Is the extra 5 amps chewing up my range?

Recently I've moved from a 20 amp controller to 25 amp and I'm seeing a significant drop in range on full power, I'm ending with 2 volts less than normal on a 15 mile trip. Is this typical for this increase or am I pushing the battery too hard?

if you ride faster, then it's down to the extra speed.

If you ride at the same speed, then the drop of 2V (or 20% of capacity) cannot be explained by the change of controller, possibly a more serious issue.

Pulling more current will affect battery range and mileage, that extra current has to come from somewhere so the cells are being asked to work 20% harder.

Firstly, at 25 amps, you're draining the battery 25% more quickly, but you're not going 25% faster. Secondly, the capacity of your battery varies with the amount of current you take from it, so it'll have less effective capacity at a higher current.

I'll experiment with the amps settings and see if that helps, was pretty sure more current would drain more was just surprised how much. Doesn't help that it's been windy so that might have contributed although I have been pedalling. 25a is the max continuous rating of my battery so maybe it's just the hard graft it's doing

Doesn't help that it's been windy so that might have contributed although I have been pedalling.

I notice on windy rides, that overall performance suffers, so you might be on to something there. You can really feel the motor trying to overcome the extra wind resistance.

Here you can see the effect of current on capacity. The closest lines on that graph to what you did are the 1.5C and 2.0C, which show a 20% difference in capacity. More releastic would be 2.0c and 2.25C, which you could interpolate to 10% difference. That only affects the capacity for the time that you're actually using the 25 amps - say 25% of the time, so the overall reduction in capacity would be 2.5%. When a battery is listed as 11Ah, 15Ah etc, that's normally at much less than 1C.

 

I tested a 6Ah (LG HG2 cells) battery at 1 amp. It gave the full 6Ah. At 5 amps, it only gave 5Ah.

Those graphs are very interesting: I will use them to try to interpret better the vagaries of the battery meter on my KM529 as the battery is under load. (I guess the Samsung 2600 cells will be broadly similar to the LG 2400 ones).

 

You calculations indicate how much less battery capacity the OP will get under the different settings. They don't allow for the fact that he will be using more capacity per mile, which is probably a bigger factor. This is as you suggest in your earlier post; just clarifying in case anyone takes your number in the more recent post out of context.

Those graphs are very interesting: I will use them to try to interpret better the vagaries of the battery meter on my KM529 as the battery is under load. (I guess the Samsung 2600 cells will be broadly similar to the LG 2400 ones).

 

You calculations indicate how much less battery capacity the OP will get under the different settings. They don't allow for the fact that he will be using more capacity per mile, which is probably a bigger factor. This is as you suggest in your earlier post; just clarifying in case anyone takes your number in the more recent post out of context.

 

In today's experiment I lowered to 20a, the performance was crap and the battery usage wasn't really any better, again pretty windy. What I have noticed though is that at higher current the battery starts to really plummet once it gets below like 48v so I think the sag is really killing it off. Once I get to that level again I'm going to try and back off to pas 4 and see if it improves. Maybe it's just the wind but I pedalled a lot to minimise the effect, on calm days my bike has enough grunt for throttle only riding

When I select cells/battery packs I ignore the mah rating and look for discharge stats 1a - 5a discharges and there mah rating down to 3.2v as this effectively is the most you will discharge a cell to and the actual capacity you will get.

In today's experiment I lowered to 20a, the performance was crap and the battery usage wasn't really any better, again pretty windy.

what is the capacity of your battery?

what is the capacity of your battery?

 

13ah

 

When I select cells/battery packs I ignore the mah rating and look for discharge stats 1a - 5a discharges and there mah rating down to 3.2v as this effectively is the most you will discharge a cell to and the actual capacity you will get.

 

There's no individual ratings just pack spec, 25a continuous/40a pulse. They are generic cells

That rating is probably for the BMS. If it has crappy cells, they won't be able to cope with that.

That rating is probably for the BMS. If it has crappy cells, they won't be able to cope with that.

 

How much sag is too much?

Any sag is too much but in truth all cells sag over 0.2 a current draw , just depends on how many in parallel and quality.

My 13s 7p PF's show an average of 0.1v per cell with about 200w applied. If I apply more W's I can see nearly 2v sag temporary with my 25a controller whilst climbing in higher PAS , voltage bounces back immediately once in lower PAS with very little actual overall voltage decrease.

Edited September 17, 20196 yr by Nealh

Any sag is too much but in truth all cells sag over 0,3a current draw , just depends on how many in parallel and quality.

My 13s 7p PF's show an average of 0.1v per cell with about 200w applied. If I apply more W's I can see nearly 2v sag temporary with my 25a controller whilst climbing in higher PAS , voltage bounces back immediately once in lower PAS with very little actual overall voltage decrease.

 

Mines the same, nothing significant unless going hard and bounces back pretty well unless it's a big climb