Overheating DC power packs (plural)!

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trailrider

Well-Known Member
#1
I have continuous run layout in a 14' x 14' room (folded dogbone), wired in blocks for DC, but with a DPDT toggle on the control panel so I can switch to DCC, with the appropriate decoder-equipped locomotives, But I have recently started encountering problems with the DC power packs tripping their internal thermal circuit breakers after I run a pair of Athearn "blue box" GP-7's for a few minutes. I have an analog ammeter on my control panel which is showing only 1-1/2 amp Because of the track layout, which has what is effectively a reverse loop with manually operated DPDT switch to match polarities at either end, I first thought I might have a short circuit somewhere. But I shut off all the blocks, and turned them on one at a time, running one of four GP-7's one at a time, and...NO PROBLEM! But run two of them in any combination and after a couple of minutes, the breaker pops. Turn the power off for a couple of minutes until the pack cools down, and try it again with two units, and the same thing happens! I have a fifth GP-7 with a non-sound decoder, and can run it separately almost indefinitely on DC. Switching to DCC, this unit shows NO SIGN of any short circuit. I have a MRC Tech 4 280, which has a fairly good capacity. Thinking perhaps that this unit, which is a few year old, might be becoming sensitive, I obtained some slightly lower capacity packs, a Tech II and a 1380. Same thing! I'm baffled. Don't recall having this problem with two powered unit before. Any ideas?o_O:(
 

santafewillie

Well-Known Member
#2
Are these blue box locos old enough to have the snap-on plastic coupler cover? Have they been converted to Kadee or other metal couplers? Are you running the consists with B-ends coupled, or are you running them nose to tail?
 

bnsf971

Well-Known Member
Staff member
#3
Some of those old Blue Box GP7s had the old iron ring motors, which were notorious for drawing gobs of power. If you have that setup, it could very well overload a power pack.
 

trailrider

Well-Known Member
#4
I guess I've found part of the "answer", as it were. Santafewillie: Yes, they have the snap-on plastic covers, which I converted to Kadee. However, I have just tried running an F7A alone. It draws 1.5a at 10vdc. So does the B-unit (which is, of course, the same chassis). It draws 1.5a run separately. When run together, 3a. That is when the pack overheats and the breaker kicks in. When I had my old layout, before we moved in to my present house, I used Troller powerpacks. I still have them, but something is messed up with the rheostat or variable transformer, and it is either on or off! That was 30 year ago, and I don't know what happened internally. When I used the Troller, I never had any trouble running an A/B set. Guess the rating of those monstrosities was much higher than the current MRC packs. I do have an MRC Tech 6 6.0, and I will try to see if it will handle the load in DC mode. Appreciate the input.
 

trailrider

Well-Known Member
#5
I guess I've found part of the "answer", as it were. Santafewillie: Yes, they have the snap-on plastic covers, which I converted to Kadee. However, I have just tried running an F7A alone. It draws 1.5a at 10vdc. So does the B-unit (which is, of course, the same chassis). It draws 1.5a run separately. When run together, 3a. That is when the pack overheats and the breaker kicks in. When I had my old layout, before we moved in to my present house, I used Troller powerpacks. I still have them, but something is messed up with the rheostat or variable transformer, and it is either on or off! That was 30 year ago, and I don't know what happened internally. When I used the Troller, I never had any trouble running an A/B set. Guess the rating of those monstrosities was much higher than the current MRC packs. I do have an MRC Tech 6 6.0, and I will try to see if it will handle the load in DC mode. Appreciate the input.
Update: Tried the Tech 6 6.0 with 2 Blue Box F7's, with the control unit in the analog (DC) mode. Works like a charm, with no overloads. (With a 6.0a capability, 2.5-3.0a is no problem.) The only thing about the Tech 6 is that it has no line switch to shut off the power unit, and plugging and unplugging it is a pain. I'm either going to see about buying a surge protector with an ON-OFF switch, or possibly cutting into the line cord and installing a switch. The other thing about the dual capability of the Tech 6 is that I MUST BE SURE it is in DC mode, especially when I have one of my steam locomotives that I upgraded to Canon Coreless motors, when those were still available. DCC on the track will burn those coreless motors out quick! And they are no longer available! (Probably the best thing to do with those locomotives is to install Soundtraxx Tsunami 2 sound decoders in them. As I have at least 4 that would have to be converted, at about $160 per engine, that is going to have to wait...quite awhile!

Anyway, thanks for your suggestions. Have a safe Memorial Day, and remember those who fell so we could be free!
 

trailrider

Well-Known Member
#6
Update #2: Bought a surge protector with a 3ft long cord and a line switch. Got everything hidden in a shelf under the layout. I do notice that, even with the start and stop momentum (ACC and DEC) set to 0 out of 35, there is a noticeable lag in starting a locomotive. The number in the display must be about 50 before the engine will begin to move. After that, further rotation of the control knob seems to provide power increases or decreases in a fairly linear manner (just by eyeballing). That's with the Athearn Blue Box motors. Haven;t tried any of the Canon-motored locos yet.
 





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