Chief Delphi - Cheap replacement for the Power Distribution Board

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Re: Cheap replacement for the Power Distribution Board

Quote:

Originally Posted by Al Skierkiewicz (Post 886206)

How about we just stick with the 24 volt requirement for all discussions. That will simplify matters for the majority of the people who read these posts.
Yes, you can stack (series wire) two 12 volt batteries to produce the 24 volt requirement. However, everyone should note that the load on any given battery will change it's terminal voltage dependent on the current supplied to the load and the internal resistance of that battery. It is not uncommon for our robot batteries to be pulled below 8 volts during normal running conditions. That is why the 8 volt trip point was selected in the IFI controller and why Eric and Russ designed the 24 volt power in the new 2008 PD to maintain output below 5 volts. The internal resistance of our batteries is typically 11 mohm and can deliver over 600 amps at full charge. CIM motor stall current is 129 amps so four or more motors in stall can draw down the terminal voltage significantly.

I agree 100% - I was suggesting two batteries in series in addition to the 12V main, not a single battery connected in series with the main. Sorry for not being clearer. I figured a veteran team would have plenty of old batteries around - not competition-worthy, but enough to power a cRIO. Now, how to fit two more batteries on a robot, that'll take some creativity.

Re: Cheap replacement for the Power Distribution Board

Just listening in, you could use 2 of the standard robot batteries in series, use 1 for primary power and series in the second one with the hot only connected to the cRio. For power flux, you could use a large capacitor or a group of smaller ones in parallel (>20,000microF Should work). This would offset the instant V-drop from the start or reveres of motors. (The primary 12 might drop to 8V and the secondary battery in series won’t be affected so it should output 12. 12+8 =20) That is within minimum operating specs for the voltage. Easy, 2 batteries, a few caps that can be found lying around or in power supplies…. It’s a bit jerry rigged I know but it looks like it should work.

p.s. The "secondary" battery would not need to be a full sized FRC battery, it could be any 12V, a smaller one would be a lot easier to fit in.

Re: Cheap replacement for the Power Distribution Board

I would suggest that you look into a voltage doubler. This would give you double whatever the voltage is on the battery. I would also be sure to put in a voltage regulator circuit and some filtering, such as a capacitor. The motors on the robot cause a lot of EMI (electro magnetic interference) that can cause strange things to happen if you don't use a filter.

Re: Cheap replacement for the Power Distribution Board

Just so we can keep everybody calibrated, the robot battery voltage fluctuates during operation from over 13 volts to under 5 volts. Filters and regulators can not help on those issues. A voltage doubler works if the input voltage doesn't change and the load current remains fairly constant. The boost/buck regulator can handle these fluctuations and provide a fairly constant output.

Re: Cheap replacement for the Power Distribution Board

Agreed, I have to get back into this mind set, lab conditions are good only in the lab. The load current should remain fairly constant, but the voltage will be all over the map, you may look into pre-built regulated power supplies. I am unsure whether they are mad for this low of a voltage or even if they are whether they would be cheap enough.

Be sure before you hook it up to anything, have someone who is very knowledgeable with electrics look it over, if you are not comfortable doing it. Also be sure to hook a meter to it and make sure that the output is within tolerances of the device being plugged into it, do this while the robot is under simulated playing conditions.