# DIY 72V DC controler



## EcoReality (Mar 10, 2014)

There are open source controller designs at the Open ReVolt Wiki.


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## Qer (May 7, 2008)

If the task is to build just one single unit, don't bother. It's not worth doing a new design for a mere one shot because it will cost more than just buying an off the shelf-controller. In theory a DC/DC is simple, in reality it's actually rather complicated and odds are that you will blow up a prototype (or five...) before you have a working system to deliver.

If the task is to construct a controller that will then go into serial production (even if it's a limited amount of units) it can be worth it. It will probably take longer and be more complicated than you anticipate, you will blow up a few units (it's especially fun when you blow up a unit due to some stupid bug in the software...) and you'll learn a lot, mostly the hard way.

If you're not a skilled software developer, team up with one. Preferably one that's experienced enough to know that test cases should be considered mandatory, at least for the most critical parts of the code.

If you're not a skilled hardware engineer... You'll have a very interesting adventure ahead of you...

About finding a schematics etc; the good constructions aren't publicly released simply because if they're good they probably did cost a lot to develop and if you release the documentation you risk not getting your invested money back so why should you? Where's the business incentive for releasing the documentation so someone else can build a cheap knock-off?

The only one I know of is the ReVolt. If you can modify the ReVolt to fit your needs it'll simplify things for you (and at the same time you're kinda proving my point why it's bad business manners to release the documentation...  ), but it'll probably still be a lot more complicated than you anticipate right now and odds are that you'll sink a lot more money and time into the project than you anticipate...

Are you absolutely sure you can't just pick an existing controller off the shelf and live with it...?


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## EcoReality (Mar 10, 2014)

Yea, I agree with Qer.

I was going to point out that building "from scratch" can be a form of self-actualization, and a very satisfying activity, but world like "I have one order to build" makes me think the reasons for doing this are not of that nature.

If someone is paying you to do this, by all means, go buy something proven -- if for no other reason, to avoid product liability issues! What happens if your home-brew controller catches fire and burns someone's house down, or electrocutes someone? Is it worth possibly spending years in court and losing your life savings over?

If you're taking money for this, and insist on "rolling your own," by all means sink whatever you make into product liability insurance, which even then, won't cover negligence -- which having been warned on this forum, someone would have a good case for.


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## EVmot (Sep 19, 2010)

I agree with your suggestions and of course security must be on the first place. For now we have build few 2KW dc/dc converters and two 35A controllers but precision is always necessary and detail testing must be included in whole project.

The order consist of:
- donor car: 650 kg 
- user desired speed ( 130 km/h )
- battery system ( lion or lead acid or something else )
- DC motor ( i was thinking on this :
http://www.amazon.com/PMG-132-Permanent-Magnet-Electric-24-72V/dp/B005USWNDE
or
http://www.goldenmotor.com/

Controller that we plan to build would be 72V / 100A. 
What do you think would this be enough for this setup ?

Evmot


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## Yabert (Feb 7, 2010)

EVmot said:


> ... would this be enough for this setup ?


No!
Despite your car is fairly light, you will need more than 7.2 Kw (72v x 100A) to maintain highway speed. Probably more around 15-25 Kw and more during climbing.

All your specs should be good if you move user desired speed from 130 km/h to 80 km/h...


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## EVmot (Sep 19, 2010)

. 
I was thinking the same. It's quite light so i was thinking that this would be enought but when you calculate all 200 / 300A should be better solution. We ware thinking on using 5x 60A FET and min. 200V FET's , but this can be changed. Anyway, thnx for reply !


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## EcoReality (Mar 10, 2014)

If something looks too good to be true, it probably is.


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## PStechPaul (May 1, 2012)

I calculate about 16 kW at 130 k/hr on a 1% slope, and 650 kg total including driver and cargo. And that is just the power needed at the wheels. At 85% overall efficiency it is more like 19 kW.
http://enginuitysystems.com/EVCalculator.htm


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## EVmot (Sep 19, 2010)

Nice EV calc !
Thank you for this info.

Technical stuff that I would go with:
6 FET 200V, 130A, 9mOhm
6 diode 200V, 2x15A, 35ns
6 driver's 10A
12 capacitors 200V, 1500uF

Big cooler and vent with current tranducer.
Converter 72/12 over 7805 ...


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## onegreenev (May 18, 2012)

My initial build was a 64 VW Ghia and I used a 9" GE motor and a GolfTech 72volt 550amp controller. Was it enough? NO. I do not recommend anything below 96 volts for any street or even light freeway driving. If you do build a 72 volt controller be sure it is capable of 550 amps or more. The lower the voltage the higher the amperage you will need in order to have a reasonable vehicle. Around town at 45mph or less the 72 volt system would be OK.

And you will want a nice finned heat sink on that as well. You will need to get the heat away. Without a nice finned heat sink with cooling fan you will not be going very far. Once I put on the finned heat sink and fan the controller never went into cut back mode due to over heating. You will also want to put into your controller a function to protect your controller in the event of overheating. Even this old controller had that function. It is still in use today in another low voltage build with another 9" GE motor. Good for around the town driving.


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## EVmot (Sep 19, 2010)

Can you share some schematic or maybe some basic info like, what kind of FET, drivers, diodes did you use and how many ? Is this 96 or 72V setup? 
If you want to you can send PM also.

Evmot


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## onegreenev (May 18, 2012)

Not really. The controller was built by GolfTech. An older company long gone now. Most likely built like a curtis but with the ability to handle 550 amps where the curtis was at best 400 amps. That extra 150 amps is needed on such a low voltage system.


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## EVmot (Sep 19, 2010)

OK.
I will go with the open revolt project.

One more thing.
What do you think about motor setup and where to get such motor ?

Reminder:
- car weight is cca 700 kg
- max speed up to 130 kmh.

Am a bit sceptic regarding golden motor products. 
I need 10 - 15 kw motor at 3000 Rpm at least.

What would you suggest, what kind of motor and where to buy.

Evmot


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