power supply 2

It is kinda rough on a 25 volt transformer to slap a 12 volt load across it. You need to big resistor in series (or do something more like a switching step down regulator) if you expect5 the on state current to be reasonable. Or you could start looking for another transformer that was better suited to this task. The cheapest might be one from a battery charger.

I basically used a similar circuit to antoon:

without the Lm317, I just dump the DC voltage to the battery. How is it so much differnt then what i am doing ? So I should be charging a 24v battery with this apparatus and it will not get hot?

ken

The LM317 is a linear regulator, that drops all the extra voltage (acts like a self adjusting variable resistor).

It would be better. But the current still is uncontrolled in any intentional way. If the battery developed a short, it would still overheat the transformer. A good charger limits the current into the battery, for an battery voltage below normal, and also cuts the charging process off, if the battery voltage gets too high (above full charge voltage). I don't know what your 555 circuit is supposed to accomplish, but I don't see either of these features.

You have a real world problem that will require dealing with real world currents and voltages that exceed the "twink limit" of 12V and 100mA. This is a twinky forum but I will gladly risk blowing the twinkys fuses by pointing out that a large marine battery can draw hundreds of amps when charging. You should think about regulating the current on the input (mains voltage) side of your charger where the current is lower, but the voltage is higher with a lamp-dimmer type circuit using (for example) a triac.

I 2000uF

hot,

A triac sounds good, I never work with them before. Will have to study it a bit more before I can implement it. So from what I just read, I can change the gate voltage of the triac using a voltage divider from the main, hum mm is triac any good for Ac voltage ?? I,ll have to switch the gate voltage too..

ken

Ok How do I do that ???

for an battery voltage below normal, and also cuts the

yes I did a circuit that will do that, a comparator will evaluat the battery voltage and when so, the output will a activate a MOsfet that will bypass the charging. I saw a few version of this on the net, But I have not ssen a version using Mosfet, they usually go with a transistor. I just did not show this because I dont think it is relevant to the heating of the transformer.

I don't know what your 555 circuit is supposed to

The 555 is used to pulse charge the battery. I read some things on the net about desulfating batteries using pulses. I want to see if its true.

ken

How would I control the current, ... I would need a big ass resistor. I think

k

I just saw that the chip L200C can reduce current. would that be an approach?? The transformer I use is rated 2 Amp. Should I be using a 1.0 amp transformer then ?

K

Look here for the circuit on desulfating:

i want to charge at the same time. I did his circuit, the battery discharge very quickly, even more with a badly sulfated battery. the idea of using a pulse charger is a bit better I think. k

This was the first of many triac light dimmer circuits that I found. I would substitute the transformer primary for the lamp, and hope the change from a resistive load to an inductive load didn't make too much difference. Other possibilities would be to use an SCR instead of your transistor. SCRs can control huge currents.

voltage

Now that I'm starting to think about it I am starting to wonder if the lamp dimmer wouldn't just cut the voltage to the point where your charger wasn't charging! May be you will have to control it with some feedback from the output? Well at least I am bringing up the subject of Triacs and SCRs (Silicon Controlled Rectifiers).

voltage

yes I did, in my first post. Just add a rectifier and a transformer to the capacitor like I mentionned Its that simple of a circuit, nothing more.

ken

I just got a huge transformer, Its about three times the size from the previous. The rating is not mentionend but I get the right voltage I try it out tonight

ken

yes that fixed it, just the transistor is getting a bit hot, but thats not a big deal.

k

You are on the right track with a bigger transformer, but, if I were doing this job I wouldn't be happy until I found a circuit that could protect the charger even if the output leads got shorted together. That happens sometimes by accident.

John

You mentionned earlier that I would need a circuit to supply the timer. I was going to use the LM317, but that has a maximum of 36 v. Now the transformer is given me 44v, that do not matter, Should I be just using resistors for a voltage divider and feed my timer directly with that? would there be any problem ?

Ken

^putting a zener diode on the positive end would work ?

k

This has to be designed, just like anything else.

Start with the voltage and current your 555 circuit requires. What current is it supplying to the base of the power switch? You have to get rid of all the extra voltage and still supply that total current. I would be thinking of a several watt resistor and a 15 volt zener to lower the voltage. The resistor would have to be sized to carry the peak circuit load current, and the zener would have to burn that additional current when the circuit was in the low current phase of its operation. If you wanted more precise regulation than that, you could add the LM317 downstream of that.