WBB E unit board rating

You will want to determine the stall current of the motor. Figure out a way to keep the motor from spinning and apply full voltage just long enough to get a stable current reading AND NO LONGER THAN THAT! That will give you a number to compare to the WBB board rating which I think is 6 amps (but I’m not sure). The motors in the 70 tonner would have been wired in parallel to the same driver circuit.

The 70-Ton board will most certainly NOT handle that motor!  The two motors in the 70-Ton WBB engine are tiny.

Upon further investigation the board I have came out of a twin motored BL2, so the board should handle more than the 70 ton board.  I is very different and has two bridge rectifiers on it.

@NHVRYGray posted:

Upon further investigation the board I have came out of a twin motored BL2, so the board should handle more than the 70 ton board.  I is very different and has two bridge rectifiers on it.

That one should be good for 6 amps. I believe the two items you referring to are actually relays.

Pete

They call them 6 amp boards, but I note the relays are rated at 2 amps.

How wonderful.  I don't anticipate much running (thus no ERR).  If it burns up, oh well it was surplus from a conversion anyway.

They are pretty bulletproof. I use them to replace dead Lionel and K-Line E units.

Pete

@Steaming Jon and others... you don't have to keep the motor from spinning, that risks burning it out and pinching or burning your fingers!

@NHVRYGray is blessed with a well-designed O scale 2-rail mechanism.  NO rubber tires.  High-quality 7-pole motor (good luck finding one of those in a Lionel or MTH loco these days!)  And probably, a conservative gear ratio for smooth operation at scale speeds.  It all makes me quite jealous!

The RIGHT way to figure out "stall current" (more appropriately, max current) is to put the shell back on the loco and an ammeter in series with the track feed.  Grab hold of the loco's drawbar or the tender coupler, NOT THE BODY.  Advance the throttle, and note the current draw just before the wheels begin to slip.

(I'm guessing that the loco is properly weighted, and given enough voltage the wheels will spin.  In other words, there's more torque at the wheels than available traction.)  Lower the throttle and repeat the experiment, making note of the results.  That's the current capacity your E-unit or DCC decoder needs to handle.  Add a little more for a margin of safety.

Now how well those 2-rail driving wheels, all flanged, will cope with 3-rail track and switches is a harder problem!!

If you don't have the motor(s) connected there is a way to find the max current draw using Ohm's Law:

I=V/R

Where:

We'll see about tracking at some point.  My min curve is 072 Atlas T section track.

@Darrell posted:

If you don't have the motor(s) connected there is a way to find the max current draw using Ohm's Law:

I=V/R

Where:

V is voltage in Volts
R is resistance in Ohms
I is current in Amperes

Example from a recent project

18v on track means about 16.5 max to motor after being rectified, the motor resistance measured 56 ohms. So 16.5 divided by 56 equals 0.294. So the max current draw for that motor is 294 milliamps, to keep it simple if you have 2 motors in parallel it's still under 600 milliamps, in series it would be only be 147 milliamps. To draw 6 amps the motor would only have 2.75 ohms of resistance. I have on my bench a MTH motor ( RS-385 ) that measures 109 ohms so it would draw 151 milliamps which is only 2.5 watts. This is why many of the modern loco's draw less than an amp even though they have duel motors, lights and smoke!

Darrell, I don’t think the Mabuchi reading is actually correct. Stall currents are typically 2.5 amps at rated 12v. Its not uncommon for the brush to commutator reading to be high for whatever reason.

You can look up the Mabuchi RS385PH on their website to get this info on true stall currents.

https://product.mabuchi-motor.com/detail.html?id=101

Pete

You are correct Pete, one only has to do a bench test to see that stall currents are way more than 300milliamps, that's more like the unloaded running current!

Here's a Mabuchi RS365 running at 6 volts, .127 amps running current, no load.

Here's the stall current at 6V, a little bit more than 300ma!