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This is a surfmaster pi with modified timings, tx pulse 60us, prr 248us. Coil has 280uh with 24awg wire. Mosfet is warm with the heatsink but dumping resistor become very hot. I think is 3w, not sure. I don't have tool to measure consumption wich i assume is very high. What should i do, buy a powerful dumping resistor? Any advice? Decreasing prr may give depth reduction.
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garbage. sorry but your board is one.
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Janne Peltonen. uses CAD, makes perfect PCB. SHE IS FEMALE.
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I know is crap, but this is one of my first detectors made and looks like this because it need to fit exactly in a small ikelite waterproof enclosure. Performance is what matters. Anyway i don't do pi detecting and is just a way of spending time in long cold winters.Originally posted by kt315 View PostComment
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Originally posted by ionut_mtb View Post
First is to look at the Coil switching, on & off, with an O'scope. Ensure the Damping R value is correct.Originally posted by ionut_mtb View Post
If this is correct and the Coil fly-back ringing is critically dampened then unsure what to do. Possibly just add some series R to the coil to decrease Peak current.
My guess is that you will see on the O'scope some pretty ugly stuff due to the Mosfet leads and other Bad layout.
Grab and post some scope pictures for us to look at.Comment
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overdamping R value?Comment
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Dumping resistor is good, flyback voltage looks like 250v ? (New scope, digital). Resistance of the coil is 1.6 ohm and dumping 360ohm. Like i said pps is quite high, helping with stability, noise and good depth on gold.
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you do a mix? 4khz pps?Comment
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I don't know why the photos are upside down, in my phone are normal.
Kt i don't understand what you mean. Pps is high, not sure exactly, i was aiming 10000pps like goldquest ss, but my tx pulse is 60us not 40.Comment
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you want to kill two rubbits but you forgot that Eric did NOT make a detector with 10000pps on 300uH coil.Originally posted by ionut_mtb View Post
goldquest ss working with 1mH (MILLI-) coil. and plus there is a resistor in serial on board.
so there is NOTHING of the heat and Eric uses 4pin dip mosfet with 0.8A current.Comment
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Eric Foster: My Beachscan uses a coil of 1mH as does the C.Scope CS7 and CS6PI.Comment
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"Your post prompted me to get out a development model of the Goldquest SS and run it up on a scope. This will run at a minimum delay of 8uS from the TXoff initiation. TX pulse is 30uS wide and 13K PPS. The coil is a tapped mono of 450uH total but with a tap at 150uH. The TX drives the tap and the RX connects to the whole coil. The TX Mosfet is a IRFD210 with 27R in series with the drain ON resistance, and with the R of the coil we have about 0.3A pulse current. The rise time is 8.8uS so the pulse is substantially flat top for over 20uS and at switch off there is no avalanche.
The original GQ SS ceased production about 5 years ago but that used a standard 300uH mono and the minimum delay was 10uS with 10K PPS. EF"
This is only an experiment, which perform better than original surf pi, and is P channel mossfet, not N channel like Eric Foster uses in his detectors. I don't know schematic of Goldquest SS, it might have series resistor. Setting up good a PI detector require theoretical knowledge that i don't possess.Comment
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you killed three rubbits by one shot.
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Beachscan
Posted by: Eric Foster(---.ipt.aol.com)
Date: April 6, 200004:35PM
This is an example of aPI detector that breaks with traditional principles to some degree. Instead ofpulsing a high current through a low resistance and low inductance coil itpulses only 0.2A peak through a 10 ohm coil that has an additional 39 ohms inseries. The coil also has an inductance of over three times the usual amountbut we are still able to sample at the magic 15uS for use on a wet beach. TheMosFet can be a small one with a relatively low voltage rating and the mean dccurrent taken from the batteries is only 65mA giving good life from 8AA cells.
Eric.
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Try another electrolytic capacitor, with a capacity of 1200μFComment
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dip4Comment
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