SEEP point went up in smoke

[LlandudnoJunction]

I need some major help now as I had a slight mishap with my SEEP point motors, to the point it started smoking very badly and melted the whole thing.

Well what happened is what your thinking?

 

In a nut shell my old power supply which I had for controlling the points stopped working, so while I was searching the forum to try and repair it i found an article stating you could use a old laptop charger. So i found one in the cupboard it was 16V AC pumping out 3.25 amps, So I removed the plug, set up the connections and switched on. Bingo lights came on and seemed all was fine that was until i started smelling plastic burning. This was in the middle of me running some trains doing a bit of shuntting, i was flicking a point back and too no problem but then loads of electrical smoke and point was dead. Switched off the old laptop charger ASAP and then went to investigate the damage. Noooooooo!!!! point RIP.

 

So my questions as I really need help with this otherwise it maybe a costly affair.

 

1) Has anyone used laptop chargers as a power supply for points / lights etc?

2) If you have what protection have you got before the points ie will a CDU work with it or will that go up in smoke?

 

Cheers

Mark

[adb968008]

Seep point motor work at <1.5 amps, so in this case 3 amps is overloading it, especially if the points are "live" all the time.

At 1a it would get warm and burn out faster, and in your case at 3amps it melted.

 

I would recommend using a CDU, as having constant current at the point motor means it's On, and burning the motor constantly if your wires are attached. (i.e. like leaving a train running non-stop) a CDU would cut the feed and fire a burst when activated giving them a much longer life and a stronger "burst".

 

3 amps is much more than most model accessories need, upto 1.5a is more the norm for most accessories, so a laptop charger may not be the best solution.

[LlandudnoJunction]

Seep point motor work at <1.5 amps, so in this case 3 amps is overloading it.

 

Arhh missed that  cheers for letting me know.

[Ray H]

I'd be tempted to check the actual output voltage of the transformer as well.

 

Solenoid based point motors are meant to be supplied with a momentary pulse of power to energise the relevant coil. I doubt that repeated throwing of the point during shunting would cause the symptoms experienced because the power is only there for a fraction of a second and even with the most fervent shunting it is unlikely that the point would be thrown repeatedly so fast that the coils would overheat.

 

I'd be more inclined to think that there's a fault with either the switch being used or the circuit between the power supply and the point motor itself

[Edwin_m]

Seep point motor work at <1.5 amps, so in this case 3 amps is overloading it, especially if the points are "live" all the time.

At 1a it would get warm and burn out faster, and in your case at 3amps it melted.

 

I would recommend using a CDU, as having constant current at the point motor means it's On, and burning the motor constantly if your wires are attached. (i.e. like leaving a train running non-stop) a CDU would cut the feed and fire a burst when activated giving them a much longer life and a stronger "burst".

 

3 amps is much more than most model accessories need, upto 1.5a is more the norm for most accessories, so a laptop charger may not be the best solution.

If the supply is rated at more amps than the load, the only problem is if the wiring can't stand that current in the event of a short circuit.  It's the supply voltage that causes problems if it is too high for the voltage rating of the load. 

 

However I would agree with the CDU.  The solenoid in a Seep is made of very thin wire and although it needs a high current for a short period (it's actually 4-5 amps) it will get too hot if this current flows for too long.  That might happen if you feed it directly from a big power supply via a push button or passing contact switch and that switch sticks so the current is being fed continuously.  For the same reason a steady contact switch feeding a solenoid is a really bad idea!  The CDU ensures that the motor only gets a big current for a short time even if something else fails.  Also because the current from the power supply just recharges the capacitors relatively slowly, the supply feeding the CDU doesn't need to have a high current rating. 

 

For reasons to do with average and peak current, a CDU works much better if fed from AC than from DC of the same voltage.  But don't exceed the voltage rating of the CDU or the capacitors will explode! 

[cliff park]

It doesn't matter at all if a power supply is capable of supplying more than a circuit needs. If you connect a bulb which consumes 1 amp in a circuit capable of supplying 50 Amps the current is limited by the supply volts and the bulb resistance. Assuming of course that the supply voltage is regulated and appropriate. You cannot push a current through anything. The problem is that a Seep point motor has a very low resistance and will take a very high current if the supply is capable of supplying it. Most of the power supplies we use are not. Or we use a CDU to limit the current to a very short, high current pulse. I suspect that the supply was being fed to the motor continuously, when it should be pulsed.

[kevinlms]

I'd be tempted to check the actual output voltage of the transformer as well.

 

Solenoid based point motors are meant to be supplied with a momentary pulse of power to energise the relevant coil. I doubt that repeated throwing of the point during shunting would cause the symptoms experienced because the power is only there for a fraction of a second and even with the most fervent shunting it is unlikely that the point would be thrown repeatedly so fast that the coils would overheat.

 

I'd be more inclined to think that there's a fault with either the switch being used or the circuit between the power supply and the point motor itself

Definitely a problem with whatever means was employed to control the power. If that device fails and keeps supplying power, the point motor (SEEP or otherwise) will continue to get hot very quickly & will cook, as the OP has found out.

 

Light duty switches are very suspect and often fail when trying to turn OFF the power, they arc & stay stay closed thus keeping the power going. So its a switching device failure, rather than a fault with the point motor or power supply.

[melmerby]

Laptop charger pushing out AC?

 

That's a new one on me.

All the ones I've seen are DC varying from 15v - 20v.

 

Keith

[chaz]

Seep point motor work at <1.5 amps, so in this case 3 amps is overloading it, especially if the points are "live" all the time.

At 1a it would get warm and burn out faster, and in your case at 3amps it melted.

 

I would recommend using a CDU, as having constant current at the point motor means it's On, and burning the motor constantly if your wires are attached. (i.e. like leaving a train running non-stop) a CDU would cut the feed and fire a burst when activated giving them a much longer life and a stronger "burst".

 

3 amps is much more than most model accessories need, upto 1.5a is more the norm for most accessories, so a laptop charger may not be the best solution.

 

There is a basic misunderstanding here. The 3 amp rating is the designed maximum for the power supply. the actual current will depend on the voltage and the effective resistance in the circuit. Ohms law in fact. The current flowing will be the voltage (in volts) divided by the resistance (in Ohms) and the answer will be in amps. If the effective resistance is at a level to draw less than 1.5 amps then that's what would flow in the circuit. If you make a circuit with a very large resistance then the current flowing will be tiny. If the circuit has a low resistance then the current will be high. It sounds like your point motor circuit has a fault, producing a low resistance and a consequent high current. 3 amps has quite a heating effect.

 

I work the points on my new layout with a 15V laptop power supply (from a retired Toshiba) with no problems (although I use Tortoise motors rather than solenoid types). Laptop PSUs have to be good - nobody wants their nice new laptops damaged by a faulty one! Checking mine with a meter showed it to deliver 15V (DC!) - spot on.

 

Chaz

[rdr]

thought i'd pop in and make a comment, hope i don't offend anyone.

 

1. A 3.5amp psu will only deliver what is required from the device it's connected to, up to a maximum of 3.5amps. Seep point motors require around 1amp and that's what will be delivered.

 

2. Laptop power supplies/chargers can be either ac or dc depending on the laptop, and the seep point motor will run on either.

 

3. Seep point motors need a pulse rather than a continuous voltage. Here's a quote from gaugemasters site.

"Please remember these motors only require a short burst or pulse of power. Connection to a standard On-On type switch (or a permanent connection) will lead to irreversible damage."

 

4. Sounds like the fault lays in the control of the motor, rather than the supply.

 

Hope this helps.

[Edwin_m]

Light duty switches are very suspect and often fail when trying to turn OFF the power, they arc & stay stay closed thus keeping the power going. So its a switching device failure, rather than a fault with the point motor or power supply.

Especially when the contacts are being opened when carrying the high currents drawn by a solenoid motor.  Changing from an AC to a DC supply will exacerbate this because DC tends to arc for longer across the contacts (the reversal of current in AC tends to stop the arc).  So it may be that the change to a DC supply has led quite quickly to the switch contacts welding up, which in turn has cause the solenoid to burn out. 

 

So if the OP has other motors similarly wired they are quite likely to fail too, unless something is changed such as fitting a CDU. 

[melmerby]

A bit of fact:

 

A  Seep point motor has a coil resistance of about 2.6 Ohms

If you connect a 15v supply across it (assuming the supply can give the current) it will have about 5.8Amps flowing through it.

That will mean the coil is dissipating 87 watts, enough to boil water!

It will heat up extremely rapidly and burn out.

 

Never use a fixed voltage supply, only use pulse (e.g. CDU) or via a momentary switch

 

Keith

[melmerby]

thought i'd pop in and make a comment, hope i don't offend anyone.

 

 

 

2. Laptop power supplies/chargers can be either ac or dc depending on the laptop,

 

Never seen one. (Not saying there aren't any)

All the ones I've seen are SMPS. an AC one would need a conventional transformer and for 60W would be much, much bigger and heavier. (not what's required for a laptop)

 

Keith

[Brian]

Hi

As stated, Seeps PM1 2 and 4, Peco PL10, Hornby R8014 etc solenoid style motors will draw (depending on supply volts) around 3.5 to 5 Amps.  However, they will work with a 1.0Amp 16 volt AC power source.  As the power applied is just a momentary pulse of current. So the supply transformer barely sees the excessive loading. (Power is normally only applied for less than 0.5 second). Using a CDU will also... A) Reduce that power On time period and.... B )  Prevent accidental coil burn out should ever a lever or switch remain in the On position, as the CDU cannot recharge all the while a solenoid motor coil is connected to its output. It will also deliver the pulse as one large 'beefy' pulse of power.

 

I too haven't seen laptop AC output power packs (doesn't meant they don't exist?). But using a 19 to 22 volt DC laptop power supply usually rated at somewhere around 3 to 5 Amp will work a Seep or other type of solenoid motor. It can also be used to charge a CDU and have then have the same benefits as outlined in A and B above.

 

The reason the solinoids coil smoked and burnt out is because power was allowed to remain being fed to the coil for too long a period of time > typically greater than 2.0 Seconds.     

 

It wouldn't really matter whether the supply was rated at 3.0Amp or 10Amp under normal operation the current taken is only what is needed.  However the larger the current available the greater the risk to the wiring, unless the wiring is rated sufficiently high to cover the maximum output current of the supply or a lower current circuit breaker or fuse if used. e.g. 10Amp power supply with a 5Amp CB fitted.  Then the wiring only needs to carry the 5 Amp load as it should then easily carry the fault current load needed to trip the 5 Amp CB.