So confused over battery discharge current. I still cannot wrap my head around battery discharge rate and current maximums. I'm building a go kart with a Manta II motor at 48V which the specifications state a maximum motor current of 330A for 2 minutes or 480A for 45 seconds. Now I don't ever expect to ever get near those numbers but what about if I'm pulling say 100, 150, or 200 amps - how do I know the battery or batteries can safely output that current (and for how long)?
What the motor draws rom the *controller* can be very different than what the controller draws from the *battery* (true both for brushed controllers like yours, and brushless ones) so...
The battery would need to be rated for the maximum current the *controller* is capable of drawing.
Some controllers have a peak battery current and a continuous battery current rating, and some also have motor (phase) current ratings. The battery doesn't see motor/phase current, only battery current.
The battery has to have *better* specs than those, because as it ages it will become less capable over time, so say a year down the line it might be say, 5-10% less able to supply the current than it was when new, causing more voltage sag in it, wasting that power as heat within the cells instead of getting it to your wheel.
How much better it needs to be than the controller requirements depends on the actual battery, and how long you intend to keep the system as-is, using that battery, etc. For instance, if you expect to keep it around using it at full power for 3-5 years, and you get a high-quality battery made of well-matched EV-grade cells, you might only need to add a few percent to it's requirements to keep it from degrading below your needs. If it's made of typical unmatched middle-grade or low-grade cells, you might need as much as 25%+ better, or more for low-quality stuff that ages worse.
The C rating doesn't make any sense at all to me. I believe I saw one statement that claimed the C rating multiplied by the amp hour rating gives you the maximum discharge current, but I've never seen or heard that repeated and not sure if that is valid information.
That's correct, if confusing, since the Ah doesn't actually have "anything" to do with the A rating, directly. The C rate is an artificial number used to cause those to correlate. It is often used for marketing, so that a battery can be claimed to be a higher C-rate than another, rather than comparing A ratings which might not seem as good in a particular hobby. I recommend not worrying about C-rates, but just actual A (current) ratings.
If they don't provide actual full specifications for a battery you're looking at, including which specific cell brand and model, and their ratings (which you can use the brand/model to verify thru the cell manufacturer's spec sheets), right in the sale ad, then you might want to first check other batteries before trying to finagle details out of them via communication attempts that should be in the ad. (it's not uncommon for them to just ask you what you want the battery to do and then tell that oh, sure it can do that! yes please buy now!, rather than being honest and directly answer questions with real specification sheets and testing data).
You also need to know the details of any BMS they provide, and I highly recommend a contactor-based BMS instead of a FET-based one, because you can then use the BMS to also control your contactor for emergency system shutoff to protect the cells, or simply let it use it's own contactor. For these high-current systems, the contactor is more likley to work better for longer than the FET types, with less wasted power (voltage drop) in the BMS, so more power gets to your wheels. JBD makes good contactor-based BMSes, including some that are 'smart" and can be programmed and monitored via a BT phone app, so if you don't like the BMS a pack comes with but otherwise the pack is great for your needs, you can ask for them to build it without a BMS and install your own yourself, or have them build it normally but then you swap out the BMS when you get it.
If I want to use this go kart for more than 5 seconds I'm going to need a very, very, very expensive battery or batteries and I would very much so not burn them up because the motor is pulling so many amps for a sustained period. Everything on the kart, Alltrax SR48500 controller, 48V 400A fuses, 400A rated solenoids, 48V 400A Rated SW202 reversing contactor, so I'm going on the high end to try and protect everything, but not sure how to protect the battery or batteries.
What is the absolute max the controller will draw from the battery, peak, and for how long?
What is the absolute max the controller will draw from the battery, continuous?
Those are what you need to know to get the right battery.
According to one ad for the controller you list, it says "12-48 Volts 500 Amps Peak 575 (Peak Amp Mode)", so unless it's programmable to turn down that current, you need everything in the system to handle *at least* 500A continuous and 575A peak, because that's what the controller will draw under every load sufficient to do that, like hard accelerations from a stop, etc. (usually karts are intended for hard usage and fun, so they usually are setup to pull as much current as possible with as little voltage sag as possible, so unless you use yours differently, it's likely to pull the controller's max limits quite often).
Now, your motor is not as capable as the controller, so if you don't program (if it's capable) the controller to output less current to it than it can handle, then any load the motor places on the system higher than it's capabilities will heat it up beyond it's design, so you'd need to cool it better than typical. High currents on brushed motors also wear the brushes faster, and the commutator, so you may have to replace those sooner if it's overloaded enough often enough.
How much the motor will draw from the controller depends on the physical load on the motor; at startup from a stop that's theoretically "infinite" (practically it's very very high, almost solely limited by the winding resistance, inductance, and average of the PWM'd voltage the controller places across them (based on throttle input signal), and any other resistances in the current path).
I never see any information on batteries stating how many amps can be safely consumed and for how long. Must be a another weird mathematical formulae they use for that as well. I've also read other threads on this site but they lose me as well. Any help would be much appreciated. And for expample - If I were to purchase 4 each 48V 200AH Lithium Iron Phosphate batteries at $5000, would they be able to handle this motor? And if yes how do you know?
You need to know the above information about the controller's requirements, what it will draw from the battery.
Then you need to know what the batteries themselves are actually capable of.
