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Discussion Starter · #1 ·
Hi all

I'm busy planning my first EV conversion and I'm looking at options for controlling the motor on a very tight budget.

I plan on converting a small car similar to a Nissan 1400 with a max speed of 100 km/h and a range of about 50 km.I understand that the lower the voltage the cheaper the controller will be. I was hoping to use a 96v pack but maybe 72v would be sufficient. The controller would need to pull about 500A max for a very short period of time.

My questions are:
1) What are the cheapest controllers available that would actually work and not blow up after a couple of drives?

2) As this is my first build I've also been looking at making my own controller. What are the different methods (do you have examples of people who have built them before?) of controlling a motor if I go the homemade route?

3) With regards to the homemade route. Is there a REALLY REALLY simple method of controlling a motor? (For example using a lot contactors or something, using something to limit the amount of current that flows through each contactor, and connecting more if you want to go faster and less if you want to go slower?)

I am really new at this but I hope you get the idea that I'm looking for really simple and really cheap (preferably something along the lines of "#3")

Thanks in advance!! :)
 

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Hi all

I'm busy planning my first EV conversion and I'm looking at options for controlling the motor on a very tight budget.

I plan on converting a small car similar to a Nissan 1400 with a max speed of 100 km/h and a range of about 50 km.I understand that the lower the voltage the cheaper the controller will be. I was hoping to use a 96v pack but maybe 72v would be sufficient. The controller would need to pull about 500A max for a very short period of time.

My questions are:
1) What are the cheapest controllers available that would actually work and not blow up after a couple of drives?
Probably buying a controller. None of the options are going to be particularly cheap.

2) As this is my first build I've also been looking at making my own controller. What are the different methods (do you have examples of people who have built them before?) of controlling a motor if I go the homemade route?
The gold standard in this area is the Open Revolt Controller.

But again cheap is still only relative to comparable controllers (144V, 500A)

3) With regards to the homemade route. Is there a REALLY REALLY simple method of controlling a motor? (For example using a lot contactors or something, using something to limit the amount of current that flows through each contactor, and connecting more if you want to go faster and less if you want to go slower?)

I am really new at this but I hope you get the idea that I'm looking for really simple and really cheap (preferably something along the lines of "#3")
Well with #3 you can do simple. But it's not going to be cheap. Lots of contactors and simple to control is Lee Hart's rectactor.
With contactors running close to $100 each and needing at least 8 of them to get decent steps (not to mention the full amperage diodes required), again cheap isn't on the menu.
Thanks in advance!! :)
I wish you luck on your build.

ga2500ev
 

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1) What are the cheapest controllers available that would actually work and not blow up after a couple of drives?
Since I'm biased I'm not gonna recommend any brand, but there's that old saying that goes something like "Price, Performance, Reliability, choose two". It's very fitting for controllers imo. Controllers that are cheap, are usually cheap for a reason...

2) As this is my first build I've also been looking at making my own controller. What are the different methods (do you have examples of people who have built them before?) of controlling a motor if I go the homemade route?
I've written some about this in this thread:

http://www.diyelectriccar.com/forums/showthread.php?t=94224

In short; it won't be both harder and more complicated than you think.

3) With regards to the homemade route. Is there a REALLY REALLY simple method of controlling a motor? (For example using a lot contactors or something, using something to limit the amount of current that flows through each contactor, and connecting more if you want to go faster and less if you want to go slower?)
Yes. You can use a whole battery of contactors like in old school fork lift motor controllers. It's neither efficient nor cheap (unless you manage to find a whole bunch of old contactors for free or cheap) but it's simple (on a scale).

It's probably also a bad idea for a car.
 

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Discussion Starter · #4 ·
Thanks for the replies!

The Open Revolt Controller looks really cool but the kit (which i would be more comfortable working with) costs over $600 and that's without the shipping costs all the way down to SA!

Is the contactor method similar to the old golf cart method of speed control using a rheostat? If so, they both seem pretty crude and would probably hurt my range significantly!

I was also wondering whether it would be possible to join two 48v golf cart controllers together in series? This would create a 96v controller at whatever amps one single controller is able to carry. I might be able to find some cheap (probably old) controllers off disused golf carts which might work perfectly. (I really hope there are no major problems with this idea!! :) ) Let me know of any thoughts and/or inherent problems!

Thanks
J
 

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Thanks for the replies!

The Open Revolt Controller looks really cool but the kit (which i would be more comfortable working with) costs over $600 and that's without the shipping costs all the way down to SA!
As I said, there are no cheap options.

Is the contactor method similar to the old golf cart method of speed control using a rheostat? If so, they both seem pretty crude and would probably hurt my range significantly!
No. Because it's a switch it doesn't burn power as heat like a rheostat.

Again the problem is the cost, not the setup.

I was also wondering whether it would be possible to join two 48v golf cart controllers together in series? This would create a 96v controller at whatever amps one single controller is able to carry. I might be able to find some cheap (probably old) controllers off disused golf carts which might work perfectly. (I really hope there are no major problems with this idea!! :) ) Let me know of any thoughts and/or inherent problems!
It doesn't work like that. All controllers are based from ground. So you cannot start a second controller starting at 48V.

ga2500ev


Thanks
J
 

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Discussion Starter · #6 ·
Thanks

Okay it makes sense now. Just another thought... Can I join two controllers in parallel, increasing the current, then using something like a transformer on the other side to increase the voltage. Due to the parallel controllers I would have accommodated the current drop with increased voltage. It would probably have to be a big transformer though...

Thanks in advance!
 

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Can I join two controllers in parallel, increasing the current, then using something like a transformer on the other side to increase the voltage
No!

Controllers are semiconductor units that chop up the current to transform power to power, but changing the Voltage*Ampere-ratio in the process, you can't think of them like transformers (which are passive units). For two controllers to cooperate like that they have to be built for that from the beginning and I don't know anyone that has done that. We looked at doing that and scrapped the idea as impractical.

And honestly, if $600 is expensive I don't think you're prepared for the cost of batteries, motor, DC/DC, adapter plate, charger etc. If you want to drive cheap, buy a beat up gasser and be content.
 

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Can I join two controllers in parallel, increasing the current, then using something like a transformer on the other side to increase the voltage.
If designed to do so from the start it is possible to parallel the power stage. But no controllers have been designed this way.

A device to increase the voltage could be built but at EV power levels it costs more and weighs more than a motor controller would that can handle the higher voltage.
 

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Discussion Starter · #9 ·
Thanks for the input! I was just interested and decided to bounce some ideas but I'm sure I'll end up buying an Open ReVolt kit or production controller from somewhere!

If there are any other cheap, simple and interesting ideas out there please let me know!

Thanks! :)
 

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Discussion Starter · #11 ·
Thanks that's great!
The EV I'm planning will be very light and not very powerful so 450 amps at 72 volts should be plenty!! I like the price!
 

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Discussion Starter · #13 ·
Thanks! Yes I don't plan on breaking any speed records and the car I'm planning on converting will be very light! If there is any other info out there that will help me I'll gladly appreciate it!
Thanks :)
 
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