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Car battery charger.

 
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Car battery charger.

Post by malcscott » Sat Nov 16, 2013 3:41 pm

Hi, i have built a car battery charger and it works fine. I would like to add a trickle charge option. How is this done? I imagine a large w/w resistor would do the trick, but what size/where to add it i am not sure.
Any ideas? Cheers, Malc.

 
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Re: Car battery charger.

Post by Michael Watterson » Sat Nov 16, 2013 5:38 pm

In series with output.

Trickle Charge R2 Value is (PSU volts - 14.2) / (Desired output trickle current).

But HOW does your charger work? Usually set to give a max current simply using a series resistance,

Main Charge R1 Value (PSU volts -10) / (Desired output current).

Where PSU volts is the AC voltage less 1.2V (silicon bridge).

No electrolytics are used.

Old models R1 is resistance of the Metal Rectifier! R2 only existed if there was a Trickle mode.

A Car Battery charger is MUCH simpler than NiMH (constant Current), which is MUCH simpler than Lithium.

There are such things as "Smart" chargers for UPS use and different kind of Smart Charger for Lead Acid disconnected from Equipment.

Only 6V & 12V car Radios (Valve, Hybrid or Transistor) or In Car systems can be operated while charging a Lead Acid Battery, stand alone Vintage 2, 4 or 6V vintage stuff not designed for vehicle use usually would be over stressed to be used while Battery is on Charge.

 
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Re: Car battery charger.

Post by malcscott » Sat Nov 16, 2013 5:45 pm

Using a bridge rectifier in this case. Do i limit the i/p to the rectifier or the o/p?

 
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Re: Car battery charger.

Post by crackle » Sat Nov 16, 2013 6:27 pm

I would put the resistor in the OP, but depending on what value you use to set the trickle charge it is going to get hot.
What is the output voltage of the transformer.
Mike

 
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Re: Car battery charger.

Post by rob t » Sat Nov 16, 2013 6:52 pm


 
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Re: Car battery charger.

Post by Ed Dinning » Sat Nov 16, 2013 7:11 pm

Hi Malc, a tap on the trans secondary is also a good way to reduce the charge rate and no energy dissipated in resistors.
#
Ed

 
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Re: Car battery charger.

Post by Michael Watterson » Sat Nov 16, 2013 7:42 pm

Malc Scott wrote:Using a bridge rectifier in this case. Do i limit the i/p to the rectifier or the o/p?


Makes no difference if it's the simple charger with NOTHING except a transformer, a bridge and a resistor.

 
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Re: Car battery charger.

Post by Michael Watterson » Sat Nov 16, 2013 7:44 pm

rob t wrote:Found this circuit may help,
http://www.circuitdiagram.org/car-battery-charger.html
Rob T


No, that's insane overkill for a car battery charger. It ONLY needs
Transformer, Bridge, resistor.
Optionally a Current meter (very useful).

 
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Re: Car battery charger.

Post by GlowingAnode » Sun Nov 17, 2013 11:56 am

That's a matter of opinion.
It really depends on the application.
A basic charger is fine if it is to recover a flat batery, for instance by leaving your lights on overnight.
Ideally any lead-acid battery should be charged at a constant curent of roughly 10 - 20% of the Ah rating.
Once the cell voltage has reached around 2.15 V per cell, the charger should the switch to constant voltage float to minimise gassing and damage to the cell plates.
Ed's suggestion of tapping down the secondary winding is a good one, you can acheive the same effect by tapping up the primary if it has multiple input taps.
Constructing an automatic charger such as the one Rob mentioned is well worth the trouble, as it will maximise battery life and can be left connected indefinitely without hazard.
Cheers, Rob.

 
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Re: Car battery charger.

Post by Michael Watterson » Sun Nov 17, 2013 12:54 pm

For Lead Acid generally the smart charger is better.

But for a Car battery, it's only occasional and never left on float charge for more than 1/2 a day. Unless the Car Battery isn't for a car, in which case "Car" battery is misleading.

The Charger design depends on Battery type and application, which I indicated earlier. If I did want a smart charger I wouldn't use that circuit either though! I'd use a smarter one.

 
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Re: Car battery charger.

Post by boyblue » Sun Nov 17, 2013 1:18 pm

Yes I,d use a smarter one too Michael, to reduce charge current, disconnect one of the diodes of the bridge.

Peter


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