Electric Bikes – high current connectors

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.

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.

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!

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.

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.

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.

So, time for a change. I wish I had come across this post at electricbike.com 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.

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

Hobby King can supply all of these connectors, just look for XT60, XT90 or MT60 using their search bar to have a look at whats available.

Posted in Computer Stuff, Electric Bikes
9 comments on “Electric Bikes – high current connectors
  1. Dave says:

    12 months on, and yes the connectors (and my soldering) are performing faultlessly. Last report, I promise!

  2. Dave says:

    An update on these connectors is due. I have been using them for about 8 months and a couple of thousand kilometres, on two bikes, and they have performed faultlessly. No cut outs, no overheating, easy to separate and join when maintenance is required, and they look really good too. I really wish I had found these at the start. I spoke to a radio control modeller friend of mine who swears by them for his high amperage model aircraft, which draw almost the same wattage as my bike motor!

  3. Dave says:

    I suppose the other thing that is relevant is that 300 watts is an average power consumption, peak usage may top out at 600 to 700 watts. That of course only happens when slogging up hill. So the notional ampage may go even higher, or the PWM (pulse width modulation) may get closer to 100% power. So 36v times 18 amps would be 648 watts. Translate that to a 12 volt system (which is what anderson connectors will be rated at), and it comes to about 54 amps! Maybe 45 amp connectors are just not enough, and the XT90s are a better bet than the XT60s for the same reason.

  4. Dave says:

    Its really annoying the way battery chargers show fully charged when anything unusual happens, at the start I had the connections into the charging plug reversed, and all the charger did was show fully charged. Better than blowing up I suppose!

    I am still using andersons for connecting single cell chargers etc, at low ampages they work fine.

  5. Phil says:

    Well that answers my question about the Andersons – bummer I have bought 6 pairs for connecting volt/amp/watt meter between battery and controller! I reckon solder is worth a go given that I’ve already bought them 🙁
    I’ve done a pretty big walk home – only once – over Moonshine Hill from SH58 to Riverstone with a dead battery – with a long uphill stretch and a 28kg bike/battery. There was a couple of kms of quite a steep descent at the Riverstone side of the hill – pretty wasted when I got home! I discovered (the hard way) that the charger was reading fully charged even when connected to the discharged battery and not actually charging the battery at all 🙁 I must not have looked at it when I connected the charger the night before.

  6. Dave says:

    Tyre all fixed, and several days riding over the hills with no cut outs. Looks like 45amp Anderson connectors are not something I should be using, much too finicky connection wise to be reliable. XT90s look like the best choice so far.

    Tyre blow out is down to some CST brand thorn resistant tubes I was trying. They were possibly marked and boxed wrongly, I ordered and apparently received 700×35/43C tubes. Out of the box they looked awfully skinny, especially as the thorn proof side looked like it was not going to stretch much. The first one lasted less than 10km before splitting the inside seam, and the second one did nearly over 100 km before exactly the same thing happened, just after I increased the tyre pressure a little to reduce my rolling resistance. When I get round to it they will get sent back for a refund. Normal tubes are working fine.

  7. Dave says:

    So last night I powered over the big hill on a sweltering hot evening, and there was no cutting out. Compare this with 3 or 4 cut outs the night before! It’s not conclusive yet, but looking good for having fixed the cut out problem! On the way down the other side of the hill, while busy feeling smug about the battery, my rear tyre blew out, fortunately I kept it under control, but with no spare tube, I had to take it home to fix it. So I rang the better half to come and pick me up, and she rang back 5 minutes later telling me that the car also had a flat tyre, so no go on the lift home! With 4km by the road, or two km via walkways over even bigger hills, I sweated home along the walkways. Fortunately, the “6kph” button on the controller helped me walk the bike up the hills (and along the flat bits too). Doesn’t seem like I can win with tyres and inner tubes.

  8. Dave says:

    The XT90 connectors also came, and today I finally got round to fitting them to my bike. I used 4 pairs altogether.
    Firstly, connecting the main battery cable to the controller.
    Secondly on each pack of 6 cells, to connect to the BMS.
    Thirdly, the connecting wire between the pack not on the same side as the BMS, and the BMS.
    It took nearly 4 hours to solder them all on. The power leads needed disconnecting from the cell packs for safety reasons, and soldering 50 amp cable to 90 connectors takes an unusual technique. The cable is stiff, large diameter, and unmanageable when trying to hold it into a shallow connector! Clamps, wet cloths (lots of heat involved) and lots of disassembly and reassembly was involved. High physical pressure for many seconds was required before a good solder joint is made.

    The MT60s above have performed faultlessly to date, and I did a few kilometres along the flat at lunch time, and the new XT90s worked very well. It felt like there was more power, but that may have been just wishful thinking. Going over the big hill tonight should be the acid test! There should be much less resistance in the system, some of the Andersons just pulled off again, so they can’t have been doing much good! With all connections how soldered instead of crimped, hopefully the bike will be a lot more reliable.

  9. Dave says:

    The MT60 motor connectors arrived, and have been soldered into my bike. Shrink wrap was applied to all three wires in each terminal, the terminals were put together while the soldering took place, to act as a bit of a heat sink and to stop the connectors distorting. Clever little cable covers were also used, and the finished article looks very good. Unfortunately, due to a knee problem, I have not really test ridden them yet, so more to come, as well as some photos eventually!

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