can some one please help me figure out how to design a battery charger that automaticly cuts off at a....?

Question

certian voltage. i have some expeirence with electronics and designing them so dont be afraid to speak geek lol. but i need to design a simple automatic battery tricle charger i will be chargeing a 12 volt sealed lead acid 5 AH for 1HR used for home made emergency lighting system i need it to charge the battery then at a certian voltage automaticly cut off then start a charge small enough to keep the battery full but not overcharged

Answer 1

The only thing that comes to mind with me is have your output from the power supply "compared" to a separate DC charge in the way of a battery. Downside is the battery (or batteries) would have to be kept fresh.
Your power output would have to be converted with a transformer down to 12V (I assume that's already done) and then converted to DC (ask me how to do that with diodes - I can explain that). Then, put the output up against the battery comparator. If current is coming out of the battery it means the output is not done. When current stops, they're the same. This can be controlled with a diode and picked up with a logic circuit element. I'd start with a "not" and use it to shut down the circuit by actuating a relay to shut it off.
Another solution that's simpler and less homemade is to use a toroidal-type coil to detect current in the output, then use non-flow as a trigger to trip a relay and shut down the charging.

Answer 2

There are various ways you can do this - one would be to use a zenner diode such that:

Desired battery voltage - zenner voltage = 0.7V and use this to trigger a "switch off" - either driving a transistor holding a relay coil or something similar.

Problem is you need either some sort of timer OR a latch, because as soon as the battery charger switches off, the voltage over the terminals will drop - and thus the 0.7v will no longer be present - and thus the charger comes on again - perhaps half a second later!

Having the 0.7V charge a 4700uF cap and have that discharge into the base of the transistor via a 1M resistor might give you a nice long hold-off though.

As for the trickle part, that is easy, just have a wirewound resistor going over the relay contacts so that when the relay opens, there is still a circuit through the resistor - and then just pick the value you want according to the maximum trickle current you will permit.

Play with values from about 2 Ohms to 47 Ohms and see what sort of charge levels you want.

Mark

Answer 3

A fully charged 12V battery has a PD of about 14.4V. So, easy way is a charger with a voltage overhead of around 18V and a shunt regulator with the regulator input fed from a voltage comparator (LM311 or LM339) fed from a 14.4V zener stack on one leg and the battery on the other. Any more info than that and I'd be drawing the schematic for you.

Answer 4

This one will work (I looked at it). You'll have to calculate the value of 1 resistor (formula given) for your larger battery.
http://www3.telus.net/chemelec/Projects/Charger/Charger.htm

Note: it's OK to keep a small charging current flowing through a lead-acid battery, continually. This charger is designed for a C/10 rate. You could also make it a 100 mA charger which would be a C/50 charger -- also acceptable for long-term continual charging.

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Answer 5

A small relay will do the this for you with two pairs of contacts .
1pr. normally open 1pr. normally closed Arrange the relay to close when your fully charged voltage is reached. The hi charging circuit is connected to the normally closed pair of contacts. The trickle charge circuit is connected to the normally open contacts.
So your charger will switch between hi charge and trickle charge automatically I suggest a relay with pick up voltage of about 13 Volts and drop off voltage about 9 Volts

Answer 6

Try getting the battery limiter. Install it but i have no clue where to get it. Sorry.

Answer 7

I've done things like that and the satisfaction comes from figuring it out by yourself.