Power during 3rd rail gaps.

I've noticed that when a car passes through a traction power gap, sometimes the lights turn off, sometimes they don't. The signs and other electronics seem to stay on. I would imagine the entire cab stays powered. The HVAC always cuts off. I assume traction cuts off. What powers what on these things? I'm guessing there are batteries, inverters, and chargers to power the lights and electronics?

The low voltage control circuts run on battery power,that includes Emergency lights while the car is in the gap,
and the destination signage as well.
Everything else is powered by inverters or MG sets,and covers battery charging as well.

I'm guessing since they always operate as trains and not single cars, they don't all have to be powered at the same time to move the train. If one car completely shuts off, the others can probably still push/pull it forward.

The traction power is always only within a car. But there are 2 shoes per side. And yep, if one car loses all power, you hope the other push/pull it along.

I'm told that some models bridged low voltage/lighting between the pair, but not all. Some have a UPS for lighting, others not.

I've been booted from a car as the lighting failed/restored/failed. The supervisor locking the car down told me both shoes on one side had been damaged, and as the third rail moved from one side to the other....

Also note the Money Train is 4 cars long, not 2. You would not want a train full of cash stuck somewhere because neither car had 3rd rail power.

BTW, wonder how much less cash it carries now than in years past?

It varies by car series. The 2/3/5/6/7000 series cars all use AC drive motors for all HVAC functions. Each one of these cars carries an auxiliary converter called an APS (aux power supply) that converts the DC third rail traction power to 3ph 230VAC and single phase 120VAC. When the cars go through a gap, the APS isolates itself from the third rail and all loads of course shut down.

After the car passes through the gap, the APS restarts itself and, with the exception of the 5000 series, the loads are sequenced to avoid overloading the APS. The priority is:

1. Air compressor
2. Propulsion inverter cooling fans
3. Evaporator blower motors (the ones you hear in the car)
4. Condensor fan motors
5. HVAC compressors

The 5/6/7000 series cars have a crossover feature that has two effects. First, the rear HVAC system on each car is powered by the APS on it's mate. So when an APS fails on one car, it will still have 50% of it's HVAC capacity. There's also series of contactors that will automatically switch the air compressor and prop cooling fans to the mate's APS when its own fails. These features combined permit cars from these series with a single failed APS to continue operating without creating a service disruption.

When a car is gapped for more than about 30 seconds, they go in to what's called load shedding mode. This is when you see most of the interior lights switch off. The pair is running off the battery located in the B-car and/or the battery trainlines from the adjacent cars. The only system affected is the interior lights. Everything else operates as usual.

The 7000 series use a more aggressive and complicated load shedding algorithm as they have many more loads: additional exterior destination signs, the passenger information displays, etc. However as before only passenger-facing loads are shed. All core rail car systems continue to be powered through the battery or the adjacent cars.

Neat. Thanks. You described how all except the 1000 series cars operate. How do the old clunkers deal with gaps? Personally, I do not ride in those things anymore, I go for the ends I'll wait for the next train if I can't make it. So I don't even remember what they do.

MCL1981 wrote: How do the old clunkers deal with gaps?

Not very well.

The low voltage systems operate similarly to all the other cars. The HVAC systems (as in the 4000s) are all DC drive motors which operate much quieter so people usually don't notice them slowing down through gaps.

The biggest flaw (IMO) with the 1000 cars was the choice of hydraulic friction brakes. Each car needs to be on third rail at all times to keep the hydraulic power unit running. If a car is gapped for more than just a few minutes, hydraulic pressure will drop below a safe threshold resulting a full emergency brake application. The BIE condition will disable the train until power is restored.

With air brakes, this isn't a big deal as air can be shared between cars to make up for a gapped or even failed air compressor. Not so with hydraulic brakes.

dcmike wrote:

MCL1981 wrote: How do the old clunkers deal with gaps?

The biggest flaw (IMO) with the 1000 cars was the choice of hydraulic friction brakes. Each car needs to be on third rail at all times to keep the hydraulic power unit running. If a car is gapped for more than just a few minutes, hydraulic pressure will drop below a safe threshold resulting a full emergency brake application. The BIE condition will disable the train until power is restored.

Those pieces of crap have juice brakes?!?!?! Who thought that would be a good idea?? What applies the emergency braking if the hydraulic pressure has dropped out? If a single car is gapped too long and goes into emergency, is there a way to manually release the emergency on that car so it can be moved out of the gap and restore power?

MCL1981 wrote:
Those pieces of crap have juice brakes?!?!?! Who thought that would be a good idea?? What applies the emergency braking if the hydraulic pressure has dropped out? If a single car is gapped too long and goes into emergency, is there a way to manually release the emergency on that car so it can be moved out of the gap and restore power?

I have seen an operator lift the center seat, and trip something he said was a brake cutout. This after it arrived with a flashing external light that I later learned here indicated a brake FUBAR.

Hydraulic brakes are faster actuating/releasing than air, at least on highway vehicles. They likely have a high pressure hydraulic reservoir for emergency stop.