Battery Charger and Charging Cart

We are a third year team focusing on robot reliability. One element in this endeavor is to have a reliable battery source. In order to do so, we plan to round out our batteries to 6-8 and have a six battery charging cart.

Questions. What battery chargers do you recommend? We are currently planning on using two of the AndyMark am-2026.

Are there any chargers that have built in battery diagnostics. We are planning to purchase the CTRE Battery Beak for testing, but this seems to have some limitations.

Any other recommendation as we embark on this project?

Here are the “rules of thumb” I always go by when advising new or young teams on batteries:

  1. You should plan to acquire 6 new batteries every year.

  2. You should only ever use batteries in your robot for official matches which were purchased for this year or the previous year. For example, I would recommend AGAINST using a 2016 battery in your robot for an official match in 2018. You can use older batteries for things like testing, practicing, or charging pneumatics.

  3. You should be capable of charging at least 6 batteries simultaneously. Have chargers that you can set to 2 A or 6 A. I have never felt the need to acquire new battery chargers on a regular basis; as long as a they are working, you can keep them in circulation.

  4. Only put batteries in the robot for an official match that are measuring above 13 V with a voltmeter. (Other more sophisticated battery health information is useful, but voltage is a quick check with a multimeter that will 99% of the time tell you what you need to know).

Using these rules of thumb brings us to 12 batteries in service at any given time, and at least 6 chargers. If you play in a full set of playoffs, that will be 9 matches in possibly as short as 3 hours. Playoffs is the last time you want to be throwing an uncharged battery in your robot, so 10 is the lowest I would ever want to go in number of batteries from this year or the previous year, but then you leave yourself very little wiggle room for a teammate to drop a battery, or lending one to an alliance partner in need.

(Pre-emptive disclosure: for about 16 more work hours, I work for AndyMark.)

The am-2026 charger and Battery Beak are excellent choices. Some people go for lower wattage and more banks, but a smart charger (like that one) knows better than to dump six amps in all the time.

One thing I’d suggest, since you’re building a cart from scratch: make your workflow more idiot-resistant while you build. (You don’t want idiot-proof, you know what happens then.) Two things I’d implement on my next battery setup:

  1. A simple 30-minute countdown for batteries that get placed on it, so you know when the internals have had a chance to cool down and it’s good to charge. (This is a step that I’ve screwed up for years, either charging too soon or letting them sit too long and needing a new battery.) I think the most idiot-resistant way to time this would be momentary switches (so you just put the battery in its spot), an Arduino to keep time, and some LEDs (or an addressable strip) for an indicator.

  2. Two spots at the end. Your battery chief puts the two best available batteries there. Pit crew loads one in the robot and one under the cart. The second is a paranoia spare, but when your partner freaks out because they forgot to put one in or they don’t know if they swapped it out in the pits you’re the good guy.

And while you didn’t ask: Battery Tips - AndyMark, Inc :slight_smile:

Edit to add:

A multimeter is going to miss a bad cell inside, which you aren’t going to catch until the battery is under load. It is better than a poke in the eye, but a Battery Beak is a better measurement. If your battery takes a tumble (which along with carrying by the cables is the top killer of batteries before they reach old age), better still would be Big Al’s favorite: the West Mountain Radio CBA. The steady 10A draw would suss out a bad cell for sure.

wait wait wait wait wait wait… WHOA Are you leaving andymark?

Considering Billfred’s location and this post, I’d say he is.

Yeah, I added this and “Come take my job!”](Careers - Company Info - AndyMark, Inc) to my signature too. :stuck_out_tongue: It’s nothing against AndyMark–it just happened to be the second office job I’ve had in my adult life, and that was enough to form a trend line about office jobs as a whole. So I’m moving home to South Carolina and starting my own (mobile) business. :slight_smile:

Now, batteries.

I can see how some teams need to buy 6 new batteries every year, and keep a whole bunch of them around…but not all teams really need that. We have done ok with about 6 good batteries, and then when they get to either be a few years old, or show signs of not performing reasonably well, we replace them as needed. But we also generally build relatively low demand robots, without nearly as many motors as some teams use.

We finally build a battery cart that I really like. I end up hauling the robot and equipment often, so it’s important to me. Our latest cart is small, holds 6 batteries and a triple charger. We find that even in eliminations, we can get by with only 3 chargers.

And it can be loaded into a truck or van without removing the batteries, by two people.

The best part, of course, is the wheels.


Eye twitches Those wheels… I remember those wheels…

Yes, but that wooden leg is cheating:] .

We built a couple of 3-battery boxes from 2x lumber with handles. We’ll modify a hand truck to make shelves, mount chargers, and be able to roll them around one of these days; for now they live at the right end of a workbench. I’ll try to remember to get a pic this evening.

I think the minimum number of active, competition batteries a team should have is 6, with at least 1 testing / spare / fill-the-compressor battery available. Ideally you should have 9 to get through elims without having to ever reuse a battery, but 6 is fine. I don’t think you ever need more than six charger ports in a pit at once regardless of battery count.

Any reasonably competitive team should cycle their batteries at least every 3 years - so that would mean two new batteries a year in the 6-battery plan. Batteries should be numbered and dated. In a perfect world you use new batteries every year and your 1-2 year old batteries at home for drive practice or as your tester battery, but there are budgetary and environmental concerns with such an approach.

I wouldn’t recommend any team go with any solution less sophisticated than a Battery Beak. If a Beak even saves you from one bad district qualification match (the cheapest in FRC), the Beak has paid for itself. Others have mentioned that voltmeters won’t catch dead cells, but the Beak also does a better job cutting through surface charge which can mislead you into thinking a battery is way more charged than it is.

In any case, a voltmeter sure is better than winging it.

Here’s a decent 2012 thread about battery good practices.

Here’s some things I’ve said on the subject of administrative controls on the way your batteries get used on your team. Here’s things I would add to that list today:
– give each battery a unique name
– establish a logging system that records which battery was used in each match
– you can parse the code that’s inscribed into the top of your battery to determine its manufacturing date

We too have a similar set up as team 1726 and Mr Forbes. Couldn’t be happier with triple charger ours though is built into the bottom of our rolling tool chest. What i like most about the charger is it has indicator lights on it, to tell you if the battery has a good connection and is charging and when the battery is fully charged.

One suggestion I’ve been giving people lately is to consider adding LED Voltage Meters to their battery carts. Obviously they are no replacement for a Battery Beak but they do act as good short-hand to compare all your batteries voltages at once, which you can then confirm with a battery beak. Also worth noting, if you plan ahead, you can get the same meter I linked above for less than $1 each if you buy them from China, the downside is they take about a month to get through shipping.

Additionally, I would recommend not only good ventilation of your battery cart, but active cooling through the use of fans or other means. Keeping batteries colder can drastically improve their longevity and also improves the rate they can be charged. Note that this only applies when charging and storing batteries, since cooling batteries decreases the discharge rate which isn’t a good idea if you’re trying to draw a lot of current quickly (IE during a match).

There has been a lot of good advice given already.

In addition, I would recommend the following:

  1. Don’t make the cart too tall and top heavy.
  2. Include handles so that two people can pick up the cart and move it. Holes in the body might be better than handles that stick out.
  3. Make sure the footprint of the cart will fit in your pits.
  4. Design it so that the cart can be transported upright or on it’s back while loaded.
  5. Make sure there is some mechanism to prevent the batteries from falling out while the cart is being moved.
  6. Include space for your accessories such as a log book, Battery Beak and DVM.
    *]Make the cart very sturdy since it will be subjected to a lot of shock as it is rolled around parking lots and over seams in walkways. Consider using metal angles to reinforce the corners.

Sounds like the list of requirements we came up with when we designed the cart in my post above.

Except for one that we missed, but only because we haven’t got there yet. We don’t use a battery beak, we just check voltage of the batteries (when we get a student who understands that this is important). And the log book…I think we had one student who did something like that one year. It’s a fun challenge, trying to get the team interested in batteries. A true test of a mentor’s coaching ability.