# Electric reverse solutions



## Matej (Dec 4, 2015)

Hello,
Does anyone have a diagram or pictures of how the three contactors need to be connected for electric reversing of a series motor?

Even better if they can be wired in such a manner that they will fail in open mode should a failure ever occur.

Thank you.


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## dcb (Dec 5, 2009)

not sure it is safe to do so, but you *could* use 3 contactors to switch from field+armature in series to reverse polarity field in parallel with armature.

If it didn't blow something up it would be exceedingly torqey and slow in reverse (the vast majority of the current would be in the field, and possibly not limited by the controller if it looks more like a short to the controller than an inductor). Not sure it is worth skipping a contactor for the risks. 

You probably want a four contact single action relay anyway (can probably find one in surplus) so you don't accidentally short the pack if the relays get out of sync. The "open up all the relays" is an ok idea, but you already have a contactor to disconnect the pack from the controller, and there is a bigger risk of shorting something out with seperate relays than any benefit from being able to open them.

Having said that, you hook one end of each contactor coil to whatever is powering the main contactor, and control the 3 contactors from the other coil leads, i.e. using a 12v spdt switch to power(or ground) the fwd/reverse coils (1 coil for fwd, 2 for reverse). I'm assuming that the main contactor is set to turn off when a problem is detected already.


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## Matej (Dec 4, 2015)

Focusing on a single motor at the moment, I am basically attempting to replicate the function of the Albright SW202 reversing contactor, except I want to use multiple Kilovac contactors which are rated for higher voltage and current.











I can easily see how reversing can be achieved with 4 contactors, but I am having a difficult time seeing how it could be done with only 3 contactors.
Thank you.


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## Duncan (Dec 8, 2008)

Hi Matej

I think you are worrying too much
The relay ratings that you are worrying about are for the relay to operate, - but most people don't operate the reversing relay under load
Normal practice is to stop before engaging reverse!

In my car I have an additional brake light switch that shorts out the throttle pot
I stop - and select reverse with my foot on the brake
So the contactor is switching at zero load


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## dcb (Dec 5, 2009)

good luck Matej , you've been given the warnings...

I don't know where you got the idea for 3 relay reverse, or why you are bent on it, but the attached is the only way I could see it having any chance of working. (it would be slightly less worrisome on a shunt motor fyi, just invert the truth table)


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## dcb (Dec 5, 2009)

Also, if you want cheap and purportedly heavy duty, you could double up the knives on something like this ($120 on ebay) and use it as a field reverser. Needs work in the safety department though. Should be good for 800 asian amps. if you can find a spot for it without too much motor leads. Maybe rework the pivots and contacts into something smaller with shorter throw and no metal exposed. (fold it in the middle up 90 degrees or so and make a rounded cover and sliding shield )


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## dcb (Dec 5, 2009)

fyi, the manual switch setup if you don't see it. I expect the crossovers would just be bus bars in the switch body once your done modding the switch. 

I don't know why more people don't go this route, either they like relays, or it is unworkable for some other reason, but it won't draw any power, plus you can add a middle position detent where nothing is connected (and it moves as a unit, so it is interlocked.

Basically it is a dpdt switch when you pair knives. 

http://www.ebay.com/itm/400-Amp-Dis...hash=item27ce8201ef:m:m4kx67MHK72N-oZfF1ulinw

or go to ali express and get one for $50...
http://www.aliexpress.com/item/HS-1..._7&btsid=510be3ff-9986-4e0a-90b1-e49848314ada


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## Matej (Dec 4, 2015)

dcb said:


> good luck Matej , you've been given the warnings...
> 
> I don't know where you got the idea for 3 relay reverse, or why you are bent on it,...


Is that not what people use for reverse on a direct drive conversion?
From the vague information on electric reverse that I found online it seemed that people use 'three contactors' for reversing a series motor, though I have not been able to find much further detail, which was why I finally decided to make this thread.

If there is however a more conventional or better and safer method of implementing electric reverse, I would love to learn about it!
Most of the direct drive conversions I found use the SW202-style reversing contactor, but they are all 144V and 600A max setups.


I am very curious how the reverse is implemented on cars such as the White Zombie, for example. This is from their 2006 history page. I am not sure if they still use the same setup.
_
Direct drive. Electric reverse added with Albright SW200 front motor field control contactor and twin 300 amp GE contactors (previously used for the field weakening) for high current reverse capabilities:_









I cannot really tell what is going on in that picture, but I am very interested in learning.


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## dcb (Dec 5, 2009)

You never actually said how many amps or volts you were looking for...

why not just parallel as many sw202s as you think you need? They aren't that expensive.

It is a 4 contact reverse, just like the diagram you put in post #4.


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## Matej (Dec 4, 2015)

dcb said:


> You never actually said how many amps or volts you were looking for...
> 
> why not just parallel as many sw202s as you think you need? They aren't that expensive.
> 
> It is a 4 contact reverse, just like the diagram you put in post #4.


It will initially start at about 160V and 1000A, and I would like to increase that in the future.

Is paralleling the SW202's alright to do?
Because I actually had that thought but I was too embarrassed to ask about it in case it was a really bad idea. 

My concern was that something could get damaged if the the SW202's do not switch at exactly the same moment (even though there should be no current going through them when they are being switched).
However, if I can just parallel them without worries, that is definitely the most welcome solution.

Thanks!


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## dtbaker (Jan 5, 2008)

Matej said:


> Focusing on a single motor at the moment, I am basically attempting to replicate the function of the Albright SW202 reversing contactor, except I want to use multiple Kilovac contactors which are rated for higher voltage and current.
> 
> 
> 
> ...


so.... I dug up this thread because I am looking into a conversion of a boat, that doesn't have a transmission for reverse. It will be a 120vDC setup with an ADC 8" DC motor, and I have a Zilla controller to use.

I'd like to understand the physical wiring needed to switch from forward to reverse when needed. several (3 or 4?) kilovac relays with a three position toggle switch would be perfect.

I am way better understanding pictures of actual parts than schematics... is the schematic above workable, and safe?


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## Duncan (Dec 8, 2008)

Hi
If you use the correct forklift contactors they flip between the two sets of contacts so nothing nasty can happen if one hangs up or something

I would recommend getting the Albright and making a really really good box for it to live in

I'm using a standard forklift reversing contactor on my machine - and I'm overloading it a LOT

As far as the actual reversing switch is concerned I use two toggle switches
One of which has a firing button cover

This means that I need to flip two switches to go from forwards to backwards

If both switches are the same way - nothing happens!
Its only when one contactor is ON and one is OFF that the motor can drive

I always change direction when I have my foot on the brake which has a switch that zeros the throttle


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