I have been trying to figure out what I need to do to replace a NiCd battery pack in a weed whacker. There seem to be three primary groups that talk about advanced batteries: flashlight people, RC people, and EV bikes/cars people. My needs do not fit cleanly in any of those categories, but you guys seem closest. I need a 36V pack in the range of 3-5 AH. I have spent a bunch of time (many many hours) trying to figure out what to do. I will put the new batteries in a shoulder pack rather than trying to cram them in the original case. The manufacturer's battery pack (with "long running performance") lasts 15 minutes and recharges in 24 hours. That is about one weeding a season. Before someone asks; I have a gas unit but I have a real problem with the exhaust gasses. Hot sun with breathing mask, eye protection ,glasses, and hearing protection are not fun. This B&D electric unit is the only on I have found with performance comparable with gas powered units. And I have a poorly healed hernia that is not real compatible with the amount of rope pulling I have to do to keep the gas unit running with what is currently considered gasoline.
The device has an internal electronic speed control.
My objectives
- Longer run time if feasible
- fast recharge (15 to 30 minutes)
- safety - no batteries catching fire on my shoulder pack
- decent battery life cause this is going to be expensive
- method to prevent over-discharge
I have not found an accurate way of measuring the motor current without doing something to void the warranty. If I am convinced it is feasible (technically and cost) then I will void away. There is a fair chance I will need to parallel new cells.
I am leaning toward LiFePO4. NMC seems to have a lot of merit, but scarce in small cells and more expensive.
For rapid charging I will need a balancing charger since I may well charge it fairly often before I would have a chance to use something else for balancing. And the charger would have to be fast. This may be impossible. I have seen many references to a Goodrum-Fechter BMS. But I have been unable to find a source of kits, construction/schematic information, or assembled product (in order of my interest). I have also seen some comments about those designs having failure (and taking out the batteries) problems. The site tppacks does not seem to exist anymore. I would appreciate sources of information on this device.
NOTE: WHILE JUST READING THROUGH POSTS BELOW I FOUND A CURRENT REFERENCE TO THE BMS. I JUST WAS NOT USING THE MAGIC SEARCH SEQUENCES.
For batteries, some ones I have looked at are the A123 units (which seem to be very robust but expensive and small capacity), Trunigy, Zippy, and a bunch of places selling various individual cells that are supposed to be LiFePO4.
I would very much appreciate you sharing some of your collective wisdom about my best course of action. At the rate I have been going, weeds season will be over before I get this done.
The device has an internal electronic speed control.
My objectives
- Longer run time if feasible
- fast recharge (15 to 30 minutes)
- safety - no batteries catching fire on my shoulder pack
- decent battery life cause this is going to be expensive
- method to prevent over-discharge
I have not found an accurate way of measuring the motor current without doing something to void the warranty. If I am convinced it is feasible (technically and cost) then I will void away. There is a fair chance I will need to parallel new cells.
I am leaning toward LiFePO4. NMC seems to have a lot of merit, but scarce in small cells and more expensive.
For rapid charging I will need a balancing charger since I may well charge it fairly often before I would have a chance to use something else for balancing. And the charger would have to be fast. This may be impossible. I have seen many references to a Goodrum-Fechter BMS. But I have been unable to find a source of kits, construction/schematic information, or assembled product (in order of my interest). I have also seen some comments about those designs having failure (and taking out the batteries) problems. The site tppacks does not seem to exist anymore. I would appreciate sources of information on this device.
NOTE: WHILE JUST READING THROUGH POSTS BELOW I FOUND A CURRENT REFERENCE TO THE BMS. I JUST WAS NOT USING THE MAGIC SEARCH SEQUENCES.
For batteries, some ones I have looked at are the A123 units (which seem to be very robust but expensive and small capacity), Trunigy, Zippy, and a bunch of places selling various individual cells that are supposed to be LiFePO4.
I would very much appreciate you sharing some of your collective wisdom about my best course of action. At the rate I have been going, weeds season will be over before I get this done.
