# Bypass Controller for more AMP and full throttle?



## grose (Apr 30, 2008)

Yes, this is possible. My EV is currently running a bypass setup. I did write about it on this forum, but it wasn't its own thread so don't bother searching. Here is the setup in a nutshell: 

My setup is using a 36V EV-1 controller. I have a bypass contact that kicks in the full pack voltage about a second or two after I begin accelerating (unless I'm light on the pedal). Once bypassed, the pack delivers the remaining voltage which brings the total up to 96V. When the bypass is engaged, the car gets a small jolt forward and accelerates faster. (Electric turbo if you will)

To go off what you stated, which is right on, this does deliver more amps. When the packs is engaged my ammeter peaks for a short bit at 350-400 amps. The amount of current you see will depend on your batteries. After the peak the amps drop back to 100-200 depending on gear and speed.

I do see a few drawbacks with this setup which you should know about. First, when you have a large amp draw, your voltage drops. (Peukert effect) I think I see this effect more than someone who does not run a bypass. This translates to a shorter range. The other drawback is once the bypass is engaged you don't have much for speed control. You just accelerate at a constant rate until you either shift or max that gears speed out. It is all or nothing. While full pack voltage on a cycle or drag car might get wild and unsafe, in my car at only 96V it isn't much for acceleration no matter how you wire it.


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## major (Apr 4, 2008)

Thaniel said:


> Here is the question: Instead of buying a 1000 + amp controller could I use a lower amp controller and wire in a set of contactors so at full throttle it will by pass the controller to more or less direct wire the motor to the battery.<snip>Thanks in advance. Thaniel


Hi Thaniel,

Forklifts used to use (and still may) by-pass commonly. It was integrated into the control. So it is technically feasible. However, you're a rookie. So I'd advise against it. It is not as simple as it sounds to do it right. The contactor and controls for it will not be cheap. And you have a real likelihood of blowing a controller or 2 before you get it right. Good chance by-pass will cost you more than the big controller.

Regards,

major


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## CPLTECH (Sep 14, 2007)

A controller’s job is not to just regulate MPH. It also has an internal safety circuit to limit the amperage so that motor$, wire$, and batterie$ do not melt. That can save lot$ of heartache as these components are not indestructible. Controllers are a good thing.


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## adric22 (Jan 17, 2008)

I had thought about this too. In my case, my Kelly 84600 controller will only pull about 300 amps from my batteries (yet it is considered a 600 amp controller) but after I've been driving for a few minutes, it will only pull around 200 to 250 because it starts to get hot. So the car looses performance. 

I have a very small motor in my car too. It is rated at 10 HP continuous, and 40 HP peak. It gets very hot after about 10 miles. In fact, it will boil water sometimes. I'm afraid that if I gave it more juice than my controller is already giving it, I'd probably burn it up. 

And I'm also not sure how my controller would handle having that power coming in through the output terminals. It might not like that.

Then there is the issue of the possibility of whatever contactor you are using for this bypass becomming welded shut due to the arc of high power. Then what do you do? The car would continue to barrel forward at full power. And being that my main contactor operated by the keyswitch in my car is only 180 amps, it might get stuck too. I suppose I could put the car in neutral, but unless I had a wrench with me there would be no way to stop the flow of current to the motor. And I'm not sure I'd want to pull a wire off the battery while high current was going through there. A friend of mine who is a toyota mechanic says that he has seen controlled demonstrations of this and the arcs that come off those wires can kill you.


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## CPLTECH (Sep 14, 2007)

adric22
RE: Hot controller

Just a thought concerning your heat issues, my Curtis 550A, 120V sits on a thick heat sink plate and a muffin fan on the top to help dissipate the heat.
When electronics get hot, they slow down and can self-destruct.

Your comment about a 10hp motor should encourge others to seriouly consider the 9 inch motors as a minimum.


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## grose (Apr 30, 2008)

adric22 said:


> I had thought about this too. In my case, my Kelly 84600 controller will only pull about 300 amps from my batteries (yet it is considered a 600 amp controller) but after I've been driving for a few minutes, it will only pull around 200 to 250 because it starts to get hot. So the car looses performance.
> 
> I have a very small motor in my car too. It is rated at 10 HP continuous, and 40 HP peak. It gets very hot after about 10 miles. In fact, it will boil water sometimes. I'm afraid that if I gave it more juice than my controller is already giving it, I'd probably burn it up.


Wow, you must have a small motor. 7" or smaller yet? Given what you state about heat, I don't think you should put any more voltage in. In fact, you are probably melting the insulation on wires, or at least fatiguing it.

The bypass system is a concern of mine too. If the contactor welds shut, I would get runaway power. Fortunately, my car is slow to accelerate even with full pack voltage. I'd pull it into neutral and pull the circuit breaker switch in the event of a weld. I'm hoping that never happens. I'm also looking into updating my controller and not doing the bypass anymore.


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## Thaniel (May 25, 2008)

Hey guys this is great information. Don't wouldn't worry about me blowing things up because I'm a newbe. I have you guys to help keep me from doing that .

Interesting point about drawing too much current and damaging the batteries and melting things. I had not thought of that. What would determine or limit the chances of that happening? 

My inital thought is a zilla with a WarP 9 motor but I was thinking maybe a 500 amp curtis with the by-pass. Humm...

I'm more versed in mechanical things than electrical. I probably am better off just buying a zilla controler and saying done. I'm just such an incurable DIYer. I can't help but think of other ways of doing things.

Thaniel.


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## TexomaEV (Jul 26, 2007)

I have read of an individual installing a battery pack, contactor between the motor and controller wiring. When he wanted "Turbo" he could turn on the contactor, which would insert the extra 12volt or whatever battery into the mix of the output of the controller, to the motor. He even sent me a wiring diagram on it, I hope I still have it somewhere.

The beauty of this setup, is that even if the contactor welded, the controller is still in the main loop, and you still have normal vehicle control.

The inserted pack of course is only used when needed for passing, or hill climbing.


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## CPLTECH (Sep 14, 2007)

*Re: Texoma, diagram please*



TexomaEV said:


> I have read of an individual installing a battery pack, contactor between the motor and controller wiring. When he wanted "Turbo" he could turn on the contactor, which would insert the extra 12volt or whatever battery into the mix of the output of the controller, to the motor. He even sent me a wiring diagram on it, I hope I still have it somewhere.
> 
> The beauty of this setup, is that even if the contactor welded, the controller is still in the main loop, and you still have normal vehicle control.
> 
> The inserted pack of course is only used when needed for passing, or hill climbing.


Would like to see his diagram, if you still have it. Like to use something like that in the future & not learn from my mi$take$ (if you know what I mean).


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