We, Team PyroTech have created a cheap portable battery meter.

FIRST General Forum
1

Hello FRC teams,

We, Team Pyrotech #3459, have created a product which we feel could be a great addition to any FRC team. We call them Pyro-Meters. Pyro-Meters are small, cheap, portable, volt meters that will give you a readout of your FRC batteries relative “state of charge.” These meters are used for spur of the moment in-queue battery testing action.

Imagine this: You are in queue and one of your drivers looks to you and asks “Is this Battery Charged?” instead of scrambling to line up the test leads of a multimeter, effortlessly pop a Pyro-Meter into the connector and know then and there that it is fine.

Go check out our website for more information and pricing!
http://teampyrotech.org/pyro-meter

Our team isn’t going to Championships this year but we do have some students who will be there volunteering. If you would like to have your order delivered to your pit at either Houston or St Louis, we’d be happy to do that.

Keith Mellendorf
3459 PyroTech

2

Neat product!

you could even mount the volt meter right on your robot, and see how much voltage you have by just turning on the robot main breaker :slight_smile:

3

I think that it might be interesting to do that for outreach to see how much it says the power goes down throughout it.

4

@ $20 each, every team can have one in their bag, even if they have the expensive big brother, the beak!

5

We used these at all three of our competitions, and they were very useful!

6

Even with assuming you started with healthy batteries, voltage alone won’t tell you state of charge unless the battery has been off charge for a while… And even then this won’t be a great method.

Considering what each match cost, this isn’t a good solution on rely on.

7

Here’s one we put together back around 2013.
http://team2168.org/index.php/resources/electrical/253-make-a-mini-meter

I like your use of a 3d printed anderson connector.

Like Adam said though, we dont really use this solution any more as it doesn’t identify batteries with bad cells or that have a high residual charge from just coming off the charger. These batteries can indicate a full charge under no load, but apply a few amps load and the voltage drops down to 9v immediately (bad cell).

So a suggestion for improving your product… Add a large power resistor across the battery leads on your battery tester. This shouldn’t increase cost significantly, but will give you a better feel for the charge of the battery. Just plan to address the heat the resistor will be producing. Maybe add a momentary switch on the meter so you need to hold down a button on the tester to place the power resistor in circuit… That way you can see the voltage dip under load.

Sent from my 6045I using Tapatalk

8

I agree. We used something like this last year. It just told us the voltage. Unfortunately we had a number of bad batteries which seemed good under no load (12.7V). But as soon as we started playing a match, it would brown out. Dropping to under 10V.

9

I don’t want to poke holes in anything or take away from the effort that has gone into this tester but I did test this product at NC State Championships and this tester does not check battery health like the beak does. It was only able to measure the unloaded voltage and when we grabbed a battery that had just been in a match it measured that the battery was fully charged at 12.7V but under load it did not measure as charged on the beak (like 70% charge) and the beak reading told us that this battery needed to go back on the charger.

I feel like with a bit of work and development it could become a cheaper and more obtainable solution for other teams than the very costly battery beak. Trust me if there was a cheaper solution that you guys made home grown in NC we would certainly buy several for the teams in our area.

Do not stop development on this product and keep going with it!

10

To address these concerns: We do not mean to completely replace the Battery Beak. We also do not intend to be a load tester. Our product is more in the ways a battery comparing device. We intend it for usage on already known to be good batteries. That is why we did not advertise as a battery beak replacement. Apologies for any confusion!

11

A problem arises then with residual charge after charging a battery. Any batteries you compare should probably be off of a charger for some time before comparing them in that case.

12

These are strong points made by everyone here, but I do believe that the Pyro-Meter works great as a last minute comparison device.

In response to the point

“A problem arises then with residual charge after charging a battery. Any batteries you compare should probably be off of a charger for some time before comparing them in that case.”

For the AGM Lead acid batteries that we use, to read an accurate voltage off a battery would require that you leave it at rest electrically and physically for at least 4 hours. And at 68f. Some manufacturers say it should be more like 24 hours.
*One of our mentors is an electrical engineer who has experience with these types of batteries. If desired I could send him here for some more technical talk about the batteries and the use of these meters.
The bottom of this google doc has some info on this.

In competition, our team cycles our batteries constantly, so it is never close to being at rest. With no battery sitting for very long. This puts the batteries at a fairly equal starting ground, where measuring a ‘good’ battery will be different than a ‘bad’ battery, which is exactly what we are looking for.

We have a Battery beak that we use to keep track of the health of our batteries. We aren’t trying to replace the beak for that purpose, just for the last minute in-queue quick tests.

because of how we test it just after it comes off the charger it does have that inaccurate higher than it should be voltage, but that is different than a battery that has come off a match, which allows you to not put the dead one back in.

13

Absolutely correct. However, imagine variations on this kind of situation.

Your rookie alliance partner just pulled their battery out of the robot. You call them over to talk with you, or maybe the MC starts of the Macarena.

They put their battery on their cart right next to the newly charged battery.

Then they return to the cart and, OH NO!, which battery is charged and which just came out of the robot?!? Both batteries were good on Thursday, practically brand new, never been in competition before.

It’s a reasonable bet they are both still good. That’s why the replacement was in the cart. The plan was to use the replacement. That’s still the plan.

But which one is the replacement that just came off the charger before the last match and which one is the one that was used in the last match? The Pyro-Meter solves the problem.

The one off the charger is going to read very high; it just came off the charger, lots of surface charge effects. The one that was in the match is going to read lower, it has just been used hard in a match.

Our students use our team’s battery beak regularly to assess the health of our batteries. Bad cells are generally discovered in the pits. However, drivers want something fast and easy to read in the drive queue, and this seems to fit the bill.

When addressing an unknown battery, the risks are greater of getting a meaningless reading. With batteries in fast and furious use from match to match, a voltmeter will not get an accurate reading of “state of charge” nor of “battery health.”

However, with 2 healthy batteries that have been on similarly active charge and discharge cycles, there is a good chance that the battery that reads 13.1, just came off the charger and the one that reads 12.4 or 12.5 has been used recently. So for quick and dirty comparisons, it increases the odds of getting it right.

Hop over to the pyrotech website (teampyrotech.org) and read the FAQ there and then make suggestions that the students of pyrotech can act on to help raise the overall understanding of how battery assessment works.

Rob Mackie
Co-Coach, 3459

14

Would it be possible to put a large resistor on there just to allow teams to load the battery slightly while checking it? I like the idea of this, but maybe a small draw of 10A or so would help check it.

15

If I am reading Rob’s post correctly, he seems to be saying that the whole point of their idea is to test for surface charge… as an indication that the battery just came off the charger.

Surface charge voltage is best read open-circuit, no?

16

You’re right, but I was wondering if testing it under load could be more useful as an overall charge indicator instead. The surface charge usage seems to be an edge case.