Using DC over AC

adas

Aloha, What are the effeciency economics of using as much DC instead of converting to AC? My situation is that my PV system runs a fabricating shop and I could find all sorts of motors, equipment to use 12v 24 48v etc. or just add more panels and invert it all. so...

Given that I will gain maybe 15% overall power by not using an inverter, what other advantages are there to using as much DC?

If DC is better, I could gain a huge power advantage by running a compressor on dc and converting all my power tools to air.
Is a DC motor more or less effecient?

Also if I can find a 72v dc converter I can charge my 2 Gem cars direct from the panels through the DC converter.

We are a production shop so using labor sacrificing things like DC welders, mickey-mouse this or that is not an option. (I could not even get my welder/worker to switch from Miller to Lincoln). Sacrificing things like fans, etc. are not for for moral, but I certainly make things more effecient and loosing the comfort works. We even have a saying "Go Green" that encourages the employees to turn off lites and unused equipment, with a pizza lunch now and then, etc.
Any other ideas, given my circumstances?

Frank

BB.

Re: Using DC over AC

I think a lot of the solutions/questions/answers of DC vs AC and such are very application specific...

For example, if you have a choice between air or electric tools (grinders, sanders, etc.)--no matter if AC or DC generated--electric is going to be way more efficient than air powered tools.

With the costs of electronics coming down, using Permanent Magnet DC motors with electronic controllers may get more interesting--but historically, DC motors just never lasted as long as AC motors (brushes, encoders, etc.).

Perhaps you can find a local vendor for multiple HP DC motors and controllers--and talk to them about a compressor or fan conversion (and the pluses and minuses).

-Bill

adas

Re: Using DC over AC

BB. wrote: »

For example, if you have a choice between air or electric tools (grinders, sanders, etc.)--no matter if AC or DC generated--electric is going to be way more efficient than air powered tools.

With the costs of electronics coming down, using Permanent Magnet DC motors with electronic controllers may get more interesting--but historically, DC motors just never lasted as long as AC motors (brushes, encoders, etc.).
.

-Bill

Aloha, Bill, so you think the effeciency of AC will overcome the 15% inverter loss vs air power?
Then it is a no brainer just inverter everything (especially when you have to McGiver the DC). If Elec~Air then I was going to go up to 500 gallons or so of air and run a very small compressor constantly to keep the tanks full. Then if a high demand for air tools, then a secondary bigger compressor will kick in.

Frank

BB.

Re: Using DC over AC

Frank,

I can use an air sander or mid-sized grinder for less than 500 watts most of the time... When I use an air powered sander or even small grinder, my 1.5 HP air compressor cannot keep up for continuous operation. I would believe that there is no amount of energy savings by DC conversion of an air compressor would overcome the huge losses from operating hand tools off of compressed air (vs the electrically powered equivalent hand tool).

Granted my compressor is a cheap home unit--but was my experience with smaller shop air systems too...

My suggestion would be for you to instrument your power usage... In the past, for measuring the power of larger equipment, I have simply used old utility meters wired in with a heavy extension cord. Works very well--you get accurate kWhr reading from the dial, and you can use the mechanical wheel and a stop watch to get a quick reading of watt draw (Kh). The utility meters are cheap, rugged, and measure power instead of Amps or Volt*Amps... For fixed equipment--you could hardwire in one or more utility meters.

Many times we have talked about solar systems, their efficiency and costs... But without knowing your kWhrs generated/used--tracking changes for efficiency is just guesswork.

Regarding DC motors--I would not call it McGivering--There are quite a few electric powered vehicles and pieces of equipment out there...

And given the scope of your shop and installation size--it would not be a waste of time to understand what your options would be for converting to DC shop air (for example). And, I would recommend a few Internet searches and phone calls to local suppliers to get some ball-park estimates on costs and power usage--It would be very interesting to find out what their answer(s) would be.

However, I would not be surprised to find out that that the high costs of motors, controllers, loss of efficiency from motor controllers (they switch power just like an inverter), and such--that the possible savings in efficiency by using DC would be more than eaten up by these other costs and maintenance.

AC induction motors are just plain cheap, reliable, and easy to service/replace.

Add reliable and cheap inverters--it becomes a tough combination to beat.

-Bill