TDI resistor heating up

[dbanner]

Wasn't 14.4 volts LI the proper supply for this device in the first place? I don't see 16 volts doing anything awry.

[Mark-VA]

Wasn't 14.4 volts LI the proper supply for this device in the first place? I don't see 16 volts doing anything awry.

This is the TDI SL which came from the factory with a standard 12v rechargeable battery pack.
I built a 16v LI battery to boost depth and run time. Just so happen I had run my battery to the 14.4 volt mentioned above.

[dbanner]

I see. My guess is they changed to 12 volt battery pack for economy.
The circuit should run off 14.4 no problems.

[Mark-VA]

Thanks for the replies. Hey, if you don't ask questions, you may never know. The added heat had me concerned.

[Mark-VA]

Heat

I'm still very concerned with the heat inside my TDI when using the higher voltage battery supplies. The entire left side of the control box is very warm. I think I'll borrow a IR sensor and see what the temp actually is.

[Mark-VA]

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.

As usual, Carl was correct. Q4 is the source of all the extra heat in my SL. Measure the transistor with an IR thermometer and it was 150+ degrees. Enough to burn a finger. Appears to be soldered to a heat sink attached to the main board. The board all around the FET was also hot, most places 125 degrees. One good thing, R9 was hovering around 101 degrees, not bad. What has me concerned is the heat built up inside the box. Now on the positive side, when the battery voltages drops below 15 volts the heat seems to be quite a bit lower, but the performance stays about constant.

[Carl-NC]

Q4 is soldered to a thermal pad, which isn't a very good heat sink. You could replace it with a stand-up TO220 version and put a real heat sink on it, that would help.

The reason Q4 gets hot is because it hits avalanche during flyback. You could replace it with a higher voltage FET so it doesn't avalanche and that would reduce the heat tremendously. However, you have to carefully test for one that doesn't ruin the recovery speed.

[Mark-VA]

Thanks Carl, I'm just overly concerned with whole heat issue. My beach hunting trip is less than two weeks off and I really need the machine function at max, but I'd hate to ruin the unit. Then on top of that I enclose the control box in a heavy duty zip lock bag to protect from the salt water mist from the surf. I appreciate all you help and information with this topic.

[Jim in Idaho]

Q4 is soldered to a thermal pad, which isn't a very good heat sink. You could replace it with a stand-up TO220 version and put a real heat sink on it, that would help.

The reason Q4 gets hot is because it hits avalanche during flyback. You could replace it with a higher voltage FET so it doesn't avalanche and that would reduce the heat tremendously. However, you have to carefully test for one that doesn't ruin the recovery speed.

How do you test it, Carl? What parameters are you looking for?
Jim

[Carl-NC]

If you have an oscope, you look at the output of the preamp and make sure it still settles in 10us.

If you don't have an oscope, test a small low-conductive target at 10us before & after replacing Q4 and see if sensitivity is maintained.

[Jim in Idaho]

Many thanks, Carl. That's pretty simple and straightforward. And, I've got a scope.
Jim