Lenz LZV 100 Input DC

[juke]

I have a spare LZV that I want to use with an old Gaugemaster rolling road.

 

I've had it working with my Lenz transformer and all went well.

 

I now need a transformer for the second LZV as it is in my downstairs room, the other is permanently wired in the loft.

 

As it is only for infrequent use I intend using a netbook psu that I already have.

 

It is 19v DC 2.1 amps which is fine as I will only use one loco on the road.

 

My question is, does it matter which way round I put the wires into the LZV? I guess not as the manual is silent on it.

 

 

[Dagworth]

The user manual for the LZV100 does specify 14-18v AC input.

 

Andi

[juke]

The online manual from Lenz USA states AC I agree, but on P27 of the most recent dual German English paper manual it says input voltage with AC min 14v max 19v, next line with pure (their underline) min 14v max 27v (I have tested my netbook PSU and it is measuring pure DC.

 

Since posting I came across a PDF for the Cobalt PSU, suitable in fact superior for Lenz and most other systems according to them. Their unit is regulated DC 18V. They say the Lenz does have a rectifier but not great and that using their unit means the Lenz rectifier has no work to do!

 

I was assuming until I read the Cobalt PDF that the the Lenz would be rectifying the DC as I don't see how if the connectors aren't marked plus and minus that the rectifier wouldn't be needed. I know little about the subject hence the question on here.

[Suzie]

The Lenz LZV does have a bridge rectifier on the input - but I am not sure as to whether it is rated for continuous 5A DC (would be rated for 10A AC if it was).

 

The safest way to use DC with the LZV is to put the positive input on both U and V with the negative on the adjacent T terminal. That should keep the rectifier cool and within the rated specification for AC.

[Crosland]

Since posting I came across a PDF for the Cobalt PSU, suitable in fact superior for Lenz and most other systems according to them. Their unit is regulated DC 18V. They say the Lenz does have a rectifier but not great and that using their unit means the Lenz rectifier has no work to do!

 

I don't know what's not great about the rectifier, but saying it has no work to do is nonsense. Feeding DC into a unit designed for AC will generally work (unless the AC is needed for timing or for generating +/- supplies) but is actually making one half of the rectifier work twice as hard, and risks stressing the components. Lenz specify that DC is OK, so we must assume the rectifier is suitably rated.

[Suzie]

Rectifier is a GBU802 - 8A 200V 60Hz full bridge rectifier. There is a data sheet here:-

 

http://docs-europe.electrocomponents.com/webdocs/0e33/0900766b80e3307a.pdf

 

There are several alternative manufacturers and I just had a look inside a LZV and cannot see any distinct manufacturers markings.

 

Key interesting points are that the 8A rating is 'average' and that it derates to 3.2A without a heatsink up to 100C reducing above that. Not sure how hot the LZV gets inside when running at full tilt but we will have to assume that it stays below 100C or things get a bit silly - but it is a 5A unit so is pushing the spec a bit even when running on an AC transformer since there is no heatsink on the rectifier in the LZV100 or LV102. It could have been heatsunk to the case like the transistors but it isn't.

 

What is not clear from the data sheets from the manufacturers I looked at is what they mean by 'average'. I suspect that there will be a limiting dissipation from each diode which will be assuming a 50% duty cycle (affecting maximum current), and a limiting dissipation from the whole package (affecting maximum temperature).

 

If Lenz recommend that you only use a transformer to power your LZV100 and LV102 then I can see why. If powering from DC and wanting more than 2.5A out then you really need to wire positive to both the U and V terminals, and negative to the T terminal, to keep the dissipation within the bridge rectifier to an acceptable level and to keep the average currents through the diodes at a level no greater than they would be on AC. Running on DC this way will see a maximum of 5W dissipated in the bridge, running with AC on U and V will see 10W, and running with DC + and - on U and V will see 10W unevenly dissipated in only half of the rectifier.

Edited October 23, 2017 by Suzie

[juke]

First, apologies re Cobalt, what they said was  'Additionally:If the DCC system already has some rectifier parts inside it, as many do, when it is fed by a regulated DC power supply, these diodes have NO added work to do.' My underline'

 

  goo.gl/DyZQLt    is a the whole article. It's worth a read re the remarks on the Lenz and others' power input side.

 

I'll give the DC PSU a try tomorrow, it's only 2amp so I guess it's well under any limits with only one loco involved.

 

I'm trying to understand Suzie's method but Suzie has given me good advice in the past so I'll give it a try.

 

Thanks to all!

 

Edit: didn't see Suzie's second post until after I sent this one. Thanks again for the extra info Suzie 

Edited October 23, 2017 by juke

[Suzie]

A picture paints a thousand words, so here is a little diagram that explains it a bit better. Running from DC using the 'T' terminal is the most efficient method both in lower power loss and reduced heat generation.

 

 

(edit to add extra performance data to diagrams)

Edited October 24, 2017 by Suzie

[juke]

Thanks Suzie, all the above is very clear and I got everything sorted in a few minutes. You really have gone to a lot of trouble and I very much appreciate it.

 

Having a DCC rolling road available without going up to the loft is great, especially as the temperature drops!