flowing into each other.
There are other ways of doing this. The little switch boxes available turn off one battery or the other depending on which one is at a higher voltage. It lets the higher voltage battery be used until it is the same voltage as the lower. It will then monitor and it one drops faster than the other it will shut it off. It always lets the higher voltage battery be used until it equals the lower.
Last edited:
But it would be so nice to build with these cells, INR21700-M58T, around 530Wh(2 kg) main battery and 260Wh(<1kg) extender.
Since my 720Wh battery I run now is too much in most cases. I run out before the battery does.. And removing almost one kilogram from the front of the bike would definitely be noticeable.
Since my 720Wh battery I run now is too much in most cases. I run out before the battery does.. And removing almost one kilogram from the front of the bike would definitely be noticeable.
Thanks! That’s clear now
- Thread starter
- #56
The higher voltage battery will supply more current to the motor than the 40v battery. But they will both supply given that you have ideal diodes that stop the 50v from charging the 40v.
Myalteregohamish
Active member
Mike is there an increased risk to the motor with different voltage batteries?
- Thread starter
- #58
As long as the batteries stay in range. You, of course, would not want a 50v and a 39v battery. They both need to be designed for the same motor voltage.
I suppose there is the question running internal down to cutoff, then adding external. The computer only knows about one virtual battery, it sees the new fully charged external and continues to allow full power. The essentially empty internal is not "cutoff" or throttled down. Will it damage the internal once the external also begins to get exhausted but not enough to kick in the limiter. Without ideal diodes they would equalize and act as one battery. But with ideal diodes to prevent that.... I am not sure what happens.
With the switch controller it switches out the low voltage battery and lets the new battery take all the load. The trouble with the switches is that they are big and hard to fit in the frame and two they don't handle charging so you have to have separate lines to charge independently and the charge lines to the battery can't be connected to the output of the battery.
I suppose there is the question running internal down to cutoff, then adding external. The computer only knows about one virtual battery, it sees the new fully charged external and continues to allow full power. The essentially empty internal is not "cutoff" or throttled down. Will it damage the internal once the external also begins to get exhausted but not enough to kick in the limiter. Without ideal diodes they would equalize and act as one battery. But with ideal diodes to prevent that.... I am not sure what happens.
With the switch controller it switches out the low voltage battery and lets the new battery take all the load. The trouble with the switches is that they are big and hard to fit in the frame and two they don't handle charging so you have to have separate lines to charge independently and the charge lines to the battery can't be connected to the output of the battery.
Myalteregohamish
Active member
Great explanation of the pros and cons. Thank you sir.
I'm no electrical engineer, so feel free to correct me if I'm wrong. Wouldn't it be easier to just find an aliexpress water bottle battery that outputs under 50v peak, and just plug it straight into the stock DC barrel plug instead of attempting to power the motor directly with an auxiliary battery? Would efficiency losses be too high?
Similar threads
EMTB Forums
Latest articles
-
Introducing the Forestal e-Cygnus - a downcountry and XC emtb
The new Forestal e-Cygnus is a slightly unusual emtb. It comes in two... -
2025 M1 Sporttechnik EN 8.0 review
The M1 EN is one of four M1 models built on the same frame. Well, it’s...