yes the smell that is present there is the chemical reaction that shouldn’t happen inside most likely eating the plastic shell, its a reduction reaction… that can be very bad. also the expansion is the force created by the extra reactions that is the same thing as an explosion, just not as much force, which causes the expansion. and if it did crack you could have a caustic mess in the area where it leaked.
I always thought SLA batteries will not leak acid like reagular lead acid batteries which is the reason why combat robots are only allowed to use them. Besides I also read horror stories where a piece of molten metal went through a SLA and it still worked. In reality those people are dumb but it really shows how safe the battery is. There are ways to make them explode but that would be assinine. Anyway here are some more safety tips do not pot the battery or encase it to protect it. The battery will explode since gasses build up in all batteries and will have no way to vent. Always use the right charger for the batteries. Do not think all batteries will use the same charger. Some batteries like lithium-ion do need special chargers.
*Originally posted by Adam Y. *
**That is odd my books tell me you can’t measure resistance of a motor using an ohmeter. I really do not know why though. Try getting a few D alkaline batteries or a regulated power supply. **
Your books probably say that bacause motors have a very high inductace and will have dirrerent resistances depending on a number of conditions such as mechanical load, frequency, etc. At the very low DC voltages used by most ohmeters, the inductance is negledgable and an ohmeter can be used to test for shorts if you know the resistance of a good motor of the same type. And by the way i use an variable current limited bench power supply to test motors.
Your books probably say that bacause motors have a very high inductace and will have dirrerent resistances depending on a number of conditions such as mechanical load, frequency, etc. At the very low DC voltages used by most ohmeters, the inductance is negledgable and an ohmeter can be used to test for shorts if you know the resistance of a good motor of the same type.
Ackkk I figured it out. The resistance may be too small for the ohmeter to work. That is the reason why my books say that.
Ahh! Didn’t think of that. It is true many ohmeters don’t perform too well or at all when measuring very low resistances. Just out of curiosity what book is it? I might want to read it.
Ahh! Didn’t think of that. It is true many ohmeters don’t perform too well or at all when measuring very low resistances. Just out of curiosity what book is it? I might want to read it.
*Originally posted by Adam Y. *
**I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor. **
OK guys, We have talked about this before. If you stall the motor you are putting one or two windings in parallel across the power source. There is still some resistance in the windings and therefore the resistance will limit the current.( It will be high but not maximum.) This IS NOT the same as a short of zero resistance. Maximum current will be drawn from the power source. In our case the battery is capable of more than four hundred (400) amps. That is more than enough to weld wire to the terminals, create a shower of sparks (both fire hazard and burning hazard), may cause bright flashes (retinal burns) and ultimately could cause battery explosion. Just because you have never witnessed a battery exploding doesn’t meant it can’t happen. Some of you have seen a battery that was stressed, swell and deform the case. That should be evidence enough that catastrophic failure is possible.
Sealed Lead Acid batteries are still lead acid batteries. The electrolyte is a sulphuric acid compound and the plates are lead. When batteries are stressed the electrolyte heats up and the lead deforms both of which contribute to the swelling case. You can interpolate the result if the deformation was rapid, an explosion would be the result. Hot, gelled sulphuric acid and plastic shrapnel are not my idea of fun.
I would try this, start by removing all of the circuit breakers that feed motors. If the controller still shuts down, it is not the motors or controllers. (assuming you have wired them according to electrical rules.) If all is OK, then insert one breaker and try again. Continue until you find the offending device. My suspicion is a wayward connector that will be obvious under visual inspection, or a damaged drill motor. Please let us know what you find.
*Originally posted by Adam Y. * I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor.
OK, we have discussed this before but to prevent any further confusion…
When a motor is in stall, one or two windings are in contact with the brush assembly. Each winding has some resistance which limits the amount of current flowing. For the drill motor this year, stall current was rated at 129 amps. However, the SLA battery is capable of supplying in excess of 400 amps in short circuit! That is sufficient to weld wire, sending sparks (fire and skin burning hazard) bright arcing light (retinal burns) high temperature on the conductor (creating poisonous gasses) and the possible explosion of the battery. High temperatures are not only generated in the wire you use. Remember that the circuit is a series one. Current, everywhere in a series circuit, is the same. 400 amps flowing through a wire is also flowing through the battery. That amount of current will rapidly raise the internal temperature of the battery, resulting in damage to the case if you are lucky. When high currents are flowing in the battery, you boil the electrolyte and deform the lead plates. Use circuit protection when testing motors! Hot sulphuric acid and plastic shrapnel is not my idea of a fun time.
Now back to the problem. Something is drawing the power supply down below reset on the RC. Remove all the circuit breakers that feed motors and repower the robot. If moving the joystick still causes reset, then suspect a bad PWM cable or a bad PWM input on a controller. You can isolate this by removing PWM cables one at a time and repeating the joystick test.
If the RC does not reset with all the breakers removed, then add the breakers back one at a time until you isolate the bad circuit. I think you will find a wire or connector has come loose and/or is touching another contact. There has been trouble with the drill motor brush assembly and it is possible to cause a short in this area if the plastic at the brush end of the motor is damaged or out of alignment.
However, the SLA battery is capable of supplying in excess of 400 amps in short circuit!
The spec sheet says 230 amps and for five seconds. Is there overcurrent protection on these batteries?? By the way I never said I stalled the motor. Your right that is dumb and will destroy everything.
There has been trouble with the drill motor brush assembly and it is possible to cause a short in this area if the plastic at the brush end of the motor is damaged or out of alignment.
That is usually easy to tell if the motor is damaged. The brushes should pop right out.
Adam,
Read carefully when you are checking the spec sheets. A fully charged battery has an internal resistance of 10 milliohm. By Ohm’s Law I=V/R=12/.01=1200 Amps. Now asume some variables creep into the calculations like not fully charged battery, some resistance in the wire (#10 is .001 ohm/foot) and a high resistance connection on the wire doing the short and 400 amps is pretty easy to get. Let us remember that the current through the internal resistance causes a voltage drop and that lowers the terminal voltage at the outside of the battery. A stalled motor is still a higher resistance than a dead short and therefore lower current when at stall. Teams stall motors all the time during competition and do not damage batteries or motors unless the stall condition continues for a great length of time.
The brush assembly on the drill motor can easily be damaged and the brushes can be out of alignment without any obvious damage. I came across several in Houston where the brushes were not touching the commutator or were severely misaligned enough to be be damaged by the wire contact at the edge of the commutator.
Sorry for the double post, it had something to do with the spell checker and I am still trying to work that out.
The resistance may be too small for the ohmeter to work. That is the reason why my books say that.