Controller pre charge resistor in series with bulb?

[NeilP]

I was wondering about using a momentary push button switch to pre charge the capactitors before engaging the main contactor, rather than a on/off switch and was thining maybe a bulb in series with the resistor.

The idea being the buld would illuminate/glow while a voltage is across it, but dim whn the capacitors are charged.

Have seen the many automatic latching relay ideas, but want to keep this simple at least to begin with.

Will using a push button be OK? what I ma getting at is...how long do the caps hold their charge ...what sort of time would you have between releasing the push button and turning the contactor? I am imagining the caps are going to stay as near enough fully charged for the few seconds it is going to take to release the push botton and turn the main contactor


Choice of bulb and resistor ( or just bulb? ) yet to be worked out....20 S LiPo system

Just done a quicl callc...but got to do some work now....so will fire up these figures...

12v 22W bulb in series gives 6.6 ohm...in series with 40 ohm resistor....46 Ohm at hot voltage 84 volt...1.8 amp...


comments?

 

[olaf-lampe]

A light bulb is a good idea. It has a PTC resistance behaviour, which means it regulates the inrush current itself. A common household 110/220V bulb will do the trick. Make sure, the push button can stand the current or use it to trigger a relais.
When the capacitors are precharged you have plenty of time, maybe minutes to switch the maincontactor. Even when they are already half empty, the inrush current will then be much smaller.

Good luck
Olaf

 

[NeilP]

I was thinking a 12 volt 22 watt car brake light bulb..if my figures are correct with a 40 ohm resistor I think that will give about 2 amps at 84 volt at start current...
I wonder if I have missed out something obvious though, as other pre charge resistor figures I have seen are around 500 ohm or so.

just for space, a household 240volt bulb would be a bit big...plus I do not think the filament would survive the vibrations

Neil

 

[olaf-lampe]

2 ampere doesn't sound much, but means about 150W for the resistor. You should pick at least a 50W resistor. That'll do the trick, since it's just a short period of overload.
-Olaf

 

[whatever]

I have an 86v ( 72v nominal system) that has been working well for a long time, I use an led ( green in my case but colour doesn't matter) in series with some resistors, it glows bright initially and then dims, it takes about 30seconds to dim, I'm happy with that, I could lower the time by reducing the number of resistors,
in reality I've found that it doesn't take long to get enough charge in the caps to stop a big spark when main switch is on.

 

[fechter]

The light bulb should be rated for the full pack voltage. A 12v bulb on a 84v pack will probably burn out.
A 120v bulb should be fine. The higher wattage the bulb, the faster it will precharge. I'd suggest something that resembles a night light bulb or christmas tree bulb. A 7W bulb would be under 100mA, so a small switch would handle it.

 

[NeilP]

I imagined that with a resistor in series with it, you would be get most of the voltage drop across the resistor.

I thought the buld would jsut be acting as a resistor in series with the other...a 22Watt bulb across 12 volts draws 1.8 amps...therefore 6.6 ohms...add a 40 ohm resistor in series...get most of the voltage drop across the resistor? or is my theory knowledge lacking here?

 

[spinningmagnets]

Go to the appliance parts section of a large hardware store. The bulbs that light up when you open a clothes dryer or refrigerator are quite small, and most run off of 120V. Easy to see which is the smallest one. There may even be some very tiny ones for inside the illuminated control panel of a stove, microwave, etc...

Just a thought...please post what you end up with, I think this is a good idea and I want to copy it!

 

[NeilP]

Well I'd have difficulty finding a 120volt bulb over here...all 240 volt. I believe you only have 120volt of in the USA? ...that must mean high current ratings for things like kettles, toasters, electric heaters etc

 

[heathyoung]

Well, use a higher wattage 240V bulb then! 150W linear halogen used in floodlamps would work OK. Doesn't need a resistor either, just use it instead of a resistor.

 

[NeilP]

Can't see a halogen bulb filament lasting more than 10 seconds before it rattled itself to pieces!

 

[olaf-lampe]

I imagined that with a resistor in series with it, you would be get most of the voltage drop across the resistor.

I thought the buld would jsut be acting as a resistor in series with the other...a 22Watt bulb across 12 volts draws 1.8 amps...therefore 6.6 ohms...add a 40 ohm resistor in series...get most of the voltage drop across the resistor? or is my theory knowledge lacking here?

It is related to the PTC-behaviour again. A cold bulb is almost a shortcut. That's why they all die while switching the lights on. With another resistor in series, you should be safe with a 12v bulb. I'd give it a try, you'd only kill a bulb, so what?

-Olaf

 

[NeilP]

Well, yes exactly...have boxes of them

I'll try it later today..got the bike running at last night

 

[fechter]

You could also try multiple 12v bulbs in series if a single one burns out.

 

[NeilP]

Well I may not do any of that..unless what I am doing is bad for the controller and CA.

I have the Ignition wire wired directly to the cold side of the main contactor, along with the cold side of the pre charge resistor switch.

When I flick the pre charge switch, the CA comes on..and the voltage is displayed...it soon stabilises when the caps are charged and there is full battery voltage on the still OFF, but 'warm' side of the main contactor...stabilised voltage there is a good indication that current has stopped flowing and the caps are fully charged...then I flick the main contactor.


Just wondering what if anything this does do the VOltage reg chip in the Controller. I have heard they do not like low voltages...cant remember the reasoning behind it though...comments on that?

 

[vanilla ice]

The momentary push button with an high voltage appliance display bulb sounds like a winning combo! I got to do that.

 

[ericslai]

I tested with a 120V 50W halogen bulb and it worked. The bulb's resistance was 20 ohm. I tried a 75 Kohm resistor and it did not work. Finally I used a 36 ohm 10W resistor and it reduced the spark to be a very fainted one. You may want to try a 50 ohm resistor and see how big the spark is. My fully charged voltage is 83.5V.

 

[NeilP]

I am only on the second or third charge cycle for this LIpo pack.keeping the fully charged voltage down to 82 volts ...4.1 per cell.

I did a run to work and back today...8 miles each way plus a bit around town. ...18 miles in total Used 11 Ah by the time I was home, cells were down to 3.79 volts per cell, so still a good amount left.

 

[olaf-lampe]

Just wondering what if anything this does do the VOltage reg chip in the Controller. I have heard they do not like low voltages...cant remember the reasoning behind it though...comments on that?

I believe its related to the gate voltage of the FETs. If the v-reg isn't able to deliver the full 12V, the FETs will only switch 'half' as fast and the ON-resistance is higher. When this happends during driving, it can kill the FETs.
-Olaf

 

[NeilP]

Yes, thanks, remember now
So as long as I do not open the throttle immediately with just Pre charge resistor on, should be ok
Thanks

 

[whatever]

if in series you can use led lights, each led has a given voltage drop , no need for a high volt bulb, led in series with resistors works fine, very unlikely you would throttle while precharging, if you did I doubt anything would go wrong, there will only be a tiny amount of current going via the precharge circuit, I also use a switch for the power to low voltage circuit, it has a separate led ( orange in my case) that comes on when low voltage circuit is live. Its very reliable system.