# Question about relay



## Yabert (Feb 7, 2010)

Hello

I'm converting a really nice tractor* and I have a question about a relay.
Because it's a tractor the motor need to spin by itself. No accelerator pedal, just a ''clutch'' who is press to give 0K signal to the controller and releise to accelerate the motor (a mecanical system is acting as throttle. Variation of 0-5K).

So, everything is good except one thing. When the tractor is turn OFF, if the driver don't push the clutch when it turn ON the tractor the controller will receive up to 5K and that will be dangerous (motor will spin).
My plan is to have a relay who is open when the tractor is turn off and don't energised when the tractor is turn on, but only energised (and stay energised) when the driver press the clutch down (a limit switch will take this signal and energised the other relay).
Hope the shematic will help you a bit to understand.
I think I'm looking for a ''bistable'' relay, but I don't know. My strenghts are in the mecanical side.

So, is this kind of relay exist?


*Sadly, the customer don't understand batteries and decided to go wih lead.


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## onegreenev (May 18, 2012)

Should use a controller and throttle. Be safe. If its for someone else it should be mandatory to use a controller and throttle of some kind. You could put a stick throttle. I have one on my Kubota. I have a foot one and stick one to put it in one speed and go. It over rides my foot throttle. Pull back on the stick and slow down. Pull back and you get your throttle back. I can over ride the stick if my foot throttle goes above the speed set by the stick. But don't just rely upon a contactor for your speed and throttle switch. If it fails at a bad time bad things happen.


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## Yabert (Feb 7, 2010)

onegreenev said:


> Should use a controller and throttle. Be safe. If its for someone else it should be mandatory to use a controller and throttle of some kind.


I use a controller and a 0-5k throttle. But the throttle is working in reverse direction (release = full speed, pressed = no speed). So, no need to press the pedal to cruise at 3 mph down the field.


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## Duncan (Dec 8, 2008)

Hi Yabert

Just use a hand throttle - like a proper big tractor - not on a spring but held by friction so that it stays where you put it

You can control on the hand throttle or push the pedal to go SLOWER

Just wire the two throttle pots in parallel

The foot pedal would go from 10K - foot off to 0 foot down
The hand throttle would go from 10K - max (rabbit) to 0 Min (turtle)


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## Yabert (Feb 7, 2010)

Yes, but same shit can happen if someone turn on the tractor when the throttle aren't at 0.

In fact, same shit can happen with a diesel tractor, but a 12v starter produce a way lower torque than the 11 inchs motor powered by 700A controller.
A diesel tractor will move a bit and stop. The electric tractor will pop a wheelie and crush anything on his way.


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## piotrsko (Dec 9, 2007)

Then use a foot switch on the left side to connect the stick throttle when depressed. Much like a clutch sense switch on a CAT D9. If the switch isnt depressed you get nothing.


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## Duncan (Dec 8, 2008)

Hi Yabert
Yes - I have been working out how to do this and you are right
you need a "latching relay"

http://nz.rs-online.com/web/c/relays/general-purpose-relays/latching-relays/

Use the hand throttle but with a limit switch wired to the relay - or your clutch


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## Yabert (Feb 7, 2010)

Exactly!!! Latching relay.
Today Duncan, you have saved a farmer to do an undesirable wheelie with his tractor 
Thanks

So now, what do you guys think about cutting the ''key switch'' terminal of the motor controller. Is it safe enougnt? 
Latching relay will fail open if it fail. So, what wrong can happen.

And let me know if you know a good/reliable latching relay who work on 48v and is seal (weather proof). Ebay, mooser, etc.


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## Duncan (Dec 8, 2008)

Hi Yabert

If you use the latching relay in the throttle circuit then you don't need a big expensive one


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## Yabert (Feb 7, 2010)

This schematic should be way clearer for everyone. This tractor doesn't have clutch, but the clutch pedal is link to the pot box.
Presss the clutch = 0K
Release the clutch = 1 to 5K (mecanically adjust)


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## Yabert (Feb 7, 2010)

Definitely, I drew the schematic too fast last time. This one should be better.

I found a 48vdc latching relay on Newark: http://canada.newark.com/te-connectivity-schrack/rtx3-1at-b048/relay-spst-no-250vac-16a/dp/28W5718
If no, there is this nice one at ev power, but the shipping will be long : https://www.ev-power.eu/DC-Contactors/DC-Power-Latch-100A-Coil-48V.html

Any advice? Comment?
Thanks


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## Duncan (Dec 8, 2008)

Hi Yabert

I don't understand your diagram - where is the clutch switch?


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## Yabert (Feb 7, 2010)

Thanks to ask. I understand isn't so clear... In my head it's clear 

So, the ''clutch'' is in fact a reverse throttle and this one is mecanically link to the pot box (PB-6 Pot Box in my shematic). There is a switch on this pot box originally use to open the contactor on a golf cart. 
Here I will use it to give the signal to the latching relay (blue and green wires).

Well, when the farmer want to drive the tractor, he pull the emergency button*, but nothing happen. He need to press the ''clutch'' down (pb-6 switch) to energised the controller and when it release the clutch the motor will start to spin.

Make sense?

*I also added a key switch, but this don't appear on my schematic.


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## Patriotic Motors (Jun 20, 2011)

If I were to build an electric tractor, I would put a switch on the seat, throttle and one on the clutch. I would wire these in series with the ignition switch. If you stand up or fall off, the tractor stops. If you press in the clutch, the tractor stops. If the throttle is full off, the tractor stops.

For a throttle, I would put a potentiometer on the normal tractor throttle handle.


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## Yabert (Feb 7, 2010)

Patriotic Motors said:


> ... If you stand up or fall off, the tractor stops. If you press in the clutch, the tractor stops...


The problem here is when you release the ''clutch''* or seat back on the seat, the tractor will pop a violent wheelie if the throttle is full on. 

*there is no mechanical clutch in my case.


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## PStechPaul (May 1, 2012)

Make an interlock that requires the throttle to be at minimum to reset the system to apply power to the controller. All such safety interlocks should be designed so as to "trip" a latching relay and not allow reset unless all are in "safe" condition.


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## Duncan (Dec 8, 2008)

Hi Yabert 
That makes perfect sense to me
So the latching relay will not activate unless the throttle is at zero - just what you need

One other safety - big light / little buzzer for when it is "on" and ready to go

You don't want the owner grabbing the throttle when he doesn't think it's going and getting a fright
You know when a diesel one is running!


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## Yabert (Feb 7, 2010)

Duncan said:


> One other safety - big light / little buzzer for when it is "on" and ready to go
> You don't want the owner grabbing the throttle when he doesn't think it's going and getting a fright
> You know when a diesel one is running!


Yes, for this one, just in face of the driver, the cycle analyste screen will turn on when the tractor is energised and ready to drive.


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## Yabert (Feb 7, 2010)

So few news about this project.
I spent 12 bucks for nothing to buy a latching relay at Newark. I learn the hard way 
Well, I finally find a regular 48v relay for 3$ locally and I create a latching relay by putting this one in parallel with the micro swich on the pot box.
Now nothing is moving without pressing the clutch down when you turn the tractor ON.

I did the same on another tractor by simply selecting the ''high pedal disable'' option on the Alltrax controller 
Way easier!

In picture bellow you can see the mecanical parts link to the throttle who is used to adjust the tractor speed without playing with a pedal (a spring who lift the clutch pedal doesn't appear on the pic).


Now, I have to do the same on another tractor with a 5k-0 none programable Alltrax controller and I would like to use two 10k-0 pot to do a similar job (like Duncan suggested post #4).
But is there a risk of WOT if one of the pot fail?
5K = no speed, 0K = full speed..... so if a wire is cut the controller will receive the full throttle signal, right?


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## Duncan (Dec 8, 2008)

Hi Yabert
The two pots are in parallel - so if you lose one pot you go to twice what the other pot is commanding - BUT with my controller anything over about 6Kohms = a fault and shuts down


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