VEX Battery Charging

So we understand that if the light is blinking that means that the battery isn’t charging correctly right? Well it seems that all the batterys are blinking no matter what. Does this mean that they are already charged, does it mean that some how all our chargers are damaged? What does this mean?

It’s been my experience that this occurs when you try to charge an already charged battery (or only a slightly discharged battery). Try running it some more and then charging it.

As I understand it, the light on solid means the battery is charging, when it starts blinking it means it is mostly charged, but still a bit more to go, and when it goes off then the battery is fully charged.

But if you put two batteries in one charger, and either is very low on charge, it will charge one with a solid light and not charge the other at all, until the first is charged enough that it goes into “blinking” mode, then it will switch to charging the second battery.

Comments? Link to the instructions for the battery charger? Make some voltage measurements of batteries in various states of charge, and see what happens with the light?

Hey, how well do the vex battery chargers work for you? We get better results with other chargers.

Its my understanding that a flashing light corresponding to the slot the battery SHOULD be in means some type of charging error. The problem could be the battery or the charger. If the light is off it means the battery is fully charged. If the light is solid on, it means it is currently charging.

Now, above I said SHOULD because I frequently see teams in a rush to recharge batteries for the next match, just lay the battery on the table and plug the connector into the charger. If this is done, you run the risk of permanently damaging your 7.2V transmitter battery due to overcharging. For the 9.6V robot battery, you run the risk of undercharging and not being prepared for the next match. Either way it is not a good condition. If you look closely at the charger, there are two pressure switches in both slots that look for the presence of the larger 7.2V battery. This is how it knows which battery is being charged and sets the appropriate charging voltage and current.

My team currently has 5 power pack kits and we have identified 2 of the 7.2V robot batteries as being bad. We cycled them through all the chargers in all the slots and they consistently resulted in a flashing LED no matter what charger or slot they were in. We did the same for the remaining batteries including the 9.6V transmitter batteries with no charging error seen.

If you have multiple chargers, you may want to try the above exercise to determine where the problem is. Do this while making sure you properly seat the batteries in the slot.

PS… make sure you seat the battery before you plug it into the charger.

We have always made sure that the battery was properly seated so the batteries aren’t bad. I’m thinking that maybe if the batteries are already charged that maybe that will also result in a blinking light. We had a competition yesterday so we had the batteries on charge throughout the week, then friday night we put them back on and that was when we got an abundance of blinking lights.

That is what the instructions say.

The instructions do not however indicate what kind of error could be occurring.

You can connect the 7.2-volt battery to a VOM and measure the voltage across it. It should read a voltage > 7.2 volts if it charged correctly. The 9.3 Volt battery should read a voltage > 9.3 volts if it is correctly charged. If you still have problems charging the batteries then make sure that they are firmly seated in the slots correctly in order to trigger the correct voltage selection switch (7.2 volts vs. 9.3 volts).

You can insure that the battery is completely discharged by connecting a small 12 volt motor to either battery and letting it run until it stops, or just connect a 12 volt car signal bulb and leave it on until the battery is completely discharged.

Actually the 7.2v and 9.6v battery normally read higher on a voltmeter than 7.2 and 9.6 respectively. Another thing is that checking a one other the batteries with a Voltmeter doesn’t tell you much, from what I understand with these batteries the voltage will remain more or less the same and then suddenly drop when the battery is close to being discharged. It was described to me as a graph like this,


With voltage on the Y-axis and time on the X-axis. So you might be right before the fall and the battery would read fine.

Hmm can’t seem to get it to format correctly, hopefully you can see what I mean, Ignore the 0s look at the line.

The battery has to be in the holder right? This one got me.

The VOM can still be used to check for shorted cells that would give readings of < 7.2 volts for the 7.2 battery or < 9.3 volts for the 9.3 battery even after being charged. Another test you can perform is to measure the voltage under a full load by connecting the VOM leads on the (+) and (-) terminals of a 12 Volt DC Motor and see if the voltage drops too low.

Quick FYI - The transmitter battery is a 9.6 Volt battery, not a 9.3 Volt battery. - Blake

Bold words are corrected.