Overheating problems when charging 7.2 volt RC battery.
Dobermann (Black Dog Systems, LLC)
Posts: 71
Hello All,
I have come across a nasty little problem that is making me go bald(er). I have a robot project that is using a 7.2 3000Mah R/C battery. This battery resides inside my robots base allowing me to charge the battery without having to remove it. The dilemma is that the battery really gets HOT when recharging. I'm afraid that it may end up melting the ABS frame it is constructed from. Or worse yet result in my poor robot going up in flames and taking my house with it. Has anyone else had such a problem, and if so how was it solved. I'm thinking of using some sort of makeshift heatsink/fan combo to cool it down. I'm not sure why this battery pack would get so hot during a recharge. I am using the correct charger set for NiMh as that is what this battery pack is. I'm certain that no shorts are present. I'm loosing sleep and going out of my mind with this problem. Any help is appreciated.
Respectfully,
Michael G. Jessat
I have come across a nasty little problem that is making me go bald(er). I have a robot project that is using a 7.2 3000Mah R/C battery. This battery resides inside my robots base allowing me to charge the battery without having to remove it. The dilemma is that the battery really gets HOT when recharging. I'm afraid that it may end up melting the ABS frame it is constructed from. Or worse yet result in my poor robot going up in flames and taking my house with it. Has anyone else had such a problem, and if so how was it solved. I'm thinking of using some sort of makeshift heatsink/fan combo to cool it down. I'm not sure why this battery pack would get so hot during a recharge. I am using the correct charger set for NiMh as that is what this battery pack is. I'm certain that no shorts are present. I'm loosing sleep and going out of my mind with this problem. Any help is appreciated.
Respectfully,
Michael G. Jessat
Comments
Respectfully,
Michael G. Jessat
When you're charging a battery pack, wich of the two LEDs lights up - RED or GREEN?
Please measure the AC voltage at the wall outlet where you normally plug in the charger. This particular charger seems to be quite sensitive to the line voltage. What is that voltage?
How restricted is the area within the robot base? Is there any room for natural air convection to occur, or is it extremely "cramped" in that area?
I take it that you've had this charger for quite some time, since Radio Shack doesn't seem to show it on their web site, and the documentation would appear to be written around 04/99?
After you charge a 7.2 volt R/C battery pack, what kind of voltage to you see at the battery terminals before you use the battery pack?
Your idea about a fan is fine, but wait on that effort for a bit. I'd be concerned that there might be a faulty cell in the battery pack if the pack has been used for any significant period of time or if it was purchased as "surplus" (not that I'm against surplus goods!). Therein, the heat problem may only get worse until the bad cell is removed from the battery pack. If this IS the case, there is a potential safety hazard here as well, and not just from the excessive heat! If the gassing vent has become clogged on any of the cells, there is a potential for that cell to actually EXPLODE during charging.
Regards,
Bruce Bates
How long into the charging period does the battery become "hot?"
maunfactor, not him is responsible for warranty coverage (meaning, no, I won't give you a replacement or exchange for the
defective battery I may have sold to you). So if it turns out to be a bad cell, looks like I'm eatting at $38.99 battery. The charger
is on clearance at most Radio Shack stores in my area (Southern New Jersey). Its documentation did state that it will handle the 3000mAh rated batteries. The LED that lights up when I put the battery on the charger lights green, as it should for a NiMh battery pack. I do have slight variations in power around my house, seems living in the sticks has its drawbacks. The AC power normally will be anywhere from 115-120 volts, with the every now and again spike to 123 volts. The battery is not really cramped, but the
case will be enclosed, making direct air contact very limited. I have even tried charging this battery out of the robot, leaving it in a nice cool location in the house, but alas it will still get very hot to the touch. I'm really leaning toward the bad cell theory, but it does output its correct 7.2VDC at 3000mAh. I'm left really confused.
P.S.- The battery seems to get the hottest after about 4-5 hours on the charger.
Thanks guys!
Michael G. Jessat
Post Edited (Dobermann (Black Dog Systems, LLC)) : 6/20/2005 6:29:37 PM GMT
· I think your biggest problem is the charger you have is not a peak charger. You are doing a great dis-service to you battery pack by using this charger.· If the battery was completely drained, which it shouldn't ever be, charging at a maximum of 560mA your 3000mAhr battery should theoretically be charged in 5.35 hours.· But NiMh batteries are more sensitive to overcharging, hence the reason yours are getting hot.· A peak charger will·reduce the·charge amount to a trickle, once the battery has received the maximum charge that it wants.· It does this by detecting the peak voltage, as the battery is charged the voltage in the pack will rise, once the voltage starts to go down it has reached its peak.· If you continue to charge the batteries·it starts to dissipate the over charging in the form of heat.
· I know you just purchased·your charger but I would suggest purchasing a peak charger.· The local hobby shop that you purchased your battery from will have several to choose from.· They will have very expensive ones designed for R/C racing but you do not need to spend the money on those.· The additional "features" they have won't do you any good when just charging a battery for a robot.· If you don't find one in your local·hobby shop then check online you should be able to find one that is affordable but will still give you a peak charge.· Just make sure that it will handle your 3000mAhr battery as this is a fairly large capacity battery.
Kevin
P.S. Battery charging is a art/science/variable opinionated on what works, subject· it has been debated many times by many different people, with many different outcomes on what works best.· Somewhere I have a really good article on the science of battery charging, if I can find it I will post the link.
Post Edited (Kevin B Slater) : 6/21/2005 6:06:14 AM GMT
You really should use the correct type of charger for NiMh batteries such as the one above from Ramsey. It may seem expensive at first but you can also use it to charge other NiCad or NiMh batteries that you have lying around the house. Another nice one is the MAHA series MHC777 chargers. With that constant current charger that you have and that NiMh battery pack, it will cook all day long until one of the cells fails. I'm not pushing Ramsey in any way so check the web and see what's available out there in the smart charger category and choose for yourself but by all means get rid of that constant current zero protection charger.
Mike
Respectfully,
Michael G. Jessat
As Kevin stated........NiCads, NiMH batteries are sensitive to the way they are charged. Nothing like a lead acid.
I totally agree that a lead acid battery would have made the better choice. But, this project is a lightweight robot. The Hitec quarter scale HS-805BB servo's I'm using just wouldn't handle the additional weight. I have four 12VDC 5aH lead acid batteries in my workshop that I have been wanting to use for almost a year now. But, I have so many more servo's than DC motors at the moment it just didn't make sense to head in that direction (yet). One day I'll wise up and make use of all the stuff I bought with the intentions of using it, only to have it gather dust in my basement. Its surprising how much of a pack rat you become when you get involved in this hobby.
Thanks for your reply!
Regards,
Michael G. Jessat