Hi,
I have this electric car project i am working on, and now i have one problem with running my mosfet driver board. There is an arduino running the whole game and it's supply is a standalone 12v battery, and the driver board and the motor itself is being supplied by a 6x12V battery pack.
Now my question is, how can i get 12V at about 1A from that 72V battery pack.

Resistor - zener is obviously not right here cause there would be like 100w dissipation on the resistor and well bad things happen.
Connecting the other battery is out of the question because these supplies need to be galvanically isolated otherwise my arduino goes haywire and again, bad things happen.
I cant stick a 7812 directly in there cause of 72V, and bad things happen.
I tried looking into switching ICs however they require 12V to operate in the first place so errr...

Can anybody point me in the right direction here?
Thanks

 

A switch mode regulator.. (aka buck or step-down regulator)
A linear regulator like 7812 will dissipate far too much heat even if it could take the 72V input as the input to output ratio is large.. But a switcher is more efficient.

Not sure if you could find a ready made module out there already but there are plenty of "roll your own" solutions.

oops didn't see your isolated requirement.. Not sure why you really need that though..

 

Well that is the thing, I would love to do that but i've been scouring tme.com and i can't seem to find an IC that would do that. These batteries are more like 84V when full and due to the motor this voltage could easily spike to 100V maybe more

 

If the Arduino GND *must* be galvanically isolated from all of the 7 voltages in the battery stack, then consider a fully isolated DC/DC converter, 12V/12V or 24V/12V, running from any one or two of the batteries. Off the shelf at 1 100 watts from most distributors and many surplus shops.

ak

 

Most decent quality SMPS based wall warts will run just fine on voltages far lower than their input rating suggest provided the output load is proportionally lowered in relation to the input under voltage level.

Find a 12-volt wall wart with a ~85 - 250-volt universal input and feed it your 72 volts DC. Odds are it will work just fine. I've done it many times.

 

Most decent quality SMPS based wall warts will run just fine on voltages far lower than their input rating suggest provided the output load is proportionally lowered in relation to the input under voltage level.

Find a 12-volt wall wart with a ~85 - 250-volt universal input and feed it your 72 volts DC. Odds are it will work just fine. I've done it many times.

I was thinking about integrating the dc-dc on the driver board itself but If this is the simplest way i'll just go with that

 

Why do you need the isolation?

 

Get a mains smpsu with a 12v output, crack it open, and put your 72v dc straight on the input capacitor by-passing the bridge rectifier, these will work from 80v to 220vdc.

I would recommend leaving rectifiers in place being the DC supply that is going to be used is also the primary power source for the drive motor and it's related controls which means that there is a good chance that it will be loaded with all sorts of high powered electrical noise that the tiny switching device in the power pack may not like having fed directly to it.

I tried that scheme with a few AE power experiments and it was surprisingly easy to pop a wall warts switching devices when directly fed by the HVDC whereas feeding it through the rectifiers and related AC side filtering components first seemed to effectively cure the problem.

 

Why do you need the isolation?

I need isolation because there are transients from the motor on the ground line and the arduino goes crazy. I have some spare smps adapters laying around so i'll try that solution from tcmtech

 

you can get the design guide of an industrial dc to dc converter from pi suite an smps design software.
as a matter of time a working smps can be re modified. usually a 12 or 15v will satisfy your needs. if more than one output supply available then analog and digital grounds can be avail easly.

http://www.danyk.cz/iz_osc.html

 

I need isolation because there are transients from the motor on the ground line and the arduino goes crazy. I have some spare smps adapters laying around so i'll try that solution from tcmtech

You should be okay without isolation if you just run your ground and 12 volt line directly to the negative and positive terminal of the first battery. You may want to run it thru something like a 7808 to make sure the voltage stays in a happy place for the mico.

 

does it look like this?

 

You have six 12 volt batteries in series. To power your low voltage electronics, connect to the bottom 12 volt battery. There is no need to convert down from the maximum battery voltage.

 

Just use the last battery to supply your circuit...

 

it's quite possible that ordinary ac/dc wall type psu should do... while most of them work from as low as 65V...ac input simply means that you have no need to look at polarity of voltage input from 70V battery...

otherwise, it can be done in form of classical, self made dc/dc flyback - to keep it simple and isolated... but i suppose, make the one from scratch is not everybody thing...