help with diy electric moped

[Slice64]

Hey, some friends and I have tried to build an electric moped. We succeeded today and drove 50km on one charge to test the reach.

But we had a problem that after the first 20km the controller seems to be going off at some times and we have to manually restart it. We thought it's due to the controller being 48V and up and the battery delivering 48V normally but slowly falling below that. Thus restarting gives it a second to "volt up".

So is there a solution to that? Maybe some sort of always 48V stepper that would step down a fully charged 50 and step up a depleted 42.

This is the only major concern we have, others are a speed meter, charge meter and lights, but for those we have some ideas.

Thanks for helping!

 

[amberwolf]

When you say it's "going off", do you mean the entire system loses all power? Or just that the motor stops working but all displays / battery-meter lights still work? (each is a different cause)

What exactly is your battery? (link to page it was purchased from often helps)

What exactly is your controller? (link to page it was purchased from often helps)

We need to know this to help you find a good fix.


If the controller is expecting a 48v battery, that's 13s Li-Ion, and it will have an LVC around 42v, and shut off each time the voltage goes below that.

A 13s Li-Ion battery is full around 54v, and empty around 42v. (the battery itself may have a BMS that shuts off at an even lower voltage, around 38-39v, but that is a safety-shutoff, not an everyday LVC; the 42v LVC of the controller is to keep the BMS from having to do this and not run the battery as hard)

Hey, some friends and I have tried to build an electric moped. We succeeded today and drove 50km on one charge to test the reach.

But we had a problem that after the first 20km the controller seems to be going off at some times and we have to manually restart it. We thought it's due to the controller being 48V and up and the battery delivering 48V normally but slowly falling below that. Thus restarting gives it a second to "volt up".

So is there a solution to that? Maybe some sort of always 48V stepper that would step down a fully charged 50 and step up a depleted 42.

This is the only major concern we have, others are a speed meter, charge meter and lights, but for those we have some ideas.

Thanks for helping!

 

[Slice64]

When you say it's "going off", do you mean the entire system loses all power? Or just that the motor stops working but all displays / battery-meter lights still work? (each is a different cause)

The motor stops working, lights still on.

What exactly is your battery?

Should be this one https://www.akkushop-24.de/Lithium-Ionen-Akku-48V-30Ah-1440Wh-Akkupack-incl-60A-BMS-Ladegeraet-wasserfest-fuer-Scooter-E-Bike-Pedelec_1 sorry that the website ain't available in English.

What exactly is your controller?

https://www.ebay.de/itm/313870133119?var=612598202845 this nice ebay pal, had a different one before that came with the motor, but it died.

A 13s Li-Ion battery is full around 54v, and empty around 42v. (the battery itself may have a BMS that shuts off at an even lower voltage, around 38-39v, but that is a safety-shutoff, not an everyday LVC; the 42v LVC of the controller is to keep the BMS from having to do this and not run the battery as hard)

That makes sense, but it is already doing it around 45V and just for the engine...

 

[amberwolf]

The motor stops working, lights still on.

THen that means the battery's BMS is not turning off, it's just the controller stopping, probably due to LVC, specifically voltage sag under load.

What exactly is your battery?

Should be this one https://www.akkushop-24.de/Lithium-Ionen-Akku-48V-30Ah-1440Wh-Akkupack-incl-60A-BMS-Ladegeraet-wasserfest-fuer-Scooter-E-Bike-Pedelec_1 sorry that the website ain't available in English.

That's ok, google translate works on text ok. I quoted their specs below. Looks like if it is what it says it is, it should be good enough to run the controller.

Lithium-ion battery pack 48V 30 Ah 1440Wh waterproof for scooter / e-bike
- Voltage: 48V
- Capacity: 30Ah
- Energy: 1440Wh
- LiCoxNiyMnzO2 / battery
- 18650 lithium ion single cells
- Weight: 8.1 kg
- BMS battery management system
- Temperature and overcharge protection
- Dimensions: 295 x 140 x 135 mm
- max. continuous discharge current: 60A
- max. peak discharge current: 180A (1-3 sec.)
- cut-off voltage: 35.75V
- charging voltage: 54.6V
- Battery 48V 30Ah waterproof
- Connection cable incl. 70A fuse
- Charger 54.6V 3A XLR/3Pin
The batteries must not be operated in series or in parallel.
BMS continuous current: 60A

What exactly is your controller?

https://www.ebay.de/itm/313870133119?var=612598202845 this nice ebay pal, had a different one before that came with the motor, but it died.

What little specs they provide are below

THey don't specify what the LVC is for each voltage, but it does say it autodetects teh battery voltage and sets the LVC appropriately. So if it is not detecting that correctly, it may set the LVC too high. Additionally it says it's setup for lead-acid, not lithium, which means it's LVC may be wrong for your battery (probably not, but it doesn't say what it is).

For 45v, it means they could be using an LVC of 11.25v per lead-acid battery (there'd be four of those in series for a 48v system; 5 for a 60v, which would then have an LVC of 56v or so). That would be higher than most, which are usually around 10.5v per SLA (so about 42v, just like a lithium battery).

It's more likely that it's still using a 41-42v LVC, but that your battery is sagging in voltage to taht point under load, when it's no-load voltage drops to 45v (so when you see the meter it is at 45v)

Specifications:
*Power: 1500W
*Optional Voltage: 48V/60V
*Undervoltage: automatic identification
*Brake: high / low level
*Phase: automatic identification
*Current limit: 40A
*Size: 9*4*2in (Approx.)

If you have a wattmeter, most of them store the Vmin, or lowest voltage seen during operation. This would tell you how much voltage sag you're getting, and whether it is low enough to trigger the controller's LVC.

 

[Slice64]

First off, thanks for the help.

If you have a wattmeter, most of them store the Vmin, or lowest voltage seen during operation. This would tell you how much voltage sag you're getting, and whether it is low enough to trigger the controller's LVC.

I'll try that, too see how much it is and maybe ask the seller/manufacturer.

And is there maybe a way to fool or disable the lvc, since the battery got its own management system? I'll also ask that the seller manufacturer, otherwise crack it open and take a look lol.

 

[amberwolf]

And is there maybe a way to fool or disable the lvc, since the battery got its own management system? I'll also ask that the seller manufacturer, otherwise crack it open and take a look lol.

There often is, but depending on the BMS's safety shutoff for your everyday LVC is pretty hard on the battery. It won't last as long as if the controller's LVC was allowed to protect it instead. If you decide to do this anyway, there's a thread I replied to today (so you can see it in the list of posts in my profile) where someone shows pictures of doing this in their particular controller.

Plus, if it is dropping that much under load at the 45v, it may indicate a problem with the battery that will only be made worse by doing this.

I'd first recommend the wattmeter test. Plenty of cheap ones, like this
https://www.amazon.com/HTRC-150A-200A/dp/B07H1B4PN1
or this
https://www.amazon.com/Meter%EF%BC%8C1Pc-Digital-Wattmeter-Checker-Balance-Voltage/dp/B07KPGYSKX
or these
https://www.ebay.com/b/rc-watt-meter/bn_7024879202
(except the ones that are obviously not the correct item for sale like the antennas listed as wattmeters :lol: )
etc. They're useful for diagnostic tests like this, among other things.

 

[Slice64]

there's a thread I replied to today

you replied to quite a lot of post, could you maybe send me a link? I can't find it

 

[amberwolf]

https://endless-sphere.com/forums/viewtopic.php?f=49&t=116155#p1715440

 

[Slice64]

https://www.youtube.com/watch?v=a2Yuq9MPqWo

I tried it with the Watt meter in between and those are the results. It is filmed in slow motion and I didn't let off the throttle. On the last try I even tried a really, really slow acceleration, and it also stopped working after a second.

So, what should I do? Fool the controller, to maybe accept down to 38V or so

 

[eee291]

A 48V Battery is empty at 42V, going any lower isn't going to give you any more range.
Your charger should be charging that battery up to 54.6V. If it is, then there is nothing wrong with the battery.
you may need a bigger battery if you are not getting enough power or range out of it. Its not a controller issue.

 

[Slice64]

A 48V Battery is empty at 42V, going any lower isn't going to give you any more range.
Your charger should be charging that battery up to 54.6V. If it is, then there is nothing wrong with the battery.
you may need a bigger battery if you are not getting enough power or range out of it. Its not a controller issue.

Yeah, I know that everything works fine, but I don't like the range I'm getting. With a controller I had before, which died, I could go further. Also the Battery charge monitor says it still could go a bit and the Voltage itself is still at 43.5 at standstill. Thus I think the old controller didn't shut off the battery and rather restricted it from pulling less than 42V.

 

[eee291]

I don't think you fully get it though. Look at a battery discharge curve to see what I mean.
when you discharge a battery at 50A, a fully charged battery at 54V might drop to 50 or 48V due to internal resistance, that is called voltage drop/sag.
if you let off the gas a few seconds afterwards it will climb back to 54 or 53.9V.
a bad battery or one that cant handle that sort of current will have a higher voltage drop.

The same happens when its empty, under load its at 40V and when the Controller disconnects it goes up to 43V.
at this point the Battery is EMPTY.
There is no more range to be gained, maybe a few more seconds if you somehow manage to bypass the controller BMS limit.

I bet the old controller was a weaker one, that didin't pull as much current as the one you have now.

 

[Slice64]

I don't think you fully get it though. Look at a battery discharge curve to see what I mean.

Thanks for the explanation, after seeing that I realized I really didnt understand it fully!

at this point the Battery is EMPTY.

But it just started doing that way early, the shutting off part. Maybe I'll conduct another test to see at which Voltage it is gone.

There is no more range to be gained

There was actually quite a lot to still be gained. It took 20km till the first power cut and then we drove another 30.

bypass the controller BMS limit.

Since the battery has its own BMS, I might just do that.

But first more testing and thanks a lot!