DesignMan

Per the instructions in Sirius "jumpering" site and the recommendation of Red Scholefield (did I spell that right?), I soldered a jumper across the diode in my Futaba 7UAF super Transmitter.

After very carefully checking polarity (center is positive on both tx and Digipace) I plugged it in and hit cycle. All I got was a buzz.

Upon disassembly (again), I found the 3 amp fuse blown.

Should I try again with a new fuse, get a bigger fuse, or bypass the fuse? Or is something else going on that I should check?

Thanks!

laryboy

My Feedback: (2)

if you bypass the fuse you will find out quickly why it melted.

JNorton

My Feedback: (2)

Double check how you jumpered the fuse. You've done something wrong! The 3Amp fuse should not have blown.

DesignMan

I soldered a single piece of wire from one lead of the diode to the other without removing the diode. I have the photo from the Sirius site to be sure I have the right item. There is nothing near it to accidentally bridge to. I don't see how much can go wrong. Even if I fried the diode, it is effectively out of the circuit now.

The battery can only be installed in the transmitter one way, and before plugging in the charger I checked the voltage and it was just fine. I checked the polarization twice, and after frying the fuse, I checked it yet again. Center is + on both plug and socket.

Voltage coming out of the Digipace is 14.5, and the battery was fully charged and measures about 10.5.

Very strange!

DesignMan

That is what I am afraid of!

JNorton

My Feedback: (2)

Larry,
Have you got the wall wart that came with the transmitter? Try it. If you bypasses the fuse properly in the transmitter it should work. If it works then the problem is elsewhere. What does the jack that is coming from the Digipace look like. It may be shorted! Divide and conquer!

John

PS I like your ST40!

Doug D.

Also check where you soldered in your jumper. Look for any wicking of the solder to other solder joints. A friend of mine and yes I've accidently done it. Can cause similar problems.
[&:]

DesignMan

Current status is that I am cycling (successfully) the raw battery with the Digipace, and it got 103 minutes on the first cycle (old battery, BTW). I am using alligator clips on the battery contacts. I will cycle it again tomorrow when it has charged fully.

In addition, I found my little LED charge direction finder, and yes, both the TX plug and charger jack light up when the + end is contacted to the center.

Do fuses get old? I am tempted to just put in another 3a fuse and try again.

JNorton

My Feedback: (2)

Fuses cycled repeated at or slightly over their maximum ratings can fatigue. But it is really rare. Usually it is a lot easier to say that fuses don't get old because they are not normally used near their ratings.

If you are using the digipace it is not it. But it still could be a solder problem like Doug D detailed in the transmitter or it could still be the cord.

John

DesignMan

It just occured to me that I may not have been clear. The fuse that blew is on the charge receptical board inside the transmitter, not in the Digipace. So come on guys, if I can charge with the cord and get the correct +/- readings, why would the fuse blow? The cord can only short, and that would protect the fuse, not blow it.

I briefely shorted across the fuse connectors and then hooked up the Digipace just as a charger. It is fine. I discharged and am recharging the raw battery, it is fine.

I dismounted the little charge socket board to see what all was on it. There is the fuse, the socket and the diode. That is IT! The diode is off by itself, and I jumpered it on the side away from the PC leads. I absolutely guarantee that no other component is or could be affected by this particular solder job. (I have successfully built micro servos from kits).

My problem is that the fuse blew as soon as I tried to discharge through it. I would worry that the Digipace is discharging at too high a rate, but it took 103 minutes to discharge a 500mah pack.

Any chance ithe Digipace is allowing a current spike as you hit the discharge cycle switch? Would a capacitor across the fuse fix that?

Any chance that the fuse was designed with the voltage drop of the diode in mind and the added .7 v through it blew it? If so, how about jumpering it with a reversed diode instead of a wire? Then I would always get the .7v drop in either direction.

JNorton

My Feedback: (2)

Larry,
Makes more sense now. Put an ampmeter in line with an external battery (the one you are just charging) or if you don't have an ampmeter another 3 amp fuse. Have the Digipace do a discharge cycle. I bet the fuse blows. If it does I would cycle the battery out of the transmitter.

I hate jumpering fuses. The capacitor would have no effect. The original diode prevented discharging and protected the transmitter against reverse polarity. Putting another diode in backwards would prevent the radio from turning on!

If you absolutely must discharge the battery in the transmitter, jumper the fuse. Cringe! Oh how i hate doing that!

John

JNorton

My Feedback: (2)

Oh forgot to say that I think fuse blowing is caused by the Digipace momentarily drawing in excess of 3 amps blowing the fuse. It is not staying at a a high discharge rate as evidenced by the 105 minute discharge of the 500mAh pack.

I'm going to bea 4:30 AM comes early the older we get.

John

laryboy

My Feedback: (2)

john, when i was a small boy my father used to put a penny behind the blown fuse in the fuse box. he didnt like buying fuses. we moved right after our house burnt down

JNorton

My Feedback: (2)

Been an Electrical Controls Engineer for the last 15 years or so. Been involved with electronics since I was 9. Shorting a fuse is like scratching your fingers on a chalk board to me, if your old enough to remember what a chalk board is?

I caught my Mother's boy friend (Father has been deceased for 10 years) replacing 15 amp fuses with 30 amp ones. He doesn't do that anymore.

In this case if you are willing to jumper the protective diode and take the responsibility to always double check to make sure the polarity is correct, jumpering the 3 amp fuse to prevent overcharging is not really a big deal. You really need to make sure everything is right, I doubt the house would burn down but the smoke could be released from the transmitter and as we all know that smoke is awful hard to put back!

John

JNorton

My Feedback: (2)

Larry,
It should not be blowing that 3 amp fuse. Try a 3 amp fuse on the outside. If it does blow it try a 3 amp slo blo.

Man I can't get to sleep. Wish I could look at that puppy.
John

DesignMan

I think you are on to a good test. I will set up the battery and a fuse externally and we will see what we will see!

DesignMan

Well, I tried the test where I wired a fuse in with the battery external to the TX. No problem. Installed the battery and fuse in the TX, charged it for another 10 minutes just to be sure it was peaked, and then hit the cycle switch. No problem. Buttoned everything up, gave it another 10 minute peak to top it off, and hit the switch. No problem.

I am really pleased that it turns out to just have been a weak fuse. Tempest in a teapot, but who knew? Blown fuses USUALLY indicate potential for something really bad to happen.

Thanks everyone for your advice and help.

JNorton

My Feedback: (2)