Solar bike battery needs replacing within 26 months / 2000kms?

[Mububban]

I got the Swift conversion kit from Solarbike at the start of 2014. I log my kms and have only done 2059km on this system since then. I ride 13km to work, then 13km home and charge it up as soon as I get back. When I didn't ride for 4 month due to my bad back, I followed the advice of charging it a few times during that period and disconnecting it from the bike to minimise any "trickle drain".

I've been commuting more regularly so far this year, but lately the battery has started konking out near the end of some of my rides home as I go up some inclines. It’ll go on and off. My route/terrain never changes and it's not happening every ride but it's something I've started to notice.

Solarbike reckons 2-3 years is about normal. This is very disappointing for a $530 Panasonic battery (replacement cost for 36V 9Ah) with such low usage.

Can anyone else share battery life details and usage for comparison?

[mikedufty]

I think it is quite common. I'm using a solar bike hub, but with zippy flight max LiPo batteries from Hobbyking. I've done about 6000 km over 18 months now and am only getting half the rated capacity, but it is only $100 to replace them, and they are a lot lighter than the panasonic ones. Still good for about 15km which is OK for me as I can charge at work.

[eldavo]

http://batteryuniversity.com/learn/arti ... _batteries

[Mububban]

I think it is quite common. I'm using a solar bike hub, but with zippy flight max LiPo batteries from Hobbyking. I've done about 6000 km over 18 months now and am only getting half the rated capacity, but it is only $100 to replace them, and they are a lot lighter than the panasonic ones. Still good for about 15km which is OK for me as I can charge at work.

Could you link the specific batteries you're using? Did you have to assemble a battery pack yourself or do they make a unit to replace the tube shaped batteries?

I guess I can just bring the charger to work to eke out the last of the battery life by charging at work and then again at home. I'm just disappointed to get such a short lifespan considering the low/moderate use I've subjected it to.

[cj7hawk]

My battery died nearly completely at 1000km - Down to a few KM range - but I have the generator onboard so just run it everywhere and get unlimited range ( while fuel is available )

Anyway, I'm running VRLA which is heavy and has less cycles, but even lithium isn't perfect and optimal battery life is at around 50% drain.

That means, for my 52km 3 hour trip ( just under 3 hours ) I need to reliably handle around 750WH of power, so I'd need a battery of around 1.5 kWH for optimal use, at an average of 2 cycles per week, or 100 cycles per year, which is about the limit of a lithium battery, and don't forget as it ages, the aging accelerates.

Actually, to equal the generator output, I'd probably need around 2 kWH of battery, and a maximum 3 year life span for design.

Unfortunately, most commercial batteries are about 1/10th of that, and I know of no legal 250W bicycles that come with about more than 15% of that value, so battery drain in most user cases is probably going to be affected by operational duty cycle and realistic range more than anything.

Or, you can buy more advanced batteries, and pack them yourselves like the EV guys do.

Or you can go Generator Capable like I do.

Or just build a 200W PAPC with a 2kWH battery, which should just about fit into the space in the main triangle of the bicycle ( although, 2kWH is for my use - other cyclist needs may be different - I'm at about 2500km presently ).

Also, if it's a common battery, you can get cheaper ones on Ebay and Aliexpress.

David

[mikedufty]

Mine wouldn't be a drop in replacement for yours.
I use two of these in series for 5Ah 48volts
http://www.hobbyking.com/hobbyking/stor ... P_20C.html
They need to be separated to charge on a 6 cell balance charger, which are about $30.
I've just got them in a fire resistant bag in my pannier.

Needs a fair bit more attention than the more standard batteries, but nice if you like fiddling with things.
I also needed a cycle analyst to limit the power to 200w because I am running more voltage than the motor and controller were intended for.

I get at least 15km out of this even in it's current state, so should only need 3 for a 50km commute = 0.72 kwH, so I can only imagine cj7hawk's drive system is very inefficient if he needs 2kwh.

3x my current battery would be a 150x150x100mm battery pack, which would take up a third of my pannier though. I'd have to put my other pannier on to carry stuff.

[Mububban]

I'm not electrically minded so a "plug and play" solution would probably be the go for me.

Would this battery seem okay? Low feedback volume but 100% positive in the last 12 months. Looks almost identical to my current battery that came with the Solarbike kit, except it's Samsung cells not Panasonic.

http://www.ebay.com.au/itm/E-bike-batte ... Swo0JWJnfH

[koshari]

I'm not electrically minded so a "plug and play" solution would probably be the go for me.

Would this battery seem okay? Low feedback volume but 100% positive in the last 12 months. Looks almost identical to my current battery that came with the Solarbike kit, except it's Samsung cells not Panasonic.

http://www.ebay.com.au/itm/E-bike-batte ... Swo0JWJnfH

thats exactly the supplier and battery i put on my wifes e-bike, however it has only been on it for a few weeks and she has only ridden it about 6 times on longer rides so i cant give any advice as per its longivity. the free controller that came with it wasnt bad though.

[cj7hawk]

I get at least 15km out of this even in it's current state, so should only need 3 for a 50km commute = 0.72 kwH, so I can only imagine cj7hawk's drive system is very inefficient if he needs 2kwh.

You said 0.72kWH - I said 0.75kWH, not a lot of difference there - I just pointed out that you need to keep your use under 50%, which means you need 1.5kWH, and then a little extra to allow for aging of the battery - 2kWH - Would give you optimal lifespan of the battery.

Regards
David.

[mikedufty]

You said 0.72kWH - I said 0.75kWH, not a lot of difference there - I just pointed out that you need to keep your use under 50%, which means you need 1.5kWH, and then a little extra to allow for aging of the battery - 2kWH - Would give you optimal lifespan of the battery.

But my 0.75kwh was based on performance of my actual well aged battery, only used to 50% rated capacity, so is addressing the requirement your 2kwh figure is for.

[cj7hawk]

You said 0.72kWH - I said 0.75kWH, not a lot of difference there - I just pointed out that you need to keep your use under 50%, which means you need 1.5kWH, and then a little extra to allow for aging of the battery - 2kWH - Would give you optimal lifespan of the battery.

But my 0.75kwh was based on performance of my actual well aged battery, only used to 50% rated capacity, so is addressing the requirement your 2kwh figure is for.

OK, I can understand that better.

My 0.75kWH = 0.25kWH x 3 hours, or a constant load of around 250W, which provides for 2 x 1.5 hour trips, running lighting, start/stop, high current draw periods averaged out, a slight increase in range as required and an average speed of around 19~20 kph, for wind and such, for at least the assist component. Some days I use less, but I also know what the most I might use is too. 750kWH is a reasonable actual use for 55-60km of travel under those circumstances -

Then the rest of the 2kWH is just for maximising battery life.

Regards
David

[mikedufty]

Still, I'm saying 0.75 kwh of capacity does the job, so it is only 0.375kwh of actual power use, as I only use 2500mAh out of a 5000mAh battery. Probably partly due to me pedalling harder, I average around 30kph. In fact 200w draw gets me well over 20kph without pedalling so I think there may be issues with your set up. I also think you may be you are overestimating how much extra is needed to prolong battery life. May be right for Lead Acid batteries but Lithiums cope much better with full cycles. Given the weight and cost disadvantages I can't see many people using lead acid for a practical bike these days.

[cj7hawk]

I also think you may be you are overestimating how much extra is needed to prolong battery life.

Primarily I was talking about optimizing battery life, which really does require a capacity well above usage. Is it needed? No. But it does optimize battery life. Also, you're probably not getting the most benefit from the electric, whereas my system simply takes whatever power is coming in from the pedals and adds 200W to them, regardless of speed.

So, yes, I do consume more power, but I get the full benefit of it at all times also - which helps me get to where I'm going quicker.

Regards
David.

[mikedufty]

As I said before, my calculations are for only using half the rated capacity. I use the full 200w pretty much all the time, it is electronically limited. Only at around 40kph does it reach the limits of the motor set up and not give the full 200w, and that doesn't happen without a serious tailwind or a big downhill.

[cj7hawk]

As I said before, my calculations are for only using half the rated capacity. I use the full 200w pretty much all the time, it is electronically limited. Only at around 40kph does it reach the limits of the motor set up and not give the full 200w, and that doesn't happen without a serious tailwind or a big downhill.

Something seems out with your calculations then - If you're pushing 200W to the wheel, then you should be consuming around 250W at the PSU, at the very least somewhere between 220W and 230W even if your motor is super-efficient.

If your consumption is 250W, and you ride on full boost for 3 hours, then you have to consume at least 750Wh of power - if you're only consuming half that, then the energy must be coming from somewhere else - eg, your legs. Otherwise, you might be set to 200W pre-controller, in which case the consumed power would be 600Wh but still not close to the 350Wh you mentioned earlier.

Sounds like your setup is pretty nice - I assume the input voltage is around 48v from the batteries? So you're likely to have some serious inefficiency at lower speeds also if it's all PWM - Brushless efficiency drops off pretty quick under those circumstances -

Regards
David

[mikedufty]

Speed is obviously the difference, I average 30kph, so 50km is 1.66 hours not 3 hours. I typically averaged about 25 without it, so I'm guessing I'm contributing about as much power as the motor does for a nicely balanced 2 wheel drive setup.

I have a geared hub motor, so the motor is not running too slow. Don't know what the efficiency is but it gives plenty of assistance even from a standstill. Batteries are around 50v fully charged, controller cuts them off at 39V (loaded) to preserve the batteries, usually bounces back up to about 46v when you put it on the charger. The hub motor is nominally a 36v unit, it becomes ineffective at much over 30kph with 36v, but will go to near 40 with 50v. Can't say I noticed any deterioration in low speed performance with the higher voltage.

[cj7hawk]

Speed is obviously the difference, I average 30kph, so 50km is 1.66 hours not 3 hours. I typically averaged about 25 without it, so I'm guessing I'm contributing about as much power as the motor does for a nicely balanced 2 wheel drive setup.

I have a geared hub motor, so the motor is not running too slow. Don't know what the efficiency is but it gives plenty of assistance even from a standstill. Batteries are around 50v fully charged, controller cuts them off at 39V (loaded) to preserve the batteries, usually bounces back up to about 46v when you put it on the charger. The hub motor is nominally a 36v unit, it becomes ineffective at much over 30kph with 36v, but will go to near 40 with 50v. Can't say I noticed any deterioration in low speed performance with the higher voltage.

That makes sense. If you're riding faster, you get there quicker. I can maintain close to 30 if I push it, but I just can't push that hard, so normally don't go that fast without a tailwind. I guess how fast/far you want to go is an important consideration for battery capacity - and I usually start mine at zero effort and assume around 19kph average speed, over nearly 60km.

You won't notice the loss of power - it's just a small loss of efficiency - you could measure it, but I doubt you'd feel it within under 200w of propulsion. The acceleration difference is just too low.

Regards
David.

[mikedufty]

I just remembered the cycle analyst actually logs wh/km. For my ride home yesterday it was 7wh/km so 350 wh actually consumed per 50km.