brandonh
1 mW
Hi all,
First off, props to magudaman for pointing me to this forum at the Silicon Valley EV Rally last August. There’s a ton of great info here.
I’m building a gyro-balanced scooter (aka custom Segway) powered by A123 M1 cells taken from Dewalt 36v packs. My plan is to eventually use 4 of them in the scooter, but I have a few questions about charging and pack-building that I wanted to ask before buying anything more. I’ve purchased one charger and two packs so far. Questions are in bold.
The options for one pack seem clear: (1) leave it stock and physically move the batteries to charge (2) pop out the charger connector to make a remote one, or (3) pop out the BMS and charge with a “dummy packâ€￾. Options 2 and 3 would be fine. Or, I could buy a dedicated charger like Astroflight and others make.
Going to two or more packs adds some complication.
Stage 1: Multiple packs, multiple charge connectors
To enable these to be separately charged, I’d need a high-current switch with one pole per pack, or a relay with one contact per pack. This “stage oneâ€￾ setup will use a relay and two packs, like Trevor Blackwell has done for his scooter. With one charger, I’d have to manually open the scooter and move the packs. With a second charger, I can pop both charger connectors, attach them to the batteries, and use an inline plug to keep the batteries permanently mounted. This should work fine, especially with diode protection inline in each battery, but does require a second charger, and the number of wires and connectors goes up linearly with the number of packs. For 4 packs, I’m looking at 40+ charge connections (10 each), 4 charger connectors, plus all the relay and wiring space. Not ideal.
Stage 2: Single larger pack, single charge connector
To reduce the space and cost, it’d be nice to have a single charge connector for all batteries. Does anyone know if the Dewalt charger can handle parallel packs? My guess is that it would either work fine and take longer, or a charge-time-exceeded cutoff would kick in and stop the charge. Has anyone tried connecting the Dewalt charger+BMS to a 10s2p pack? This would be the most elegant, least-cost solution. I know I’d have to connect the positive and negative of all corresponding cells (balancing leads) – not just connect the positive and negative of each pack together. I guess this could be done with soldered wires between the packs. Another option is to create a single custom pack to remove the wires between packs. Let’s say I do this – should I capacity match the cells like doctorbass did on his pack of used cells? Would I need to buy a fancy charger to measure the capacity of single cells (for capacity matching)? Might there be some way to do it with my Power Analyzer Pro? If the Dewalt charger+BMS can’t handle 10s2p, then I’d have to buy a charger plus balancer.
Stage 3 would add a custom charger and BMS, but I’ll save those ideas for a later post.
Pack building questions:
Does soldering really damage the cells? High-current, pro-grade packs like the Killacycle pack and the Hybrids-plus Prius pack use spot welding, and A123 warns against soldering the cells directly. Assuming spot welding is the answer:
Where does one find a spot welder? Anyone know of one in the SF Bay Area? There plans for building one on the net, like a capacitive discharge welder, AC welders, and you can even just use a few lead-acid batteries in series, but I’d prefer to use a real one.
What does one use for straps? Does anyone know where to buy the straps used in real A123 packs, like those on the Killacycle pack? These tabs (go to bottom of page, pre-cut nickel strips) look like a reasonable choice.
Any answers to the above questions would be really appreciated.
First post!
-Brandon
First off, props to magudaman for pointing me to this forum at the Silicon Valley EV Rally last August. There’s a ton of great info here.
I’m building a gyro-balanced scooter (aka custom Segway) powered by A123 M1 cells taken from Dewalt 36v packs. My plan is to eventually use 4 of them in the scooter, but I have a few questions about charging and pack-building that I wanted to ask before buying anything more. I’ve purchased one charger and two packs so far. Questions are in bold.
The options for one pack seem clear: (1) leave it stock and physically move the batteries to charge (2) pop out the charger connector to make a remote one, or (3) pop out the BMS and charge with a “dummy packâ€￾. Options 2 and 3 would be fine. Or, I could buy a dedicated charger like Astroflight and others make.
Going to two or more packs adds some complication.
Stage 1: Multiple packs, multiple charge connectors
To enable these to be separately charged, I’d need a high-current switch with one pole per pack, or a relay with one contact per pack. This “stage oneâ€￾ setup will use a relay and two packs, like Trevor Blackwell has done for his scooter. With one charger, I’d have to manually open the scooter and move the packs. With a second charger, I can pop both charger connectors, attach them to the batteries, and use an inline plug to keep the batteries permanently mounted. This should work fine, especially with diode protection inline in each battery, but does require a second charger, and the number of wires and connectors goes up linearly with the number of packs. For 4 packs, I’m looking at 40+ charge connections (10 each), 4 charger connectors, plus all the relay and wiring space. Not ideal.
Stage 2: Single larger pack, single charge connector
To reduce the space and cost, it’d be nice to have a single charge connector for all batteries. Does anyone know if the Dewalt charger can handle parallel packs? My guess is that it would either work fine and take longer, or a charge-time-exceeded cutoff would kick in and stop the charge. Has anyone tried connecting the Dewalt charger+BMS to a 10s2p pack? This would be the most elegant, least-cost solution. I know I’d have to connect the positive and negative of all corresponding cells (balancing leads) – not just connect the positive and negative of each pack together. I guess this could be done with soldered wires between the packs. Another option is to create a single custom pack to remove the wires between packs. Let’s say I do this – should I capacity match the cells like doctorbass did on his pack of used cells? Would I need to buy a fancy charger to measure the capacity of single cells (for capacity matching)? Might there be some way to do it with my Power Analyzer Pro? If the Dewalt charger+BMS can’t handle 10s2p, then I’d have to buy a charger plus balancer.
Stage 3 would add a custom charger and BMS, but I’ll save those ideas for a later post.
Pack building questions:
Does soldering really damage the cells? High-current, pro-grade packs like the Killacycle pack and the Hybrids-plus Prius pack use spot welding, and A123 warns against soldering the cells directly. Assuming spot welding is the answer:
Where does one find a spot welder? Anyone know of one in the SF Bay Area? There plans for building one on the net, like a capacitive discharge welder, AC welders, and you can even just use a few lead-acid batteries in series, but I’d prefer to use a real one.
What does one use for straps? Does anyone know where to buy the straps used in real A123 packs, like those on the Killacycle pack? These tabs (go to bottom of page, pre-cut nickel strips) look like a reasonable choice.
Any answers to the above questions would be really appreciated.
First post!
-Brandon
