Taking the plunge with building my own Vruzend battery, couple of questions please.
Hello everyone. Like everyone else here ( probably) I grew tired of buying pre-made batteries of dubious specs and reliability. I decided to take the plunge and ordered the Vruzend kit and 78 LG MG1 (3500mAH, 10A) batteries to build my own pack. I have a couple of things I want to be sure about and would welcome any input from the forum.
Firstly , I intend to build just a basic rectangle with 13 x 6 pattern so that is 13s6p for a 48v 21ah battery. In mapping it out it appears I will end up with the overall pack positive terminal on top left and the overall pack negative terminal on the opposite end of the battery, on the bottom right as I am facing the battery pack. I assume this is because of the odd number (13) of cells in series and the alternating pattern needed for the series bus bars.
Secondly, I will be using this on a system that has a 1,000 watt motor and a 35 amp controller. After reading more closely it appears the 35 amp controller might be a problem since the pack supposedly will only support 30 amps peak (6 parallel @ 5 amps per cell). I will be riding in the Bay Area with a combination of flat, rolling, and fairly steep hills and pulling a trailer sometimes. Am I asking for trouble with this 1,000 watt motor and 35 amp controller? Last thing I want is my bike crapping out on me pulling a load up a hill because I have overloaded the battery pack. Should I go shopping for a controller rated at 30 amps or less? I expect most of the time I will not be drawing anywhere near the 35 amps but don't want to court disaster or throw away my money on this expensive battery pack.
Any help from more experienced folk would be most appreciated. Thank you in advance!
Yes, the positive and negative terminals will be on opposite sides because of the odd number of parallel groups. Not so much an issue, but something to note. You'll just run your wires to each of the terminals regardless of which side of the pack they are on. One other thing though: You mentioned the terminals being in the top left and bottom right. I'm not sure if you're referring to the single cell in the top left and bottom right, but keep in mind that every cell in the first and last parallel group will form the terminal, not just the last cell in the group. So all 6 negative ends of the first cell group are -1, and all 6 positive ends of the 13th group are the +13 terminal. So its best to use 3 brass wire clamps across all of the cells in the first and last group when adding your charge/discharge wires.
For amp draw, your 35A controller will be pushing the limit. Will it work? Yes. But your performance will be somewhat degraded. The kit will have higher resistance and at that current level will create excess heat. What this will translate to is more voltage sag and getting less capacity out of the pack. So you'll feel a bit weaker up those hills and you probably wouldn't go as far as you could. If you were in a flat area, I might say not worry about it, but in the Bay area I think you'll feel the difference. If you could swap in a 25 or 30A controller, you'll probably get better performance, as long as that level of controller can still do what you need to do.
Thanks so much for the reply Micah! I've been riding ebikes exclusively (sold my car in fact) for the last 4 years and this is the first time I've really paid much attention to the details because everything has been pre-built and I just put it all together from kits and everything worked ok. I even built my own solar charging station in my dedicated bike shed with two 12-volt solar batteries kept charged up with a solar panel. Hooked an inverter to the batteries to give me a 110 standard outlet and I plug my chargers into that to charge all my batteries. Works great and zero emissions along with zero transportation cost - I haven't been to a gas station or mechanic for 4 years now.
I also looked more closely at my controller and it is RATED at 17 amps with a MAXIMUM of 35 amps. So it should be fine. I also ordered your 30 amp BMS so I think I should be ok with everything in this configuration. I'm a tad apprehensive after knowing how dangerous lithium ion batteries can be so I'll be going very slowly and carefully!
Thanks again for your help and for coming up with such a great idea. I would never have considered doing this if it involved welding/soldering all those batteries together but your kit seems very straightforward and I'm hoping to end up with a nice homemade battery with good range and performance. Always more gratifying to have something you made yourself.
Thanks again for the quick reply and helpful commentary!