Official information and sizing can be found here:
https://www.ringengineering.com/PBM.htmSize is 1.27" x 0.66" x 0.32". They are larger than the KA-4 because of the added electronics. This may not be the easiest thing to see, but I have the beta PBM-2 installed to the left of the LM-3S module here:
Size is actually comparable to the LM-3S. This will make it difficult for tighter spaces, so for the time being tough installs may still require something like the KA-1 or KA-2. Perhaps RE will design another, smaller capacity PBM to better work with tight spaces. We'll see.
So why the extra circuitry and electronics? Traditional KA's are pretty much just capacitors that have no regulation on the output. As soon as power is lost, the power from the super caps drains rapidly and logrithmatically. This means that as soon as power is dropped from track power (say 14 V) the voltage provided by the KA drops rapidly as well from 12V down to almost nothing. The locomotives will stop moving under 9-10 volts, so you will get at most a couple seconds of movement (albeit greatly decreased speed) before the train stops. The lights and sound will stay on, but no movement.
Here are some initial testing notes I sent to Tim after I first installed it:
" I ran some side-by-side tests with another locomotive that has a TCS KA-4 installed in it. Both tested on Railpro power (PWR-56). Both locomotives have LED lights with the same resistors. The speakers on the KA-4 equipped locomotive are at 8 ohms, and the speaker on the PBM-2 locomotive is 4 ohm. All times tested were with track power completely shut off. Movement measurements were made with 50% load and throttle at 50%. Here are the results.TCS KA-4 (Installed with a bridge rectifier to a LM-3S, v 2.12)- Voltage at the LM-3S = 12.5V (due to bridge rectifier)
- Time with lights only = 24.64 seconds
- Time with sound only = 18.20 seconds
- Time with light and sound = 15.82 seconds
- Time with lights, sounds, and movement = 11.29 (though the locomotive completely stopped moving at 5 seconds)
PBM-2 (installed on LM-3S, v2.12)- Voltage at the LM-3S = 13.9 V
- Time with lights only = 18.30 seconds
- Time with sound only = 17.51 seconds
- Time with lights and sounds = 14.78 seconds
- Time with lights, sounds, and movement = 7.79 seconds (locomotive was moving the entire time until power totally quit)
The biggest difference between the two is that the PBM-2 keeps the locomotive moving at nearly the same speed. Once the power quits the locomotive experiences a slight drop in speed, but after that it stays constant and the lights are constant as well. On the KA-4, the speed drops dramatically when power is lost, and the lights dim slightly. The locomotive stops moving within a few seconds after power loss due to insufficient voltage to keep the motor running."In all the running and testing I've done the PBM-2 has kept the train moving through power drops, whereas the KA has a noticeable drop in speed. I haven't seen any issues so far in performance or compatibility. The only downside is the size, which will make installations more difficult in some cases. Connecting the two wires on the LM-3S is as simple as connecting one to the common blue, and the other to the yellow input on the rear of the LM-3S. For the LM-2S it requires a bridge rectifier due to the differing circuitry on the LM-2S.
-Kevin
