Adding lights (DC-Moto controller)

[Scooter McGavin]

New (and first) build - using a CSC kit. Everything went together *really* well on a Giant Sedona DX frame.

I have the generic DC Moto controller and a SC-900 display. I'd like to add some lights and have them switchable from the existing function on the SW-900.

I don't have a switched wire at the controller controlled by the light function. There is an unused red/black wire feed that shows main battery voltage when the SW-900 is turned on. I believe I read that there are potentially solder pads inside the controller for a switched light signal. Can anyone confirm this. I'm quite competent at soldering and if I can add a switched feed to drive a relay I'm off to the races.

Thanks people! First post. Managed to get 120km on the bike a few weeks ago before we plummeted back into winter in Canada.

 

[calab]

What are the voltages of the lights that you require?

 

[Scooter McGavin]

I'm guessing that 12v will give me the most options. Once I have the LCD switching a relay I can decide on wiring, whether it be in series at battery voltage or with a DC-DC converter.

 

[amberwolf]

Even if there is a place in there to run a light, it's going to be for something very low power (a few mA to a few dozen mA) and at your battery voltage.

Some of the displays have a direct switch inside them to do the lighting, which turns the backlight on and off as well. If it turns out there's no electronics inside the controller to do any lighting control, then you can use the display's internal switch to turn a relay driver chip or transistor on/off with it. (I don't recommend directly driving a relay with it, so you don't potentially damage the display itself from any of a number of possible problems).

Then you can use the relay to switch battery power to either lights that run off battery power directly, or to a DC-DC that powers them.

I don't recommend running lights in series to get them to work on a higher voltage; if anything fails shorted inside any of them the rest will suddenly have MUCH higher voltage on them.... If anything fails open inside any of them you suddenly have no lighting at all.

 

[calab]

Does your battery have a bms?
You can get lights that are 12v-80v to run right off the battery.
Hate to leave the light on accidentally and drain your main ebike battery for riding. When riding, your light will use up watt-hours and that will reduce your total distance ridden. Could be an aspect to look at if you have a low watt-hour battery. Could use a 18v tool battery for a light then thats now 2 batteries you'll have and maybe 2 chargers - its an option.

 

[Scooter McGavin]

Even if there is a place in there to run a light, it's going to be for something very low power (a few mA to a few dozen mA) and at your battery voltage.

Some of the displays have a direct switch inside them to do the lighting, which turns the backlight on and off as well. If it turns out there's no electronics inside the controller to do any lighting control, then you can use the display's internal switch to turn a relay driver chip or transistor on/off with it. (I don't recommend directly driving a relay with it, so you don't potentially damage the display itself from any of a number of possible problems).

Then you can use the relay to switch battery power to either lights that run off battery power directly, or to a DC-DC that powers them.

I don't recommend running lights in series to get them to work on a higher voltage; if anything fails shorted inside any of them the rest will suddenly have MUCH higher voltage on them.... If anything fails open inside any of them you suddenly have no lighting at all.

This is excellent stuff here. I was hoping I'd know if there are pads in the controller before I opened it up but I guess we could possible all learn something here. I suppose I'll carefully probe it with a meter and see if I can find a display controlled signal.

 

[amberwolf]

Myself I prefer that my lighting and my motor are totally separate systems, including power, so that failure of one does not impinge upon the other.

Everyone's situation and needs are different, but for me, riding on the streets, lighting is so important that I wouldn't want a controller failure of any kind to cause the lights to go out--even if I'm stuck pedalling (or *especially* so, since I'd be so very much slower, less than walking speed), from traction-system failure, I still need lights to see and most especially to be seen.

So my own system uses a separate battery for the lights, and I use the headlight switch on a handlebar control (that also has the turn signal switch on it) to turn a regular 30A automotive relay on that turns all my lights on. I *do* have it wired so that turning on the main traction battery turns on a small DC-DC that turns on a relay that connects my lighting battery to the system, but I also have a bypass switch to short across that relay if anything goes wrong with that relay, the DC-DC, or the traction battery.

Some links to various images of my lighting; I don't have a complete wiring diagram of it ATM, though (something I need to make).

The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier

Completely overcast, midday; these are still easily visible so make reasonable DRLs. With just power on, the white lights They're so bright at night I might setup a switch to cut in a set of diodes or a power resistor to drop the current to the white lights down for nighttime in...

endless-sphere.com

Ebike lighting


Also note that if you're using DOT lighting, it actually uses 13.6v for proper operation, though most of it will run as low as 10v and as high as 15v.

 

[fill]

I would suggest either using a 2nd dedicated lights battery or pulling a full voltage supply directly from the battery, and using a step down voltage convertor if necessary. Even when controllers/displays have a switched lighting circuit its often limited in the amps or milliamps it can switch and supply without burning out. many aftermarket lighting options can easily surpass the amp ratting of controller switched lighting power which can if blown have a knock on effect with other controller/display components and functions.

 

[Scooter McGavin]

Yes I agree completely. As mentioned, I planned on using a relay to protect the fragile transistor doing the switching.

 

[Scooter McGavin]

What's the consensus on running battery voltage to a dedicated switch and stepping it down afterwards to lamp voltage to avoid any parasitic power draws? Obviously a fuse would be mandatory.

 

[harrisonpatm]

What's the consensus on running battery voltage to a dedicated switch and stepping it down afterwards to lamp voltage to avoid any parasitic power draws? Obviously a fuse would be mandatory.

I do this on a regular basis with DC-DC converters, in multiple different applications. Switch and fuse the input side, just make sure your switch is overrated for that purpose (not sure what voltage you said you're using)

 

[amberwolf]

What he said ^^ ; make sure the switch you use is rated for DCV (not just ACV) higher than your battery full voltage, to minimize the chances of the switch welding during the usual arcing as it turns on.


But...if you already have a main battery cutoff switch, then you don't have to worry about parasitic draws, because that will turn the DC-DC off, too. In this case you can simply use any of the common "12v" switches for automotive or motorcycle / etc use. This is what I do, using a handlebar control for lights, turn signals, etc.; there are many of them. (mine controls a relay to switch the lights but that's because I have so many I didn't want to run all that current thru the tiny wires I have from all the handlebar controls; it's not necessary for setups with properly thick wires for the current, etc).


This is the general type of control I'm using; there are many styles; I've had to figure the wiring out for each one I've used over the years as none had accurate (or any) wiring diagrams.

https://www.amazon.com/gp/product/B07JXSBZMR

 

[Scooter McGavin]

Still gathering parts to make my lighting dream a reality. A couple more simple questions;

Looking for a 12v (13.8 is fine) headlight that will be at least as bright as my current trustfire torch - (Cree LED, single 18650) It throws out a good 100 meters and has a nice spill.

Is there a buck converter that can handle the 55ish volts that my fully charged main battery holds? I've always got a pile of the LM2596 based ones in the parts jumble but the highest input voltage I've seen is 40v.