PM1 point motors - another questions please

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Ogster
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PM1 point motors - another questions please

Postby Ogster » Mon Jul 11, 2016 1:14 pm

Chaps

Pursuant to a previous post - and my thanks for all replies - to power the PM1s dotted about the layout - 7 so far, I have used a laptop transformer/adapter as the DC power source. So far, it has worked well, but lately has been blowing the fuse, which is a small 1A in the mains plug of the transformer.

I must state that I have not got a CDU installed in the circuit

Questions then

Why does it blow fuses? Could some motors draw slightly more than the 1A?
I realize a CDU protects the motors somewhat and is recommended, but would it also prevent blowing of the fuse in the transformer plug?
If so, where is the best place to do to purchase a CDU? What type do I require..
If not, where next....larger rated fuse ...3A perhaps....

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Flashbang
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Re: PM1 point motors - another questions please

Postby Flashbang » Mon Jul 11, 2016 1:41 pm

Hi

Hardly surprising a 1.0Amp fuse bows.. It is far too small current rating. Assuming its placed in the PSU output lead.
While you haven't mentioned the output voltage of your power supply, a Seeps coil resistance is around 4.0 Ohm, so the current flow will exceed 1.0Amp and a 5.0Amp fuse might be a better option.
Calculations for DC Current are.... Voltage divided by the Resistance e.g. 12v / 4 = 3.0Amp. 16v / 4 = 4.0Amp. 20v / 4 = 5.0Amp

A CDU will be limited to the total current it can take from the power supply. So its a better option to use. Gaugemaster CDUs are popular - sold by Gaugemaster suppliers throughout the UK. Or obtain one of the excellent CDU sold on ebay by Blocksignalling
Link to ebay CDU
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Roger (RJ)
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Re: PM1 point motors - another questions please

Postby Roger (RJ) » Mon Jul 11, 2016 1:48 pm

Seep point motors are a type of solenoid motor, as are Hornby and Peco,. All of these point motors take about 3 to 5 amps when operated so I would suggest you may need to look at replacing your power supply with a more capable unit or installing a CDU which will significantly reduce the power drawn from the power supply.

Ogster
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Re: PM1 point motors - another questions please

Postby Ogster » Mon Jul 11, 2016 2:26 pm

Gents

My thanks for this. Yes, basic electrical theory returns thanks to your prompting! Fuse is in the mains plug of the PSU power supply - the transformer plug that is. I now appreciate the need for something bigger.....but strange it did not blow before now...

Ordered a CDU anyways from micro-models from Ebay. If I install this and as Roger states, will this mean a 1A fuse will still suffice or do I still go with a 3 or 4A?

Just another quick Q - the 1A fuse is smaller in dimension than the typical fuses found in household mains plugs. Does anyone produce a 3,4 or 5A of similar dimensions?

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Flashbang
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Re: PM1 point motors - another questions please

Postby Flashbang » Mon Jul 11, 2016 2:47 pm

The 'standard' UK plug fuses are 3Amp and 13Amp.
However, other current ratings are available. Typically 5Amp and 10Amp.

Are you stating the plug of the power supply comes with a 1.0Amp fuse fitted? This rating of fuse is not a conventional plug fuse and is often found in adaptors used for electric razors.

If it's your plug fuse blowing then it should be rated at 3Amp. This should overcome any surge current flow produced in the primary windings.
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Ogster
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Re: PM1 point motors - another questions please

Postby Ogster » Mon Jul 11, 2016 4:06 pm

Yes, I appreciate it a non-standard rating. As I say, it is used as a fuse for the mains plug for a laptop power adapter/transformer. I also appreciate a need for a 3A, but the 1A is dimension-wise smaller than "standard" fuse size, so I need something rated at 3A but same size as the 1A.

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Flashbang
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Re: PM1 point motors - another questions please

Postby Flashbang » Mon Jul 11, 2016 4:42 pm

Ogster wrote:Yes, I appreciate it a non-standard rating. As I say, it is used as a fuse for the mains plug for a laptop power adapter/transformer. I also appreciate a need for a 3A, but the 1A is dimension-wise smaller than "standard" fuse size, so I need something rated at 3A but same size as the 1A.

UK fused plug tops should conform to BS1363/A and be fitted with a ASTA certified fuse. There are exceptions, but these are usually electric shaver plugs and tooth brush charger plugs that are two pin.

If you take the fuse to a Maplin store or a local TV repair shop they should be able to provide you with an identical sized replacement fuse. If the transformer/power supply was supplied with a 1.0Amp rated fuse then you shouldn't increase it!

Is it actually a three pin plug on the end of a flexible mains cable? Or a plug-in style transformer?
Also what is the rating of the power supply - output volts and output current.
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Bufferstop
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Re: PM1 point motors - another questions please

Postby Bufferstop » Mon Jul 11, 2016 5:02 pm

Is it a non standard plug? Is the lead noticeably thinner than that of a table lamp or similar? If both are yes, what else have they skimped on? Seek expert advice.
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Ogster
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Re: PM1 point motors - another questions please

Postby Ogster » Mon Jul 11, 2016 6:00 pm

It is a plug in style transformer for a laptop. Made by Hewlett Packard fitted with a standard mains plug with the inbuilt problematic 1A fuse. Wiring from this plug to transformer is pretty thick, nothing detrimental there I think. From transformer it goes to the points bus wiring.

Input 100-240V AC 1.5A
Output 18V DC 4.74A

I have now bought the correct size 3A fuses from Ebay and also intend to fit a CDU.

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Bufferstop
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Re: PM1 point motors - another questions please

Postby Bufferstop » Mon Jul 11, 2016 11:21 pm

HP often err on the side of caution, if it's intended for use down to 110V then the wiring is likely to be OK at 3A. Never worked out how they decide their fuse ratings, but we had a spate of printers blowing their internal fuses on 230V. They were fused at 5A but they'd used a surge protecting type, feeding a large auto-transformer. There was a surge suppressing circuit which relied on it being switched off at the device rather than the wall. Of course the switch was round the back next to the cable entry, so lots of blown fuses.
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