Is there a crucial need for a contactor/switch and precharge resistor?

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eazl
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Is there a crucial need for a contactor/switch and precharge resistor?

Hello everyone much smarter than me in things with the volts and the amps and things.

First, some quick background:

I've built electric cars before through a highschool competitive team, but I was mostly in charge of frame structure, weight reduction, and aerodynamics. We used a 24 system with an etek motor and curtis controller, but we used simple Anderson disconnects as our on/off switch, and had nothing in the way of a precharge resistor (a shunt for a meter and brake lights, a fuse, and a throttle were everything else).

Fast forward to now: I am building an electric "flat track racer" with a curtis controller, and an etek motor (do what you "kind of" know) the controller I could afford can only run 36-48 Volts, and for purely aesthetic reasons I decided to run 48 volts (the bike is even with 4 batteries.)

The Questions: Can I use anderson disconnects as a "switch", and will a conspicuous lack of a precharge resistor fuse the connections together and fry the controller?

If i can use an anderson disconnect, but need a precharge resistor, any idea how to do this? a smaller disconnect with the resistor? I've heard you can use light bulbs for this.

I am trying to keep this build bare bones, but safety of course needs to be paramount. we never had trouble with our disconnect setup on a 24 volt system, but if I'm about to fry myself on startup, let me know!

Thanks

Mike

Spaceangel
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Re: Is there a crucial need for a contactor/switch and ...

Can you explain why you think might need a pre-charge resistor? Usually a precharge resistor is needed to prevent contactor from welding upon charging of B+ caps. If you run a 120 volt or more yes a precharge resistor is needed for welding can occur very easily but 24-36-48 well maybe.
As for an Emergency Disconnect, how about~Anderson P/N 114200s1 and also Anderson P/N 114200s2 ?
http://www.andersonpower.com/ and then type in under search the Part Numbers to view drawings
The sale rep for the Northeast area is Eric Brown of Sterling MA area and he covers New York to Maine area, but there are other reps for CA and the center of USA too.

Another choice is to use a Handle connected to SB-120 like P/N 929G1 for a buck seventy two. A less expensive way out.

The Questions: Can I use Anderson disconnects as a "switch",

YES - it will not fry controller. Yes you can use as disconnect switch.
will a conspicuous lack of a precharge resistor fuse the connections together and fry the controller?

Again precharge is for welding upon charging of input Capacitors and breaking circuit is more than safe for you to do. In any way you want to do it whether via handle or real disconnect switch. Use a disconnect of some sorts to be safe. The only real good way to fry controllers is draw max current for max time Not charging and discharging of caps another way to fry controller is use 96 volts on a 48 volt controller. You will have tons of aluminum and paper and smoke.
QD_#1.jpg
I also inserted a pix of QD-1 disconnect if you want to go this way. There are so many ways to disconnect electrons.

Rus

KB1UKU

Mik
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Re: Is there a crucial need for a contactor/switch and ...

If you need an ICL depends on the equipment you use to build your EV.

Have a look at these pages for why you need an ICL to service a Vectrix:
http://visforvoltage.org/book/ev-collaborative-hand-books/6146

This information may be used entirely at your own risk.

There is always a way if there is no other way!

Spaceangel
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Re: Is there a crucial need for a contactor/switch and ...

Mr Mik
I do believe you are absolutely correct especially for Vectrix and my S-10 with 144 volt pack. But what do you think of inrush current on some thing under 50 volts? I personally wouldn't worry too much about it. I know from experience it is needed on higher voltage things with large capacitors. I hardly seen precharge resistors on Golf Carts.
Even if his flat track racer did weld a contactor, then just remove KSI. Right? Without KSI you get no PWM output. A good Hg switch could remove KSI on a spill.

KB1UKU

e-doggies
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Re: Is there a crucial need for a contactor/switch and ...

I very recently welded the stock on/off switch in my Schwinn scooter. I was running 48V to a 48V 50A controller (Yi-Yun LB-37). I guestimate that I had about 200 cycles on the switch when it failed. I am replacing the stock DPST rocker switch with a 100A manual battery disconnect with a big red plastic "key". I was still planning to use a pre-charge resistor across the 100A switch. Do you think a 250 Ohm, 10W resistor would be about right? Anyone?

I don't believe you would weld an Anderson. The arcing would occur at the tips anyway, and not on the contact surfaces. Still, I think it's a good idea to eliminate the sparks, since it's so easy to do. Having a separate smaller power pole to connect the resistor first should eliminate any potential damage to your Anderson Connectors. I like the idea of fastening one side and a having a pull handle on the other.

Spaceangel, I can't seem to think of what KSI stands for.

Spaceangel
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Re: Is there a crucial need for a contactor/switch and ...

Yamaha, Curtis, Alltrax have Key Switch Input on their controllers Without a little bit of input usually as low as 8 or 9 volt up to full B+ will usually keep PWM going. I always make sure if parking brake is on KSI gets no signal so Inspection station won't try and smoke a winding on motor. They always seem to try and that is why I dislike DC motors now. So easy to smoke one winding on armature.
So in answer of your question KSI=Key switch input.

KB1UKU

Mik
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Re: Is there a crucial need for a contactor/switch and ...

Mr Mik
I do believe you are absolutely correct especially for Vectrix and my S-10 with 144 volt pack. But what do you think of inrush current on some thing under 50 volts? I personally wouldn't worry too much about it. I know from experience it is needed on higher voltage things with large capacitors. I hardly seen precharge resistors on Golf Carts.
Even if his flat track racer did weld a contactor, then just remove KSI. Right? Without KSI you get no PWM output. A good Hg switch could remove KSI on a spill.

The voltage does not matter, only the size of the capacitors.

Check out what a 15V capacitor bank does in a welder here: http://www.99mpg.com/blog/batterypacksexpose/

I don't have the foggiest idea what sort of caps are in which controller. But if I had an unknown EV, I'd just use a light globe of sufficient voltage and see how long it lights up when used as an ICL. That gives you an immediate idea of how much energy flows in that spark upon connection!

This information may be used entirely at your own risk.

There is always a way if there is no other way!

eazl
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Re: Is there a crucial need for a contactor/switch and ...

Rus,

Thanks! That is what I needed to know. I hoped I didn't need a precharge resistor, but didn't know enough about them to rule their necessity out.

Mike

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