This is a simple little project made in ½ hour from scrap parts I had lying around which I thought I’d share: The idea was to enable me to:
1) Partially discharge a fully charged e-bike battery to a suitable storage level for winter
2) Exercise the battery to extend its’ life when my e-bike batteries aren’t getting used much
3) Measure the true capacity of the battery
All this really involves is having a suitable load to drain the battery. I used 3 x 40-watt 12v halogen B&Q lamps I had spare. Wired together in series, this gives an ideal load of 120 watts for my two Phylion Lithium 36-volt, 374 watt, 10.4 amp e-bike batteries. The load is comparable to normal leisurely on-bike use: It’s neither too demanding for the cells, yet not so relaxed it takes ages to discharge. I added an on/off switch for ease and a 5-amp fuse for safety.
The idea came about simply because neither of my two e-bike batteries get used much over winter. Both are usually left stored at half-capacity after a ride. If the weather looks fair and I plan a morning ride, I’ll charge one/both to full capacity the evening before. If the weather then turns out to be truly horrible, I could be left with a fully charged battery that ends up not being used – perhaps for several weeks. Rather than leave the battery in this “stressed” fully charged state, an hour using this takes about 30% of the charge back out, 1¼ hours about 40% – perfect!
You can use a multi-meter to periodically check battery voltage, but the LED’s on the pack is probably enough to tell if the battery is at half-charge for storage, or near empty when the BMS should in any case cut-off the circuit when the cells are near flat before any damage occurs. Timing the battery over a full discharge gives you a good indication of what capacity is left in the battery: For me: A fully charged 374w battery / 120w load should take a shade over 3 hours if the cells are still performing as new (which they do seem to be).
There are probably neater ways of doing this, but for ½ hour time and a few spare garage bits, this works really well for me.
1) Partially discharge a fully charged e-bike battery to a suitable storage level for winter
2) Exercise the battery to extend its’ life when my e-bike batteries aren’t getting used much
3) Measure the true capacity of the battery
All this really involves is having a suitable load to drain the battery. I used 3 x 40-watt 12v halogen B&Q lamps I had spare. Wired together in series, this gives an ideal load of 120 watts for my two Phylion Lithium 36-volt, 374 watt, 10.4 amp e-bike batteries. The load is comparable to normal leisurely on-bike use: It’s neither too demanding for the cells, yet not so relaxed it takes ages to discharge. I added an on/off switch for ease and a 5-amp fuse for safety.
The idea came about simply because neither of my two e-bike batteries get used much over winter. Both are usually left stored at half-capacity after a ride. If the weather looks fair and I plan a morning ride, I’ll charge one/both to full capacity the evening before. If the weather then turns out to be truly horrible, I could be left with a fully charged battery that ends up not being used – perhaps for several weeks. Rather than leave the battery in this “stressed” fully charged state, an hour using this takes about 30% of the charge back out, 1¼ hours about 40% – perfect!
You can use a multi-meter to periodically check battery voltage, but the LED’s on the pack is probably enough to tell if the battery is at half-charge for storage, or near empty when the BMS should in any case cut-off the circuit when the cells are near flat before any damage occurs. Timing the battery over a full discharge gives you a good indication of what capacity is left in the battery: For me: A fully charged 374w battery / 120w load should take a shade over 3 hours if the cells are still performing as new (which they do seem to be).
There are probably neater ways of doing this, but for ½ hour time and a few spare garage bits, this works really well for me.
