Since the recent surgery on my battery pack I have done 7.85 amp-hours without any cut offs from the battery management system. So it would seem the early cut offs around the 6 amp-hour mark are a thing of the past! The minimum voltage this time around was 32.9, resting voltage was 35.8 and I used 288 watt hours.
The local bike shop is organising a Sheldon Brown memorial ride tomorrow which will involve a bit of distance and some hills thus I'm charging the pack up tonight so I don't run out of juice half way home! I'll probably aim to recharge around the 8 amp-hour mark from now on.
Wednesday, March 31, 2010
Monday, March 29, 2010
Battery range
Seeing as the big trip in my last post did not flatten the battery I thought I would have another go to see how it was performing in terms of capacity. Unfortunately after not doing any top up charges last week it cut out after about 6.4 amp-hours which is where it has cut out on my previously. I should at least be getting 8 or 9 amp-hours so I sent an email query to Justin at ebikes.ca. As usual I got a reply very quickly! Justin informed me that yes I should be getting more out of the pack and that it was likely a cell balance issue. He offered me a replacement pack straight away or a chance to pull it apart and have a go at fixing it. I went for the chance to fix it as sending mine back to Justin overseas may have been problematic with our laws regarding postage of battery packs. And I was also keen to see the inside of the pack!
I was instructed to do a full recharge and then pull the pack apart and check the voltage of each battery cell. Getting it apart was fairly easy and I must say it is very well put together. As you can see from the photo it has 2 separate groups of 5 battery cells that are securely attached and wired together with some circuitry to manage the charging, balancing and low voltage cutoff (LVC) to protect the cells.
When fully charged each cell should be 4.15 volts or higher however one of mine was only 4.02 and Justin thought this cell might be prematurely tripping the LVC. To fix it I found an old charger that put out about 5 volts and soldered some alligator clips to the output wires. I attached the clips to the weaker battery cell (making sure they were the right polarity!) turned it on and waited.... and waited .... and waited for the voltage to increase. Eventually it got up to 4.04 and we were on our way. It took about 7 hours to reach 4.17 volts! I asked Justin why it was taking so long and he figured that given my charger was only 500 mili-amps, and that the cell was cutting out about 3amps short of where it should (ie at 6 instead of 9 amp-hours), that it would likely take about 6 or 7 hours to put another 3amps of capacity in to it.
So I got it all charged, put it back together and have been riding around this week to see how far it would go. Today I hit 8.5 amp-hours before it cut out! The lowest voltage was 28.9 and for the last little bit of riding (around 8.3 to 8.5 amps) it got a bit sluggish as I hit the 30 volts limit I had on the Cycle Analyst. At 8 amps the lowest voltage was 33.3 so the last bit of use really drops the volts off quickly. The range was 42 km which I am very happy with!
So the battery is back on the normal charger and hopefully I will get a similar range next time without having to pull the pack apart again. I am confident that will be the case. As an added bonus Justin offered me 25% off any future battery pack I purchase off them in recognition of my receiving an unbalanced pack and the work I put in to hopefully fix it up! Outstanding!
I was instructed to do a full recharge and then pull the pack apart and check the voltage of each battery cell. Getting it apart was fairly easy and I must say it is very well put together. As you can see from the photo it has 2 separate groups of 5 battery cells that are securely attached and wired together with some circuitry to manage the charging, balancing and low voltage cutoff (LVC) to protect the cells.
When fully charged each cell should be 4.15 volts or higher however one of mine was only 4.02 and Justin thought this cell might be prematurely tripping the LVC. To fix it I found an old charger that put out about 5 volts and soldered some alligator clips to the output wires. I attached the clips to the weaker battery cell (making sure they were the right polarity!) turned it on and waited.... and waited .... and waited for the voltage to increase. Eventually it got up to 4.04 and we were on our way. It took about 7 hours to reach 4.17 volts! I asked Justin why it was taking so long and he figured that given my charger was only 500 mili-amps, and that the cell was cutting out about 3amps short of where it should (ie at 6 instead of 9 amp-hours), that it would likely take about 6 or 7 hours to put another 3amps of capacity in to it.
So I got it all charged, put it back together and have been riding around this week to see how far it would go. Today I hit 8.5 amp-hours before it cut out! The lowest voltage was 28.9 and for the last little bit of riding (around 8.3 to 8.5 amps) it got a bit sluggish as I hit the 30 volts limit I had on the Cycle Analyst. At 8 amps the lowest voltage was 33.3 so the last bit of use really drops the volts off quickly. The range was 42 km which I am very happy with!
So the battery is back on the normal charger and hopefully I will get a similar range next time without having to pull the pack apart again. I am confident that will be the case. As an added bonus Justin offered me 25% off any future battery pack I purchase off them in recognition of my receiving an unbalanced pack and the work I put in to hopefully fix it up! Outstanding!
Friday, March 5, 2010
A ride in the wet!
Well my 'big' (for me at least) bike ride to test the range of the battery went better then I thought it would. It was 11.5 km each way and I only used .87 of an amp on the way there and 2.24 on the way back! The trike was empty though so if I add 50kg of children I expect those figures would increase. However even if I double them that is still only about 6 amp hours for a round trip.
Though it is a hilly trip I was able to use the downhills to gather a fair amount of speed to tackle at least some of the next uphill. I have the Cycle Analyst set to a 23km/h speed limit and I found that this worked as a great 'cruise control' eg go down hills at around 30km/h then start going up the next one and as speed gradually dropped the motor would kick in around 23km/h and I could pedal in higher gears for most of the hill. After a while I could then kick down a few gears and pedal to match the gradually slower speed of the trike up the hill. By not maxing out the motor with this method the range seems to be quite impressive. The uphills are longer and steeper on the way back hence the higher use of the battery coming home.
I was not counting on the rain being as heavy as it was though! I guess this was a good test for the 'waterproofness' of the motor and all my wiring and it looks like it passed as no sparks flew!
Thursday, March 4, 2010
Electric motor range
Am only now getting back into riding the trike regularly as the kids are back at school and we were away for Christmas and New Year.
I have been careful not to overtax the battery and have only twice hit the BMS cutoff (on recharge cycle 1 and 3) after I had pulled about 5 or 6 amp hours out of the 10 amphour pack. The cutoffs both happened whilst going up some sort of monstrous hill with a full load of groceries. However I only use the motor when going uphill so I guess that is the only time it is ever going to cut off for me!
My most recent recharge (prior to any shutoff) was when I had pulled 6.2 amp hours out of the battery and it still seemed to be travelling pretty well with minimum volts a fairly good 34.7 (at least I think that is fairly good as on previous charges I had dropped to 32). To date I have always recharged after about 5 or 6 amp hours and I am averaging about 7 watt hours per km actually travelled. However that includes travelling downhills and on the flats where the motor is not used at all.
In the next few days I plan on doing a big ride with a fully charged (and now hopefully well worn in) battery towards some of the more distant attractions we take the kids to. This trip involves some pretty horrendous hills that go on for a while so it will be a good test to see if I can get there and back on one charge and how many amp hours I can now pull out of the pack before it shuts down.
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