After cal3thousand's reply to my posting about how I nearly killed my battery, I've done some thinking. He's right, I should be hooking my batteries up in parallel. So here's my plan.
I have 14 batteries, Hobbyking 4s 20C hardcases. They're all good, I measured the internal resistance using lamps for load and measrung the voltage sag. I want to use 8s because I have a 24v motor, and I've been using them as 8s with good results.
I'll wire them up as two groups, one of 6 (maybe upgrade later to 8) and one of 8. For each group, I'll have four pairs of 4s. I'll connect the pairs + to -, and take the two remaining connectors out to a junction, where I'll connect the four + together, and the four - together, and connect all those to an EC5 female. That gives me 8s4p, 20 AH. I have a 60 terminal connector strip to get all this screwed tightly together - the bike can pull up to 30 amps, maybe a little more (I've checked the peak amps under load).
Between this and the bike, I'll have a connecting cable, that has a 40A fuse, a switch (with a 220 ohm lead across the switch to act as a spark-stopper, so that even while the switch is off, a small current can go from the battery to the controller so the capacitors get charged), and then I switch on and I'm ready to roll. The switch is actually a 63 amp domestic circuit breaker. And there's also a wattmeter to measure the amp-hours consumed (and peak amps, etc). The connecting cable will use a pair of EC5s, and I'll have a spare connecting cable with just a fuse inline, in case the more complex one develops a fault while I'm riding. I want to use EC5s because soldering them is easier than XT90s.
The bike will have an EC5 male, and so will the charger. And I'll put a fuse inline, 10A on the charger cable, because the charger should be supplying a maximum of 7A.
Next, the balance leads. I'll solder up a lead that connects two 4s balance ports, to one 8s balance port. And I'll make one of those for each battery-pair. While I'm running, I'll have an 8s battery monitor on each balance port, so I'm monitoring all 32 cells. For balance charging, I'll use a one-to-two 8s splitter. with three of those, I get a one-to-four splitter for the charger's balance port.
The only tricky bit, will be making the lead that connects two 4s balance ports, to one 8s balance port. To make each of those, I'll use two 4s extensions and one 8s extension, cut them in half, and solder them up as per:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=42324#p618928
Except I'm doing 4s to 8s, not 5s to 10s.
Cutting extensions in half will be easier for me than using 8s and 4s jst-xh plugs and sockets and trying to solder those.
When the 4/8 balance lead is made, I'll test it by connecting the two 4s leads to two batteries, then the 8s to a cell monitor; that should tell me that the voltage of each of the 8 cells is 4v or so. If that works, I'll connect the main leads of the batteries together, being very careful to connect the correct + with the correct -, because if I do it the wrong way round, there will be a bang and the balance cables will melt. But I only have to do that once, I won't be plugging and unplugging this when I'm out. I'll use a multimeter to check before I make that connection.
The 8 HK batteries fit very nicely in a good box that I got off ebay (I posted previously about that) and that box will go in my saddle bag. If I'm going on two routes during the day, I'll use on box, then the other. If I'm doing one long route, I can carry the two boxes in two saddlebags.
Can anyone see any fatal flaws in this plan?
I have 14 batteries, Hobbyking 4s 20C hardcases. They're all good, I measured the internal resistance using lamps for load and measrung the voltage sag. I want to use 8s because I have a 24v motor, and I've been using them as 8s with good results.
I'll wire them up as two groups, one of 6 (maybe upgrade later to 8) and one of 8. For each group, I'll have four pairs of 4s. I'll connect the pairs + to -, and take the two remaining connectors out to a junction, where I'll connect the four + together, and the four - together, and connect all those to an EC5 female. That gives me 8s4p, 20 AH. I have a 60 terminal connector strip to get all this screwed tightly together - the bike can pull up to 30 amps, maybe a little more (I've checked the peak amps under load).
Between this and the bike, I'll have a connecting cable, that has a 40A fuse, a switch (with a 220 ohm lead across the switch to act as a spark-stopper, so that even while the switch is off, a small current can go from the battery to the controller so the capacitors get charged), and then I switch on and I'm ready to roll. The switch is actually a 63 amp domestic circuit breaker. And there's also a wattmeter to measure the amp-hours consumed (and peak amps, etc). The connecting cable will use a pair of EC5s, and I'll have a spare connecting cable with just a fuse inline, in case the more complex one develops a fault while I'm riding. I want to use EC5s because soldering them is easier than XT90s.
The bike will have an EC5 male, and so will the charger. And I'll put a fuse inline, 10A on the charger cable, because the charger should be supplying a maximum of 7A.
Next, the balance leads. I'll solder up a lead that connects two 4s balance ports, to one 8s balance port. And I'll make one of those for each battery-pair. While I'm running, I'll have an 8s battery monitor on each balance port, so I'm monitoring all 32 cells. For balance charging, I'll use a one-to-two 8s splitter. with three of those, I get a one-to-four splitter for the charger's balance port.
The only tricky bit, will be making the lead that connects two 4s balance ports, to one 8s balance port. To make each of those, I'll use two 4s extensions and one 8s extension, cut them in half, and solder them up as per:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=42324#p618928
Except I'm doing 4s to 8s, not 5s to 10s.
Cutting extensions in half will be easier for me than using 8s and 4s jst-xh plugs and sockets and trying to solder those.
When the 4/8 balance lead is made, I'll test it by connecting the two 4s leads to two batteries, then the 8s to a cell monitor; that should tell me that the voltage of each of the 8 cells is 4v or so. If that works, I'll connect the main leads of the batteries together, being very careful to connect the correct + with the correct -, because if I do it the wrong way round, there will be a bang and the balance cables will melt. But I only have to do that once, I won't be plugging and unplugging this when I'm out. I'll use a multimeter to check before I make that connection.
The 8 HK batteries fit very nicely in a good box that I got off ebay (I posted previously about that) and that box will go in my saddle bag. If I'm going on two routes during the day, I'll use on box, then the other. If I'm doing one long route, I can carry the two boxes in two saddlebags.
Can anyone see any fatal flaws in this plan?
