An electronics question...

north coast kook · 02-23-2006, 05:20 PM

Hello! I decided to ask this question on this site because you guys are some of the smartest people I've found on the net!

I've had to take some time off of fishing lately to deal with a divorce, and a couple of moves. But my question has to do with a battery charger I am using as a DC power source. It's a 12V/10A charger. But when I measure the voltage that it puts out, it's around 17 or a little more. That's too much for the amplifier it's running. I'm looking for about 13 or 14V. I was thinking maybe I could just wire a resister inline on the + wire. Would that work? And if so, how many ohms should it be? I'm somewhat confused by electricity, so any help you can offer would be greatly appreciated!

Thanks!
-KooK

GSD · 02-23-2006, 05:37 PM

Wouldn't it be easier to go to an electronics store like Radio Shack and buy a transformer, with the power rating you need?

William

north coast kook · 02-23-2006, 06:37 PM

That's kinda what I thought. As it turns out, the guys at radio shack told me they dont know anything about electronics! They only do cell phones! And couldnt help me. They did have transformers, but I wouldnt know how to wire one up.
~KooK

Cloud-Nine · 02-23-2006, 08:03 PM

I don't think you have a problem. The 17 volts is with no load. When the amp is running it should be about 14 volts. That is just fine with a solid state amp. If you were to try a resistor it would have to be a very very high wattage one. If you were drawing 10 amps and tried to drop 5 volts, that is 50 watts. Resistance needed would be 1/2 Ohm.
Dick

Gus Orviston · 02-23-2006, 09:46 PM

You have a non linear power supply ... that said it needs a load like cloud nine said. that load must be enough to get the supply to regulate.. so that will be the first thing to check. The best way to get it to stabilize to about 14V like mentioned is to hook it up to a battery.. then tap off the cables. The battery load would be good as long as your load isn't too much.

a resistor.. not a good idea. Based on the Non Linear thing, but you would also have to know the current draw or experienct with your Unit under power to see what it took to drop the right voltage.. but like said the 17 should come down.. if it isn't then you still aren't loading it enough. OR the charger is on the blink.

gus

DAB · 02-23-2006, 11:34 PM

Batery Chargers ( unless it states that in can be )should not be used as a power supply , Car Bat. chargers don't give you clean DC power. Get a power supply from a Ham radio place and it will work just fine,
DAB

StickFish · 02-24-2006, 07:15 AM

What kind of amplifier are you running? If the amp will run from a 12/14 volt supply and you must use you charger also use a car battery with it. Otherwise get your self a regulated power supply, Fry's, Norvac Electronics, Ham Radio Outlet, Radar Electronics, Wacki Willies. You could also use a switching supply which is simular to a computer power supply and doesn't have the boat anchor transformer in it.

I would not use the battery charger by it self.

Oh if you do use a battery with it please be aware that it will off gas Hydrogen while it is charging - needless to sat H is a tad explosive so please only use the battery in a ventilated area.

Gus Orviston · 02-24-2006, 07:47 AM

Agree and should have stated the same... That is not a good power source for many reasons... but in a pinch it can work.

gus

north coast kook · 02-24-2006, 09:14 AM

Ok, thanks for the help guys! The amplifier is a mono block subwoofer amp. Meant for car audio, but I wanted to see if it could be adapted to home use. If you look at home theater subwoofers that are as powerful as what Im using, you will expect to pay from 500 to 700$$ I put this one together for about $250. The amplifier may not present enough of a load to the charger to drop it down to the 13 or 14 volts I want. When it's running at an average volume, I read 16.75 volts and 1 or 2 amps. When I really turn it up and the bass hits HARD it will drop to 15V or a little more, and pull 7 to 8 amps. I'm really not sure what is meant by linear, so I cant follow why a resister might not be a good idea. I do like the idea of hooking a battery up to it. I would try to wire it up outside, there is a window I could run the wires through. It wouldn't be much trouble. Maybe I'm just a cheapskate! (maybe???) But I had these car audio parts already so decided to put them to good use. I already have another set up in my car. Do you think the 17 volts is more than would be safe for the amp?
~Jay

Smj · 02-24-2006, 09:39 AM

I think your neighbors(if close by)are gonna love you.

Smj

PDXSteelhead · 02-24-2006, 09:56 AM

I used to run a car CB at home and just got a regulated 12v power supply from Radio Shack. It has ***. and neg. posts to hook up 12v stuff. They're not that expensive.

StickFish · 02-24-2006, 10:22 AM

He should have at least a 10am regulated supply - I'm pretty sure the little RS supplies are much smaller capacity.

I do know one thing my Yamaha sub for my home theater system didn't cost $5-700. My Onkyo in the bedroom the entire system was less than $400 and rattles the windows but good.

Good luck

Gus Orviston · 02-24-2006, 12:05 PM

non linear or Switching supplies require a load, sometimes built in.. PC power supplies are switchers and if they are not hooked to a motherboard, or a HDD they will float their outputs.

No way to know if your amp can handle 16V.. I assume they would be designed for automotive maximums ... say upper 14.x ... and then some margin.

gus

north coast kook · 02-24-2006, 12:27 PM

ofcourse, I have likely gone overboard with the power of this system. I'm running two MTX 10" subs at 300 watts rms each. I dont think your onkyo could match that

I hooked it up to a car battery and it seems to be running well at about 12.6 to 13.5 Thanks everyone!