Basic current draw question

[BoD]

I have a basic knowledge of volts, amps and things but it is only basic - hence the following, probably daft question.

 

Background:  I am using the Lenz LZV100 combined command station/power unit.  The instructions say the output current is limited to 5A.  I have a Lenz 45VA transformer which, I understand,  can supply approx. 3A.  As I needed slightly more than this I was looking to buy the next transformer up which supplies about 5A. The dealer didn't have one of these but sold me one of his own as suitable.  The rating of this transformer is 150VA. which I believe can supply about 10 Amps. I have no concerns about the safety of the transformer just its suitability. 

 

My question, which clearly shows that I only have a basic understanding, is this.  Will the command station only 'draw' the current it needs or will the transformer 'push out' the full 10Amps and possibly damage the command station.  I apologise for the terms 'draw' and 'push out' and hope you understand my meaning.  Can I safely use this transformer or have I been sold a pup?  

 

A secondary question.  If I can use the transformer, will I then need to take steps to ensure I don't overload the Lenz LZV100 or does it have its own protection/cut out.

[johnb]

The transformer won't 'push' 10 Amps, it will only supply what the command station draws.

I don't know the Lenz but yes there will need to be a fast acting limiter maybe internal or maybe not I can't answer that point. No doubt someone knowledgeable will be along soon to sort your second question.

[BoD]

Thank you, John.

[melmerby]

46 minutes ago, johnb said:

The transformer won't 'push' 10 Amps, it will only supply what the command station draws.

I don't know the Lenz but yes there will need to be a fast acting limiter maybe internal or maybe not I can't answer that point. No doubt someone knowledgeable will be along soon to sort your second question.

The Lenz command station does indeed have an internal cut out so you cannot overload it.

I have a pretty chunky toroidal transformer with quite a reserve in power supplying mine and the Lenz system operates exactly as it should.

[Phil S]

Two parts to this answer:

Currently, ALL such CURRENT products should be supplied with energy-efficient switched-mode power supplies (in the EC) ... once old stocks of traditional 50Hz tranformers have been used up - they should then only be supplied as spare parts for existing or non-dc-input compatible controllers. 

This is why all present models come with SMPS ... Roco, for example, having changed from their 230:16Vac transformer of similar rating (and perhaps the same factory) as the Lenz model, to more energy efficient and compact SMPS of 18Vdc output (at upto 3.2-3.5A range) - which again has to do with EC toy regulations.

 

An unregulated and traditional transformer will give a higher voltage output than labelled when the current taken is LESS than the quoted maximum  [ The voltage qioted will occur WHEN the maximum current quoted is taken]... on the Roco badged version this could rise to 22-23Vac ish !!! (at least, in the UK, with the mains reaching 250Vac at going home time on a friday)

I believe the Lenz Controller offers a controllable track/dcc voltage output ... the Roco Amplifiers did not - just limited to 22Vdcc maximum as per NMRA spec..... this meant coach lighting could get quite bright when no trains were running:  This was no longer a problem once people swapped to using an SMPS of 18Vdc (regulated) as the track voltage remained the same (16Vdcc on the Roco)

 

You have used the word 'transformer' for your new power supply of 10A maximum - ASSUMING this has the same STATED output voltage as the original, and is equally unregulated ... when less than 10A is being taken, the voltage out will be higher - and if this is being regulated down inside the Lenz COntroller - this might end up running hotter than previously !!! .CHECK if you can - use a voltmeter on ac volts and compare the output voltages of the 2 power supplies with NO LOAD connected (just the voltmeter).

IF, HOWEVER, you have bought a 10A output SMPS with a fixed (or switchable) regulated dc output to supply the Lenz Controller - then NO PROBLEM - the voltage will not rise when no trains are running, and the controller won't get hotter either !!  And because SMPS's are energy efficient - when less current is taken from a SMPS, it runs cooler too !!.

 

SO, ideally, if it IS a SIMPLE TRANSFORMER you have bought - it would be better to have one with only the rated output you are likely to use - for the reasons explained.  Safety-cutouts at 3-5A would probably act inside the Lenz - and definately with a 10A capability in the supply !   I would also recommend considering PSX like devices - to provide lower current limits track-side on an area-by-area basis.

[melmerby]

Phil

The output voltage off load depends on the quality of the transformer.

The one I have (a toroid rated higher current then the Lenz system) has a regulation of 8%.

i.e the voltage with no load will be 8% higher than the rated output voltage (15v)

That's less than 2 volts more and well within the LVZ100 rating

Edited February 15, 2019 by melmerby

[Phil S]

3 minutes ago, melmerby said:

Phil

The output voltage off load depends on the quality of the transformer.

The one I have (a toroid rated higher current then the Lenz system) has a regulation of 8%.

i.e the voltage with no load will be 8% higher than the rated output voltage (15v)

That's less than 2 volts more and well within the LVZ100 rating

I know toroidal transformers are more efficient and have better regulation than 'traditional' transformers. BUT MY ANSWER is in relation to the UNKNOWN DEVICE of the original poster !!! Also remember the mains voltage variation - a lenz or roco transformer labelled for 220-230Vac and subjected to 240-255Vac perhaps in the UK adds another 10%approx.

I omitted to add:

Whether the extra heating of the lenz controller regulating down the higher voltage becomes a problem is more likely to be affected by whether the sun is shining onto it!!! - Experience of several peoples LGB MTS 5A controllers - if not kept in the shade when we have sunshine may well get hot and cut out or fail.

 

[NIK]

Hi,

 

The Lenz like all command stations should have a fast acting internal current trip.

 

I've found that my NCE 5 Amp system can cause quite a bit of local heating if a low resistance is created but not quite low enough to operate the 5 amp trip.

 

The very thin wiring burnt out in a friends Hornby ex Lima diesel when I was using the 5 amp system.

 

So if you can split your layout into a couple of power district with the District cutouts set to 2.5 amps that might be the ideal.

 

Regards

 

Nick

 

 

[Pete the Elaner]

7 minutes ago, NIK said:

 

The very thin wiring burnt out in a friends Hornby ex Lima diesel when I was using the 5 amp system.

 

So if you can split your layout into a couple of power district with the District cutouts set to 2.5 amps that might be the ideal.

 

 

 

 

The decoder will only draw the current it needs, mainly for the motor. The fault you described will have been caused by a fault within the loco itself.

Layout wiring can be overloaded if you have too many locos running at once & this is 1 reason for using power districts, not for restricting the current available for any decoder to use.

[BoD]

Thanks for the replies so far.

 

I have checked the voltages of my two transformers under no load.  The original 45VA gives a reading of 16.8V and the 150VA a reading of 16.0V.   It's not the most expensive meter mind you.  That seems to go against the theory as explained earlier unless there is some regulation going on.

 

Both transformer's stated voltage is 15V.  I'm assuming they are standard transformers as the labels talk about primary and secondary  voltages and they weigh a ton.    The 45VA is a LENZ product.  The second was designed for (or rebadged for) one of the DCC suppliers in this country.  Neither mention regulation but both are sold with DCC in mind.

Edited February 15, 2019 by BoD

[NIK]

9 minutes ago, Pete the Elaner said:

 

The decoder will only draw the current it needs, mainly for the motor. The fault you described will have been caused by a fault within the loco itself.

Layout wiring can be overloaded if you have too many locos running at once & this is 1 reason for using power districts, not for restricting the current available for any decoder to use.

Hi,

 

I didn't explain the fault as I was just using it as an example, not to ask another question. I never mentioned a decoder.

 

The loco had derailed and caused a partial short via the wheels and pickups. The very thin wiring between the pickups got hot very quickly and soon burnt out.

 

Regards

 

Nick

[melmerby]

2 minutes ago, BoD said:

 

Both transformer's stated voltage is 15V.  I'm assuming they are standard transformers as the labels talk about primary and secondary  voltages and they weigh a ton.    The 45VA is a LENZ product.  The second was designed for one of the DCC suppliers in this country.  Neither mention regulation but both are sold with DCC in mind.

It is not unusual for higher rated transformers to have better regulation.

The regulation is not normally mentioned in sales brochures but is given when buying a naked transformer from a component supplier (e.g Rapid, Farnell etc.)

The Toroid I am using has about half the value of no load increase than the one with half the current rating (same maker)