Electric bikes don’t use excessively high ampages, or at least they shouldn’t in theory. A 300w motor on a 36v battery, should use just 300\/36 amps, or 8.333 amps. Of course this is not how smart motors work, nor how electronic controllers work. What happens is (as described by someone with the simplest of knowledge) is that a controller gives a consistent current and voltage, but uses pulse width modulation to simulate reduced voltage and ampage to control motor speed. for a 250w motor this is about 15amps, and for a 300 about 17 amps (I may be a couple out, but you get the idea). From this, I would quite happily assume that the controller will draw 36v at about 8.5 amps, and the motor will be drawing 17 amps or so.<\/p>\n
Either way, I fully expected 45amp Anderson connectors to provide adequate connections, even at 36v. Early on in the adventure which is electric bikes, I melted the bullet connectors provided with the controller and the motor, which were flimsy at best. So I replaced these, and all battery connections internally and to the controller with the 45amp Andersons. The exception to this is the 50amp Anderson used to plug the battery onto the bike.<\/p>\n
Before I go any further, none of the problems I have had have been seen on my wifes bike, which is built to the identical specification. But she does weigh 40kg less than me, and gets a lot more distance out of her batteries, so I am assuming she uses less current at peak moments than I do!<\/p>\n
Our batteries are built in two packs of 6 cells, which are held in a pair of panniers. Heavy gauge wire is used to connect one pack to the other, and plugs are used to connect into the BMS and into the bridge wire which is part of the pannier set up. So each set of batteries has three pairs of Anderson connectors within each battery. I also use Andersons to connect the battery lead to the short leads out of the controller, and to connect the green, blue and yellow motor power wires to the controller.<\/p>\n
Anyway, 45amp Andersons are crimped onto the cables. I am using a fairly heavy duty cable (50amp) for the wiring within the battery, but it fits just nicely into the connector, and appears to crimp down very well, nice and tightly. However, I have melted two sets of motor to controller connectors, and this appears to be at the actual metal to metal connections within the Anderson connectors. This could be because the connectors are getting slightly distorted when I crimp them, or just a weak piece of metal, or maybe the current is going too high for two long a period. One of these actually burnt out at the bottom of a long descent, so there was no real work going on to warm things up.<\/p>\n
The other problem happens where the connections are taken apart and reconnected regularly. Despite making excellent crimps, I repeatedly find that the wires are loose in the connectors, and suspect this may be the cause of some of the random cut outs. Last night I found two bad connections on one battery pack while attempting to diagnose the cutouts.<\/p>\n
So, time for a change. I wish I had come across this post at electricbike.com<\/a> before now. It doesn’t have many good things to say about Anderson connectors, or the other common alternative Deans Plugs. It does have many good things to say about the hexTronics XT60 and XT90 connectors. These appear to be high quality bullet connectors in a nylon moulding, which have positive and negative terminals, and are polarised and therefore very safe to use with LiFePO4 or any other LiPo batteries. The wires do have to be soldered rather than crimped, which is a very good thing given the results I am getting with crimping! I soldered the very heavy gauge wires into the 50amp Andersons OK, so these will not be an issue. Given that I seem to be drawing some momentary or maybe longer duration high ampages in my system, I have decided to go with the XT90 plugs and sockets rather than the XT60.<\/p>\n So what to do about the three motor connectors? Obviously the three colour coded bullet connectors are long gone, and the colour coded Anderson connectors connected together and arranged into plugs and sockets that cannot be connected incorrectly are already partially gone. So I need something that is not possible to get wrong! The best I can find is the MT60 from a company called Amass, which looks like a three terminal version of the XT60, soldered in wires, and a clover leaf type pattern of three bullet connectors. They don’t get very good reviews from some users, but I might try them anyway, otherwise I may have to go for just high quality bullet connectors<\/p>\n