we just built a swerve for the first time and it worked perfectly, about 2 week after we are working on some stuff and we see a very high battery drain (less than 70 seconds of driving the battery went from 130% to 92%) and we tried it with multiple batteries and the same result pls help why could it be and what to do.
No need for new replays thanks
Alternate:
Wild guess: if it’s been two weeks into your first swerve you probably just have maintenance to do and/or something has come loose during your initial burn-in of everything.
Use the Driver Station Log Viewer to review the current on each channel. Find out which motors are drawing too much power.
Consider setting current limits.
Put the robot on blocks. Does it still experience the same drain? Are all the wheels running in the correct direction?
Couple things to add:
We have tested all-out abusive driving on our drive train (while running flywheel), and found that we brown-out after 8 minutes (plenty of time for an FRC match). I suggest you try running your drive assuming everything is tuned (make sure ur not dragging a wheel).
I’m pretty sure there is a STEEP drop in battery charge, from 130 to 100. The top charge in a battery isn’t ACTUALLY equivalent to 30% more battery.
Check your driver station logs for power usage. How many joules are you using? Our bot his year was using about 130 joules per match. That requires a good battery. If you aren’t using much more than that it is probably your batteries.
Just to add to this. Here’s some testing of 6 of our batteries. The initial high voltage doesn’t really last that long.
Good point, hot off the charger voltage isn’t always a good indicator of actual charge.
Thank for the help we think we found the problem we think its a cable that was loss
We didnt check it yet but will check in a few days
Could you please clarify? I would hope that another team with a similar issue could find this post to see what worked for you.
I didnt do it yet beacuse we havent tested it yet so i dont wont to spred misinformation when we will test it if it will really be the problem i will explain more and mark it as the solution
Always the first thing to check.
Now that we think we know the right answer your testing suggestion includes touching all cables and connections. Bad crimp appears to be the likely culprit.
A loose cable may be present. However, it does not directly explain the rapid loss of battery charge. A loose connection has a higher resistance, and passes less current, and thus discharges the battery at a SLOWER rate. Loose connections will result in degraded performance, but longer battery life because you can’t get the electrons out of it as quickly (speaking very generally).
Also: test or monitor your batteries. How old are they? How many cycles have they been through? Have you run a desulfation charge in the last year? Bad batteries discharge quickly.
that is exactly what I said when this was suggested but we found a loose connection and fixed it and it seem that the problem has been resolved(not 100% sure yet) I cannot explain it but maybe the loose connection had made one wheel to not be in place and to be dragged and then the other motors had to work harder
so I don’t know why but we fixed the loose connection it seems to have resolved the problem, maybe it was something else we did like some maintenance or something.
Have you been keeping your batteries in good health? It might sound ridiculous, but it is entirely possible to overfeed, starve, and injure batteries. Now, the batteries in FRC (12 volts, 18 amps, sealed lead acid) are a little bit more robust than something like a smartphone battery, but you still need to properly care for them to get the best performance.
When you plug them in, charge them all the way up!
however, don’t overcharge your batteries!
Don’t leave your batteries at 0%!
Store them with 70-90% charge
These practices should keep your battery in good health, and they’ll last for longer!
The robot sees the voltage at the SB50 connector and so does the charger. A high resistance connection between the SB50 and the battery terminals will lead to a voltage drop no matter which way the current is flowing. The charger stops charging (or changes to trickle mode) based on the voltage it senses at the SB50 so it will cut off at a lower state of charge than it should. The charging current is typically much lower than the discharge current but a loose connection can have quite a high resistance. When visiting a friend’s rookie team, I noticed that all their battery cables were so loose they flopped around when the battery was moved. The battery cables were not connected to anything. He asked “is that bad?”
This is all accurate.
This is not always true, depending on the type of charge profile. Most smart chargers will use this charge profile:
Note that the current drops almost to zero, thus the voltage loss from a high resistance in the charge circuit will drop almost to zero.
In the constant-voltage float portion of charging the high resistance connection will result in a smaller charge current vs a good connection, but at ambient temperature the battery will still be charged up effectively and efficiently. At least, efficiently from an energy perspective, not a time perspective.
So, while I very much agree that loose or degraded battery-related connections are REALLY bad, and will increase charging time, they ought not to have an outsized impact on the final SOC of a battery.
A qualitative example is charging a car battery on a charger with spring clamp terminals. The spring clamps make pretty lousy contact and cannot transmit much power, but my car battery still gets to the same 13.x volts of a full charge.
This depends on the control logic in the charger being used. A high sensed voltage can cause it to switch to trickle charge and stay in that mode. It is possible that the control logic may detect the lower voltage due to a lower state of charge and switch back to a high current but a simple control scheme probably won’t.
The charge current graph assumes a good, low resistance connection. The OP did not have that.
A lose connection provides more resistance increasing the current draw for the required voltage discharging the battery faster. I have seen it many times.
Pretty sure we’re in violent agreement there.
I don’t think that’s true, but that’s a little immaterial to my main point. I also thing the CV/float portion will bring the batteries to the same charge point, eventually. But, if you’re not convinced by that… let us crayola the math:
A 100mOhm resistance (which is crazy high for a contact resistance) at max charge current of 6A will cause a loss of 0.6V. You’ll charge to 13.0V instead of the nominal 13.6V float. I suspect most people would agree that starting at match at 13.0V should provide far more than the ~70s of runtime OP is describing.
A 100mOhm resistance would only allow the battery to discharge at 68A, which would be observed as a nearly-instantaneous brown-out while driving. Yet the SOC is still decent (not great, just decent).
If you’re talking about maintaining equivalent mechanism performance, I agree. But I think you’ll also agree that between two controllers at 100% throttle the one connected to a higher resistance load will discharge less power. In that case the extra resistance is acting as an inefficient throttle.
My thought was that a drivetrain, which operates at or near 100% throttle most of the time in my experience, won’t actually consume more power because of a loose connection. It will underperform though. (Unless there’s a compounding issue in there, like swerve wheels scrubbing a lot because steering can’t keep up).
