Will a battery charger drain the battery?

[Mentor58]

If a battery is connected to a charger, and the charger is left off, will that put a load on the battery that would drain it over time?

Reason I ask, I'm starting to sketch out the electrical plan, and if an unpowered charger drains the battery I may want to throw a relay into the charging circut, so that if the charger is off, the circuit is open.

Other than hooking up a battery to the charger and checking for a current flow how could you tell? If you read resistance across the charger I'm thinking that anything other than an infinite reading (or very high resistance) would indicate a potential drain.

Thank

Steve

[Steve_Cox]

Steve,

I have an older type 10 Amp battery charger permanently connected to my battery. The charger has a rocker switch 6V/off/12V, if I leave it on and the 120V power turned off to the charger, (it is on it's own breaker) it does discharge the battery. I don't know about the newer solid state chargers, but I think even if they don't discharge the battery you might have to press a button to initialize charging on some of them each time you power your charger up.

[Dale M.]

Several ways to tell..... Simple light bulb between charge lead and battery terminal will tell you if there is a drain, bulb will light (charger unplugged from AC)....

Another test it to monitor voltage.... IF it drops over time while charger connect then there is drain.........

Placing a VOLT-OHM meter in circuit in CURRENT READ MODE will tell if there is a drain...

IF tther is a problem, solution may be as simple as a "isolation diode" in charge lead to prevent any current flow, BUT will allow charge to take place...

The there may not be any problem at all...Depending in charger internals...

Dale

[PaulC]

Most of the cheaper style chargers will drain your battery if left connected.
The better (think CTek style) have an isolation diode to prevent this happening, to a certain degree.
For the diode to know what it's supposed to be doing, it has to draw current from somewhere.
Your best bet is to disconnect if you have the AC switched off. You can fit an inline switch on the 12v side to achieve this.
Cheers
Paul

[Dale M.]

For the diode to know what it's supposed to be doing, it has to draw current from somewhere.

Paul

Umm... ONE purpose of a diode is to prevent a current draw.... It knows what to do with out any "external current flow" to tell it what to do.... It can operate as a unconditional one way electronic valve... That is why the are called ISOLATION diode.

http://www.the12volt.com/diodes/diodes.asp

Dale

[SteveH]

My charger is connected to the battery always, and never drains the battery. The only way a charger will drain the battery is if it has an internal load resistor, or the rectifier "leaks", or if the charger has leaky filter capacitors. The thing is, in most cases, the rectifier is a bridge built from four diodes, and diodes installed correctly do not draw current. If they are not installed correctly, the charger will not work.

[Gerdo]

I have had an automatic charger permanently connected to a truck for about 15 years. It is an automatic one but I can't remember if it even has a off switch (I can't remember because if it does I don't turn it off. It has two LEDs on it, charged and charging. If it isn't plugged in the charging light is on. Sometimes the truck will sit for months unplugged and I have never had a bead battery. It works with this charger.