12v connection Question

Steve English · From: Baja, Arizona

I have a Yamaha sound module that uses a wall-wart to convert 120v AC to 12v DC, 700ma.

Can I connect this sound module directly to a 12v DC supply system in my RV (eliminating the wall-wart)?

Thanks!
_________________
Always remember you're unique..... Just like everyone else

Lane Gray · From: Topeka, KS

As long as you have the polarity right.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects

Jack Stoner · From: Kansas City, MO

I would be careful with connecting directly to 12VDC on a vehicle. The 12VDC is not regulated and the voltage can vary, plus or minus. The unregulated voltage can be an issue in some electronic equipment.

Ray Anderson · From: Jenkins, Kentucky USA

Voltage in you RV can vary from 13.2 volts up to 14.4 volts depending on battery load and altenator output. Some newer vehicles offer a regulated output supply for accessories. Whoa!

Steve English · From: Baja, Arizona

Thanks, I was thinking about the variances in the dc voltage. I'll measure the wall-wart tonight. I know many of them actually put out more voltage than listed.

I typically run off the inverter, but was just curious.

My solar system is very well regulated via controller, and at night the batteries would be the sole power source, which are also protected from draining too low.

Thanks again for any advice....
_________________
Always remember you're unique..... Just like everyone else

Ray Anderson · From: Jenkins, Kentucky USA

If you're using an inverter you should be good to go. That is a regulated supply. Winking

Joseph Meditz · From: Sierra Vista, AZ

I would not worry about the unregulated voltage in the RV. It's very unlikely that, say, 15 volts would damage an amplifier.

Were the old transformer wall warts regulated? I would guess that many of them were not.

So, I would run it right off the RV's system. It would run right off the battery. As a bonus I'm pretty sure the amp will sound better running off that clean, high current battery than a 700 mA wall wart running off an inverter.

My dos centavos.

Ray Anderson · From: Jenkins, Kentucky USA

Not so much the voltage that is the issue here. I would hate to see you lose your toy. It is the amperage that comes into play especially with Solid State equipment. That accessory uses a system up to 700Ma and that is the determining factor, not alot of amperage. A battery stores a capability of 600 to 800 amps. That is common knowledge in the automotive world. In a power supply the amperage is cyphoned off and regulated. Yes you can drive the accessory harder with more amperage, but for how long? I've worked with and around DC voltage for 40 years, that should say something. Don't destroy your toys by experimenting, you only get one shot. Shocked

Stephen Cowell · From: Round Rock, Texas, USA

As long as you don't reverse the polarity no problem... and I've worked around DC voltages for 50 years, all my childhood toys were DC.... and I understand Ohm's Law to boot.
_________________
Too much junk to list... always getting more.

Ray Anderson · From: Jenkins, Kentucky USA

Stephen I didn't say that it would not work. Just think it's a gamble to play with something that you don't understand or are unsure of without getting the facts before you try it. I too, understand Ohms law. Why not make a "one size fits all" power supply? Why have different rated fuses with different characteristics? I won't argue the issue but I too have been on the bad side of improper matching i.e stereos ,phones and etc. I guess that's how you learn "trial and error". Smile

Don Poland · From: Hanover, PA.

Why not simply install a 700ma fuse in the supply cord?

Lane Gray · From: Topeka, KS

Ray, unless _I_ misunderstand things, the capacity of a supply, as long as it exceeds the demand of the device, isn't a concern. My (well, my boss's) Kenworth has 3 1125 amp batteries in parallel, total of 3375 amps. It's perfectly content operating nothing more than the clock and whatever else runs when the key's off (ISTR under 1A, plus 700 mA for my phone charger).

I think the reason they make 'em in different ratings is just to keep copper costs down; more current, bigger wire.

I'm posting this mainly for correction of my misunderstandings, if I got 'em. I find electrickery fascinating, I've just forgotten most of what I learned in '83.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects

Michael Maddex · From: Northern New Mexico, USA

Steve, the Yamaha should work just fine connected straight to the RV 12 VDC. If you have any doubts, you can always put a voltage regulator inline between the RV and the Yamaha. A 7812 chip with heat-sink is rated for 1 Amp (1000 mA) continuous and should do the job just fine. Chip, heat-sink and heat-sink grease (for assembly) all together should run less than $10. You can find voltage regulator chips and heat-sinks at Radio Shack, real electronics stores or some other vendor of your choice. HTH.
_________________
"For every expert, there is an equal and opposite expert." -- Arthur C. Clarke

Ray Anderson · From: Jenkins, Kentucky USA

Good point Lane, but if all you can see are the batteries then you have missed a lot in between. You are in my world now, I have a T300 Kenworth that is setup the same way. What you are not seeing on this rig is the fact that there are 2 control modules or computers as they are referred to, 1 is for the ENGINE CONTROLS, the other is for cab and chasis functions. These carefully control and maintain current to their components and to regulate them. The amperage in your batteries is for STARTING purposes and other non-electronic devices i.e power seats, windows and such "electrical" devices that demand amperage output. When you use your starter the voltage can jump as high as 15 to 17 volts through you system because of the demand and "Ohms law". I have worked on trucks, farm equip,mining equip, earth moving equip and anything else that is diesel powered for 40 years and a Master Mechanic by trade. Any thing hooked to your system unregulated will feel this spike and the rest is history.

Stephen Cowell · From: Round Rock, Texas, USA

... but connecting to the volt-pak is fine. No spikes after the regulator.
_________________
Too much junk to list... always getting more.

Steve English · From: Baja, Arizona

Well, it worked Smile

The wallwart measured 17.1v dc (with no load)

My battery bank will supply a constant 12.6v dc for more hours than I'll ever need. In the day the solar is recharging/generating.

I can plug my steel/effects into the stereo input, and do BIAB with the little Acer computer. I use a Goodrich 4A for tone and volume.

I was thrilled to see it only drew .5amps, a typical 12v auto bulb draws 1.8amps

I tried to heed everyone's advice so thanks for the replies!

....and Thanks for the regulator build Michael. I'll put that to use.
_________________
Always remember you're unique..... Just like everyone else

Joseph Meditz · From: Sierra Vista, AZ

Michael Maddex · From: Northern New Mexico, USA

Thanks for the clarification, Joseph. For some unknown reason, I was under the impression that the 7812 chips would function in the 10 - 15 VDC range. I just grabbed a data sheet which clearly states that the Input Voltage Required to Maintain Line Regulation is 14.6 VDC.

Sorry, Steve, I told you wrong. The chip won't work right in this application, but as Joseph says it is not necessary anyway.
_________________
"For every expert, there is an equal and opposite expert." -- Arthur C. Clarke

Paul Arntson · From: Washington, USA

Michael, that's very gentlemanly. I wish I could be that gracious all the time. You are a good example for all of us on the forum. Well said!!

Forum Index > Electronics		Next oldest topic :: Next newest topic