Heat From Dimmer Unit.

[Charlie Crackle]

Do the Dimmer units need to dissipate a lot of heat ??

Are there going to be any heat issues mounting 3 x 8 channel dimmers in a IP rated SEALED 36Way DIN SWitch Board. The outside switch box temp wound never get above 30 degrees.

[UncleDick]

Charlie,
More questions than answers at this stage:

What are OS dimensions of IP box?

Metal or plastic?

Cable entries sealed or vented into wall cavity etc?

Dimmer channels disipate ~2W each at full load so 24ch X 2W = 48W worst case

[Charlie Crackle]

It is the standard Clipsal 3 row 36 unit IP56 Rated Switch board

Plastic.

Cable entrys at the top sealed.

[UncleDick]

Checked out a board, all sealed up with all loads running at full (240W). for 24hours

True ambient 26C

Temp in board 38C

Temp of load terminals at the dimmer 53C

The effective ambient that the dimmer was operating in was 38C

The dimmers are rated to work in up to a 45C 'outside' ambient but in a sealed enclosure the temp of the air in the board becomes the effective ambient

your 'outside' ambient won't exceed 30C so extrapolating that I would expect to see a 42C 'inside' ambient and this was a severe test with all loads running at full load continuously so I wouldn't expect you to experience any problems.

[Charlie Crackle]

Thanks for you effort. This is good news.

Do the dimmers produce more heat when they are dimming rather that full load (IE not doing any dimming).

Can you really push all channels to 1A (240W). I always like to leave a little head room so things are not stressed.

I was looking at using a single channel to run 4 x 50W LV lights on 4 x ATCO Iron core transormers. Maths says is should be fine. The trusty Current Clamp show .92A which is also fine. Just did not like to run that close to the rating when temperature rises due to the enclosure may also stress components. Was going to split on 2 channels. Do the 1A channels have a bit extra before they fail ?? Could you run 8 channels at the full 1A without shortening the life of the dimmer ?

Thanks Heaps

Charles

[dbuckley]

Have a related question... Do the DIN rail relay units without power supplies (eg L5508RVFP) put out any appreciable heat? I'd have thought not...

Thanks.

[UncleDick]

Charlie, 0.92A suggests they are running a comfortable ~8% below max, the max was worked out on the subsiquent temperature rise within the product (specificaly the max allowable terminal temperature rise - which is specified in the manufacturing standards and the maximum allowable junction temp of the semi conductors - particularly the dimmers TRIAC which is specified by the component manufacturer). The setup I ran was at 8 x 1A for the dimmer package and temp rise was acceptable. All the loads are unlikely to be running at full brighness (max temp is dissipated at max brightness on these dimmers) so the temp is unlikely to reach anywhere near the max allowable. I think the ~8% headroom you have would be adiquate, but going to two channels each with 2 TX would give you more flexibility in light control.

DBuckly, There will be a small amount of heat dissipation from the dimmers power supply even when no loads are being controlled. Even though the Dimmer (or Relay) has no sourcing, to C-bus, power supply (ie it is a 'P' varient) it does have a power supply that powers its internal electronics, local control/channel status LED's and triac drive circuits etc.

[greg0ry]

Bear with me all because I've yet to find my feet in forums - I hope you all suffer fools gladly!

The dimmers are working their hardest when they are dimming to the greatest effect - ie the lights are on at their _lowest_ light level. Is the heat load in the dimmer enclosure greatest when all dimmers are all dimming the most?

That's when the dimmers are dissipating power as heat, how else - they're switching their greatest load to the greatest effect aren't they?

So isn't the big test what temperature rise there is in the enclosure when the dimmers are all set at minimum light level?

I actually signed on for a different question so I'll go and ask about the Saturn input device (5086) elsewhere as i intended b4!!

I really don't want to be a smart a*s* already - and its a different thread anyhow i guess, but if it's an IP reated enclosure - the numbers will tell us where what holes are - IP00 might as well be a wire mesh box and IP88 is a US Naval submarine! There's anything between except IPXX where neither mechanical ingress nor liquid ingress are defined (eg IPX8 - water can't get inside so they didn't test whether anything else (including talcum powder)could). I'm learning here guys so tell me if i'm out of order - and i'll refrain.

[Newman]

Greg0ry

When the dimmers are dimming down the lights they are not wasting the extra power. They are actually constantly turning the mains on and off to the lights (in a fashion).

Depending upon the design of the dimmer and the load type the typical losses will be greatest at maximum brightness because that's when the most power is actually passing through the dimmer and the power losses are greatest. Some dimmer types run hottest when dimmed to about the 50% - 60% mark but these are less common.

The issues involved aren't always as straight forward as they appear so different dimmers need to be considered independently. Just be aware.

[UncleDick]

Spot on Newman

[[IL]NewGen]

large DBs and comms closets should have in-take and exhaust fans if your worried...

[UncleDick]

Michael, I guess the problem Charlie has is that (for whatever reason) he needs to use an IP56 (ie whether proof) enclosure in this instance so the use of vents or fans etc is ruled out. When installed correctly IP56 enclosures need to be able to withstand being hosed (at a nominated pressure) from all directions for a nominated time (a number of minutes) with no ingress. Even the cable entries must be through water/dust tight glands. Therefore in this situation the only avenues for heat to dissipate from the cabinet are conduction through the copper of the wires (a relativly small amount) or via conduction through the plastic walls of the enclosure and then by convection and radiatrion into the surrounding air. In a perfect world you are right a couple of simple vents top and bottom of the cabinet will keep thing plenty cool. The PRO dimmers may need forced ventelation if they are enclosed in a cabinet as they were designed to be mounted in free air.

[[IL]NewGen]

note taken uncle... :D