Re: Running Two Batteries
 

Unless you wrapped the foil very very tightly (tightly enough to rip it), it's going to trap air between the layers and act as an insulator.

What you need for cooling motors isn't a heat sink, it's a radiator. The black surface of a CIM is probably a lot more efficient at radiating IR than shiny aluminum foil, but I have no data to back up my supposition. Fins and a fan will do a much better job of cooling the case than any amount of foil wrap. But it's the temperature of the windings inside the motor that matters, not the outside of the case, and a CIM isn't particularly good at getting rid of its interior heat to begin with.

Re: Running Two Batteries
 

Sorry guys, like I was saying several posts ago,

:mad: :mad: I WAS JUST JOKING :mad: :mad:

Re: Running Two Batteries
 

We have been running two FRC batteries in parallel for years without issue on a few of our demo bots. Once nice feature is you can hot swap batteries without turning the robot off which is especially nice for LabView programmers who haven't permacoded. We have also use a deep cycle battery on a robot without issue, just make sure the bot can handle the weight of a typically larger marine battery and watch out for leaks if you're driving it.

Re: Running Two Batteries
 

Be sure to be careful of the duty cycle of the compressor. For example, the Viar 90c is only rated for a 9% duty cycle and a 1 gallon fill (approximately 3 minutes operation for every 30 minutes). If you run it too long, it will heat up enough to melt the pneumatic tubing plugged into it.

Re: Running Two Batteries
 

Have you actually calculated what these LEDs will draw? Compared to the large current demands of motors, LEDs draw comparatively small amounts.

Re: Running Two Batteries
 

LED's won't make a difference.
Something that would make a difference would be an extra CIM motor, so I'll use that for comparison.

A single CIM motor might be expected to draw about 40 amps at 12 volts during normal usage. That's 480 watts.

If you had one really bright led, LEDs are about 90 lumens per watt, so 480 watts is 43,200 lumens, which is insanely bright. A "typical" home lightbulb is about 700 lumens. 50,000 lumens is the intensity of a Nightsun, the searchlight that gets mounted to Coast Guard helicopters. If you look into one, you can go blind very quickly.

If you had a bunch of normal LED's. A high output LED uses 20 mA at 5 V or 0.1 watts. 480 watts is around 4,800 led lights, way more than you'll ever see on a FRC robot.

Re: Running Two Batteries
 

Our underwater robot has 4 three watt LEDs on it, and they aren't actually getting that much power...it's too bright to look at.

Re: Running Two Batteries
 

LEDs are beast when it comes to using little amounts of electricity and producing tremendous amounts of light.

Re: Running Two Batteries
 

Out of pure curiosity, why is the compressor running constantly? I thought they only ran when necessary.

Re: Running Two Batteries
 

One solution to the compressor issue is to get a bigger compressor. Viar has ones with a 100% duty cycle & a stainless braid hose on the outlet to deal with heat issues.

Re: Running Two Batteries
 

What do you mean by permacoding? Sounds like it is something not everybody does...

Re: Running Two Batteries
 

I think it's a word he made up, which to him means the code has been uploaded into the cRIO's flash memory.

Re: Running Two Batteries
 

I should have stated this earlier but there is a reason the manufacturers do not recommend using the batteries in parallel. While several people have done it in the past, this is not good practice. Even if the batteries are from the same lot, made on the same day, and using the same materials, there is a difference from cell to cell within the battery that will make no two batteries exactly alike. As such, it is inevitable for one battery to have a slightly higher voltage which when placed in parallel will force some current into the lower battery. As that battery voltage diminishes, the other battery will try to back feed the first. This seesaw action will continue until both batteries are fully discharged. If the batteries are closely matched and charged and the same age (charge/discharge cycles included) this back and forth will take place very slowly in most cases. However, certain variables may change that, rapidly drawing down both batteries in a destrcutive cycle. Applications that place multiple batteries in parallel, constantly monitor battery health using specific gravity tests and other procedures to prevent damage. It is possible to use Schottky diodes to isolate the batteries from each other and from the load. These are available from RV centers and are designed to parallel batteries in RV applications.

Re: Running Two Batteries
 

I wonder how GM got away with it? They ran two batteries in parallel on the diesel engine vehicles in the 1970s-80s....connected together with big fat cables. No diodes.

Huh.

Re: Running Two Batteries
 

UPS's regularly operate many sets of batteries in parallel. The batteries we use in FRC are very commonly used in these applications.