Dual 1176 MNATS-PSU problem

[Flea]

Hi everyone!

Just finished my dual 1176! Now the problem: I'm using the MNATS PSU with the LM317 and LM337. I put the regulators also on those metal things, for the heat, sorry don't know the english word.... But the LM337 is getting hot, hotter, hottest! The Voltage is -10, as it should be, I measured also the current and its 187mA, so everything should be o.k., but it isn't! After a few minutes the sifam lights begin to blink - on - off, a sign, that the -10V drops up and down, must be kind of a protection of the LM337. Don't know, whats wrong!? Maybe someone can help me here!

Greets, Flo

 

[Guest]

[quote author="Flea"]
I put the regulators also on those metal things, for the heat, sorry don't know the english word.... [/quote]
No problems - better than my german and french
"heatsink"

What VA rating are you using for your mains transformer?

 

[Flea]

yeah, that's the word! Thanks!

The main transformer is a toroid, has primary 230V AC and secondarily 2x30V AC 0,83A.

 

[AnalogPackrat]

Flea,

Ouch! :shock: Your power transformer is putting out 30VAC per side, which when rectified gives you well over 40V into the regulator. If you are trying to regulate that down to 10V, then the regulator is dissipating about:

P = IV
P = 0.187A * (40V-10V) = 5.6W

That is an awful lot of power to waste as heat and you will need a LARGE heatsink to keep the thing from going into thermal shutdown. What sort of voltage do you need on the positive side? 15V? 18V? I would recommend that you get a 2x15V or 2x18V transformer. This will give you plenty of voltage for your application and your 10V regulator will work a lot better:

P = 0.187 * (25V-10V) = 2.8W
or
P = 0.187 * (21V-10V) = 2W

You'll still need a good heatsink, but nothing like what you'll need with your current setup.

A P

 

[Flea]

Thanks AnalogPackrat!

I need two Voltages -10V and +30V!? I see, I need a smaller transformer...
Is it enough to take 2x22V AC it's rectified ~ 32V DC. Or is this one to small for the 30V DC I need then? And if I would take 2x25V AC, rectified 36V DC, should be again to much for the LM337!? What do you think! But, I will also take a bigger heatsink for sure!

grz, Flo

 

[jlearman]

I'm in a similar situation. I'm a total noob and don't even know what a toroid does. I can't figure out which toroid to get off of this list:
http://www.avellindberg.com/transformers/y23_range_specs.htm
can anyone reccommend which toroid to get for the dual 1176?

 

[dissonantstring]

hi jlearman,
i've ordered avel lindberg model: Y236106 (30VA, 25V-0-25V) for my SINGLE G1176 with no problems, but you're looking for one which will power a DUAL G1176 right?
this is what mnats had to say about his dual G1176 build:

Found they were only drawing about 37.4mA each from the positive rail (no lights) so I put a smaller 30VA transformer in there to power both sides instead of the 50VA I had in there before.

so that model should work fine as well for a dual.:grin:
hope this helps.
-grant

 

[AnalogPackrat]

[quote author="Flea"]Thanks AnalogPackrat!

I need two Voltages -10V and +30V!? I see, I need a smaller transformer...
Is it enough to take 2x22V AC it's rectified ~ 32V DC. Or is this one to small for the 30V DC I need then? And if I would take 2x25V AC, rectified 36V DC, should be again to much for the LM337!? What do you think! But, I will also take a bigger heatsink for sure!

grz, Flo[/quote]

Ah, I'm not familiar with the 1176--haven't built one yet. I don't think you could get away with the 2x22V. Maybe 2x25V, but then you'd be pretty close to where you are now. Probably not worth the trouble.

You're just going to have to put big honking heatsink on there. If you can find a big chunk of Al plate (say 3-6mm thick and 10 sq cm or more in size), you could drill it and mount it flat against the case and then mount the neg regulator against it (drill for a mounting screw--tap the hole if you want to be fancy) using an insulated pad or mica washer/gasket thing and nasty white heatsink grease. You've gotta get that heat sucked out of the 337.

My recently built 312ish pres have a 7812 reg for relays and it gets hot even with two stacked heatsinks. I measured 50C just above the heatsinks, so the device is probably around 60C. Too hot to touch, but it doesn't shut down.

A P

 

[Flea]

Thanks AnalogPackrat!

I'm gonna try a 2x25V transformer and use a big heatsink, putting it to the case! This should be the best solution!

Thanks a lot and greets from Germany!