can i charge a car battery with a simple home transformer

[transgalactic]

bridge rectifier just transformes a AC current into DC current (with gaps)
what the 25 amp part means?

 

[giftiger_wunsch]

It means it's rated for 25A...

 

[bountyhunter]

i have a 12v car battery

can i charge it with a device
AC input
220v
0.2-0.5 A
60/50 hz

dc output
12 v
1.25A
and i would pore a distilled water .

its a transformer for my scanner
is it possible?

You can make a very good lead acid battery charger without too much circuitry. Here is a design I did some years back that was published in EDN magazine. I still use it to keep my motorcycle battery topped off year around. It has built in temperature compensation. It requires no heatsinks. The circuit operation is explained in the article text.

 

[giftiger_wunsch]

You can make a very good lead acid battery charger without too much circuitry. Here is a design I did some years back that was published in EDN magazine. I still use it to keep my motorcycle battery topped off year around. It has built in temperature compensation. It requires no heatsinks. The circuit operation is explained in the article text.

Neat. I'm sure you enjoyed the opportunity to show off your published article as well

 

[bountyhunter]

Neat. I'm sure you enjoyed the opportunity to show off your published article as well

Not really. I had about 40 published over last 20 years. The thrill pretty much goes away after the first ten or so......

What's really bad is when ED magazine published an article and omitted the last column and nobody seemed to notice (I didn't get any notes asking about the missing info). That's when you know either nobody is reading it or nobody is UNDERSTANDING it......

 

[giftiger_wunsch]

Not really. I had about 40 published over last 20 years. The thrill pretty much goes away after the first ten or so......

Aww, that's kinda depressing

What's really bad is when ED magazine published an article and omitted the last column and nobody seemed to notice (I didn't get any notes asking about the missing info). That's when you know either nobody is reading it or nobody is UNDERSTANDING it......

What was in the last column? Maybe they understood it so well, they didn't even need the last column

 

[unclejed613]

i've used open frame regulated power supplies to charge car batteries. first of all, they're cheap (usualy about $10.00 if you actually have to buy one). they usually have very stable foldback current limiting, and usually have a voltage adjustment as well as a current limit adjustment. if the voltage adjustment doesn't have enough range, you can fool the power supply into giving you enough voltage by putting a couple of forward biased diodes between the output terminal and the sense terminal. i have one that's rated at 12V@10A. i have two diodes between the +out and +sense terminal, which boosts the nominal voltage up to 13.5, and the voltage adjustment will now max out at 14.5, so 13.8 is within the adjustment range. the current limit is set at 6A, and will give a rock solid 6A even into a short without any ill effects to the power supply. if you know somebody that does industrial equipment repair, they probably have a few of these laying around, usually with a shorted overvoltage protect circuit. the protection circuit is usually a crowbar circuit (an SCR triggered by a zener). usually just removing the SCR from the circuit restores normal operation of the power supply. in many cases the crowbar circuit is a little add-on board anyway, and can be removed. the crowbar is there to protect the end user's equipment from power surges, and since the application doesn't require such protection, the crowbar is unneccesary.

 

[bountyhunter]

Aww, that's kinda depressing




What was in the last column? Maybe they understood it so well, they didn't even need the last column

I don't think so......

 

[MrAl]

5 amp diode
??
diode is short circuit on positive voltage
and open circuit on negative voltage

so it doesnt matter what is the size of the current
just its direction
thats what ive been tought so far

Hi there,


Well, no, the diode has to have a high enough rating to handle the
current flow into the battery, so you have to buy the correct diode.

The diode is a short circuit only in the simplified diode model, which
isnt the same as the real life diodes. Real life diodes have voltage
drop and internal resistance, and the package size and shape and
die size limits the current handling ability.

I suggested a 5 amp diode for 100watt light bulb, but since a 100 watt
bulb can have cold resistance as low as 10 ohms, maybe a 10 amp
diode would be better here. As soon as the bulb warms up however
the current will fall down to around 1 amp peak, about 0.5 amp average.

 

[mel8030]

Maybe. Check the open circuit voltage of the adapter. If around 15 volts, it should charge the battery ok, just slowly. If the voltage is 12 volts, it has an internal regulator and won't fully charge the battery.
I use small adapters all the time to charge batteries. I mount them on diesel vehicles and tractors to keep the battery perked up in winter. They are attached to the block heater cord.
I once used a 1 amp adapter to charge a battery that was too low to start the engine. Took over 2 days of charging to start the engine. Diesel usually have bigger batteries than most cars. I think a few hours of your 1.5 amp on a small car battery would let it start, if the battery was not too low.
I have measured the final charge rate of an assortment of adapters and its around .25-.5 amp so I don't think you need to be concerned about adding water.