TDI Battery Pack Conversion

[Jim in Idaho]

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

[chiil]

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.

[Jeff McClendon]

Got my SPP back from Centreville Electronics NW. Todd replaced U3 IC and a 100uf SMD Capacitor.

It is definitely back up and working well for very little expense. 

My only small gripe is that it is not as sensitive to smaller targets .5 gram and under as it was before those parts fried. It air tests to less distance with coin sized targets than it did before also by about an inch using the MJD 9X5 folded Mono and Detect 8" Mono. Both are detecting a .5 gram gold coin at 6" and will barely hit a .25 gram nugget. The .5 gram gold coin was air testing out to 7" and the .25 gram nugget was testing out to 2" before the parts fried.

Also, I am seeing no difference in depth or sensitivity with the 14.8 volt 4 lithium battery pack and the 12.6 volt 3 lithium battery pack and the 12.6 volt NiMH 9 battery pack......... 

I will keep testing and maybe get to hunt with it tomorrow a little. 

[Jim in Idaho]

Jeff, what voltage are you charging the 4-cell pack to? It should be making a noticeable difference.

Jim

[Jeff McClendon]

4 minutes ago, Jim in Idaho said:

Jeff, what voltage are you charging the 4-cell pack to? It should be making a noticeable difference.

Jim

Hi Jim

I am being super careful and only charging to 3.7v per battery so 14.8v.

[Jeff McClendon]

I got some time today to test the repaired SPP.

I went ahead and charged the lithium pack to 16 volts, got a 9 AA NiMH rechargeable battery tray charged to 12.6 volts, some targets..... US quarter, US nickel, 0.5 gram gold coin, 1.2 gram specie and .25 gram flat nugget and headed out to the testing area I usually go to that has next to no audible EMI.

I had the Miner Johns 9X5 folded Mono and the Detech 8" Mono.

I found the 16 volt tray got about an inch more air test distance than the 12.6v tray. Results with the 16v tray were = the .5 gram gold coin (7"), US nickel (11"), US quarter (11.5") while .25 gram flat nugget was barely detectable at 1" and the 1.2 gram specie was detectable to 2" using the Detech 8" Mono.  The Miner Johns 9X5" folded Mono was about 1/2 inch shorter distance than the Detech 8" on all the coins, hit the specie at about 1" and could not detect the .25 gram flat nugget unless it was touching the coil.

So the 16v tray was marginally better than the 12.6v tray. However, the 16v tray got a lot warmer to almost hot at the +/- terminal end of the tray where the tray is closest to the PCB. The 12.6v tray got slightly warm but definitely not hot.........

I also had the Ukrainian orange, three lithium battery 12.6v tray with me. I tried all four batteries in that tray to see if I might have a bad cell among the four. That tray did not get hot, only slightly warm. Maybe I made a lousy 4 lithium tray or something else is going on.

thanks for reading.

Jeff

[Jim in Idaho]

I ended up selling my MJ 5x9., Jeff. I just didn't think it was very good. I much prefer the DF 71/2, or 8 x 6 Sadie. I do like the MJ 8 x 12, however. Sorry to hear your detector gets hot with the 16v battery. it does make a difference.

Jim

 

[Jeff McClendon]

On 10/10/2022 at 8:09 PM, Jim in Idaho said:

I ended up selling my MJ 5x9., Jeff. I just didn't think it was very good. I much prefer the DF 71/2, or 8 x 6 Sadie. I do like the MJ 8 x 12, however. Sorry to hear your detector gets hot with the 16v battery. it does make a difference.

Jim

 

I've never owned a 7.5 DF so I have no idea how it performs. I love the Sadie coil. Personally I had the exact opposite experience with the MJD 8X12 versus the MJD 5X9. I really like the 5X9 that came with my SPP.

So, I got to do a lot more testing today. I think the entire overheating and maybe fried U3 and 100uf cap were caused by the Detect 8" coil. On power up I get all kinds of weird, loud tones for almost 3 seconds and all three of my battery trays heat up quite a bit. With the MJD 5X9 I get the normal quick startup tone that I am used to with TDI Sls and all of my battery trays from 12 volt to 16 volt just get warm not hot.

Does that make any sense?

[Jim in Idaho]

Yup, does to me. Maybe that one coil has lower resistance than the SL circuit requires. That would allow more current to flow, raising the heat. That's good for you. It means you can charge your pack to 16v and enjoy the benefits, using the other coils. Good deal!

 I've found the Sadie, and 7 1/2DF to be very near equals. Actually slightly prefer the DF, but wouldn't feel handicapped with nothing but the Sadie in tight quarters.

Jim