replace wallwart with 100+ah 12vdc?

notsobright

hello,

I am intrested to learn if I can directly wire a large 12vdc battery into various tools and aplliances that use wallwart (small ac to dc transformer/converters that plug into wall outlets)

specifically Im wondering if a large battery can harm the appliance that is normally charged or powered by 12vdc @ x milli amps.


it would be great if I could plug in everything that uses mini 12vdc input into a large battery.

thanks

mikeo

Re: replace wallwart with 100+ah 12vdc?

I am intrested to learn if I can directly wire a large 12vdc battery into various tools and aplliances that use wallwart (small ac to dc transformer/converters that plug into wall outlets)

Yes, mostly you can. Some devices may object to charging and equalizing voltages (near 15 volts), so beware. If you can shut or unplug the devices when you are maintaining your batteries, you will have no problems. It is important to properly fuse each device with an inline fuse to protect your wiring in case of a short. IHTH

AntronX

Re: replace wallwart with 100+ah 12vdc?

Sure you can. Just make sure you got right polarity and use a fuse in series with every load, rated at least double the Amps that your load draws. Wiring the polarity is very important, because your 12V appliance may not have polarity protection because it was not assumed it would be used from 12V DC source directly.

notsobright

Re: replace wallwart with 100+ah 12vdc?

great! thats what I wanted to hear/read.

what about doing this on the aplliances that also charge from this 12vdc input?

for some reason I was thinking a big battery would overload the small devices with way more amps than they can deal with. I guess it doesnt work this way and they only draw what they need.

mike95490

Re: replace wallwart with 100+ah 12vdc?

notsobright wrote: »

great! thats what I wanted to hear/read.

what about doing this on the aplliances that also charge from this 12vdc input?

for some reason I was thinking a big battery would overload the small devices with way more amps than they can deal with. I guess it doesnt work this way and they only draw what they need.

Just like the 15w bulb in a socket, does not draw 100w from the 15A circuit.

BB.

Re: replace wallwart with 100+ah 12vdc?

You do have to be sort of careful anytime you attempt to go from a "12 volt wall wart" or small 12 volt battery pack to a full blown lead acid battery bank.

(warning--this is the engineer/safety talk--boring and obscure):

As Mikeo and AntronX say--make sure you have an inline fuse/breaker to protect the WIRING from shorts (you are not, technically, protecting the device from damage--just the wiring and attached devices from FIRE).

The problem is that a small wall wart or battery pack may have only 1-2 amp output before it current limits or pops an internal fuse.

A 100 Amp*Hour lead acid battery can, with heavy enough wire, output more than 1,000 amps into a dead short.

So--if the "little DC" device has, for example, some electrolytic filter capacitors in it (to keep the wall wart noise down)--connecting to a short/heavy cable and lead acid bank can create huge currents through the DC power switch and into the capacitors--possibly stressing them for early failure or worse.

Another common thing done with small flashlights--they put a few LED's in series than connect them to a AAA or AA or coin cell battery pack. The internal resistance of the battery packs limit current through the LED's... You get bright LED's and a cheap flashlight. However, if you were to "surgically remove" the flash light head and do a direct connect to the battery bank--you could over current the LED's and kill them.

There are also functional issues--Solar Battery systems have a pretty wide voltage range (from 10.5-14.5 or even 15.5 volts) -- and many "12 volt devices" really don't like it (may not operate at low voltage, or may fail at high voltage--As many of them were designed to operate in a car).

Even the case of the device can be an issue... An internal device short on a 500 mAmp wall wart supply is not going to melt the plastic case... An internal device short when connected to a 10+ amp 12 volt battery branch circuit can melt the case/cause fire.

I am not saying to never connect to a 12 volt battery bank with your 12 volt devices--but just to be aware that there can be issues that are not obvious at first glance.

Testing the devices on a flame resistant bench, checking temperature and for proper operation before placing the device into service is probably not a bad idea (if it was not already designed to at least work with a car's 12 volt system).

-Bill "buzz kill" B.

notsobright

Re: replace wallwart with 100+ah 12vdc?

so to do this safely and without equipment damage I need to find a voltage regulator that will limit it to precisely 12 volts. (and proper fusing)

Ive got some voltage regulators from old cars laying arround but they all have what looks to be ceramic resistors in them so I assume they would waste alot of power.

I wonder if there is a smart transistorized voltage regulator that would limit..


hey what about a recotron type converter? the ones that plug into cigarrette outlets and lets you drop voltage down in increments. that would work for one thing at a time but Id like to have several things at once if need be.


there is probably something made just for this purpose. what would be ideal would be something that has multiple outputs and can limit 12v on some while limiting to 9v,6v and even a 5v USB all at the same time.

surely theres something. if I knew what it was called I would do a search..

I'll see what I can come up with.

bryanl

Re: replace wallwart with 100+ah 12vdc?

take a look at distribution boxes like the West Mountain Radio rigrunners or qsradio.com - these are things radio amateurs use to power a lot of 12v shack appliances. The Anderson connectors make for a very convenient connection method.

There are a number of solutions for 12v regulated power from a 12v battery bank. Two intended for radio use were reviewed in _QST_ recently.

For some low power loads, you can add a resistor in series to help limit current or use a simple zener diode to avoid over-voltage situations.

notsobright

Re: replace wallwart with 100+ah 12vdc?

hi Bryanl, those WMR units are nice. Ive been making something similar with the same anderson connectors they use available from http://www.powerwerx.com/
these are great for indoor uses.

Im still looking arround for a multi-output, Adjustable Voltage Regulator and they dont seem to exsist! (common theme in my life)

I could probably make my own but considering the time involved I would be better off just buying a few of these

http://www.powerstream.com/dc6.htm

notsobright

Re: replace wallwart with 100+ah 12vdc?

Ive been checking actual voltage output on seceral wallwarts I have and very few output what they indicate on them. several rated @ 9vdc are above 14v, several that indicate 12vdc are above 17v.

I have only found one that is within a volt of what is indicated. that is my largest 12v one rated 1amp @12vdc, actual output is 12.96v


I guess the ratings printed on back of these things are only accurate when loaded with the exact amperage indicated.

mikeo

Re: replace wallwart with 100+ah 12vdc?

these things are only accurate when loaded with the exact amperage indicated.

That is correct the ratings are under load.
I run my Davis weather station, Zhone DSL modem and Linksys RF modem all off a 12 volt battery with no problems. The Zone modem has an AC walwart rated at 15 volts AC. I just placed 12 volts DC across the input and it has worked fine for months now. The Weather station works on 5 volts and I used one of these to regulate the voltage http://www.dimensionengineering.com/DE-SWADJ.htm down. The Linksys has a 12 volt rated wall wart and I made a POE cable that provides 12 volts from the battery as it is mounted in a weatherproof case on a pole on top of the house. I have WIFI over most of my 40 acres. I have a GoPower 10 amp charger that I keep the battery topped up with utility power. When utility power drops out, the Wifi and weather station keep on working.

bryanl

Re: replace wallwart with 100+ah 12vdc?

also consider that the output waveform of many walwarts may not be pretty and influence voltage readings depending upon the voltmeter.