Another Car Battery question

Has to be at least 48 volts, or telephone wires would have to be handled as power, not signal, wires. And ring power on telephone lines is 100 volts 20 Hz riding on top of the -48 volts DC.

One can measure the 48 volts across any telephone pair with no off-hook telephones. When a phone is taken off-hook, the voltage drops to about

Phantom power in microphone circuits is also 48 volts DC.

Joe Gwinn

I am a bit surprised. In general firefighters try to disconnect the house power, but if they can't, hit the fire with lots of water. The water will pop the breakers, the firemen are wearing insulating boots, and if using a hose from a hydrant, are holding a grounded hose. Also a stream of water from a fire hose is not contiuous and does not conduct.

Dan

Nope. 48 volts has not been in the running except in electric drive apps where even 96 and above have been used.. The scuttlebutt for the last several years has been 36/42

I'm likely one of the few on this list who has both been an auto mechanic and built and driven his own electric car.

If that 120 and 240 volts was DC instead of AC, I'd be VERY CONCERNED.

wrote in message news: snipped-for-privacy@s12g2000prg.googlegroups.com...

The training I've received on hybrid cars, SUV's and buses offered no such advice (don't go near). The primary tactical changes in dealing with hybrids concerned extrication techniques. IE: don't cut the orange wires, don't try to disconnect the power. As far as fire conditions go we now need to be concerned with the run off water due to acid/basic electrolyte volume & fumes. Also some time is spent on battery locations because the weights involved can affect the center of gravity and how you might stabilize the vehicle.(some hybrid buses have the batteries on the roof) Concerning electricity and structure fires we (my dept, others handle it different) list shutting off the power as a priority but it's not at the top of the list unless the power is the main problem... like the panel is on fire or the metal roof/siding is charged... as a rule we shut off the main breaker prior to overhaul and almost never pull meters, that gets left for the utility workers. Over the years more firefighters have gotten injured pulling meters then just fighting fires with the power on. In probie school our instructor told us fire boots will not protect from shock any better then a wet pair of sneakers and that electricity will only travel a few feet up a hose stream. I have been zapped but not often and I could always id the source.. like burned wires. About 2 months ago my ladder truck became entangled in the high tension primaries in front of a fire building :( lucky for us the ladder stopped on a well insulated section so the arc damage was minimal, I really would of hated to stand by and watch my NEW hook & ladder burn. We waited for the utility guys to come and shut off the juice.

Andrew

I'd be real interested in hearing more about it. I built an electric car out of a friend's rusted-out VW bug. No way would it pass inspection, so it was for tinkering, only. I used a jet engine starter motor/generator, rated at 400 A 28 V continuous. I ran it from an armature supply of 48 v (4 90 AH trolling motor batteries). I had a switching regulator on the field supply. It ran suprisingly well, had LOTS of pep. One problem was the motor was real loud. I was trying to make a hybrid, and had a motorcycle engine that I'd brought out an extension from the crankshaft to a stratofortress generator (the smallest, lightest 400A 28 V electric machine you will EVER see!) My coupling was junk, and the inline-twin engine had uneven power strokes, so it was going to snap the shaft real soon.

If I could get another stratofort generator, that might make a really fine drive scheme. I'd need some reduction gears, though.

Jon

They have an inertial interrupter that splits the battery system into two 150 V sets. That works like the inertial fuel cutoff switch that is on many cars today.

So, is thes for real, that no rescues are to be performed on hybrids? You just let them burn, then tow the hulk to the junkyard with the skeletons inside?

Or, is this an insane reaction by some higly misinformed fire chief who knows nothing about electricity except that it "can hurt you"?

Since I consider myself to actually know something about electricity, I have REAL doubts anyone could get hurt spraying water on a burning hybrid car. It is a self-contained electrical system, so how the current could get back through the water spray is hard to imagine. Now, I CAN imagine how somebody extricating an accident victim from a smashed car could get hurt by touching the wrong thing, especially when using various extrication gear (saws, jaws of life, bolt cutters, etc.) But, that's part of why the inertial cutoff system is there.

Jon

Mine was a 1975 Fiat 128L Sport Coupe with first a 200 amp aircraft generator, later updated to a 400. Series aprallel switching (24/48) through a startup resistor of 16ga stainless steel ribbon, with a rheostat on the field for feild weakening. A drum switch handled the switching (using 200A contactors) and an industrial magnetic circuit breaker handled overload protection (with very good arc suppression). Ran 8 GC2H cart batteries. They were configured as a 24 volt pack for charging, using a charger from a Sebring Vanguard.