Woosh Rio first ride with a low state of charge in the battery

[Brittas]

I have done over 600 miles on my woosh Rio solely commuting to work and back always on the maximum assist. The trip is 6.4 miles each way with some hills. I usually do to work and back then top up the battery after only 12.8 miles. Yesterday I forgot to charge the battery at work. This morning I only had a maximum of 2-3 bars of assist. My journey was 5 minutes longer and I was knackered lol. It seems when the battery gets below half The electric assistance goes way down. It certainly showed up how much assistance the Rio gives to my journey.

 

[sjpt]

Can you clarify 'bars of assist'. There are two sets of bars (I think it has the same controller as our kit). One the the level of assist as chosen by you (1 to 5 of 5 bars), and the other is the battery voltage (also shown by just 5 or so bars).
I find the battery voltage drops a lot as you use lots of power, eg on hills. Even on chosen 2/5 or 3/5 levels of assist the battery voltage sags by 2 or even 3 battery bars on a big hill. I certainly agree that the power available is much less on a low battery than a full one. The voltage will be 42v on a full 26v battery, and it probably cuts out at 30 or 32v, but I think the loss of power is more than linear with the loss of voltage.

 

[Brittas]

There is a bar showing the level of assist on the right hand side of the LCD while you are moving going from top to bottom. It is not the battery bar or the level of assist. For example, going up a hill all bars are shown. When peddling downhill the bar is empty.

 

[sjpt]

Thanks, my assumption on what controller it had was wrong; I see yours has that extra power indicator display.

Seems to indicate what we feel, that there is more than linear loss of power with decreased voltage. If it were a resistive load current would reduce with voltage and power as a square, but a controller+motor combination is much more complicated than that and I don't understand the implications.

Have you got the 13aH or 17aH battery? I suspect (but ???) that as well as having lower capacity, the 13aH has significantly less ability to deliver current as the battery empties.

 

[Brittas]

17 aH. I happy keeping the battery topped up every day at the moment. Hopefully, that will not shorten the life of the battery too much.

 

[vfr400]

The bars are a current eter. The more current you take from the battery, the more bars light up.

A run down battery goes as low as 31v. Wheb fully charged, it's 42v, so you get 33% more power when fully charged compared with when it's run down.

I'm not sure if that's the same with a Bosch motor because although they use a 36v battery, the motor effectively runs at 24v.

 

[sjpt]

The bars are a current eter. The more current you take from the battery, the more bars light up.

A run down battery goes as low as 31v. Wheb fully charged, it's 42v, so you get 33% more power when fully charged compared with when it's run down.

So if the current meter is only showing around 1/2 when charge has reduced AND the voltage has dropped from 42v to 31v (3/4) then the power must have dropped to around 1/2*3/4 or 3/8 of full?

I'm not sure if that's the same with a Bosch motor because although they use a 36v battery, the motor effectively runs at 24v.

Does that mean that it is able to use a fixed 24v regardless of whether the battery is at 42v or at 31v?

 

[vfr400]

So if the current meter is only showing around 1/2 when charge has reduced AND the voltage has dropped from 42v to 31v (3/4) then the power must have dropped to around 1/2*3/4 or 3/8 of full?

Yes in some circumstances - mainly in the upper speed range. It's a little complicated because the current is constant up to a certain speed, then it depends on the battery's voltage, and the speed that that happens becomes lower and lower as the battery runs down. I made this graph that shows how current changes with speed at any particular voltage. the maximum speed depends on the battery voltage, so if you had actual speed on the X axis instead of % max speed, the whole graph would shift to the left as the battery voltage goes down. In other words, if that graph was for a battery at 42v, at 31v the line would start at 53 amps and run down parallel to the red line and cross the X-axis at 75%, so you'd still get 15 amps up to about 56% of the theoretical maximum speed, which would be about 11 mph. All that is assuming that the battery can still give 15 amps when run down. Some can't.

Does that mean that it is able to use a fixed 24v regardless of whether the battery is at 42v or at 31v?

Probably. It depends on how they've configured the software in the controller, but anecdotally, that's correct.

 

[sjpt]

Yes in some circumstances ...

Thank you, very informative. I must mull on that. For us

• running mostly at assist levels 1 or 2 of 5 (so the yellow line is lower), very occasionally more for hills,
• not going that fast (so keeping to left of graph)
• especially as higher assist is on hills and going even less fast

it means we will almost always be on the controller limit yellow part of the graph. So our power will fall linearly with voltage.

On the other hand, Brittas (OP) running at maximal assist even on the flat will hit that low battery red/black slope even at 1/2 motor's max speed