# help with PB-8



## Coulomb (Apr 22, 2009)

Tarnacc said:


> ... the PB-8 has three wires and they are white, red and black which finally brings me to my question...
> 
> How do I tell which wires on the PB-8 are the supply output, throttle input and signal return?


My guess is that black will be for the signal return, red is to be connected to the supply output, and the white will be for the analog input. But you should definitely check with a multimeter. [ Edit: and indeed my guess was wrong. ]

A cheap one from an automotive store will do for this purpose, but if you don't yet have a decent multimeter, perhaps now is the time to invest in one.

The pot box is a resistor, usually 5 kΩ (kilo-ohms). So two of the leads should show that same fixed resistance no matter what the pedal position. The other connection is to a "wiper", that can connect to one or other end, or anywhere in between, depending on the throttle position. So at rest position, I expect to see little resistance (perhaps 100Ω maximum) between two of the wires (white and black are my guesses), and that will increase as the pedal is pressed until at maximum pedal depression it should equal nearly the full resistance of the "pot" (potentiometer). At full depression, there should be little to no resistance (a few hundred ohms maximum) between the wiper and the end that you will connect to the supply output.

If you get this wrong, you could have your controller provide full power to the motor at switch-on, which of course could be dangerous. Hopefully, your controller will detect this and assert a "pedal stuck" error of some such instead of applying full power, but the simpler and/or cheaper ones may not. Best to be sure. There is also the chance that you could short the supply output and damage the controller. Again, unlikely, but again, more likely in the simpler and/or cheaper controllers.

Hopefully, you'll know how to use a multimeter to measure resistance. If not, you can find it online, and this is a good skill to have when dealing with EVs (including boats, of course).


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## Tarnacc (Feb 19, 2017)

Coulomb, thank you for the reply. I have been digging around and I have come up with some of the information you have provided but i am still not certain how to interpret my findings and translate that in to which wire goes where. I do have a multimeter and a decent understanding of how to use it, just not sure what to do with the information once I have it...

Let me put down here what I have gleaned with the meter and I am sure it will mean more to you...

testing the wires in pairs for resistance with the pot at rest and then fully rotated gives me this:

red + white = resistance of 5K resting and 5K full rotation
red + black = resistance of 5K resting and 0 at full rotation
black + white = resistance of 0 resting and 5K at full rotation



and here is what I need to figure out from that...

5V supply output = ???? (red ?)
throttle analog input = ???? (black?)
signal return = ???? (white?)


Thank you again for your time and help


edit:
OK, after posting this I sat here going over your post again and I think I got it so edited my post with what I think are the answers but i would very much appreciate it if someone can check my work.


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## brian_ (Feb 7, 2017)

Tarnacc said:


> testing the wires in pairs for resistance with the pot at rest and then fully rotated gives me this:
> 
> red + white = resistance of 5K resting and 5K full rotation
> red + black = resistance of 5K resting and 0 at full rotation
> black + white = resistance of 0 resting and 5K at full rotation


That sounds like a 5 kOhm potentiometer with the red and white wires attached to the fixed ends, and the black wire attached to the moving wiper.



Tarnacc said:


> and here is what I need to figure out from that...
> 
> 5V supply output = ???? (red ?)
> throttle analog input = ???? (black?)
> signal return = ???? (white?)


That makes sense... the black wire is the output of the pot. Red and white are constant-voltage supply and return/ground/reference... which is which of red and white depends on whether you want the output voltage to go up or down with rotation (max voltage signal at max rotation would be the arrangement which you listed).


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## Tarnacc (Feb 19, 2017)

brian_ said:


> which is which of red and white depends on whether you want the output voltage to go up or down with rotation (max voltage signal at max rotation would be the arrangement which you listed).


And i guess that is the problem. I dont understand well enough what is going on to know which way the controller wants it so i am trying my best to follow the recipe as layed out in the diagram. Really the only information I have to go on is how it is listed in that diagram...

5V supply output 
throttle analog input
signal return


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## Coulomb (Apr 22, 2009)

Tarnacc said:


> and here is what I need to figure out from that...
> 
> 5V supply output = ???? (red ?)
> throttle analog input = ???? (black?)
> signal return = ???? (white?)


Yes, this is correct, assuming that zero volts means zero RPM. The only EV I've worked on had the pot that way around. The possibility of going the other way didn't even occur to me until Brian_ mentioned it.


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## Moltenmetal (Mar 20, 2014)

You definitely want zero volts (a broken wire) being zero throttle...and come to think of it, you want, if possible, to use the pot in two-wire rather than 3-wire mode- otherwise a broken - wire would still mean full throttle...


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## Moltenmetal (Mar 20, 2014)

...and to be sure, when you use the PB-8, make sure you use the microswitch- that way you will have a means to tell the controller you want zero throttle irrespective of broken wires!


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## Tarnacc (Feb 19, 2017)

Thank you all for your responses, I feel i have a better understanding now and am proceeding with getting it together. With regards to the micro-switch... yes my pot does have one and I did not mention it here in this post because I had examined that part of the pot first and had already figured that part out.


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