# Do i need a controller



## toysdoneright (Feb 20, 2012)

I built a jr dragster last yr using a me 1003 motor, Alltrax 7245 controller with 7-12 volt 18 amp hr jumper pack battery's. Your best time was a 11.02 1/8 mile We want to step it up a bunch Looking for 7.90 @85.00 mph My question is sense this is only used for drag racing. Could I just use a small contractor @ 12 volt for staging and a large contractor with 120 volt system for the race? We plan to gear the car down for quicker reaction and with the extra voltage still be able to run 85 mph The controller was a major pain to stage when we had it turned up to go fast LOOKING FOR IDEAS


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## david85 (Nov 12, 2007)

Welcome to the forum. I moved your post to the correct section, so you should get some replies shortly.


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## Qer (May 7, 2008)

Closing 120 Volt over a non-moving motor will result in insane levels of currents and you risk a welded contactor, crazily spinning tires and a completely uncontrollable go-cart tiat will run amok until the batteries die (or you pull the emergency braker).

You simply need a better controller.


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## piotrsko (Dec 9, 2007)

my$.02 (Usd): Go look over at the Plasma boy thread in EV performance. 

IMHO, launching will always require some sort of throttle action that can be regulated, Just because; when the vehicle starts going sideways (yes it will at least once), you want it to stop NOW. No IF's, ands, or BUTS. Them lanes are really long but they ain't all that wide; steerable wheelie bars don't.

Having said that, you could use the controller for staging and initial launch then contactor it like plasma boy did.


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## Yabert (Feb 7, 2010)

toysdoneright said:


> to go fast LOOKING FOR IDEAS


Hey toys

To have higher performance at 72v you need higher performance battery.
These is probably your weakest link.
Please share the batteries spec and we can help.

But don't expect miracle, a 72v 450A systems is limited to around 30-35 motor hp. This isn't that much!


Sorry, I missed your intention to go at 120v...
A proper 120v controller seem the safest way to go.


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## PhantomPholly (Aug 20, 2008)

It is actually possible to skip a controller; however, the contactors necessary might end up being as expensive as the controller you're trying to avoid. Old equipment like cranes used to use a similar system; they were heavy and bulky, the enemy of fast. At lower voltages it might be possible

In a scenario like yours, assume your entire pack is divided into 2 sub-packs (let's say each sub-pack is 5 * 12v batteries). You would use a combination of one master contactor (on/off) and two 2-position contactors to change the wiring configuration so that "low" would result in 2 60v packs in parallel (lower voltage, higher amperage for starting), and "high" would link the packs in series for 120v (higher top end). A three-position switch (off/low/hi) would control accelleration; you would need some empirical testing to determine the optimum speed at which to switch from "low" to "hi."

Warning: I'm neither a racer nor a builder (yet); just know that in theory this could be done. However, as Einstein said:
"In theory, theory and practice are the same. In practice, they never are."


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## toysdoneright (Feb 20, 2012)

Sorry to say it but price isn't the problem the problem is having a car that will stage very slowly and smoothly yet run the 1/8 mile @ 7.90 and 85 mph The total package weight with driver is 400# TO 450# We have raced alcohol powered jrs for yrs My son won the western conference finals 2 yrs ago and my daughter was Iowa state champion the same yr WE KNOW HOW TO RACE and no if this thing runs 7.90 @ 85 mph it will not spin unless the track is garbage The problem is it needs to soft stage and hard hard hit we 60 foot with the alcohol cars in the 1.48 to 1.49 area. If we use a controller what can I do to make it stage softer? A contactor with 12 volt to stage then turn on the controller?


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## Ziggythewiz (May 16, 2010)

toysdoneright said:


> If we use a controller what can I do to make it stage softer? A contactor with 12 volt to stage then turn on the controller?


A controller goes as slow and smooth as you want. That's what your foot is for.


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## toysdoneright (Feb 20, 2012)

Ziggythewiz said:


> A controller goes as slow and smooth as you want. That's what your foot is for.


 REALLY DID YOU READ WHAT I SAID it wont stage soft enough if you have it turned up to go fast If you know anything about drag racing .You know we need to put the front wheels within a 1/4 inch each time staging for contestant reaction times. We try to get .005 to.015 lights If your just playing around it doesn't matter. But it does to us


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## Ziggythewiz (May 16, 2010)

What controller do you have? With some you can set your own ramp curve, so you could set it as low as necessary. Alternatively you could setup a resistor or whatever yours runs on with a momentary push button to signal 1% throttle or whatever you need.


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## toysdoneright (Feb 20, 2012)

PhantomPholly said:


> It is actually possible to skip a controller; however, the contactors necessary might end up being as expensive as the controller you're trying to avoid. Old equipment like cranes used to use a similar system; they were heavy and bulky, the enemy of fast. At lower voltages it might be possible
> 
> In a scenario like yours, assume your entire pack is divided into 2 sub-packs (let's say each sub-pack is 5 * 12v batteries). You would use a combination of one master contactor (on/off) and two 2-position contactors to change the wiring configuration so that "low" would result in 2 60v packs in parallel (lower voltage, higher amperage for starting), and "high" would link the packs in series for 120v (higher top end). A three-position switch (off/low/hi) would control accelleration; you would need some empirical testing to determine the optimum speed at which to switch from "low" to "hi."
> 
> ...


This is what I was looking for My next question is if we hit the motor with 120volt from a dead start will it or the contactor take it? I'm guessing 400 amp Also if we spin the tires we will run faster than 7.90 and we cant do that by the NHRA rules Then we would regear it or take a battery away


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## toysdoneright (Feb 20, 2012)

Ziggythewiz said:


> What controller do you have? With some you can set your own ramp curve, so you could set it as low as necessary. Alternatively you could setup a resistor or whatever yours runs on with a momentary push button to signal 1% throttle or whatever you need.


I have a Alltrax 7245 but its not big enough to run 7.90 in 1/8 I was thinking of the kelly KDH 1600d ? Now how do I do the 1% staging button ? I think if I can figure what how to do that it might just work. Because the controller would be cranked up to kill but it would still stage slowly. Thanks Very much would never thought of that THANKS THANKS Thanks please give me the basics


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## Ziggythewiz (May 16, 2010)

Looks like that kelly uses a 0-5K pot, so you just have to find the right resistance value.

Just run a second pair of wires off the controller throttle pins, and add a resistor and momentary (or regular, just don't forget to turn it off) switch. When engaged, this button will add the resistor in parallel to your pedal control, driving the throttle signal to essentially the lower of the two.

Pot throttles are usually around 400 ohm or less is 0, and 4500 or more is full, so you'll probably want something around 500, but just play with a few values and see. Total circuit cost ~$5.

Some guys use something similar for a valet mode, limiting the controller to whatever max output you want when anyone else is behind the wheel.


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## Qer (May 7, 2008)

toysdoneright said:


> REALLY DID YOU READ WHAT I SAID it wont stage soft enough if you have it turned up to go fast If you know anything about drag racing .You know we need to put the front wheels within a 1/4 inch each time staging for contestant reaction times. We try to get .005 to.015 lights If your just playing around it doesn't matter. But it does to us


I would like to rephrase Ziggys response to:



> A *good* controller goes as slow and smooth as you want. That's what your foot is for.




Look at for example White Zombie, it's a street legal drag racer and it doesn't seem to have a problem with coexisting with mundane cars in every day traffic or accelerating in a controlled manner from the red lights etc despite having lots of more power under the hood than your racer. We also know that our controllers can control such a low current as 5 Ampere in a controlled fashion (which is so low it won't even move the car) without jerks or other nasty surprises.

I can't explain to you why your controller doesn't like to play nice (since I, fankly, don't have a clue what goes wrong) but that it does doesn't mean that all of them do. Will a resistor in series solve the problem? Maybe. Depends on if it's your foot or the regulation loop within the controller that's the problem. Does your foot feel troublesome? Has it had these problems with other cars?

If not, I'd say your foot is fine and the problem lies within the controller or, possibly, a flaky throttle pot assembly. A resistor might solve the problem but my guess is that it won't. However, it might lessen the problem to acceptable levels.

YMMV and all that.


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## Yabert (Feb 7, 2010)

toysdoneright said:


> I have a Alltrax 7245 but its not big enough to run 7.90 in 1/8 I was thinking of the kelly KDH 12600d ?


I used a KDH14100D in my car before upgrade to a Soliton 1.
The KDHD series are correct controller. Good programmability, throttle effective position, throttle rate, motor current, battery current, motor voltage.... good things to play with.

In my small car, the KDHD work fine at both low speed and at high speed / high power.... but not for long time before thermal derating start to cut power.
Probably not a big deal for 8 sec 1/8 miles!

Anyway, it the only choise of controller for 120v 600A sub 1K$


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## toysdoneright (Feb 20, 2012)

Qer said:


> I would like to rephrase Ziggys response to:
> 
> 
> 
> ...


 I really like the resistor idea If I understand you correctly we could put a large resistor then stage with full throddle or anything under that and bearly move forward while stageing. Then once stagged flip back to normal for the run. P.S. the throddle control is smooth just to sensitive when the controller is on kill. What would you recommend for a controller? We will be maxing out with 144 volt and approx 650 amp The ME 1003 motor is only rated for 72 volt and 400 amp. Shane Lawless said the ME 1002 was good to 120 volt but it only has 1 brush set this has 2 THANKS FOR EVERYTHING


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