ebike brake wiring

[jhw528]

Hi, I am building an ebike with a Fardriver ND72450 controller and I have been trying to decide how to wire up the brakes.
The controller kit came with a 36V regulator for the brakes and lights. I keep seeing that the Brake High pin on the 72450 needs to be 12V to activate it. I've been searching and can't get a clear answer on this. If I apply more than 12V to the Brake High pin on the controller will that fry it, or is this simply a 12V minimum required? Thanks!

 

[amberwolf]

moved to motor + controller technology forum out of bike mechanical and structural as it is neither a mechanical nor a structurual question, but is a controller question.


That said--it is *likely* that the brake high pin will accept anything up to battery voltage, but unless the manual for the controller specifies this in no uncertain terms, it is safer to use only the voltage it does list, as a maximum.

You can always test it to see what happens at higher voltage, but it could damage or destroy the controller MCU if it's not designed to deal with it.

As a side note, most automotive / motorcycle "12v" systems are 13.6-14.4v (sometimes higher), and that brake high input was designed to be activated by that level of voltage on those systems, so it is likely that it does handle at least 15v or thereabouts. Higher than that depends on how they designed the input.

The controller kit came with a 36V regulator for the brakes and lights.

Is that 36v *output* or *input*?

Typically the DC-DCs and lights would take some higher voltage and downconvert it to "12v", which is sometimes actually just 12v (which doesn't light them up as bright as they should be, if htey are actual DOT-rated lights), and sometimes "automotive 12v" as noted above.

If so, and it's 36v *input*, then you'd need to be sure your battery is no higher than that (42v full), assuming it's meant for a 36v *battery* input rather than a 36v *power supply* input (which would be just 36v).

Just want to be sure what you have, so we can help you get it working and not damage anything.

 

[jhw528]

My apologies for the improper thread location.
the regulator takes 40-90VDC input and *outputs* 36VDC.

the lights i have are all rated from 36-72V and i tested them with my 60V battery. the only thing throwing me off is what voltage this brake high pin needs. Normally i'm the kind of person who would just throw the 36V on it and see what happens, but these controllers are a few hundred bucks a piece so id rather not blow it up for the hell of it. the only real info i have on this thing is here: NS72450/NS84450/NS96450 | far-driver where it shows brake high connected to a 12V converter. the manual as a pdf here: https://www.far-driver.com/wp-content/uploads/Fardriver-controller-Manual.pdf also shows 12V in the description on page 5.

My initial idea was to run everything at battery voltage and then put a 12V converter directly onto this pin. the issues i found here are
1) when the input voltage is removed from the converter the output still hangs at 12V for a second, meaning the after i release the brake lever the motor will still be cutoff.
-However this is measuring the unloaded output of the converter. If the brake high pin has a pulldown resistor it will drain the voltage quick enough i think
2) contantly connecting and disconnecting 72V via the brake levers may cause ecessive arcing, so having lower voltage in the brake levers may be a better idea

My ideas to mitigate both the above issues would be to either
1) use a relay, where the output of the converter hits the brake levers and the brake levers apply 12V to the brake high pin and to the relay. when the relay has 12V on its trigger input, it will connect the circuit to the brake lights with the 72V battery voltage.

-OR-

2) have the 12V conveters output connected to the brake levers as described above, but instead of a relay there is an upconverter that would take the 12V input and spit out 36V or something useable by the lights.


I was really just trying to avoid boogering up the electronics with a bunch of converters but it seems i can't really avoid that

 

[amberwolf]

the only real info i have on this thing is here: NS72450/NS84450/NS96450 | far-driver where it shows brake high connected to a 12V converter. the manual as a pdf here: https://www.far-driver.com/wp-content/uploads/Fardriver-controller-Manual.pdf also shows 12V in the description on page 5.

I poked around and while I find references to a few people on the web that have used "battery voltage" on that pin, they don't specify which controller brand or model they used, or what that voltage actually was, in the post / page linked in the websearches. They might say elsewhere in their project stuff, but I did not peruse that.

Most just say they used 12v, if they say what voltage they used at all.

You could ask Nanjing Fardriver themselves if you can get any response from them, and you can get a real answer instead of a parrot-back of the manual info. :/

My initial idea was to run everything at battery voltage and then put a 12V converter directly onto this pin. the issues i found here are
1) when the input voltage is removed from the converter the output still hangs at 12V for a second, meaning the after i release the brake lever the motor will still be cutoff.

Instead of a second DC-DC, you could use a "linear regulator", like the 7812, and no capacitor on it's output (so it just dies instantly to zero at input power loss). But IIRC the max input voltage on those is 30v...so you'd have to drop the DC-DC's output (from the brake lever to the BH pin circuit) down below that first.

Another option is a 12v zener diode, and a resistor. the resistor goes between the brake lever output and the zener. the zener goes from the brake high input to ground, and limits any input to a max of the zener rating, and voltage drops to zero as soon as the input goes away..
Like this example for a 9.1v zener. In your case the current needed for the BH input is virtually zero, so you don't need a low value resistor, and can use the max value to provide whatever current the zener requires for regulation per it's datasheet.



You'll have to check the math for this, but this is the google search AI output for the values. It used a 30ma example, but you don't need even a hundredth of that, I'd bet. You could compromise for a 1mA max output and figure out the values for a 30x higher resistance. You don't need or want any capacitors. Just hte zener and resistor.

Google Search

Calculation Example (for a tiny 30mA load):

• Voltage Drop across R1:
  
  36V−12V=24V36 cap V minus 12 cap V equals 24 cap V
  .
• Resistor Value (R1):
  
  24V/0.03A=800Ω24 cap V / 0.03 cap A equals 800 cap omega
  (use a standard value like
  
  820Ω820 cap omega
  or
  
  1kΩ1 k cap omega
  ).
• Power Dissipated by R1:
  
  24V*0.03A=0.72W24 cap V * 0.03 cap A equals 0.72 cap W
  (use a 1W or 2W resistor).
• Power Dissipated by Zener (D1):
  
  12V*0.03A=0.36W12 cap V * 0.03 cap A equals 0.36 cap W
  (use a 0.5W or 1W Zener).

The relay (DPST, 2P to keep the 12v and 36v separate, but you only need on off so 1T) plus the zener would fix boht the lever and BH pin having ot deal with higher voltages.

No second upconverter needed, etc. Can probably be built into a sugar-cube-sized "deadbug" configuration, siliconed up, and stuck wherever is convenient.

 

[jhw528]

I find it odd, it seems fardriver is fairly common controller i was convinced someone had come across this before. maybe they didn't think too hard about it lol. i reached out to fardriver via their whatsapp about the pinout and got nothing back. there's many different versions of the pinout online. i eventually just started measuring voltage on pins to figure it out.

I like the zener idea, hell i was even considering a straight up voltage divider since the 36V will be constant despite the battery draining from 84 to whatever. I could easily hide that anywhere too by just wrapping it in shrink wrap.


with the relay you are saying to use the 36V regulator as input into the zener diode/resistor network above. take the 12V off the the zener output for the brake levers. 12V from brake levers hits the BH pin and relay trigger. the relay connects the 36V to the lights. lights get proper voltage, BH pin gets proper voltage, brake levers wont arc, zener drains voltage immediately when brakes are released. it's gonna be a bit cramped but i think this is the way to go

 

[amberwolf]

FWIW I use a relay system triggered by the lever switch on SB Cruiser. I didn't have a 3PDT relay, so I used three rtiny 1/2-sugar-cube-sized seaprate SPDT ones out of some old UPS board, I think it was. All coils wired in parallel, and uses the 12v (actually 16v on my system) from the lights at the lever and the coil, so when the lever is pulled all three relays switch. The first relay switches the brake lights on, connecting 16v to them. The second relay switches the CA's ebrake input on, connecting the CA's own 5v output to that. (or maybe it was the ground that it switches, been a few years). The third relay changes which throttle is fed to the CA's input (the one on the thumb throttle or the one pulled by that swtiched brake lever). That setup allows me to use that separate throttle-on-the-lever for variable regen.

 

[jhw528]

So, on the test bench i had the relays. turned out they needed an order of magnitude more current than i was trying to provide. it wanted 150mA, and at 150mA by a 24V drop it was blasting my 1Watt resistor with 3.6W and burnt it up.... then it occurred to me that 36V is a multiple of 12V, so i flipped the circuit around and used two zeners to drop from 36V to 12V, and used the resistor to as the shunt to drain the lingering voltage at the output. I decided to drop the relay since i didn't have the correctly rated resistors on hand. removing the current requirement of 150mA i used a 10k resistor for 12V/10k = 1.2mA.

i tested the circuit and simulated the brake levers closing by just touching the wire to the 36V output of the converter, and for whatever reason this wasn't creating sparks like it initially had, so i decided this is how i will do it.

no need for another converter to occupy space, and no need for a relay to occupy space either, and to drain the voltage i use less than 1% of the current i would have with the relay (perhaps 150mA is negligible on the system i am making, but it's a nice bonus).

Thanks for the suggestions @amberwolf! I'll have to create a post once the whole thing is done