resistor on 100v lipo pack

wojtek

wojtek

100 kW
Joined
Nov 29, 2009
Messages
1,021
Location
Luxembourg
following ES members' advice, i have installed a resistor on my battery pack:
17w / 100 Ω / 10% tolerance
https://www.electronic-shop.lu/passive-bauelemente/widerstande/draht-hochlast-vitrohm/kh-serie-10-17-w/110463.html

When connecting the battery to controller, i am getting only a weak spark. But there is still a spark. I wonder if i could get another resistor that could completely eliminate the spark? what would the spec be?
And what is the relation between those the spec [17w / 100 Ω / 10% tolerance] and eliminating the spark. Which spec plays the role to kill the spark? [all?]

I also got wirewound resistor , 50 Watt at 25°C *, aluminium housed, fully insulated, 1% tolerance, 100 Ω..
https://www.electronic-shop.lu/passive-bauelemente/widerstande/draht-mil-standard-vishay/rh-serie-1-50-w/107166.html

just found this one with lower 0.5W but higher 470 Ω.... would that be better?
https://www.electronic-shop.lu/passive-bauelemente/widerstande/metallschicht-yageo/mf0204-serie-1/102293.html

thanks!
 

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I use a 1kohm 10 watt. Also, you can't just tap the resistor into the main line like that. You need to plug in the resistor first (so all electricity flows through only the resistor), then the main (thick red wire), then unplug the resistor. In other words, you need 2 connectors, not just one for the red main.
 
Like this, but more elegant...
After the resistor is plugged in, then connect the main connector that I have sketched in.
IMG_0016.jpg


Edit: In the above version, your resistor will be plugged in while riding. I prefer not to do that, so I have the resistor on its own wire, so that I can disconnect it without disconnecting the main power wire.
 
Yeah, the resistor doesn't do a thing in parallel like that, it needs to be in series to function.

I use (2) switches. I bypass the 2nd switch with a resistor by connecting it to both poles of the switch. This puts the resistor in series full-time, parallel to the power line.

1) I start with both switches powered off, and no current can get through.
2) When I power on the 1st switch, full current goes through it, then a little bit of current passes through the resistor around the second switch. This slowly charges the capacitors in the controller, but not enough current can get through to actually move the bike.
3) When I power on the 2nd switch, current now has an alternate path through the switch that completes the circuit, so it doesn't need the path through the resistor any more. At this point the bike is fully powered up.

I hope that makes sense.

-JD
 
thank YOU! :) it all makes perfect sense now

i guess i can use use 20awg wire for the secondary wire with resistor?
 
wojtek said:
thank YOU! :) it all makes perfect sense now

i guess i can use use 20awg wire for the secondary wire with resistor?
Click to expand...

You can use quite thin wire and it will be perfectly fine. With that resistor, you should't get any spark at all. You need to have the controller off, plug in the pre-charge, plug in the main power, then you can turn the bike on. You don't need to remove the resistor if you want to leave it plugged in so its not flopping around.
 
i doubt if you need a big power resistor. a little 1/2 watt would work i bet, about 5k if you feel you need to use the precharge resistor.

if you can charge the pack while it is on the bike, then just leave the main power cables connected all the time so you don't have to deal with the spark. then put the controller circuit current, the small red wire, on a switch to turn it off. no current will leak out of the battery. and so you don't need the precharge resistor then.
 
dnmun said:
if you put a switch in the controller circuit current wire, there is no drain on the battery when the switch is off.....
Click to expand...

This is with the controller red wire disconnected, and battery connected to the main power lead only. So the controller power was off. Just the caps and FETs powered up.

Perhaps this is true with some controllers, others have a resistor to drain the caps. In a little more than two weeks it drained my 18S 10AH pack 30%. The resistor is 10K ohms, do the math. Not a good plan to leave the controller connected to the battery.
 
im planning to keep the mains on during the day for shorter breaks when not in use [shopping, lunch ect] and disconnect the main wires for longer periods of time..
 
I agree with the others and have a similar setup:
DSC00752.jpg
The power comes from the fuse side. There are two parallel paths, one through the
big 100A switch and one through the 100 Ohm / little switch. I have a 2W resistor but
1/2W should also be OK (but a bit more risky maybe so I went for the bigger one).
The reason for 100 Ohm: with my 80V battery this limits the capacitors initial
charge current to 0.8 Amps.

You don't want to choose too big a resistor. The capacitor in the controller will take
some time to charge, typically something like 3*R*C. I have 100 Ohm and my main cap
in the controller is 220uF -> it charges in 0.066 seconds. A 10 kOhm resistor increase the
charge time to 6.6 seconds so high values should be avoided.

On power up I first throw the little switch. After that I turn on the main switch and
switch off the little one again.
 
wojtek said:
im planning to keep the mains on during the day for shorter breaks when not in use [shopping, lunch ect] and disconnect the main wires for longer periods of time..
Click to expand...

No problem with that. It would take 60 days to drain my pack completely via the resistor in the controller. If it was parked with a dead pack a few days could be bad. But a few hours is not going to be a problem.

I'm working on an FET switch that does the precharge and controls the main power and a few other features.
 
Why is everyone using 2 switches? All you need is one, with the precharge resistor wired in parallel. Flip the switch one way (the normally open position) to connect only the precharge circuit, flip it the other way and it shorts out the resistor, closing the primary circuit. Am I overlooking something?
 
"Perhaps this is true with some controllers, others have a resistor to drain the caps. In a little more than two weeks it drained my 18S 10AH pack 30%. The resistor is 10K ohms, do the math. Not a good plan to leave the controller connected to the battery."

which controller does this? if this is true then you should be able to show the current drain with an ammeter. but this is not true, and there is no resistor to drain the capacitors.

this is not a charger so there is no resistor to drain the capacitors in a controller.

if you disconnect the controller circuit current with a switch, then there is no current drained from the battery by the controller through the large red wire to the output mosfets.
 
psycholist said:
Why is everyone using 2 switches? All you need is one, with the precharge resistor wired in parallel. Flip the switch one way (the normally open position) to connect only the precharge circuit, flip it the other way and it shorts out the resistor, closing the primary circuit. Am I overlooking something?
Click to expand...

For those with high voltage/high current (like me), wouldn't the switch have to handle 126v & 100a peak? Hard to find a good compact switch like that.
 
dnmun said:
Alan B said:
Perhaps this is true with some controllers, others have a resistor to drain the caps. In a little more than two weeks it drained my 18S 10AH pack 30%. The resistor is 10K ohms, do the math. Not a good plan to leave the controller connected to the battery.
Click to expand...

which controller does this? if this is true then you should be able to show the current drain with an ammeter. but this is not true, and there is no resistor to drain the capacitors.

this is not a charger so there is no resistor to drain the capacitors in a controller.

if you disconnect the controller circuit current with a switch, then there is no current drained from the battery by the controller through the large red wire to the output mosfets.
Click to expand...

It seems that dnmun is on the warpath about there being no drain in the controller. Perhaps in his controller the drain is low. But in many others this has been documented to be false.

It is R203 on the popular infineon controllers that drains the battery if it is installed. It is about 10K and right across the capacitors. You can clearly see where it was in the following link's photo where it has been removed:

http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=17944&start=105#p477106

In my case I left the controller main power connected with the controller's small red wire disconnected with a PowerPole for a couple weeks. I was surprised to find, when I topped up the charge, that it was down about 30%. When I unplug the main power connector the topping up charge is an order of magnitude less.

Anytime someone tells you that the leakage is zero you should know that it is not true. There is leakage current in the capacitors and in the FETs even in the absence of R203, so leakage current is not zero. However what is important is the magnitude of these currents. In a healthy controller these leakages are quite low, but in an overstressed or just plain old controller they may be substantial. Capacitors especially can develop increased leakage as they age. Leakage is also a function of temperature, even healthy components can have notable leakage at high temperatures.

My experience with various batteries in various systems over many years has universally found that disconnected batteries live longer. There are always small leakage currents in systems that tend to kill batteries given enough idle time. This leads to a simple rule:

"Disconnects save batteries"
 
thank You for this interesting discussion..

i can see there are 2 approaches :)

On my other bike i have actually gone with Lebowski approach.. 100a breaker and resistor with momentary switch [i think best solution] ... so just press the button, wait a second and then switch on the breakaer switch.

this one i wanted to make as simple as possible but somehow i like to have 2 switches.. when i leave the bike and go to work or shopping, i like to switch off everything and place main switch in discreet places as an extra protection against thieves or stupid people touching anything and accidently starting the bike.

i have just ordred some 125a disconnectors ...
 
itchynackers said:
psycholist said:
Why is everyone using 2 switches? All you need is one, with the precharge resistor wired in parallel. Flip the switch one way (the normally open position) to connect only the precharge circuit, flip it the other way and it shorts out the resistor, closing the primary circuit. Am I overlooking something?
Click to expand...

For those with high voltage/high current (like me), wouldn't the switch have to handle 126v & 100a peak? Hard to find a good compact switch like that.
Click to expand...

Yes, you would need a switch capable of handling the high "DC" voltage and amperage. Unfortunately these are big and expensive. By using a precharge resistor in parallel you can get away with using a switch with a somewhat lower rating (although you may have to replace it occaisionally).

This still doesn't answer my question of why you guys are using 2 switches. I gotta know!
 
Using a single switch leaves power on the controller all the time, so the leakage problem drains your battery. Both current paths must be separately opened to prevent battery drain.

Stevil's technique of using a DPDT center off switch is one way to do both things with a single switch. SPST center off would also work, but the DPDT allows paralleling the two sets of switch contacts for greater current capacity. Still, finding a properly rated switch is not easy, many switches are not quite up to this current level.
 
Edit: Oops, I was beaten to the punch:
[Repeat]
I think the deal with people here is that they want to be able to A) have a switch for the precharge component, when disconnecting and reconnecting and B) have a switch to turn disconnect the battery without having to disconnect the plug so the controller doesn't drain the battery. Perhaps you were disregarding (B).
[Repeat]
The two switch solution is also the same, although neater, than the precharge resistor + unplugging your wires to fully disconnect.
 
Kin said:
B) have a switch to turn disconnect the battery without having to disconnect the plug so the controller doesn't drain the battery. Perhaps you were disregarding (B).
Click to expand...

Ahh Yes, You're right. I overlooked this possibility for those that leave their batteries connected. In my situation I will be removing the batteries to charge and for the brief periods that I leave them connected when not riding, the battery drain is not a concern. I'll simply turn off the controller FETs via the controller switch. This is why I prefer the convenience of the one switch method.
 
I don't use any switches. Just unplug the battery harness and use a bullet in parallel with the resistor which is permanently wired across it it. What I'd like is a dual connector with a long 2-4mm bullet connection for the resistor and then a shorter 8mm bullet that would then make contact after the long bullet for the resistor does. Maybe I'll mold one one of these days.
 
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