discharge and charge simultaneously?

[al.short]

Would it be possible to "float" a LiMn pack; i.e.- discharging at .6C while charging at >35C, the object being to extend e-bike range via a ICE driven
charger in a trailer? The folks at batteryspace inform me that the bms would not support charging/discharging together, but by his wording I was not
certain he understood my intention. Thoughts?

 

[grindz145]

It's certainly possible. However, the BMS he's talking about probably has separate charge and discharge FETs which are designed to be on while the other is off. It is just a matter of battery management design.

 

[BatteryMooch]

You can't charge and discharge at the same time, no matter what the circuit topology is. Either the voltage outside the pack/BMS is higher for any reason (pack charges) or the voltage is lower (pack discharges). You can use any BMS with a charger that can either supply current to a load and/or current to the pack.

If you have a charger available during an e-bike ride, it will supply current to the motor(s). Depending on pack/charger voltage levels and circuit resistances, the pack might supply current too. The BMS will either accept current from the charger if the pack voltage is low enough or the BMS will deliver current to the load along with the charger.

IMHO, it's the same setup as in any car/motorbike with an ICE, alternator and, and Pb-Acid battery. Or, at least, at 1:50am it sure seems like it.

 

[grindz145]

But you can technically allow the charge and discharge to remain active at the same time. This is much different than allowing current to pass straight to the load. The end result is more effective use of a high impedance source when integrated over time.

It's a very good point though, that you have either a net positive or negative net current at any given point in time.

 

[BatteryMooch]

I think I'm confused as to what you're describing when you say you can allow charge and discharge to remain active at the same time.

Are you saying that the charger could power the load and charge the battery at the same time...
or...
the charger and the battery could power the load, i.e., discharge the battery?

 

[dogman dan]

As long as the charger will cut down the amps when the battery gets too high voltage, why couldn't you run a charger constantly while also discharging the battery? If the charger is going to put out x amps at all times, then you would need some kind of bms to stop the charge when it gets too full.

 

[todayican2]

Ive been thinking along these same lines for my build. Cant the "buzzer signal' used to alert of approaching LVC coming from the bms be used to engage the starter (be it human pulling a rope, or electric starter) and "approaching HVC buzzer signal be used to kill the gen?

 

[al.short]

for camlight (john)-
Both statements would, I believe, be correct depending on motor current draw. At lighter loadings the charger might be powering the bike and charging the
batteries; at larger draws both the charger and batteries would supply the motor. The setup is a bionx 500 cuurently powered by the OEM 10A/h and 2-16 A/h
LiMn's. I would like to add about 2 more 16A/h batteries to a trailer and charge the 4x16A/h setup via a 800w generac 4-stroke. I think the idea would work
out but I want to run this by some folks with more experience than myself before I possibly fry several thousand dollars worth of batteries.
Thanks again for all the great comments
Al

 

[grindz145]

for camlight (john)-
Both statements would, I believe, be correct depending on motor current draw. At lighter loadings the charger might be powering the bike and charging the
batteries; at larger draws both the charger and batteries would supply the motor. The setup is a bionx 500 cuurently powered by the OEM 10A/h and 2-16 A/h
LiMn's. I would like to add about 2 more 16A/h batteries to a trailer and charge the 4x16A/h setup via a 800w generac 4-stroke. I think the idea would work
out but I want to run this by some folks with more experience than myself before I possibly fry several thousand dollars worth of batteries.
Thanks again for all the great comments
Al

Again, what this comes down to is being able to keep both the charge and discharge FETs on at the same time. The motor is a dynamic load, and generally the battery bank is a nice low impedance load so that the generator will be consistently providing power whether it's actually providing more current to the motor or to the batteries.

 

[BatteryMooch]

[Again, what this comes down to is being able to keep both the charge and discharge FETs on at the same time.

Arrgghhh...is that what you guys were talking about? Of course both can be left on. In my BMS', that's just plain old normal operation.
That's completely different than saying you're charging and discharging at the same time. Which is, of course, impossible.