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PL-10 and PL-10W coil resistance?


SimonBa
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Hi all,

 

Would someone do me a favour and measure the coil resistance on the PL-10 and a PL-10W Peco point motors please? I find a number of values quoted around the 'net (and am surprised Peco don't provide specs).

 

Reason for asking is that I'm planning a layout with a complex diode matrix that will need to shift up to 10 points at a time, via a number of CDUs distributed around the place. Rather than attempt to push several dozen amps through subminiature push buttons on the mimic panel, I'm going to use a pair of transistors (actually a pair of darlington pairs, TIP121s) mounted locally to the point motors that will switch in the relevant coil to the local CDU bus when the mimic's route selection button is pressed. The current to the transistors only needs to be a few mA each which will reduce the gauge needed for the wire from the panel to the point motor and allow the use of smaller panel buttons. This approach will also reduce the length of cable run from CDU to each individual motor. The CDU common return buses will be >ahem< somewhat hefty - probably 30A mains wire :-)

 

Without knowing the resistance of the motor coils it's difficult to calculate the values for various things. I'm also trying to decide whether to use 12Vdc or 5Vdc for the mimic panel PSU and obviously that choice also impacts on resistor values etc.

 

Anyone able to provide the data I need, it'd be much appreciated.

 

I've attached the circuit for the small stripboard carrying the transistors and flyback diodes that will go near to each point motor.

 

Cheers

Simon

Screen Shot 2020-05-24 at 01.16.27.png

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I read 4.1 ohms on a PL-10 so I would assume PL-10W would be more as they take less current.

I also assume you don't have a multimeter to do your own testing which I think is essential when doing electrics.

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As a retired electrician my knowledge of electronics is limited

I have added a local CDU to the drawing as I understand your description

 

If you provide local CDU feed & return busses then the local return & feed busses only need to carry the firing current to the points on that bus &

Then the Main return & feed busses only need to carry the charging current to the CDU's

 

I feel that a change to the circuit might be doable*

With the changed circuit I don't thing the resistance of the point motors comes into the equation

The value or the resistor needs to be enough to turn the Darlington pair fully on

 

By moving the transistor to it new location you could control it with an Arduino or similar

Adding a opto-isolator** electrically isolates the control circuit from the point circuits & protects the control circuit

 

1848104033_Pointcontrolmatrix.png.ce13c1cbb9cb31e9cf12864dba1edd06.png

 

**Someone smarter than me can tell me if I got the opto-isolator circuit correct

*& if the new position of the Darlington pair will work

 

John 

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I'm wondering if an SCR would be better than a Darlington Pair transistor.

 

The reason for my thinking is that a pulse could be applied to the SCR, causing it to conduct. It would then discharge the CDU. Once the CDU is discharged the SCR would be automatically turned off, until it next gets a pulse.

 

A Darlington Pair, would continue to conduct if switched on.

 

I guess a lot depends on your actual method of firing the points.

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PL10 standard should be 4 Ohms giving 6A current at 24V. The TIP120, 121, 122 are 5A continuous with a good heatsink, but should be OK I guess for a short 6A pulse - I have used them to drive a matrix directly with about 30A on a good day with a short pulse and no heatsink.

 

The big problem will be how many of these you will be firing at once. You can make a big CDU that will fire 30A of solenoids, but you will probably be better off using the PL10W.

 

As for what power supply to use to drive the transistors via the buttons, probably best to derive it from whatever is charging the CDU. If using a switchmode DC PSU (best option for many reasons) use the 24V DC, if using a 16V AC transformer then it gets more complicated and will probably be cheaper to just replace the transformer with a 24V DC switchmode PSU.

 

The gain of the TIP121 is 1000+ so at 24V for 6A (assuming 4R solenoid) you will need a quarter watt 4000 Ohm resistor for the base (use next lower preferred value of 3K9).

 

Hopefully someone has a PL10W to hand and can measure the coil resistance to see how it compares.

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PL-10W to be discontinued by Peco (recent distributor advice note)

"When introduced, the PL-10W and PL-10WE motors were targeted at the continental market, where traditionally analogue transformers were rated with less amps than those available in the UK. But in actual fact there was very little difference between the original motors, and the newer "W" versions. With the introduction of DCC it was also perceived that the "W" versions were preferable. Over the years we have carried out testing with numerous DCC systems and found that in reality the standard PL-10 is more powerful. So in order to simplify the number of motors available we have decided to drop the PL-10W and PL-10WE from the range permanently. "

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A bit of a bonkers idea from Peco. There are very few DCC decoders that can supply the 4A+ that a PL10 requires, the popular Lenz LS150 solenoid decoders for example overload when driving PL10s and shut down.

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5 hours ago, kevinlms said:

A Darlington Pair, would continue to conduct if switched on.

 

Would it? I plan to fire the points from a diode matrix with routes initiated by push button momentary contact switches, and had assumed (perhaps incorrectly) that once the push button was released the base current would drop to zero and the TIP12x would turn off.

 

( I do have a multimeter, just no PL-10s or PL-10Ws to hand - the layout is in the planning stages)

Edited by SimonBa
Add note re: multimeter.
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6 hours ago, John ks said:

If you provide local CDU feed & return busses then the local return & feed busses only need to carry the firing current to the points on that bus &

Then the Main return & feed busses only need to carry the charging current to the CDU's

 

That's an interesting and useful mod - thanks. Not quite sure what effect moving the transistors has, but I'll give it some thought. Haven't planned to go the Arduino route.

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2 hours ago, Suzie said:

PL10 standard should be 4 Ohms giving 6A current at 24V. The TIP120, 121, 122 are 5A continuous with a good heatsink, but should be OK I guess for a short 6A pulse - I have used them to drive a matrix directly with about 30A on a good day with a short pulse and no heatsink.

 

Thanks - I was hoping that since the action is momentary and the duty cycle is light I could get away without heatsinks.

 

The control panel PSU will also be driving LEDs route indicators via 12V (or 5V) latching relays taking their coil power from the output side of the diode matrix, so I was considering a separate supply from the CDU charging PSU.

 

Check my math? Assuming 4Ω for the motor coil, that gives 6A via the TIP, so 6mA minimum maximum to the base when hfe >=1000 and if supplied from a 12V supply that means the base resistor ought to be around 1k7 - 2k2 (with the 1.4V drop across the TIP from the CDU factored in). I was planning to use 1k5 1/4W resistors in this case. Figures dependent on motor coil resistance of course, hence the original question.

Edited by SimonBa
Change minimum to maximum
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1 hour ago, MAURICE040947 said:

So in order to simplify the number of motors available we have decided to drop the PL-10W and PL-10WE from the range permanently. "

 

Curses! Their higher Ω meant I would be able to drive them with c.2A rather than c.6A (if they are 11Ω rather than 4Ω) which had lots of useful consequences. Better go and buy a job lot before they disappear (I'll need about 70 in total).

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5 hours ago, SimonBa said:

 

Thanks - I was hoping that since the action is momentary and the duty cycle is light I could get away without heatsinks.

 

The control panel PSU will also be driving LEDs route indicators via 12V (or 5V) latching relays taking their coil power from the output side of the diode matrix, so I was considering a separate supply from the CDU charging PSU.

 

Check my math? Assuming 4Ω for the motor coil, that gives 6A via the TIP, so 6mA minimum maximum to the base when hfe >=1000 and if supplied from a 12V supply that means the base resistor ought to be around 1k7 - 2k2 (with the 1.4V drop across the TIP from the CDU factored in). I was planning to use 1k5 1/4W resistors in this case. Figures dependent on motor coil resistance of course, hence the original question.

You won't need heatsinks.

 

Use 24V latching relays, they are readily available. It keeps things simple - one less PSU to have to worry about. Nowadays I usually use a single 12V PSU with an adjustable DC-DC step up to give me 24V, and I can wind up the voltage higher if I need it (sometimes need 35V with dodgy wiring and sticky points).

 

6mA is the minimum you want to the base, but you should be OK with a bit more. Not enough in this scenario is a bad thing because potentially the transistor will not switch fully on and will start to dissipate anything up to 36W (with typically 3mA drive), and you will only be seeing a quarter of the power at the point motor (36W instead of 144W). It is well within the transistors capability but not desirable. 2K2 will be too big at 12V, so 1K5 is excellent.

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7 hours ago, Suzie said:

A bit of a bonkers idea from Peco. There are very few DCC decoders that can supply the 4A+ that a PL10 requires, the popular Lenz LS150 solenoid decoders for example overload when driving PL10s and shut down.

 

An alternative is to use a SEEP, which is less powerful than a PL-10.

It's resistance may well be 4ohms but ohms law only works for steady DC, which a CDU will not produce. The coil's reactance therefore needs to be considered & this will not be consistent because the current is not.

It gets very complicated once variable voltages are involved, but a decoder should not need to provide 4A. You may need some pretty specialised equipment to observe exactly what the maximum current is.

 

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If a motor is 4 Ohms then to drive it from most DCC decoders which are 3A (obviously not the DCCconcepts ones which are high power) you will be limited to 12V, and there are not many situations when you will get reliable operation of either Seep or PL10 motors at 12V.

 

Yes working out the currents when a CDU is involved can be complicated, but simply the inductance of the motor limits initial current, and the discharge of the capacitor limits the end current, but in between when things actually happen the current will be very similar to the DC current.

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8 hours ago, Suzie said:

You won't need heatsinks.

 

Use 24V latching relays, they are readily available. It keeps things simple - one less PSU to have to worry about. Nowadays I usually use a single 12V PSU with an adjustable DC-DC step up to give me 24V, and I can wind up the voltage higher if I need it (sometimes need 35V with dodgy wiring and sticky points).

 

Thanks Suzie - just for fun, I decided to simulate the circuit using lushprojects online tool, including a CDU for good measure (I took John's advice and repositioned the point motor in the circuit so the transistor switches the ground of the coil rather than the feed).

 

The graphs are interesting, and reassuring. CDU in the design is based on RK Education's circuit. If anyone fancies having a play, it's here: http://tinyurl.com/y8zxlfp9

Edited by SimonBa
Change to simulated circuit
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The base-collector junction of a bipolar transistor is a diode so when the collector voltage on the TIP121 drops below 1.3V you will start to charge the CDU capacitor (very slowly) from your 12V supply via the base-collector junction.

 

I don't think this is a problem that you need to worry about! It will only happen while the button is pressed and those currents are pretty small and hard to measure.

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3 hours ago, Suzie said:

I don't think this is a problem that you need to worry about! It will only happen while the button is pressed and those currents are pretty small and hard to measure.

 

I probably shouldn't trust the circuit simulator implicitly, but it shows rapidly the varying minute voltages and currents when the button isn't pressed.

 

I'll try not to worry about it :-)

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