Batteries parellel

[fmcgee1110]

Can you run the batteries parallel on the robot?

[Oblarg]

Originally Posted by fmcgee1110

Can you run the batteries parallel on the robot?

You are only allowed to run the robot off of one battery at a time.

This is in the rules; be sure to read them thoroughly.

[Christopher149]

Do you mean to have multiple batteries on the robot? That would be illegal per:

The only legal source of electrical energy for the ROBOT during the competition, the ROBOT battery, is one of the following approved 12VDC non-spillable lead acid batteries:

whether they were in series or parallel.

If you mean something else, you'll have to be more clear.

[fmcgee1110]

Thanks for the help

[pntbll1313]

If you are meaning "will it break the robot", then no. You can definitely do it however it is not legal at competition. You could for a parade or demo though. It may not be healthy for your batteries however.

[BBray_T1296]

Is it legal on a competition bot?, no, for reasons stated above.

Is it possible, yes it is. We have a robot dubbed "chairbot" that ran on two batteries plugged into a custom made Anderson splitter that Y'ed off of the main breaker (robot was once competition worthy) to accept 2 batteries simultaneously for extended life.

One important thing to note is to ALWAYS! ensure that both batteries are fully charged before plugging them in together. The current rush from a fully charged battery into a dead one could be catastrophically bad. For this reason, hot-swapping batteries one at a time is a no-go.

[Jon Stratis]

Outside of FRC applications (the replies above should make it clear dual batteries are illegal on our robots!), pairing these types of batteries in parallel should always be done in a permanent basis - pair two fresh, brand new batteries, and leave them paired permanently, while charging and discharging both. As BBray_T1296 indicated, hooking two batteries up with a voltage differential between them can be very bad for the batteries and even dangerous!

[Ether]

Originally Posted by Jon Stratis

pairing these types of batteries in parallel should always be done in a permanent basis - pair two fresh, brand new batteries, and leave them paired permanently, while charging and discharging both.

Can you please cite an authoritative source for this statement (e.g. an article on a battery manufacturer's website or a technical paper in a relevant journal).

[Daniel_LaFleur]

when connecting 2 power sources (such as 2 batteries) together, you should always use OR'ing diodes to ensure you do not get a catastrophic current if the 2 power sources are not exactly matched.

[Kevin Selavko]

Originally Posted by Daniel_LaFleur

when connecting 2 power sources (such as 2 batteries) together, you should always use OR'ing diodes to ensure you do not get a catastrophic current if the 2 power sources are not exactly matched.

Would this allow for hot swapping or would that still be insanely bad?

[Alan Anderson]

Originally Posted by Daniel_LaFleur

when connecting 2 power sources (such as 2 batteries) together, you should always use OR'ing diodes to ensure you do not get a catastrophic current if the 2 power sources are not exactly matched.

What kind of diode would you suggest for this application? Keep in mind that FRC robots use tens of amps on a regular basis, spiking briefly to hundreds of amps. Also consider that a diode's worth of voltage drop is significant.

[Al Skierkiewicz]

This discussion comes up every year. I discussed this with application engineers at MK a few years ago. They do not recommend a general statement that paralleling batteries is OK. If the batteries are known to come from the same lot, and have the same age (charge/discharge cycles) and are charged to the same exact level, then it might be OK to connect them in parallel, outside of FRC use. Lead acid batteries are used in parallel applications all the time, battery/diesel submarines for instance and large UPS applications. In these cases, the specific gravity of each cell is monitored and maintained during operation. RV applications use parallel batteries as well and there are diode accessories that are available for these applications. In most cases these are high current Schottky diode arrays used for their low forward voltage drop.

[Daniel_LaFleur]

Originally Posted by Kevin Selavko

Would this allow for hot swapping or would that still be insanely bad?

Possibly, but not recommended. The Schottky diodes allow the power source with the highest voltage to flow current until it's voltage sags below the voltage of the second source. Then they 'share' the current requirements.

Originally Posted by Alan Anderson

What kind of diode would you suggest for this application? Keep in mind that FRC robots use tens of amps on a regular basis, spiking briefly to hundreds of amps. Also consider that a diode's worth of voltage drop is significant.

One of these(Silicon power Schottky diode) might work, although I'd prefer something a little beefier.

Done properly, it's not too dangerous, but done improperly could be catastrophic. That's probably why FIRST doesn't allow it.

[tr6scott]

Ok, can someone enlighten me with some data on what we should see/best practices/avoid in the future?

When we do parades, we use a y battery connector, so that we can keep the bot alive as we hot swap batteries. We do not run the robot while in this parallel connection, it is done to keep the cRio alive, and able to continue on without a reboot.

Typical scenario:
Battery starts off at 13.5v and we drive, shoot, pick up balls with our rebound rumble bot. Typically about 10 mins into the parade, battery voltage is around 10v and things get wonky, (that is the technical term, that is really only understood by the students and drivers.) We stop the robot, plug in a 13.5V battery into the secondary connector of the y, unplug the 10v battery, and continue on with the parade. This swap usually takes about 30 seconds total. While we are doing the swap, there is little power being used on the bot, no motors running, just keeping the electronics alive.

We do this 2-3 times in a typical parade that lasts about 30 mins in Oxford. By the end of the parade the motors are hot, and ready for a cool down.

We have done this 2-3 times a year, for the last two years.

Am I risking the lives of the students, and the entire Oxford community?
Should the Y connector be redesigned with some diodes?
Should the Y connector have a some lower amp protection say 40amp automotive fuse for some catastrophic failure of the "keep alive" leg, and only use that leg to keep the bot alive? ie, time for a battery swap, plug in "keep alive" battery into the 40amp protected connector, pull 10v battery, replace with 13.5 volt battery, unplug keep alive battery. A little more cumbersome, but is it significantly safer?

Data please?

[Al Skierkiewicz]

Scott,
While not the best way to do this, I believe you are minimizing risk with the procedure you wrote. The issue with fully wiring batteries in parallel comes when they are mismatched in some way. The two batteries can actually discharge each other. If left unattended, this will result in total discharge of both batteries. While lead acid batteries are more tolerant of this fault, other batteries are not. Any search for RV battery isolators should show a variety of methods and products designed to charge and separate electrical loads with multiple batteries.