Dumping Yard Cart Power Review

Hey,
I am building a yard cart with a dump trailer. I am a professional programmer, so understand the code side pretty well. I would like to have someone with more experience with the power/wiring side to review what I am planning. It will be powered by 2 12v batteries, and those batteries will power everything. I don't want to burn anything out.

Here are items it will features:

  • 2 wheel chair motors (will be using the brakes as well)
  • Linear actuator for dumping up to 300lbs.
  • Remote control with an XBee receiver
  • rotating caution light (goes on when unit is moving - nerd factor only)
  • front lights
  • Touchscreen for changing settings and provide info
  • Cooling fan for enclosure
  • Thermometer to monitor the enclosure temp.
  • Voltage meter

I plan to use:

  • Ardunio Mega
  • Sabertooth 2x60
  • Wheel chair motors/brakes
  • 12 V motor control
  • 24v to 12v step down module
  • Linear Actuator
  • Touchscreen
  • (2) 12V LED Front Lights
  • Rotating Caution Light
  • (2) Voltage Regulators (for 3.3V power for XBee)
  • 12V Relay (4 on board)
  • 24V Voltage Meter
  • 5V Thermometer
  • LED Power Light

I have a save a drawing of what I plan to do, not a schematic but I hope everyone can get an idea. You can view it here:
Imgur

You'll probably want some fuses in there somewhere; at minimum put a fuse near the positive terminal of your battery. What you should do is after that main fuse, run the positive to a "power distribution panel" - and branch off from there to fuses, one for each "branch" of your system. This panel might also include (after the fuses) the voltage regulation systems for each branch (as needed - some parts may not need anything because voltage regulation may be provided on-board the PCB - but you should have fuses for everything).

I also fail to see your physical emergency cut-off switch - put one on (ideally, it would be something that could physically kill the power between the motors and the battery, if nothing else). You should include such a switch (as well as a remote activated one).

When you decide to build and test the chassis of this machine, test the drive function with the machine "up on blocks". I have seen more than a few experimenters build wheelchair-based robots not do this, and they have either been injured or have had property damaged because of a "runaway" system.

Finally - when your system is complete, you might want to invest in and place on the areas needed (such as around the lift/dump mechanism) stickers and such indicating potential hazardous "pinch/crush" points in the mechanism. You may be the only one using this machine, but even then - one moment of inattention or complacence can be enough to ruin your day. Such stickers won't stop this, but it may serve as a bare reminder that might just keep you from sticking your fingers or hands where they don't belong...

It will be powered by 2 12v batteries, and those batteries will power everything.

Are the motors 12V or 24V.... From the bill of materials, it appear that they are 12V. So why run the batteries in series? The 24V to 12V step-down module is probably only 92% efficient, at best. If 12V motors, I would suggest a single larger 12V battery, or two 12V feeding the high-current motors separately and balancing other 12V needs between the two.

There are certain considerations for parallel wet/gel cells:

Ray

cr0sh:
Thanks for the information. I am playing around with the wiring diagram to add the stuff you mentioned - great ideas. I am going to just replace the main power switch with a large red kill switch that is easy to access and play around with using a 24V relay as a remote kill switch. I found some 24V marine breakers with a reset switch, plan to try those out and see what I can find for further up the power grid.

I agree on the stickers, we have a vinyl cutting machine here and will add these to the finished cart.

Thanks again!

mrburnette -
They are 24V motors each. I found that I can run a separate positive lead from just one batter to create a 24V feed and a 12V feed, but I see a lot of mixed reviews on doing that. Do you know of a more reliable way to get 24V down to 12V?

run a separate positive lead from just one batter to create a 24V feed and a 12V feed, but I see a lot of mixed reviews on doing that.

If the 12V feed is to supply the Arduino, etc. then I do not think that is a serious concern since the Arduino has a 5V regulator. If the current draw on the 12V tap is significant the this causes the lead-acid cells to discharge in a non-uniform fashion, so your recharge schedule would always have to be based on the "lower" battery since it is affected by all currents flowing.

Ray

But the normal 12v deep cycle battery is running at 40 to 50 amps, doesn't the Ardunio Mega max out at 1 amp, just want to fry it.

Looks like your biggest 12V burden will be the linear actuator. Could you buy a 24V version of it? Then your only 12V load would be Arduino and lights. The other option is to let it be a 12V actuator and run it from another 2x60 motor controller off 24V. Just don't take it over 50% speed very long. Not sure what your question is about the "Arduino amps". The Arduino will most likely pull about 50mA so that's insignificant. As Mr. Burnette pointed out, it's when you SIGNIFICANTLY unbalance the draw on the batteries is when you get charging problems since the battery you're using for your 12V tap will be more heavily loaded. I would think if you stayed below about 10% difference you should be OK.

-Rob.

Hey,
I think I did what was suggested, did away with the step down and ran a line from the battery so I have a 24V and 12V feed. Also added breakers breakers on each feed, made the main power switch a larger one for emer. cut off ease and added a remote cut switch. I added the power and remote cut to the negative lead, any problems with that. Since there are now two positive lines, didn't know a way around that. Didn't have to worry about reducing down to 5V for Ardunio as the Sabertooth supplies the controller with a 5V feed.

You can view here, again, any input is greatly appreciated.
Imgur

main power switch a larger one for emer. cut off ease and added a remote cut switch. I added the power and remote cut to the negative lead, any problems with that.

YES!
Do not do that. Use a double-pole single-throw to kill the two positive feeds.

Attempting to kill ground causes the +12 V feed to become ground! While proper safety diodes in the SaberTooth "should" prevent current leakage, it is just not a good idea - my opinion.

Ray

Gotcha! I will get a double pole switch and use 2 relays (for remote kill) - all on the positive.

So, something like this:
Imgur