12V Power Supply Feeds My Robot

[MikeDubreuil]

I was thinking about using a 12V power supply capable of providing about 30 amps while working on the robot in the pits. Does anyone have any reccomendations, horror stories or insight? Thanks.

[Biff]

I was thinking about using a 12V power supply capable of providing about 30 amps while working on the robot in the pits. Does anyone have any reccomendations, horror stories or insight? Thanks.
Depending on What you are trying to drive and how clean the output is results may vary, I would not try to flat out test our drive line this year as wheels up with 4 motors and the drive line friction, we pull 20 amps a side, total over 40. (yes I know it should be lower) If your just running the air pump and motors one or two at a time with no real loading, 30 with regulation to a real 12 or 12.5 not the normal 14 that comes out of some 12 v supplies. Life will be good. Btw Sony makes a Camera power supply AC-500. It's a switch mode that is very costly new But can be found on E-Bay, I had one, I fixed years ago, and it would Supply over 30 amps (tested) even though they are "rated at about 7" It would not start up with that kind of load on it but took it over night on a resistor load. Reason I mention this is Switch mode will be lighter and portable camera power supplies like this are clean and built to take the beating video crews put on them.

[MikeDubreuil]

Depending on What you are trying to drive and how clean the output is results may vary, I would not try to flat out test our drive line this year as wheels up with 4 motors and the drive line friction, we pull 20 amps a side, total over 40. (yes I know it should be lower) If your just running the air pump and motors one or two at a time with no real loading, 30 with regulation to a real 12 or 12.5 not the normal 14 that comes out of some 12 v supplies. Life will be good. Btw Sony makes a Camera power supply AC-500. It's a switch mode that is very costly new But can be found on E-Bay, I had one, I fixed years ago, and it would Supply over 30 amps (tested) even though they are "rated at about 7" It would not start up with that kind of load on it but took it over night on a resistor load. Reason I mention this is Switch mode will be lighter and portable camera power supplies like this are clean and built to take the beating video crews put on them.

Currently, our drivetrain is composed of 4 motors and draws about 18 amps under no load. With the pump on board, I would say add another 10 amps for a total of around 30 amps average. Perhaps, I should look for something a little beefier than 30 amps.

For instance:
Pyramid 40 Amp - http://www.brilliantstore.com/electronics/pyramid-ps52kx.htm

I took a look at the sony power supply. It's a nice unit. I would like one that easilly shows me amperage. Plus, after calculating the numbers 30 amps would be close to the threshold anyway.

[Al Skierkiewicz]

I was thinking about using a 12V power supply capable of providing about 30 amps while working on the robot in the pits. Does anyone have any reccomendations, horror stories or insight? Thanks.

Mike,
Astron makes a series of heavy duty power supplies for amatuer radio use up to about 70 amps. You do not want a switch mode power supply since the start load on drills or chalupas will kill the feedback and shut down the supply. If you have multi motor drive with any kind of friction in the drive train than you can expect easy spikes to over fifty amps at start up or direction change.

[MikeDubreuil]

Mike,
Astron makes a series of heavy duty power supplies for amatuer radio use up to about 70 amps. You do not want a switch mode power supply since the start load on drills or chalupas will kill the feedback and shut down the supply. If you have multi motor drive with any kind of friction in the drive train than you can expect easy spikes to over fifty amps at start up or direction change.

So something like the Astron RS-70M (http://www.astroncorp.com/linear.shtml) ?

[Greg McCoy]

Yeah, I would think that that would work well for light testing.

[Al Skierkiewicz]

So something like the Astron RS-70M (http://www.astroncorp.com/linear.shtml) ?
Mike,
The 70 A would be OK and cheaper I think. The "M" indicates meters and you usually get a premium for those. Again, the wires you use will drop some voltage so you might want some welding cable (#2 or larger)to run from the supply to robot. Before you commit dollars, use a current meter and find out what the current draw actually is. A supply with enough current to drive the robot might easily be worth several batteries.

[MikeDubreuil]

Mike,
The 70 A would be OK and cheaper I think. The "M" indicates meters and you usually get a premium for those. Again, the wires you use will drop some voltage so you might want some welding cable (#2 or larger)to run from the supply to robot. Before you commit dollars, use a current meter and find out what the current draw actually is. A supply with enough current to drive the robot might easily be worth several batteries.

Thanks, I'll check out the current situation when I get back to Boston :D

Right now I'm on co-op at home and just putting together a list of problems and areas my team needs to work on when I get back to Boston in May. Power was an issue for us this year. We never seemed to have fully charged batteries.

Therefore, another plan of mine is to take your advice and just buy the charger that came in the kit. I thought I could make a mobile power station. Buy 4 of the midtronic chargers. Make 4 slots for the Exide batteries. Even keep a smaller spot avaliable for charging a 7.2V backup battery. Then get some sort of power supply to power the robot while in the pits. Slap some wheels on it and you've got the "mobile power station." So after many hours, and probably close to $600 later, our power problems will be solved... hopefully.

[coreyjon]

You could also build your own power supply? It would be alot cheaper, maybe not a nice looking, but definatly cheaper.

[coreyjon]

Howdy again, Just a site that might be of interest..

http://www.mitedu.freeserve.co.uk/Circuits/Power/1230psu.htm

enjoy!

To increase the ammount of current this circuit can handle, all you would need to do I beleive is add more transisters and resisters in parallel, once you look at the circuit you will understand what I mean, You will see six transisters that take the brunt of the current load, simply add more and It should be able the extra current, but this circuit can already handle spikes of more than 100 amps.

[andy]

Hmmm...

I had been seriously considering taking a 750 or 1000 watt 12 volt lighting transformer and using it. However, the idea was kinda scrapped when I discovered, the output was AC and it was not regulated or filtered.

I was thinkin about building a bridge and adding some smoothing caps, but I figgred I should probably test its output before I hook it up to our 'bot.

Btw, it is a linear supply, simply a big transformer in a box, nothing fancy.

Just thoughts...

-Andy

[Max Lobovsky]

We bought a large full sized car battery for this purpose and put the standard quick disconnect on it. We just plug it in when we go back to the pits and dont worry about anything. It lasts us all day at competition no problem.

[MikeDubreuil]

Howdy again, Just a site that might be of interest..

http://www.mitedu.freeserve.co.uk/Circuits/Power/1230psu.htm

enjoy!

To increase the ammount of current this circuit can handle, all you would need to do I beleive is add more transisters and resisters in parallel, once you look at the circuit you will understand what I mean, You will see six transisters that take the brunt of the current load, simply add more and It should be able the extra current, but this circuit can already handle spikes of more than 100 amps.

Yeah, I saw that on a search of google myself. The problem is that you still need a power supply, called the secondary in the schematic. Your current output is not limited by the number of transisters but by the power of the secondary, which in the case of the schematic is 35 amps.

[Al Skierkiewicz]

OK Guys,
There was a lot posted since my last post. So one at a time...
There was a team at Midwest that had just such a cart, Mike. it looked like it had four, six amp chargers on a top shelf and room for 6 batteries on the bottom. The cart followed the robot onto the playing field.
Building your own (or rolling your own in experimenter's terms) does save money but you must know what you are doing. 35 amp, 12 volt power supplies are after all, 500 watt devices. The right size wiring and layout are extremely important. In these designs, even the resistance of the transformer comes into play.
Corey, the power supply you reference looks really wrong to me. The output regulation is dependent on the current through R7 being constant and for our purposes it never will be. The base voltage on the pass transistors will vary with voltage developed across R7 and therefore the output will vary proportionally. The output of a 24 Volt transformer will be more than 33 volts peak. Throw away a few volts for the drop of the internal resistance of the transformer, diode drops and R7 and you have the 7812 trying to drop almost 20 volts. At 871ma that is close to 20 watts so I disagree with the designer that the 7812 will run cold. I do agree that the currents and voltages as shown, would be the expected values with the stated load, but regulation would be comprimised with a varying load. Of course a hard regualted supply is not needed for our purposes as long as the stated maximums for the RC are not exceeded.

[MikeDubreuil]

OK Guys,
There was a lot posted since my last post. So one at a time...
There was a team at Midwest that had just such a cart, Mike. it looked like it had four, six amp chargers on a top shelf and room for 6 batteries on the bottom. The cart followed the robot onto the playing field.


Yes, I think it's a great idea.

I've been debating the power supply issue. Another idea I had was to create a new robot cart powered by a large 12V deep cycle battery. Use the creation of the cart to get the kids interested in the pre-season. Use the 2004 mini-RC to create a control system onboard the cart that could activate lights and such, maybe even have power driven wheels. The 12V onboard the cart could also be used to power the robot in the pits.

[Venkatesh]

Why would you guys need a power supply of any kind to run the robot in the pits? I can see the use if you guys don't have many batteries available - then a power supply unit could be handy. But in my humble opinion, purchasing another battery might be a better use of resources.

The batteries available should provide sufficient power for both testing and field operations. Last year, team 30 had established an interesting rotation cycle on batteries, to determine which ones were charged and which ones weren't ready. This year, with freedom to use old batteries, we had far more power available. =)

By the way, these batteries seem to hold charge for tremendously long periods of time. I have a battery in my garage from FIRST which has not been charged since the 1999 season. It is still holding a lot of energy, enough to run a toaster for up to five minutes. Repeatedly.

[Al Skierkiewicz]

Yes, I think it's a great idea.

I've been debating the power supply issue. Another idea I had was to create a new robot cart powered by a large 12V deep cycle battery. Use the creation of the cart to get the kids interested in the pre-season. Use the 2004 mini-RC to create a control system onboard the cart that could activate lights and such, maybe even have power driven wheels. The 12V onboard the cart could also be used to power the robot in the pits.

There was a team that had a powered cart at GLR and another at Midwest. I have to admit, though, I am not a fan of powered devices in the pit or on the way to the playing field. There are justs too many bodies to have a powered device getting out of control in tight spaces. Although, dragging a cart up the ramps at last year's nationals was tough on the crew.

[MikeDubreuil]

There was a team that had a powered cart at GLR and another at Midwest. I have to admit, though, I am not a fan of powered devices in the pit or on the way to the playing field. There are justs too many bodies to have a powered device getting out of control in tight spaces. Although, dragging a cart up the ramps at last year's nationals was tough on the crew.

Yeah, I agree, safety would be a major concern. I'd have a kill switch and the mechanics of the cart would only allow it to go approximately 2fps. A safe enough speed for when you are walking down a crowded pit row.
The idea behind the powered cart comes from having to push our current cart over the plastic speed bump style cable covers. I don't want a lot of speed, but a huge amount of torque.