Large Scale Central

MiMH -- Li-Ion

Electronics Power and Sound
#1

Somebody 'splain this to me:

For years, I’ve run Madam Mallet on 19.2v NIMH batteries. She’s quite happy to run that way even today.

Last spring, while I still had the new job, I bought a Tenergy Li-Ion 14.8v 5200mAh pack and a charger to go with it. I put the connectors on, charged the pack. All seems fine, but Madam Mallet does not see anything coming out of it. The little red light on the old TE receiver comes on, and promptly goes out. “Hmm. I thought the old TE would work at 14.8.”

Well, now, both the old NiMH chargers have gone to pot and will only give me 20 hour trickle-charge rate, so I decided to get to the bottom of the Li-Ion pack problem.

So here’s what I did. I measured the unloaded battery at 16v. Looks Ok. I connected it up to the loco and nothing. Measures 1v. “Hmm. Wonder how much current I’m drawing.”

I turned my meter to 10A scale thinking I must be drawing lots of amps and shutting the thing down. I used clip leads to connect the black wire of the battery to the black wire of the loco, and connected the red wire of the battery to the red wire of the loco and read 380mA and the lights and sound turned on! If I use the remote to give her some juice, she’s moving at about 1 amp (no cars). I don’t go far 'cause all the gory guts are laying beside her connected by clip leads.

“Perhaps my connector is bad.” That wouldn’t be a BIG surprise. I unhooked the clip leads and connected the battery back up. Nada, as anticipated. I measured the battery voltage ahead of the connector, 1v. (This is now the battery side of the connector.)

I unplugged the connectors and hooked it back up with clip leads and 10A meter. 380mA. Loco is on. Even moves when I tell it to. So I took the meter out of the circuit and just used clip leads. Big sparks when I went to clip red to red, and no life. I put the meter back in, and it says 380mA and the sound and lights come on.

Do you think maybe: The old TE draws such an inrush of amps that the little board shuts the battery down and the shunt in my 10A meter reduces it enough to work?

Baffled, mystified, and moderately grumpy over this.

#2

Tom - I know you know enough to confirm the polarity of the Li-Ion pack output. TE’s must be fed in the correct polarity. Just 'cause Tenergy uses a red wire doesn’t mean that it’s positive!

#3

But the volt meter tells me it’s positive. Yes, if you reverse the polarity to the old trackside TE receiver, the fuse blows in a very short time.

Yes! With something to control the inrush and turn the power on more gently, the Li-Ion battery powers up the loco.

Digging in the junque box, I find an IRF540N mosfet, some 100K resistors and a .1 uF capacitor. A 100V 33A mosfet should be adequate, don’t you think?

Theory of Operation:

When you apply power, the capacitor slowly charges through the 100K resistor, raising the gate voltage to about V/2. When the gate passes the mosfet’s threshold voltage, about 3v, the mosfet turns on and connects the - to the loco. When you remove the battery, the capacitor discharges through the other 100K resistor, so the mosfet will be turned off next time you connect the battery.

#4

Tom Ruby said:

(Sorry, I clicked “Quote” instead of “Edit.”)

#5

The inrush of current is too high? Huh? That could be what I experience on my track-side TE. I hadn’t considered that. So you need to slowly ramp up the power so the current draw isn’t too high at the start. Dave Bodner could probably suggest a good thermistor for that kind of application.

#6

Tom… I found that the old Trackside 27 mhz TE liked the higher voltages…

And, I have had that battery pack shut down with an “overload” when using the 27 mhz trackside… Could be that the battery has a “bad or weak” protector PCB… Been there, done that as well…

Now that I using the REVOLUTION, I haven’t had one “battery overload”… I have had the REVOLUTION receiver overheat in extremely hot conditions, (90 degrees and hotter) and running a Dash 9 with the extra weights up a 10 foot diameter 1.5% grade.

In the 90 degree condition, I take the roof off the battery car to let air circulate through the car and over the receiver… In the Dash 9’s case, I took the extra 3 weights out and it ran like a champ…

#7

I did battery installs for a guy on 2 sets of aristo PA units, an A-B-B-A and an A-B-B. I used 14.8v LiIon 6000Mah batteries and Aristo 27Mhz train engineers onboard, all what the customer wanted. We found the same thing you did. My solution was a bit simpler. I turned the switch on then off then back on. Works every time.

Terry

#8

I’ll give her a workout this weekend, assuming I finish realigning the wheels. She’s developed a bit of a rod bind.

hehe

I started out with 100uF. I thought I’d miswired something 'cause nothing came on. To see what was going on, I connected my meter to the gate and saw it slowly counting, 1.02, 1.03, 1.04, 1.06… After a minute, it got to 3.something and the lights came on. “Oh, too many microfarads.” I multiplied 100000 * 100E-6 and got a reasonable number BEFORE I built it.

#9

Terry Burr said:

…I turned the switch on then off then back on. Works every time…

The first Train Engineers ran on Windows… Who knew? :wink:

Later,

K

#10

“Do you think maybe: The old TE draws such an inrush of amps that the little board shuts the battery down and the shunt in my 10A meter reduces it enough to work?”

YES! It has happened before…

Actually just a MOV in series with the input would do it…

Greg

#11

Didn’t have a mov in the junk box

She didn’t get any workout this weekend

She had a bit of a rod bind last time I ran her, so I thought to fix that. Took the rods off the back drivers, and, yep, 2 wheels spin freely. Didn’t take long to get the back driver squared away. Now for the front. No loose wheels, but I see one on the right side is WAY out of sync with the others. Since I’ve moved and been rather unsettled since I last did this, it took a while to find the big screwdriver I use on wheel screws. “Here it is!”

“Let’s see if this screw will turn.”

“Hmm, came right off. I can’t imagine I didn’t locktite it.”

Oh, gross. I DID locktite it. Twisted the head off.

A friend is sending me another axle barrel.