How to: use hard drive dc converter to charge car battery?

[bobbo123]

I have several 12 volt 1 amp converters laying around. Stripped the wire ends and attached clips. The wires sparked when applied across battery terminals....and the wires stayed cool BUT the converter itself got warm and stopped working...so I assume I had the polarity crossed?

Tried again with a 12 volt 2 amp supply that had a white strip on one wire for the positive lead? The clips would spark when swiped against each other but there was no sparking at all across the battery posts.

What am I doing wrong? Should this work, or not at all?

Similarly....I also have some old power supply units for old computers. I could do the same thing with one of those with higher amps provided.....but why doesn't the small guy work? I don't mind waiting 12 hours or whatever it would take?

Thanks.

 

[13thmonkey]

I think that a lead acid battery has a really really high internal impedance, and those chargers are just not designed for that, to be frank you're lucky that's all it did.

 

[little_me]

As has been noted in other posts, car batteries usually need higher voltage (13 to 14V) to charge.
computer power supplies usually output 11.5 to 12.5 (depends on PSU and it's quality and load and all else) in the 12V rails.

That will not charge the battery.

The second part that you have skipped is that most chargers have chip that monitors both input and output voltages and current and stops charging periodically to check how far/if battery charge/voltage has risen and automatically stops once it's "full"

This part of course only comes into play once the charging process itself actually works.

It is usually far easier to just go and buy simple charger from shop.
https://www.amazon.com/MOTOPOWER-MP00205A-Maintainer-Motorcycles-Powersports/dp/B06XWDZ2KQ/
that is 15 USD and would save all the trouble and work more reliably. other and more expensive models also exist.

 

[bobbo123]

Thanks guys. I can accept it in reality doesn't work.....I was just hoping it would as I have the spare parts just sitting around....and I wanted to avoid buying another battery charger just because I can't find the one I already had. Supposed to be in the Car Trunk BUT maybe I put it somewhere else....or maybe it grew legs and walked off.

Not related: I've had great success recharging standard non-rechargeable batteries. don't even need to monitor them for overheating or anything....charger (from 20 years ago) just "works" on them. Either everyone is wrong about this...……….or...…..I got a batch of mislabeled rechargeables for the cost of standard?

But...…….FACT IS....the little DC chargers don't provide any juice at all across the car battery terminals. They will run the 12 volt air pump in short 1/3rd second bursts...so not really?....Just shows the wires do have juice.

I feel like a "pan handler" whenever I ask a neighbor for a jump or a trip to Sears for a new battery...…...call Uber?

Thanks again.///bobbo (How can I pick both of you for "the answer?"

REREADING: I find it hard to believe a 12 or even 10 or lower volt supply would not charge a 12 volt battery? Even the small hard drive power unit at 1 amp should only take more time to do it....like a trickle charger does? I don't see any safety issues either as I would disconnect as soon as the battery got enough power to crank....which could take a day or more to do???...……..if it worked at all, which it doesn't. I might try another small hard drive converter just because I have so many of them. Got to get into a case to pull a PSU though....I'll google later to try and find a hobbyist with the same interest. If we have the parts...…..why not try??? Thanks again...…….

 

[13thmonkey]

'have juice' is not really a concept. It outputs Amps in a limited range of voltages. The fact that it is pulsing kind of indicates to me that something is no longer functioning in the charger. Having essentially put a dead short across it, something (probably in the voltage regulation) has died.

 

[bobbo123]

Monkey....you are talking about a PSU?===right? so far, I've only used two dc converters for external hard drives. No variable charging. the first unit I think I shorted out is totally dead. The second unit I tried still sparks and will drive the 12 volt air pump so I think it "works" as it should.....I have no knowledge at all for this but I can imagine some "impedence" think in the car battery or maybe some kind of internal resistance is causing the trickle charge not to work? Ha, ha....I ALSO have a trickle charge that is lighter in weight than the hard drive converter, but I think it has more circuitry as well. The trickle charge works 50/50 to bring back a well drained car battery. Supposed to only work on fully charged batteries. Lots of things work/don't work as they are advertised?

 

[13thmonkey]

Not a psu, a power brick, they will output between say 11 and 12v,this will vary depending on the current drawn, which depends on the impedance at any given point in time, most circuitry will cope with this range of voltages.

As above a battery needs more voltage applied to it to charge than it puts out, else the power flows the other way.

If you connect it wrong I believe that you can generate hydrogen... This is bad, a spark will ignite it..

Your other device might be a conditioner that keeps it topped up, rather than a charger. Because lead acid batteries are essentially a continuous chemical reaction in a box the conditions required to top it up are very different than if it was dead. Get the proper device for the job in hand.