Several problems with passenger train 7938

[moretrains]

Hi all,

I own some push-along trains, 4.5v trains, 12v trains and 9v trains and recently extended my collection with the 7938 power functions train. Unfortunately, I have had nothing but trouble with it so far. Things I ran into so far have been:

- Unlike the manual claims, the power functions battery box does not work with rechargeable batteries, only with non-rechargeable batteries. The green light does not burn when switching on the battery box with rechargable batteries inside. I am using the same rechargeable batteries in other devices and they work fine there. So broken batteries are not the problem.

- The (new alkaline) non-rechargeable batteries are drained within 10 minutes of running. The motor does get reasonably warm during that time but not exactly hot. Which means I'd have to spend a fortune on batteries to keep it running.

- There is a large amount of wheel-spin all the time and the train makes a lot of noise when that happens. It just doesn't run as good as the old 9v system.

I suspect both my battery box and motor are broken. The train is brand new and I have a lot of experience building Lego trains since decades and I am sure I have build the train correctly. I am not considering to buy the Lego rechargeable battery box 8878 as it is too expensive. I am running the train on the old style metal 9v tracks.

What I have tried so far is call the Lego service line and explain the issues. They are very kind and helpful and will ship a new battery box. I doubt however if that would solve all the issues.

Has anybody ran into these problems before? And any thoughts of what might be the issue?

Edited May 17, 2014 by moretrains

[garethjellis]

kids have a 7938, we use Duracell rechargeable batteries Nickle Metal Hydride. and it works fine. some good traction too.

[ronenson]

I don't recognize the problems you're facing. Here it runs fine on rechargeables.

[dr_spock]

Check the tips of your rechargeable AAA batteries and make sure they fit into the hole in front of the metal contacts. Some rechargeables have larger diameter tips that don't permit good contact to the metal. Some people enlarge the hole in the plastic.

[moretrains]

Check the tips of your rechargeable AAA batteries and make sure they fit into the hole in front of the metal contacts. Some rechargeable have larger diameter tips that don't permit good contact to the metal. Some people enlarge the hole in the plastic.

Thanks for your reply, I have checked this and it appears to be the case indeed. My rechargeable batteries have larger diameter tips than the non-rechargeable batteries. I will try to modify the battery box or try again with another brand of rechargeable batteries.

What about the continuous wheel spin, did someone experience that? Or should I be running the power function trains on plastic tracks for better traction rather than the old 9v metal tracks?

[BimmerBoy]

I use Rayovac nickel metal hydride rechargeable batteries and they work great. About two hours of run time, depending on how many motors (I use two on my longer/heavier trains) I'm powering and/or how heavy the train is. I also acquired the Lego rechargeable box, it lasts even longer (have not tested its limits yet). If you run trains often, this is a good investment even though the price is high.

As for wheel spin, no problems with 7938 for me. I do use the plastic track, though.

[v6TransAM]

Should not be getting hot.

Hot makes it sound like there may be a defective piece in there somewhere, like a bad motor. The 7938 by itself does not really exhibit wheel spin.

From the time of the drain, it seems something is excessively drawing current. That leaves a physical bind causing it, a shorted motor, or shorted battery box.

Battery box in your hand, a 3/8 drill bit followed up with a 7/16 to clean up the contact "holes" will do wonders with about 3/4 turns of each. I have had to do this with two out of three of mine running Eneloop batteries.

[Hrw-Amen]

I have had no problems like that. I use the ordinary battery box and ENergiser rechargable batteries. They seem to stay charged for ages and the only time I have had slippage on the wheels is going up too steep an incline, but that was my fault not the motors. Sometimes If I run them alot in a day the motors do get a little warm, but nothing worryingly so, no more than you would expect.

[BricksMcgee]

I run PF trains on 9V track too (don't own a 7938 yet though). The yellow cargo train was slipping quite a bit, but I found adding some Lego weight bricks (see ebay or bricklink) helped (or even coins, failing those); just needs a bit more weight to ensure traction!

[Redimus]

I believe you can buy a Lego weight which when applied on top of the motor bogie/powered wheels, allows for better grip. That said, I have the yellow fright set, plus additional wagons, and even up a very slight hill, on a rather wobbly piece of track that includes two points and a semi circle curve it managed to standing start a train of 2 of each type of truck in the set, plus 3 of the older octan wagon and a very heavy (and rather rubbish) MOC coach with little wheelspin as long as it was accelerated slowly. Your set should really not be troubling the motor.

[moretrains]

I run PF trains on 9V track too (don't own a 7938 yet though). The yellow cargo train was slipping quite a bit, but I found adding some Lego weight bricks (see ebay or bricklink) helped (or even coins, failing those); just needs a bit more weight to ensure traction!

That is good to hear the PF trains run well on 9v tracks as well. I found out now the train has much less wheel spin and also runs faster when running backwards so when the motor is pushing instead of pulling. I will see if I can add some additional bricks inside the engine.

So what I will try to do additionally:

- replace the batteries by Duracell nimh which fit the battery box as mentioned above. (Apparently, they don't sell Rayovac or Energiser batteries over here at online stores)

- replace the motor to hopefully prevent the batteries from draining too fast

- replace the battery box by the one Lego has shipped to me if the above fails

Thanks for your replies so far. I will let you know how it worked out in time.

Finally, I have replaced the batteries with rechargeable Duracell batteries and the train runs fine now although still has some wheel spin. Running it backwards gets rid of most of the wheel spin.

Edited August 17, 2014 by JopieK

[Dutchiedoughnut]

Is the battery drain any better? I'm concerned about that because if the batteries are dead after 10 minutes, its a sure sign of a short circuit or at least a drain somewhere in the system.

[Rail Co]

If the batteries are still draining very quickly you may need to contact Lego about the motor.

As for wheel spin, you can use O-Rings for better traction than the bands around the normal wheels. Here are a couple of pictures:

Use O-rings for traction by Railco1, on Flickr

Small change but big difference in performance by Railco1, on Flickr

Hope this may remove your problem with wheel slip and get your trains more traction!

Have fun with your train!

-RailCo

[moretrains]

Is the battery drain any better? I'm concerned about that because if the batteries are dead after 10 minutes, its a sure sign of a short circuit or at least a drain somewhere in the system.

I'm not sure what to expect as far as run time is concerned. This is my first PF train. The non-rechargeable batteries I tried drained really fast. I got about 30 minutes run time at top speed from the pre-charged Duracell nimh batteries. I am charging them now for the first time and yet have to see what run time I get.

If the batteries are still draining very quickly you may need to contact Lego about the motor.

As for wheel spin, you can use O-Rings for better traction than the bands around the normal wheels. Here are a couple of pictures:

I will try a new motor as I want to buy a spare motor anyway. I will look into the O-rings. Thanks for mentioning that.

[zephyr1934]

If the batteries are still draining very quickly you may need to contact Lego about the motor.

As for wheel spin, you can use O-Rings for better traction than the bands around the normal wheels. Here are a couple of pictures:

Use O-rings for traction by Railco1, on Flickr

Small change but big difference in performance by Railco1, on Flickr

Hope this may remove your problem with wheel slip and get your trains more traction!

Have fun with your train!

-RailCo

I wouldn't be surprised if the traction bands are the source of both problems- wheel slip and quickly draining your battery. The first few generations of the RC/PF motor wheels had loose bands. They improved greatly on the more recent trains, but I do not know about the newest sets that just came out.

The o-ring solution works if you have the loose bands, but for others who do not have traction problems, they probably do not need the o-rings (hence this post)

You could probably get replacement wheels from lego customer service and at the same time ask them about battery life expectancy.

[StephenTrains]

Thanks for your reply, I have checked this and it appears to be the case indeed. My rechargeable batteries have larger diameter tips than the non-rechargeable batteries. I will try to modify the battery box or try again with another brand of rechargeable batteries.

Just a as quick side-note - I had the same problem (batteries not fitting) in the blue freight train - one hole was slightly too small (for Eneloops) and a few turns of a drill bit fixed it completely.

To find the one hole, I a small strip of foil into each hole to improve the electrical contact until it started working, then cleaned that hole and removed the other strips one by one (in case there was more than one hole), testing that the light came on after each.

[moretrains]

Just a as quick side-note - I had the same problem (batteries not fitting) in the blue freight train - one hole was slightly too small (for Eneloops) and a few turns of a drill bit fixed it completely.

I ended up buying Duracell batteries and they work fine in the stock battery box. I don't like to drill in Lego much .

Does anyone know what runtime I should expect with 800 mAh rechargeble batteries? I get about 2 hours of continuous run-time when the train is at half speed.

[Paperballpark]

I've used Duracell batteries in my Motorised Constitution at Lego shows, and it will quite happily pull 6 MOC'd wagons for nearly 4 hours before the batteries need changing. TBH I've started using the rechargable battery boxes now. Yes they're more expensive, but they don't eat batteries, and I get about the same life from them before they need recharging.

Regarding the wheelspin, it definitely shouldn't do that.

[cgarison]

For our train layouts, we use the Panasonic (Formerly Sanyo) Eneloop rechargeable batteries in our triple A battery packs and we can typically expect 3 to 4 hours of running time for our trains. The trains that run more than one motor are closer to three hours while single motor trains get closer to 4 hours of running time. The reason for the Eneloop batteries is that they function more like the Li-Ion battery packs and usually run strong up until the last couple of laps of our circuit where the speeds drop off considerably. The Energizer rechargeable batteries that we ran last year would lose power gradually over a two hour span and barely have enough power to move as the trains approached their third hour of running.

I feel your pain on issues with Power Functions as I have been fighting an issue for the last six months where every so often I will take a battery box filled with fully charged batteries and plug it into the train and I have no power. I have marked all my battery boxes to see if one of them is causing the issue as well as marked the batteries to see if their is a particular group that might be the issue. I am also changing up my receivers to make sure that I do not have any V2 receivers powering train motors and M motors and only my L motors are connected to a V2 receiver. This weekend I plan on running a couple of my trains in a loop to see if I can fix the issue prior to my next display coming up in mid-September. I have my fingers crossed.

And yes, I have horrible wheel spin with the power functions train motors when running them on smaller track layouts. The Railco o-rings will make a huge difference in stopping this. Before using the o-rings, I also doubled up the motors on my Horizon Express and the increased tractive power on the single locomotive which made it possible to run 2 HEs without spinning the wheels. (Note the second locomotive has no power functions.) On the 60052, I have not had any of the issues that I have had with the HE or my MOCs with the train motor.

Best of luck with your issues.

[zephyr1934]

I am also changing up my receivers to make sure that I do not have any V2 receivers powering train motors and M motors and only my L motors are connected to a V2 receiver.

I have a locomotive with a pair of PF train motors that keep tripping the "V1" receiver's overload resistor. I was hoping the V2 receivers would solve that problem, is that not the case? Or does the V2 receiver introduce a new problem?

[cgarison]

I have a locomotive with a pair of PF train motors that keep tripping the "V1" receiver's overload resistor. I was hoping the V2 receivers would solve that problem, is that not the case? Or does the V2 receiver introduce a new problem?

I am having the same issue on the V2 receiver with the overload resistor getting tripped after running 2 sets of batteries in a train. The third set of batteries will light the receiver and battery box, but the train will not move. After 15 to 20 minutes, the train takes back off. I have switched that train back to the V1 for testing this weekend because a couple of members of my LUG think I might have a bad battery box. By Monday, I will have either found my bad battery box or proven that I am tripping the overload. If prior experience holds true, I am going to trip the V1 after 4 hours of running the train so about halfway through the life of the second set of batteries. I will have more information in the next 72 hours. I do not think I have a new problem with the V2, just a different manifestation of the same problem in the V1.

The solution for our displays is simply have more trains available to run and change them out every two hours. Good news for me because I get to build more MOCs.

[cgarison]

Well that did not take long.....

I found my problem and I have a bad motor! And now that I compare the symptoms of my latest MOC to those with Peter Morris' SpaceTrain at BrickFair, VA (where I killed 3 motors in one day) they were exactly the same.

Lesson here, don't build a MOC around a reconditioned motor. (sigh)

Edited August 23, 2014 by cgarison

[zephyr1934]

Thanks for the info CG and Ugh! Sorry to hear about the misfortunes with the motors. You might want to try calling lego customer service, they might still replace them.

[cgarison]

I would feel guilty going back to TLG for them to replace motors that we wore out over the course of an AFOL show. Lego makes wonderful toys that are reliable but when I look at the amount of use (to the threshold of abuse) we throw at a MOC over the course of a 3 day show and compare that to the time that a child would play with that toy over a period of several years, I can see where we might be pushing the limits of their testing program. There is nothing like rolling a train over a layout for hours and hours to find all the week clutch points in Lego parts and make the running gear scream for mercy. I know we have one unit that will need a complete overhaul because the clutch on the Lego pieces has worn to the point where it drops parts off the MOC as it rolls around the moonbase.

With that said, I have not seen many of these issues on the old monorail that AFOL's want back in production or the traditional track powered train motors. But that represents a different era where childrens were using system to build decortive trains compared to today when we build the entire running gear with parts from the Technic bins. So another level of building detail leads to another level of trouble to keep these pieces chugging reliably for a long time.

[zephyr1934]

Taking the discussion of burned out motors to its own topic...