KW As Accessory Power Source

1) Figure 5-6 watts per bulb, and the KW able to deliver about 130-135 watts continuously.

2) There are more than two constant power terminals on the transformer. None of them would be my choice - I would use a variable channel(A-U or B-U), or both actually, to be able to fine tune and/or adjust the lighting as needed/wanted.

Thanx Rob - one more question:

If I use the two variable channels does that mean that 20-25 bulbs per channel or 20-25 bulbs split between the two channels?

Paul

You might figure about 1/4 amp per bulb. They vary but I think that is a safe average. The ZW is 275 watts input. Output is probably 85% of that at about 235 watts. At 20 volts that's about 12 amps. I don't know but I would figure that as the max amps total out of the four outputs. So about 3 amps from each output and that's 12 bulbs connected to each output.

Hmmm...25 to 30 bulbs...I would connect half of them to each of two outputs and see how that goes.

Oh...KW...I was thinking ZW. So that's 190 watts input. About 8 amps total output so about 8 bulbs per output.

Paul,

   As ADCX Rob advised you will have plenty of power using the variable A-U or B-U channels, adjusting your voltage with the handles as needed, at 130-135 watts I ran lots of different accessories and still had power to run a bumper street car or fire car on my upper most individual track.  Wired correctly you should have plenty of power for your small lights, thru out your entire layout.  The KW is not as small as a lot of people think.  If however you are powering a lot of 072/711 type high voltage drawing, Lionel Switches, I recommend a ZW for doing it.

PCRR/Dave

Paul, in the old Model Railroading handbook, Lionel said an 18-volt bulb drew 5 watts.  It also said not to draw more than 75% of a transformer's rating continuously.  

I agree with Rob's analysis above.  His figure are aggregate for the transformer, across all terminals.

Pretty much all of the post-war transformers were rated on input power, not output power.  Given an efficiency of 80-85% for the transformer, the 190W KW can only be expected to deliver 150W maximum.  Also, this power is only at full voltage as efficiency falls off when you only tap part of the secondary windings.  You can't expect 150 watts at 6 volts out, that would be 25 amps, and that just isn't going to happen!

I'm with Rob on the maximum as well, I've loaded a KW to 150 watts at full throttle with a really huge resistor, and after about 1/2 an hour, it was getting pretty warm outside, and I'm sure a lot hotter inside!  The voltage also dropped to around 15 volts at 10 amps under this full load, and that's with 126-127 VAC in, so a lower line voltage would probably only give you around 14 volts at that kind of load.

The rule of thumb I use is this:  Since amps times volts equal watts, I divide the watt rating by the maximum voltage the transformer can output.  The product is the maximum amperage of which the internal windings are capable of carrying.  Note that this figure should not be adjusted for the amount of voltage actually being outputted.  Putting 10 amps through 12 feet of wire generates more heat overall than putting 10 amps through an inch of wire, but the temperature of the wire at any point is the same.

Having obtained this maximum amperage figure, for the postwar and prewar transformers, multiply by .75 to obtain maximum continuous operation in amps.

This is the maximum that should be pulled from the transformer, regardless of how many output circuits are used.  These transformers had only one secondary wiring.  If you are using a postwar ZW, as an example, this reading would be current flowing through the U terminals.  Thus, a 10-amp fuse on each of the 4 outputs would not adequately protect the transformer, because that would allow up to 40 amps to be drawn.  In fact, the internal resistance of the transformer would probably limit the amperage, but the heat would be disastrous for the windings insulation; if you're lucky, the internal breaker, which Lionel put in the U circuit, would open.

My "rule of thumb" is that if the transformer is a 150 watt real power out at 18 volts, that makes it less than 10 amps of capacity.  Therefore, I don't believe you should try to draw more than 10 amps at any voltage from it.

I think we said the same thing.  My example was a ZW.

I think we may have, I got lost in your computations.   I figure a "rule of thumb" shouldn't be longer than the thumb.

Per Lionel's repair manual the KW is rated at 190 watts input and 140 watts output at 10 amps.

All ZW's per the repair manual have an output of 180 watts at 14 watts. I personally verified this for the ZW's at

http://tranz4mr.com/ZW_250_vs._ZW_275_Type_R.html