Battery continuous discharge amp and controller amp need to match?

[PitBull]

Noob question; Whenever someone discusses a controller's amp rating, if not specified (i'm guessing over 90% of the time it's not) does that refer to the peak or continuous rating? I'm thinking it is referring to the peak rating as rule of thumb, but just want to be sure. Thank you

 

[Chalo]

Most controllers (all the ones I've ever used) are self-restricting, and there's no good reason not to impose such restriction at a level the controller can tolerate continuously. Some small controllers without their own heat sinking (e.g. Phaserunner) feature thermally actuated power limiting to prevent destructive overheating.

But if you're using a generic no-name 35A controller, yes it will do 35A until the battery runs out, unless you stuff it in a bag or otherwise restrict its ability to reject heat.

 

[fatty]

Nice thing about a pedicab is, you can just add a "virtual extra passenger" worth of weight in the form of a multi-kW bank.

Since you are looking for several hours' run-time per day you need that anyway right?

So your burst peak draws are still relatively low C-rate compared to the pack as a whole

no need to pay the extra for high **power** cells

and lots of room under the seats and even the floor

means high **energy** density is not even "that critical"

I'd focus on cycle lifespan, good longevity drastically reducing your wear-cost per month per year.

Consider LFP or maybe even LTO, even in a propulsion use case, properly cared for may get a decade or more!

Agreed, lowering TCO via infrequent pack replacement should be prioritized.
But I would get there via cheap commodity Li-ion: use the extra capacity over LFP to avoid routine deep discharge, while also having that extra capacity as a cushion if needed.

As always, get the highest voltage and greatest capacity pack you can afford & fit.
If you want to stick with BRT: 72V 48Ah

 

[pongyboy1]

100A BMS okay with a 4000w motor?


Sent from my iPhone using Tapatalk

 

[e-beach]

It's not that simple. Is your battery rated for 100A continuous discharge? Is your controller rated for 100A continuous discharge?

 

[pongyboy1]

Planning to buy 72V batteries for my 4000W motor from a distributor. The 72V 100A BMS battery description on the website says it’s suitable for motors of between 1000W-6000W. Is that normal for a 100A BMS to be compatible with 1000W-6000W motors?

Also I have a 40A controller and my motor is 45A. My understanding is that the controller is the main component that must be lower than the BMS as well as the motors amp rating.

 

[Chalo]

Planning to buy 72V batteries for my 4000W motor from a distributor. The 72V 100A BMS battery description on the website says it’s suitable for motors of between 1000W-6000W. Is that normal for a 100A BMS to be compatible with 1000W-6000W motors?

72V X 100A = 7200W
After efficiency losses, that corresponds pretty well to 6000W output from a motor. So it's fair to say that battery is usable for motors from zero to 6kW. It's always best not to completely max out the power rating of a battery, though.

Your controller is the only part of the system that will consistently and automatically limit max power to a certain value. Therefore it's best if all the other parts of the system are capable of handling more power than that, so everything operates within its rating.

Note that a BLDC controller typically sends up to double the current to the motor as it draws from the battery. So if your motor's maximum phase current rating is only 45A, a 40A controller may be pushing it way past its rating. If on the other hand your motor was originally intended to be paired with a 45A controller, then your 40A controller is probably fine.