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DQ828  
#1 Posted : Saturday, July 5, 2014 7:21:48 AM(UTC)
DQ828

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I have purchased a couple of LCBPS kits from another DIYer but wasn't told & didn't realise they where the older version 1.1b

I will have 18V AC going into the rectifiers and ideally wanted 12V out but could go with 15+- out.

I do have some 50mm (2") heat sinks I could use.

1) Does anyone know how much current I can safely get out of EACH SIDE of the LCBPS.
2) should I short the 4 Resistors
3) I assume by shoring the resistors it will increase the ripple
4) Given the Regulators are good for 1.5A each, whats the limiting factor?
5) Does it matter if the PSU is asymmetrically loaded?

David

Edited by user Saturday, July 5, 2014 10:32:41 AM(UTC)  | Reason: Not specified

avr300  
#2 Posted : Saturday, July 5, 2014 3:05:42 PM(UTC)
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1. If you can cool the LM317/337 1.5A. 18v AC and 12v DC, that's quite a gap. You will burn a lot of energy. Better go for a bit less AC or accept a tat more DC.

You need no more than ~2.5v across the LM317 in order for it to work. The closer to 2.5v the cooler it will run. With 18v AC and 12v DC you're about 10v above the sweet spot.

15v AC and 15v DC is a good match.

As pr. datasheet: "Included on the chip are current limit, thermal overload protection and safe area protection"

2. Depends on the demand for current. If the resistors on your board are 10R, they will play a limiting factor when you go for high current.

3. If not done you will loose a lot of voltage. High current = short those resistors.

4. The limiting factor of what, current?

5. No.

Consult the LM3x7 data sheet in depth insight.
thanks 1 user thanked avr300 for this useful post.
DQ828 on 7/6/2014(UTC)
DQ828  
#3 Posted : Sunday, July 6, 2014 12:10:43 AM(UTC)
DQ828

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Originally Posted by: avr300 Go to Quoted Post
1. If you can cool the LM317/337 1.5A. 18v AC and 12v DC, that's quite a gap. You will burn a lot of energy. Better go for a bit less AC or accept a tat more DC.

You need no more than ~2.5v across the LM317 in order for it to work. The closer to 2.5v the cooler it will run. With 18v AC and 12v DC you're about 10v above the sweet spot.

15v AC and 15v DC is a good match.

As pr. datasheet: "Included on the chip are current limit, thermal overload protection and safe area protection"

2. Depends on the demand for current. If the resistors on your board are 10R, they will play a limiting factor when you go for high current.

3. If not done you will loose a lot of voltage. High current = short those resistors.

4. The limiting factor of what, current?

5. No.

Consult the LM3x7 data sheet in depth insight.


Thanks

4. The limiting factor of what, current? Yes the current, I suppose there are many limiting factors

The transformer I purchased for the job is suppose to be 15V but my AC at home is in the very high end of the AC limit 252V which is probably why I'm getting 18V at the secondaries.

If I get the AC down to say 15V and run the DC at 15V, any thoughts on what level of current I could safely get from the PSU.

Edited by user Sunday, July 6, 2014 4:51:27 AM(UTC)  | Reason: Not specified

avr300  
#4 Posted : Sunday, July 6, 2014 10:44:32 AM(UTC)
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Define safely.

The LM317 has thermal overload protection. If it gets too hot it shuts down.

And tell us your needs.

Why don't you just try? You have all the ingredients.

At 15v AC and 15v DC @1A out, you have to get rid of 4.6w into the heatsink(s).

Edited by user Sunday, July 6, 2014 10:48:43 AM(UTC)  | Reason: Not specified

DQ828  
#5 Posted : Sunday, July 6, 2014 12:30:22 PM(UTC)
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I,ve never had so many issues with PSU's, the reason I decided to use the LCBPS was the BP supply I was using kept playing up & I couldn't figure out what the problem was. I have just put the LCDPS together and the negative side doesn't work ):

I did have to re-solder the negative regulator to put the bigger heatsink on as the holes didnt line up, maybe I fried it.

Work tomorrow time for bed.

Thanks for help
DQ828  
#6 Posted : Monday, July 7, 2014 12:32:22 PM(UTC)
DQ828

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Originally Posted by: avr300 Go to Quoted Post


Define safely.



free from hurt, injury, danger, or risk: :)

I found the problem, didn't solder half of the negative inductor :) Of course it was on the inside half so it was a very difficult thing to see.

Anyway, given it's obviously very difficult to give an exact answer to this question, as you say I'll just give it a go & see how hot it gets. As the boys are away I ordered a BP-PSU from DIYINHK which states it can give 1A at 12/15V so I'll have a backup should I need it.



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