What would happen in this scenario?

Hi guys,
What would happen if I had a controller rated at 60V 50A, but the continuous battery amps for the cells in my battery pack are rated at around 30A with NO BMS, just pouch cells assembled together, in this case 18s pack. At the moment, I am self monitoring the battery pack. The motor is also a MXUS 3000 turbo. Its for a spare bike. I need the high voltage to properly power the MXUS, so Im overvolting the controller a bit, but the caps are 100V so I think 72V pack will be ok, however the cells have a low continuous amp rating so I matched it up with the smallest controller I had which is 60V 50A. During testing, everything ran properly but havent ridden it yet as I need to do a few more things. I just tested everything with no load.

The 60V rating must be there for a reason, other components not 100V rated?

If you end up pulling 50A you'll stress those too-weak cells, if you can't program the controller to limit current, consider using a CAv3 to do so, to protect the pack longevity.

john61ct said:

The 60V rating must be there for a reason, other components not 100V rated?

If you end up pulling 50A you'll stress those too-weak cells, if you can't program the controller to limit current, consider using a CAv3 to do so, to protect the pack longevity.

Click to expand...

Hi..I didnt check the other componants but I will, but Ive overvolted controllers before, Im thinking 14V over rated might be ok. The main caps are 100V but like you said, Ill have to check the other parts. Assuming that side of things is ok, what would happen if you slightly over stress too weak cells without a bms or cycle analyst?

Isn't 60v pretty close to 18s? I would not worry a lot about the controller.

The cells will tell you when you hit them with too much amps. If sag is only 4v, then the system is still only drawing amps the cells can handle. If it sags 10v, you are killing them. What I mean is that you only draw that max amps briefly on flat ground, then motor rpm increases. So test in the real world, and see if you need to take action, such as amp limiting by snipping a shunt.

A CA is ideal, but lacking that you should at the very least have a voltmeter so you can watch your sag under load as you ride. Or a cheaper watt meter, so you can at least know what the amps you pull are.

dogman dan said:

Isn't 60v pretty close to 18s? I would not worry a lot about the controller.

The cells will tell you when you hit them with too much amps. If sag is only 4v, then the system is still only drawing amps the cells can handle. If it sags 10v, you are killing them. What I mean is that you only draw that max amps briefly on flat ground, then motor rpm increases. So test in the real world, and see if you need to take action, such as amp limiting by snipping a shunt.

A CA is ideal, but lacking that you should at the very least have a voltmeter so you can watch your sag under load as you ride. Or a cheaper watt meter, so you can at least know what the amps you pull are.

Click to expand...

thanks for the info!
I seen 2 small shunts side by side inside the controller.
Is it possible to cut one of these off by cutting both legs? i always wondered but didnt need to limit amps until now
Also regarding the battery itself, so your saying the worst thing that might happen is high sag/battery life? so nothing dangerous would really happen? ie: pouch cell puffing etc.?
thx

If you cut one of the shunt resistors, you will half the controller current (assuming they are both the same)
Only cutting one end of them is enough. No need to completely remove them.

You need to check the controller mosfets maximum breakdown voltage (VDS max.)
If your voltage is 2 high, they can go bad.
They usually provide some marge like 100V mosfets for a 60V controller.
This is needed as you can have voltage spikes that are higher than your battery voltage.
Another thing to check is the voltage regulator for the controller microcontroller.
It's often an LM317 and it has a big power resistor to dissipate some power.
You might need to increase that resistor it's value if you feed a higher battery voltage.
Some displays have a buildin voltage regulator as well and don't like a higher voltage either.

Junk lipos cells puff easy on hard hot discharges. Depends on the quality and how hard you hit them. Ive puffed lipos believe me.... that and the hitting LVC constantly make you bonkers.

ebike11 said:

what would happen if you slightly over stress too weak cells without a bms or cycle analyst?

Click to expand...

50A for a pack (perhaps optimistically?) rated for 30A is not what I would call "slightly".

Best case you reduce lifespan by **a lot**.

Maybe it only sags a bit but performance is "good enough"

IMO more likely you wreck the pack within 20 cycles **and** you are unhappy with acceleration, hill climbing etc performance.

A CAv3 is usable for many many years with any controller, great investment compared to the cost of multiple replacement battery packs, and plenty of other benefits.

Unless your controllers are so sophisticated that CA functionality becomes redundant. Apparently Nucular are an example.

what does a 3 speed switch for a throttle do? like this one. I don't know

https://ca.dhgate.com/product/24v-36v-48v-60v-ebike-twist-grip-throttle/427845819.html?utm_source=adcenter&utm_medium=cpc&utm_term=427845819&utm_content=024057009001&utm_campaign=topbikekit&f=bm|Bing|PA|384604843|1202866270989820||pla-4578778771279907||CA||c||

60v/30amp with a v3 sounds disappointing, 1800 watts
can you just use a cheap 30 amp blade fuse to protect the battery while testing

if you snip 1 shunt and then butter the other shunt with a little solder, would that work?

Just snip one shunt, or leave it intact and unsolder one end. Then you have a wimpy 25 amps controller to go with your wimpy 30 amps battery. If they say 30 amps, it will be happiest with 15 amps continuous anyway. Likely that's about 25 mph tops.

Not exactly real fun, but just saying, if you want that battery to last, don't give it 30 amps continuous.

dogman dan said:

Just snip one shunt, or leave it intact and unsolder one end. Then you have a wimpy 25 amps controller to go with your wimpy 30 amps battery. If they say 30 amps, it will be happiest with 15 amps continuous anyway. Likely that's about 25 mph tops.

Not exactly real fun, but just saying, if you want that battery to last, don't give it 30 amps continuous.

Click to expand...

Yeah will do...this bike isn't for me..spare for someone so it doesn't need to be fancy