Powering Maestro's? NimH batteries frying/ over heating?

I have used both a Mini Meastro 12 Channel and Micro Maestro 6 channel controllers and I was wondering if there is a proper way/order to connect power to the board. I use 2 x 6v NiMH batteries… one to power the servos and one to power the board. I’m not sure if it’s a battery issue, a board issue, or my order of operations, but there are times where i will smell something burning and I realize it is one of the batteries frying. It’s happened to me 3 times where I have had a set of batteries become scalding hot to the touch and burn marks will appear on the plastic casing. I have disposed of the batteries each instance, and since this is the third time this has happened I wanted to post here to check if I may be doing something wrong. Thanks for your help

Hello.

If your batteries are getting so hot that they start to burn, that is a good indication that something is wrong. Could you describe in more detail what happened when the batteries failed? How long did you use each battery before it failed? What type of servos are you trying to control? Could you also post some pictures of your setup?

-Jamee

I can take pictures later when I have access to my controller, but I can do my best to describe my setup.

  • Servos used: 4 x Power HD High-Torque Servo 1501MG (bought from here)

Q: Could you describe in more detail what happened when the batteries failed?
A: Servos already connected to mini-maestro 12 channel. I connect one 6v NiMH to power the servos. I connect the other 6v NiMH to power the board. I smell something burning and when I touch the battery powering the servos it is extremely hot to where I cannot hold the battery so I disconnect by pulling wire. I notice 3 small burn marks on the plastic casing. I rip open the plastic casing on the battery assuming a short circuit, but I do not see any. I have a spare battery which I use to power the servos. Everything works fine.

Q: How long did you use each battery before it failed?
A: Immediate heat up and failure. This does not always happen though.

Set up is as follows

  • Push button connected to channel 0 using 5v output and pull-up resistor
  • Push button connected to channel 6 using second 5v output and pull-up resistor
  • Servos connected to channel 1 and 2
  • Servos connected to channel 7 and 8 via servo extension cables

Could this possibly be a problem with over-charged batteries?

[quote=“Jamee”]Hello.

If your batteries are getting so hot that they start to burn, that is a good indication that something is wrong. Could you describe in more detail what happened when the batteries failed? How long did you use each battery before it failed? What type of servos are you trying to control? Could you also post some pictures of your setup?

-Jamee[/quote]

Hello.

Improperly charging the batteries could damage them. Could you tell me exactly how you are charging the batteries? Another possible explanation might be if power and ground are being shorted together in your setup. Could you think of anything that could be shorting them (e.g. placing your setup on a metal workbench)? Maybe those photos will help me get a better idea of what is going on.

-Jamee

I charge the batteries with the iMAX-B6AC charger sold on this site.

For my 6v 2200 mA batteries, I charge at 2a, discharge to 5v at 1A
For my 6v 900mA batteries, I charge at .8a, discharge to 4v at 1A
For my 4.8v 2200 mA batteries, I charge at 2a, discharge to 5v at 1A

Everything else is default on the iMAX.

I’ll take a look at the chip later and if there are any shorts

[quote=“Jamee”]Hello.

Improperly charging the batteries could damage them. Could you tell me exactly how you are charging the batteries? Another possible explanation might be if power and ground are being shorted together in your setup. Could you think of anything that could be shorting them (e.g. placing your setup on a metal workbench)? Maybe those photos will help me get a better idea of what is going on.

-Jamee[/quote]

Hello.

Since the battery powering the servos is the one that heats up, the short could be somewhere in the servo power rails. Could you please send the pictures of your setup? Also, could you tell me where you got your batteries?

-Jamee