# DC to DC Boost Converter - 12V to 96V at >9 amps

Thread Starter

#### danielb33

Joined Aug 20, 2012
105
Hello - new design coming up that is much different than I normally work with. I need to convert 12V to 96V - the 96V will need to supply >=9 amps.

Can anyone point me in the right direction? Not sure where to start. Boost converters will obviously not do the trick. I will need to design from scratch.

#### Brownout

Joined Jan 10, 2012
2,390

#### Papabravo

Joined Feb 24, 2006
17,583
Here is the very first, back of the envelope calculation that you need to do regardless of the converter technology:
Code:
96 Volts * 9 Amperes = 864 Watts of output power
Initial efficiency target 80%
864 Watts, output power / 80% = 1080 Watts, input power
1080 Watt, input power / 12 Volts = 90 Amps
A 50 Ah battery will last about 33 minutes.
That tells you that your 12 Volt battery wont last long at these levels. It also tells you that you are going to need specialized circuit construction and magnetic components to handle these current levels. Are you even remotely prepared to deal with these challenges. The reason I ask is that most graduate engineers are manifestly not prepared to deal with these kinds of circuits. No offense is intended if you are prepared.

For example a PCB with 3 oz. copper platting might not handle the current levels required in the inductor of a boost converter.

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Thread Starter

#### danielb33

Joined Aug 20, 2012
105
I work as a EE, but have a year left of school. Frankly, I have never been prepared for the designs I have done over the years, but I spend the time necessary to figure the problems out. I only have a few years experience though, and typically work with intermediate circuity but advanced firmware.

I suppose a boost converter would work. I read a few places that boost converters at that scale would be expensive. Just looking into potential options.

The power calculations make sense. We want to run a higher voltage motor for higher efficiency from the motor. Maybe our team can compromise with something in the middle. Thanks for the responses, let me know if there is anything else you think would be helpful to know. Thanks.

Thread Starter

#### danielb33

Joined Aug 20, 2012
105
I should note I have created PCBs that take 160A continuously. I think I can handle the PCB development and control alogorithms - but stepping of voltages like this is something I have never encountered.

#### Brownout

Joined Jan 10, 2012
2,390

#### Brownout

Joined Jan 10, 2012
2,390
I came across this as a possible starting point: http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=2996&whichpage=53 This was, apparently, a design that was distilled by AudioGuru, a former member. It's only 500W, but you might be able to modify it to the wattage you need. Also, you might be able to modify it for 9V input.
On closer inspection, at least some of AG's mods aren't shown on the schematic. I would suggest you find the modified one if you want to use this as a start, or else we can figure out how it should look.

#### ronv

Joined Nov 12, 2008
3,770
I don't know what your constraints are, but have you considered more batteries. 48 volt motors are pretty common and 4 12 volt deep discharge batteries are also pretty reasonable. I would try to limit it to 48 volts for safety.

Thread Starter

#### danielb33

Joined Aug 20, 2012
105
Batteries would not work for us. The end product will be on Ford/Chevy trucks. http://ezylift.com/ I just make the electronics for the system - but I don't have enough space for extra batteries. Brownout - I am looking into your suggestion.

#### #12

Joined Nov 30, 2010
18,223
Batteries would not work for us. The end product will be on Ford/Chevy trucks. http://ezylift.com/ I just make the electronics for the system - but I don't have enough space for extra batteries. Brownout - I am looking into your suggestion.
You're loading multiple tons on to trucks and don't have room for more batteries? I find that difficult to understand.

#### tcmtech

Joined Nov 4, 2013
2,867
The power calculations make sense. We want to run a higher voltage motor for higher efficiency from the motor. Maybe our team can compromise with something in the middle.
I not buying the efficiency excuse.

Pulling a 800 - 900 watts off of a stock 12 volt vehicle system in terms of electric motor load is no problem. There are loads of 12 volt motors used for winches and hydraulic pump units and numerous other things like power inverters that put out power well above that wattage level with efficiency levels equal to that of any higher voltage version of themselves.

#### Papabravo

Joined Feb 24, 2006
17,583
I should note I have created PCBs that take 160A continuously. I think I can handle the PCB development and control alogorithms - but stepping of voltages like this is something I have never encountered.
The next level problem with a boost converter is that when raising the output voltage there is an inductor that will require 2 times the input current. In your case this will be 180 Amps. There are several things you need to be aware of with an inductor of this size. The first is what gauge wire are you going to use, how many turns, and how much heat will the inductor have to dissipate. There are several bad things that can happen to inductors at these current levels that you need to be aware of.

#### #12

Joined Nov 30, 2010
18,223
I think TCM just said, "Tell the guy that demanded 96 volt motors to go pound sand".
and Papa said, "If you try to make a boost converter, it's going to weigh more than the motor".

This has already been done, many times, with 12 volt motors.

#### Brownout

Joined Jan 10, 2012
2,390
I have a 2000 watt inverter what doesn't weight anywhere near what a motor does. I also have a 12V 4 ton wench which is quite heavy. As for the inductor, there is no reason to limit construction to a single inductor. Commercial inverters use multiple parallel inverter modules.

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#### Papabravo

Joined Feb 24, 2006
17,583
I have a 2000 watt inverter what doesn't weight anywhere near what a motor does. I also have a 12V 4 ton wench which is quite heavy. As for the inductor, there is no reason to limit construction to a single inductor. Commercial inverters use multiple parallel inverter modules.
Yes, but an inverter is a different problem than a DC-DC converter. I also never mentioned weight as one of the problems since it was not listed as a requirment.

"Well, why didn't you list that among our assets in the first place?"
Wesley, The Princess Bride

#### Brownout

Joined Jan 10, 2012
2,390
Yes, but an inverter is a different problem than a DC-DC converter.
How so? You're converting power either way. Actually, inverter techniques can be used to build DC-DC converters, and DC-DC converter techniques can be used to build inverters.

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#### tcmtech

Joined Nov 4, 2013
2,867
I think the point is that np matter how anyone plays it the DC - DC conversion cant justify itself.
Motor efficiency gains wouldn't add up to justify it. Cost of power cables wouldn't cut it and cost of motor or motor reliability wont either.

Thread Starter

#### danielb33

Joined Aug 20, 2012
105
Thanks. I will let you know what I come up with.

#### Brownout

Joined Jan 10, 2012
2,390
Just thinking last night,

Inverter using 120v/15v transformer (full wave rectified output): Simple, heavy, large, moderate price, lots of ripple (ripple may not be important)

DC-DC converter(parallel converters or single): complex, small, lightweight, higher price, less ripple.

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