Sealed battery fumes?

[spuggy]

I heard about a guy who made a sealed plexiglass casing for an rc boat battery (not sure what type). The fumes had no where to escape and blew up (or atleast the plexiglass casing).

Do you think this is a viscious viscious rumour... or is there some truth? I am planning on using a 12v sealed lead acid battery.

[pompebled]

No it's not.

Allways charge with the lid off, so there's ventilation!

When car batteries are getting close to full charge and the charger doesn't cut of (in time), is starts venting combustable gas, if you have a switch or brushed motor, anything that can spark, an ignition is possible.

I haven't experienced it, but sealed lead batteries, commonly used in scale boats also have safety vents, so, if properly abused, they will also vent gas that will ignite under 'favourable' circomstances.

NiMH cells have safety vents too, if overloaded, either on the charger, or in the boat (deep discharging) the cells will overheat and vent hydrogene gas, again, if there is a spark, the air / hydrogene mixture can explode.

I've had two fast electrics blown up that way, one sank without a trace, the other blew up like a balloon on dry land, once I pulled the tape, holding the hatch, it went back in it's original shape (with a few cracks in the epoxy hull).
This boat still runs (after repairs) and currently leads the competition here.

Regards, Jan.

[Umi_Ryuzuki]

No it is not a rumor.

In the case that personlly I know of, it happened twice.
There is also a key factor involved in the construction, and the type of boat.
The "boat" was a submarine owned by L Chiu. He had everything packed into
a sealed plexiglass/perspex Water Tight Compartment. Battery, servos, motor and
a motor for the worm drive ballast system.

The first occurance Mr. Chiu showed up at the pond, launched his submarine and
sailed out into the pond. The next thing everyone heard was a large boom. When
the submarine was recovered, it could be seen that the hatch had blown off.
No one could explain it..

The second time, Mr Chiu had refitted and repaired the damage and returned to
the pond with a fresh boat, with a freshly charged battery. Again, everything was
sealed in his WTC. The same sequence of events occured as the first time.
While I did not witness either event, When I ran into Mr Chiu at the pond and asked
about the occurances, he explained the purchase of a brand new SLA battery, and the
sequence of the two events. His analysis of the second occurance tied the explosion
to the operation of the ballast motor. Upon examination, the ballast motor brushes were arcing.
A charging SLA battery vents hydrogen. Hydrogen plus sparking brushes equals gas explosion.

Mr. Chiu showed me that he now had two vents in his WTC.
These were opened during charging, and before he closed them he would place the
hose from his vacuum cleaner over one and run the vacuum to evacuate any hydrogen
gas in the WTC out and bring fresh air in. Then seal the both vents before heading
out to the pond.

I imagine that the fast electrics are creating the same environment.
Battery and motors in same sealed chamber.

[boater_dave]

Ditto on the sealed tube explosion. A fellow club member blew the bow off his Robbe submarine. I helped him repair the damage, but it was a shelf model after we were done. He had rigged up a charging jack on the outside so he didn't have to take the tube apart every time he ran the boat. It had two 6 volt gel type SLA's inside. It was on the dock, under his nose, when he switched the radio power on and BANG! The cause of ignition was arcing from the brushed motors. He was not injured, but the force of the blast sent the bow 15 feet down the dock and into the water and it blew the shafts out of the tubes. It was a mess.

Dave

[keith S]

have seen the same effect with another modelers submarine that was charged and ready to go in the trunk of his car. Batteries were sealed in the boat with no way for the gas to discharge. When he turned the boat on to demonstrate it to some one befiore a meeting--BOOM--. Never seen so many grown men run from the trunk of a vehicle. Same problem gas being trapped.
If you look at your SLA batteries, you will see that there are little circles on top. That is for the gas to escape if the battery is overcharged and "burps" the gas out.