How do you prevent your connectors from arcing?

[TopherTheME]

I'm currently working on my battery pack for my E-bike and of course the wires arc every time I connect the battery to the controller. Does anyone have any good solutions to stop this from happening? I was going to make a second set of connectors in series with a 100Ohm resistor to precharge the caps in the controller but am wondering if there's a better way.

 

[oatnet]

The sparks come from the capacitors in the controller charging up fast. They often mar the contact surfaces of the terminals thereby reducing their conductivity. Put a resistor across one of the connectors to slowly charge them first; some folks add a third connector using a resistor.

Or put a power switch on the positive lead, switch it "off" before hooking up the battery, although the controller still sucks in a spike when it turns on.

My favorite, protect your controller from spikes too. Put a power switch on the negative lead too, and a resistor across the terminals. Turn the positive-side switch on first and the caps in the controller will charge slowly through the resistor on the negative-side switch. Turn the negative-side switch on too for full power. This gives you the added bonus of being able to shut your batt down from both sides.

Add a fuse or breaker in the very middle of the pack to split the voltage, and you will have a lot of important safety features covered.

 

[neptronix]

That's the best way to do it

http://scriptasylum.com/rc_speed/nospark.html

 

[TopherTheME]

OK, so it looks like the simplest way to do it is the way I've already considered. Well, a pre-charge with a 100Ohms resistor it is then.

Anyone tried using a big inductor in series with the battery? I thought about it for a second but figured that when cutting the throttle back there would probably be large voltage spikes that could blow the mosfets.

 

[Joe Perez]

I can't see how this arcing behavior would cause any damage; at least, not with any of the sort of connectors I'd imagine being used in this application. Be it a fancy Anderson connector or a simple hardware-store bullet connector, the initial point of contact (the tip) shouldn't be the same area that's bearing the full electrical load when the connector is seated and the motor is operating.

 

[fechter]

Anyone tried using a big inductor in series with the battery? I thought about it for a second but figured that when cutting the throttle back there would probably be large voltage spikes that could blow the mosfets.

In theory, the capacitors in the controller would take out any spikes from an inductor on the battery. In practice, the battery behaves like a large part of the controller's input cap, so isolating it might cause the controller caps to heat up and blow. It would also have significant DC resistance which would create loss.

 

[John in CR]

I can't see how this arcing behavior would cause any damage; at least, not with any of the sort of connectors I'd imagine being used in this application. Be it a fancy Anderson connector or a simple hardware-store bullet connector, the initial point of contact (the tip) shouldn't be the same area that's bearing the full electrical load when the connector is seated and the motor is operating.

The connectors get damaged with each arc and the current surge wears on the caps. In addition there has been an odd controller failure attributed to the lack of a precharge resistor. Proper EV wiring has included precharge resistor requirements for decades.

My suggestion is to set your bike up to very rarely need to disconnect the pack. Why go to that inconvenience regularly. I use precharge resistors to protect my controllers, but eg the battery pack on my daily rider hasn't been disconnected in almost a year. I just have a keyswitch to power up the controller via the low current wire. That also is my emergency cutoff in the event of a runaway condition, and a fuse at the battery is the safety in the event of a short. Not only is disconnecting your pack an unnecessary inconvenience, but it also opens you up to a variety of potential failures. How often do you think Prius owners disconnect their battery mains?

 

[Joe Perez]

The connectors get damaged with each arc and the current surge wears on the caps. In addition there has been an odd controller failure attributed to the lack of a precharge resistor. Proper EV wiring has included precharge resistor requirements for decades.

I'm not really clear on what the failure mode would be for the capacitors in question. Drawing a spark in this manner should not create a voltage potential greater than BattV, and we subject large power supply caps to huge inrush loads every day in our industrial power supplies, without precharge resistors. Generally speaking, we tend to kill electrolytic caps by subjecting them to prolonged high temperatures (power supplies located in poorly ventilated areas), but these failures don't usually occur at turn-on.

As to the connectors, yes you will see a pattern of degradation over time. But again, this will occur at the point on the connector where initial contact is made, which in the case of any connector likely to be of interest to us, will not be the same point across which current flows when fully seated.

How often do you think Prius owners disconnect their battery mains?

It's funny that you mention this. My first Hybrid experience was when I rented an Altima in Carlsbad for the purpose of driving to Phoenix and back. Late one night while at the jobsite in Phoenix, I found that if you tap the power on button in a certain way, it "hangs" the car (basically a controller crash), and the only way I could figure out to clear this condition was to pop the trunk and power cycle the car by releasing and re-inserting the HV quick-disconnect which Nissan rather helpfully placed within easy reach. (I don't recall that it sparked when re-connected.)

Hopefully Nissan has corrected whatever allowed this to happen.

 

[spinningmagnets]

I don't understand all of the many things that affect the potential controller damage (I have a reluctance to learn about inductance) , but....

A precharge button and resistor is pretty cheap, and the controller costs a lot more. I will also be adding a permanent charging socket so I can charge the battery while its still connected to the controller in order to reduce the number of main lead dis-connects

 

[amberwolf]

(I have a reluctance to learn about inductance)

Inductance is just like capacitance, except it is in series with the circuit in question, rather than in parallel. So it works teh same way, storing a charge, though it's mechanics are different.

A capacitor stores it chemically/statically, as a voltage across the plates. When the voltage of things connected to it are above that of the capacitor, current flows out of the circuit and into the capacitor. When the voltage of the things connected to it drops below that in the capacitor, current flows out of the capacitor into the circuit.


An inductor stores it magnetically, as a field around the wires/core. When the current flow thru it changes, that field changes trying to keep the current the same as it had been. When the current flow decreases, the field (partially) collapses, forcing more current to flow to try to keep the current the same. When the current flow thru it increases, the field expands, "absorbing" some of the current to create that field, which reduces that increased current flow closer to what it had been.

 

[John in CR]

I thought inductors slowed electricity, not stored it. Not something I'd want to intentionally place between by battery and controller, but I understand it can be a good thing between our controller and motor, since typical ebike controllers simply aren't up to the task of delivering the current many of our low inductance motors want to draw.

 

[amberwolf]

You can think of it as "delaying" the electricity, I suppose (though "slowing" it bugs me for physics reasons ).

Either way, the energy is at least temporarily stored as a magnetic field, as long as the current flows thru the inductor, and changes to the current flow change the field, which change the current flow itself.