First some background: I guess I never shared it here, but I've made my own ebike, including the battery, and everything works, but I like to leave the battery disconnected from everything when not using it. Both for safety, and to prevent any phantom draws. The battery is 33.6V when fully charged and could deliver over 80A briefly, though I have a BMS which prevents that. The motor/controller doesn't use more that 40A at full throttle, though I'm not sure that's important.

So the issue is that I have the battery connected to everything else via an XT60 connector, and there is a pop every time I plug it in. I'm assuming there's a capacitor getting charged very quickly somewhere? I'm thinking of replacing and/or adding a switch to the connector so the switch will pop instead of the connector. But ideally I'd like to eliminate the pop or at least reduce it. I feel like that would be better for all the components involved.

All I can think of is to put a resistor and momentary switch in parallel with the main switch to slow the initial current down until the capacitor is charged, then turn on the toggle switch. I feel like that could get old quickly though. Is there another relatively simple solution that I'm not thinking of?

 

Is this pop from the connector when plugged in or somewhere else?
What is everything thing else?
Can you isolate the pop to one of those peripheral devices?

 

could use a battery disconnect switch. A snap acting one. Connect your battery pop free then turn the disconnect on. That type are designed to slap the contacts together real quick, minimizing arc on forklifts and stuff.

 

The pop is definitely happening at the point of connection; the XT60. The "everything else" are two voltage regulators, one 12V out for fans and lights, one 54V out to the motor controller. I suspect the 54V regulator is what has the large inrush current. It's pretty beefy to handle the current for the motor.

I figure a proper switch with substantial contactors would handle the inrush current ok. I'm curious though if there is a simple way to reduce the inrush current so as to be easier on whatever capacitor is on the receiving end.

 

If you could find a SPDT 40A switch with center-off, you could wire one side through a small-value resistor (e.g. 10Ω) and the other side direct.
You would first go to the resistor side to charge the capacitors without a pop, and then quickly switch to the direct side for normal operation.

Here's an example of a 20A DPDT center-off switch.
That should work if you connect both contacts in parallel so it acts as a SPDT switch.

 

Use a three position (PIN) connector with one shorter pin. Add a suitable resistor between one long pin and the short pin, with the power circuit using the lone long pin anad also the short pin of the long-short pair. Then when the long pins connect the system is powered thru the resistor, and when the shorter pin connects then the system is already charged, so no pop.

 

if you do not like switching manually, one could build a small inline circuit that has the mentioned 10 Ohm power resistor which is then automatically bypassed after suitable delay or when voltage difference between input (battery) and output (bike) is sufficiently small.

bypass could be done with either MOSFET or relay.

if using mosfet, pick one with low Rds on (1 milliohm or less) to minimize losses (heat dissipation). for example NTBLS0D8N08XTXG or AOTL66608 is just few bucks and it would dissipate only about 1W at 40A. this is less than relay coil would need or a relay that can handle the same specs. everything could be fitted on a small board. for a piece of mind i would still fit small heatsink on the mosfet. the biggest component would be the 10 Ohm resistor as it would need to handle some 160W for few seconds.

 

Keep in mind that this is a "motorbike", probably of some serious capability. At least that is what I get from the picture. Although 40 amps is not HUGE, it could be exciting if things go wrong.
so now I just had another idea, which is to add another connector that would connect thru a resistor to charge the capacitor before making the main power connection. The benefit is no electronics to build, just one resistor , so it will not take much room. Much simpler, as well. The down-side is adding another connector, but it will not need to be a high current connector.