simple electronics help please

[averhamdave]

I've completely rewired my Torq all the way through to a new controller and have disposed of the led "battery meter" etc - because it was broken.

I am going to handlebar mount a small (say 50x50) abs box and fit toit a couple of switches: a switch to operate the 36v lighting and one coupled to the cables intended for the "brake cut off" to effectively provide a kill switch.

I would also like to mount on the box a couple of dashboard lights to indicate "power ON" and another for "Lights ON". Problem for me is that I am dealing with 36 volts and these warning lights tend to be for 12 volt operation.

How do I deal with this? Do I connect a resister in series, if so to what value? Is there an even easier way?

Thanks, Dave

 

[Deleted member 4366]

You need to put a resistor in series with the LED, For a normal low powered red LED, You need a resistor of about 3.3k to limit the current to 10ma for a red, yeloow or green LED. You can get the current rating from the catalogue if you want to use a higher powered LED or a blue or white one. The current will only go one way through an LED, so you need to connect the long leg to the +36v. You can solder the resistor directly to one of the legs of the LED. If you want to shorten the legs of the LED by cutting them, you can still see which leg is which by viewing from the top. There is a small flat on the lower flange that indicates the -ve leg.
The formula to calculate the value of the resistor is R =((Vs-V)/i
where Vs is the supply voltage, Vl the LED working voltage, i the LED working current.

 

[fishingpaul]

After fitting a replacement controller on my torq,i still use the same lighting on of switch as before,and just use that as an indication that if the front light is on power is switched on and ready for use,or a slight turn of the throttle always shows everything is ok,it takes a bit of getting used to not having a battery meter to look at,but you will soon get used to it.

 

[aseb]

I've completely rewired my Torq all the way through to a new controller and have disposed of the led "battery meter" etc - because it was broken.

I am going to handlebar mount a small (say 50x50) abs box and fit toit a couple of switches: a switch to operate the 36v lighting and one coupled to the cables intended for the "brake cut off" to effectively provide a kill switch.

I would also like to mount on the box a couple of dashboard lights to indicate "power ON" and another for "Lights ON". Problem for me is that I am dealing with 36 volts and these warning lights tend to be for 12 volt operation.

How do I deal with this? Do I connect a resister in series, if so to what value? Is there an even easier way?

Thanks, Dave

Resistor in series

R = (Vs - Vf) / If

= (Supply Voltage - Forward Voltage) / Forward Current

Note that If is in Amps, NOT Milliamps! (20mA = 0.02A). Current drawn by your bulb depends on the bulb you use- but far better would be an led which last longer and are more vibration resistant , lower current than bulbs, come in lots of pretty colours, brightnesses, you can get mounts for fixing them into boxes (or just use silicone sealant). They can have different forward voltages but there are loads of calculators on the web to work out the resistor needed to drop your voltage to the needed level. How about a battery meter- there are led ones that indicate different voltage levels on ebay, some already set up for ebike voltages. And the there are digital gauges that will give a read out of the voltage (but will need a 5V or 12V feed- there are voltage converters to do that)

led voltage indicator
meter in blue- other colours available
voltage converter
Electronics 2000 | LED Series Resistor Calculator

 

[NRG]

Just to add to the other helpfull posts: A picture is worth a thousand words etc: LED calculator for single LEDs

Use a 1~2w resistor @ 36v depending on LED.

 

[z0mb13e]

You might want to look at a voltage regulator rather than a resistor as at 36v you are going to be wasting a lot (relatively speaking) of power just to light up an LED. I say relative as its a lot of power dissipated by the resistor in comparison to the power required to light an LED. Something of the order of 1Watt when compared to around 100mW.

Perhaps this would do the trick http://www.maplin.co.uk/media/pdfs/Module 8067-1.pdf

On the other hand when you have several hundred watt hours to play with, what's a watt between friends!