My Short Fuse
May 26th, 2010How About That Amazing German Engineering?
I hate it when something bad happens, which I could not predict. But then I also hate it when something bad happens that I should have seen coming, because then I kick myself for months for not preventing it. So I don’t know which is worse.
Today I was straightening up the garage so I can actually use it. I was sucking swarf off my workbench, which held the chargers for my impact driver and Bosch hammer drill. I picked up the impact driver charger to vacuum under it, and it touched the Bosch charger, and there was a flash and a popping sound. Afterward, the Bosch charger didn’t work.
This one is new to me. I have no idea why letting one battery charger touch another will cause an explosion.
I am a little tired of silly things going wrong. I decided to march in the house, go on the web, and order a new charger. I didn’t need the aggravation of trying to fix the old one.
But then I looked at all my tools. Sitting there, all lonely and whatever.
I cleared some space and got out a Philips screwdriver, from my stainless rolling chest/cart combination. I moved my magnifying fluorescent lamp over the workbench. I took the stupid charger apart and checked it out.
Here’s something amusing. It has a fuse on the circuit board…which is soldered in place.
I know times are hard, but the logic evades me. I would rather have Bosch spend an extra four cents on a fuse holder and pass the cost on to me.
I put my variable-heat Weller soldering station on the bench and turned it on. I opened up my blister-packaged soldering tool set. I removed the fuse.
I looked for new fuses. I had 4-amp and 2-amp fuses. Why? Search me. This kind of crap just accumulates. I needed 5 amps. Because I have a physics degree, I am just barely savvy enough to know that I can get 6 amps by paralleling a 4 and a 2. That’s pretty close to 5. So I knew I could fix this thing reasonably well without leaving the garage.
I felt tremendous satisfaction. It’s wonderful to be able to DO something with all this junk once in a while.
I obtained a 5-amp fuse anyway, and I’m going to solder it in there whichever way I can. It will not look cute, but then, no one will ever see it. With any luck, the fuse was the only thing damaged, and I’ll be in the clear. If not…INTERNET.
And I’ll be able to say I tried.
May 27th, 2010 at 2:09 AM
Were the two chargers plugged into different outlets? If so, one of the outlets may be wired incorrectly. One way to find out would be to pick up both chargers at once and be electrocuted. You can figure out a better way, I’m sure.
If I was replacing a fuse and had to err one way or another on the rating, I’d err on the low side. I might just be setting up to burn another fuse, but I’d be sure of protecting the device.
I thought of one more smarty-pants thing. Putting two fuses in parallel, you don’t get the full sum of their current capacity UNLESS the fuses’ resistances are in the exact same ratio as their capacities, which seems unlikely. The current probably divides in some other ratio, so one of the fuses will be, comparatively, overloaded. This is actually good news in your case, because 4 + 2 is too high. Knowing that one of the fuses is overloaded, you also know that if the current gets north of the device rating of 5 amps, it must be really close to blowing the overloaded fuse.
May 27th, 2010 at 10:40 AM
In my experience 50% of the difficulty in repairing something is courage to try. The other 50% is divided among persistence, proper tools, and common sense.
I am currently waiting for an A/C compressor for my car to arrive so I can survive the summer. Should save us $1000 bucks if God gives me favor and skill enough to get the installation correct.
May 27th, 2010 at 10:59 AM
I appreciate the help. When I got the 5-amp fuse in place, the charger blew it up immediately. I decided to bridge the circuit and find out if something else was wrong. The board started to smoke, so I realized there was something wrong other than the fuse. I have a new charger on the way.
May 27th, 2010 at 11:36 AM
It is AWESOME you put the fuses in parallel to get the proper rating. Well, close enough… which in itself is outstanding.
May 27th, 2010 at 11:46 AM
I had a series of 4 battery chargers from one company explode on me. They worked fine for a random number of hours, then Pop! Crackle! Smoke! Warranty Replacement!
.
Fortunately I was home when they failed… had I been gone when a charger failed I might not have had a place to sleep when it was all done.
.
So, I’m sorry to hear that your charger died… but the blessing could be that it happened when you were there.
.
May 27th, 2010 at 1:42 PM
The material in fuses has a positive thermal resistivity coefficient. Which means that is the fuse gets warmer, it becomes more resistive, gets hotter, and melts (blows). I doubt the charger blew because they touched.
One of them has an internal short to the case which is a bad thing. You could have been shocked. Having been a tech, I often laughed at being shocked, but you never know which event is going to be the one that will do you in.
But like a prior writer said, you may have a wiring problem. Especially see if the ground line is “hot”.
On your outlet, the smaller hole should be the “hot” wire. The larger hole is “neutral”, and should be directly tied to the “ground” in your fuse box.
May 27th, 2010 at 2:44 PM
“I doubt the charger blew because they touched.”
.
It may sound weird, but that’s what happened. The instant they touched, one charger blew up.
.
“One of them has an internal short to the case which is a bad thing.”
.
I don’t think my house has enough juice to electrify a plastic case.
.
I’m pretty sure I’ve checked the wiring on this socket before, but I can always plug the LED doodad in one more time. It’s a very crappy Chinese socket, so it needs to be replaced, regardless.
May 27th, 2010 at 2:56 PM
“The material in fuses has a positive thermal resistivity coefficient. Which means that is the fuse gets warmer, it becomes more resistive, gets hotter, and melts (blows).”
.
Am I missing something here, or have you just described everything that isn’t a dielectric or a superconductor?
May 27th, 2010 at 7:40 PM
I can get 6 amps by paralleling a 4 and a 2.
.
That particular rule is for resistance…not current flow. Unless the current carrying capabilities are widely mismatched (i.e. 10-amps and 0.1-amp), you increase the total current tripping point when putting fuses in parallel. When putting a 4-amp fuse in parallel with a 6-amp fuse, the new trip point is around 10-amps.
.
It’s not exact because there will be slight differences in the thermal response of the two different fuses.
.
Also, it sounds like the bridge rectifier is fried…