Do backup batteries actually help?

Hi Everyone,

At our team’s last competition, we used a Backup Battery for the first time. We never believed it made any difference before but we wanted to try it out (as we heard from our coach that it helps with a resetting Cortex).

Well, the Backup Battery did more harm than good. For two of our first four matches, we had battery problems. With a fully charged battery (8.4+), our robot would blink red on the cortex and then reset at the start of the match. It was frustrating as it was our only loses for the competition :(. We then tried unplugging the Backup Battery for the remainder of our matches and we never had an issue.

So I would like to know how many of you guys actually use backup batteries and if they work well? It’s possible that our Backup Battery was DoA, as it was brand new.

Thanks for the help!

I think we generally start the competition with a backup battery plugged in (our inspectors usually look for it). Then, at some point during the competition, we get annoyed with the cortex not turning off when we turn off the power switch (because the backup battery is plugged in and it thinks it’s on field control), so we unplug the backup battery and never plug it back in. :smiley:

They might have fixed this in the new (in April) firmware update, or maybe that was just the robot LED showing the backup battery status?

Anyways, it’s probably a good idea to use the backup battery, and it can help if you overdraw the cortex.

A non fully charged or non plugged in back up battery causes the robot led on the cortex to be red instead of green when plugged into field control
Refs and field control don’t care if the led is red though, as long as you are linked they won’t say anything

In my experience back up battery causes disconnection and linking problems
Some people’s response to that is that the back up battery is not fully charged
I think that may be true since I only use it to pass inspection, thus half the time the battery is actually dead.
Another pain to back up batterys is that if you shut the controller off first then the robot the back up battery keeps the cortex on which is annoying.

In my opinion, the cortex can still relink if it loses connection without a back up battery, and the negative affects of the back up battery when not fully charged outweighs having one plugged in.

What I do is plug it in halfway so it looks connected but the leads are not actually touching thus at all times the robot apears to have a back up battery plugged in.

Also only large events like nationals, worldchampionships, or large regionals like pacific-northwest require you to have back up batterys. Small regional competitions like in your city or whatnot do not require you to MUST have one but only reccommend the installation of one.

In short, my opinion is that back up batterys do not help.

Backup batteries can help during matches as sometimes motors overdraw current, or wear and tear on the cortex battery port can occasionally cause dips in power. A backup battery allows you to maintain a steady vexnet connection when these events happen, rather than disconnecting in the middle of a match.

Yes, we do, but 95% of the time students ignore us.

A backup battery with low voltage is probably worse than no backup battery.

Thanks for the tip, we will be on the lookout for you at worlds.

There’s nothing to fix, this is a feature not a bug. Disconnect from field control before turning of the cortex.

Using a backup battery is a good thing. It keeps VEXnet connected when your motors cause the main battery to brown out. Don’t let anyone tell you otherwise.

Long (quite old) thread about the backup battery here.

Fair enough, but why have the Cortex stay on after the switch is turned off?

andre here, never had any problems with a dead or nonexistent backup battery
with the old keys it seemed like the backup battery was more of an issue

it seems like brown-outs should be prevented on the cortex using a capacitor

using a battery extension cable to prevent the cortex battery connector from being damaged would help

Ah the cables are finally in stock! We’ll have to add them to our next part order.

But that’s the point, the backup battery takes over when main battery is not available. Unfortunately it’s not possible to tell the difference between a low main battery, a missing main battery (ie. it became disconnected) and the power switch being turned off.

Okay, so it sounds like having a backup battery is a good thing, besides the annoying act of unplugging it and re-plugging it after every match.

If this is the case, why do you believe we were having problems when we were using the Backup Battery?

Ahh, I see. I wish it could tell the difference, but that can’t be fixed at this point.

Was your backup battery dead? Was the main battery connector bad?

That could not possibly become an issue. :smiley:

Seriously though, when motors are turned on to full power, they draw a lot of power. If code doesn’t ramp up power, going from -127 to 128 on several motors will certainly strain the electrical system.

I am not sure how the power expander would affect this issue, but perhaps when the cortex is updated in the far future, the two batteries are controlled by the same DPST switch.

Both the Backup Battery and the 9V Battery were brand new. The battery connector in the Cortex, from what I know, is working well.

For the two matches our robot died, everything worked well until the start of auton. All lights were green, and batteries were fully charged. Once auton started, the red light for robot went red and we lost power. Any ideas?

I’m sorry, I don’t know what you mean. If you change the motor values to a higher number, you won’t strain the electrical system?

Anyway you explain that a bit more please? :slight_smile:

This hinges on how electrical energy is converted into mechanical power.

If you need to go from full speed reverse to full speed forward, you need an acceleration. The formula F=ma has the rotational equivalent: torque = rotational inertia * angular acceleration.

Changes in rotational velocity are due to angular accelerations, which are supplied by torque. Torque from the motors correlates to power. I am not entirely familiar with with this exactly, but you should be able to find motor curves by searching on the forums.

I hope this helps.

Having a backup battery also allows you to control pneumatics if you do not have a regular battery. In a match, out battery got pulled out when we were about to score, and we were still able to release our pneumatic to score our 3 Bucky balls.

The backup battery is only used when the robot is connected to field control, and when it isn’t it will turn off with it plugged in. After the match, just unplug your controller from the field, then turn off your robot, and it go off right away as it recognizes it isn’t on field control anymore.

One time our back up battery saved us from losing a match.
We thought our batteries were good but they died shortly after autonomous
And some how we played the match and won using nothing but that little 9v. It some how managed to power the entire robot.

We have done that before that’s why we use rechargeable 9v batteries. We have 2 of them and we swap them out very time we have a match. I know that a little over kill but it has saved us.

There has already been a lot of thoughts posted here but I also believe that back up batteries do have their part on our robots. We have always used one to be safe and while unplugging it quickly after each match at competitions is annoying I think it is worth it. Plus if you lick the leads on the battery you get a pretty neat shock so it’s a win/win situation.