12V Car Battery charger - 0.2 amps :(

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Good evening guys .. wow it have been like 3 years since the last time I made a post in an online forum :D ... Facebook have eaten the whole competition you know :).

Ok let's enter directly to the subject ...

First of all let me mention that I'm a mechanical engineer and not an electronic or communication engineer so excuse me if I mentioned any wrong information below.

I made a circuit (actually two) to charge a 12 V car battery (not because I don't want to buy one - but because I love electronics and this is a good chance to learn something new :D) ... anyway ... This is the original circuit I made:



(see attachments for the circuit I built)

I did everything as in the drawing but only the transformer is 12v - 5 A

For the 4 diodes I bough a rectifier instead.

The output DC voltage from the rectifier is around 15 V and so from the output of the circuit. But the problem is in the current when I measure the current passes to the battery it's around 0.2 Amps only !!

I measured the amps that out from the circuit without any load and it was around 1.5 amps.

If I measured the amps out from the rectifier also before the circuit it self it is very high that I did it for few seconds only because everything becoming heated.

So I want to know why is the current is small passing through the battery ?

Also I have to mention that the battery have a hydrometer and it tells if the battery is either ... Good .. Need to be Charged ... Unusable ... (see attachments) .. It seems that it just need to be charged ? That's what made me think of charge it at first place :)

Thanks in advance for the help .. I wish I could post great useful posts like you does ...

Greetings from Egypt <3
 

Attachments

bertus

Joined Apr 5, 2008
21,592
Hello,

You are using the wrong transformer.
A 15 Volts transformer will deliver the expected 1.5 Amp.
A 12 Volts transformer does not have enough voltage to reach that.

Bertus
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Thank You ... But .. I need actually more than just 1.5 amps ... this circuit gives the 1.5 amps already when its with no load ....

About the transformer ... The rectifier after the transformer gives around 15 Volts and half ... The transformer current rating is 5 amps ?

Isn't we count the starting voltage after the rectifier or still I have to change the transformer ??

**Another important thing is that the voltage on the battery is more than 12.7 Volts but It didn't start the car ?!

When I use a car jumper and connect with another car it works so I'm sure it's a battery problem ...

Thank you and sorry for all the questions ... I just don't want to stay stupid as you said in your signature :D
 

wayneh

Joined Sep 9, 2010
17,153
I agree. [with Bertus]

If I understand your tests, you connected your DMM, in current-measuring mode, directly to the poles of your power supply. That's not a good idea. You may get away with it from time to time, but you'll eventually blow the fuse in your meter and/or destroy a power supply. Imagine testing your battery this way; poof!

Does your circuit include that "extra" diode? Unless someone can remind me why it's there, I'd eliminate it. You'd pick up a wee bit of voltage and thus a bit more current.
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Thank you wayneh .. and yeah I had that feeling of something will blow up soon while I was measuring the current :D .... Thank you for the advice ...

I will try that advice of measuring the voltage while cranking .. I'm using an old another transformer to power the DMM LOL .. Now I have to buy a new 9V batter XD ...

About that extra diode do you mean that 6A4 diode ?

Can I just bypass it with a wire and see what will happen to the passing current ?
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Another thing can I do something instead of changing that relatively expensive transformer :'( :D ... I read about dc to dc converters with LM317T would it change the volt ... etc
 

wayneh

Joined Sep 9, 2010
17,153
Add a Fuse to where ... The 240V line ? or the output
Yes! :D

Proper fuse placement is an ongoing debate and there is no hard and fast answer. The general idea is to protect the user and at least the more expensive parts of the machine. A fuse on the transformer secondary will protect the transformer against, for instance, a shorted rectifier and it would protect the relay and battery against excessive charge current. It wouldn't protect the 555, but that's a cheap part (perhaps difficult for you to replace though). I don't think many of us would add a separate fuse for the 555, but there's nothing wrong with that. One thing to think about is what your charger will do if the 555 fails to "on" or "off".
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Yes! :D

Proper fuse placement is an ongoing debate and there is no hard and fast answer. The general idea is to protect the user and at least the more expensive parts of the machine. A fuse on the transformer secondary will protect the transformer against, for instance, a shorted rectifier and it would protect the relay and battery against excessive charge current. It wouldn't protect the 555, but that's a cheap part (perhaps difficult for you to replace though). I don't think many of us would add a separate fuse for the 555, but there's nothing wrong with that. One thing to think about is what your charger will do if the 555 fails to "on" or "off".
Thanks again for the great advises I really appreciate it. I will put a fuse on the secondary ... You know everything is hard to replace right now not because the market .. But because there is no car :D ... About that 555 where can I add the fuse in the vcc line ?

About the on or off failure ... That's why I'm putting the whole project on the bed .. I almost sleeps with it ^_^

I can hear the relay (and the green LED tells that the relay is on)

The variable resistor if I change it I can see after awhile the led goes off and the relay also so I guess it works .. I re change the resistor to change the off voltage (as I understand that's what changing resistance for) ... But still I keep an eye on it to be sure everything is going fine ...

Also as you see I put a fan to cool the transformer I even added some fins to it ... Last time after few minutes the transformer was very hot ...
 

wayneh

Joined Sep 9, 2010
17,153
About that 555 where can I add the fuse in the vcc line ?
Now that I think about it, that may not be a good idea because it's generally very bad to apply voltages to the pins of an IC that is not powered.

Also as you see I put a fan to cool the transformer I even added some fins to it ... Last time after few minutes the transformer was very hot ...
That's bad. The wire insulation of the transformer coils can be destroyed by overheating. At 200mA, you should be fine. Keep an eye on it. Was the heat from your high current testing, as opposed to low current charging? Given its rating, it should not be at risk at low current.
 

t06afre

Joined May 11, 2009
5,934
The circuit use a 15 volt 5A transformer. That shouls give about 20 volt over the filter cap at no load. As I see it that circuit is not very good for charging a car battery at all.
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
Now that I think about it, that may not be a good idea because it's generally very bad to apply voltages to the pins of an IC that is not powered.
Ok you're the boss :D

That's bad. The wire insulation of the transformer coils can be destroyed by overheating. At 200mA, you should be fine. Keep an eye on it. Was the heat from your high current testing, as opposed to low current charging? Given its rating, it should not be at risk at low current.
No, I don't think so. The heat comes after like 15 minutes the whole transformer is so hot even if there was no load at all (like I didn't put the battery). But now after the fan and cooler it's going fine ..

I think I will reconsider building another effective circuit other than this because I saw some devices for recharging works on 40 amps ... 75 amps ...

But to be honest I don't know if it's cheaper to buy those devices than to build such circuit :D

This way I may take weeks to recharge that poor battery !!
 

Thread Starter

hesham1216

Joined Oct 18, 2010
35
12 V Car battery Lead Acid I think they call it ... I use it in the car :D .. Engine start ... etc

Here its specification (see attachments)

If those numbers on it's specification can be counted in the charging process ... does that mean with 0.2 amp it will take forever to be fully charged ? :D
 

Attachments

wayneh

Joined Sep 9, 2010
17,153
The heat comes after like 15 minutes the whole transformer is so hot even if there was no load at all (like I didn't put the battery). But now after the fan and cooler it's going fine ...
That's odd. In my opinion it should run cool if there is no load. How much current does your relay coil draw? (You can measure it by removing the battery and measuring voltage across your 2 10Ω resistors.) This adds to the secondary current and perhaps it's more than we expect.
 
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