help needed ,1 or 2 controllers

[martinev]

Hi.
We are looking at adding a battery 72v 20ah to our scooter. But not connected in parallel .
We have fitted a 72v 45ah battery
We have fitted a controller is a Kelly kls7230n.
My question to you knowledgeable guys.
If we used the smaller battery as a reserve power. Would that controller be ok drawing from the smaller battery to our hub?when the larger ones has gone flat.. ( 20ah just as a reserve battery)
I am a bit concerned the controller would try to pull to much. Sorry we are running a qs motor 3000w v2. Thanks

 

[E-HP]

If we used the smaller battery as a reserve power. Would that controller be ok drawing from the smaller battery to our hub?when the larger ones has gone flat.. ( 20ah just as a reserve battery)
I am a bit concerned the controller would try to pull to much. Sorry we are running a qs motor 3000w v2. Thanks

Shouldn't be a problem unless you pull more current than the smaller battery pack is capable of. :thumb:

 

[martinev]

hi E-HP
yes thats just what i was thinking if it tries to pull max amps
etc via the controller ( which will be configured to get the best range at about 45mph , i think it would damage the 20ah battery, is there a way i can do it, what about if i gave the 20ah battery it its own controller and linked it to the hub on the same wires as the 45ah battery controller and fitted some diodes ?, i really don't know what's best or what my options are , i really want this smaller battery to be the reserve only battery ( get you home etc ),
thanks for your reply
the build is getting there,

 

[martinev]

Hi.
on our first build
We are looking at adding a battery 72v 20ah to our scooter. But not connected in parallel .
We have fitted a 72v 45ah battery
We have fitted a controller is a Kelly kls7230n.
My question to you knowledgeable guys.
If we used the smaller battery as a reserve power. Would that controller be ok drawing from the smaller battery to our hub?when the larger ones has gone flat.. ( 20ah just as a reserve battery)
I am a bit concerned the controller would try to pull to much.
we are running a qs motor 3000w v2. Thanks

its getting there ,,

 

[lnanek]

I've found that if I use the popular Y splitter for dual batteries that has an ideal diode to prevent one battery feeding the other, I can turn either my 22Ah 30A continuous discharge battery on, or my 12Ah 20A continuous discharge battery on, or turn on both. All off them will run the bike fine if my controller is set to 20A battery limit. If using 30A limit, I have to turn off the weaker battery to prevent BMS shut down:
https://a.aliexpress.com/_mLyxia0

It's easy to switch between limits on my setup, though, since the Cycle Analyst display I use has savable presets for two different batteries, and similarly I keep a phone mounted on the handlebars running the Phaserunner suite app and connected to the controller via a USB on the go cable.

Might work for you as long as your batteries have individual on off switches like mine and you have a way to adjust current limit settings.

I've heard the other freaky way to do this is to just plug the weaker battery into the charging port of the stronger battery, then the stronger battery is wired to the controller as normal. Should contribute some capacity to the stronger battery without tripping the BMS on the weaker battery due to too high continuous discharge. Haven't tried it, though. Might destroy something.

 

[martinev]

hello inanek
thanks for your input

i want to run a set up like this,
ride on the 45ah battery through via the kelly the controller and ride ,
then when that battery has almost gone flat ,
i want to be able then to manually unplug the 45ah battery supply to the controller via the main leads
and plug straight in the 20ah battery straight in and use that to get home etc,
but what will the controller do or ask from the smaller battery, ( will it kill the battery or will the motor suffer power and speed compared tot he 45ah battery,
or should i run the 2 batteries on separate controllers as independent system
but both linked to the hub cables ?

i hope i made that clear,
i dont want 2 batteries permanently linked ,so one goes flat and the other kicks in,
seems to be lots of problems with charging both together etc,

 

[E-HP]

I've found that if I use the popular Y splitter for dual batteries that has an ideal diode to prevent one battery feeding the other, I can turn either my 22Ah 30A continuous charge battery on, or my 12Ah 20A continuous charge battery on, or turn on both. All off them will run the bike fine if my controller is set to 20A battery limit. If using 30A limit, I have to turn off the weaker battery to prevent BMS shut down:
https://a.aliexpress.com/_mLyxia0

It's easy to switch between limits on my setup, though, since the Cycle Analyst display I use has savable presets for two different batteries, and similarly I keep a phone mounted on the handlebars running the Phaserunner suite app and connected to the controller via a USB on the go cable.

Might work for you as long as your batteries have individual on off switches like mine and you have a way to adjust current limit settings.

I've heard the other freaky way to do this is to just plug the weaker battery into the charging port of the stronger battery, then the stronger battery is wired to the controller as normal. Should contribute some capacity to the stronger battery without tripping the BMS on the weaker battery due to too high continuous discharge. Haven't tried it, though. Might destroy something.

You control how much your controller pulls from the battery, with your throttle hand (unless you have a self-riding bike, like Tesla does for cars). So basically, you want to put something in place to protect your battery from you? Usually I'd say go easy on the throttle, but maybe a post it note stuck to the display that says "go easy on the throttle" as a reminder and secondary layer of protection.

 

[mehmetoz1980]

hi
72v 20ah battery seems sufficient for 3000 watt motor.

so it can be used

 

[lnanek]

I see things like current percent, battery limit, and max speed in the controller settings:
https://kellycontroller.com/wp-content/uploads/kls-nm/KellyKLS-M-N-UserManualV2.5.pdf

They also mention a Bluetooth app. I think if the weaker battery cuts out when you use it due to too much current draw, you could just use the settings and lower those.

 

[amberwolf]

The "reserve" battery, if not paralleled with the other one, will have to be able to supply the same kind of power / current that the other one does, by itself. If it can't, several possible problems can happen.

If the BMS isn't capable of the current, it can simply fail. Some failures are silent, just FETs failing shorted and leaving the BMS unable to protect the cells from overcharge or overdischarge, and you wont' even know this has happened or that the cells are being damaged, until more severe symptoms (up to and including a fire) occur. Sometimes the FETs actually blow up, and all power output ceases. Sometimes they get so hot so fast the solder melts, and that can short things out or the FETs can move on the PCB or even fall off.

If the BMS can handle the current but the cells can't, then when it's near full charge it may "work" but under high power demands the voltage may sag enough to notice it doesn't respond like it should. Less than full, the sag may begin to actually cause the controller or the BMS to shutdown to try to protect the pack against overload. The cells will heat up more than they should in either case, and be stressed, and won't have as long a lifespan as normal.



If the outputs of the two packs are always paralleled during a ride, then they will work together to supply power, and performance of the system may even improve (because there will be less voltage sag). They will drain together, and the ride will simply last proportionally longer with the both packs than with just the first one.

To connect them the first time, they have to be at the same voltage. Easiest is to first fully charge both of them, then verify theyr'e the same voltage before connection.

There are a few things to take care of when paralleling packs, it depends on the BMS in each one. If the BMS both have common charge/discharge ports, then it's simple--just connect the two in parallel, and leave them that way all the time, for both charging and discharging.


If either BMS has a separate charge / discharge port, then you should disconnect it from the other pack when doing the "opposite thing". meaning, if you are charging it, disconnect it's discharge port. If discharging it, disconnect it's charge port. That keeps the other battery from backfeeding it in a potentially problematic way.


Alternately, using the battery Y-connectors to prevent any backfeeding would also work, but you will need them on charge and discharge ports if they are separate on your BMSs. .

 

[E-HP]

The "reserve" battery, if not paralleled with the other one, will have to be able to supply the same kind of power / current that the other one does, by itself. If it can't, several possible problems can happen.

Not really. The main battery should be sized to provide power needed for the system running at the maximum output level the system is designed for. That doesn't mean the battery will always be supplying that much, but it can. The OP wants to get home without pushing the bike, and will use common sense, and get home fine.

I've had to use my reserve on my motorcycles several times. On those occasions, I looked at how far I had to go to get to the next gas station, and would tailor my riding accordingly. Nobody wants to walk in the desert when they could ride. So my impulse wasn't to go wide open throttle and hope I make it, I'd go 55 in the slow lane and hope to make it.

For an electric motor, the technique is as simple as applying the throttle slowly and gradually. I can ride my bike easily on throttle only with 300W and never exceeding that. I can't believe anyone, even with the crappiest throttle in the world, couldn't do the same.

EDIT: I have a reserve on my ebike, or did. My franken battery is 32Ah 14S plus 24Ah 6S lipo. When I'm at 3.7V/cell, I can bypass the lipos and run 14S (or could, but need to figure out how to lower the LVC on the new controller). I could run the lithium ion pack down lower to get me home; at least that was the plan, since I've never ridden more than 50 miles at a time, so only a contingency. I wouldn't be pulling 90A on the way home, because I don't like walking/pushing. A guy I used to work with used to tell me "you gotta use your coconut", LOL.

 

[amberwolf]

The "reserve" battery, if not paralleled with the other one, will have to be able to supply the same kind of power / current that the other one does, by itself. If it can't, several possible problems can happen.

Not really. The main battery should be sized to provide power needed for the system running at the maximum output level the system is designed for. That doesn't mean the battery will always be supplying that much, but it can. The OP wants to get home without pushing the bike, and will use common sense, and get home fine.

After having read this forum for so many years, and seeing so many people that apparently don't like coconut I was trying to not assume that a rider will use common sense and limit their usage in this type of scenario, even if they say they will...both because some riders won't, and also because there are situations in which it doesn't matter if they try to limit their usage. If a rider has to go up a hill, for instance, current may be high even if throttle is low, depending on the type of controller and how it's setup, as well as how the motor-to-ground system works.

But yes, if caution is used, and especially if there is a battery current monitor on there that the rider can see and keep to the limits of the reserve pack....it can be just fine.


However, I expect that the many riders that don't really know the details of how stuff works use the reserve battery like they would a reserve gas tank, which unlike a (smaller less capable) battery lets the system itself work exactly the same as with the regular tank.

So, because this thread will probably be read by others in similar situations, each with varied knowledge, I provided the details that will help a rider try to prevent the problem, without trying to go into the extreme technical detail of why exactly it might be a problem, and without trying to do my usual analyze-their-needs-and-system-to-death. :lol:

 

[martinev]

ok thanks for all the posts,
the problem is people don't always look at he reasons for things happening or prevention,
ie running out of power,
so i want this second battery fitted so the rider can swap over plugs and get his arse back home,
after he's learnt the scooter wont ride indefinitely there is a reaction after riding for 1000mls, :lol:

but it think my smaller battery being plug into the controller will be at risk, ,
do i really need to put a second controller in the system for the smaller battery ?
main battery 72v 45ah
reserve battery 72v 20ah
one controller fitted KLS7230N 270A
QS MOTOR HUB V2
thanks


,

 

[E-HP]

ok thanks for all the posts,
the problem is people don't always look at he reasons for things happening or prevention,
ie running out of power,
so i want this second battery fitted so the rider can swap over plugs and get his arse back home,
after he's learnt the scooter wont ride indefinitely there is a reaction after riding for 1000mls, :lol:

but it think my smaller battery being plug into the controller will be at risk, ,
do i really need to put a second controller in the system for the smaller battery ?
main battery 72v 45ah
reserve battery 72v 20ah
one controller fitted KLS7230N 270A
QS MOTOR HUB V2
thanks


,

You've only state the voltage and capacity of your batteries, but nothing about the cells and configuration. You could easily have a 20Ah battery that outperforms and 45Ah battery if the latter is made up of generic or recycled cells, and the 20Ah is composed of Samsung 25R or some other high output current cell, or lipos. That's the reason people can only offer you generic advice, building in some assumptions that may or may not be correct. More info, better advice.

 

[martinev]

Hi E-HP
Yes your right sorry.
Battery details.
I hope this is enough
Just want to be able to move plug from one battery to another so the other battery would be totally isolated from Any unit. I would
link the battery power plug connection at the controller terminals Maybe I'll need to put a additional controller in line to the hub.. Thanks

 

[E-HP]

Hi E-HP
Yes your right sorry.
Battery details.
I hope this is enough
Just want to be able to move plug from one battery to another so the other battery would be totally isolated from Any unit. I would
link the battery power plug connection at the controller terminals Maybe I'll need to put a additional controller in line to the hub.. Thanks

Not quite. need more info or a link for the 20Ah battery. The specs can't be met by any 18650 cells. Possibly 21700 cells, but only specific brands/models. Seems suspect.

 

[martinev]

 

[martinev]

 

[E-HP]

IMG_20221013_163852.jpg

If the specs are accurate, then the battery should have sufficient discharge capacity. However, it's hard to find a 21700 cell that has the combination of capacity (Ah) and discharge rating (A) that line up with the ratings in the spec. For 4P, the cells need to provide 5000mAh, say a Samsung 50E, which is a high capacity cell. But the discharge rating based on the specs is fairly high for that type of cell (spec implies 11.25A continuous, 22.5A peak), since the 50E example will do 2C and 3C respectively (10A and 15A). So, I only halfway trust the specs. Others may have more familiarity on what types of 21700 cells are available, since I've only been researching for building a future pack.

 

[martinev]

thanks E-HP i only understood some of your figures , sorry i am still learning , i have been a volvo , scania own business etc
mechanical / electrical engineer for 35 years now happy in my home workshop with mig , tig , lathe ,milling machine, plasma cutter sheet bender , blah blah always learning every day,,
, so are you saying if the specs are correct the one controller would cope with both batteries,
( connected battery one at a time not permanently)
to be honest i am considering many options,
if i fitted 2 controllers i could have 45ah battery connected to one controller and the other battery 20ah connected to the other controller,
but the battery cable plug could be a 3 wire connector and make and break plugs on the 3 phase wires , would that work, theres no danger of backfeeding up the 3 phase wires,, what do you think, ?
thanks

 

[lnanek]

so are you saying if the specs are correct the one controller would cope with both batteries,

I think that's only true in two situations:
1) you change the controller settings when you change the batteries
2) you set the current limit on the controller to the weakest of the two batteries

In case 2 you'd lose performance, however. E.g. if you had one battery with a 20A continuous discharge rating and another battery with a 30A continuous discharge rating, your controller would treat them both the same, even though the later battery is capable of more power.

 

[martinev]

hi inanek
yes you can see my issue
i really don't want to compromise speed or range, or the reassurance of having a reserve on board power supply,
so i really could run 2 controller's i think is doable, the batteries seem to be not to far apart if the specs are correct,
on continuous one is 90amp the other i think is 60amp
has anyone do it do you know ? i know many people have linked in parallel, but this is not what i want to try and do,
thank you for your help and interest ,it is really appreciated ,

a pic of our own swing arm,

 

[E-HP]

hi inanek
yes you can see my issue
i really don't want to compromise speed or range, or the reassurance of having a reserve on board power supply,
so i really could run 2 controller's i think is doable, the batteries seem to be not to far apart if the specs are correct,
on continuous one is 90amp the other i think is 60amp
has anyone do it do you know ? i know many people have linked in parallel, but this is not what i want to try and do,
thank you for your help and interest ,it is really appreciated ,
IMG_20221006_070304.jpg
a pic of our own swing arm,

So your statement "we are running a qs motor 3000w v2" seems to imply you have your controller already limited to ~40A. So what's the issue? What is the controller limit set to?

 

[martinev]

Hi yes statement is correct. no I did not imply we are running a controller I said we have a controller. It came in the items we bought from Harry. QS Motor sales. But that was all based on installing a 75ah 80ah battery. But now we are building with the 2 batteries as stated above. Our initial build was just going to get the largest battery we could fit in the frame space. But we have now decided to go for a reasonably sized main battery. And a small battery as a back up/ Reserve battery.. So as stated the controller we originally purchased is the Kelly. See pic I hope that clears that up. It's a new build on a 1960 scooter..thanks for post

 

[lnanek]

I think he's pointing out that 3000W at 72V is 42A, basically. So if you are really only running the motor at 3000W, the whole thing is a non-issue, because either of your batteries can handle that. 42A < 60A. 42A < 90A. If controller is set to draw 42A max, it's fine as it is with either battery.