A 9Volt battery, A Megaphone... and a 2A Fuse

[Blue-Frog]

My problem concerns a car speaker megaphone (think Ice Cream Truck Speaker system (?)
Probably intended to run off a car cigerett lighter... (specs say 13.2V 1.5A, and somewhere 10 W is mentioned) but I arranged to run it off a household AC adapter producing 12V... and that worked well for a long time.... didn't use it for about a year, then tried to get it to run off of a 9V without success ; then went back to the AC without success... curious so I examined it and found the 2A fuse had burnt out.

I bought a new one but was wondering... if it could have been the 9v battery I attached that blew the fuse and how, if I use 12 AA batteries, I can prevent the 2A fuse from blowing in the future.

Anyone giggling at my mistake?
What went wrong?

 

[IslandLizard]

Sounds more like a short in the megaphone.

 

[Blue-Frog]

so you think I should be able to run it off 6AA batteries?
There are several splices in the cables, i was just thinking I know ac adapters come in various amperage ratings, yet I have no idea of how to create varring amperage ratings in connection with dry cells.

 

[TallDan]

What are you actually trying to accomplish? If you want to supply 12-13.5V with AA batteries, you'll need 8-9 of them wired in series. Assuming that your device pulls a constant 1.5A, you should expect to exhaust that set of batteries in a little over 90 minutes.

 

[IslandLizard]

You first need to trace and fix the short.
Spliced cables? Check the splices, 2 wires may be touching which they shouldn't.

You can run the megaphone on 6 AAs that gives you 9V (6 x 1.5V). It may not run optimally at that lower voltage, as it was designed to run at 12V, but won't burn it out.
8 AAs will give you the proper 12V.
If it needs to be portable, and on for a longer time, it will eat your wallet over time. You can buy 12V rechargeable batteries, or use 8 rechargeable AA cells.

A power source basically only delivers the voltage. The "load" (your megaphone) draws whatever current (amperage) it desires, up to what the power source can deliver (that's it's amperage rating), or up to what the fuse will allow.

• If there's an overdraw or short somewhere, it will draw more amperage than the fuse's capacity and the fuse will melt. That's what it's designed to do.
• If the fuse doesn't melt it may damage the power source if it's not up to the task to deliver that amperage for that length of time.

 

[Blue-Frog]

Summary/Update
I bought an 8 battery power pack to deliver 12V (to run a 13.2 V megaphone)
I tested the concept of using batteries rather than an AC adpter with a 9V battery...but it did not work
So I went back to using the AC adpter and it still didn't work.
That caused me to look at the fuse; indeed, it was burnt out.

Islandlizzard suggested that there looks like there is a short somewhere.

So I found what looked suspect and redid it... a quick preliminary test with the AC adpter resulted in a succsful test!

Next I plan to test it with the battery pak but first have to make a cable for the pak to the power jack.
I guess I can test the AC setup for an extended while as I fabricate the battery cable.

I don't think I will be needing the portable PA system that often but will be using rechargeable batteries.

So,

While it does look like I found a wishy washy splice, how would that affect the fuse?
It would seem that an iffy wire would simply act like a switch... just turning the thing on or off.
Why would that burn a fuse?
(Perhaps what I "fixed" was not a true short; as it couldn't function to actually make the circut "shorter"...?)

Talldan,
Do I have the information I need to calculate the amount of Amps the device will pull?
Can that be known from the provided information (above) from Watts Volts and Amps mentioned on the device itself?

In anycase, if correct, 90 min is good to know, and should be fine.

 

[IslandLizard]

While it does look like I found a wishy washy splice, how would that affect the fuse?
It would seem that an iffy wire would simply act like a switch... just turning the thing on or off.
Why would that burn a fuse?
(Perhaps what I "fixed" was not a true short; as it couldn't function to actually make the circut "shorter"...?)

You're right, a loose wire will simply interrupt the current, shutting the unit of. A blown fuse is a sign of an overdraw of current, higher than the fuse's rating, hence it melts.

Is there something you did that made it blow the fuse? Poking around with a screwdriver or other metal object? Where's the fuse? Inside the megaphone? Or inline in the power pack wire?

Anyway, something got short circuited somewhere past the fuse. Look for areas where wires are spliced and then taped together, open those up and check. Could be a loose or frayed wire touching other wires or components, 2 wires touching, missing or damaged wire insulation, a wire touching part of metal housing, or when you're poking around with a screwdriver while it's on, etc. You really need to look for it, chances are it will happen again. Aside from thorough visual checking, the next best way is with a multimeter on the resistance setting with the power pack disconnected. But you'd need to have some idea of circuitry testing.

 

[TallDan]

If there was a frayed wire that could have touched another part of the circuit, that could explain the blown fuse. For that matter, the fuse could have been blown while messing around with connecting a different power supply if there isn't something to turn the device off during that time. Either way, a blown fuse indicates a problem, so (as @IslandLizard stated) checking out everything on the circuit would be advised if you don't know why the fuse blew.

Talldan,
Do I have the information I need to calculate the amount of Amps the device will pull?
Can that be known from the provided information (above) from Watts Volts and Amps mentioned on the device itself?

In anycase, if correct, 90 min is good to know, and should be fine.

You stated in your first post that it's specs were 1.5A. That could be a peak current, so it may not use that much constantly, which would mean that the batteries would last longer. On the flip side, most rechargeables have lower capacity than their disposable counterparts, so you may not get that much run time with them. If you have an ammeter, you could measure the current that it pulls during typical use, and calculate expected run time based on the capacity of the batteries that you are using. Or, just verify your circuit, connect the batteries, and test the run time by using it.

 

[Blue-Frog]

Humm,

Ok, There are several things I haven’t mentioned, that might be important.

1. The bad fuse wasn’t “burnt” as in a burnt piece of toast; the metal inside the glass tube was simply found in two pieces; There was no discoloration. Does this count as having “burnt out”? Do fuses sometime, due to old age etc. simply break? I have no idea if that is a reasonable assumption or not.
   
   
2. I had used the item for a while then forgot about it for a year or two. Then I tried to connect it directly to a 9V battery. It didn’t work so I tried the AC adapter & that wouldn’t work either so that is when I looked at the fuse... so if the 9V try couldn’t be the cause of the problem, it is likely the metal broke while the unit was not being used (hot humid summers snowy winters) .
   
   
3. There are several things that I do not understand about the PA system. (It came as is - in a purchase of something else) There are 2 ohm choices... 4 and 8 ohms. Each has its own wire, but there is no knob or switch to change a setting. (don’t really understand why there are two choices but I guess it relates to sound quality) SETUP: from the amp box a 4 ohm and an 8 ohm wire extends. The 4 ohm lead ends in a ripped up plastic connector that looks like it had been used previously but no longer; it just hangs there in mid air.) The 8 ohm wire and the “COM” are run side by side and are connected to wires going into the speaker by plastic connectors under electrical tape (at least such can be felt under the wound tape) and so the 8 ohm wire and the “com” go from the amp to the speaker. What I do not understand is

1. Why there are two ohm choices?
   
   2. If it is actually optional to connect the second ohm lead
   
   3. Where the second ohm lead would be connected...
   (It would seem that there should be a switch allowing selection of quality, unless it is completely dependent upon the speaker being used)
   (Perhaps I did not get the full set up?)

My original thought was that by attaching a 9V to the power the megaphone, I somehow broke the fuse... if that is not the case then the lose 4 ohm wire could be involved. The connection of the 8 ohm and the “COM” to the speaker is under tape and feels very secure... so I haven’t actually looked inside yet. It just doesn’t seem suspicious.

 

[DU99]

wouldn't two 6volt lantern batteries connected in series be better for a supply....the speaker it's not open circuit

 

[Blue-Frog]

For power yes, and while I do not really understand your question, portability and weight are important concerns to me. In addition, those lantern batteries may be harder to come by where I am; not really sure... but I haven't seen one in years!

 

[ancientmariner52]

Humm,

Ok, There are several things I haven’t mentioned, that might be important.

1. The bad fuse wasn’t “burnt” as in a burnt piece of toast; the metal inside the glass tube was simply found in two pieces; There was no discoloration. Does this count as having “burnt out”? Do fuses sometime, due to old age etc. simply break? I have no idea if that is a reasonable assumption or not.
   
   
2. I had used the item for a while then forgot about it for a year or two. Then I tried to connect it directly to a 9V battery. It didn’t work so I tried the AC adapter & that wouldn’t work either so that is when I looked at the fuse... so if the 9V try couldn’t be the cause of the problem, it is likely the metal broke while the unit was not being used (hot humid summers snowy winters) .
   
   
3. There are several things that I do not understand about the PA system. (It came as is - in a purchase of something else) There are 2 ohm choices... 4 and 8 ohms. Each has its own wire, but there is no knob or switch to change a setting. (don’t really understand why there are two choices but I guess it relates to sound quality) SETUP: from the amp box a 4 ohm and an 8 ohm wire extends. The 4 ohm lead ends in a ripped up plastic connector that looks like it had been used previously but no longer; it just hangs there in mid air.) The 8 ohm wire and the “COM” are run side by side and are connected to wires going into the speaker by plastic connectors under electrical tape (at least such can be felt under the wound tape) and so the 8 ohm wire and the “com” go from the amp to the speaker. What I do not understand is

1. Why there are two ohm choices?
   
   2. If it is actually optional to connect the second ohm lead
   
   3. Where the second ohm lead would be connected...
   (It would seem that there should be a switch allowing selection of quality, unless it is completely dependent upon the speaker being used)
   (Perhaps I did not get the full set up?)

My original thought was that by attaching a 9V to the power the megaphone, I somehow broke the fuse... if that is not the case then the lose 4 ohm wire could be involved. The connection of the 8 ohm and the “COM” to the speaker is under tape and feels very secure... so I haven’t actually looked inside yet. It just doesn’t seem suspicious.

Speakers are usually marked either 4 ohm or 8 ohm. Use the common and the wire that matches the speaker rating, and tape up the unused wire. You don't have a switch because you don't swap back and forth. Hope this helps.

 

[Blue-Frog]

Yes that makes perfect sense. Can't see why the plastic connector at the end of the 4ohm was ripped up; unless it used to be connectd to a diferent speaker... (could have been an up grade)or perhaps the first connection was in error. So I guess the question is could the dangling 4 ohm wire have cause the fuse to blow?

I finished the power cable make... so I can hook it up any time now, but now a bit concerned that I am only half-way home, and that as IslandLizard said, it might happen again.

IslandLizard:
You wrote:
Aside from thorough visual checking, the next best way is with a multimeter on the resistance setting with the power pack disconnected. But you'd need to have some idea of circuitry testing.

I will do a bit of both. Mainly focusing on external, post purchase manipulations and not internal (out of sight) circuity. .. so I guess just testing for "zero" resistance where there should be no connection.

Right now the best guess is the 4 ohm wire touched something and blew the fuse or the old fuse just broke. Either way sealing off the 4 ohm lead and keeping an extra fuse on hand is where I am at.

 

[day_trippr]

You ever get the impression there is a Higher Power that doesn't want this effort to succeed?

 

[Blue-Frog]

Well, now that you mention it... not exactly. I'm quite certain it is a cloud of evil low-life scum sucking hemmoroidal flavored agitator's goblin gibblets that are trying to keep me from being reuninted with my sweet cat who was trapped and dumped on a local mountain a few weeks ago. Days of typhoon rains followed by record making extream heat, a wild bear visit, an aggressive intimidating wild bore, small but freaky cat-food hunting spiders, poisonous insect bites, walk-stopping painfully swollen feet, a frigid cat-fearing nagging wife... the list goes on ... certainly not a "Higher Power" source. Pure Evil!

 

[Blue-Frog]

Well I checked the connections redid them and hooked it up... it is working off AA's now.
I'll see how long it powers the unit today, with alkalines.
Two things if someone could answer, question 1 in post#9 and the more challenging...
Why are there 2 input jacks, one "mic" & one "tape"; it doesn't seem to matter which I plug the digital device I am using into, they both work. (I also have a dedicated mic, but haven't tried that yet);

could it be as simple as being able to play a tape and do voice over at the same time
or
is a technical difference between the two jacks?

Anyway thanks for holding my hand as I've tried to get things back on track. Things are looking up.
Now it's time to see if this idea can help my cat find me! (and keep the other wild life at bay!)

 

[day_trippr]

Typically a microphone input is much higher impedance than a "line level" input - microphone outputs being fantastically low energy compared to the output of pretty much any digital device. Whether both inputs can be used simultaneously is a device design dependent thing - could be, might not be...

Cheers!

 

[Blue-Frog]

OK
I looked at the definition for impedance and after reading several an~nd wikipedia's entry I realised your post was the most understandable! Nevertheless, I am amazed at how hard it is for those professionals to construct a simple lay person explanation that is both true and clear.

I gather (mostly from your post) mic jacks are high impedance... meaning that the circutry behind the jack functions to assist the low power microphone output, to produce (ultimately) the desired level of volume, while this extra assist is not needed for "line level" input.

Is this about right? I hope I got it.

 

[day_trippr]

That's pretty much it. Typically line-level inputs go directly to an amplifier stage while a mike input goes through a pre-amp first.
That said one can usually over-drive a mike input with a line-level device though distortion can be a result...

Cheers!

 

[Jayjay1976]

F@#k fuses. What are they protecting except the silence? Hardwire that thing and be heard already!

 

[TallDan]

F@#k fuses. What are they protecting except the silence? Hardwire that thing and be heard already!

Owly?

 

[day_trippr]

ahahahahaha! Nooooooo!

 

[Jayjay1976]

Owly? Please elaborate.

 

[TallDan]

Owly? Please elaborate.

https://www.homebrewtalk.com/forum/threads/gfci-failure-rate-up-to-57.621835/

 

[ba-brewer]

An AC adapter may have some form of over current protection and could limit the available current. A battery has the potential to supply a large amount of current for a short duration.

Any chance when you first tried the 9V battery it got connected backwards? If there are active circuits inside the device a reverse polarity could make those active circuits look like a short or lower impedance.

 

[Blue-Frog]

It is certainly possible...