How to stop AC bleed over ?

Stick a diode in series with it.

It sounds like your power supply is putting out rectified, but not filtered, DC.  The AC voltage you measure is the "ripple" on the DC.

 

Add a 1000 uF, 25V electrolytic capacitor across the output of the supply.  The "-" on the capacitor connects to the minus lead from the supply.

Thanks for the info Dale.

 

Here's a question, Will that still work even when you switch direction with the direction button?  (basically switching polarity)

 

Thanks,

 

Ralph

Not unless you have a non-polarized capacitor.  One that size will be a pretty hefty beast!

You could put your own polarity reversing switch after the capacitor.  A double pole, double throw switch will do the job.  If you do this, put a mechanical lock on the power supply so that you can't send any reverse voltage to the capacitor, or maybe add a diode in series between the supply and the capacitor.

So I guess if I can get it opened I could put the capacitor before the switch that's already there.

 

Thanks again Dale

 

 

Ralph

Ralph,  Interesting, I have not had any problems running MTH engines in conventional on the layout with the same Transformer.  G

Hi G, The transformer was working fine before and I had an engine that was messing up the customers DCC system. He was having to reset a couple of times to get it to run. When I got it it did the same thing to my stuff and I'm wondering if it didn't do something to the transformer. I also use the 1370 for running engines with the TIU. I did get the engine to run but when I pushed the whistle button the engine went dead. I talked to the techs at MTH and got the same thought about the bleed over making this happen. I e-mailed MRC and asked them about it so I will see what they say. Ralph

Ralph,

after getting your e-mail..I checked with the repair tech and also pulled a couple of 1370's from stock to test. they are and always have been a 1/2 wave rectified siganal. we checked them on an "O" scope and the sinewave is correct for these units, even though with a meter on the a.c. scale shows approx. 3.94 to 7.94 vac depending on the throttle setting both directions. this should have no bearing on your testing of the mth locos. if they ran on a 1370 before, they should still run on these powerpacks, unless of course mth changed something in the decoders.

Ralph, what HO engine is not starting up with the 1370?

 

I don't have a 1370 but I took a Z-4000 and attached a bridge rectifier (no cap) between it and the track.  My MTH HO K-4 started up fine, went fwd, reversed, etc. with unfiltered full-wave.  Then I put just a rectifer between the Z-4000 and the track (no cap) for unfiltered half-wave and the K-4 started up fine, went fwd, reversed, etc.  Yes, the Z-4000 was cranked way up with only half-wave to the track!  And I had an o-scope hooked up and the track voltage was textbook full and half wave.

 

MRCRRTECH makes a good point that something might have changed in the MTH decoder - especially since your engine does this with 2 different 1370's.  I believe the K-4 was the first HO engine MTH released so its at least 5 years old.  If I'm not mistaken more recent MTH decoders use supercaps that must charge up before the engine starts - or something to this effect.  Perhaps this causes it to behave differently with controllers that don't put out pure-DC.

It's the newest SD-70 ace. I'm going to grab another transformer from the store and see what happens. The big thing is the customer has this exact issue and just trying to figure out what is going on. The engine runs fine on the other systems. I never had a problem with that transformer before.

 

Thanks for all the help and I will post my findings later tonight when I get the new equipment.

 

Thanks,

 

Ralph

 

Ralph,

let me know what you find out...The only straight line D.C., [filtered] pack we made was the Control Master 20. but i have run most MTH H.O. locos here on everything from 1370's, Tech ll's and tech 4's without any problems, even the SD70's. I know that initially when the 70's were released they had a problem with out Tech 6 powerpacks, and i was in contact with the MTH crew regarding the issue and they fixed the problem. You may have an early release of the loco.

Hi,

 

Well my findings were the same. I got a new 1370 and it wouldn't run the engine. I then tried the Tech 4 260 and it ran the engine fine.

 

MRCRRTECH you may be right that this an earlier engine. I didn't know when this one actually came out. This was my first time running into this with these engines. I will get in touch with MTH tomorrow and see what can be done to update this engine for the customer. I learn more and more each time I get an engine.

 

Thanks again for all the help.

 

Ralph

 

Ralph,

The easiest thing to do is test another type of MTH loco if you have one in stock, with the same 1370 and see if that loco has the same issues as the SD70.

I searched on “transformer compatibility” on the MTH site and the first result was this document which lists recommended DC transformers. I see 6 different MRC supplies but not the 1370.  The filename path has "HO" in it so I'm guessing this applies to HO.

 

MRCRRTECH, can you comment on the earlier suggestion of placing a large electrolytic cap inside the 1370 before the direction switch?

 

 

 

 

 

 

Stan,

I can only give you the company line on your question..."Any modifications to any of our products will result in voiding the warranty" [basically i'm not allowed to tell people how to modify any MRC product]

That said...If you know what you are doing, and there is no warranty...It's up to you