Simple high voltage Precharge resistor.

[shock]

Don't blow up your controller, a simple very cheap, very effective precharge resistor before assembley.

Put inline between batt and controller for 10 seconds. Remove. Plug in Battery as normal.

 

[Racer_X]

Will this really work?

 

[Ypedal]

that's a HUGE resistor..

I do it using a tiny one, and watch the votlage climb on the CA.. 3 or 4 seconds.. then click in the main contactor on my RC bike.. works well..

 

[Racer_X]

So the caps stay charged for a couple seconds after you disconnect the Precharge resistor? Then just connect the battery and no spark?
WoW the best Ideas are truly simple!

 

[Ypedal]

i've done it both ways.. on my RC bike i rigged up 2 switches.. 1 is the pre-charge.. flip it first.. leave it hooked up.. then flip the 2nd switch for the main contactor.

The other method will still spark if you dont work fast...

 

[Racer_X]

OK, the catch with technique is the window of opportunity is short, maybe 1 second?

 

[neptronix]

Here's my take on it. You can keep this one permanently connected, and your on/off switch is a single 4mm bullet.
No spark at 125v. Nice slow voltage climb up to 80-130v

The large resistor size is just extra insurance. the 5-10w units just dissipate a lot of heat.
You may not need such a high wattage rated resistor, but i always overbuild things and thank myself later when i start running more power because i never have to screw with it

It would be cool to put something like this into a little project box with a proper switch that can handle a lot of constant current going through it.

Sorry to threadjack, but this is just another idea to think about.

 

[teklektik]

Pre-Charge Resistor Help.

 

[Racer_X]

Nice precharge resistor solution Neptronix, those pictures and illustration help alot. I have read that whole thread teklektik, and it was pretty long, though It did help me understand what value resistor I needed. Now I bought a 10 pack from ebay for 99cents.

 

[shorza]

Why can't the resistor be on the negative line?

 

[Hyena]

It can be. Traditionally in electrical circuits you tend to switch the +ve as the -ve is often earthed or has a common rail where there may be an alternate path through. But in a case like this when you're interupting the main high current battery source either wire is fine.

 

[shorza]

Cheers.

 

[recumbent]

Thanks guys I'm makin one tomorrow 8)

 

[John in CR]

Some controllers draw down the caps pretty quickly, so precharging and disconnecting to connect the main wire doesn't always prevent the snap. I simply use a resistor with alligator clip terminated extensions, but I rarely disconnect so a temporary rig is fine.

Also, I don't have much patience for waiting, so I use a 100 ohm resistor, and I can only see a spark if I look very closely and no snap at all.

 

[Racer_X]

John in CR, sounds pretty simple, can you share a picture. Thanks

 

[John in CR]

John in CR, sounds pretty simple, can you share a picture. Thanks

It's gotta be the least worthy of a pic item I've posted, but here you go. A pair of 50ohm resistors in series and taped up. Most of the time I just use the resistor. Note that it's also good for discharging caps, something you should always do before opening a controller or storing it, so you don't accidentally short it on something. I like to plug the +/- leads together, but be darn sure to discharge first, especially with the bigger controllers. The snap is more like a gunshot on discharge. My son and I each forgot once, and you don't forget again.
View attachment 1
Here's what I used it on last. The Sheriff, my Cannondale SuperV with Hubmonster in the rear wheel. Probably the most powerful hubmotored electric bike on the planet. I had to get that in before Esoria figures out his controller problem, since his hubbie is even more powerful.

Due to the overly simple pic requested, I just had to include a gratuitous pic, especially since I haven't shared any pics of the Sheriff since I prettied her up a bit.

John

 

[Racer_X]

WoW what a bike! Thanks for sharing the pictures. I just got back from the store with a 10pack of banana clips. Without your picture I was thinking of putting banana clips on one edge and andersons on the other edge. I think Banana on both is even better than I thought so I am not limited to just andersons, can do bullets or whatever else.

 

[John in CR]

WoW what a bike! Thanks for sharing the pictures. I just got back from the store with a 10pack of banana clips. Without your picture I was thinking of putting banana clips on one edge and andersons on the other edge. I think Banana on both is even better than I thought so I am not limited to just andersons, can do bullets or whatever else.

Thanks. I can't do the refined finished stuff like the real artists around here, but I'm pleased with how this one looks and performs.

I use Deans, and usually just use the resistor, one leg touching the male and the other touching the female to precharge. Then just plug together.

 

[shock]

You do need to work fast for this method, how fast depends on the controller.

I understand that connecting a switch circuit is a better solution but it is more complex.

This is supposed to be as simple as possible, and can work on any pack & controller quickly.

Basically just tops the caps off, so they are not completely empty when you connect.

 

[nicobie]

Hey John,

Who cares if you jacked this thread!

That is one seriously good looking bike. It is your best yet and I'll bet it goes like a bat out of hell.

Wish you weren't so far away. I'd love to take it out for a spin. That bike is just begging to be raced along side Luke and the other fast boys. You need to find a way to get to one of the SoCal races.

 

[John in CR]

Thx Nicobie. She's definitely F.U.N., not in LFP's class, but getting close to as much as I can handle despite being severely controller limited. I'll definitely get there someday, though it's starting to get too fast for me to be the pilot.

John

 

[sn0wchyld]

why is everyone using such massive resistors? I've got 2 2watt 150ohm resistors in series for my 100v pack... no spark, and the resistors don't warm up by any noticeable amount (they still feel room temp after connecting up my controller) I have mine shrink wrapped against my wires so its ultra low profile... and I use a short piece of ~20g wire to connect it. sure, when I first connect my pack the resistors will see about 33 watts, or about 15 watts each, but that drops off so rapidly that they dont even get warm.

My circuit is pretty much the same as neptro's, minus the switch. I just leave it permanently connected in parallel with the main discharge wires. even if you're drawing 100A through that circuit (ie the reistor in parallel with your main wires+connector) you're only going to have about 16mA going through the resistors (assuming a very generous 50mohms for the connector+main wire). At 100v thats 1.6W of power going through the resistors. So there's no issues leaving them connected during normal ebike use, even when drawing 10kw.

 

[shorza]

I have a 300ohm resistor for my 20s pack, but it's only 0.5 watt.
Is that too small?

 

[neptronix]

You're out, what, $1 if it's not?

It would be interesting to see a cycle analyst shunt model, or turnigy watt meter to measure the incoming current spike.

The bigger the caps you have, the higher the voltage, the larger the spark.

 

[shorza]

I know it's cheap, but i just don't want to screw anything up. If it doesn't sound too bad, i'll go ahead and do it.