Battery discharge

[Cool Hand Lurker]

I had a problem with my battery discharging and determined that the generator cut-out was the problem. The generator worked fine but apparently the cut-out didn’t do its job and the battery went dead overnight. I charged up the battery with a charger and the cells tested out fine with a hydrometer. So I replaced the cutout.

I know you can put a battery disconnect in the line from the battery to the starter to keep this from happening but I decided to try something different. Instead of the heavy duty battery disconnect switch, I figured I could use a lighter duty solenoid or relay and just interrupt the smaller wire that runs from the starter to the terminal box. When the engine is shut off that wire still conducts power to all circuits except the starter and the ignition coil. And it will allow a discharge through the generator if the cutout relay is bad. Interrupting that wire would also prevent troubles caused by a short in any of those circuits. Like a fire.

Here is a diagram of how I wired in the solenoid. I just used a 6V starter solenoid that I had in the parts box, but I think a 6V headlight relay would be heavy duty enough to carry the required load when operating the car. I put a toggle switch under the dash that I manually flick to activate the solenoid when starting up and to deactivate it when shutting off the engine.

 

[Ed Saniewski]

looks like a great idea. We used to wire up our paramedic trucks the same was. With all the radios and equipment we had, it didn't take long to kill our batteries if the engine wasn't running. If you are using an after market ignition switch you might be able to wire the solenoid to the accessory lead so when the key is off the battery disconnects.

 

[ford1]

why not just buy a new diode cut out?

 

[MAG]

A properly sized and and installed diode in that wire will accomplish what you are trying to do. Very simple installation.

 

[Cool Hand Lurker]

Ford1, MAG, like I said it does more than cutout the generator.

"When the engine is shut off that wire still conducts power to all circuits except the starter and the ignition coil. And it will allow a discharge through the generator if the cutout relay is bad. Interrupting that wire would also prevent troubles caused by a short in any of those circuits. Like a fire. "

 

[Art Bjornestad]

Good idea! Why can't you pick the relay when you turn the ignition on? This would eliminate one looking dumb when the A won't start in front of friends. Don't ask........

 

[Cool Hand Lurker]

Art, the problem with using the ignition switch to also control the relay is that the ignition switch connects the ground wire to the coil. You would need to run a separate hot wire to the relay. You would have to use a relay that had two terminals on it that are insulated from the case so you could connect both a ground wire and a hot wire. Then you could run a hot wire directly to the relay and use the ignition switch to supply the ground wire.

 

[Cool Hand Lurker]

Wait a minute! The blood isn't getting to my brain. Connecting to the ignition switch wouldn't work. It would only send a ground charge every time the points close. The relay would be switching on and off everytime the plugs fired. But the plugs wouldn't fire either because the relay would cut off the hot charge to the coil.

You have to have a separate switch for the relay.

Maannnnnnn.... this is too complicated. The horse was good enough!

 

[Rainmaker Ron]

Keep your fire extinguisher handy, Starter solenoids are not designed for continous duty.

Rainmaker Ron

 

[Paul from Maine]

I just take the ground strap clamp off the positive terminal when I'm done driving for the day. I have the clamp bolt just tight enough so that when I put it on the terminal it doesn't jiggle, but when the day's driving is done I can wiggle the clamp off with a few back and forth twists. I realize that some barners are going to jump all over me saying its unsafe or could bounce off and arc or blowup the battery or destroy the terminal post or cause the car to catch fire, or burn up the generator or cause static in the radio or destroy the carpet or get acid on your skin and kill you or cause a nuclear war between the Soviet Union and Red China or cause gas fumes to ignite or a Hindenberg disaster because of an overcharged battery venting hydrogen gas. OK, I admit it...its a dumb idea. Don't do it. But I'm going to.

 

[Cool Hand Lurker]

Jeez Paul, I didn't know you had that many international problems up there in hard rock country. Come to think of it, you are close to Canada, eh? But there is nothing wrong with pulling the battery cable, I just want to flip a lazy switch.

Ron, the solenoid that I am using is a continuous duty one off an old electric golf cart. But I am not sure that using a regular solenoid just for the 20-30 amps that might run through it would be a fire hazard at all. The contact points in a starter solenoid are capable of handling much higher amps during starting. The circuits that I am talking about do not include the starter circuit though. I think the only danger might be that the coil may burn out inside the solenoid and the only effect that would have is that the solenoid would no longer work.

I am sure there are electronic relays available that will handle 30-40 amps with no problem but the only ones I could find were 12 volt. I just used the solenoid because I had it already.