Battery power dependent on level of charge?

[6zfshdb]

Another issue with these buck converters is, they reduce the voltage to 48V. A 48V lithium battery at full charge is 54.6V, which provides a significant boost in motor performance. 48V is about equal to a battery that is discharged to just 60% of capacity. Sure, the buck converter would provide 48V for a longer period of time but at a significantly lower performance level than a fully charged 48V battery.

Of course all this is speculation and may indeed not be practical on a DIY basis. I guess my point really was, every bike maker should be able to incorporate this "voltage regulation" into their controllers for just a few extra pennies.

As mentioned above, this voltage sag is really just a minor annoyance and is easily compensated on many bikes by just bumping up the PAS level. In my case, using cruise control and pedaling to assist the bike, the problem is not noticeable at all. IMO, the problem isn't worth spending a lot of $$ to correct. I do enjoy the theoretical challenge though.

 

[Gionnirocket]

Perhaps if it could be implemented only when the voltage has fallen continuously below 48v... but then again adding even more complexity.
For me smaller lighter battery technology would be worth more. Then you could go 8+ in parallel

 

[harryS]

Using a converter will cost you in efficiency. I tested a boost converter to raise my 36V battery to a constant 48V. Lost 15% range, going at the same speed. Where's the power lost? Conversion. You could get better efficiency with better magnetics.

The converter was about $25, and it worked surprisingly well for a inexpensive piece of gear.

Bicycles are simple enough that it's enough for the rider to simply pedal harder or just go slower, as the battery voltage runs down.

 

[PCeBiker]

,.. I tested a boost converter to raise my 36V battery to a constant 48V. Lost 15% range, going at the same speed.

And,.. That 15% loss of range is all turned into heat almost entirely in the converter, so 15% of your battery's ah rating would be how much energy the converter has to dissipate as heat.

Another thing that bothers about the idea, is that as the battery's voltage drops, it has to put out more and more amps into the converter, for the converter to have the same output.

Right when you should start going easy on a tired battery, is when you ask the most of it.

 

[6zfshdb]

And,.. That 15% loss of range is all turned into heat almost entirely in the converter, so 15% of your battery's ah rating would be how much energy the converter has to dissipate as heat.

Another thing that bothers about the idea, is that as the battery's voltage drops, it has to put out more and more amps into the converter, for the converter to have the same output.

Right when you should start going easy on a tired battery, is when you ask the most of it.

Yes, heat is the main reason for the loss, however a booster is less efficient than a buck voltage reducer. They don't generate as much heat.