Technical Reverse Unit question

[LittleTommy]

This is a question about the reasons that electronic reverse units may fail, and I am asking for technical advice to prevent this from happening again.  My electronic skills are limited by what I learned in High School Physics in 1967. 

The Specifics are that  I have a Putt Locomotive which has a DC can motor and is fitted with a ELECTRONIC REVERSE UNIT  (Dallee Stock # 518).  The Locomotive is about 8 years old and is run about once every month.  I am not a speed demon, I run my engines at slow speeds and I seldom, if ever, have a derailment.

Last month, the engine would only run forward, not in reverse, although the reverse unit  would sequence.  I suspected that there might be an internal short (the headlight would dim when the engine should be reversing).

I traced all the wires, finding no shorts, and made sure that no portion of the reverse unit was in contact with any metal parts. The reverse unit is in the tender and the interior of the tender is pristeen, with no obvious dirt or dust present. There is a thick coat of foam insulating tape between the bottom of the reverse unit and the tender floor

I purchased a new reverse unit and the engine works just fine now after replacing the unit. 

I assume that this is due to some sort of electriclal gremlin in the reverse unit, but I wonder if it is somehow preventable, and/or if there is some sort of precaution I can take to not have this happen again.

Thanks in advance for any ideas/ guesses.

Little Tommy

 

 

 

[richhotrain]

Little Tommy,

You asked for ideas/guesses, and this response is somewhere in between.

According to Dallee Electronics, the 518 is a 1 amp unit for use with DC can motors which you have in the Putt locomotive.

That particular unit has four wires to connect. The two black wires are input power coming from the track.  One black wire connects to each rail pickup.  The red and gray wires connect to the motor brushes such that the locomotive will start in the FORWARD direction when power is initially applied.

Dallee includes this cautionary note in its instruction sheet.  "Be sure that only the motor is connected to the E-unit and not the smoke unit (if applicable) or the head light(s).  They will cause excessive current to be required of the E-unit and possibly destroy it prematurely.  Be careful to not let any components on the electronic E-unit come in contact with any other metal part, this will also damage the E-unit."

Hope this helps

Rich

[lionelsoni]

The electrical phenomenon most likely to damage your locomotive electronics is high voltage.  A transformer can easily produce very brief high-voltage spikes.  You can keep these from getting to your trains by wiring a transient-voltage suppressor across the track voltage supply.  A good choice is the 1.5KE36CA, which you can get from a distributor like Mouser for well under a dollar.  Be sure you order it with the "CA" suffix, for AC operation.

[submmbob]

Bob

I believe the 1.5KE36CA is a diode, correct? If so, do you have to observe polarity when connecting it? Also, this should go across the input and return from the track?

I just got my first locomotive w/ an electronic reversing unit and want to protect it, as I am using older transformers.

Thanks

Bob

 

[ADCX Rob]

richhotrain

According to Dallee Electronics, the 518 is a 1 amp unit for use with DC can motors which you have in the Putt locomotive...

Everything I've seen from Dallee indicates the 518 is rated for 2 amps.

I still think that's sort of on the low side.   They will always fail eventually, sooner  without a TVS.

I would be more comfortable with the extra overhead of a Williams 6 amp reverse unit, if it fit.

These are available at a discount from many dealers(Ma & PA Junction comes to mind).

[lionelsoni]

It is a diode in the literal sense that it has two leads.  But it is not a rectifier.  It conducts only when the instantaneous voltage, of either polarity, across it exceeds its 36-volt rating, thus clamping the voltage to that value and protecting any electronics that cannot stand higher voltage.  It should be connected in parallel across the supply.  Exactly where is not important, whether inside the transformer box, at the transformer terminals, at the lockon, or even inside the locomotive.  If it has the "CA" suffix, it is symmetrical and can be connected either way.

Notice that the voltage rating should be a little higher than the peak voltage in normal operation.  The peak voltage of a sinusoid is about 40 percent higher than the root-mean-square voltage, which is how AC voltage is usually described.  So a transformer voltage of 21 volts needs at least a 30-volt TVS.

[richhotrain]

ADCX Rob

richhotrain:

According to Dallee Electronics, the 518 is a 1 amp unit for use with DC can motors which you have in the Putt locomotive...

Everything I've seen from Dallee indicates the 518 is rated for 2 amps.

Not quite everything.

I have seen references to both 1 amp and 2 amp ratings for the 518.  Apparently, Dallee has replaced all of its older e-units, including the 518, with a new 400 e-unit.

Anyhow, here is the data sheet that I referenced for the 518 rated at 1 amp:

www.dallee.com/PDFs/e_unit-old-style.pdf

Rich

[LittleTommy]

Thanks to all that took the trouble to try to help me.

The little Putt engine has so little room in the tender that the 518 is about the only reverse unit that is low profile enough to fit, otherwise a more robust unit might be a good choice.

I appreciate all the help.  I LOVE this forum! 

Little Tommy