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TDI Battery Pack Conversion


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I also ordered the orange battery pack from Kiev Ukraine about 3 weeks ago. It arrived today. Outstanding product and a great way to get 12.6 volts of power from three 18650 lithiums.

I made the 9 AA battery holder recommended by Auminesweeper since I had an extra battery tray and several single battery holders. Since I like to use rechargeable NiMH batteries which are 1.2 to 1.4 volts that gives me another way to get 12 volts into my SPP.

A word of extreme caution. I also made a 4 Lithium battery pack out of another Whites battery tray. I only charged the Lithiums to 3.7 volts so I had exactly 14.8 volts going into my SPP that I got from Snakejim. I had been hunting for about half an hour but it was a really hot day. I heard a really loud rise and fall in the threshold tone and something popped. Turned it off and back on. All I had was a steady threshold tone. It was like there wasn't even a coil on the detector since the SPP could not detect any targets. When I got home I tested the charge level and volts of the battery pack=14 volts exactly.

So, my nice SPP has been sent to the Oregon repair facility. Hopefully it can be fixed. 

If it is repairable.......no more 14+volts. I will keep the voltage at 12.6 maximum from now on.

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Oh dang.  Sorry to hear that.  Isn't the SPP based on the SLI?  I recall Geotech stating the SLI could handle up to 20V, and possibly 25V.  I wonder if something else popped.

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Sorry to hear about your SPP Jeff. I ran my TDI SL for many hours with the 16.8v Li-ion setup, on hot Summer beaches, without any issues. My guess would be something unrelated let go inside your machine… I hope it’s repaired and back in your hands soon!

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I seem to remember somebody with a whole lot more knowledge of the TdI SL than I will ever have....(Carl or Reg) once mentioning that part of the audio circuitry was only rated for roughly 12 volts......maybe I misunderstood.

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Link to the information.  According to Carl... "There are a couple of 16V caps in the audio stage but they are on a regulator that maintains 11.2V regardless of battery. I did that so audio volume remains the same if you use a bigger battery."

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I remember reading that from Carl, thanks for sharing again. I was getting similar depth on my TDI SL (with the 16.8v battery) as my TDI Pro. The main difference was the TDI SL had a much smoother threshold and was a lot lighter in weight. I ran many hours with that pack fully charged to 16.8v and never had a problem.

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Thanks Chiil for reposting that information.

Makes me feel a little better……….😶

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Jeff, it's likely that something in the transmitter popped, maybe the TX FET overheated. Components should be able to handle up to a 20V battery but there is a chance that a high battery voltage will cause the TX to run hot. Unlike the TDI, the FET on the SL does not have a heat sink, rather it uses the PCB as a heat sink. I'm surprised that 14V caused a problem. Let me know what you find out from Todd.

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I've read (maybe Reg told me) that the flyback resistor (R9) will run hot with increased voltage. That's the first place I'd look if my SL puked. So far, running hot batteries, I haven't had an issue over several years of use.

Jim

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23 hours ago, Geotech said:

Jeff, it's likely that something in the transmitter popped, maybe the TX FET overheated. Components should be able to handle up to a 20V battery but there is a chance that a high battery voltage will cause the TX to run hot. Unlike the TDI, the FET on the SL does not have a heat sink, rather it uses the PCB as a heat sink. I'm surprised that 14V caused a problem. Let me know what you find out from Todd.

Hopefully when Jeff gets feedback of the failure... and if it indeed ends up being the Tx FET... I'm wondering if a heatsink could be added to help mitigate any future failures.  Similar to one like this: https://www.adafruit.com/product/1515

Edit: I'm not a EE... but looking at these FETs, looks like the heat is dissipated from below.  I'm guessing it couldn't hurt to place a heatsink on top of the FET - but how effective it would be is another issue.

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