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After building a 16 volt battery pack I noticed extra heat on the battery when taking it out of the machine. I dissembled the unit and found that R9 was getting hotter when using the 16v battery pack. The resister gets hot when running the stock 12 volt battery pack but there is a lot more heat when using the 16 volt battery. It appears R9 might be a current limiting resistor and is hooked to the TX side of the coil. Anyway of know what the value might be and just how hard is it to change a surface mount component. R9 is in the bottom left hand corner.
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R9 is a 1k input resistor for the preamp, it works with the input diodes (I see D1 in the photo) to provide flyback clamping. If it's getting a lot hotter, it means you are probably getting a lot more flyback voltage. This seems reasonable since the higher battery will create more coil current, hence higher flyback. It's not too hard to remove if you glob up both ends with excess solder and then move quickly. -
To answer your question:
1. R9 is marked 1001 which is 100X10^1 or 1K.
2. A hot air station is the normal way to remove surface mounted parts. Sparkfun has one for about $129.
The bigger question is why make a 16V battery pack for a system designed for 12V? If you think that parts are overheating then that should act as a warning.Comment
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The reason for the 16 volt system is because of two added benefits.
Longer run time and I actually get about 2 1/2" more depth on low conductors, when using the 12 dual field coil. I'm hoping to use this machine at the beach again this year. The added depth may turn up even more goodies than the last time. My last TDI trip yielded some first time ever finds at this beach. Hoping the added depth will or could provided the added depth to find more gold targets.
Thanks for both replies.
I guess I'm just want to get the most from a near obsolete machine. I could use the F75 or The Equinox 800 but this PI is well suited for beach hunting as long as I stay away from the water. The last time I took a 2 gallon zip lock bag and sealed the control box to prevent any salt water spray from entering. It worked well for that.Comment
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I see. Given Carl responded while I was responding and didn't raise any objection, I assume this is OK. I was just giving a common sense answer from general experience outside of metal detecting. There is also a difference between hot to the touch and stupid hot. Most circuit board components can tolerate 100C without damage. If the battery pack is lithium based and is getting very hot, then I would worry that it will have a short lifespan and if stupid hot could catch fire. I once had a power supply overheat so badly that some surface mounted parts fell off the board. I guess that is the easiest way to remove parts LOL.Originally posted by markg View PostComment
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Mark, besides R9 the main FET (Q4) and the damping resistor (R14?) are also subject to running hotter. You might want to measure the total supply current with the 14V pack... with the coil it should be around 500mA. Also measure without the coil. This will tell you the total TX current. Then do it again at 16V, see what the increased current looks like. I designed the circuit to fundamentally work at 18V (maybe more, I don't remember now) but that doesn't include the extra heat.Comment
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Not hot enough to burn my finger, just quite a bit hotter than when the 12v battery pack is running.Originally posted by moorejl57 View Post
Don't think it would be close to 100C, I can touch with my finger without damage (with power turn off of course). Actually the entire area cools very quickly when the power is switched off. To start with I thought the batteries were getting hot during discharge but they're not, a good thing.Comment
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Carl, thanks for this important information. It appears all the heat is coming from R9 and R14, the FET (Q4) is not even warm to touch. In fact when I was looking at my board photo that was the first component I thought would be hot. I'm just trying to get the most from the machine (without damage) for my once a year beach trip. I might add a short story: When I was a child 50 years ago my dad took use to this beach on vacation, may times. At the time there was a different ocean front group of homes until a bad hurricane came through and destroyed them all. The area is very old and I tend to only hunt at low tide, which I surmise is where the homes once stood.Originally posted by Carl-NC View Post
Well anyway, that is my motive, thanks again, sir.Comment
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16 volt battery supplies .50 amps to the circuit when running.
Best reading I could get with my multi-meter.
You know instead of a 16 volt system, the SL might require only 14 volt to get the same results.
That would be interesting to know.
That said I might test different voltages with my power pack and see what the cross over is.Comment
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500mA with the coil is exactly what Carl advised. Now what about without the coil? That would tell you the exposure to R9 and R14.Comment
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Wasn't sure exactly how to test that.
Maybe disconnect the coil from the control box and measure the current of the TX circuit (2 pins going to the coil)?Comment
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I think you've got to measure the battery supply current (current drawn directly from the battery), first with the coil connected and then without the coil. The difference between the two would be the current drawn by the tx (coil) circuit. That's gonna give you idea of stress (power dissipation) on those two resistors.Comment
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Okay, now I understandComment
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I had run the machine for a couple hours and the voltage was down to 14.43.
14.43 volts
.46 amp coil attached
61.8 ma coil not attached
10.8 volts
.36 amp coil attached
60.4 ma coil not attachedComment
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The rest of the circuit runs off of a regulated supply, so it's current draw remains stable at around 60mA idle with no target.
The coil tx circuit runs directly off of battery, so you see about 400mA vs 300mA with about 14Volts vs 10 Volts.
That's about 100mA difference.
100mA represents a significant difference.
The flyback voltage will be higher, hence R9 will dissipate more power.
Now that's at 14.4 vs 10.8.
16 volts makes the situation even more pronounced.
Hopefully there is some built-in room in the design to tolerate 16+ volts.Comment
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