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Old 16th June 2017, 12:18 PM   #11
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by AndrewT View Post
the third 15k is across the "timing" capacitor.
That can ruin the timing to such an extent that the relay does not trigger.
In my view using a simple RC from an unregulated supply is a bad timer. Adding in the third resistor turns a bad timer into a worse one.

If you were to run the isolator from a regulated supply which then turns it into a resonable timer, then you find that the effect on timing of adding that third 15k is not as bad and can leave you with an effective way of "tuning" the delay period.

But I just miss it out and tune the delay by using a suitable value of plastic film capacitor where there is space to accomodate such.
Using an electrolytic REQUIRES one to slowly reform it to well above any voltage it may see in future operation. One of the biggest risks of using an unreformed electrolytic as the timer element in an unregulated arrangement is non triggering because the 15k and the electro draw so much "leakage current" that the timer NEVER triggers.

Finally before you try any of these unknown (no build guide) contraptions, it is incumbent on the user to first understand how it works. Then critically assess it's ability to do the job you the user requires.
It uses a 12v regulator - so is not unregulated. I agree an elfctrolytic is not best choice for critical timing.
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Old 16th June 2017, 02:21 PM   #12
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I like this uPC1237 protection because it does not require separate secondary for protection. It works from the power amp transformer, but you must make your own pcbs, there is no kit. I made 10 pcbs and the photo of one of these is attached

DIYfan: Speaker protection with uPC1237
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File Type: jpg uPC1237 DIY Fan moja.JPG (458.4 KB, 330 views)
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Old 16th June 2017, 03:33 PM   #13
xrk971 is offline xrk971  United States
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I don't use a secondary transformer for the 12v (or some people like 24v), just stick one of these cheap DC step down converters from your +ve rail (up to 35v) and you get an easy source to drive your protect circuit. If you are above 35v, you will need a different converter.

LM2596 DC-DC 4V-35V to 1.23V-30V Step Down Power Module Voltage Regulator 3A | eBay
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Old 16th June 2017, 04:07 PM   #14
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Very useful info. Didn't know that these little converters are available at such low price.
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Old 16th June 2017, 04:24 PM   #15
thimios is offline thimios  Greece
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I wonder how clean are the rails after adding this thing

Last edited by thimios; 16th June 2017 at 04:32 PM.
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Old 17th June 2017, 11:47 PM   #16
xrk971 is offline xrk971  United States
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It's a passive connection via a relay so not sure how the circuit of this protection circuit would affect the power amp rails. Or do you mean connecting a DC to D.C. boost effect on the rail? I can measure when I get the next chance.
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Old 17th June 2017, 11:53 PM   #17
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Do these little guys protect against turn off thump? I have some compression drivers I'd rather not destroy
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Old 18th June 2017, 05:13 AM   #18
thimios is offline thimios  Greece
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Quote:
Originally Posted by xrk971 View Post
It's a passive connection via a relay so not sure how the circuit of this protection circuit would affect the power amp rails. Or do you mean connecting a DC to D.C. boost effect on the rail? I can measure when I get the next chance.
Exactly,is a switching regulator....
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Old 18th June 2017, 06:21 AM   #19
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Here is the seller's description in perfect Chinese English:

SKT Flyer Protection board

Features

The speaker protection board has the power delay (3 seconds) and DC protection (from the control voltage is about 1V) function, a simple circuit board, making easy, safe and reliable. With LED status display, when the protection light, the normal work time off. using 15A high current relay, suitable for the vast majority of amplifier board. Operating voltage AC 12-15V, requires a separate power supply.

After installation size: length 65mm x width 40mmx high 25mm . BTL circuit need two sets.





They don't mention loss of AC detection function.
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Old 18th June 2017, 07:05 AM   #20
sajti is offline sajti  Hungary
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Quote:
Originally Posted by ivanlukic View Post
I like this uPC1237 protection because it does not require separate secondary for protection. It works from the power amp transformer, but you must make your own pcbs, there is no kit. I made 10 pcbs and the photo of one of these is attached

DIYfan: Speaker protection with uPC1237
I use separated small transformer for the speaker protection. I cost approx. 2Euro, and PCB mounted.

Sajti
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