12 volt power for bench testing car parts?

JeffreyNMemphis · 04-24-2009, 09:05 AM

Hello Pelicans,

My clock is running slow. I think it is losing 15 minutes per day. The clock is mechanical, I can hear it ticking. This weekend I plan to take it out of the car and adjust the +/- to get it accurate. Which brings up this question:

What amps do electrical parts from the car need to function correctly and safely? I have a 12v battery charger with a 2 amp setting; would this work to run the clock on my work bench for a few days while I continually adjust closer to correct timing? I have other 12v power-supplies from household appliances, but don't know if the the amps would blow the clock. Also, I have some other electical parts I want to test besides the clock; what is the correct power source for bench testing automotive electrical parts?

I also want to test some other stuff that is automotive. What would you suggest as a power source for testing 12v car parts? I could use a car battery that is available... But my preference is for something powered by household current and converted to 12v like an appliance. My wife has been through several "Litter Maid" cat boxes that run on 12v converter and break eventually; so I have a 12v converter available. My first thought was my 12v trickle charger for car battery.

Thanks in advance!

DW SD · 04-24-2009, 09:35 AM

I would use a regular car battery. Not sure how extra voltage from a charger or similar would effect the clock or other devices. I doubt it would break, but maybe it would run faster with a higher voltage. I know small - battery powered clocks will run slower when the voltage decreases.

SpeedracerIndy · 04-24-2009, 09:41 AM

I used a cell phone charger (12V and had an output in the milliamps range) to test a spare clock. I kept it plugged in for several days and it kept perfect time. That would lead me to believe that the amperage draw of the clock is very low.

How do you adjust the +/- on the clock? I don't remember seeing anything like that when I had mine apart.

RWebb · RWebb's Garage

most items will work fine with what you have - adding a fuse is a good idea

one exception is an electronic device - for any of those, you may run into issue with ripple from an AC to DC conversion

you can design or buy filters to reduce ripple to any level

simplest thing to do is charge up your battery and then run the clock or other devices off it for a week or so - then check and see if it needs charging again

of the commonly used devices, only a motor will draw much current
- if you do something weird like run a Peltier heating device (often found in new-fangled coolers, ice chests etc. nowadays) then batt. will get sucked down fast

teenerted1 · 04-24-2009, 10:31 AM

remember that a car battery charger might have a surge to get up to usable amps then drops in amps to keep the battery up to snuff.

just use an old good battery and you should be ok

dad911 · 04-24-2009, 10:53 AM

I use one of those 'portable jumper packs' for testing 12v stuff.

Charger does not put out clean power, and some of the new smart/automatic chargers will not work correctly w/o a battery.

JeffreyNMemphis · 04-25-2009, 10:27 PM

Thanks to all for support and wisdom... SpeedracerIndy, the clock that I am adjusting is in my 1973 Mercedes. I think the quartz clocks in our 911s stay extremely accurate. The clock in the Benz is mechanical, old school wheels and gears wound up by electrical pulse.

Turboo934 · 04-25-2009, 11:55 PM

A model train transformer /with adjustable knob.

CruiseControl · 12:05 AM

+1 ....... follow RWebb's advice above.

Most battery chargers are not suited as a standalone power supply !! This due to the voltage regulation and the ripple. Having the battery charger connected to a battery and then drawing of the battery is OK, Just make sure that you never have the load (the device you are testing) connected to the charger only without the battery,

There are purpose make battery chargers that are manufactured to suit lead acid type batteries that can also be used as a power supply, however these are rarely seen in the automotive industry or garage due to their price.

In the industrial arena it is suprising the equipment that is damaged where the battery is disconnected from the system, leaving the "economical" battery charger supplying the system devices. The only way to confirm if a battery charger is suited for use as a power supply is conducting tests with a crow. The tests including analysis of the sinewave; level/ripple/spikes under all conditions including spike while disconnecting from a charging battery.

As for the 12vDC supplies that are supplied with varioius electronic/domestic type products, they may be OK to use in some instances but generally thay have lousy voltage regulation and moderate ripple. It is the voltage regulation and current capacity that needs to be addressed in using such units.

I suggest having your "continuous" trickle charger connected to battery terminals using screw/bolt/clamp connectors. This provides a good undisturbed connection as you connect/disconnect your other load devices.

Don't forget the use of fuses which are protection devices against over current (the accidental short, etc).

Paul