Assist OFF going downhill or flat roads, how much of a savings?

[Luto]

Hi All,

So lately, I have been using the assist (eco) only to warm up at the start (up a gravel road) and at the end to cool down. However this question came up.

Assume you are on flat ground or going slightly down hill. How much battery juice would you, should you, be using, as opposed to having the assist OFF on these section? (Assuming things like speed- wind resistance are the same.) Or put another way, what if you only used assist going up hills and had it off the rest of the time. How much less energy would you use?

I know it is hard to get all the variables out, but it seems the answer is quite a bit more. i.e. it seems the assist really does not help that much on flats or downhill sections but still is sucking up disproportionate amounts of energy. Even consider a heavier bike going downhill, moves more easily, than a lighter one.

The scenario to consider is you are trying to go say 120% of your normal range. What if one only turned ON assist when there is resistance, such as hills or wind (again speed being the same otherwise). Do you think you would get more range?

So far, it seems like a lot, actually too much, more than I expected. I have done about 50 miles and used it only on up hills sections and am down 10% on a 500watt pack. To me, some savings is expected but not this much, because at 50 miles with assist on all the time, I would be at 20%, but only moving slightly faster on flats and initially on downhills.

At this rate, I could go 200 miles, which would allow me to go overnight away from any charging facility, eliminate the need for a second battery or any solar solution.

Anyone done any of this? comments? I would be interested if others try this.

 

[6zfshdb]

I asked myself this same question. I think every e-bike is slightly different in this respect but I got the following test results with mine:
When coasting with the power turned on but providing no assist, the current used by the display and controller was 250ma (a quarter of an ampere). The measurement was the same when the bike was parked with the power left on.

The manual for the bike recommends turning the power off when the bike is parked for a "significant" amount of time. Considering the size of the battery, a quarter of an ampere isn't much but it does add up over time. I haven't done any actual range testing but when the bike was new, I got in the habit of switching off the power when coasting and also when parking the bike. After a while, I got lazy and stopped doing it. There was no noticeable loss of range.

My rides average +/-50 miles over a period of around 5 hours. During a ride I estimate I coast or park the bike for approximately a half hour. Leaving the power on, the bike would consume .25 amps X 48 volts X .5 hours or 6 watt hours. Riding conservatively, the 720 watt hour bike battery normally yields around 50 miles or 14.4 WH per mile. In theory, using these rough numbers, the loss of 6 WH equates to less than a half mile of range or just under 1%.

None of this may answer your question and, as I said, every bike is different. Some even have regen systems which charge the battery when braking or coasting. The only way to know for sure is to measure with a good quality meter and do the math.

 

[rich c]

My first thought is how you measured the 10% drop. A bar on your display? I was a mechanical engineer, not a test engineer. But when you do an analysis you need accurate repeatable data. One concern is how your controller is programmed and how much voltage sag you will get as the battery range drops. One test to 50 miles is hard to develop a conclusion. With your current assumption, if you had regeneration going downhill, you have almost developed a perpetual motion machine

 

[BarryS]

I would think just from a basic standpoint . Switching off assist going down a Hill to conserve battery . Is probably lost when you boot back up I turn off my lights on Bike trails . Just ride the Bike . For the average rider to use up the number of charges usually under their warranty is never going to happen in the 2 year period . I live in Michigan . My Specialized Vado Battery warranty is 2 years . If I ride 5 months every day and completely exhaust and recharge My battery 150 times . I would be right at the 300 full charge warranty at the end of 2 Years .

In Reality during that 5 months I probably get to ride maybe a total of 90 times . Considering work, rain days ,etc. I will not exhaust my battery charges for probably closer to 4 years of riding seasons. Plus I personally know 2 people who have Vados from 2015. One guy lives in Florida . He is approaching 600 charges and says he's lost some battery life. But not enough to make much difference. So just go ride .

HAVE FUN : Technology is progressing to fast to worry about batteries longevity . Or gain an extra mile or 2 from a single charge

 

[harryS]

Years and years ago, I used to believe that turning off my car engine at stoplights would save gasoline, but automotive writers claimed that I'd pull that energy out of the battery to restart the car. Now production gasoline cars shut off the motor all the time when stopped.

Sure, turn off the assist. It saves power.

 

[Roxlimn]

Theoretically, if you're open to pedaling the bike without power, your range is infinite. 200 miles no power? Yeah. You can definitely do that. I do generally shut off the power downhill or on flat roads if I'm not concerned about speed. I can usually add about 20 miles to my range doing this conservatively - that is, without any meaningful sacrifice on my end. It challenges more of my personal strength, but nothing that I mind in any way.

I could probably do 100 miles on flat road without sweating it too much or getting body aches the next day being very conservative about my power. But 200 miles feels like a lot of work.

 

[Luto]

My first thought is how you measured the 10% drop. A bar on your display? I was a mechanical engineer, not a test engineer. But when you do an analysis you need accurate repeatable data. One concern is how your controller is programmed and how much voltage sag you will get as the battery range drops. One test to 50 miles is hard to develop a conclusion. With your current assumption, if you had regeneration going downhill, you have almost developed a perpetual motion machine

@rich c , I totally agree, there is not enough data and in fact the data I have is so flawed, I can't even really use that! But since this forum is SOOOO friendly, I did not hesitate to post because, well everyone is cool here. I did use the power meter indicator on the KIOX drive. I am pretty sure it is not accurate. To wit, I when I put it back on, I was using about 1/3 the leg effort as when OFF and it claimed I was generating 235 watts of energy, about the same amount. It was almost as if the 235 watt number was my legs AND the assist. Anyways, those KIOX readings are very suspect, imo, and not enough to do accurate data collection and I am not sure it would even be precise.

In the end, I think I have found my "range extender" solution. My goal is to be able to go somewhere overnight where there is no power, and continue on the next day to a power location. E.g. Camp one night, go motel the next. Seriously, I did not really want to do all the testing as that was my old job, and this is more about fun. THANKS everyone for 1) being cool, and 2 the comments, they helped.

PS: Roxlimm, the 200 miles is over 2 or more days. 200 in a day, are in my past, and my sore butt appreciates it.

 

[Roxlimn]

@rich c , I totally agree, there is not enough data and in fact the data I have is so flawed, I can't even really use that! But since this forum is SOOOO friendly, I did not hesitate to post because, well everyone is cool here. I did use the power meter indicator on the KIOX drive. I am pretty sure it is not accurate. To wit, I when I put it back on, I was using about 1/3 the leg effort as when OFF and it claimed I was generating 235 watts of energy, about the same amount. It was almost as if the 235 watt number was my legs AND the assist. Anyways, those KIOX readings are very suspect, imo, and not enough to do accurate data collection and I am not sure it would even be precise.

In the end, I think I have found my "range extender" solution. My goal is to be able to go somewhere overnight where there is no power, and continue on the next day to a power location. E.g. Camp one night, go motel the next. Seriously, I did not really want to do all the testing as that was my old job, and this is more about fun. THANKS everyone for 1) being cool, and 2 the comments, they helped.

PS: Roxlimm, the 200 miles is over 2 or more days. 200 in a day, are in my past, and my sore butt appreciates it.

Ah. If it's over a couple days, then 200 miles if perfectly doable! That's a situation where your real limitation should be expressed in feet of climbing. I'd say a 500 Wh should be good for about 2000 feet. If you don't need to climb more than that, then 200 miles is quite a doable!

 

[AHicks]

If you shut the power off completely, you're turning off the power that handles the internal housekeeping within the display and controller, possibly what it takes to run the speedometer. This is like turning off a pilot light - a negligible amount of power.

Most bikes are equipped with an auto shut off that sense inactivity, and shut off within 5 minutes or so.